82398146 ac drives control abb

AC Drives Technical Guide Book


This is the first AC Drives Technical Guide Book, a completeset of ABB's Technical Guides 1-8.

We wish that the accumulated knowledge of world'sleading AC Drives manufacturer will work for your benefit.The aim of this book is to provide you a solid tool for everyday use in the arena of AC drives.

Best regards,

Mika Kulju

Product Management

We updated existing Guides over time, so the latestversions and new Technical Guides can be found from ourweb site: http://www.abb.com/motors&drives

Dear Reader,

Contents

1. Direct Torque Control explains what DTC is; whyand how it has evolved; the basic theory behind itssuccess; and the features and benefits of this newtechnology.

2. EU Council Directives and Adjustable SpeedElectrical Power Drive Systems is to give astraightforward explanation of how the various EUCouncil Directives relate to Power Drive Systems.

3. EMC Compliant Installation and Configuration fora Power Drive System assists design and installationpersonnel when trying to ensure compliance with therequirements of the EMC Directive in the user'ssystems and installations when using AC Drives.

4. Guide to Variable Speed Drives describes basics ofdifferent variable speed drives (VSD) and how they areused in industrial processes.

5. Bearing Currents in Modern AC Drive Systemsexplains how to avoid damages.

6. Guide to Harmonics with AC Drives describesharmonic distortion, its sources and effect, and alsodistortion calculation and evaluation with specialattention to the methods for reducing harmonics withAC drives.

7. Dimensioning of a Drives system. Makingdimensioning correctly is the fastest way of savingmoney. Biggest savings can be achieved by avoidingvery basic mistakes. These dimensioning basics andbeyond can be found in this guide.

8. Electrical Braking describes the practical solutionsavailable in reducing stored energy and transferringstored energy back into electrical energy.


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Direct Torque Control- the world's most advanced AC drive technology

Technical Guide No. 1 Technical Guide No. 1

Technical Guide No.1- Direct Torque Control2

Contents

1 Introduction ......................................................General ......................................................................This Manual’s Purpose .............................................Using this Guide ........................................................

2 Evolution of Direct Torque Control ...................What is a Variable Speed Drive? ..............................Summary ...................................................................DC Motor Drives .......................................................

Features.................................................................Advantages ...........................................................Drawbacks ............................................................

AC Drives - Introduction ...........................................AC Drives - Frequency Control using PWM ............

Features.................................................................Advantages .........................................................Drawbacks ..........................................................

AC Drives - Flux Vector Control using PWM .........Features...............................................................Advantages .........................................................Drawbacks ..........................................................

AC Drives - Direct Torque Control .........................Controlling Variables ...........................................

Comparison of Variable Speed Drives ...................

3 Questions and Answers ..................................General ....................................................................Performance............................................................Operation .................................................................

4 Basic Control Theory ......................................How DTC Works ......................................................Torque Control Loop...............................................

Step 1 Voltage and Current Measurements ......Step 2 Adaptive Motor Model ............................Step 3 Torque Comparator and Flux ComparatorStep 4 Optimum Pulse Selector .........................

Speed Control .........................................................Step 5 Torque Reference Controller ..................Step 6 Speed Controller .....................................Step 7 Flux Reference Controller .......................

5 Index ...............................................................

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Technical Guide No.1- Direct Torque Control

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Direct Torque Control - or DTC - is the most advanced ACdrive technology developed by any manufacturer in the world.

The purpose of this Technical Guide is to explain what DTCis; why and how it has evolved; the basic theory behind itssuccess; and the features and benefits of this new technology.

While trying to be as practical as possible, this guide doesrequire a basic understanding of AC motor control principles.

It is aimed at decision makers including designers, specifiers,purchasing managers, OEMs and end-users; in all marketssuch as the water, chemical, pulp and paper, powergeneration, material handling, air conditioning and otherindustries.

In fact, anyone using variable speed drives (VSD) and whowould like to benefit from VSD technology will find thisTechnical Guide essential reading.

This guide has been designed to give a logical build up as towhy and how DTC was developed.

Readers wanting to know the evolution of drives from earlyDC techniques through AC to DTC should start at Chapter 2(page 6).

For those readers wanting answers about DTC’s performance,operation and application potential, please go straight toChapter 3 (page 15) Questions & Answers.

For an understanding of DTC’s Basic Control Theory, turn topage 26.

Chapter 1 - Introduction

This manual’spurpose

General

Using thisguide


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Summary

What is avariable speeddrive?

Chapter 2 - Evolution of Direct Torque Control

To understand the answer to this question we have tounderstand that the basic function of a variable speed drive(VSD) is to control the flow of energy from the mains to theprocess.

Energy is supplied to the process through the motor shaft.Two physical quantities describe the state of the shaft:torque and speed. To control the flow of energy we musttherefore, ultimately, control these quantities.

In practice, either one of them is controlled and we speakof “torque control” or “speed control”. When the VSDoperates in torque control mode, the speed is determinedby the load. Likewise, when operated in speed control, thetorque is determined by the load.

Initially, DC motors were used as VSDs because they couldeasily achieve the required speed and torque without theneed for sophisticated electronics.

However, the evolution of AC variable speed drive technologyhas been driven partly by the desire to emulate theexcellent performance of the DC motor, such as fast torqueresponse and speed accuracy, while using rugged,inexpensive and maintenance free AC motors.

In this section we look at the evolution ofDTC, charting the four milestones ofvariable speed drives, namely:

• DC Motor Drives 7• AC Drives, frequency control, PWM 9• AC Drives, flux vector control, PWM 10• AC Drives, Direct Torque Control 12

We examine each in turn, leading to a total picture thatidentifies the key differences between each.


DC MotorDrives

• Field orientation via mechanical commutator• Controlling variables are Armature Current

and Field Current, measured DIRECTLY from the motor• Torque control is direct

In a DC motor, the magnetic field is created by the currentthrough the field winding in the stator. This field is always atright angles to the field created by the armature winding.This condition, known as field orientation, is needed togenerate maximum torque. The commutator-brushassembly ensures this condition is maintained regardlessof the rotor position.

Once field orientation is achieved, the DC motor’s torque iseasily controlled by varying the armature current and bykeeping the magnetising current constant.

The advantage of DC drives is that speed and torque - thetwo main concerns of the end-user - are controlled directlythrough armature current: that is the torque is the innercontrol loop and the speed is the outer control loop (seeFigure 1).

• Accurate and fast torque control• High dynamic speed response• Simple to control

Initially, DC drives were used for variable speed controlbecause they could easily achieve a good torque and speedresponse with high accuracy.

Figure 1: Control loop of a DC Motor Drive

Evolution of Direct Torque Control

Features

Advantages


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CustomerLocation

ApplicationEquipment Supplied

A DC machine is able to produce a torque that is:

• Direct - the motor torque is proportional to the armaturecurrent: the torque can thus be controlled directly andaccurately.

• Rapid - torque control is fast; the drive system can havea very high dynamic speed response. Torque can bechanged instantaneously if the motor is fed from an idealcurrent source. A voltage fed drive still has a fastresponse, since this is determined only by the rotor’selectrical time constant (i.e. the total inductance andresistance in the armature circuit)

• Simple - field orientation is achieved using a simplemechanical device called a commutator/brush assembly.Hence, there is no need for complex electronic controlcircuitry, which would increase the cost of the motorcontroller.

• Reduced motor reliability• Regular maintenance• Motor costly to purchase• Needs encoder for feedback

The main drawback of this technique is the reduced reliabilityof the DC motor; the fact that brushes and commutatorswear down and need regular servicing; that DC motorscan be costly to purchase; and that they require encodersfor speed and position feedback.

While a DC drive produces an easily controlled torque fromzero to base speed and beyond, the motor’s mechanicsare more complex and require regular maintenance.

• Small size• Robust• Simple in design• Light and compact• Low maintenance• Low cost

The evolution of AC variable speed drive technology has beenpartly driven by the desire to emulate the performance ofthe DC drive, such as fast torque response and speedaccuracy, while utilising the advantages offered by thestandard AC motor.

Drawbacks

AC Drives -Introduction



• Controlling variables are Voltage and Frequency• Simulation of variable AC sine wave using modulator• Flux provided with constant V/f ratio• Open-loop drive• Load dictates torque level

Unlike a DC drive, the AC drive frequency control techniqueuses parameters generated outside of the motor as controllingvariables, namely voltage and frequency.

Both voltage and frequency reference are fed into a modulatorwhich simulates an AC sine wave and feeds this to the motor’sstator windings. This technique is called Pulse WidthModulation (PWM) and utilises the fact that there is a dioderectifier towards the mains and the intermediate DC voltageis kept constant. The inverter controls the motor in the formof a PWM pulse train dictating both the voltage and frequency.

Significantly, this method does not use a feedback devicewhich takes speed or position measurements from themotor’s shaft and feeds these back into the control loop.

Such an arrangement, without a feedback device, is calledan “open-loop drive”.

Figure 2: Control loop of an AC Drive with frequency controlusing PWM


Features

AC Drives -frequencycontrol usingPWM


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• Low cost• No feedback device required - simple

Because there is no feedback device, the controlling principleoffers a low cost and simple solution to controlling economicalAC induction motors.

This type of drive is suitable for applications which do notrequire high levels of accuracy or precision, such as pumpsand fans.

• Field orientation not used• Motor status ignored• Torque is not controlled• Delaying modulator used

With this technique, sometimes known as Scalar Control,field orientation of the motor is not used. Instead, frequencyand voltage are the main control variables and are applied tothe stator windings. The status of the rotor is ignored,meaning that no speed or position signal is fed back.

Therefore, torque cannot be controlled with any degree ofaccuracy. Furthermore, the technique uses a modulator whichbasically slows down communication between the incomingvoltage and frequency signals and the need for the motor torespond to this changing signal.

Advantages

AC Drives -flux vectorcontrol usingPWM


Features

Drawbacks

Figure 3: Control loop of an AC Drive with flux vector control using PWM

• Field-oriented control - simulates DC drive• Motor electrical characteristics are simulated

- “Motor Model”• Closed-loop drive• Torque controlled INDIRECTLY


To emulate the magnetic operating conditions of a DC motor,i.e. to perform the field orientation process, the flux-vectordrive needs to know the spatial angular position of therotor flux inside the AC induction motor.

With flux vector PWM drives, field orientation is achieved byelectronic means rather than the mechanical commutator/brush assembly of the DC motor.

Firstly, information about the rotor status is obtained by feedingback rotor speed and angular position relative to the statorfield by means of a pulse encoder. A drive that uses speedencoders is referred to as a “closed-loop drive”.

Also the motor’s electrical characteristics are mathematicallymodelled with microprocessors used to process the data.

The electronic controller of a flux-vector drive creates electricalquantities such as voltage, current and frequency, which arethe controlling variables, and feeds these through a modulatorto the AC induction motor. Torque, therefore, is controlledINDIRECTLY.

• Good torque response• Accurate speed control• Full torque at zero speed• Performance approaching DC drive

Flux vector control achieves full torque at zero speed, givingit a performance very close to that of a DC drive.

• Feedback is needed• Costly• Modulator needed

To achieve a high level of torque response and speed accuracy,a feedback device is required. This can be costly and alsoadds complexity to the traditional simple AC induction motor.

Also, a modulator is used, which slows down communicationbetween the incoming voltage and frequency signals andthe need for the motor to respond to this changing signal.

Although the motor is mechanically simple, the drive iselectrically complex.


Advantages

Drawbacks


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With the revolutionary DTC technology developed by ABB,field orientation is achieved without feedback using advancedmotor theory to calculate the motor torque directly andwithout using modulation. The controlling variables aremotor magnetising flux and motor torque.

With DTC there is no modulator and no requirement for atachometer or position encoder to feed back the speed orposition of the motor shaft.

DTC uses the fastest digital signal processing hardwareavailable and a more advanced mathematical understandingof how a motor works.

The result is a drive with a torque response that is typically10 times faster than any AC or DC drive. The dynamic speedaccuracy of DTC drives will be 8 times better than anyopen loop AC drives and comparable to a DC drive that isusing feedback.

DTC produces the first “universal” drive with the capabilityto perform like either an AC or DC drive.

The remaining sections in this guide highlight the featuresand advantages of DTC.

AC Drives -Direct TorqueControl

Figure 4: Control loop of an AC Drive using DTC


ControllingVariables


Comparisonof variablespeed drives


Figure 1: Control loop of a DCDrive

Figure 3: Control loop with fluxvector control

Figure 2: Control loop withfrequency control

Figure 4: Control loop of an AC Drive using DTC

Table 1: Comparison of control variables

The first observation is the similarity between the control blockof the DC drive (Figure 1) and that of DTC (Figure 4).

Both are using motor parameters to directly control torque.

But DTC has added benefits including no feedback device isused; all the benefits of an AC motor (see page 8); and noexternal excitation is needed.

Let us now take a closer look at each of these controlblocks and spot a few differences.


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As can be seen from Table 1, both DC Drives and DTC drivesuse actual motor parameters to control torque and speed.Thus, the dynamic performance is fast and easy. Alsowith DTC, for most applications, no tachometer or encoderis needed to feed back a speed or position signal.

Comparing DTC (Figure 4) with the two other AC drivecontrol blocks (Figures 2 & 3) shows up several differences,the main one being that no modulator is required with DTC.

With PWM AC drives, the controlling variables are frequencyand voltage which need to go through several stagesbefore being applied to the motor. Thus, with PWM drivescontrol is handled inside the electronic controller and notinside the motor.


What is Direct Control?

Direct Torque Control - or DTC as it is called - is the verylatest AC drive technology developed by ABB and is set toreplace traditional PWM drives of the open- and closed-looptype in the near future.

Why is it called Direct Torque Control?

Direct Torque Control describes the way in which the controlof torque and speed are directly based on the electromagneticstate of the motor, similar to a DC motor, but contrary to theway in which traditional PWM drives use input frequency andvoltage. DTC is the first technology to control the “real” motorcontrol variables of torque and flux.

What is the advantage of this?

Because torque and flux are motor parameters that are beingdirectly controlled, there is no need for a modulator, as usedin PWM drives, to control the frequency and voltage. This, ineffect, cuts out the middle man and dramatically speeds upthe response of the drive to changes in required torque. DTCalso provides precise torque control without the need for afeedback device.

Why is there a need for another AC drive technology?

DTC is not just another AC drive technology. Industry isdemanding more and existing drive technology cannot meetthese demands.

For example, industry wants:

• Better product quality which can be partly achieved withimproved speed accuracy and faster torque control.

• Less down time which means a drive that will not tripunnecessarily; a drive that is not complicated by expensivefeedback devices; and a drive which is not greatlyaffected by interferences like harmonics and RFI.

• Fewer products. One drive capable of meeting all applicationneeds whether AC, DC or servo. That is a truly “universal”drive.

• A comfortable working environment with a drive thatproduces much lower audible noise.

General

Chapter 3 - Questions & Answers


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These are just some of the demands from industry. DTCcan deliver solutions to all these demands as well asbringing new benefits to many standard applications.

Who invented DTC?

ABB has been carrying out research into DTC since 1988foll owing the publication of the theory in 1971 and 1985by German doctor Blaschke and his colleague Depenbrock.DTC leans on the theory of field oriented control ofinduction machines and the theory of direct self control.ABB has spent over 100 man years developing thetechnology.

What are the main benefits of DTC technology overtraditional AC drive technology?

There are many benefits of DTC technology. But mostsignificantly, drives using DTC technology have thefollowing exceptional dynamic performance features, manyof which are obtained without the need for an encoder ortachometer to monitor shaft position or speed:

• Torque response: - How quickly the drive output canreachthe specified value when a nominal 100% torquereference step is applied.For DTC, a typical torque response is 1 to 2ms below40Hz compared to between 10-20ms for both flux vectorand DC drives fitted with an encoder. With open loopPWM drives (see page 9) the response time is typicallywell over 100ms. In fact, with its torque response, DTChas achieved the natural limit. With the voltage andcurrent available, response time cannot be any shorter.Even in the newer “sensorless” drives the torqueresponse is hundreds of milliseconds.

• Accurate torque control at low frequencies, as wellas full load torque at zero speed without the need for a feedback device such as an encoder or tachometer. WithDTC, speed can be controlled to frequencies below 0.5Hzand still provide 100% torque right the way through tozero speed.

• Torque repeatability: - How well the drive repeats itsoutput torque with the same torque reference command.DTC, without an encoder, can provide 1 to 2% torquerepeatability of the nominal torque across the speed range.This is half that of other open-loop AC drives and equalto that of closed-loop AC and DC drives.

Performance

Questions and Answers


• Motor static speed accuracy: - Error between speedreference and actual value at constant load.For DTC, speed accuracy is 10% of the motor slip, whichwith an 11kW motor, equals 0.3% static speed accuracy.With a 110kW motor, speed accuracy is 0.1% withoutencoder (open-loop). This satisfies the accuracy requirementfor 95% of industrial drives applications. However, for thesame accuracy from DC drives an encoder is needed.

In contrast, with frequency controlled PWM drives, the staticspeed accuracy is typically between 1 to 3%. So thepotential for customer process improvements issignificantly higher with standard drives using DTCtechnology.

A DTC drive using an encoder with 1024 pulses/revolutioncan achieve a speed accuracy of 0.01%.

• Dynamic speed accuracy: - Time integral of speeddeviation when a nominal (100%) torque speed is applied.DTC open-loop dynamic speed accuracy is between 0.3 to0.4%sec. This depends on the gain adjustment of thecontroller, which can be tuned to the process requirements.

With other open-loop AC drives, the dynamic accuracy iseight times less and in practical terms around 3%sec.If we furnish the DTC controller with an encoder, the dynamicspeed accuracy will be 0.1%sec, which matches servodrive performance.

What are the practical benefits of these performancefigures?

• Fast torque response: - This significantly reduces thespeed drop time during a load transient, bringing muchimproved process control and a more consistent productquality.

• Torque control at low frequencies: - This is particularlybeneficial to cranes or elevators, where the load needs tobe started and stopped regularly without any jerking. Alsowith a winder, tension control can be achieved from zerothrough to maximum speed. Compared to PWM fluxvector drives, DTC brings the cost saving benefit that notachometer is needed.

• Torque linearity: - This is important in precision applicationslike winders, used in the paper industry, where an accurateand consistent level of winding is critical.



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• Dynamic speed accuracy: - After a sudden load change,the motor can recover to a stable state remarkably fast.

Apart from excellent dynamic performance figures,are there any other benefits of DTC drive technology?

Yes, there are many benefits. For example, DTC drives donot need a tachometer or encoder to monitor motor shaftspeed or position in order to achieve the fastest torqueresponse ever from an AC drive. This saves initial cost.


Table 2: Dynamic performance features and benefits offered by DTCtechnology

Investment costsavings. Increasedreliability. Betterprocess control.Higher productquality. Leads to atrue universal drive.

Similar performanceto DC but withouttachometer. Reducedmechanical failuresfor machinery. Lessdowntime. Lowerinvestment.

Cost effective, highperformance torquedrive; providesposition control andbetter staticaccuracy. Highaccuracy control withstandard AC motor.

Investment costsaving. Better loadcontrol. Can use ACdrive and motorinstead of DC.Standard AC motormeans lessmaintenance andlower cost.

Allows speed to becontrolled better than0.5% accuracy. Notachometer needed in95% of all applications.

Drive for demandingapplications. Allowsrequired torque at alltimes. Torquerepeatability 1%.Torque response timeless than 5ms.

No mechanical brakeneeded. Smoothtransition betweendrive and brake.Allows drive to beused in traditional DCdrive applications.

Servo driveperformance.

Good motor speedaccuracy withouttachometer.

Excellent torquecontrol withouttachometer.

Control down to zerospeed and positionwith encoder.

Full torque at zerospeed with or withouttachometer/encoder.

FEATURE RESULT BENEFIT



Table 3: User features and benefits offered by DTC technology

Rapid control DC linkvoltage.

Power loss ride through. Drive will not trip. Lessdown time. Avoidsprocess interruptions.Less waste incontinuous process.

Automatic start(Direct restart).

Starting with motorresidual inductancepresent. No restartingdelay required.

Can start into a motorthat is running withoutwaiting for flux to decay.Can transfer motor fromline to drive. No restart.No interruptions onprocess.

Controlled brakingbetween two speedpoints.

Investment cost savings.Better process control.No delay required as inDC braking. Can beused for decelerating toother than zero speed.Reduced need for brakechopper and resistor.

Flux braking.

Flux optimisation. Motor losses minimised.Less motor noise.

Controlled motor.

Self identification/ Auto-tuning.

Tuning the motor todrive for topperformance.

Easy and accurate set-up. No parameter tuningrequired. Lesscommissioning time.Guaranteed startingtorque. Easy retrofit forany AC system.

No predeterminedswitching pattern ofpower devices.

Low noise. No fixedcarrier, thereforeacoustic noisereasonable due to“white” noise spectrum.

Cost savings in acousticbarriers in noisesensitive applications.No harmful mechanicalresonances. Lowerstresses in gearboxes,fans, pumps.

Can accelerate anddecelerate in quickesttime possible withoutmechanical constraints.

Automatic start(Flying start).

Synchronises to rotatingmotor.

No processinterruptions. Smoothcontrol of machinery.Resume control in allsituations.

No limits on maximumacceleration anddeceleration rate.

Better process control.

BENEFITFEATURE RESULT


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Also a DTC drive features rapid starting in all motorelectromagnetic and mechanical states. The motor canbe started immediately without delay.

It appears that DTC drives are most advantageous forhigh performance or demanding drive applications. Whatbenefits does DTC bring to standard drives?

Standard applications account for 70% of all variable speeddrives installed throughout industry. Two of the most commonapplications are in fans and pumps in industries like Heating,Ventilating and Air Conditioning (HeVAC), water and food anddrinks.

In these applications, DTC provides solutions to problemslike harmonics and noise.

For example, DTC technology can provide control to the driveinput line generating unit, where a conventional diode bridgeis replaced with a controlled bridge.

This means that harmonics can be significantly reducedwith a DTC controlled input bridge. The low level currentdistortion with a DTC controlled bridge will be less than aconventional 6-pulse or 12-pulse configuration and powerfactor can be as high as 0.99.

For standard applications, DTC drives easily withstand hugeand sudden load torques caused by rapid changes in theprocess, without any overvoltage or overcurrent trip.

Also, if there is a loss of input power for a short time, thedrive must remain energised. The DC link voltage must notdrop below the lowest control level of 80%. To ensure this,DTC has a 25 microseconds control cycle.

What is the impact of DTC on pump control?

DTC has an impact on all types of pumps. Because DTCleads to a universal drive, all pumps, regardless of whetherthey are centrifugal or constant torque type (screw pumps)can now be controlled with one drive configuration, ascan aerators and conveyors. DTC technology allows a driveto adjust itself to varying application needs.

For example, in screw pumps a drive using DTC technologywill be able to adjust itself for sufficient starting torque for aguaranteed start.



Improved power loss ride through will improve pumpingavailability during short power breaks.

The inherent torque control facility for DTC technology allowsthe torque to be limited in order to avoid mechanical stresson pumps and pipelines.

What is the impact of DTC technology on energysavings?

A feature of DTC which contributes to energy efficiency is adevelopment called motor flux optimisation.

With this feature, the efficiency of the total drive (that iscontroller and motor) is greatly improved in fan and pumpapplications.

For example, with 25% load there is up to 10% total energyefficiency improvement. At 50% load there can be 2% totalefficiency improvement.

This directly impacts on operating costs. This feature alsosignificantly reduces the motor noise compared to thatgenerated by the switching frequency of a traditional PWMdrive.

Has DTC technology been used in many installations?

Yes, there are hundreds of thousands of installations in use.For example, one of the world's largest web machinemanufacturers tested DTC technology for a winder in afilm finishing process.

The Requirement:Exact torque control in the winder so as to produce highquality film rolls.

The Solution:Open-loop DTC drives have replaced traditional DC drivesand latter flux vector controlled AC drives on the centredrives in the rewind station.



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The Benefits:Winder station construction simplified and reliability increased.The cost of one tachometer and associated wiring equals thatof one 30kW AC motor. This provides significant investmentcost savings.

What is the difference between DTC and traditionalPWM methods?

• Frequency Control PWM and Flux Vector PWM

Traditional PWM drives use output voltage and outputfrequency as the primary control variables but these needto be pulse width modulated before being applied to themotor.

This modulator stage adds to the signal processing time andtherefore limits the level of torque and speed responsepossible from the PWM drive.

Typically, a PWM modulator takes 10 times longer than DTCto respond to actual change.

• DTC control

DTC allows the motor’s torque and stator flux to be usedas primary control variables, both of which are obtaineddirectly from the motor itself. Therefore, with DTC, there isno need for a separate voltage and frequency controlledPWM modulator. Another big advantage of a DTC drive isthat no feedback device is needed for 95% of all driveapplications.

Why does DTC not need a tachometer or position encoderto tell it precisely where the motor shaft is at all times?

There are four main reasons for this:

• The accuracy of the Motor Model (see page 27).• Controlling variables are taken directly from the motor

(see page 27).• The fast processing speeds of the DSP and Optimum

Pulse Selector hardware (see page 28).• No modulator is needed (see page 12).

Operation



When combined to form a DTC drive, the above featuresproduce a drive capable of calculating the ideal switchingvoltages 40,000 times every second. It is fast enough tocontrol individual switching pulses. Quite simply, it is thefastest ever achieved.

Once every 25 microseconds, the inverter’s semiconductorsare supplied with an optimum switching pattern to producethe required torque. This update rate is substantially lessthan any time constants in the motor. Thus, the motor isnow the limiting component, not the inverter.

What is the difference between DTC and othersensorless drives on the market?

There are vast differences between DTC and many of thesensorless drives. But the main difference is that DTCprovides accurate control even at low speeds and down tozero speed without encoder feedback. At low frequenciesthe nominal torque step can be increased in less than1ms. This is the best available.

How does a DTC drive achieve the performance of aservo drive?

Quite simply because the motor is now the limit ofperformance and not the drive itself. A typical dynamic speedaccuracy for a servo drive is 0.1%s. A DTC drive can reachthis dynamic accuracy with the optional speed feedbackfrom a tachometer

How does DTC achieve these major improvementsover traditional technology?

The most striking difference is the sheer speed by whichDTC operates. As mentioned above, the torque response isthe quickest available.

To achieve a fast torque loop, ABB has utilised the latesthigh speed signal processing technology and spent 100 manyears developing the highly advanced Motor Model whichprecisely simulates the actual motor parameters withinthe controller.

For a clearer understanding of DTC control theory, seepage 26.



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Does a DTC drive use fuzzy logic within its control loop?

No. Fuzzy logic is used in some drives to maintain theacceleration current within current limits and therefore preventthe drive from tripping unnecessarily. As DTC is controllingthe torque directly, current can be kept within these limitsin all operating conditions.

A drive using DTC technology is said to be tripless.How has this been achieved?

Many manufacturers have spent years trying to avoid tripsduring acceleration and deceleration and have found itextraordinarily difficult. DTC achieves tripless operationby controlling the actual motor torque.

The speed and accuracy of a drive which relies oncomputed rather than measured control parameters cannever be realistic. Unless you are looking at the shaft,you are not getting the full picture. Is this true withDTC?

DTC knows the full picture. As explained above, thanks tothe sophistication of the Motor Model and the ability to carryout 40,000 calculations every second, a DTC drive knowsprecisely what the motor shaft is doing. There is never anydoubt as to the motor’s state. This is reflected in theexceptionally high torque response and speed accuracyfigures quoted on pages 16 and 17.

Unlike traditional AC drives, where up to 30% of all switchingsare wasted, a drive using DTC technology knows preciselywhere the shaft is and so does not waste any of its switchings.

DTC can cover 95% of all industrial applications. Theexceptions, mainly applications where extremely precisespeed control is needed, will be catered for by adding afeedback device to provide closed loop control. This device,however, can be simpler than the sensors needed forconventional closed loop drives.

Even with the fastest semiconductors some dead timeis introduced. Therefore, how accurate is the auto-tuning of a DTC drive?

Auto-tuning is used in the initial identification run of a DTCdrive (see page 27). The dead time is measured and is takeninto account by the Motor Model when calculating the actualflux. If we compare to a PWM drive, the problem with PWMis in the range 20-30Hz which causes torque ripple.



What kind of stability will a DTC drive have at lightloads and low speeds?

The stability down to zero speed is good and both torqueand speed accuracy can be maintained at very low speedsand light loads. We have defined the accuracies as follows:

Torque accuracy: Within a speed range of 2-100% and aload range of 10-100%, the torque accuracy is 2%.

Speed accuracy: Within a speed range of 2-100% and aload range of 10-100%, the speed accuracy is 10% of themotor slip. Motor slip of a 37kW motor is about 2% whichmeans a speed accuracy of 0.2%.

What are the limitations of DTC?

If several motors are connected in parallel in a DTC-controlledinverter, the arrangement operates as one large motor. It hasno information about the status of any single motor. If thenumber of motors varies or the motor power remains below1/8 of the rated power, it would be best to select the scalarcontrol macro.

Can DTC work with any type of induction motor?

Yes, any type of asynchronous, squirrel cage motor.



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Figure 5, below, shows the complete block diagram forDirect Torque Control (DTC).

Walk around the block

The block diagram shows that DTC has two fundamentalsections: the Torque Control Loop and the Speed ControlLoop. Now we will walk around the blocks exploring eachstage and showing how they integrate together.

Let’s start with DTC’s Torque Control Loop.

How DTCworks

Figure 5: DTC comprises two key blocks: Speed Control andTorque Control

Chapter 4 - Basic Control Theory


In normal operation, two motor phase currents and theDC bus voltage are simply measured, together with theinverter’s switch positions.

The measured information from the motor is fed to theAdaptive Motor Model.

The sophistication of this Motor Model allows precise dataabout the motor to be calculated. Before operating theDTC drive, the Motor Model is fed information about themotor, which is collected during a motor identification run.This is called auto-tuning and data such as statorresistance, mutual inductance and saturation coefficientsare determined along with the motor’s inertia. Theidentification of motor model parameters can be donewithout rotating motor shaft. This makes it easy to applyDTC technology also in retrofits. The extremely fine tuningof motor model is achieved when the identification runalso includes running the motor shaft for some seconds.

There is no need to feed back any shaft speed or positionwith tachometers or encoders if the static speed accuracyrequirement is over 0.5%, as it is for most industrial applications.

TorqueControl Loop

Step 1 Voltageand currentmeasurements

Step 2AdaptiveMotor Model

Basic Control Theory


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27

This is a significant advance over all other AC drivetechnology. The Motor Model is, in fact, key to DTC’sunrivalled low speed performance.

The Motor Model outputs control signals which directlyrepresent actual motor torque and actual stator flux. Alsoshaft speed is calculated within the Motor Model.

The information to control power switches is produced inthe Torque and Flux Comparator.

Both actual torque and actual flux are fed to the comparatorswhere they are compared, every 25 microseconds, to a torqueand flux reference value. Torque and flux status signals arecalculated using a two level hysteresis control method.

These signals are then fed to the Optimum Pulse Selector.

Within the Optimum Pulse Selector is the latest 40MHzdigital signal processor (DSP) together with ASIC hardwareto determine the switching logic of the inverter. Furthermore,all control signals are transmitted via optical links for highspeed data transmission.

This configuration brings immense processing speed suchthat every 25 microseconds the inverter’s semiconductorswitching devices are supplied with an optimum pulse forreaching, or maintaining, an accurate motor torque.

The correct switch combination is determined every controlcycle. There is no predetermined switching pattern. DTC hasbeen referred to as “just-in-time” switching, because,unlike traditional PWM drives where up to 30% of all switchchanges are unnecessary, with DTC each and everyswitching is needed and used.

This high speed of switching is fundamental to the success ofDTC. The main motor control parameters are updated 40,000times a second. This allows extremely rapid response on theshaft and is necessary so that the Motor Model (see Step2) can update this information.

It is this processing speed that brings the high performancefigures including a static speed control accuracy, withoutencoder, of ±0.5% and the torque response of less than 2ms.

Step 4OptimumPulse Selector

Step 3 TorqueComparatorand FluxComparator



Within the Torque Reference Controller, the speed controloutput is limited by the torque limits and DC bus voltage.

It also includes speed control for cases when an externaltorque signal is used. The internal torque reference from thisblock is fed to the Torque Comparator.

The Speed Controller block consists both of a PID controllerand an acceleration compensator. The external speedreference signal is compared to the actual speed producedin the Motor Model. The error signal is then fed to both thePID controller and the acceleration compensator. The outputis the sum of outputs from both of them.

An absolute value of stator flux can be given from the FluxReference Controller to the Flux Comparator block. The abilityto control and modify this absolute value provides an easyway to realise many inverter functions such as FluxOptimisation and Flux Braking (see page 19).

Speed Control

Step 5 TorqueReferenceController

Step 6 SpeedController


Step 7Flux ReferenceController


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Chapter 5 - Index

AAC drive 5, 6, 8, 9, 10, 12, 13, 14,15, 16, 17, 18, 21, 24, 28AC drive using DTC 12, 13AC drive with flux vector control 10AC drive with frequency control 9AC induction motor 10, 11AC motor 5, 6, 8, 13, 18AC variable speed drive 6, 8acceleration compensator 29accuracy control 18aerators 20air condition 5, 20angular position 11armature current 7armature windings 7ASIC 28auto-tuning 19, 24, 27

BBlaschke 16braking 19, 29

Cclosed-loop 10, 11, 15, 16closed-loop drives 10, 11commissioning 19commutator-brush assembly 7control cycle 28control loop 7, 9, 10, 12, 13, 24,26, 27, 29control variables 10, 13, 15, 22controlled input bridge 20controlling variables 9, 11, 12, 14,22conveyors 20costs 8, 10, 11, 18, 19, 21

DDC bus voltage 27, 29DC drive 7, 8, 9, 10, 11, 12, 13,14, 18DC link voltage 19, 20DC motor 6, 7, 8, 11, 15DC Motor Drive 6Depenbrock 16digital signal processing 12diode bridge 20diode rectifier 9Direct Torque Control 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 26drive input line generating unit 20DSP 22, 28DTC 5, 6, 12, 13, 14, 15, 16, 17, 18,19, 20, 21, 22, 23, 24, 25, 26, 27, 28dynamic speed accuracy 12, 17,18, 23dynamic speed response 8


Eelectrical time constant 8electronic controller 11, 14elevators 17encoders 8, 11, 12, 14, 18, 22,23, 27, 28energy savings 21external speed reference 29external torque signal 29

Ffan 10, 19, 20, 21feedback device 9, 10, 11, 13,15, 16, 22, 24field current 7field orientation 7, 8, 10, 11, 12field oriented control 16film finishing 21flux braking 19, 29flux comparator 28, 29flux optimisation 19, 21, 29Flux Reference Controller 29flux vector 6, 10, 11, 13, 16, 21, 22flux vector control 6, 10, 11, 13flux vector PWM drives 11food 20frequency control 6, 9, 13, 22fuzzy logic 24

Ggearbox 19

Hharmonics 15, 20heating 20HeVAC 20hysteresis control 28

Iinertia 27initial cost 18input frequency 15

Lload torque 16, 20loss of input power 20low frequencies 16, 17, 23

Mmagnetising current 7maintenance 6, 8, 18mechanical brake 18modulator 9, 10, 11, 12, 14, 22motor controller 8motor flux optimisation 21motor magnetising flux 12Motor Model 10, 22, 23, 24, 27,28, 29motor noise 19, 21Motor static speed 17

30


1motor torque 8, 12, 28mutual inductance 27

Nnoise 15, 19, 20, 21nominal torque step 23

OOEMs 5open-loop drive 9open loop AC drives 12operating cost 21optical link 28Optimum Pulse Selector 28output frequency 22output voltage 22

Ppaper industry 17PID controller 29pipelines 21position control 18position encoder 12, 22position feedback 8power factor 20power loss ride through 19, 21predetermined switching pattern 19,28Pulse Width Modulation 9pump 10, 19, 20, 21PWM 6, 9, 10, 11, 14, 15, 16, 17,21, 22, 24, 28PWM AC drive 11, 14, 21, 22, 24,28

Rreliability 8, 18restart 19retrofit 19RFI 15rotor 7, 8, 10, 11rotor flux 11rotor position 7rotor speed 11

Ssaturation coefficient 27scalar control 10, 25sensorless 23servicing 8servo drive 18, 23signal processing 12, 22, 23signal processing time 22speed 5, 6, 7, 8, 9, 10, 11, 12, 13,14, 15, 16, 17, 18, 19, 20, 22, 23, 24,25, 26, 27, 28, 29speed accuracy 6, 8, 11, 12, 15,17, 18, 23, 24, 25, 27speed control 6, 7, 24, 26, 28, 29Speed Control Loop 26

speed control output 29Speed Controller 29speed response 7, 8, 22stability 25start 5, 19, 20, 26starting 19, 20static accuracy 18static speed accuracy 17, 27stator 7, 9, 10, 11, 22, 27, 28, 29stator field 11stator flux 22, 28, 29stator resistance 27stator winding 9, 10stress 19, 21switching pattern 19, 23, 28switching pulses 23

Ttachometer 12, 14, 16, 17, 18,22, 23, 27time constant 8, 23torque 5, 6, 7, 8, 9, 10, 11, 12, 13,14, 15, 16, 17, 18, 19, 20, 21, 22,23, 24, 25, 26, 28, 29- control 5, 6, 7, 8, 10, 12, 18, 21,26- control at low frequencies 16- full load at zero speed 16- linearity 17- loop 23- repeatability 18- response 6, 8, 11, 12, 18, 23,24, 28- ripple 24Torque and Flux Comparator 28Torque Comparator 28, 29Torque Control Loop 26Torque Reference Controller 29trip 15, 19, 20, 24

Uuniversal 12, 15, 18, 20

Vvariable speed drives 5, 6, 13,20ventilating 20voltage 8, 9, 10, 11, 14, 15, 16,19, 20, 22, 23, 27, 29voltage fed drive 8VSD 5, 6

Wwater 5, 20web machine 21winder 17, 21, 22

Zzero speed 11, 16, 18, 19, 23, 25

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ABB OyDrivesP.O. Box 184FIN-00381 HelsinkiFINLANDTel: +358 10 22 11Fax: +358 10 222 2681Internet: http://www.abb.com/motors&drives

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EU Council Directives andAdjustable Speed Electrical PowerDrive Systems

Technical Guide No.2- EU Council Directives2

Contents

1 Introduction .........................................................7This guide’s purpose .................................................... 7How to use this guide .................................................. 8

Responsibilities and actions..................................... 8Tickboxes................................................................. 8Cross-referencing .................................................... 8Key Points ................................................................ 8

2 General questions and answers ...........................9What is all the fuss about? ........................................... 9

What are these EU Council Directives? .................... 9How does EMC affect me? ...................................... 9What is EMC? ........................................................ 10What is an electromagnetic environment? ............. 10How does electromagnetic interference show up? 10What emissions can drives cause? ........................ 11How is this emission seen? .................................... 11How do I avoid electromagnetic interference? ...... 11Drive manufacturers must comply with EMCstandards then? ..................................................... 11If a drive is CE Marked, I need not worry. True?..... 11

3 CE Marking ........................................................ 13What is CE Marking and how relevant is it for drives? 13What is CE Marking for? ............................................ 14

Is CE Marking a quality mark? ............................... 14What is the legal position regarding CE Marking? . 14What is the importance of CE Marking forpurchasers of drives? ............................................. 14If I buy a CE marked drive, will I meet thetechnical requirements of the Directives? .............. 14What happens if, as an End User, I put together asystem - do I have to put CE Marking on? ............. 15What about spare parts that I buy for a drive? Do Inegate the CE Mark if I replace a component? ...... 15If drives are classed as components, they cannotbe EMC certified or carry a CE Mark, is this true? . 15

In Summary ................................................................ 16Component ............................................................ 16Components with direct function ........................... 16Components without direct function ...................... 17Apparatus .............................................................. 17Systems ................................................................. 17Installation .............................................................. 17

4 Purchasing decisions for PDSs .......................... 18What you need to know and do ................................. 18If you are a Machine Builder buying a PDS ............. 22

Technical Guide No.2- EU Council Directives

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Actions you must take ........................................... 23If you are a System Designer buying a PDS ............... 26

Path 1 ..................................................................... 26Actions you must take ........................................... 27Path 2 ..................................................................... 27Actions you must take ........................................... 27Path 3 ..................................................................... 28Actions you must take ........................................... 28

If you are an End-User buying a CDM/BDM or PDS .. 28You have the following responsibilities ................... 29Actions you must take ........................................... 29

If you are a Panelbuilder buying a CDM/BDM............ 30Additional actions .................................................. 32

If you are a Distributor buying a CDM/BDM ............... 32If you are an Installer buying a CDM/BDM or PDS ..... 32

5 Terminology ....................................................... 34Technical Construction File (TCF) ............................... 34

What is a Technical Construction File? .................. 34When do I use a TCF?............................................ 34Why is a TCF deemed to be important? ................ 34Will customers always receive a TCF copy? .......... 35What is the shelf life of a TCF? .............................. 35Is there any way I can avoid the TCF? ................... 35How do I ensure that tests are always carried out? 35Can drive manufacturers help more? ..................... 35

How to make up a TCF .............................................. 361. Description of the product ................................. 362. Procedures used to ensure product conformity . 373. A report or certificate from a Competent Body .. 374. Actions by the Competent Body ........................ 38

Technical File (for mechanical safety aspects) ........... 38What is a Technical File? ........................................ 38

How to make up a Technical File ............................... 39Drawings and diagrams ......................................... 39Health and safety ................................................... 39Machine design ...................................................... 39Other certificates required ..................................... 39

Technical File (for electrical safety aspects) ............... 40What is a Technical File? ........................................ 40

How to make up a Technical File ............................... 40Drawings and diagrams ......................................... 40Standards............................................................... 40Electrical Safety Aspect ......................................... 40Other requirements ................................................ 40

Certificate of Adequacy ............................................. 41What if standards cannot be wholly implemented? 41

How to obtain a Certificate of Adequacy ................... 41Technical Report or Certificate ................................... 41

What if standards cannot be wholly implemented? 41How to obtain the Technical Report or Certificate ..... 41


Report ........................................................................ 41What if standards cannot be wholly implemented? 41

How to obtain a Report .............................................. 42Declaration of Conformity (for EMC and electricalsafety aspects) ........................................................... 42How to obtain a Declaration of Conformity ................ 42Declaration of Conformity (for mechanicalsafety aspects) ........................................................... 43How to obtain a Declaration of Conformity ................ 43Declaration of Incorporation ...................................... 43

What is a Declaration of Incorporation?................. 43Is there no way out of this type of Declaration? ..... 44

What a Declaration of Incorporation contains ............ 44Type Certification ....................................................... 45How to obtain Type Certification ................................ 45

6 Authorities and Bodies ....................................... 46Competent Authority .................................................. 46Competent Body ........................................................ 46Notified Body ............................................................. 46

7 Standards and Directives ................................... 47Directive or Standard? ............................................... 47Harmonised Standards for PDSs ............................... 47

How to recognise a European Standard ................ 48Your questions answered ........................................... 48

Which standards directly relate to drives? ............. 48What are the issues of EN 61800-3 and drives? .... 49What are the solutions to radiated emissions? ...... 49Do I have to conform to the standards? ................ 49Can I be fined for not conforming? ........................ 50

The Product Specific Standard EN 61800-3 ............... 50Mode 1 ................................................................... 50Mode 2 ................................................................... 50Mode 3 ................................................................... 51Mode 4 ................................................................... 51

Applications of different Modes ................................. 51Machinery Directive 98/37/EC .................................... 52

How does the Machinery Directive affect my drive?52Where can I obtain a Machinery Directive copy? ... 53

Low Voltage Directive ................................................. 53How does the LVD affect my drive? ....................... 53Why is the Declaration of Conformity important? .. 54

EMC Directive ............................................................ 54How does the EMC Directive affect my drive? ....... 54Who has the responsibility to ensure CE Marking? 55Summary of responsibilities ................................... 56Achieving conformity with EC Safety Directives .... 57

8 Installation ......................................................... 58General installation concerns ..................................... 58


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Technical requirements of the legislation ................... 58How can EMC be improved? ................................. 59

General installation practice ....................................... 60Cabling ................................................................... 60Relay Outputs ........................................................ 60Earthing .................................................................. 61Shielding ................................................................ 62Filtering .................................................................. 63Testing and installation ........................................... 64

Your technical concerns answered ............................ 65What is the affect of varying impedance? .............. 65What are the effects of multiple drives? ................. 65Large installations with many drives can take upto 3 months and be costly. What can we do? ........ 65

9 Index ................................................................. 66



This guide'spurpose


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The aim of this Technical Guide No.2* is to give a straight-forward explanation of how the various EU Council Directivesrelate to Power Drive Systems (PDSs). For an explanationof the terminology of PDSs, see pages 18 and 19.

While Electromagnetic Compatibility (EMC) is the subjectof most concern within the industry, it must be realisedthat the EMC Directive is only part of the overall EU initiativeon common safety standards.

It is the intention of this Guide to offer users of AC or DCpower drive systems - whether Machine Builders, SystemDesigners, Distributors, OEMs, End-Users or Installers -some clear practical guidelines and courses of action.

*Notes

1 The content of this Technical Guide is ABB Oy's, Drivesinterpretation of events as of November 1999. However,we reserve the right to develop and evolve theseinterpretations as more details become available fromCompetent Bodies (see Chapter 6), CompetentAuthorities (see Chapter 6), organisations and from ourown tests.

2 Other Technical Guides available in this series include:

Technical Guide No.1 -Direct Torque Control (3AFE 58056685).

Technical Guide No.3 -EMC Compliant Installation and Configuration for aPower Drive System (3AFE 61348280).

Technical Guide No.4 -Guide to Variable Speed Drives (3AFE 61389211).

Technical Guide No.5 -Bearing Currents in Modern AC Drive Systems(3BFE 64230247)

Technical Guide No.6 -Guide to Harmonics with AC Drives (3AFE 64292714)

Technical Guide No.7 -Dimensioning of a Drive system (3AFE 64292714)

Technical Guide No.8 -Electrical Braking (3BFE 64362534)

The Guide is divided into 9 Sections.

Section 4 looks at Purchasing Decisions for PDSs.Please note the following about the structure of thissection:

Each type of purchaser is offered an explanation of theirResponsibilities. This is for awareness. No action is needed.

Following the Responsibilities is a set of Actions. If thepurchaser follows these Actions, step-by-step, thenconforming to the relevant Directives will be straightforward.

Alongside the Actions are tickboxes. Purchasers canphotocopy the relevant pages and use them as a checklistwith each item being ticked off as it is achieved.

Because of the complexity of conforming to each Directive,this Guide inevitably carries a lot of cross-references toother sections. In the margin you will come across:

Defined on page XXYou are advised to turn to the page number reference.

You will also notice other references within the text. Thesecan be referred to if the item is unclear but is not essentialfor achieving compliance.

Within the text you will see:

Key PointThese are key observations that must be observed.

How to Usethis Guide

Responsibilitiesand actions

Tickboxes

Cross-referencing

KEY POINTS:


Chapter 2 - General questions and answers

What is all thefuss about?

I have had no problems with drives in the past so whydo I need to be concerned with EMC now?

Beware! Electromagnetic Compatibility (EMC) is only oneof a number of EU Council Directives relating to commonsafety standards for electrically powered equipment likePower Drive Systems.

It is very important that users of PDSs fully understand allthe various rules and regulations and how they apply toPDSs. That is the purpose of this Guide.

It is important to realise that EMC cannot be divorced fromother European legislation. So before answering thisquestion, we need to look at the other legislation and howit affects the purchase and installation of drives.Quite simply there are three Directives that mainly affecta drive’s safety against risks and hazards. These are:

But more on each of these Directives later. Let us firstexplain EMC and look at some concerns of the industry.

From January 1, 1996 the EU Council’s ElectromagneticCompatibility Directive (89/336/EEC) has been compulsory.It applies to all electrical and electronic equipment soldwithin the EU and affects virtually all manufacturers andimporters of electrical and electronic goods.

KEY POINT:

What are theseEU CouncilDirectives?

How does EMCaffect me?

Directive Applicable Mandatory Page

Machinery Directive 1993-01-01 1995-01-01 pg 52Low Voltage Directive 1995-01-01 1997-01-01 pg 53EMC Directive 1992-01-01 1996-01-01 pg 54


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Electrical equipment that does not conform to theregulations may not be sold anywhere in the EEA (EuropeanEconomic Area).

EMC stands for Electromagnetic Compatibility. It is theability of electrical/electronic equipment to operateproblem-free within an electromagnetic environment.Likewise, the equipment must not disturb or interfere withany other products or systems within its locality.

The electromagnetic environment is everywhere but itvaries from place to place. The reason is that there aremany different sources of disturbance which can be naturalor man-made.

Natural sources consist of electrical discharge betweenclouds, lightning or other atmospheric disturbances. Whilewe cannot influence these sources we can protect ourproducts and systems from their effects (see Installation,page 58).

Man-made disturbances are those generated by, forexample, electrical contacts and semiconductors, digitalsystems like microprocessors, mobile radio transmitters,walkie-talkies, portable car telephones and Power DriveSystems (see page 18).

Such a variety of equipment, each with its own emissioncharacteristics, is often used so near to other electricalequipment that the field strengths they create may causeinterferences.

It is important that all PDSs are immune to these naturaland man-made disturbances. While drives manufacturersstrive to make their products immune, the Directive laysdown minimum standards for immunity, thereby ensuringall manufacturers achieve the same basic level.

Electromagnetic interference shows up in a variety of ways.Typical examples of interference include a poorlysuppressed automobile engine or dynamo; an electric drillcausing patterning on the TV screen; or crackling from anAM radio.

The microprocessor and power electronic component,switch rapidly and therefore, can cause interference at highfrequencies, unless proper precautions are taken.

KEY POINT:

What is EMC?

What is anelectromagneticenvironment?

KEY POINT:

How doeselectromagneticinterferenceshow up?


The normal operation of any drive involves rapid switchingof high voltages and this can produce radio frequencyemission. It is this radiation and emission that have beenseen to have the potential to disturb other circuits atfrequencies below 200 MHz.

Modern equipment contains considerable communicationsand other digital electronics. This can cause considerableemissions at frequencies above 200MHz.

The main emission is via conduction to the mains. Radiationfrom the converter and conducting cables is another typeof emission and it is especially demanding to achieve theradiated emission limits.

You need to ensure two things:

• that the equipment generates minimum emission.

• that the equipment is immune to outside effects.

In the case of Power Drive Systems, a lot hinges on thequality of the installation. See Installation, page 58, formore details.

Electromagnetic interference needs to be conducted toearth (ground potential) and no system can work unless itis properly connected.

Unfortunately, the process is not that simple. Virtuallyeveryone in the supply chain has a responsibility to ensurea product, a system and an installation complies with theessential requirements of the EMC Directive.

The key is to clearly understand who has responsibility forwhat. In the forthcoming pages we take a look at varioustypes of purchasers and examine the steps each shouldtake to meet all three Directives mentioned on page 9.

Everyone from manufacturer to installer to user has aresponsibility in complying with EMC rules.

Again this is a big misconception. Just because a drivehas CE Marking does not necessarily mean it meets theEMC Directive.

How is thisemissionseen?

How do I avoidelectromagneticinterference?

KEY POINT:

Drivesmanufacturersmust complywith EMCstandardsthen?

If a drive is CEMarked, I neednot worry.True?

Whatemissions candrives cause?


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This will all become clear by referring to the sectionPurchasing Decisions for PDSs, page 18.

CE Marking according to the EMC-Directive cannotnormally be applied to a module that is no more than achassis with exposed terminals.

KEY POINT:


Chapter 3 - CE Marking

What is CEMarking andhow relevant isit for drives?

CE Marking, shown below, is the official signature of theDeclaration of Conformity (see pages 42 and 43) asgoverned by the European Commission. It is a very specificgraphic symbol and must be separated from other marks.

CE Marking is a system of self-certification to identifyequipment that complies with the relevant applicableDirectives.

If a drive is the subject of several directives and, forexample, conforms with the Low Voltage Directive (seepage 53), then, from 1997, it is compulsory that it showsCE Marking. That marking shall indicate that the drivealso conforms to the EMC Directive (page 54). CE markingshall indicate conformity only to the directive(s) appliedby the manufacturer.

NOTE: If the standards route is used, then there must be aTechnical File supporting the Declaration of Conformity.However, if standards cannot be complied with then aTechnical Construction File (TCF) needs to be compiled.

For more on Technical Construction Files and TechnicalFiles, please refer to pages 34 and 40.

KEY POINT:


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What is CEMarking for?

CE Marking is mainly for the benefit of Authoritiesthroughout the EU and EEA countries who control themovement of goods. CE Marking shows that the productcomplies with the essential requirements of all relevantDirectives, mainly in the area of technical safety andconformity assessment. There are three Directives that arerelevant to drives, but CE Marking may be attached toindicate compliance with one (see the previous page).

Most definitely not. As CE Marking is self certification,you can be assured that certification has been carried out.

Anyone applying CE Marking is legally liable and must beable to prove the validity of his actions to the authorities.CE Marking confirms compliance with the Directives listedin the Declaration of Conformity (see pages 42 and 43).

As far as a purchaser of a drive is concerned, anythingthat carries the CE Mark must have a functional valueto him.

Thus, a complete drive product, which can be safelycabled and powered up on its own, may carry the CEmarking.

In practice, you will see drive products with CE Marking.But it is important to understand just why the product wasgiven CE Marking in the first place.

Basically a drive has no functional value. It is only ofpractical use when connected to, say, a motor which inturn is connected to a load.

Therefore, as far as the Machinery Directive is concerneda drive cannot have CE Marking unless it is part of a“process” comprising the drive, motor and load.

As for the EMC Directive, the equipment that make up a“process” include cabling, drives and motor. CE Markingcan only be affixed if all items forming such a “process”conform to the requirements of the Directive.

However, in the eyes of the Low Voltage Directive, a builtdrive does have functionality. That is, through the drive'sParameters you can program the drive and obtain an inputand output signal. Thus, if a drive conforms to the LowVoltage Directive it can carry CE Marking. Refer to pages52, 53 and 54 for explanations of the three Directives.

Is CE Markinga quality mark?

What is the legalposition regardingCE Marking?

What is theimportance ofCE Marking forpurchasers ofdrives?

If I buy a CEmarked drive,will I meet thetechnicalrequirementsof theDirectives?


Yes. Anyone putting together a system and commissioningit is responsible for the appropriate CE Marking.

Turn to page 29 for more details about the End-User'sresponsibilities.

Equipment supplied before the application of theDirectives, can be repaired and supplied with spare partsto bring it back to the original specification. However, itcannot be enhanced or reinstalled without meeting theDirectives.

For equipment supplied after the application of theDirectives, the use of the manufacturer's spare partsshould not negate the CE Marking. However, themanufacturer or supplier should be consulted aboutupgrading, as some actions could affect the CE Markingcriteria.

You need to first understand the terminology now beingapplied to drives. See below and page 18 for this.

A Complete Drive Module (CDM) is normally a componentin a system and as such has no functional value unless itis connected to the motor when it becomes a PDS.

The CDM shall be CE-marked if it is to be installed withsimple connections and adjustments that do not requireany EMC-knowledge.

If awareness of the EMC implication is needed in order toinstall a CDM, it is not considered as an apparatus. Thus,it shall not be CE-marked according to the EMC-directives.

If a CDM or BDM is intended for incorporation in PDS byprofessional manufacturers only (panel builders, machinebuilders), it shall not be CE-marked, nor is declaration ofconformity given by the CDM/BDM manufacturer. Insteadinstallation instructions shall be supplied in order to helpthe professional manufacturers.

KEY POINT:

What happens if,as an End-User,I put together asystem - do Ihave to put CEMarking on?

What aboutspare partsthat I buy for adrive? Do Inegate the CEMark if Ireplace acomponent?

If drives areclassed ascomponents,they cannot beEMC certifiedor carry a CEMark. Is thistrue?


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In Summary Under the Directives, Components with direct functionavailable without further adjustment other than simpleones, Apparatus and Systems have to be CE marked.Components with direct function not available withoutsimple adjustments and Components without directfunction and Installations, while required to satisfyvarious elements of the Directives, shall not be CE marked.

In this context the interpretation of component can bedivided into two main categories. The component caneither deliver a ‘direct function’ or not.

Direct function:Any function of the component itself, which fulfils theintended use, specified by the manufacturer in theinstruction for use for an end user.

Components with a direct function can be divided into twosub-groups:

1) The direct function is available without furtheradjustment or connections other than simpleones, which can be performed by any person not fullyaware of the EMC implications. Such a componentis an ‘apparatus’ and it is subjected to all provisionsof the EMC Directive.

2) The direct function is not available without furtheradjustment or connections other than simple ones,which can be performed by any person not fully awareof the EMC implications. Such a component is not an‘apparatus’. The only requirement for such acomponent is to provide it with instructions for usefor the professional assembler or manufacturer ofthe final apparatus into which the component willbe incorporated. These instructions should help himto solve any EMC problems with his final apparatus.

If a component performs a direct function without furtheradjustment other than simple ones, the component isconsidered equivalent to apparatus. Some variable speedpower drive products fall into this category, e.g. a driveinstalled into a cabinet or drive with enclosure and sold as acomplete unit (CDM). All provisions of the EMC Directive apply.

If a component performs a direct function that is not availablewithout further adjustment other than simple ones, it isconsidered as a component. Some variable speed power driveproducts fall into this category, e.g. basic drive module (BDM).These are meant to be assembled by a professional assembler

Componentswith directfunction

Component


(e.g. panel builder or system manufacturer) into a cabinetnot in the scope of delivery of the manufacturer of the BDM.According to the EMC Directive, the requirement for theBDM supplier is instructions for installation and use.

According to the EMC Directive the system manufactureror panel builder is resonsible for CE-mark, Declaration ofConformity and Technical Construction File.

Components with no direct function are not consideredas apparatus within the meaning of the EMC Directive.The EMC Directive does not apply to these. Thesecomponents include resistors, cables, terminal blocks, etc.

A finished product containing electrical and/or electroniccomponents and intended to be placed on the market and/or taken into service as a single commercial unit.

Several items of apparatus combined to fulfil a specificobjective and intended to be placed on the market as asingle functional unit.

A combination of items of apparatus, equipment and/orcomponents put together at a given place to fulfil a specificobjective but not intended to be placed on the market asa single functional unit.

Componentswithout directfunction

Apparatus

Installation

Systems


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Chapter 4 - Purchasing decisions for PDSs

What you needto know and do

Starting on page 20, we offer a step-by-step guiderelating to your purchasing requirements for PowerDrive Systems.

Before turning to page 20, you need to know the followingIEC terms for PDSs and their component parts, which maybe unfamiliar to many users.

KEY POINT:

TERMS THAT YOU MUST KNOW1. Basic Drive Module (BDM) consists of the convertersection and the control circuits needed for torque orspeed. A BDM is the essential part of the Power DriveSystem taking electrical power from a 50 Hz constantfrequency supply and converting it into a variable formfor an electric motor.

2. Complete Drive Module (CDM) consists of the drivesystem without the motor and the sensors mechanicallycoupled to the motor shaft. The CDM also includes theBasic Drive Module (BDM) and a feeder section. Devicessuch as an incoming phase-shift transformer for a 12-pulse drive are considered part of the CDM.

3. Power Drive System, or PDS, is a term usedthroughout this Technical Guide. A PDS includes thefrequency converter and feeding section (the CDM andBDM), motors, sensors, all cabling, filters, panels andany other components needed to make the PDS workeffectively.

Note: The load is not considered part of the PDS, butthe CDM can incorporate the supply sections andventilation.


Now we strongly advise you turn to page 20, to discover the type of person you are.

Power Drive System (PDS)

CDM(Complete Drive Module)

Feeder sectionField supplyAuxiliaries

Others

Motor & sensors

Driven equipmentor load

Installation or part of installation

HOW THE TERMSFIT TOGETHER

BDM (Basic DriveModule)

Control sectionConverter section

System contrSystem contrSystem contrSystem contrSystem control and sequencingol and sequencingol and sequencingol and sequencingol and sequencing


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19

22

WHO ARE YOU?IF THIS IS

YOU, TURNNOW TOPAGE.....

Machine Builderis a person who buys either a PDS, CDM or BDM andother mechanical or electrical component parts, such asa pump, and assembles these into a machine.Note: A machine is defined as an assembly of linkedparts or components, at least one of which moves. Itincludes the appropriate actuators, control and powercircuits joined together for a specific application, inparticular for processing, treatment, moving orpackaging of a material.

System Designercarries out all the electrical design of the Power DriveSystem, specifying all component parts which comprisea PDS.

26

To make this Technical Guide easy to use, we havealso identified certain types of people who will beinvolved in the purchasing of drives.

Please identify the type nearest to your job function andturn to the relevant section.

End-Useris the final customer who will actually use the machine,PDS or CDM/BDM.

28

Panelbuilderconstructs enclosures into which a panelbuilder willinstall a variety of components, including a CDM/BDMand sometimes the motor. However, the built enclosuredoes not constitute a machine.

30


End-User - page 28

Drive Manufacturer

Panelbuilder -p.30

Distributor -p.32

System Designer- p.26

Panelbuilder -p.30

MachineBuilder

or OEM -p.22

Installer - p.32Installer - p.32

IF THIS ISYOU, TURN

NOW TOPAGE........

222630

Distributoracts as the sales distribution channel between the CDM/BDM manufacturer and the End-User, Machine Builder,OEM, Panelbuilder or System Designer.

Installercarries out the entire electrical installation of the PDS.

Original Equipment Manufacturer (OEM)For the purposes of purchasing drives, an OEM willnormally fall into the category of a Machine Builder,System Designer or Panelbuilder. Therefore, if youidentify yourself as an OEM, refer to the relevant pagesfor each of these job functions.

32

32

WHO ARE YOU?


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21

NOTE: Before reading this section we strongly urgeyou to familiarise yourself with the terms explainedon pages 16-19.

...You have the following responsibilities:

1. Because you are building a complete machine, whichincludes coupling up the motors to the PDS andproviding the mechanical guarding and so on, you areliable for the total mechanical and electrical safety ofthe machine as specified in the Machinery Directive.

Therefore, the PDS is ultimately your responsibility. Youneed to ensure that the entire PDS meets theMachinery Directive. Only then can CE Marking beapplied to the whole machine.

2. You are also responsible for the electrical safety of allparts of the PDS as specified in the Low VoltageDirective.

3. You must ensure electrical parts are manufactured inaccordance with the EMC Directive. The manufacturerof these parts is responsible for EMC for that particularpart. Nevertheless you are responsible for EMC for themachine. You may choose electrical parts not inaccordance with the EMC directive, but then you havethe responsibility for compliance of parts.

Note: Be aware that combining CE-marked sub-assemblies may not automatically produce anapparatus that meets the requirements.

4. You must ensure that the PDS or its component partscarry Declarations of Conformity in accordance withthe electrical safety requirements of the Low VoltageDirective.

5. You must be able to assure a Competent Authorityand customers that the machine has been builtaccording to the Machinery Directive, the LowVoltage Directive and the EMC Directive. It may benecessary to issue a Technical File and a TechnicalConstruction File to demonstrate compliance. You mustkeep in mind that you and only you have responsibilityfor compliance with directives.

6. A Declaration of Conformity according the directivesabove must be issued by the Machine Builder andCE Marking must then be affixed to the machine orsystem.

If you are aMachineBuilder buyinga PDS...


7. Any machine that does not comply must be withdrawnfrom the market.

1. To meet the Machinery Directive (see page 52) youneed to:

a. Comply with the following mechanical safety checklist.The aim is to eliminate any risk of accident throughoutthe machinery’s life. This is not a complete list, thedetailed list is contained within the MachineryDirective:

Eliminate risk as far as possible, taking the necessaryprotective measures if some risks cannot beeliminated.

Inform users of the residual risks; indicate whetherany training is required and stress the need forpersonal protective equipment.

Machinery design, construction and instructionsmust consider any abnormal use.

Under the intended conditions of use, thediscomfort, fatigue and stress of the operator mustbe reduced.

The manufacturer must take account of theoperator’s constraints resulting from the use ofpersonal protective equipment.

Machinery must be supplied with all essentialequipment to enable it to be used without risk.

Detailed instructions relating to materials, lighting, controls,protection devices are given in Annex 1 of the MachineryDirective.

b. Comply with the following electrical safety checklist:To ensure the electrical safety of all parts of the PDSas specified in the Low Voltage Directive (refer topage 53) you need to comply with the following safetychecklist, which is not necessarily complete.

Note: the detailed list is given in EN 60204-1. This can beobtained from CENELEC or the National StandardisationAssociation.

Actions youmust take


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The electricity supply should be equipped with ahand-operated disconnecting device and withemergency devices for switching off the supply inthe event of an unexpected start-up.

The equipment shall provide protection of personsagainst electric shock from direct or indirect contact.

The equipment is protected against the effects of:

overcurrent arising from a short circuit.

overload current.

abnormal temperatures.

loss of, or reduction in, the supply voltage.

overspeed of machines/machine elements.

The electrical equipment is equipped with anequipotential bonding circuit consisting of the:

• PE terminal.• conductive structural parts of the electrical

equipment and the machine.• protective conductors in the equipment or the

machine.

The control circuits and control functions ensure safeoperation including the necessary inter-lockings,emergency stop, prevention of automatic re-start,etc.

Defined on page 38

c. Compile a Technical File for the machine,including the PDS.


Generally, must carry CE Marking and have a Declarationof Conformity.

For machines that pose a high risk of accident, a TypeCertification (see page 45) is required from a NotifiedBody (see page 46). Such machinery is included in AnnexIV of the Machinery Directive.

The Type Certificate issued should be included in theTechnical File for the Machine or Safety Component.Refer now to page 38.

2. Declarations of Conformity from each of thecomponent suppliers whose products make upthe PDS and incorporate them into the TechnicalFile, referring to all three Directives. If buying aPDS from a System Designer (see below), heshould be able to provide all Declarations. Ifsystem designer or component supplier cannotprovide Declaration of Conformity , theresponsibility of demonstrating complianceaccording to EMC Directive or Low VoltageDirective lies on Machine Builder. Refer to pages30-32 in this case.

3. Pass this Technical File to a Competent Body(refer to page 46). The Machine Builder SHOULDNOT pass the File on to an End-User. Based onthe Technical File, obtain a Certificate ofAdequacy or Technical Report from aCompetent Body.

Defined on pages 42 and 43

4. Issue a Declaration of Conformity for the entiremachine. Only then can you apply CE Marking(see page 13).

5. Pass the Declaration of Conformity related toall three directives on to the End-User of themachine (refer to page 28).

6. Apply CE Marking to the machine.

7. Congratulations! You have successfully compliedwith the main requirements for safe and efficientoperation of a machine.

KEY POINT:


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If you are aSystemDesignerbuying aPDS...

NOTE: Before reading the next section, we stronglyurge you to familiarise yourself with the termsexplained on pages 16 - 19.


1. The PDS is a complex component of the machine.Therefore, the Machinery Directive has to be compliedwith by issuing a Declaration of Incorporation.

2. Because a PDS is not a machine, the only Directiveswhich need to be complied with are the Low VoltageDirective and the EMC Directive.

3. The responsibility for Declaration of Conformity andapplying CE Marking rests with both the SystemDesigner and the supplier of the component partswhich make up the Power Drive System.

The System Designer has to decide if he is going to placehis delivery on the market as a single functional unit or not

• if the answer is YES, the delivery shall be classified asa system (refer to page 16 - 17).

• if the answer is NO, the delivery shall be classified asan installation (refer to page 16 - 17).

A. If the delivery is classified as a system, the systemdesigner has to choose one of two paths to follow:

All components have EMC compliance

1. EMC behaviour is based on a component'sperformance.

2. Responsibility lies with the Component Suppliers forCE Marking of individual complex components

3. PDS is an System according to the EMC Directive(as placed on the market as a single funtional unit).

4. The Declaration of Conformity as well as the instruc-tions for use must refer to the system as whole. Thesystem designer assumes responsibility for compliancewith the Directive.

Note 1: The system designer is responsible forproducing the instructions for use for the particularsystem as whole.

Path 1



Note 2: Be aware that combining two or more CE-marked sub-assemblies may not automatically producea system that meets the requirements.

5. No CE Marking is required for a system as whole, aslong as each part bears the CE-mark.

1.Follow all Installation Guidelines issued by eachof the component suppliers.

2. Issue instructions for use in order to operate thesystem.

3. Issue a Technical Construction File for the System.

4. Issue a Declaration of Conformity.

5.DO NOT issue a CE Mark.

Components without EMC compliance

1. EMC behaviour is designed at the system level(no accumulated cost by device specific filters etc).

2. Responsibility lies with the System Designer whodecides the configuration (place or a specific filter etc).

3. PDS is a System according to the EMC Directive(as placed on the market as a single functional unit).

4. Declaration of Conformity and CE Marking arerequired for the System.

1.Follow the Installation Guidelines issued by eachof the component suppliers.

2.Optimise the construction of the installation toensure the design meets the required EMCbehaviour, i.e. the location of filters.

3. Issue instructions for use in order to operate thesystem.

4. Issue a Technical Construction File for theSystem.

5. Issue a Declaration of Conformity and CE Mark.


Path 2

Defined on pages 34 - 40


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If you are anEnd-Userbuying a CDM/BDM or PDS

KEY POINT:

B. If the delivery is an installation, the system designer hasone path to follow:

All components have EMC compliance

1. EMC behaviour is based on a component's performance.

2. Responsibility lies with the Component Suppliers forCE Marking of individual complex components.

3. PDS is an Installation according to the EMC Directive.

4. No Declaration of Conformity or CE Marking isrequired for a fixed Installation, (such as an outsidebroadcast radio station) DOC and CE marking are needed.

1. Follow all Installation Guidelines issued by eachof the component suppliers.

2. Transfer all Installation Guidelines andDeclaration of Conformity (see page 42) for eachof the components, as issued by suppliers, to theMachine Builder.

3. DO NOT issue a Declaration of Conformity orCE Marking as this is not allowed for fixedinstallations.


An End-User can make an agreement with the drive'ssupplier so that the supplier acts as the Machine Builder.However, the End-User is still responsible for the machine'ssafety.

The supplier who acts as the Machine Builder will issue aDeclaration of Conformity when the work is complete.

Once an intermediary Panelbuilder incorporates a CDM/BDM into a panel, he creates a part of a PDS.


Path 3


The Panelbuilder then has the same responsibilities as thedrive’s manufacturer.

1. For the total mechanical and electrical safety of themachine of which the drive is part of, as specified inthe Machinery Directive (see page 52).

2. For the electrical safety of the drive as specified in theLow Voltage Directive (see page 53).

3. To ensure the drive carries a Declaration of Conformityin accordance with the electrical safety requirementsof the Low Voltage Directive.

4. To be able to demonstrate to the Authorities that themachine to which the drive is being fitted has been builtto both the Machinery Directive and Low VoltageDirective.

5. The manufacturer of the drive is responsible fordetermining the EMC behaviour of the drive.

6. The resulting EMC behaviour is the responsibility of theassembler of the final product, by following themanufacturer’s recommendations and guidelines.

The following needs to be completed by either the End-User directly or the third party engaged to build themachine.

1. To meet the Machinery Directive (refer to page 52)you need to follow the Actions listed for a MachineBuilder on pages 22-25.

2. Follow installation instruction issued by manufacturersin order to fulfill the requirements of the EMC Directiveand the Low Voltage Directive.

3. Ensure that equipment (CDM/BDM/PDS) is operatedaccording to manufacturer's instruction in order toguarentee right way of operation.

...You have thefollowingresponsibilities



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If you are aPanelbuilderbuying a CDM/BDM



1. The Panelbuilder has two options:

Option A - To buy non-CE marked components

This could save the Panelbuilder money because he buyscomponents which are not tested for EMC. However, theresponsibility for EMC is then the Panelbuilder's and thiswill incur considerable costs as the entire panel needs tobe tested.

If the Panelbuilder buys non-CE marked components, thedrive may be made to conform without further testing ifthe components themselves have been tested. However,tested components do not carry the CE mark but mustcarry suitable instructions for installation. It is theseinstructions which must be demonstrably met.

Option A - Actions to meet these responsibilities

1.Follow the Installation Guidelines issued byeach of the component suppliers.

2.Optimise the construction of the installation toensure the design meets the required EMCbehaviour, i.e. the location of filters.

3.Issue a Technical Construction File for theSystem.

4.If you choose to test yourself you must makereference to EMC Directives:

89/336/EEC;91/263/EEC;92/31/EEC;93/68/EEC.

Harmonised standard:

EN 61800-3.

Defined on pages 47 to 54


Defined on pages 34-40

5. Once testing is completed, the results need to beincluded in the Technical Construction File(TCF) for the panel.

6. If testing is incomplete or full compliance cannotbe demonstrated, a TCF must be created andresults included for approval by a CompetentBody.

7. You must then issue the Declaration ofConformity and CE Marking for the panel (referto page 13).

Option B - To buy CE marked components

Option B - Actions to meet these responsibilities

1. Buying CE marked components creates a systemor an apparatus (refer to page 16-17) dependingon the nature of the panel.

2. Although the Panelbuilder does not have to carryout tests, he must ensure he conforms to theinstallation guidelines given by each of thecomponent manufacturers.Note: Be aware that combining two or more CE-marked components may not automaticallyproduce a system, which meets the requirements.

3. Beware! These guidelines could differ greatly fromthose given for normal installation purposesbecause the components will be in close proximityto each other.

4. Issue instructions for use in order to operatethe system or apparatus.

5. Issue a Technical Construction File.

6. Issue a Declaration of Conformity.

7. Apply CE Marking to your panel in the case of anapparatus. In the case of a system DO NOT applyCE Marking.


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The Panel can be either sold on the open market or use aspart of a machine. For each option there is a differentrequirement:

1. If you know that the panel is to be used as part ofa machine then you must request from the CDM /BDM manufacturer a Declaration of Incorporation.

2. The Declaration of Incorporation must besupplied with the panel to the Machine Builder,but CE Marking MUST NOT be affixed. This isbecause CE Marking always needs a Declarationof Conformity.

The Declaration of Incorporation CANNOT be used toapply CE Marking.

3. The Machine Builder will need this Declarationof Incorporation because he has to construct aTechnical Construction File (TCF) for themachine and in that file all the declarations needto be included.


1. If a Distributor is selling boxed products, like CDMBDMs (drives), direct from the manufacturer, his onlyresponsibility is to pass on the Installation Guidelinesto the End-user, Machine Builder or SystemDesigner. In addition, the Declaration of Conformitymust be passed to the Machine Builder or SystemDesigner.

2. Both the Installation Guidelines and the Declarationof Conformity are available from the manufacturer.

Actions you must take to meet these responsibilities

1. Pass all Installation Guidelines and Declaration ofConformities to either the End-User, MachineBuilder or System Designer.


1. You must ensure that the Installation Guidelines ofthe Machine Builder and/or System Designer areadhered to.

KEY POINT:

If you are aDistributorbuying a CDM/BDM...

If you are anInstaller buyinga CDM/BDMor PDS...

Additionalactions


Actions you must take to meet these responsibilities

1. Follow Machinery Builder and/or System DesignerInstallation Guidelines.

2. Turn to page 58, Chapter 8 for recommended installationguidelines.


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Chapter 5 - Terminology

APPLIED TO: Electrical equipment

RESPONSIBILITY: Electrical Equipment Manufacturer

REQUIRED BY: EMC Directive

A Technical Construction File (TCF) must be providedfor the entire equipment or system and if required is toshow a Competent Authority that you have met theessential requirements of the EMC Directive (see page54).

The TCF consists of three parts:

1. A description of the product.

2. Procedures used to ensure conformity of the productto the requirements.

3. A report or certificate from a Competent Body.

The full contents of the TCF are given on pages 36-38.

A TCF is needed if you are:

a. claiming compliance without necessarily meeting thestandards.

b. or where suitable standards do not exist.

c. or where the system may be complex and involve theinclusion of more than one equipment.

d. or where the Equipment can have several variants.

Anyone placing a product onto the market within the EUmust be able to show that the product meets therequirements of the appropriate EU Council Directive andmust be able to demonstrate this to a CompetentAuthority without further testing.

This may be by a Technical File to show that the standardsroute has been complied with (see page 38). Alternativelythe Technical Construction File (TCF) route is necessary.

A TCF allows the appropriate Declaration of Conformityto be drawn up.

TechnicalConstructionFile (TCF)

KEY POINT:

What is aTechnicalConstructionFile?

When do I usea TCF?

Why is a TCFdeemed to beimportant?


If there is any doubt in the manner of compliance, the TCFis the preferred route.

The content of the TCF file is meant for the Authorities,and thus the electrical equipment manufacturer does nothave to give the TCF or any part of it to the customer.

However, as the customer needs to know whether theproduct is in conformance, he will obtain this assurancefrom the documentation delivered with the product. It isnot required to supply a declaration of conformity with theproduct, but the end-user may ask for this from themanufacturer.

Any TCF must be accessible to the appropriate Authoritiesfor 10 years from the last relevant product being delivered.

Yes. Use the standards route to compliance.

Although TCFs may appear onerous and time consumingthere is often no way of avoiding their use. Even softstarters, PLCs, intelligent motor protection relays and ahost of other microprocessor based devices are subjectto TCFs, if the manufacturer opts for that route.

The whole system is based on self certification and goodfaith. In various parts of Europe the methods of ensuringcompliance will vary. Supervision of these regulations isachieved through market control by a Competent Authority.If the equipment fails to meet the requirements of the EMC-directive, Competent Authorities can use the safeguardclause of the EMC-directive (withdraw the product fromthe market, take legal action).

Manufacturers accept that there is a need to work moreclosely with OEMs and Machine Builders where theconverter can be mounted on the machine. A standardassembly or design should be achieved so that the TCFdoes not have to be repeated.

However, the idea of mounting drives in motor controlcentres (MCCs) must be much more carefully thought outby system specifiers.

For a straightforward single drive application, it may wellbe possible to demonstrate compliance by the standardsroute and evidence of type tests using specified types andlengths of cable with fixing methods and segregation.

Will customersalways receive aTCF copy?

What is the shelflife of a TCF?

Is there any wayI can avoid theTCF?

How do I ensurethat tests arealways carriedout?

Can drivemanufacturershelp more?


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This would only need a Technical File (see page 38),otherwise the Technical Construction File route is stillneeded.

However, the concept of mounting several drives in a motorcontrol centre must be more carefully thought out, as thesumming of high frequency emissions to determine theeffects at the MCC terminals is a complex issue and thepossibilities of cross coupling are multiplied.

(Note: You can photocopy these pages and use as atickbox checklist)

i. identification of product

a. brand name.

b. model number.

c. name and address of manufacturer or agent.

d. a description of the intended function of theapparatus.

e. any limitation on the intended operatingenvironment.

ii. a technical description

a. a block diagram showing the relationship betweenthe different functional areas of the product.

b. relevant technical drawings, including circuitdiagrams, assembly diagrams, parts lists,installation diagrams.

c. description of intended interconnections withother products, devices, etc.

d. description of product variants.

How to makeup a TCF

1. Descriptionof the product


i. details of significant design elements

a. design features adopted specifically to addressEMC problems.

b. relevant component specifications (e.g. the use ofcabling products known to minimise EMCproblems).

c. an explanation of the procedures used to controlvariants in the design together with an explanationof the procedures used to assess whether aparticular change in the design will require theapparatus to be re-tested.

d. details and results of any theoretical modelling ofperformance aspects of the apparatus.

e. a list of standards applied in whole or part.

f. the description of the solution adopted in order tocomply with the directive.

ii. test evidence where appropriate

a. a list of the EMC tests performed on the product,and test reports relating to them, including detailsof test methods, etc.

b. an overview of the logical processes used todecide whether the tests performed on theapparatus were adequate to ensure compliancewith the directive.

c. a list of the tests performed on critical sub-assemblies, and test reports or certificates relatingto them.

This will include:

i. reference to the exact build state of the apparatusassessed, cross-referencing with Part I of the basicrequirements of a TCF.

ii. comment on the technical rationale.

iii. statement of work done to verify the contents andauthenticity of the design information in the TCF,cross referenced with part 2 (ii) of the basicrequirements of a TCF.

2. Proceduresused to ensureproductconformity

3. A report orcertificate froma CompetentBody


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iv. comment, where appropriate, on the proceduresused to control variants, and on environmental,installation and maintenance factors that may berelevant.

v. an analysis of the tests performed either by themanufacturer, an authorised third party, or theCompetent Body itself, and the results obtained.This analysis will determine whether the tests showthat the apparatus should comply with the essentialrequirements of the directive.

The Competent Body (see page 46) will study the TCFand issue the Technical Report or the Certificate andthis should be included in the TCF.

Note:When compiling the TCF you may need all Declarationsfrom suppliers, i.e. Declaration of Conformity andDeclaration of Incorporation depending on the parts, toensure they carry CE Marking.

APPLIED TO: Machines and Safety Components

RESPONSIBILITY: Machine Builder/ System Designer

REQUIRED BY: Machinery Directive

A Technical File is the internal design file which shouldshow how and where the standards are met and is all thatis needed if self certifying the equipment by the standardscompliance route.

If a Declaration of Incorporation (see page 43) is includedin a set of papers and this claims to meet the appropriateparts of the standards and simply instructs the user tomeet the standards with other parts of his machine, it ispossible to use this as a part of a Technical File.

4. Actions bythe CompetentBody

TECHNICALFILE (formechanicalsafety aspects)

What is aTechnical File?


1. Overall drawings of the machine.

2. Control circuit diagrams.

1. All drawings, calculations and test results used to checkthe machine’s conformity with essential health andsafety requirements.

1. Lists of the essential health and safety requirements,Harmonised Standards, other standards and technicalspecifications used when designing the machine.

2. Description of methods used to eliminate hazardspresented by the machine.

1. A technical report or certificate issued by a NotifiedBody (see page 46) - if required.

2. If required by a Harmonised Standard (see page 47)to which conformity is declared, a technical report isissued by a Competent Body (see page 46). Thistechnical report shall include test results.

3. A copy of the instructions for the machine.

4. For series produced machines, the control measuresthat are used to ensure that subsequent manufactureremains in conformity with the Directive.

How to makeup a TechnicalFile

Drawings anddiagrams

Health andsafety

Machinedesign

Othercertificatesrequired


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RESPONSIBILITY: Drive Manufacturer/SystemDesigner/Panelbuilder/OEM/ Installer

REQUIRED BY: Low Voltage Directive

A Technical File is the internal design file which shouldshow how and where the standards are met and is all thatis needed if self certifying the equipment by the standardscompliance route.

If a Declaration of Conformity (see page 42) is includedin a set of papers and this claims to meet the appropriateparts of the standards and simply instructs the user tomeet the standards with other parts of his equipment, it ispossible to use this as a part of a Technical File.

1. A general description of the electrical equipment, orelectrical equipment of machines.

2. Conceptual design and manufacturing drawings andschemes of components, sub-assemblies, circuits, etc.,

3. Descriptions and explanations necessary for theunderstanding of said drawings and schemes and theoperation of the electrical equipment.

1. A list of the standards applied in full or in part, anddescriptions of the solutions adopted to satisfy thesafety aspects of this Directive where standards havenot been applied.

1. Description of methods used to eliminate hazards

2. Results of design calculations made, examinationscarried out, etc

3. Test reports

4. A technical report issued by a Notified Body orCompetent Body (see page 46) - if used.

1. For series produced equipment, the control measuresthat are used to ensure that subsequent manufactureremains in conformity with the Directive.

TECHNICALFILE (forelectricalsafety aspects)

What is aTechnical File?

How to makeup a TechnicalFile

Drawings anddiagrams

Standards

ElectricalSafety Aspect

Otherrequirements


APPLIED TO: Machines/Safety Components

RESPONSIBILITY: Notified Body/Machine Builder


In this case the adequacy of the Technical File (see page38) is proved by a Certificate of Adequacy issued by aCompetent Body.

The Certificate of Adequacy is a document drawn up bya Competent Body (see page 46). Once the Body hasestablished that the Technical File contains all thenecessary information, the Certificate of Adequacy willbe issued.

The Certificate of Adequacy provided should be includedin the Technical File.


RESPONSIBILITY: Competent Body

REQUIRED BY: EMC Directive

In this case the adequacy of the Technical ConstructionFile (see page 34) is proved by a Technical Report orCertificate issued by a Competent Body.

The Technical Report or Certificate is a document drawnup by a Competent Body (see page 46). Once the Bodyhas established that the Technical Construction Filecontains all the necessary information, the TechnicalReport or Certificate will be issued.

The Technical Report or Certificate provided should beincluded in the Technical Construction File.


RESPONSIBILITY: Notified Body/Competent Body

REQUIRED BY: Low Voltage Directive

In the event of a challenge the manufacturer or importermay submit a Report issued by a Notified Body. Thisreport is based on the Technical File (see page 38).

What if standardscannot be whollyimplemented?

CERTIFICATEOF ADEQUACY

How to obtaina Certificate ofAdequacy

KEY POINT:

TECHNICALREPORT ORCERTIFICATE

What if standardscannot be whollyimplemented?How to obtainthe TechnicalReport orCertificate

KEY POINT:

REPORT

What if standardscannot be whollyimplemented?


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DECLARATIONOF CONFORMITY(for EMC andelectrical safetyaspects)

The Report is a document drawn up by a Notified Body(see page 46). Once the Body has established that theTechnical File contains all the necessary information andthe equipment fulfils the requirements of the Low VoltageDirective, the Report will be issued.

The Report provided should be included in the TechnicalFile.

APPLIED TO: Electrical equipment and electricalequipment of machines

RESPONSIBILITY: Equipment manufacturer

REQUIRED BY: Machinery Directive, Low VoltageDirective and EMC Directive

As a Machine Builder, you must ensure you obtain all theDeclarations of Conformity from each equipmentsupplier. The Declaration of Conformity must contain:

1. Manufacturer's details and/or his authorised EUrepresentative.

2. Equipment description including name, type andserial number.

3. Safety function offered by the component, if notobvious from the description.

4. Details of the Competent Body and number ofType Certification - if required.

5. Details of the Competent Body to which theTechnical File was sent - if required.

6. Details of the Notified Body which carried out theverification - if required.

7. A list of Harmonised Standards, other standardsand specifications used.

8. Details of the person authorised to sign on behalfof the responsible person.

How to obtain aDeclaration ofConformity

How to obtain aReport

KEY POINT:


DECLARATIONOF CONFORMITY(for mechanicalsafety aspects)

APPLIED TO: Machines

RESPONSIBILITY: Machine Builder


You need to provide the following:

1. Name and address of the responsible person.

2. Machinery description including the name, typeand serial number.

3. All regulations complied with including, ifappropriate, a statement of conformity with therelevant health and safety requirements or withthe example that underwent Type Certification.

4. Details of any Competent Body used and numberof Type certification.

5. Details of the Competent Body holding theTechnical File - if required.

6. Details of the Competent Body which has drawnup a Certificate of Adequacy - if required.

7. A list of Harmonised Standards used or the otherstandards and technical specifications used.

8. Identification of the Authorised signatory.

APPLIED TO: Machines or equipment intended forincorporation into other machinery

RESPONSIBILITY: Drives Manufacturer/MachineBuilder/Panelbuilder


Drives manufacturers must meet the appropriate parts ofthe Machinery Directive and provide a Declaration ofIncorporation which states that the drive does not complyon its own and must be incorporated in other equipment.

This Declaration will show the standards that have beenapplied to the parts of the system within the manufacturer’sscope.

How to obtain aDeclaration ofConformity

DECLARATIONOFINCORPORATION

What is aDeclaration ofIncorporation?


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43

This Declaration includes a statement restricting the userfrom putting the equipment into service until the machineryinto which it is to be incorporated, or of which it is to be acomponent, has been found, and declared, to be inconformity with the provisions of the Machinery Directiveand the national implementing legislation, i.e. as a wholeincluding the equipment referred to in this Declaration.

The Declaration then lists the standards relating to theMachinery and Low Voltage Directives which themanufacturer has met.

It concludes that the entire equipment must meet theprovisions of the Directive.

Quite simply, the manufacturer passes on the responsibilityto the machine or system builder.

No. You must understand that because the manufacturermay be supplying only one part in a machinery, such asthe inverter, the manufacturer is legally obliged to ensurethat whoever puts the system together must check that itis safe.

Only then can the Machine or System Builder use theDeclaration of Incorporation in his Technical File ofthe machine.

Most manufacturers will include a Declaration ofIncorporation covering the Machinery Directive for allbuilt PDS products.

1. Name and address of the responsible person.

2. Machine description.

3. Details of the Notified Body and the number ofthe Type Certification - if required.

4. Details of the Notified Body to which theTechnical File has been sent - if required.

5. Details of the Notified Body which has drawn upa Certificate of Adequacy - if required.

6. A list of the Harmonised Standards(see page 47) used - if required.

Is there no wayout of this typeof Declaration?

KEY POINT:

What aDeclaration ofIncorporationcontains


7. A warning that the machinery must not be put intouse unless the machine into which it is to beincorporated is the subject of a Declaration ofConformity.

8. Details of the person authorised to sign on behalfof the responsible person.

APPLIED TO: Machines and Safety Components

RESPONSIBILITY: Machine Builder/Approved Body


Type Certification is carried out by an Notified Body(see page 46) who will establish that the unit supplied,along with a Technical File, may be used safely and thatany Standards have been correctly applied.

Once the Type Certification has established this, a TypeExamination Certificate will be issued.

TYPECERTIFICATION

How toobtain TypeCertification


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45

Chapter 6 - Authorities and Bodies

The responsibility for product conformity is given to themanufacturer. If there is any doubt about conformity, thenthe Authorities can demand technical documentation toshow that a product complies with the directivesconcerning the product.

When assessing product conformity, a manufacturer canuse a third party to examine the conformity.

The following types of Authorities and Bodies exist:

A Competent Authority in any EU or EEA countrysupervises markets to prevent hazardous products beingsold and marketed. They can also withdraw such productsfrom markets.

To find a suitable Competent Authority or Notified Bodyyou can contact: EU Commission, Rue de la Loi 200,b,1049 BrusselsPh: +32 2 296 45 51

A Competent Body is a third party which can be used toassess a product’s conformity. They also issue theTechnical Report or the Certificate for the product’sTechnical Construction File (see page 34).

To find a suitable Competent Body contact your localCompetent Authority or:EU Commission, Rue de la Loi 200,b, 1049 BrusselsPh: +32 2 296 45 51

A Notified Body issues Type Certificates for products,which have their own Directives and/or require type testing.

CompetentAuthority

CompetentBody

Notified Body


Chapter 7 - Standards and Directives

KEY POINT:

The use of standards is voluntary, but compliance withDirectives without the use of Harmonised Standards isextremely difficult.

There are two ways to show that a Power Drive System orpart of it conform:

• Use of Harmonised Standards (EN).

• By way of a Technical Construction File when noHarmonised Standards exist, or if all parts of aHarmonised Standard cannot be applied.

It is recommended to use a TCF even when standards areharmonised as it makes it easier to show conformityafterwards, if required by Authorities.

The legislation of the European Union is defined by differentDirectives.

The Directives concerning Power Drive Systems are knownas New Approach Directives, which means that they donot include exact figures or limits for products. What theydo include is essential requirements mainly for Health andSafety which make the application of the relevantHarmonised Standards mandatory.

The requirements of Directives are firmly established inStandards. Standards give exact figures and limits forproducts.

The responsibility for defining standards in Europe restswith three committees: CEN, for areas of common safety,CENELEC, for electrical equipment and ETSI, fortelecommunications.

To remove technical barriers to trade in EU or EEAcountries, the standards are Harmonised in MemberStates.

In the harmonisation procedure, all Member States areinvolved in developing the Committee's proposals for theirown national standard. A standard becomes harmonisedwhen published in the Official Journal of the EU.

Directive orStandard?

HarmonisedStandards forPDSs


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47

The idea is that if a product conforms to the HarmonisedStandard, it is legally manufactured and when placed ontothe market in one country, it must be freely marketed inother member countries.

Harmonised Standards come in the following format:

XX EN 60204-1

where

XX = the national prefix (eg BS = UK; SFS = Finland)EN = the abbreviation of Euronorm60204-1 = an example of a standard number

The first number in each standard index tells the origin ofthe standard:

2 = standards based on ISO40 = standards from CENELEC50 = standards from CISPR

(a committee dealing with radio interference)60 = IEC based standards

There is also some clue as to a standard's status:

prEN 50082-2 = proposal for standard sent to MemberStates

ENV 50 = pre-standard which is in force for 3 yearsto obtain practical experience fromMember States.

At the moment, there is a Product Specific Standard(see page 50) covering EMC from Power Drive Systems.

The important standard for PDSs is EN 60204-1, ElectricalEquipment of Machines, which, in addition to being a LowVoltage Directive standard for all electrical equipment, isalso an electrical safety standard under the MachineryDirective. Other important standards are EN 50178according to Low Voltage Directive and EN 61800-2, whichgives rating specifications for Power Drive Systems.

How torecognise aEuropeanStandard

Your questionsanswered

Whichstandardsdirectly relateto drives?


What are theissues of EN 61800-3 anddrives?

For emissions there are two main aspects to consider:

Conducted emissions: these are seen on the powersupply cables and will also be measured on the controlconnections, while radiated emissions are air borne.

Conducted emissions at low frequencies are known asharmonics which have been a familiar problem to manyusers of a PDS. Where harmonics are concerned EN 61800-3 refers to EN 61000-3-2 which does apply for equipmentunder 16 A per phase and after 1.1.2001.

At the moment two groups can be separated

• Professional, over 1kW => No limits.

• Other > The limits specified.

Conformity with conducted emissions can be helped bygood product design and is readily achieved, in mostsituations, using filters, providing this is for a single drive.

Radiated emissions: These are more problematic. Whileit is possible to make the drive enclosure into a Faradaycage and thereby have all radiation attenuated to earth, inpractice it is the outgoing connections where inadequatecabling radiates emissions and cross couples with othercables in the vicinity. Important attenuation methods areshielded cables and 360o earthing.

The most important solutions are good installation practice,tight enclosure, shielded cables and 360o earthing. (Seepage 58 for tips and advice).

The use of standards is voluntary, but compliance with aDirective without the use of Harmonised Standards isdifficult in the majority of cases.

There are two ways to show that a Power Drive Systemconforms:

• use of Harmonised Standards - EN 61800-3.

• if the Harmonised Standards cannot be applied, it isnecessary to use a TCF. This does, however, involve thirdparty (Competent Body) scrutiny of the file and aCertificate or a Technical Report from this body, whichwill incur additional costs (See pages 34-38 for a fullexplanation of how to use TCFs).

What are thesolutions toradiatedemissions?

Do I have toconform to thestandards?


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49

It is recommended to use the TCF where the HarmonisedStandards are applied as it makes it easier to showconformity afterwards if required by the authorities.

Yes. Failure to comply with any of the Directives will be acriminal offence.

This standard defines the required emission and immunitylevels of PDSs and the test methods to measure the levels.

In Europe, the standard takes precedence over all genericEMC standards previously applicable.

The standard defines two modes of sales distribution andapplies them to the PDS. It puts PDSs and their componentparts into four modes depending on the functionalcharacteristics.

A PDS with unrestricted distributionComplex component (PDS/CDM) sold “as built” to theEnd-User

DescriptionPlaced on the market. Free movement based oncompliance with the EMC Directive. EC Declaration ofConformity required. CE Marking required.

The PDS manufacturer is responsible for EMC behaviourof the PDS under specified conditions. Additional EMCmeasures are described in an easy-to-understand way andcan be implemented by a layman.

When PDS/CDM is going to be incorporated with anotherproduct, the resulting EMC behaviour of that product isthe responsibility of the assembler of the final product, byfollowing the manufacturer's recommendations andguidelines.

Restricted distributionA PDS (or CDM/BDM) sold to be incorporated into anapparatus, system or installation.

Description:Intended only for professional assemblers who have thelevel of technical competence of EMC necessary to installa PDS (or CDM/BDM) correctly. The manufacturer of thePDS (or CDM/BDM) is responsible for providingInstallation Guidelines. The EC Declaration ofConformity and CE Marking are required.

Can I be fined fornot conforming?

The ProductSpecificStandard EN 61800-3

Mode 1:

Mode 2:


Mode 3:

Applications ofdifferentModes

Mode 4:

When a PDS/CDM is to be incorporated with another product,the resulting EMC behaviour of that product is theresponsibility of the assembler of the final product.

Standard assembly:The manufacturer restricts the supply of equipment tosuppliers, manufacturers or users who separately or jointlyhave technical competence of the EMC requirements forthe application of drives.

InstallationOne or more PDSs, either Restricted or Unrestricted,brought together at a given place, in or with anapparatus, system or other components.

Description:Not intended to be placed on the market as a singlefunctional unit. Each apparatus or system included issubject to the provisions of the EMC Directive. NoDeclaration of Conformity or CE Marking of theinstallation. The manufacturer of the PDS (or CDM/BDM)is responsible for the provision of Installation Guidelines.Resulting EMC behaviour is the responsibility of theInstaller (e.g. by following an appropriate EMC plan).Essential protection requirements of the EMC Directiveapply regarding the neighbourhood of the installation.

Apparatus or systemIncludes one or more PDS(s) (or CDM/BDM).

Description:Has an intrinsic function for the final user and placed onthe market as a single commercial unit. EC Declarationof Conformity and CE Marking required (for the apparatusor system). Resulting EMC behaviour is the responsibilityof the manufacturer of the apparatus or system.

1. BDM used in domestic or industrial premises, soldwithout any control of the application.The manufacturer is responsible that sufficient EMCwill be achieved even by a layman. Althoughcomponents are excluded from the Directive, it statesthat when sold without any control over the application(Unrestricted components), components must have asufficient degree of EMC. Thus, if members of the public(End-Users) buy a component off the shelf, they willnot have to worry about compliance when they fit it totheir machine. Therefore, the responsibility for CEMarking such components under EMC lies with themanufacturer.


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How does theMachineryDirective affectmy drive?

2. PDS or CDM/BDM for domestic or industrial purposes.This is sold as a sub-assembly to a professional assemblerwho incorporates it into a machine, apparatus or system.

Conditions of use are specified in the manufacturer’sdocumentation. Exchange of technical data allowsoptimisation of the EMC solutions.

Inverters come under the second category of components- Restricted distribution. On their own they do not havean intrinsic function for the End-User, but are sold toprofessional Installers who incorporate them into amachine, apparatus or system. They are not on saledirectly to the End-User.

3. PDS for use in installations.The conditions of use are specified at the time of theorder, consequently an exchange of technical databetween supplier and client is possible. It can consistof different commercial units (PDS, mechanics, processcontrol etc).

The combination of systems in the installation shouldbe considered in order to define the mitigation methodsto be used to limit emissions. Harmonic compensationis an evident example of this, both for technical andeconomical reasons.

4. PDS combined with application device (machine) suchas a vacuum cleaner, fan, pump or such like, i.e. readyto use apparatus.

89/392/EEC modified by 91/368/EEC, 93/44/EEC and93/68/EEC has been replaced by a new numberingscheme which simply refers to 98/37/EC

This Directive concerns all combinations of mechanicallyjoined components, where at least one part is moving andwhich have the necessary control equipment and controland power input circuits.

The Directive concerns all machines but not those like lifts,which have a specific Directive.

MachineryDirective98/37/EC


KEY POINT: As far as drives are concerned, the new version of EN60204-1 will be in force after 1st October, 2000.

On its own, the Complete Drive Module (CDM) does nothave a functional value to the user. It always needs itsmotor coupled to the driven load before it can functioneffectively. Thus, it cannot carry the CE Marking basedon the Machinery Directive.

To obtain a copy of the Machinery Directive you cancontact a local Competent Authority or EU Commission,Rue de la Loi 200, b-1049 Brussels.

73/23/EEC, modified by 93/68/EEC

This Directive concerns all electrical equipment with nominalvoltages from 50V to 1kV AC and 75V to 1.5kV DC.

The aim of the Directive is to protect against electrical,mechanical, fire and radiation hazards. It tries to ensureonly inherently safe products are placed on the market.

All parts of a PDS from converters and motors to controlgear must conform with the Low Voltage Directive.

To guarantee that a product complies, the manufacturermust provide a Declaration of Conformity. This is aDeclaration that the product conforms to the requirementslaid down within this Directive.

If a product conforms to the Directive and has aDeclaration of Conformity, then it must carry the CEMarking (for more on CE Marking, see page 13).

In the case of a Power Drive System, the Declaration ofConformity is needed for each of its component parts.Thus, the Declaration of Conformity for the CompleteDrive Module (CDM) (see pages 18 and 19) and for theMotor have to be given separately by the manufacturer ofeach product.

Where can Iobtain aMachineryDirective copy?

Low VoltageDirective

How does theLVD affect mydrive?


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Most manufacturers will include a Declaration ofConformity covering the Low Voltage Directive for allbuilt PDS/CDMs. These are drives built into an enclosure,which can be wired up to the supply and switched onwithout any further work being undertaken. This is incontrast to an open chassis (BDM), which is a componentand needs an enclosure.

Without the Declaration of Conformity the CDM couldnot carry the CE Marking and therefore it could not beused legally in any system.

89/336/EEC modified by 91/263/EEC, 92/31/EEC and93/68/EEC

The intention of the EMC Directive is, as its name implies,to achieve EMC compatibility with other products andsystems. The Directive aims to ensure emissions from oneproduct are low enough so as not to impinge on theimmunity levels of another product.

There are two aspects to consider with the EMC Directive:

• the immunity of the product.

• the emissions from that product.

Although the Directive expects that EMC should be takeninto account when designing a product, in fact EMC cannotbe designed - it can only be measured quantitively.

CE Marking CANNOT be given automatically on the basisof this Directive. This is because the drive is not a finalfunctional product to the customer, but is always part of amachine or process.

The Machine Builder, therefore, has the final responsibilityto ensure that the machine including any VSD and otherelectrical devices, meets the EMC requirements.

At each stage of the manufacturing process, from componentto system, each manufacturer is responsible for applying the

KEY POINT:

Why is theDeclaration ofConformityimportant?

KEY POINT:

EMC Directive

How does theEMC Directiveaffect mydrive?

KEY POINT:


appropriate parts of the Directive. This may be in the form ofinstructions on how to install or fit the equipment withoutcausing problems. It does not imply that there is a string ofDeclarations of Conformity to be compiled into a manual.

A frequency converter is likely to be only a part of a PowerDrive System.

Yet it is the entire system or machinery that must meet therequirements of the EMC Directive.

So, drives manufacturers are in a position to choosewhether to put CE Marking on to a frequency converterto indicate compliance with the EMC Directive or to deliverit as a component without CE marking.

It is the responsibility of the person who finally implementsthe system to ensure EMC compliance.

Either the Machine Builder or System Supplier has thefinal responsibility that the machine or system includingthe drive and other electrical and electronic devices willmeet the EMC requirements.

Who has theresponsibilityto ensure CEMarking?

KEY POINT:


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55

Summary of Manufacturer's responsibilities in theapplication of EC Directives to systems containing a PDS:

If some of the Directives result in CE Marking, the PDS (or CDM orBDM) can be CE marked with the corresponding Declaration ofConformity.

Warnings & GuidePower Drive System

Machinery Directive Low VoltageDirective

EMC Directive

Any safety relevantstandard such asEN 60204-1 etc

TECHNICAL FILE

Apply HarmonisedStandards as far as

possible

Declaration ofIncorporation

No CE Marking asthe PDS is a

component of themachine

EN 60529,EN 60204-1EN 50178

EN 61800-3

TECHNICAL FILE TECHNICAL FILE orTECHNICAL

CONSTRUCTION FILE

Apply HarmonisedStandards

Competent Body toreview TCF or apply

HarmonisedStandards

EU Declaration ofConformity

EU Declaration ofConformity

CE Mark applied CE Mark applied

An analogue of this procedure occurs for each end product which isto be combined with a PDS. However, check all Directives applicableto the end product.

Summary ofresponsibilities


Achievingconformitywith EC SafetyDirectives

* Only if required during market surveillance.

Machine

PDS

Compliance byApplication of

Standards

Declarationof

ConformityTechnical File

Competent Authority

*

*

*TCFfor

EMC

CompetentBody

Reportof

Certificate


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Chapter 8 - Installation

Generalinstallationconcerns

The aim of this section is to provide general installationguidelines to ensure the Power Drive System functions inaccordance with the legislation detailed previously.It is worth highlighting some of the problems whichindustry now faces as a result of the EMC legislation. Forexample,

• To avoid EMC problems it is now important that motorcables should be terminated in the inverter - not at aterminal board in a motor control centre. They certainlymust not be run in parallel with unshielded conductorswhere some pick up is inevitable.

• Implementing features like by-passes becomes difficultto prevent cross-coupling.

• Where a panel builder puts a converter into a secondaryenclosure, the ventilation louvres can quite easilybecome waveguides, if poorly designed or finished.

• In theory, every small installation needs a TechnicalConstruction File (TCF) (see pages 34-38) to confirmcompliance with the EMC Directive and a TechnicalFile for the LVD. This means that the idea of mountingdrives into motor control centres must be much morecarefully thought out by system specifiers.

• Testing on site is likely to be needed on large installations.

• In theory, the manufacturer can deliver, in conjunctionwith a Machine Builder, a perfectly good CE markedsystem which can be installed, and due to site problemswe can still get problems of radiation blotting outsomeone’s radio.

There are several technical requirements of the proposedlegislation:

There must be an on-load disconnecting device ineach supply, unless an auxiliary contact switchesoff the load (except for units up to 3kW/16A wherea plug and socket connection is used). The isolatormust be between 600 and 1900 mm from the floor.

Technicalrequirementsof thelegislation


Means of preventing unexpected start, for exampleduring maintenance, is required, i.e. padlocking theisolator in the off position.

Electrical equipment has to be protected againstdirect and indirect contact. Doors must be lockedby a tool or IP2X protection fitted internally withwarning labels.

The voltage inside must be below 60V after 5seconds from switching off, otherwise special labelsstating the time must be fitted (i.e. for DC-linkcapacitors).

Every machine must be equipped to allow stoppingby removing voltage from a circuit unless it isdangerous to do this. Programmable electronicequipment shall not be used for this function.

The Stop and Emergency Stop function has to beselected by a risk assessment of the machine.

Drawings must use standard IEC formats andsymbols.

Motors must comply with IEC 34-1/EN 60034-1standards.

Warning flash symbols shall be fitted to covers toshow they contain electrical equipment.

The best way is to follow good installation practice and tothoroughly read the Product Specific Manuals.

This way you can be assured that the motor driveinstallation is within the limits of EN 61800-3.

There are four main approaches to improving theelectromagnetic compatibility (EMC) of drives and therebyreduce the emissions of susceptible equipment. These are:

• good general installation practices.

• good earthing.

• good shielding.

• good filtering.

How can EMCbe improved?

KEY POINT:


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59

VaristorVaristor

230 VACDevicee.g.converter

Diode

24 VDC

RC-filter

230 VAC

+

-

Motor cabling is a source of interference. Other cablesalso become sources if they run parallel with motor cables.Therefore, separate motor cables from other cables by500 mm. Otherwise, the use of the RFI filter is almostuseless.

Power and signal cables should cross each other at rightangles.

Relays, contactors and magnetic valves must be equippedwith spark suppressors.

This is also necessary when these parts are mountedoutside the frequency converter cubicle.

Generalinstallationpractice

Cabling

Relay Outputs


Earthing You need to note that, just because there is a good safetyearth at DC or at power frequencies, this does not imply agood earth at radio frequencies. There are several stepsto ensuring good earthing improves EMC:

Follow all local safety regulations on earthing.

The largest possible area should be used as the earthconductor, e.g. the cabinet wall construction.

The parts of the earth system should be connectedtogether using low impedance connections. Flatbraided wires have a much lower high frequencyimpedance than round wires. Earth connectionsshould be kept as short as possible.

Choose one central earthing point to which the wirescan be star-connected.

Paint or other insulating coatings must be removedfrom the area of the bond to achieve a low impedanceconnection.

Low impedance earthing bonds should be checkedas part of standard maintenance and serviceprocedures.


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61

LoadOutputTerminals

EarthEarth

Circuit diagram of a typical High frequency filter

L

L

L

C

R

R

LineInputTerminals

C

C

C

Shielding The principle of Faraday Cage is an attempt to provide a shieldaround a system to prevent radiated signals from entering orleaving. For a drive, this shield consists of three elements:

a. the tight drive cabinet.

b. shielded supply, motor and signal cables with 360o

earthing.

c. the motor housing.

To make the Faraday Cage effective, all these elements mustbe connected together to form one shield. This means that:

There should be no breaks in the cable shields.

The shield connections should have low impedancein the MHz range.

The separate panels of the cabinet should be bondedtogether and have low impedance at high frequencies.

To achieve low impedance bonding it may benecessary to use additional screws, remove paintfrom the surface of cabinets or use EMC gaskets.

The cable between the drive and the motor must beshielded. This cable carries more conducted noise thanthe input cabling of the drive and although it is a closedloop, it will act as an excellent transmitting aerial.

Ensure that the shield is intact along the full lengthof the cable and that each end is bonded to earththrough 360o terminations.


Filtering Filters are installed on the drive's power supply lines toprevent interference currents reaching the mains andaffecting other equipment. You cannot achieve firstenvironment (domestic) levels without using a filteron the line terminals.

Many drives incorporate filter components as part of theirbasic design. Other drives have filters as standard optionsand these should avoid any problems of installation.

Here are a few tips to improve your filtering:

A good quality filter must be mounted as close aspossible to the drive input (Refer to the RFI filtermanufacturer's instructions).

Before mounting the filter, remove any paint or otherprotective coating from the area of the panel thatwill be in direct contact with the filter.

Bond the filter to the same conductive panel as thedrive.

Always segregate the input and output cabling ofthe filter and drive.

In installations incorporating multiple drives in oneenclosure, filters should be fixed to each drive. Also,a general purpose filter should be fitted at thehousing cable to attenuate any additional coupledsignals.

Also note that a static shield between the windings of atransformer provides a very effective RF shielding and willhelp provide de-coupling between the conducted RF ininterconnected circuits.


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Testing andinstallation

There are basically two items that need to be tested whenthe electrical equipment is fully connected to the machine:

1. Electrical safety aspects

a) Continuity of the protective bonding circuit forexample, according to IEC 60364-6-61.

b) Insulation resistance test.

c) Voltage test (2 x Unom, 1s).

d) Protection against residual voltages.

e) Functional tests.

2. Electromagnetic Compatibility - these tests must becarried out in accordance with the product specificEMC-standard of the machine or in accordance withgeneric EMC-standards. The levels of interference usedshall be selected in accordance with the environmentin which the machine is intended to be used.

Note: EMC for large complex machines cannot always betested with the complete system working. In this case it ispossible to test sub-assemblies of the system before theyare mounted together.

It may not be necessary to do the tests in 1(c) and 1(d)above if the machine is tested in sections.


What is theaffect of varyingimpedance?

Your technicalconcernsanswered

You can reduce the conducted emissions by reducing thesource impedance. The impedance of the connectioncables has some “filter effect” (1,5uH) but this is usuallynot enough to reduce the conducted emission. Therefore,extra reactors and filters are required.

The higher the number of drives in parallel, the higher theemissions. Filtering of the conducted emissions isrecommended at the point of common supply input. Thecommon panel of the multiple drives must be bondedtogether as one Faraday Cage and the shields of all cablesin and out of the panel must be bonded to the panel.

The practical approach should be agreed with aCompetent Body. This should be such that the worst caseof larger panels are tested. The results shall be evaluatedby the manufacturer. The basis of evaluation shall beassessed by a Competent Body. The same procedure andmethods can then be used for the easier and smaller units.

What are theeffects ofmultiple drives?

Largeinstallationswith manydrives can takeup to 3 monthsand be costly.What can wedo?


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Chapter 9 - Index

12-pulse drive 19

AABB Automation Group 7abnormal temperatures 24apparatus 16, 17, 36, 37, 38, 50,51, 52authorised EU representative 42

BBasic Drive Module (BDM) 16, 17,19, 20, 28, 30, 32, 50, 51, 52, 54, 57

Ccables 17CE Mark 11, 12, 13, 14, 15, 16,17, 22, 25, 26, 27, 28, 30, 31, 32,38, 50, 51, 53, 54, 55, 57, 58CE Marking 28, 31, 32CEN 47CENELEC 23, 47, 48Certificate of Adequacy 25, 41,43, 44, 46, 49Competent Authority 7, 22, 34,35, 46, 53, 57Competent Body 7, 25, 31, 34, 37,38, 39, 41, 42, 43, 46, 49, 56, 57, 65Complete Drive Module (CDM)15, 16, 19, 20, 28, 30, 32, 50, 51,52, 53, 54, 57component 17, 28, 31component supplier 25, 26, 27, 30Components with direct function 16Components without directfunction 16conducted emissions 49, 65conducted noise 62contactors 60Control circuit diagrams 39cross-coupling 58

DDC- link capacitors 59Declaration of Conformity 13, 14,15, 17, 22, 25, 26, 27, 28, 29, 31,32, 34, 35, 38, 42, 43, 44, 45, 50,51, 53, 54, 55, 57Declaration of Incorporation 26,32, 38, 43, 44, 45, 57direct function 16, 17Direct Torque Control 7Distributor 7, 20

Drive 1, 7, 11, 13, 14, 15, 16, 19,20, 26, 29, 30, 35, 43, 47, 49, 53,54, 55, 57, 58, 59, 62, 63Drives manufacturer 10, 11, 43, 55

Eearthing 49, 59, 61, 62EEA 10, 14, 46, 47electrical safety 22, 23, 29, 48, 64Electromagnetic Compatibility(EMC) 7, 9, 10, 11, 12, 13, 14, 15,16, 17, 22, 26, 27, 28, 29, 30, 34,35, 37, 42, 48, 50, 51, 52, 54, 55,57, 58, 59, 61, 62, 64EMC Directive 16, 17, 28Emergency Stop function 59EN 61800-2 48EN 61800-3 30, 49, 50, 59EN 50178 48EN 60204-1.2 23EN 61000-3-2 49End-User 7, 15, 16, 20, 25, 28, 29,32, 35, 50, 51, 52equipotential bonding circuit 24ETSI 47European Union (EU) 1, 7, 9, 10,13, 14, 34, 35, 46, 47, 48, 50, 53, 57EU Council Directives 1, 7, 9

FFaraday cage 49, 65filter 19, 27, 30, 49, 59, 60, 63, 65frequency converter 19, 55, 60

Hharmonics 49Harmonised Standard 30, 39, 42,43, 44, 47, 48, 49, 50, 57

IIEC 18, 48, 59, 64indirect contact 24, 59input cabling 62Installation 7, 9, 10, 11, 15, 16,19, 20, 26, 27, 30, 31, 32, 33, 36,38, 49, 50, 51, 52, 58, 59, 63, 64Installation Guidelines 27, 30, 32,33, 58installation instructions 15Installer 7, 11, 20, 32, 51, 52Insulation resistance test 64isolator 58, 59


LLow Voltage Directive 9, 13, 14,22, 23, 26, 29, 44, 48, 53, 54, 57

MMachine Builder 7, 15, 20, 22, 25,28, 29, 32, 33, 35, 38, 41, 42, 43,45, 54, 55, 58Machinery Directive 9, 14, 22, 23,25, 26, 29, 38, 41, 42, 43, 44, 45,48, 52, 53, 57magnetic valves 60Member State 47, 48microprocessor 10, 35mobile radio transmitters 10motor 14, 15, 19, 20, 22, 36, 53,58, 59, 60, 62motor control centre 35, 36, 58motor protection relays 35

NNational StandardisationAssociation 23New Approach Directive 47Notified Body 25, 39, 41, 42, 44,45, 46

OOEM 7, 20, 35overcurrent 24overload current 24

PPanelbuilder 15, 16, 17, 20, 28,29, 30, 31, 43, 58Parameters 14PE terminal 24phase-shift transformer 19PLCs 35portable car telephones 10Power Drive System (PDS) 1, 7, 8,9, 10, 11, 12, 15, 18, 19, 20, 22, 23,24, 25, 26, 27, 28, 32, 44, 47, 48, 49,50, 51, 52, 53, 54, 55, 56, 57, 58

RRelays 60resistors 17Restricted distribution 50, 52RFI 60

SSafety Component 25, 38, 41, 45shield 62, 63shielding 59self-certification 13, 35sensor 19shielded cable 49short circuit 24single commercial unit 17single functional unit 17soft starters 35spark suppressors 60Standards 7, 9, 10, 13, 34, 35, 37,38, 39, 42, 43, 44, 45, 47, 48, 49,50, 57, 59star-connected 61System Builder 44System Designer 7, 20, 25, 26,27, 28, 32, 33, 38Systems 16

TTechnical Construction File (TCF)13, 17, 22, 27, 30, 31, 32, 34, 35, 36,37, 38, 46, 47, 49, 50, 57, 58Technical File 13, 22, 24, 25, 34,36, 38, 39, 40, 41, 42, 43, 44, 45,57, 58terminal blocks 17Type Certificate 25, 46Type Certification 25, 42, 43, 44, 45Type Examination Certificate 45

Uunrestricted distribution 50unshielded conductors 58User Manual 59

VVariable Speed Drive 7

Wwalkie-talkies 10warning labels 59


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EMC Compliant Installationand Configuration for aPower Drive System


Technical Guide No.3 - EMC Compliant Installation & Configuration for a PDS2

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Technical Guide No.3 - EMC Compliant Installation & Configuration for a PDS

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Contents

1 Introduction ......................................................General ......................................................................This guide’s purpose.................................................

The Directives concerning drives .........................Who is the manufacturer? ....................................The responsibility of the manufacturer ................OEM customer as a manufacturer .......................Panel builder or system integratoras a manufacturer .................................................Definitions .............................................................Practical installations and systems......................Earthing principles ................................................Product-specific manuals.....................................

2 Definitions ........................................................Electromagnetic Compatibility (EMC) of PDS .........

Immunity ................................................................Emission ................................................................

Power Drive System .................................................Types of equipment ................................................

Component ..........................................................Components with direct function .......................Components without direct function .................Apparatus & systems ..........................................Installation ...........................................................CE marking for EMC ...........................................

Installation environments........................................First Environment ................................................Second Environment ..........................................Propagation .........................................................

The drive’s route to market ....................................Unrestricted distribution .....................................Restricted distribution ........................................

EMC emission limits ...............................................EMC plan .............................................................

3 EMC solutions .................................................General ....................................................................Solutions for EMC compatibility .............................

Emissions ............................................................Conducted emission ...........................................Radiated emission ..............................................Clean and dirty side ............................................RFI filtering ..........................................................

Selecting the RFI filter ........................................Installation of the RFI filter .................................Drives in IT-networks ..........................................Arc suppressors ..................................................Selection of a secondary enclosure ...................Holes in enclosures .............................................360O HF earthing ...................................................HF earthing with cable glands ............................HF earthing with conductive sleeve ...................360O earthing at motor end .................................Conductive gaskets with control cables ............Installation of accessories ..................................Internal wiring......................................................Control cables and cabling .................................Power cables .......................................................Transfer impedance ............................................Use of Ferrite rings .............................................

4 Practical Examples .........................................Simple installation ...................................................Example of By-pass system <100kVA ...................Typical example of a 12-pulse drive .......................Example of common DC bus fed sectional drive ..

5 Bibliography ....................................................

6 Index ...............................................................

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This guide assists design and installation personnel whentrying to ensure compliance with the requirements of the EMCDirective in the user’s systems and installations when usingAC drives.

The purpose of this guide is to guide Original EquipmentManufacturers (OEM), system integrators and panelbuildersin designing or installing AC drive products and their auxiliarycomponents into their own installation and systems. Theauxiliaries include contactors, switches, fuses, etc. By followingthese instructions it is possible to fulfil EMC requirementsand give CE marking when necessary.

There are three directives which concern variable speeddrives. They are the Machinery Directive, Low VoltageDirective and EMC Directive. The requirements andprinciples of the Directives and use of CE marking isdescribed in Technical Guide No. 2 “EU CouncilDirectives and Variable Speed Drives”. This documentdeals only with the EMC Directive.

The European Commission has published guidelines on theapplication of the EMC Directive. These guidelines give thefollowing definition of a manufacturer: “This is the personresponsible for the design and construction of anapparatus covered by the Directive with a view to placing iton the EEA market on his own behalf. Whoever modifiessubstantially an apparatus resulting in an “as-new” apparatus,with a view to placing it on the EEA market, also becomes themanufacturer.”

According to EMC Directive (89/336/EEC) article 10 part1, the manufacturer is responsible for attaching the CE-mark to each unit. According to part 2 the manufacturer isresponsible for writing and updating the TechnicalConstruction File (TCF), if the TCF route is used.

It is well known that OEM customers sell equipment usingown trade marks or brand labels. Changing the trademark,brand label or the type marking is an example of modificationresulting in “as new” equipment.


General

This guide’spurpose

The Directivesconcerningdrives

Who is themanufacturer?

Theresponsibility ofthe manufacturer

OEMcustomer as amanufacturer


Definitions

Practicalinstallationsand systems

Earthingprinciples

Frequency converters sold as OEM products shall beconsidered components (Complete Drive Module CDM orBasic Drive Module BDM). Apparatus is an entity andincludes any documentation (manuals) intended for thefinal customer. Thus, the OEM-customer has sole andultimate responsibility concerning EMC of equipment,and he shall issue a Declaration of Conformity andTechnical Construction File for the equipment.

ABB Oy offers services to help OEM customers to issue aTCF and a DoC in order to CE mark the product accordingto the EMC Directive.

According to the EMC Directive, a system is defined as acombination of several types of equipment, finishedproducts, and/or components combined, designed and/or put together by the same person (systemmanufacturer) intended to be placed on the market fordistribution as a single functional unit for an end-userand intended to be installed and operated together toperform a specific task.

A panel builder or system integrator typically undertakesthis kind of work. Thus, the panel builder or systemintegrator has sole and ultimate responsibility concerningEMC of the system. He cannot pass this responsibility toa supplier.

In order to help panel builder/system integrator, ABB Oyoffers installation guidelines related to each product aswell as general EMC guidelines (this document).

The EMC Product Standard for Power Drive Systems,EN 61800-3 (or IEC 61800-3) is used as the main standardfor variable speed drives. The terms and definitions definedin the standard are also used in this guide.

This guide gives practical EMC examples and solutionswhich are not described in product specific manuals. Thesolutions can be directly used or applied by the OEM orpanelbuilder.

The earthing and cabling principles of variable speed drivesare described in the manual “Grounding and cabling ofthe drive system”, code 3AFY 61201998. It also includesa short description of interference phenomena.

Panel builder orsystemintegrator as amanufacturer

Introduction


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Detailed information on the installation and use ofproducts, cable sizes etc. can be found in the productspecific manuals. This guide is intended to be usedtogether with product specific manuals.

Product-specificmanuals

Introduction


EMC stands for Electromagnetic Compatibility. It is the abilityof electrical/electronic equipment to operate without problemswithin an electromagnetic environment. Likewise, the equipmentmust not disturb or interfere with any other product orsystem within its locality. This is a legal requirement for allequipment taken into service within the EEA. The termsused to define compatibility are shown in figure 2-1.

As variable speed drives are described as a source ofinterference, it is natural that all parts which are in electricalor airborne connection within the PDS are part of the EMCcompliance. The concept that a system is as weak as itsweakest point is valid here.

Electrical equipment should be immune to high-frequency andlow-frequency phenomena. High-frequency phenomenainclude electrostatic discharge (ESD), fast transient burst,radiating electromagnetic field, conducting radio frequencydisturbance and electrical surge. Typical low-frequencyphenomena are mains voltage harmonics, notches andimbalance.

The source of high-frequency emission from frequencyconverters is the fast switching of power components suchas IGBTs and control electronics. This high-frequencyemission can propagate by conduction and radiation.

The parts of a variable speed drive controlling driven equipmentas a part of an installation are described in EMC ProductStandard EN 61800-3. A drive can be considered as a BasicDrive Module (BDM) or Complete Drive Module (CDM)according to the standard.

ElectromagneticCompatibility(EMC) of PDS

Emission

Chapter 2 - Definitions

Figure 2-1 Immunity and emission compatibility.

Power DriveSystem

Immunity


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System control andsequencingBasic Drive Module BDMControl, Converter andProtection

Feeding sectionAuxiliaries and others

Motor and Sensors

Driven Equipment

It is recommended that design and installationresponsible personnel have this standard available andbe familiar with this standard. All standards are availablefrom the national bodies on standardisation and fromCENELEC, rue de Stassart, 35, 1050 Bruxelles.

Systems made by an OEM or panelbuilder can consistmore or less of the PDS parts alone, or there can be manyPDSs in a configuration.

The solutions described in this guide are used within thedefinition of Power Drive System, but the same solutionscan, or in some cases, should, be extended to allinstallations. This guide gives principles and practical EMCexamples which can be applied to a user’s system.

The EMC Directive applies to “all electrical and electronicappliances together with installations containing electrical and/or electronic components liable to cause electromagneticdisturbance or the performance of which is liable to be affectedby such disturbance”. The interpretation of the EMC Directivefor different configuration in the area of drives can be dividedinto several levels:

Figure 2-2 Abbreviations used in Drives.

Definitions

Types ofequipment


Component In this context the interpretation of component can bedivided into two main categories. The component caneither deliver a ‘direct function’ or not.

Direct function:Any function of the component itself, which fulfils theintended use, specified by the manufacturer in theinstruction for use for an end user.

Components with a direct function can be divided intotwo sub-groups:

1) The direct function is available without further adjustmentor connections other than simple ones, which can beperformed by any person not fully aware of the EMCimplications. Such a component is an ‘apparatus’ andit is subjected to all provisions of the EMC Directive.

2) The direct function is not available without furtheradjustment or connections other than simple ones,which can be performed by any person not fully awareof the EMC implications. Such a component is not an‘apparatus’. The only requirement for such a componentis to provide it with instructions for use for the professionalassembler or manufacturer of the final apparatus intowhich the component will be incorporated. These instruc-tions should help him to solve any EMC problems withhis final apparatus.

If a component performs a direct function without furtheradjustment other than simple ones, the component isconsidered equivalent to apparatus (Case 1). Some variablespeed power drive products fall into this category, e.g. adrive installed into a cabinet or drive with enclosure andsold as a complete unit (CDM). All provisions of the EMCDirective apply (CE-mark, Declaration of Conformity).

If a component performs a direct function that is notavailable without further adjustment other than simpleones, it is considered as a component (Case 2). Somevariable speed power drive products fall into this category,e.g. basic drive module (BDM). These are meant to beassembled by a professional assembler (e.g. panel builderor system manufacturer) into a cabinet not in the scope ofdelivery of the manufacturer of the BDM. According to theEMC Directive, the requirement for the BDM supplier isto deliver instructions for installation and use.

According to the EMC Directive the system manufactureror panel builder is resonsible for CE-mark, Declaration ofConformity and Technical Construction File.

Componentswith directfunction

Definitions


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Componentswithout directfunction

Components with no direct function are not consideredas apparatus within the meaning of the EMC Directive.The EMC Directive does not apply to these. Thesecomponents include resistors, cables, terminal blocks, etc.

A finished product containing electrical and/or electroniccomponents and intended to be placed on the market and/or taken into service as a single commercial unit.

Several items of apparatus combined to fulfil a specificobjective and intended to be placed on the market as asingle functional unit.

A combination of items of apparatus, equipment and/orcomponents put together at a given place to fulfil a specificobjective but not intended to be placed on the market asa single functional unit.

A component with a direct function without further adjustmentthan simple ones needs to carry CE marking for EMC (Case 1).

A component with a direct function that is not availablewithout further adjustment than simple ones does not needto carry CE marking for EMC (Case 2).

Note: The products may carry CE marking for otherdirectives than EMC.

Apparatus and systems must be CE marked.

Installations are required to satisfy various parts of theDirectives, but are not required to be CE marked.

The PDSs can be connected to either industrial or publicpower distribution networks. The environment class dependson the way the PDS is connected to power supply. Theenvironment classes are First and Second Environment.

Apparatus andsystems

Installation

CE markingfor EMC

Figure 2-3 The CE mark.

Installationenvironments

Definitions


“The First Environment includes domestic premises. Italso includes establishments directly connected withoutintermediate transformer to a low-voltage power supplynetwork which supplies buildings used for domestic purposes.”

“Second Environment includes all establishments other thanthose directly connected to a low-voltage power supplynetwork which supplies buildings used for domestic purposes"

“For PDSs in the second environment, the user shall ensurethat excessive disturbances are not induced into low-voltage network, even if propagation is through a mediumvoltage network.”

Note: Figure 2-4 shows the case when a victim isin a First Environment. The situation is the sameif a victim is in a Second Environment in anotherinstallation. The measurements are carried outonly in case of dispute (see figure 2-5).

The EMC Product Standard for PDS divides the drive’sroutes to the market into Unrestricted and Restricted salesdistribution classes.

FirstEnvironment

SecondEnvironment

Figure 2-4 Illustration of Environment Classes and propagation ofdisturbances.

Definitions

Propagation

The drive’sroute tomarket

Medium voltage network

PDS(emitter)

Equipment(victim)

Point of measurementfor conducted emission

Point of measurement forradiated emission, see figure 2-5

10 m

Public low-voltage network

Boundary ofinstallation

Industrial low-voltage network

2nd Environment

Point of measurement

1st Environment

Propagation of conducted emissions


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Definitions

“Unrestricted distribution is a mode of sales distributionin which the supply of equipment is not dependent on theEMC competence of the customer or user for theapplication of drives".

Goods can be placed in service by a person skilled in theoperation of goods, but without any specific EMC experience.

“Restricted distribution is a mode of sales distribution inwhich the manufacturer restricts the supply of equipmentto suppliers, customers or users who separately or jointlyhave technical competence in the EMC requirements ofthe application of drives.”

This means that the goods require EMC competence tobe put into service.

The EMC emission limits for PDS depend on the installationenvironment, type of power supply network and power ofthe drive. Limits for certain conditions can be selected byusing the following flow chart (see Figure 2-5).

The appropriate limits of the PDSs of the restricteddistribution class in the second environment may not bemet due to technical reasons.

“These applications are:• IT networks in complex systems• Current above 400 A• Voltage above 1000 V• Where the required dynamic performances are limited

because of filtering

… the user and the manufacturer shall agree on an EMCplan to meet the EMC requirements of the intendedapplication.”

This means that the manufacturer and the user make theEMC Plan in cooperation.

Restricteddistribution

EMC emissionlimits

Unrestricteddistribution

EMC Plan


EN 61800-3EMC Product Standard for PDS

1st Environment(public low-voltage network)

2nd Environment(industrial network)

Either Unrestrictedor Restricted Distr .

CONDUCTED

RAD IATED

DISPUTEThe polluter solves

Disturbancein power port

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See also EMC Plan

Figure 2-5 Emission limits for PDS.

Definitions


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Chapter 3 - EMC Solutions

The solutions used to fulfil immunity and both radiatedand conducted emission requirements are described in thischapter.

There are some basic principles which have to be followed whendesigning and using drive systems incorporating AC driveproducts. These same principles were used when theseproducts were initially designed and constructed, wheresuch issues as printed circuit board layout, mechanicaldesign, wire routing, cable entries and other special pointswere all considered in great detail.

This all is referred to as fully integrated EMC.

Drive products are normally immune to a majority ofdisturbances, otherwise they would be affected by theirown disturbances. So in this context only emissions needto be handled.

The emissions can be divided into two parts, the conductedemission and the radiated emission. The disturbances canbe emitted in various ways as the following figure shows:

Conducted disturbances can propagate to other equipmentvia all conductive parts including cabling, earthing and themetal frame of an enclosure.

Conductive emissions can be reduced in the following way:

• By RFI filtering for HF disturbances• Using sparking suppressors in relays, contactors, valves,

etc. to attenuate switching sparks• Using ferrite rings in power connection points

General

Solutions forEMCcompatibility

Emissions

Conductedemission

Figure 3-1 Emissions.


To be able to avoid disturbance through air, all parts of thePower Drive System should form a Faraday Cage againstradiated emissions. The PDS includes cabinets, auxiliaryboxes, cabling, motors, etc.

Some methods for ensuring the continuity of the FaradayCage are listed as follows:

Enclosure:

• The enclosure must have an unpainted non-corrodingsurface finish at every point that other plates, doors, etc.make contact.

• Unpainted metal to metal contacts shall be usedthroughout, with conductive gaskets, where appropriate.

• Use unpainted installation plates, bonded to commonearth point, ensuring all separate metal items are firmlybonded to achieve a single path to earth.

• Use conductive gaskets in doors and covers. Coversshould be secured at not more than 100 mm intervalswhere radiation could escape.

• Separate radiative i.e. “dirty” side from the “clean side”by metal covers and design.

• Holes in enclosure should be minimised.• Use materials with good attenuation e.g. plastic with

conductive coating, if a metal enclosure cannot be used.

Cabling & Wiring:

• Use special HF cable entries for high frequency earthingof power cable shields.

• Use conductive gaskets for HF earthing of control cableshield.

• Use shielded power and control cables. See productspecific manuals.

• Route power and control cables separately.• Use twisted pairs to avoid disturbances.• Use ferrite rings for disturbances, if necessary.• Select and route internal wires correctly.

Installation:

• Auxiliaries used with CDMs should be CE marked productsto both EMC & Low Voltage Directives, NOT ONLY to LV-directive, unless they are not concerned, e.g. being witha component without a direct function.

• Selection and installation of accessories in accordancewith manufacturers’ instructions.

• 360° earthing at motor end. See product specific manuals.• Correct internal wiring methods.• Special attention must be given to earthing.

Radiatedemission

EMC Solutions


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Note: When selecting equipment for a config-uration it is essential to check that both radiatedand conducted emissions have been taken intoaccount.

The circuit before the point where supply power isconnected to the CDM and where the filtering starts, isreferred to as the clean side. The parts of the BDM whichcan cause disturbances are described as the dirty side.

Enclosed wall mounted drives are designed so that the circuitfollowed by output connection is the only dirty part. That isthe case if the installation instructions of the drive are followed.

To be able to keep the clean side “clean” the dirty partsare separated into a Faraday Cage. This can be done eitherwith separation plates or with cabling.

When using separation plates the rules for enclosure holesare applicable (see section Holes in enclosures later inthis chapter).

When the Faraday cage is formed by cabling, the rules forcabling must be applied (see sections on cabling and wiringin this chapter and follow the product specific instructionsfor the drive).

The use of additional components, e.g. contactors,isolators, fuses, etc. in some cases makes it difficult tokeep the clean and the dirty side separate.

This can happen when contactors or switches are used incircuits to change over from clean to dirty side (e.g. by-pass).

Some examples of solutions are described in chapter 4,Practical Examples.

RFI filters are used to attenuate conducted disturbancesin a line connecting point where the filter leads thedisturbances to earth.

Output filters attenuate disturbances at the output of a PDS.E.g. du/dt and common mode filters help somewhat, evenif they have not been designed for RFI.

Clean and dirtyside

RFI filtering

EMC Solutions


Figure 3-2 shows an example of integral, distributedfiltering. Some drive products need a separate filter (seeproduct specific instructions).

An RFI filter is selected to attenuate the conducteddisturbances. It is not possible to compare the disturbancesmeasured from a source, and the insertion loss for a filter, asthe measurement base for the two items of information willnot correspond.

It is always necessary to test a filter in conjunction withthe source of disturbance to ensure adequate attenuationand to meet applicable emission limits.

Reliable HF/low impedance connections are essential toensure proper functioning of the filter, therefore thefollowing instructions shall be followed.

• Filter shall be assembled on a metal plate with unpaintedconnection points all in accordance with filter manu-facturer’s instructions.

• The frames of the filter cubicle (if separate) and the drivecubicle shall be bolted together at several points. Paintshall be removed from all connection points.

• The input and output cables of the filter shall not run inparallel, and must be separated from each other.

Note: Filters cannot be used in floating network(IT-network) where there is high impedance orno physical connection between the phases andthe earth.

Figure 3-2 Example of filtering integrated in drive module.

Selecting theRFI filter

Installation ofthe RFI filter

EMC Solutions


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• The maximum length of the cable between the filter andthe drive must be according to the RFI-filter manufacturer'sinstructions.

• The filter must be earthed in accordance with the manu-facturer’s instructions. Note that the cable type and sizeare critical.

Relays, contactors and magnetic valves must be equippedwith spark suppressors. This is also necessary when theseparts are mounted outside the frequency converter cubicle.

Where the BDM is to be installed, (e.g. an IP 00 openchassis converter), or if additional components are to beconnected to the dirty side of an otherwise compliant unit,it is always necessary to provide an EMC enclosure.

For enclosed chassis modules where the motor connec-tions are made directly to the converter output terminals,and all the internal shielding parts are fitted, there are norequirements for special enclosures.

Check with a meter that there are no filteringcapacitors connected to earth.

Drives in IT-networks

Figure 3-3 Examples of suppression.

Arc suppressors

Selection of asecondaryenclosure

EMC Solutions


If drives are fitted with output switching devices, forexample, then an EMC enclosure will be needed, as theintegral Faraday Cage will no longer apply.

As a reminder, EMC is only one part of enclosure selection.The enclosure is sized according to several criteria:

• Safety• Degree of Protection (IP Rating)• Heat Rejection Capability• Space for accessory equipment• Cosmetic aspects• Cable access• EMC compliance• General requirements for EMC compatibility

The safety of people and animals together with degree ofprotection (IP-rating) requirements are mainly describedin Machinery Safety standard EN 60204-1, Electrical SafetyStandard EN 50178 or Product Standard EN 61800-2 andare not described here. In this document only the EMCaspect is handled.

From the EMC point of view it means that the enclosure isfirm and proof enough to be a part of the Faraday Cage.In small systems, plastic boxes can also be used if theyare painted inside with conductive paint. The paint musthave metal to metal contact at each seam to other partsof the metal enclosure.

External safety switches can also be in plastic boxes if theboxes form a good Faraday Cage and are conductiveinside, otherwise metal boxes should be used.

The enclosure must adhere to the following parametersas a minimum:

• Thickness: 0.75 mm stainless (galvanised) steel (Normallyrecommended < 1.5 mm for stiffness).

• Outside surface: Electrostatic powder coating e.g. polyesterpowder paint (TGIC). Thickness 60µ, or other cosmeticfinish.

• Inside surface: Hot galvanised and chromated steel. Notpainted. The surfaces that make metal to metal contactshall not be painted.

• Louvres: holes in steelwork < 21 mm in width or proprietaryRFI proof type.

• Doors: Sealed with conductive gasket, and adequatelyearthed. Enough locks for high frequency earthing.

EMC Solutions


3

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• Cover plates: Metal against metal (not painted), all earthed.A number of proprietary enclosure types are available,which use a variety of materials and methods of shieldingagainst radiated emissions.

The manufacturer’s guidelines for construction and earthingmust be followed.

In most cases, some holes must be made in the enclosuree.g. for door devices, louvres, locks, cables, etc.

When an EMC enclosure is to be used, the maximumdiagonal or diameter for any hole is 100 mm, which equatesto 1/10

TH of the wavelength of a 300 MHz frequency. Thisdimension has been found acceptable in EMC tests.

It is, however, also recommended to use metal frameddevices if their assembly holes are between 30 mm to100 mm, if there is any possible doubt about problemswith HF disturbances.

Holes bigger than 100 mm must be covered with a metalframe surrounding the aperture and earthed to theenclosure.

Larger viewing holes can be covered by proprietary glazingwith conductive coating.

Glazing must be connected to non painted metal surroundswith conductive double sided tape or conductive gasket.

Holes inenclosures

Figure 3-4 Enclosure detail.

EMC Solutions


360° HF earthing should be done everywhere where cablesenter the drive enclosure, auxiliary connection box ormotor. There are different ways to implement the HFearthing. The solutions used in ABB’s CDM/BDM productsare described here.

The cable glands which are specially designed for 360° HFearthing are suitable for power cables with a diameter lessthan 50 mm.

Cable glands are not normally used for control cables dueto the fact that the distance from the control connectionsto the cable glands is often too long for reliable HF earthing.If the glands are used with control cables, the cableshielding must continue as near to the control connectionsas possible. Only the outer insulation of cable should beremoved to expose the cable screen for the length of thecable gland.

To get the best possible result from HF earthing, the cableshielding should be covered with a conductive tape. Thetape must cover the whole surface of the shielding,including pigtail, and should be tightly pressed with fingersafter every single turn. The glue must be conductive.

360° HFearthing

HF earthingwith cableglands

EMC Solutions

Figure 3-5 Typical enclosure aperture detail.

Note: If front plate of door device is plastic, make 360o earthing for cable,otherwise twisted pair is acceptable

Maximum size 72 x 72 mminstrument


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wires as possible

covered withconductive tape

HF earthing withconductivesleeve

Figure 3-7 360° earthing with conductive sleeve.

EMC Solutions

Figure 3-6 Essential points of power connections.

360° HF earthing in power cable entries can be done byusing a conductive sleeve around the cable shielding. Thesleeve is connected to the Faraday Cage by tightening itto the specially designed collar in the gland plate.

The advantage of this solution is that the same sleeve canbe used for cables with different diameters.


The cable can be mechanically supported by clamps, anda specific cable gland is not required.

Note that the sleeve does not act as a strain relief clamp.

The continuity of the Faraday Cage at the motor end mustbe ensured by the same methods as in cabinet entry, namely:

• Cable gland must be used for clamping the cable.• Cable shielding should be sealed with conductive tape.• Conductive gaskets should be used for sealing both the

cable gland plate and the terminal box cover for theFaraday Cage and IP 55 degree of protection.

• Earthing pigtail conductors should be as short as possible.

Figure 3-8 shows a Faraday Cage solution at the motor end.

For motors which are not totally enclosed, such as in coolingform IC01, IC06, etc. the continuity of the Faraday Cage mustbe ensured in the same manner as for the converter enclosure.

The 360° HF earthing for control cables can be done withconductive gaskets. In this method the shielded controlcable is led through two gaskets and pressed tightlytogether, as the figure 3-9 shows.

When gaskets are mounted at a gland plate, the cableshielding must continue as near to the control connectionsas possible. In this case the outer insulation of the cableshould be removed to allow connection to the shield forthe length of the gasket transit.

The shielding should be covered with conductive tape.

360° earthingat motor end

Conductivegaskets withcontrol cables

EMC Solutions

Figure 3-8 Essential points in motor cabling.


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Controlcables

Conductive gasket

Cable shielding coveredwith conductive tape

Unpainted gland plate

Short pigtailPE

Controlconnections

Twist the pairsup to terminals

Cable

Continuity ofFaraday

Cage

Clamp

Pull the outer insulationrequired by gasket(about 3 cm)

Press the gasketstogether

The best HF earthing is achieved if gaskets are mountedas near to the control connections as possible.

The gaskets must be installed to connect with the earthedunpainted surfaces of the gland plate to which they aremounted.

All connection tails should be as short as possible, andtwisted in pairs where appropriate. The cable shield shouldbe earthed to the connection end by a short pigtail.

The hole size in a gland plate required by these gaskets istypically 200 x 50 mm.

The variety of accessories which can be installed is solarge that only basic principles for selection and installationcan be given for them.

Accessories can, however, be divided into two categoriesdepending on how immune/sensitive they are.

Figure 3-9 Essential points for control cabling transit.

Installation ofaccessories

EMC Solutions


The protected device in this context means its ability tokeep the Faraday Cage closed. It is therefore recommendedto use metal enclosed/shielded devices wherever suchdevices are available.

The rules for holes in the enclosure must be applied if thereare devices forming a bridge between the clean side andthe dirty side which can be disturbed.

Typical open devices are fuses, switch fuses, contactorsetc., which do not have a metal covering around them.

In general, such devices cannot be installed into the cleanside without protective metallic shielding plates. The rulesfor holes in the enclosure must then be applied.

In some cases there might be some confusion betweensafety and EMC requirements. It is therefore important toremember the following basic rule:

Some examples of protected and open devices are givenin the chapter Practical Examples.

There are some basic rules for internal wiring:• Always keep clean and dirty side cables separate and

shielded from one another.• Internal clean power connections with integrally filtered drive

units, e.g. from contactor to converter input, do not requireshielded cables but may require de-coupling ferrite ringswhere they enter the converter input.

• Use twisted pair wires wherever possible.• Use shielded twisted pairs for signal level outward and

return wires exiting from the overall enclosure.• Avoid mixing pairs with different signal types e.g. 110 VAC,

230 VAC, 24 VDC, analogue, digital.• Run wires along the metal surface and avoid wires hanging

in free air, which can become an antenna.• If plastic trunking is used, secure it directly to installation

plates or framework. Do not allow spans over free air whichcould form an antenna.

• Keep power and control wiring separate.• Use galvanically isolated (potential free) signals.• Keep wires twisted as near the terminal as possible.• Keep pigtails as short as possible.• Earthing connections should be as short as possible in flat

strip, multistranded or braided flexible conductors for lowRFI impedance.

Internal wiring

Safety is always the first priority and overrulesthe EMC requirements.

EMC Solutions


3

27

DIGITAL INPUTS

RELAY OUTPUTS(pot.free)

RC filter orvaristor forAC relay

Avoid parallel running with control wiresCross in 90˚ angle

Avoid parallel running with control wiresCross in 90˚ angle

Figure 3-10 Principles of wiring inside CDM.

Control cablesand cabling

EMC Solutions

The control cabling is a part of the Faraday Cage as describedin the section Conductive gaskets with control cables.

In addition to correct HF earthing there are some basicrules for control cabling:

• Always use shielded twisted pair cables:- double shielded cable for analogue signals- single shielded for other signals is acceptable but double shielded cable recommended.

• Don’t run 110/230 V signals in the same cable with thelower signal level cables.

• Keep twisted pairs individual for each signal.• Earth directly at frequency converter side.


Mains cable

Motor cable

If instructions for the device at the other end of thecable specify earthing at that end, earth the innershields at the end of the more sensitive device andthe outer shield at the other end.

Power cables

EMC Solutions

Figure 3-11 Routing principles of control cables.

• Route signal cables according to figure 3-11 wheneverpossible and follow instructions given by the product specificmanuals.

There is more about control cabling in the documents“Grounding and cabling of the drive system” and inproduct specific manuals.

As the cables are part of the PDS they are also part of theFaraday Cage. To be able to meet the EMC requirements,power cables with good shielding effectiveness must be used.

The purpose of the shield is to reduce radiated emission.

In order to be efficient, the shield must have goodconductivity and cover most of the cable surface. If thecable shield is used as protective earthing, the shield crossarea (or equivalent conductivity) must be at least 50 % ofthe cross sectional area of the phase conductor.


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29

Figure 3-12 Galvanised steel or tinned copper wire with braided shield.

Figure 3-13 Layer of copper tape with concentric layer of copper wires.

Figure 3-14 Concentric layer of copper wires with an open helix ofcopper tape.

EMC Solutions

The product specific manuals describe some cable typeswhich can be used in mains supply and motor output.

If such types are not available locally, and because cablemanufacturers have several different shield constructions, thetypes can be evaluated by the transfer impedance of the cable.

The transfer impedance describes the shieldingeffectiveness of the cable. It is commonly used withcommunication cables.

The cable can consist of either braided or spiral shield,and the shield material should preferably be either copperor aluminium.

The suitability for certain drive types is mentioned in theproduct specific manuals.


To meet the requirements for radiated emission the transferimpedance must be less than 100 mΩ/m in the frequencyrange up to 100 MHz. The highest shielding effectivenessis achieved with a metal conduit or corrugated aluminiumshield. Figure 3-15 shows typical transfer impedancevalues of different cable constructions. The longer thecable run, the lower the transfer impedance required.

In particular cases due to high emission levels, commonmode inductors can be used in signal cables to avoidinterfacing problems between different systems.

Common mode disturbances can be suppressed by wiringconductors through the common mode inductor ferritecore (figure 3-16).

The ferrite core increases inductance of conductors andmutual inductance, so common mode disturbance signalsabove a certain frequency are suppressed. An ideal commonmode inductor does not suppress a differential mode signal.

Figure 3-15 Transfer impedance for power cables.

Use of Ferriterings

Transferimpedance

Figure 3-16 Ferrite ring insignal wire.

EMC Solutions

Limit


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31

The inductance (i.e. the ability to suppress HF disturbances)can be increased by multiple turns of the signal wire.

When using a ferrite ring with power cable, all phaseconductors should be led through the ring. The shieldingand possible earth wire must be wired outside the ring tokeep the common mode inductor effect. With power cablesit is not normally possible to make multiple turns throughthe ring. The inductance can be increased by using severalsuccessive rings.

If for any reasons the installation instructions cannot befollowed and therefore additional ferrites or filters are addedafterwards, it is recommended that measurements bemade to show conformance.

EMC Solutions


Chapter 4 - Practical Examples

Shielded cables are shown interconnecting the primaryparts, ensuring attenuation of radiated emissions. Thesupply is made through the RFI filter.

The Faraday Cage is earthed and all the emissions aredrained to earth.

In the case shown in figure 4-1, the cabinet is not requiredto be EMC proof, because connections are made directlyin an EMC compliant frequency converter.

Figure 4-1 Basic PDS Configuration.

Simpleinstallation


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33

For more details, see360˚ MOTOR EARTHING

Cabinet 1Supplyconnection

In this case it is difficult to ensure that no cross couplingoccurs between the dirty side of the converter and theclean side above the Direct On Line (DOL) contactor.Contactors are not RFI barriers, and the coil circuits arealso vulnerable.

A suitable RFI filter at the supply input connections wouldrequire to be able to pass the DOL starting current, which canbe six to seven times the normal Full Load Current, andwould be greatly oversized for normal running, which makesit difficult to design. Ferrite cores used in the feeds to thecontactor will help attenuate the coupled noise as shownin figure 4-2.

Figure 4-2 Basic scheme with By-pass.

Example ofBy-pass system<100kVA


Low voltage supply

In this case a 12-pulse rectifier is an IT system, uneartheddue to the delta winding, therefore any filter in the linemust be at the primary of the phase shift transformer.

Experience has shown that, in this case, with shortconnections to the busbars, the earth shield between thetransformer windings is not quite adequate for conductedemissions attenuation for use in the first environment.Therefore an RFI filter may be needed at the primary sideof the transformer for EMC compliance. RFI filter is notnormally needed for second environment.

For equipment fed from an IT system, a similar procedurecan be used. An isolating transformer allows the PDS tobe earthed and to use a suitable filter, for use in the FirstEnvironment. The Point of Coupling is at a medium voltageand emissions may be considered at the next low voltagepoint of coupling in the system. The level of emissionsshould correspond to those for the appropriateenvironment. For definitions, see section InstallationEnvironments in chapter 2.

Note: All equipment inside must be enclosed

Figure 4-3 12-pulse converter system fed at LV.

Practical Examples

Typical exampleof 12-pulse drive


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35

Figure 4-4 12-pulse converter system fed at LV (CDM, transformer and switch fuse have separatehousing).

Figure 4-5 12-pulse converter system fed at medium or high voltage.

Practical Examples


CommonEarth

Example ofcommon DCfed sectionaldrive

This example features a common DC bus sectional drive whichis supplied from an earthed network through an RFI filter.

The enclosure must be EMC proof as the componentsinside are not. Cable entries must be 360° HF earthed. Theenclosure is earthed to drain away all emissions.

Figure 4-6 Common DC bus fed sectional drive fed at LV

Practical Examples


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37

Chapter 5 - Bibliography

Various texts are referred to in this guide. They arerecommended further reading to assist in achievingcompliant installations:

EN 61800-3, Adjustable Speed Electrical Power DriveSystems - part 3, EMC product standard including specifictest (published by CENELEC, Brussels, Belgium andNational Standards organisations in EU member countries).

EN 61800-3:1996/A 11:2000

Guidelines by the Commission on the application of CouncilDirective 89/336/EEC, published by European CommissionDGIII - Industry.

Interference Free Electronics by Dr. Sten Benda (publishedby ABB Industry Ab, Västerås, Sweden)

Technical Guide No. 2 - EU Council Directives and AdjustableSpeed Electrical Power Drive Systems, code 3BFE 61253980(published by ABB Industry Oy, Helsinki, Finland)

Grounding and cabling of the drive system, code 3AFY61201998 (published by ABB Industry Oy, Helsinki, Finland)


Chapter 6 - Index

12-pulse rectifier 34

Aantenna 26apparatus 11

BBasic Drive Module (BDM) 8, 17, 19

Ccabinet 16, 24, 32cable gland 22, 24CE mark 3, 5, 10, 11, 16CENELEC 9, 37Complete Drive Module (CDM) 8, 27Component 3, 5, 8, 9, 11, 16, 17, 19conducting radio frequencydisturbance 8conduction 8Conductive gasket 16, 20, 21,24, 27Contactor 5, 15, 17, 19, 26, 33Control Cable 16, 22, 24, 27, 28control connection 22, 24, 25control electronics 8converter 8, 19, 24, 26, 27, 33,34, 35cross coupling 33customer 13

Ddelta winding 34direct function 16DOL 33double shielded cable 27drive 1, 3, 5, 6, 8, 9, 12, 13, 15,16,17, 18, 19, 22, 26, 28, 29, 37

EEEA 8electrical surge 8Electromagnetic Compatibility(EMC) 1, 3, 5, 6, 8, 9, 12, 13, 15,16, 17, 18, 19, 20, 21, 22, 23, 24, 25,26, 27, 28, 29, 30, 31, 32, 34, 37electromagnetic disturbance 9electromagnetic environment 8electrostatic discharge 8enclosure 15, 16, 17, 19, 20, 21,22, 24, 26Environment Class 11, 12

FFaraday Cage 16, 17, 19, 20, 23,24, 26, 27, 28, 32fast transient burst 8

ferrite core 33Ferrite ring 15, 16, 26, 30, 31First Environment 3, 12, 34frequency converter 8, 19, 27, 32fuse 5, 17, 26

Ggasket 16, 20, 21, 24, 25, 27gland plate 23, 24, 25

Hharmonics 8high-frequency emission 8High-frequency phenomena 8

IIGBT 8imbalance 8Installation Environment 3, 11, 13, 34isolating transformer 34IT system 34

LLow Voltage Directive 5low-frequency phenomena 8low-voltage network 12, 17

MMachinery Directive 5medium voltage network 12metallic screening 26motor 24

Nnotches 8

OOriginal Equipment Manufacturers(OEM) 5, 6, 9

PPanelbuilder 5, 6, 9Power Drive System (PDS) 1, 3,6, 8, 9, 11, 12, 13, 14, 16, 17, 28,32, 34, 37phase shift transformer 34pigtail 24, 26plastic trunking 26Point of Coupling 34power components 8power distribution networks 11power supply network 12, 13


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Rradiating electromagnetic field 8radiation 8, 16Restricted Distribution 3, 12, 13RF impedance 26RFI filter 15, 17, 18, 32, 33

SSales distribution 12, 13Second Environment 3, 11, 12Shielded cable 26, 32single commercial unit 11single functional unit 11strain relief clamp 24suppliers 13System Integrator 5

Ttransformer 12, 34twisted pair 16, 22, 26, 27

UUnrestricted 3, 12, 13Unrestricted Distribution 3, 13user 5, 9, 12, 13

VVariable Speed Drives (VSD) 5,6, 8, 16, 17, 22, 37

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Guide to Variable Speed Drives


Technical Guide No.4- Guide to Variable Speed Drives.2

Contents

1 Introduction .....................................................General .....................................................................

2 Processes and their requirements ....................Why variable speed control? ....................................Industrial segments with VSD processes .................Variables in processing systems ..............................Machines are used to alter materials' properties ......

Well defined shape .............................................Indefinite shape ..................................................and to transport materials ...................................Solid materials ...................................................Liquid materials ..................................................Gaseous materials ..............................................

3 The workhorse of industry: The electric motor ....Electric motors drive most machines ......................Motors convert electrical energy into mechanicalenergy ......................................................................Frequency converters control electromagneticinduction ..................................................................The efficiency of the drive system ...........................Reversed rotation or torque is sometimes required .....The load, friction and inertia resist rotation .............The motor has to overcome the loading torque ......The drive torque and load torque are equalat nominal speed .....................................................

4 Variable volumes require some form of controlVariable material flow and input/output requirementsSimpler control methods ....................................The best control method is VSD .............................Mechanical, hydraulic and electrical VSDs .............

Hydraulic coupling .............................................DC drive ..............................................................AC drive ..............................................................

Electrical VSDs dominate the market ......................Maintenance costs .............................................Productivity ........................................................Energy saving .....................................................Higher quality .....................................................

The AC drives market is growing fast .....................

55

6678999

10101010

1111

12

1314151617

18

1919202122222222232323232324

Technical Guide No.4- Guide to Variable Speed Drives

4

3

5 AC drive: The leading control method ...........The basic functions of an AC drive ......................A motor's load capacity curves with an AC drive ....AC drive features for better process control ........

Reversing .......................................................Torque control ................................................Eliminating mechanical vibrations ..................Power loss ride-through .................................Stall function ..................................................Slip compensation ..........................................Flying start .....................................................Environmental features ..................................EMC ...............................................................

6 Cost benefits of AC drives ............................Technical differences between other systemsand AC drives .......................................................No mechanical control parts needed ...................Factors affecting cost ..........................................Investment costs: Mechanical and electricalcomponents .........................................................

The motor .......................................................The AC drive ...................................................

Installation costs: Throttling compared to AC drive ..Operational costs: Maintenance and drive energy ...Total cost comparison ..........................................

7 Index ............................................................

25252627282828292930303131

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363636373839

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Technical Guide No.4- Guide to Variable Speed Drives4

This guide continues ABB’s technical guide series,describing different variable speed drives (VSD) and howthey are used in industrial processes. Special attention hasbeen given to electrical VSDs and especially to AC Drives.

The guide tries to be as practical as possible. No specialknowledge of VSDs is required, although basic technicalknow-how is required to fully understand the terms anddescriptions used.


General


4

5

To understand why variable speed control is necessary,we first need to understand the requirements of differentprocesses. These processes can be divided into two maincategories; material treatment and material transport,although there are many different sub-categories that comeunder these two basic headings.

Common to both main categories, however, is the need tobe able to adjust the process. This is accomplished withVSDs. This chapter describes the main industrial and non-industrial processes using VSDs.

Chapter 2 - Processes and their requirements

Why variablespeedcontrol?


Industrial processes are numerous, and the list abovementions just some of the industrial segments with VSDprocesses. What they have in common is that they allrequire some kind of control using VSD.

For example, in air conditioning applications (part of HVAC),air flow requirements change according to the humidityand temperature in the room. These can be met by adjustingthe supply and return air fans. These adjustments are carriedout with VSDs.

Fans are also used in power plants and the chemicalindustry. In both cases, the fans need to be adjustedaccording to the main process. In power plants, the mainprocess changes due to varying demands for power atdifferent times of the year, day or week. Likewise, the needfor VSDs differs according to the process.

Industrialsegmentswith VSDprocesses

Processes and their requirements


4

7

This diagram shows what kinds of variables affect theprocessing system. These variables can be divided intoenergy and material variables. In the processing systemitself, material or energy is processed by means ofmechanical power, electromagnetic influence, thermalinfluence, chemical and biological reactions or evennuclear power.

Each process needs the material and energy supplied toaccomplish the required process. The product or finalmaterial state is the output of the process, but in everyprocess, waste, in the form of energy and/or material, isalso produced.

In processing systems, VSDs are used to control themechanical power of the different machines involved inthe process.

Material treatment can also be controlled by VSDs. A goodexample is a drying kiln, in which the hot air temperaturemust be constant. The process is controlled by controllingthe speed of the hot air fans using VSDs.

Variables inprocessingsystems



As mentioned earlier in this guide, working machineprocesses can be divided into two categories. The firstcategory is material treatment, which is accomplished usingvarious types of processing apparatus to alter a material’sproperties into another form.

Processing apparatus can be divided into two groupsaccording to the resulting shape of the material beingtreated. The shape can be either well defined or indefinite.Materials with a well-defined shape, such as paper, metaland wood, are processed with machinery. Examples arepaper machines, rolling mills and saw mill lines.

Materials with an indefinite shape, such as various foodproducts, plastics etc., are processed with plantequipment. Examples of this kind of equipment aremargarine stirrers, and different kinds of centrifuges andextruders.

Machines areused to altermaterials'properties...


Well definedshape

Indefiniteshape


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9

The second category consists of machines which transportmaterial to a desired location. This group consists ofconveying, dosing and pressure changing apparatus.These machines can be divided into three different sub-groups according to whether the type of material beingtreated is a solid, liquid or gas.

Solid materials, such as shipping containers, metal, wood,minerals and of course people, are transported byconveying apparatus. Such apparatus includes cranes,conveyors and elevators.

Liquid materials, for example, water, oil or liquid chemicals,are transported by pumps.

Gaseous materials such as air are transported using fans,compressors or blowers. A special application of thesemachines is air conditioning.

In the diagram above, five different types of machines arepresented. They either shape or transport different typesof material, but all of them can be potentially used withVariable Speed Drives.

...and totransportmaterials

Solid materials

Liquidmaterials

Gaseousmaterials



All of the machines mentioned earlier in this guide arecommonly driven by electric motors. It can be said thatthe electric motor is the workhorse of industrial processes.In this chapter, we will take a closer look at electricalmotors - especially the squirrel cage AC motor, which isthe most common motor used in industrial processes.

Chapter 3 - The workhorse ofindustry: The electric motor

Every machine consists of four different components, shownin the diagram. These components are energy control, themotor, transmission and the working machine. Together, thefirst three components comprise the so called “drive system”.This drive system can transform a given type of energy,usually electrical, into mechanical energy, which is thenused by the working machine. Energy is supplied to the drivesystem from the power supply.

In each of the three drive system components, variablespeed control is possible. Variable speed control can beaccomplished, for example, using a frequency converter asthe energy control component, a two speed motor as themotor component and gears as the transmission component.

As mentioned earlier, most machines are driven by an electricmotor. Electric motors can be divided into AC and DCmotors. AC motors, particularly squirrel cage motors, arethe most commonly used motors in industrial processes.

Electric motorsdrive mostmachines


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An AC motor’s ability to convert electrical energy intomechanical energy is based on electromagnetic induction.The voltage in stator windings forms the current andmagnetic flux. The direction of this flux can be determinedusing the right hand rule from the stator current.

By changing the direction of the voltage in stator windings,the direction of the flux can also be changed. By changingthe voltage direction in the three phase motor windings inthe correct order, the magnetic flux of the motor starts torotate. The motor’s rotor will then follow this flux with acertain slip. This is the basic principle used to control ACmotors.

This control can be achieved using a frequency converter.As the name suggests, a frequency converter changes thefrequency of the alternating current and voltage. A frequencyconverter consists of three parts. Regular 50Hz 3-phasecurrent is fed in to the rectifier part, which converts it todirect current. The DC voltage is fed into the DC bus circuit,which filters the pulsating voltage. The inverter unit thenconnects each motor phase either to the negative or thepositive DC bus according to a certain order.

To receive the flux direction shown in the diagram, switchesV1, V4 and V5 should be closed. To make the flux rotatecounterclockwise, switch V6 has to be closed but V5 hasto be open. If switch V5 is not opened, the circuit will shortcircuit. The flux has turned 60° counterclockwise.

Motors convertelectricalenergy intomechanicalenergy

The workhorse of industry: The electric motor


There are eight different switching positions in the inverter.In two positions, the voltage is zero, i.e. when all the phasesare connected to the same DC bus, either negative orpositive. So in the remaining six switching positions thereis voltage in the motor windings, and this voltage createsmagnetic flux.

The diagram shows these six switching positions and theflux directions, which the voltage in the windings generatesin each case. Voltage also generates current in thewindings, the directions of which are marked with arrowsin each phase.

In practice, control is not quite as simple as presented here.Magnetic flux generates currents in the rotor. These rotorcurrents complicate the situation. External interference, suchas temperature or load changes, can also cause some controldifficulties. Nevertheless, with today’s technology and know-how, it is possible to effectively deal with interference.

Electrical VSDs also provide many additional benefits, suchas energy savings, because the motor does not use moreelectrical energy than required. Furthermore, control is betterthan with conventional methods, because electrical VSDsalso provide the possibility for stepless control.

Frequencyconverterscontrolelectromagneticinduction



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The total efficiency of the drive system depends on thelosses in the motor and its control. Both drive and motorlosses are thermal, so they appear as heat. Input power tothe drive system is electrical in form, while output poweris mechanical. That is why calculating the coefficient ofefficiency (η) requires knowledge of both electrical andmechanical engineering.

Electrical input power Pin depends on voltage (U), current(I) and the power factor (cosϕ). The power factor tells uswhat proportion of the total electric power is active powerand how much is so called reactive power. To produce therequired mechanical power, active power is required.Reactive power is needed to produce magnetisation inthe motor.

Mechanical output power Pout depends on the requiredtorque (T) and rotating speed (n). The greater the speed ortorque required, the greater the power required. This hasa direct effect on how much power the drive system drawsfrom the electrical supply. As mentioned earlier, thefrequency converter regulates the voltage, which is fed tothe motor, and in this way directly controls the power usedin the motor as well as in the process being controlled.

Electrical switching with transistors is very efficient, sothe efficiency of the frequency converter is very high, from0.97 to 0.99. Motor efficiency is typically between 0.82and 0.97 depending on the motor size and its rated speed.So it can be said that the total efficiency of the drive systemis always above 0.8 when controlled by a frequencyconverter.

The efficiencyof the drivesystem



In some cases, reversed rotation of the motor is required.In addition, torque direction requirements might change.These factors combined form the so called “four quadrantdrive”. The name comes from the four different quadrants(I to IV) shown in the diagram.

I quadrant: In the first quadrant, the motor is rotatingclockwise. Because the torque is in the same direction asthe speed, the drive is accelerating.

II quadrant: In the second quadrant, the motor is stillrotating clockwise, but the torque is in the oppositedirection, so the drive is decelerating.

III & IV quadrants: In the third and fourth quadrant, themotor is rotating counterclockwise and the drive is againaccelerating or decelerating, depending on the torquedirection.

With a frequency converter, torque direction changes canbe implemented independent of the direction of rotation.To produce an efficient four quadrant drive, some kind ofbraking arrangement is required. This kind of torque controlis especially required in crane applications, where the rotationdirection might change, but the torque direction remainsthe same.

Reversedrotation ortorque issometimesrequired



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15

The motor must produce the required torque to overcomethe load torque. Load torque consists of friction, inertia ofthe moving parts and the load itself, which depends onthe application. In the example in the diagram, the motortorque has to be greater than the load torque, which isdependent on the mass of the box, if the box is to rise.

Load factors change according to the application. Forexample, in a crusher, the load torque is dependent notonly on friction and inertia, but also on the hardness of thecrushed material. In fans and blowers, air pressure changesaffect the load torque, and so on.


The load,friction andinertia resistrotation


In any case, the loading torque has to be known beforeselecting the motor for the application. The required speedalso has to be known. Only then can a suitable motor beselected for the application.

If the motor is too small, the requirements cannot be metand this might lead to serious problems. For example, incrane applications, a motor that is too small may not beable to lift the required load quickly enough to the desiredheight. It might even drop the load completely, as shown inthe diagram. This could be disastrous for people workingat the harbour or site where this crane would be used. Tocalculate the rated torque of the motor the followingformula can be used:

T[Nm]=9550 xP [kW]

n[1/min]

The motor hasto overcomethe loadingtorque



4

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A motor’s torque/speed curve is unique and has to becalculated for every motor type separately. A typicaltorque/speed curve is shown in the graph as Tm. As can beseen, the maximum load torque is reached just belownominal speed.

Load torque Tl usually increases with speed. Dependingon the application it can be linear or quadratic. The motorwill automatically accelerate until the load torque and motortorque are equal. This point is shown on the graph as theintersection of Tm and Tl. Actual torque (Tact) is shown onthe y-axis and actual speed (nact) on the x-axis.

These are the principles that govern how an ordinarysquirrel cage motor works. With a frequency converter,optimal control performance can be obtained from themotor and the whole drive system. This will be introducedlater in this guide.

The drivetorque andload torque areequal atnominal speed



In most processes there is at least one variable. This variablecauses the need for process adjustment. Therefore variableprocesses and material volumes need some form of control.

In this chapter we will look at processes and their variables.We will also examine different control methods.

Chapter 4 - Variable volumesrequire some form of control

There may be many different parameters involved in aprocess, the most common being input, output andinterference. These parameters may need to be constantor they may need to be changed according to a presetpattern. As discussed in the first chapter, there are alwaysinputs and outputs present in a process and, in almost everycase, interference as well.

In some processes there is no interference and the inputis constant. This kind of process works without any variablespeed control. However, if the output parameters need tobe changed, the input is variable or there is interferencepresent, then variable speed control might be the solutionto fulfilling the process requirements.

The above table lists some processes in which variablespeed control is required. It also shows the reasons forthe control; input, interference or output.

Variablematerial flowand input/outputrequirements


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There are many simpler control methods in existence suchas throttling or bypass control. The construction of suchequipment is usually very simple and the investment maylook cost effective at first.

However, there are many drawbacks. For example the optimalprocess capacity, which gives the best quality of the process,is very difficult to achieve with simple control. An increase inproduction capacity usually requires reconstruction of thewhole process and with each direct on-line start-up there isa risk of electrical and/or mechanical damage.

The simple control methods are also energy consuming,so in addition to the total operating cost being higher thanwith VSDs, the environmental effects, such as CO2emissions from power plants, also increase. Therefore, thetotal life-cycle cost of investment in simple control methodsis much higher than with VSDs.

Simpler controlmethods

Variable volumes require some form of control


The best control method for most systems is VSD. Imagineyou are driving a car for example. If you are driving on ahighway and entering a populated area, you need to reducespeed so that you don’t risk your own and other peoples’lives.

The best possible way to do this is of course to reducemotor rotation speed by taking your foot off the gas pedaland, if necessary, changing to a lower gear. Another possibilitywould be to use the same gear, keep your foot on the gasand reduce speed simply by braking. This would not onlycause wear on the engine and brakes, but also use a lot offuel and reduce your overall control of the vehicle.Furthermore, the original goal of reducing speed withoutrisking your own and other peoples' lives would not havebeen achieved.


The bestcontrol methodis VSD


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Above are the four most common VSDs in the industrialsector. Mechanical variable speed control usually uses beltdrives, and is controlled by moving conical pulleys manuallyor with positioning motors.

In hydraulic coupling, the turbine principle is used. Bychanging the volume of oil in the coupling, the speeddifference between the driving and driven shafts changes.The oil amount is controlled with pumps and valves.

In the DC drive, a DC converter changes the motor supplyvoltage fed to the DC motor. In the motor, a mechanicalinverter, a commutator, changes direct current to alternatingcurrent.

In the frequency converter or AC drive, a standard squirrelcage motor is used, so no mechanical inverters arerequired. The speed of the motor is regulated by afrequency converter that changes the frequency of themotor voltage, as presented earlier in this guide. Thefrequency converter itself is controlled with electricalsignals.

The diagram shows the location of the control equipmentfor each type of VSD. In mechanical and hydraulic VSDs,the control equipment is located between the motor andthe working machine, which makes maintenance verydifficult.

In electrical VSDs, all control systems are situated in anelectrical equipment room and only the driving motor is inthe process area. This is just one benefit of electrical VSDs.Other benefits are presented on the following page.


Mechanical,hydraulic andelectrical VSDs

Hydrauliccoupling

DC drive

AC drive


Here are the four most important arguments for usingelectrical VSDs, presented along with estimated VSD marketshares in Europe in 2000. The four main benefits of usingelectrical VSDs are highlighted at the turning points of thespeed curve.

Direct on-line starting stresses the motor and also theelectrical equipment. With electrical VSDs, smooth startingis possible and this has a direct effect on maintenancecosts.

Process equipment is usually designed to cater for futureproductivity increases. Changing constant-speedequipment to provide higher production volumes requiresmoney and time. With the AC drive, speed increases of 5to 20 percent are not a problem, and the productionincrease can be achieved without any extra investment.

In many processes, production volumes change. Changingproduction volumes by mechanical means is usually veryinefficient. With electrical VSDs, changing the productionvolume can be achieved by changing the motor speed.This saves a lot of energy particularly in pump and fanapplications, because the shaft power is proportional to theflow rate to the power of three.

The accurate speed control obtainable with electrical VSDsresults in process optimisation. The optimal process controlleads to the best quality end product, which means thebest profit for the customer.

Due to these benefits, electrical VSDs are dominating themarket, as can be seen from the table above. AC and DCdrives together account for over 75%, and AC drives formore than 50%, of the total VSD market in Europe in 2000.


Electrical VSDsdominate themarket

Maintenancecosts

Productivity

Higher quality

Energy saving

Year 2000: Europe (estimate)


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This diagram shows the projected development of theelectrical VSDs market to the year 2000. As can be seen,the AC drives market is growing at almost 10% per year,which accounts for the entire growth of the electrical andVSD market. The market share of DC drives is diminishing,and the total DC market size remains approximatelyconstant. This progress is due to the development of ACdrives technology.

As presented earlier in this guide, the AC drive has manybenefits over other process control methods. Thedifference between the AC and the DC motor is that theDC motor has a mechanical commutator, utilising carbonbrushes. These brushes need regular maintenance and thecommutator itself complicates the motor structure andconsumes energy. These are the main reasons why the ACdrives market share is growing in comparison to DC drives.

The AC drivesmarket isgrowing fast



Taking into account everything presented so far, we canconfidently say that the AC drive is the leading controlmethod. In the following chapter we will take a closer look atthe different features of the AC drive, and the levels ofperformance the drive can offer.

Chapter 5 - AC drive: The leading control method

In this diagram, the basic functions of an AC drive arepresented. There are four different components in AC drivemotor control. These components are the user interface,the motor, the electrical supply and the process interface.

An electrical supply feeds the required electricity to thedrive; one selection criteria for the drive is the supplyvoltage and its frequency. The AC drive converts thefrequency and voltage and feeds the motor. This conversionprocess is controlled by signals from the process or uservia the process and user interfaces.

The user interface provides the ability to observe the ACdrive and obtain different process information via the drive.This makes the drive easy to integrate with other processcontrol equipment and overriding process control systems.

The basicfunctionsof an AC drive


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If the motor is driven without a frequency converter, itsload capacity curves cannot be modified. It will produce aspecified torque at certain speed and maximum torquecannot be exceeded.

With a frequency converter drive, there are different loadingoptions. The standard curve, Curve 1 in the diagram, canbe used continuously. Other curves can only be used forcertain periods of time, because the motor’s coolingsystem is not designed for this kind of heavy use.

These higher load capacity levels might be needed, forexample, during start-up. In certain applications, as muchas twice the amount of torque is required when starting.With a frequency converter this is possible, meaning thata motor can be dimensioned according to its normal use.This reduces the investment cost.

To be able to use these features it is very important thatthe load, the AC drive and the motor are compatible.Otherwise the motor or the converter will overheat and bedamaged.

AC drive: The leading control method

A motor's loadcapacity curveswith an ACdrive


AC drives also have other internal features and functionswhich are sometimes required for better process control.Examples of these features are listed in the diagram. Withinputs and outputs for example, different kinds of processinformation can be fed to the drive and it will control themotor accordingly. Alternatively, the load can be limitedto prevent nuisance faults and to protect the workingmachine and the whole drive system.

In the following sections the listed features are presentedin more detail.

AC drivefeatures forbetter processcontrol


Important features:• inputs and outputs• reversing function• ramp times acceleration/deceleration• variable torque V/Hz settings• torque boosting• eliminating mechanical vibrations• load limits to prevent nuisance faults• power loss ride-through• stall function• slip compensation• flying start


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Reversing the motor rotation is simple to accomplishwith an AC drive. With ABB’s frequency converters it can beachieved simply by pressing one button. Furthermore, itis possible to set different acceleration and deceleration ramptimes. The ramp form can also be modified according tothe user’s wishes. In the diagram (above, left) an S-ramp hasbeen presented. Another possibility could be a linear ramp.

Torque control is relatively simple with an AC drive. Torqueboosting, which was presented earlier, is necessary if avery high starting torque is required. Variable torque U/fsettings mean that maximum torque can be achieved at alower speed of rotation than normal.

Mechanical vibrations can be eliminated by by-passingcritical speeds. This means that when a motor is acceleratedclose to its critical speed, the drive will not allow the actualspeed of the motor to follow the reference speed. When thecritical point has been passed, the motor will return to theregular curve very quickly and pass the critical speed.


Reversing

Torque control

Eliminatingmechanicalvibrations


The power loss ride-through function is used if the incomingsupply voltage is cut off. In such a situation, the AC drivewill continue to operate using the kinetic energy of therotating motor. The drive will be fully operational as long asthe motor rotates and generates energy for the drive.

With an AC drive, the motor can be protected in a stallsituation with the stall function. It is possible to adjustsupervision limits and choose how the drive reacts to themotor stall condition. Protection is activated if threeconditions are met at the same time.

1. The drive frequency has to be below the preset stallfrequency.

2. The motor torque has to rise to a certain limit, calculatedby the drive software.

3. The final condition is that the motor has been in the stalllimit for longer than the time period set by the user.


Power lossride-through

Stall function

Power loss ride-through Stall function

Torque

Intermediate circuit voltage (U )

Output frequency (f)

Stall Frequency

mains

dc

m

dc

Motor torque (T )

Tstall


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If the motor load torque is increased, the speed of themotor will decrease as shown in the diagram (above, left).To compensate for this slip, the torque/speed curve canbe modified with the frequency converter so that torqueincrease can be accomplished with the same speed aspreviously.

The flying start feature is used when a motor is connected toa flywheel or a high inertia load. The flying start workseven without a speed feedback. In case of rotating motor,the inverter is first started with a reduced voltage and thensynchronised to the rotating rotor. After synchronised thevoltage and the speed are increased to the correspondinglevels.


Slipcompensation

Flying start


Any drive system has to handle different environmentalstresses such as moisture or electrical disturbances. Thesquirrel cage motor is very compact and can be used invery hostile conditions. The IP 54 degree of protectionguarantees that it can work in a dusty environment andthat it can bear sprinkling water from any direction.

The frequency converter usually has an IP 21 degree ofprotection. This means that it is not possible to touch thelive parts and that vertically dripping water will not causeany harm. If a higher degree of protection is required, itcan be obtained, for example, by installing the drive insidea cabinet with the required degree of protection. In suchcases, it is essential to ensure that the temperature insidethe cabinet will not exceed the allowed limits.

Another important environmental feature is electromagneticcompatibility (EMC). It is very important that a drive systemfulfills the EMC directives of the European Union. This meansthat the drive system can bear conductive and radiativedisturbances, and that it does not send any conductive orradiative disturbances itself either to the electrical supplyor the surrounding environment.

If you require more information about the EMC directivesand their effects on drives, please refer to ABB's TechnicalGuide No. 3, EMC Compliant Installation and Configurationfor a Power Drive System.

Environmentalfeatures


EMC


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In addition to their technical advantages, AC drives alsoprovide many cost benefits. In this chapter, these benefits arereviewed, with the costs divided into investment, installationand operational costs.

Chapter 6 - Cost benefits of AC drives

At the moment there are still plenty of motors sold withoutvariable speed AC drives. This pie chart shows how manymotors below 2.2 kW are sold with frequency converters,and how many without. Only 3% of motors in this powerrange are sold each year with a frequency converter; 97%are sold without an AC drive.

This is astonishing considering what we have seen so far inthis guide. Even more so after closer study of the costs ofan AC drive compared to conventional control methods.But first let’s review AC drive technology compared to othercontrol methods.


Cost benefits of AC drives

AC drive technology is completely different from other,simpler control methods. It can be compared, for example,to the difference between a zeppelin and a modern airplane.

We could also compare AC drive technology to thedevelopment from a floppy disk to a CD-ROM. Although itis a simpler information storage method, a floppy disk canonly handle a small fraction of the information that aCD-ROM can.

The benefits of both these innovations are generally wellknown. Similarly, AC drive technology is based on a totallydifferent technology to earlier control methods. In thisguide, we have presented the benefits of the AC drivecompared to simpler control methods.

Technicaldifferencesbetween othersystems andAC drives


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To make a proper cost comparison, we need to study theconfigurations of different control methods. Here we haveused pumping as an example. In traditional methods, thereis always a mechanical part and an electrical part.

In throttling you need fuses, contactors and reactors onthe electrical side and valves on the mechanical side. InOn/Off control, the same electrical components are needed,as well as a pressure tank on the mechanical side. The ACdrive provides a new solution. No mechanics are needed,because all control is already on the electrical side.

Another benefit, when thinking about cost, is that with anAC drive we can use a regular 3-phase motor, which ismuch cheaper than the single phase motors used in othercontrol methods. We can still use 220 V single phasesupply, when speaking of power below 2.2 kW.

No mechanicalcontrol partsneeded



This list compares the features of conventional controlmethods with those of the AC drive, as well as their effecton costs. In conventional methods there are both electricaland mechanical components, which usually have to bepurchased separately. The costs are usually higher than ifeverything could be purchased at once.

Furthermore, mechanical parts wear out quickly. This directlyaffects maintenance costs and in the long run, maintenanceis a very important cost item. In conventional methodsthere are also many electrical components. The installationcost is at least doubled when there are several differenttypes of components rather than only one.

And last but not least, mechanical control is very energyconsuming, while AC drives practically save energy. Thisnot only helps reduce costs, but also helps minimiseenvironmental impact by reducing emissions from powerplants.

Factorsaffecting cost


Conventional methods: AC drive:- both electrical and - all in one

mechanical parts- many electrical parts - only one electrical

component- mechanical parts need - no mechanical parts,

regular maintenance no wear and tear- mechanical control is - saves energy

energy consuming


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In this graph, the investment structure as well as the totalprice of each pump control method is presented. Only thepump itself is not added to the costs because its price isthe same regardless of whether it’s used with an AC driveor valves. In throttling, there are two possibilities dependingon whether the pump is used in industrial or domestic use.In an industrial environment there are stricter requirementsfor valves and this increases costs.

As can be seen, the motor is much more expensive fortraditional control methods than for the AC drive. This isdue to the 3-phase motor used with the AC drive and thesingle phase motor used in other control methods.

The AC drive does not need any mechanical parts, whichreduces costs dramatically. Mechanical parts themselvesare almost always less costly than a frequency converter,but electrical parts also need to be added to the totalinvestment cost.

After taking all costs into account, an AC drive is almostalways the most economical investment, when comparedto different control methods. Only throttling in domesticuse is as low cost as the AC drive. These are not the totalcosts, however. Together with investment costs we needto look at installation and operational costs.


Investmentcosts:Mechanical andelectricalcomponents

The motor

The AC drive


Because throttling is the second lowest investment afterthe AC drive, we will compare its installation and operatingcosts to the cost of the AC drive. As mentioned earlier, inthrottling there are both electrical and mechanicalcomponents. This means twice the amount of installationmaterial is needed.

Installation work is also at least doubled in throttlingcompared to the AC drive. To install a mechanical valveinto a pipe is not that simple and this increases installationtime. To have a mechanical valve ready for use usuallyrequires five hours compared to one hour for the AC drive.Multiply this by the hourly rate charged by a skilled installerto get the total installation cost.

The commissioning of a throttling-based system does notusually require more time than commissioning an AC drivebased system. One hour is usually the time required in bothcases. So now we can summarise the total installationcosts. As you can see, the AC drive saves up to USD 270per installation. So even if the throttling investment costswere lower than the price of a single phase motor(approximately USD 200), the AC drive would pay for itselfbefore it has even worked a second.


Installationcosts:Throttlingcompared toAC drive

Throttling AC drive

Installation material 20 USD 10 USD

Installation work 5h x 65 USD = 1h x 65 USD =325 USD 65 USD

Commissioning 1h x 65 USD = 1h x 65 USD =work 65 USD 65 USD

Total 410 USD 140 USD

Savings in installation: 270 USD!


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In many surveys and experiments it has been proved that a50% energy saving is easily achieved with an AC drive. Thismeans that where power requirements with throttling wouldbe 0.75 kW, with the AC drive it would be 0.37 kW. If apump is used 4000 hours per year, throttling would need3000 kWh and the AC drive 1500 kWh of energy per year.

To calculate the savings, we need to multiply the energyconsumption by the energy price, which varies dependingon the country. Here USD 0.1 per kWh has been used.

As mentioned earlier, mechanical parts wear a lot and thisis why they need regular maintenance. It has beenestimated that whereas throttling requires USD 40 per yearfor service, maintenance costs for an AC drive would beUSD 5. In many cases however, there is no maintenancerequired for a frequency converter.

Therefore, the total savings in operating costs would beUSD 185, which is approximately half of the frequencyconverter’s price for this power range. This means thatthe payback time of the frequency converter is two years.So it is worth considering that instead of yearly service foran old valve it might be more profitable to change the wholesystem to an AC drive based control. To retrofit an existingthrottling system the pay-back time is two years.


Operationalcosts:Maintenanceand driveenergy

Throttling AC drivesaving 50%

Power required 0.75 kW 0.37 kW

Annual energy 4000 hours/year 3000 kWh 1500 kWh

Annual energy cost with 0.1 300 USD 150 USD

USD/kWh

Maintenance/year 40 USD 5 USD

Total cost/year 340 USD 155 USD

Savings in one year: 185 USD!


In the above figure, all the costs have been summarised.The usual time for an operational cost calculation for thiskind of investment is 10 years. Here the operational costsare rated to the present value with a 10% interest rate.

In the long run, the conventional method will be more thantwice as expensive as a frequency converter. Most of thesavings with the AC drive come from the operational costs,and especially from the energy savings. It is in theinstallation that the highest individual savings can beachieved, and these savings are realised as soon as thedrive is installed.

Taking the total cost figure into account, it is very difficultto understand why only 3% of motors sold have afrequency converter. In this guide we have tried to presentthe benefits of the AC drive and why we at ABB think thatit is absolutely the best possible way to control yourprocess.


Total costcomparison


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AABB 5, 28, 31, 39, 44AC drive 5, 22, 23, 24, 25, 26, 27,28, 29, 30, 31, 32, 33, 34, 35, 36,37, 38, 39AC drives market 3, 24AC motor 11, 12active power 14air conditioning 7, 10

Bbelt drives 22blowers 10, 16braking 15, 21bypass control 20

CCD-ROM 33centrifuges 9chemical industry 7coefficient of efficiency 14commissioning 37commutator 22, 24compressors 10contactors 34conveying 10conveyors 10crane 10, 15, 17critical speed 28crusher 16current 12, 13, 14, 22

DDC bus 12, 13DC converter 22DC drive 22, 23, 24DC motor 11, 22, 24Direct on-line starting 23dosing 10drive frequency 29drive software 29drive system 11, 14, 18, 27, 31drying kiln 8

Eelectrical disturbances 31electrical equipment room 22electrical supply 14, 25, 31electromagnetic compatibility 31electromagnetic induction 12, 13electromagnetic influence 8elevators 10EMC 31EMC directives 31

Chapter 7 - Index

energy 8, 11, 12, 13, 20, 23, 24, 29,35, 38, 39extruders 9

Ffans 7, 8, 10, 16floppy disk 33flux 12, 13flying start 27, 30flywheel 30four quadrant drive 15frequency converter 11, 12, 14, 15,18, 22, 26, 30, 31, 32, 36, 38, 39friction 16fuses 34

Ggears 11

Hharbour 17humidity 7HVAC 7hydraulic coupling 22

Iindustrial processes 5, 6, 7, 11inertia 16, 30input power 14interference 13, 19inverter 12, 13, 22IP 21 31IP 54 31

Llinear ramp 28load capacity curves 26

Mmachine 8, 9, 10, 11, 22, 27magnetic flux 12, 13maintenance 22, 23, 24, 35, 38margarine stirrers 9material transport 6material treatment 6, 8, 9mechanical power 8, 14mechanical vibrations 4, 27, 28motor efficiency 14motor load 30motor losses 14motor phase 12motor size 14motor stall condition 29motor windings 12, 13


Nnuclear power 8nuisance faults 27

Ooutput power 14

Ppaper machines 9power factor 14power loss ride-through 27, 29power plants 7, 20, 35power supply 11process control 23, 24, 25, 27processing system 8pump 10, 22, 23, 34, 36, 38

Rrated speed 14reactive power 14reactors 34rectifier 12reference speed 28reversing function 27right hand rule 12rolling mills 9

SS-ramp 28saw mill lines 9shipping containers 10slip 12, 27, 30squirrel cage motor 11, 18, 22, 31stall frequency 29stall function 27, 29stator 12stepless control 13

Ttemperature 7, 8, 13, 29, 31thermal influence 8throttling 20, 34, 36, 37, 38torque 14, 15, 16, 17, 18, 26, 27, 28,29, 30transistors 14

Vvalves 22, 34, 36, 37, 38variable speed control 11, 19, 22, 36Variable Speed Drives 5, 10, 39voltage 12, 13, 14, 22, 25, 29, 30VSD 5, 6, 7, 8,13, 21, 22, 23, 24

Zzeppelin 33


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Bearing Currents inModern AC Drive Systems


Technical Guide No.5 - Bearing currents in modern AC drive systems2

1 Introduction ......................................................General ......................................................................Avoiding bearing currents ........................................

2 Generating Bearing Currents ...........................High frequency current pulses .................................Faster switching ........................................................How are HF bearing currents generated? ...............

Circulating current ................................................Shaft grounding current ........................................Capacitive discharge current ...............................

Common mode circuit ..............................................Stray capacitances ...................................................How does the current flow through the system? ..Voltage drops ..........................................................Common mode transformer ...................................Capacitive voltage divider ......................................

3 Preventing high frequency bearing currentdamage ...........................................................Three approaches ...................................................

Multicore motor cables .......................................Short impedance path ........................................High frequency bonding connections ................

Follow product specific instructions ......................Additional solutions ............................................

Measuring high frequency bearing currents ..........Leave the measurements to the specialists ..........

4 References ......................................................

5 Index ...............................................................

Contents

555

666777779

10101113

151515161717171819

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Technical Guide No.5 - Bearing currents in modern AC drive systems

5

3

Some new drive installations can have their bearings failonly a few months after start-up. Failure can be caused byhigh frequency currents, which flow through the motorbearings.

While bearing currents have been around since the adventof electric motors, the incidence of damage they causehas increased during the last few years. This is becausemodern variable speed drives with their fast rising voltagepulses and high switching frequencies can cause currentpulses through the bearings whose repeated dischargingcan gradually erode the bearing races.

To avoid damage occurring, it is essential to provide properearthing paths and allow stray currents to return to theinverter frame without passing through the bearings. Themagnitude of the currents can be reduced by usingsymmetrical motor cables or inverter output filtering.Proper insulation of the motor bearing construction breaksthe bearing current paths.


General

Avoidingbearingcurrents


5

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Bearing currents come in several different guises. However,while modern motor design and manufacturing practiceshave nearly eliminated the low frequency bearing currentsinduced by the asymmetry of the motor, the rapid switchingin modern AC drive systems may generate high frequencycurrent pulses through the bearings. If the energy of thesepulses is sufficiently high, metal transfers from the balland the races to the lubricant. This is known as electricaldischarge machining or EDM. The effect of a single pulseis insignificant, but a tiny EDM pit is an incontinuity thatwill collect more pulses and expand into a typical EDMcrater. The switching frequency of modern AC drives isvery high and the vast number of pulses causes the erosionto quickly accumulate. As a result, the bearing may needreplacing after only a short time in service.

High frequency bearing currents have been investigated byABB since 1987. The importance of system design has beenhighlighted in the last few years. Each individual item involved,such as the motor, the gearbox or the drive controller, is theproduct of sophisticated manufacturing techniques andnormally carries a favourable Mean Time Between Failure(MTBF) rate. It is when these components are combined andthe installed system is looked upon as a whole, that itbecomes clear that certain installation practices are required.

Figure 1: Bearing currents can cause “bearing fluting”,a rhythmic pattern on the bearing’s races.

Current AC drive technology, incorporating Insulated GateBipolar Transistors (IGBT), creates switching events 20 timesfaster than those considered typical ten years ago. Recent yearshave seen a rising number of EDM-type bearing failures in ACdrive systems relatively soon after start up, within one to sixmonths. The extent to which this occurs depends on the ACdrive system architecture and the installation techniques used.

Chapter 2 - Generating Bearing Currents

High frequencycurrent pulses

Faster switching


The source of bearing currents is the voltage that is inducedover the bearing. In the case of high frequency bearingcurrents, this voltage can be generated in three differentways. The most important factors that define whichmechanism is prominent, are the size of the motor andhow the motor frame and shaft are grounded. The electricalinstallation, meaning a suitable cable type and properbonding of the protective conductors and the electricalshield, plays an important role. Du/dt of the AC drive powerstage components and the DC-link voltage level affect thelevel of bearing currents.

In large motors, high frequency voltage is induced betweenthe ends of the motor shaft by the high frequency fluxcirculating around the stator. This flux is caused by a netasymmetry of capacitive current leaking from the windinginto the stator frame along the stator circumference. Thevoltage between the shaft ends affects the bearings. If it ishigh enough to overcome the impedance of the bearings’oil film, a current that tries to compensate the net flux inthe stator starts to flow in the loop formed by the shaft,the bearings and the stator frame. This current is acirculating type of high frequency bearing current.

The current leaking into the stator frame needs to flowback to the inverter, which is the source of this current.Any route back contains impedance, and therefore thevoltage of the motor frame increases in comparison to thesource ground level. If the motor shaft is earthed via thedriven machinery, the increase of the motor frame voltageis seen over the bearings. If the voltage rises high enoughto overcome the impedance of the drive-end bearing oilfilm, part of the current may flow via the drive-end bearing,the shaft and the driven machine back to the inverter. Thiscurrent is a shaft grounding type of high frequency bearingcurrent.

In small motors, the internal voltage division of the commonmode voltage over the internal stray capacitances of themotor may cause shaft voltages high enough to createhigh frequency bearing current pulses. This can happen ifthe shaft is not earthed via the driven machinery while themotor frame is earthed in the standard way for protection.

High frequency bearing currents are a consequence of thecurrent flow in the common mode circuit of the AC drive system.

A typical three-phase sinusoidal power supply is balancedand symmetrical under normal conditions. That is, the vectorsum of the three phases always equals zero. Thus, it is normal

How are HFbearing currentsgenerated?

Generating Bearing Currents

Circulatingcurrent

Shaftgroundingcurrent

Capacitivedischargecurrent

Common modecircuit


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that the neutral is at zero volts. However, this is not the casewith a PWM switched three-phase power supply, where adc voltage is converted into three phase voltages. Eventhough the fundamental frequency components of theoutput voltages are symmetrical and balanced, it isimpossible to make the sum of three output voltagesinstantaneously equal to zero with two possible outputlevels available. The resulting neutral point voltage is notzero. This voltage may be defined as a common modevoltage source. It is measurable at the zero point of anyload, eg. the star point of the motor winding.

Figure 2: This schematic shows the phase voltages of a typical three phasePWM power supply and the average of the three, or neutral point voltage,in a modern AC drive system. The neutral voltage is clearly not zero andits presence can be defined as a common mode voltage source. The voltageis proportional to the DC bus voltage, and has a frequency equal to theinverter switching frequency.

Any time one of the three inverter outputs is changed fromone of the possible potentials to another, a currentproportional to this voltage change is forced to flow toearth via the earth capacitances of all the components ofthe output circuit. The current flows back to the sourcevia the earth conductor and stray capacitances of theinverter, which are external to the three phase system.This type of current, which flows through the system in aloop that is closed externally to the system, is calledcommon mode current.



Figure 3: An example of the common mode current at the inverteroutput. The pulse is a superposition of several frequencies due to thedifferent natural frequencies of the parallel routes of common modecurrent.

A capacitance is created any time two conductivecomponents are separated by an insulator. For instance,the cable phase wire has capacitance to the PE-wireseparated by PVC insulation, for example, and the motorwinding turn is insulated from the frame by enamel coatingand slot insulation, and so has a value of capacitance tothe motor frame. The capacitances within a cable andespecially inside the motor are very small. A smallcapacitance means high impedance for low frequencies,thus blocking the low frequency stray currents. However,fast rising pulses produced by modern power suppliescontain frequencies so high that even small capacitancesinside the motor provide a low impedance path for currentto flow.

Figure 4: Simplified loop of the common mode current of a PWM inverterand induction motor. The inverter power supply acts as a common modevoltage source (Vcm). Common mode current (CMC) flows through


Straycapacitances


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the common mode cable and motor inductances, Lc Lm and through thestray capacitances between the motor windings and motor frame,combined to be Cm. From the motor frame, the current proceeds throughthe factory earth circuit which has the inductance Lg. Lg is also fed commonmode current from the stray cable capacitance Cc. The inverter frame isconnected to the factory earth and couples the common mode current/earth currents through stray inverter to frame capacitances, combined asCin, back to the common mode voltage source.

The return path of the leakage current from the motor frameback to the inverter frame consists of the motor frame,cable shielding or PE-conductors and possibly steel oraluminium parts of the factory building structure. All theseelements contain inductance. The flow of common modecurrent through such inductance will cause a voltage dropthat raises the motor frame potential above the sourceground potential at the inverter frame. This motor framevoltage is a portion of the inverter’s common mode voltage.The common mode current will seek the path of leastimpedance. If a high amount of impedance is present inthe intended paths, like the PE-connection of the motorframe, the motor frame voltage will cause some of thecommon mode current to be diverted into an unintendedpath, through the building. In practical installations anumber of parallel paths exist. Most have a minor effecton the value of common mode current or bearing currents,but may be significant in coping with EMC-requirements.

If the value of this inductance is high enough, the reactanceat the upper range of typical common mode currentfrequencies, 50 kHz to 1 MHz, can support voltage dropsof over 100 volts between the motor frame and the inverterframe. If, in such a case, the motor shaft is connectedthrough a metallic coupling to a gearbox or other drivenmachinery that is solidly earthed and near the same earthpotential as the inverter frame, then it is possible, thatpart of the inverter common mode current flows via themotor bearings, the shaft and the driven machinery back

How does thecurrent flowthrough thesystem?


Voltage drops


i+∆ ∆ i

i-∆ ∆ i

∆ ∆ i

∆ iD N

to the inverter.

Figure 5: A schematic presentation showing the circulating current andshaft grounding current, the latter resulting from high motor framevoltage with superior machine earthing.

If the shaft of the machinery has no direct contact to theground level, current may flow via the gearbox or machinebearings. These bearings may be damaged before the motorbearings.

Figure 6: Source of circulating high frequency bearing current. Currentleakage through distributed stator capacitances gives a non-zero currentsum over the stator circumference. This leads to a net magnetising effectand flux around the motor shaft.

The largest share of the motor’s stray capacitance, isformed between the stator windings and the motor frame.This capacitance is distributed around the circumferenceand length of the stator. As the current leaks into the statoralong the coil, the high frequency content of the currententering the stator coil is greater than the current leaving.


Commonmodetransformer


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11

This net current produces a high frequency magnetic fluxthat will circulate in the stator laminations, inducing an axialvoltage in the shaft ends. If the voltage becomes largeenough, a high frequency circulating current can flow,internal to the motor, through the shaft and both bearings.The motor can, in this case, be thought of as a transformer,where the common mode current flowing in the statorframe acts as a primary and induces the circulating currentinto the rotor circuit or secondary. This bearing current isconsidered to be the most damaging with typical peak valuesof 3 to 20 amps depending on the rated power of the motor,du/dt of the AC drive power stage components and DC-link voltage level.

Figure 7: The high frequency axial shaft voltage can be thought of as theresultant of a transformer effect, in which the common mode currentflowing in the stator frame acts as a primary, and induces the circulatingcurrent into the rotor circuit or secondary.

Another version of circulating bearing current occurs when,the current, instead of circulating completely inside themotor, flows via the shaft and the bearings of the gearboxor driven machinery and in a structural element that is bothexternal and common to the motor and the driven machine.The origin of the current is the same as in the currentcirculating inside the motor. An example of this “vagabond”circulating bearing current is shown in figure 8.



Figure 8: “Vagabond” circulating bearing current, where the current loopis external to the motor.

Other stray capacitances are also present in the motor,such as the capacitance between the stator windings andthe rotor, or that existing in the motor’s airgap betweenthe stator iron and the rotor. The bearings themselves mayeven have stray capacitance.

The existence of capacitance between the stator windingsand the rotor effectively couples the stator windings to therotor iron, which is also connected to the shaft and thebearing’s inner races. Fast changes in the common modecurrent from the inverter can not only result in currents inthe capacitance around the circumference and length ofthe motor, but also between the stator windings and therotor into the bearings.

Figure 9: Common mode loop of variable speed drive, showing stator,rotor and bearing stray capacitances.

Capacitivevoltagedivider



5

13

The current flow into the bearings can change rapidly, asthis depends on the physical state of the bearing at anyone time. For instance, the presence of stray capacitancein the bearings is only sustained for as long as the balls ofthe bearings are covered in oil or grease and are non-conducting. This capacitance, where the induced shaftvoltage builds up, can be short-circuited if the bearingvoltage exceeds the threshold of its breakover value or ifa “high spot” on a ball breaks through the oil film andmakes contact with both bearing races. At very low speed,the bearings have metallic contact since the balls havenot risen on an oil film.

Generally, the bearing impedance governs the voltage levelat which the bearings start to conduct. This impedance isa non-linear function of bearing load, temperature, speedof rotation and lubricant used, and the impedance variesfrom case to case.



There are three approaches used to affect high frequencybearing currents: a proper cabling and earthing system;breaking the bearing current loops; and damping the highfrequency common mode current. All these aim to decreasethe bearing voltage to values that do not induce highfrequency bearing current pulses at all, or damp the value ofthe pulses to a level that has no effect on bearing life. Fordifferent types of high frequency bearing currents, differentmeasures need to be taken.

The basis of all high frequency current mastering is theproper earthing system. Standard equipment earthingpractices are mainly designed to provide a sufficiently lowimpedance connection to protect people and equipmentagainst system frequency faults. A variable speed drive canbe effectively earthed at the high common mode currentfrequencies, if the installation follows three practices:

Use only symmetrical multicore motor cables. The earth(protective earth, PE) connector arrangement in the motor cablemust be symmetrical to avoid bearing currents at fundamentalfrequency. The symmetricity of the PE- conductor is achievedby a conductor surrounding all the phase leads or a cable thatcontains a symmetrical arrangement of three phase leads andthree earth conductors.

Figure 10: Recommended motor cable with symmetrical coreconfiguration.

Chapter 3 - Preventing high frequencybearing current damage

Multicoremotor cables

Threeapproaches


5

15

Define a short, low impedance path for common modecurrent to return to the inverter. The best and easiest wayto do this is to use shielded motor cables. The shield mustbe continuous and of good conducting material, i.e. copperor aluminium and the connections at both ends need tobe made with 360° termination.

Figures 11a and 11b show 360° terminations for Europeanand American cabling practices.

Figure 11 a: Proper 360° termination with European cabling practice. Theshield is connected with as short a pigtail as possible to the PE terminal.To make a 360° high frequency connection between the EMC sleeve andthe cable shield, the outer insulation of the cable is stripped away.

Figure 11 b: Proper 360° termination with American cabling practice. Anearthing bushing should be used on both ends of the motor cable toeffectively connect the earth wires to the armour or conduit.

Preventing high frequency bearing current damage

Short impedancepath



Add high frequency bonding connections between theinstallation and known earth reference points to equalise thepotential of affected items, using braided straps of copper 50 -100mm wide; flat conductors will provide a lower inductancepath than round wires. This must be made at the points wherediscontinuity between the earth level of the inverter and thatof the motor is suspected. Additionally it may be necessaryto equalise the potential between the frames of the motorand the driven machinery to short the current path throughthe motor and the driven machine bearings.

Figure 12: HF Bonding Strap.

Although the basic principles of installations are the same,for different products suitable installation practices maydiffer. Therefore, it is essential to carefully follow theinstallation instructions given in product specific manuals.

Breaking the bearing current loops is achieved by insulatingthe bearing construction. The high frequency common modecurrent can be damped by using dedicated filters. As amanufacturer of both inverters and motors, ABB can offerthe most appropriate solution in each case as well as detailedinstructions on proper earthing and cabling practices.

High frequencybondingconnections

Follow productspecificinstructions

Additionalsolutions


5

17

Monitoring the bearing condition must be conductedwith established vibration measurements.

It is impossible to measure bearing currents directly froma standard motor. But if high frequency bearing currentsare suspected, field measurements can be taken to verifythe existence of suspected current loops. Measuringequipment needs to have wide bandwidth (minimum 10kHzto 2 MHz) capable of detecting peak values of at least 150to 200A and RMS values at least down to 10mA. The crestfactor of measured signals is seldom less than 20. Thecurrent may flow in unusual places, such as rotating shafts.Thus, special equipment and experienced personnel areneeded.

ABB uses a specially designed, flexible, air-cored,Rogowski-type current sensor with dedicated accessoriesand has vast experience of over one thousand measureddrives in different applications worldwide.

The most important measurement points are within themotor. During measurements, the motor speed needs tobe at least 10% of the nominal for the bearings to rise onthe oil film. As an example, basic measurements are shownin figure 13. Figure 14 shows examples of measured currentwaveforms. GTO inverters were used mainly in the 1980sand IGBT inverters are used today. Note the different scalein the various graphs.

Figure 13: Basic measurements: A) circulating current measured with ajumper, B) shaft grounding current.

Measuringhigh frequencybearingcurrents



A) Circulating current

GTO-inverter, 5µs/div, 2A/div IGBT-inverter, 5µs/div, 2A/div

B) Shaft grounding current

GTO-inverter, 2µs/div, 10A/div IGBT-inverter, 5µs/div, 500mA/div

Figure 14: Examples of current waveforms at the measuring pointsshown in Figure 13.

Since suitable commercial measurement equipment is notavailable on the market and specialised experience isneeded to make the measurements and interpret theresults, it is advisable that bearing current measurementsare made by dedicated personnel only.


Leave themeasurementsto thespecialists


5

19

Chapter 4 - References

1. Grounding and Cabling of the Drive System,ABB Industry Oy, 3AFY 61201998 R0125

2. A New Reason for Bearing Current Damage in VariableSpeed AC Drivesby J. Ollila, T. Hammar, J. Iisakkala, H. Tuusa. EPE 97, 7thEuropean Conference on Power Electronics andApplications, 8-10 September 1997. Trondheim, Norway.

3. On the Bearing Currents in Medium Power Variable SpeedAC Drivesby J. Ollila, T. Hammar, J. Iisakkala, H. Tuusa. proceedingsof the IEEE IEDMC in Milwaukee, May 1997.

4. Minimizing Electrical Bearing Currents in Adjustable SpeedDrive Systemsby Patrick Link. IEEE IAS Pulp & PaperConference Portland, ME, USA. June 1998.

5. Instruction on Measuring Bearing Currents with a RogowskiCoil, ABB Industry Oy, 3BFA 61363602.EN.

6. Laakerivirta ja sen minimoiminen säädettyjen vaihtovirta-käyttöjen moottoreissa,I. Erkkilä, Automaatio 1999, 16.9.1999, Helsinki, Finland.(In Finnish).

7. High Frequency Bearing Currents in Low VoltageAsyncronous Motors,ABB Motors Oy and ABB Industry Oy, 00018323.doc.

8. Bearing Currents in AC Drivesby ABB Industry Oy and ABB Motors Oy. Set of overheadsin LN database “Document Directory Intranet” onABB_FI01_SPK08/FI01/ABB

9. The Motor GuideGB 98-12.

See also product specific installation manuals.


Chapter 5 - Index

360° termination 16

AABB 17, 18AC drive 6, 7, 8armour 16axial shaft voltage 12, 13axial voltage 12

Bball 14bearing current loops 15, 17bearing current paths 5bearing currents 5, 6, 7, 12, 15,18, 19bearing fluting 6bearing races 5bearing voltage 14bearings 5, 6, 7, 12, 13, 14bonding connections 17braided straps 17

Ccable 15cable capacitance 10cable shield 16circulating current 12common mode cable 10common mode circuit 7common mode current 8, 9, 10,11, 12, 13, 15, 16, 17Common Mode Loop 9, 13common mode voltage 7, 8, 10conduit 16crest factor 18current pulses 5

DDC bus voltage 8dedicated filters 17drive controller 6driven machine 7, 17driven machinery 7, 10, 12

Eearthing paths 5EDM crater 6electric motors 5electrical discharge machining(EDM) 6electrical shield 7

Ffield measurements 18flat conductors 17frame 17

Ggearbox 6, 10, 12GTO inverters 18

Hhigh frequency bearingcurrents 6, 7High frequency bearingvoltage 7high frequency circulatingcurrent 12high frequency currentmastering 15high frequency flux 7high switching frequencies 5

IIGBT inverters 18induced shaft voltage 14Insulated Gate BipolarTransistors (IGBT) 6internal voltage division 7inverter 7, 8, 9, 10, 13, 16, 17inverter frame 5, 10inverter output filtering 5inverter power supply 9inverter switching frequency 8

Llow frequency bearingcurrents 6

Mmagnetic flux 12Mean Time Between Failure(MTBF) 6metallic coupling 10motor 6, 7, 9, 10, 11, 12, 13, 15,17, 18motor bearings 5motor cable 15, 16motor frame 7, 9, 10, 11motor shaft 5, 7, 10motor windings 10

Nneutral point voltage 8

Ooil film 7, 18


5

21

Pprimary 12PWM 7, 9

Rraces 6, 14Rogowski-type currentsensor 18rotor 12, 13rotor circuit 12

Ssecondary 12shaft 7, 12, 13shaft ends 12shaft voltages 7shield 16stator 7, 11, 13stator frame 7, 11, 12stator laminations 12stator windings 11, 13stray capacitance 7, 8, 10, 11,13, 14stray currents 5symmetrical motor cables 5, 15

Tthree phase power supply 7, 8transformer 12

Vvariable speed drive 5, 13, 15voltage drop 10voltage pulses 5

Wwinding 7, 8, 9, 10, 11, 13



5

23

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Guide to Harmonics with AC Drives

Technical Guide No. 6Technical Guide No. 6

Technical Guide No.6 - Guide to Harmonics with AC Drives2

Technical Guide No.6 - Guide to Harmonics with AC Drives

6

3

1. Introduction ................................................. 5

2. Basics of the harmonics phenomena ........... 6

3. Harmonic distortion sources and effects ..... 8

4. Harmonic distortion calculation by usingDriveSize software ....................................... 9

4.1 Circuit diagram for the calculation example ....... 94.2 Input data for motor load .................................... 94.3 Motor selection .................................................. 104.4 Inverter selection ............................................... 104.5 Inverter supply unit data .................................... 104.6 Network and Transformer data input ................. 104.7 Calculated harmonic current and voltage .......... 114.8 Calculated harmonic currents in graphical form ... 114.9 Part of the printed report ................................... 11

5. Standards for harmonic limits .................... 12

5.1 EN61800-3 (IEC1800-3) Adjustable speedelectrical power drive systems .......................... 12

5.2 IEC1000-2-2,Electromagnetic compatibility (EMC) ................ 13




5.6 IEEE519, IEEE Recommended practices andrequirements for harmonic control inelectrical power systems ................................... 14

6. Evaluating harmonics ................................. 16

7. How to reduce harmonics by structuralmodifications in the AC drive system ......... 17

7.1 Factors in the AC drive having an effect onharmonics .......................................................... 17

7.2 Table: List of the different factors and theireffects ................................................................ 18

7.3 Using 6-pulse diode rectifier .............................. 187.4 Using 12-pulse or 24-pulse diode rectifier ......... 19

Contents


7.5 Using phase controlled thyristor rectifier ........... 197.6 Using IGBT bridge ............................................. 207.7 Using larger DC or AC inductor ......................... 21

8. Other methods for harmonics reduction ..... 24

8.1 Tuned single arm passive filter .......................... 248.2 Tuned multiple arm passive filter ....................... 248.3 External active filter ........................................... 25

9. Summary of harmonics attenuation ............ 26

9.1 6-pulse rectifier without inductor ....................... 269.2 6-pulse rectifier with inductor ............................ 269.3 12-pulse rectifier with polycon transformer ....... 269.4 12-pulse with double wound transformer .......... 269.5 24-pulse rectifier ................................................ 269.6 Active IGBT rectifier .......................................... 27

10. Definitions .................................................. 28

11. Index .......................................................... 30


6

5

General


This guide continues ABB's technical guide series,describing harmonic distortion, its sources and effects, andalso distortion calculation and evaluation. Special attentionhas been given to the methods for reducing harmonics withAC drives.


is(t) = i1(t) + Σ ih(t)Converter

load

Otherloads

Point of CommonCoupling (PCC)

Mains Transformer

Rs Lsu(t)

Chapter 2 - Basics of the harmonicsphenomena

Harmonic currents and voltages are created by non-linearloads connected on the power distribution system.Harmonic distortion is a form of pollution in the electricplant that can cause problems if the sum of the harmoniccurrents increases above certain limits.

All power electronic converters used in different types ofelectronic systems can increase harmonic disturbancesby injecting harmonic currents directly into the grid. Figure2.1 shows how the current harmonics (ih) in the inputcurrent (is) of a power electronic converter affect the supplyvoltage (ut).

Figure 2.1 Plant with converter load, mains transformer and otherloads.

The line current of a 3-phase, 6-pulse rectifier can becalculated from the direct output current by using thefollowing formula.

The fundamental current is then

the total RMS current and

direct current output from the rectifier.(valid for ideal filtered DC current)

, where


6

7

The rms values of the harmonic components are:

where

Order of Harmonic Component

Harmonic-Current (%)

Basics of the harmonics phenomena

In a theoretical case where output current can be estimatedas clean DC current, the harmonic current frequencies ofa 6-pulse three phase rectifier are n times the fundamentalfrequency (50 or 60 Hz). The information given below isvalid in the case when the line inductance is insignificantcompared to the DC reactor inductance. The line currentis then rectangular with 120° blocks. The order numbers nare calculated from the formula below:

and the harmonic components are as shown in Figure 2.2.

The principle of how the harmonic components are addedto the fundamental current is shown in Figure 2.3, whereonly the 5th harmonic is shown.

Figure 2.2 The harmonic content in a theoretical rectangular current of a6-pulse rectifier.

Figure 2.3 The total current as the sum of the fundamental and 5th harmonic.


Chapter 3 - Harmonic distortionsources and effects

Common non-linear loads include motor starters, variablespeed drives, computers and other electronic devices,electronic lighting, welding supplies and uninterruptedpower supplies.

The effects of harmonics can be overheating oftransformers, cables, motors, generators and capacitorsconnected to the same power supply with the devicesgenerating the harmonics. Electronic displays and lightingmay flicker, circuit breakers can trip, computers may failand metering can give false readings.

If the cause of the above mentioned symptoms is notknown, then there is cause to investigate the harmonicdistortion of the electricity distribution at the plant. Theeffects are likely to show up in the customer's plant beforethey show on the utility system. This Technical Guide hasbeen published to help customers to understand thepossible harmonic problems and make sure the harmonicdistortion levels are not excessive.


6

9

4.1 Circuitdiagram forthe calculationexample

Chapter 4 - Harmonic distortion calculationby using DriveSize software

4.2 Input datafor motor load

The harmonic currents cause a distortion of the line voltage.In principle the voltage harmonics can be calculated atany point of the network if the harmonic currents and thecorresponding source impedance are known. The circuitdiagrams in Figure 4.1. show the network supplying theconverter and the other essential parts of the installation.ABB DriveSize software is used for the calculation example.

Figure 4.2. The most important motor load data for harmonicscalculation is the base power in kW.

Figure 4.1. Network supplying a frequency converter in the middle andits equivalent diagram on the right. The data for this example is on theleft.

SupplySk = 150 MVAU = 22 kV

Transformer:S = 400 kVAU1 = 22 kVU2 = 415 Vz = 4,5 %

Cable:Length = 60 mR = 0,007 mΩ/m

Motor:P = 100 kWIN = 200 A

S'k

Xk

Xt

X'k

I

Motor load

Load type

Overload type

Speed [rpm]

Power [kW]

Overload [%]

Const. torque/power

One overload

min base max

0

0

1450

100

100

100

100

1500

60 600Overload time [s] every [s]


Harmonic distortion calculation by using DriveSize software

4.4 Inverterselection

4.5 Invertersupply unit data

4.6 NetworkandTransformerdata input

Figure 4.4. The inverter selection is based on the previous motorselection and here also the user has an option to select the invertermanually.

Figure 4.6. The network and transformer data input is given here. Forstandard ABB transformers the data is shown automatically.

Figure 4.5. The supply unit data is defined by DriveSize according to theinverter type selected.

4.3 Motorselection

Figure 4. 3. The software makes the motor selection for the defined load.If required there is an option to select a different motor than thatselected by the DriveSize.

Selected motor dataM2BA 315 SMC 6

SelectionVoltage [V]ConnectionFrequency [Hz]Power [kW]PolesSpeed [rpm]Max mech.speed [rpm]Current [A]Torque [Nm]T max/TnPower factorEfficiency [%]Insulation class

DriveSize415D50110

9926

230019710603,20,8295,6F

SelectionSelection methodVoltage [V]Drive power [kVA]Pn [kW]Normal Icont [A]Normal Imax [A]Phd [kW]Heavyduty Icont [A]Heavyduty Imax [A]PulseFrame typeP&F 12Nsq [A]

Selected inverter dataACS607-0140-3

UserCurrent (normal)400140110

238216

901782676R8260

Supply unit data

Pulse #

Lv [µH]

Cdc [mF]

Udc [V]

Idc [A]

6

110

4,95

560

191

Network and Transformer data

Primary voltage [V] Secondary voltage [V]

Frequency [Hz]

Network Sk [MVA]

Transformer Sn [kVA]Transformer Pk [kW]

Transformer Zk [%]

Supply cable type Cable Busbar

Cable quantity

Cable lenght [m]Impedance [µΩ]

unknow

22000

50

150

400

3,0

3,8

360

415

70


6

11

Harmonic distortion calculation by using DriveSize software

4.7 Calculatedharmoniccurrent andvoltage

4.8 Calculatedharmoniccurrents ingraphical form

4.9 Part of theprinted report

Figure 4.8. The results of calculations can be shown in table form asabove or as a graph.

Figure 4.9. The input data and calculated results can be printed out as areport, which is partly shown here.

Figure 4.7. The harmonics are calculated by making discrete Fouriertransformation to the simulated phase current of the incoming unit.Different kinds of circuit models are used, one for SingleDrive with ACinductors and one for diode and thyristor supply with DC inductors.There are also models for 6, 12 and 24 pulse connections.

THD

Data

Show Mode

VoltageCurrent

Result

IEEE CalcIEEE Limit

47,1% 0,2%

0,2%/ 0,2%/15,0% 0,5%

Primary side

Secodary side

Table

Graph

n157

11131719232529313537

50250350550650850950115012501450155017501850

2,81,20,60,20,20,10,10,10,00,00,00,00,0

100,0 %

0,6 %

41,2 %19,5 %8,6 %5,6 %4,2 %2,7 %2,3 %1,4 %1,2 %0,8 %0,5 %

21996,632,921,715,111,711,38,18,25,55,33,73,03,3

f [Hz] Current [A] In/I1 Voltage [V]

[%]

Frequency [Hz]

50

40

30

20

10

0

250

350

550

650

850

950

1150

1250

1450

1550

1750

1850

Network check

Network and Transformer data

ACS607-0140-3

Supply unit dataNormal voltage [V]Frequency [Hz]Network Sk [MVA]Transformer Sn [kVA]Transformer Pk [kW]Transformer Zk [%]Supply cable typeCable quantityCable lenght

22000 (primary side)501504003,03,8Cable360

Pulse #Lv [µH]Cdc [mF]Udc [V]Idc [A]

61104,95560191

ResultCosfiiTot. power factorUnmax mot.

0,9990,90

98 %

THD CurrentTHD Voltage

47,1 %0,2 %

THD CurrentTHD Voltage

IEEE 519 limits calc/limit0,2 %/15,0 %0,2 %/5,0 %


5.1EN61800-3(IEC1800-3)Adjustablespeedelectricalpower drivesystems

Chapter 5 - Standards for harmonic limits

The most common international and national standardssetting limits on harmonics are described below.Figure 5.1 is shown as an example for harmonic distortionlimits.

Part 3: EMC product standard including specifictest methodsThe countries of the European Economic Area (EEA) haveagreed on common minimum regulatory requirements inorder to ensure the free movement of products within theEEA. The CE marking indicates that the product works inconformity with the directives that are valid for the product.The directives state the principles that must be followed.Standards specify the requirements that must be met.EN61800-3 is the EMC product standard of adjustablespeed electrical power drive systems (PDS). Meeting therequirements of this standard, is the minimum conditionfor free trade of power electronics converters inside theEEA.

EN61800-3 states, that the manufacturer shall provide inthe documentation of the PDS, or on request, the currentharmonic level, under rated conditions, as a percentageof the rated fundamental current on the power port. Thereferenced values shall be calculated for each order atleast up to the 25th. The current THD (orders up to andincluding 40), and its high-frequency component PHD(orders from 14 to 40 inclusive) shall be evaluated. Forthese standard calculations, the PDS shall be assumed tobe connected to a PC with Rsc = 250 and with initial voltagedistortion less than 1%. The internal impedance of thenetwork shall be assumed to be a pure reactance.

In a low voltage public supply network, the limits andrequirements of IEC1000-3-2 apply for equipment withrated current ≤ 16 A. The use of the future IEC1000-3-4 isrecommended for equipment with rated current > 16 A. IfPDS is used in an industrial installation, a reasonableeconomical approach, which considers the totalinstallation, shall be used. This approach is based on theagreed power, which the supply can deliver at any time.The method for calculating the harmonics of the totalinstallation is agreed and the limits for either the voltagedistortion or the total harmonic current emission are agreedon. The compatibility limits given in IEC1000-2-4 may beused as the limits of voltage distortion.


6

13

Standards for harmonic limits

5.5IEC1000-3-4,Electromagneticcompatibility(EMC)




Part 2: Environment - Section 2: Compatibilitylevels for low frequency conducted disturbancesand signalling in public low-voltage power supplysystemsThis standard sets the compatibility limits for low-frequencyconducted disturbances and signalling in public low-voltage power supply systems. The disturbancephenomena include harmonics, inter-harmonics, voltagefluctuations, voltage dips and short interruptions voltageinbalance and so on. Basically this standard sets the designcriteria for the equipment manufacturer, and amounts tothe minimum immunity requirements of the equipment.IEC1000-2-2 is in line with the limits set in EN50160 for thequality of the voltage the utility owner must provide at thecustomer's supply-terminals.

Part 2: Environment - Section 4: Compatibility levelsin industrial plants for low frequency conducteddisturbancesIEC1000-2-4 is similar to IEC1000-2-2, but it givescompatibility levels for industrial and non-publicnetworks. It covers low-voltage networks as well asmedium voltage supplies excluding the networks for ships,aircraft, offshore platforms and railways.

Part 3: Limits - Section 2: Limits for harmoniccurrent emissions (equipment current <16 A perphase)This standard deals with the harmonic current emissionlimits of individual equipment connected to publicnetworks. The date of implementation of this standard isJanuary 1st 2001, but there is extensive work going on atthe moment to revise the standard before this date. Thetwo main reasons for the revision are the need for thestandard to cover also the voltage below 230 V and thedifficulties and contradictions in applying the categorisationof the equipment given in the standard.

This standard has been published as a Type II Technicalreport. Work is going on to convert it into a standard. Itgives the harmonic current emission limits for individualequipment having a rated current of more than 16 A up to75 A. It applies to public networks having nominal voltagesfrom 230 V single phase to 600 V three phase.


132 kV Net

33 kV Net

11 kV Net

400 kV Net

Typical Values

Min’mRsce

66

120

175

250

350

450

>600

12

15

20

30

40

50

60

10

12

14

18

25

35

40

9

12

12

13

15

20

25

6

8

8

8

10

15

18

2.36

1.69

1.25

1.06

0.97

1.02

<=0.91

I5 I7 I11 I13VOLTAGE

%THD

STAGE 2 LIMITS% I1

MAXIMUM LOAD 12p 6p

# 6.66 MW (5.0 MW)

# 2.50 MW (5.0 MW)

#

# 4.40 MW (3.3 MW)

# 1.65 MW (3.3 MW)

# 1.11 MW (830 kW)

# 415 kW (830 kW)

# 760 kW (215 kW)

# 108 kW (215 kW)

PCC

**Contribution to existing THD level at selected

PCC

(26 MVA Assumed)

(100 MVA Assumed)

(400 MVA Assumed)

(600 MVA Assumed) **


5.6 IEEE519,IEEERecommendedpractices andrequirementsfor harmoniccontrol inelectricalpower systems

The standard gives three different stages for connectionprocedures of the equipment. Meeting the individualharmonic limits of Stage 1 allows the connection of theequipment at any point in the supply system. Stage 2 givesindividual harmonic current limits as well as THD and itsweighted high frequency counterpart PWHD. The limitsare classified and tabulated by the short circuit ratio. Thethird stage of connection is based on an agreementbetween the user and the supply authority, based on theagreed active power of the consumer's installation. If therated current is above 75 A, Stage 3 applies in any case.

The structure of this standard is generally seen to be good,but it may justly be questioned whether single and three-phase equipment should have different limits in Stage 2. Itis very probable that the structure of the standard willremain as it is, but the version having the status of actualstandard, will contain different limits for single and three-phase equipment.

Figure 5.1 Limits on Harmonics in the proposed EN61000-3-4.

The philosophy of developing harmonic limits in thisrecommended practice is to limit the harmonic injectionfrom individual customers so that they will not causeunacceptable voltage distortion levels for normal systemcharacteristics and to limit overall harmonic distortion ofthe system voltage supplied by the utility. This standard isalso recognised as American National Standard and it iswidely used in the USA, especially in the municipal publicworks market.


6

15


The standard does not give limits for individual equipment,but for individual customers. The customers are categorisedby the ratio of available short circuit current (Isc) to theirmaximum demand load current (IL) at the point of commoncoupling. The total demand load current is the sum of bothlinear and non-linear loads. Within an industrial plant, thePCC is clearly defined as the point between the non-linearload and other loads.

The allowed individual harmonic currents and totalharmonic distortion are tabulated by the ratio of availableshort circuit current to the total demand load current (Isc/IL) at the point of common coupling. The limits are as apercentage of IL for all odd and even harmonics from 2 toinfinity. Total harmonic distortion is called total demanddistortion and also it should be calculated up to infinity.Many authors limit the calculation of both the individualcomponents and TDD to 50.

The table 10.3 of the standard is sometimes misinterpretedto give limits for the harmonic emissions of a singleapparatus by using Rsc of the equipment instead of Isc/ILof the whole installation. The limits of the table should notbe used this way, since the ratio of the short circuit currentto the total demand load current of an installation shouldalways be used.


UTILITY

Calculate Average MaximumDemand Load Current (IL)

Choose PCC

Calculate Short CircuitCapacity (SSC, ISC)

Calculate Short Circuit Ratio(SCR=(ISC /IL)

Yes

Yes

No

Yes

No

Is PowerFactor Correction existing

or planned?

Stage 1:Is detailed Evaluation

necessary?

No

Estimate Weighted DisturbingPower (SDW) or % Non-linear

Load

Stage 2:Does Facility meetHarmonic Limits?

Characterise Harmonic Levels(Measurements, Analysis)

Design Power Factor correctionand/or Harmonic Control

Equipment(include resonance concerns)

Verification Measurementsand Calculations (if necessary)

CUSTOMER

Figure 6.1 Evaluation of harmonic distortion.

Chapter 6 - Evaluating harmonics

The "Guide for Applying Harmonic Limits on PowerSystems" P519A/D6 Jan 1999 introduces some generalrules for evaluating harmonic limits at an industrial facility.The procedure is shown in the flowchart in Figure 6.1.


6

17

LINE

TRANSFORMER

AC DRIVE

LOAD

Short circuit power

Rated Power andImpedance

Type of Rectifier

DIODE, THYRISTOR; INVERTER:

MVA

MVA

%

mH

PWM;CSI

kW

%

6-p, 12-p, 24-p

Reactor Inductance

Type of Inverter

Rated Power andLoad

Inverter

Motor

7.1 Factors inthe AC drivehaving aneffect onharmonics

Chapter 7 - How to reduce harmonics by structuralmodifications in the AC drive system

Alternative

Harmonics reduction can be done either by structuralmodifications in the drive system or by using externalfiltering. The structural modifications can be to strengthenthe supply, to use 12 or more pulse drive, to use a controlledrectifier or to improve the internal filtering in the drive.

Figure 7.1 shows the factors in the AC drive system whichhave some influence on harmonics. The current harmonicsdepend on the drive construction and the voltageharmonics are the current harmonics multiplied by thesupply impedances.

Figure 7.1 Drive system features affecting harmonics.


The cause The effectThe larger the motor… the higher the current harmonicsThe higher the motor load… the higher the current harmonicsThe larger the DC or AC inductance… the lower the current harmonicsThe higher the number of pulses inthe rectifier… the lower the current harmonicsThe larger the transformer… the lower the voltage harmonicsThe lower the transformer impedance… the lower the voltage harmonicsThe higher the short circuit capacityof supply… the lower the voltage harmonics

6-pulse rectifier 12-pulse rectifier 24-pulse rectifier

Current Waveform Current Waveform Current Waveform

How to reduce harmonics by structural modifications in the AC drive system

7.3 Using6-pulse dioderectifier

7.2 Table:List of thedifferentfactors andtheir effects

The connections for different rectifier solutions are shownin Figure 7.2. The most common rectifier circuit in 3-phaseAC drives is a 6-pulse diode bridge. It consists of sixuncontrollable rectifiers or diodes and an inductor, whichtogether with a DC-capacitor forms a low-pass filter forsmoothing the DC-current. The inductor can be on the DC-or AC-side or it can be left totally out. The 6-pulse rectifieris simple and cheap but it generates a high amount of loworder harmonics 5th, 7th, 11th especially with small smoothinginductance.

The current form is shown in Figure 7.2. If the major part ofthe load consists of converters with a 6-pulse rectifier, thesupply transformer needs to be oversized and meeting therequirements in standards may be difficult. Often someharmonics filtering is needed.

Figure 7.2 Harmonics in line current with different rectifier constructions.


6

19

6-pulse rectifier 12-pulse rectifier 24-pulse rectifier

Harmonic order

InI1


7.5 Usingphasecontrolledthyristorrectifier

7.4 Using12-pulse or 24-pulse dioderectifier

The 12-pulse rectifier is formed by connecting two 6-pulserectifiers in parallel to feed a common DC-bus. The inputto the rectifiers is provided with one three-windingtransformer. The transformer secondaries are in 30o phaseshift. The benefit with this arrangement is that in the supplyside some of the harmonics are in opposite phase andthus eliminated. In theory the harmonic component withthe lowest frequency seen at the primary of the transformeris the 11th.

The major drawbacks are special transformers and a highercost than with the 6-pulse rectifier.

The principle of the 24-pulse rectifier is also shown in Figure7.2. It has two 12-pulse rectifiers in parallel with two three-winding transformers having 15o phase shift. The benefitis that practically all low frequency harmonics areeliminated but the drawback is the high cost. In the caseof a high power single drive or large multidrive installationa 24-pulse system may be the most economical solutionwith lowest harmonic distortion.

Figure 7.3 Harmonic components with different rectifiers.

A phase controlled rectifier is accomplished by replacingthe diodes in a 6-pulse rectifier with thyristors. Since athyristor needs a triggering pulse for transition fromnonconducting to conducting state, the phase angle atwhich the thyristor starts to conduct can be delayed. Bydelaying the firing angle over 90o, the DC-bus voltage goesnegative. This allows regenerative flow of power from theDC-bus back to the power supply.


Supplytype

6-pulserectifier

12-pulserectifier

IGBT SupplyUnit

CurrentTDH (%)

30

10

4

VoltageTDH (%)RSC=20

10

6

8

VoltageTDH (%)RSC=100

2

1.2

1.8

Current Waveform

Distortion is in % of RMS values


7.6 Using IGBTbridge

Standard DC-bus and inverter configurations do not allowpolarity change of the DC-voltage and it is more commonto connect another thyristor bridge anti-parallel with thefirst one to allow the current polarity reversal. In thisconfiguration the first bridge conducts in rectifying modeand the other in regenerating mode.

The current waveforms of phase controlled rectifiers aresimilar to those of the 6-pulse diode rectifier, but sincethey draw power with an alternating displacement powerfactor, the total power factor with partial load is quite poor.The poor power factor causes high apparent current andthe absolute harmonic currents are higher than those witha diode rectifier.

In addition to these problems, phase-controlled converterscause commutation notches in the utility voltagewaveform. The angular position of the notches varies alongwith the firing angle.

Figure 7.4 Distortion of different supply unit types. Values may varycase by case.

Introducing a rectifier bridge, made of self commutatedcomponents, brings several benefits and opportunitiescompared to phase commutated ones. Like a phasecommutated rectifier, this hardware allows bothrectification and regeneration, but it makes it possible tocontrol the DC-voltage level and displacement powerfactor separately regardless of the power flow direction.

The main benefits are:- Safe function in case of mains supply disappearance.- High dynamics of the drive control even in the field

weakening range.


6

21

Line Generating Unit

3~

Line Generating Unit

Harmonic order

In

I1

Current withoutInductor

Current withInductor


7.7 Using alarger DC orAC inductor

- Possibility to generate reactive power.- Nearly sinusoidal supply current with low harmonic

content. Measured results for one drive is shown in Figure7.5. When comparing with Figure 7.3 we can see a cleardifference. IGBT has very low harmonics at lowerfrequencies, but somewhat higher at higher frequencies.

- Voltage boost capability. In case of low supply voltagethe DC voltage can be boosted to keep motor voltagehigher than supply voltage.

The main drawback is the high cost coming from the IGBTbridge and extra filtering needed.

Figure 7.5 Harmonics in line current IGBT line generating unit.

The harmonics of a voltage source AC drive can besignificantly reduced by connecting a large enoughinductor in its AC input or DC bus. The trend has been toreduce the size of converter while the inductor size hasbeen also reduced, or in several cases it has been omittedtotally. The effect of this can be seen from the curve formsin Figure 7.6.

Figure 7.6 The effect of the inductor on the line current.


415 V, 50 Hz

5th

7th

11th

13th

17th

19th

23rd

25th

THD

DC Inductance/mH = This Figure/Motor kW

Har

mo

nic

Cur

rent

(pu)

Load 60 A, Transformer power 50-315 kVA, line fault level 150 MVA

TH

D o

f Vo

ltag

e (%

)

Short Circuit Ratio

No inductor, 6-pulse

Small inductor,6-pulse

Large inductor,6-pulse

Large inductor,12-pulse


The chart in Figure 7.7 shows the effect of the size of theDC inductor on the harmonics. For the first 25 harmoniccomponents the theoretical THD minimum is 29%. Thatvalue is practically reached when the inductance is 100mH divided by the motor kW or 1 mH for a 100 kW motor(415 V, 50 Hz). Practically sensible is about 25 mH dividedby motor kW, which gives a THD of about 45%. This is0,25 mH for a 100 kW motor.

Figure 7.7 Harmonic current as function of DC inductance.

The voltage distortion with certain current distortiondepends on the Short Circuit Ratio Rsc of the supply. Thehigher the ratio, the lower the voltage distortion. This canbe seen in Figure 7.8.

Figure 7.8 THD Voltage vs Type of AC drive and transformer size.


6

23

Example: 45 kW Motor is connected to ”a200 kVA Transformer. ”THD = ca. 3% with a“Large Inductor Drive” and ca. 11% with a“No Inductor Drive”

Tota

l Har

min

ic V

olta

ge

Dis

tort

ion Input Data to Calculations:

Rated Motor for the DriveConstant Torque LoadVoltage 415 VDrive Efficiency = 97%Supply Impedance = 10%of Transformer Impedance

SupplyTransformer

(kVA)

STOP TURN LEFT

START

TURN LEFT

TURN UP

Motor kW

No DC-Inductor,6-pulse

Small DC-Inductor, 6-pulse

Large DC-Inductor, 6-pulse

Large DC-Inductor, 12-pulse

A = Large DC-InductanceB, C = Small DC-InductanceD, E = Without DC-Inductance


Figure 7.9 introduces a simple nomogram for estimationof harmonic voltages. On the graph below right select firstthe motor kilowatt, then the transformer kVA and thenmove horizontally to the diagonal line where you moveupwards and stop at the curve valid for your application.Then turn left to the y-axis and read the total harmonicvoltage distortion.

Figure 7.9 Total harmonic distortion nomogram.

Results from laboratory tests with drive units from differentmanufacturers are shown in Figure 7.10. Drive A with largeDC inductor has the lowest harmonic current distortion,drives with no inductor installed have the highest distortion.

Figure 7.10. Harmonic current with different DC-Inductances.


8.1 Tunedsingle armpassive filter

8.2 Tunedmultiple armpassive filter

Chapter 8 - Other methods forharmonics reduction

Filtering is a method to reduce harmonics in an industrialplant when the harmonic distortion has been graduallyincreased or as a total solution in a new plant. There aretwo basic methods: passive and active filters.

The principle of a tuned arm passive filter is shown in Figure8.1. A tuned arm passive filter should be applied at the singlelowest harmonic component where there is significantharmonic generation in the system. For systems that mostlysupply an industrial load this would probably be the fifthharmonic. Above the tuned frequency the harmonics areabsorbed but below that frequency they may be amplified.

Detuned - Single tuning frequencyAbove tuned frequency harmonics absorbedBelow tuned frequency harmonics may be amplifiedHarmonic reduction limited by possible over compensationat the supply frequency and network itself

Capacitive below tuned frequency/Inductive aboveBetter harmonic absorptionDesign consideration to amplification harmonics by filterLimited by KVAr and network

Figure 8.1 Tuned single arm passive filter.

This kind of filter consists of an inductor in series with acapacitor bank and the best location for the passive filteris close to the harmonic generating loads. This solution isnot normally used for new installations.

The principle of this filter is shown in Figure 8.2. This filterhas several arms tuned to two or more of the harmoniccomponents which should be the lowest significantharmonic frequencies in the system. The multiple filterhas better harmonic absorption than the one arm system.

Figure 8.2 Tuned multiple arm passive filter.


6

25

Fundamental only idistortion

icompensation

Load

ActiveFilter

Current waveforms

Supply

Cleanfeedercurrent

Loadcurrent

Active filtercurrent

Har

mon

ics

Wav

efor

ms

Other methods for harmonics reduction

8.3 Externalactive filter

The multiple arm passive filters are often used for largeDC drive installations where a dedicated transformer issupplying the whole installation.

A passive tuned filter introduces new resonances that cancause additional harmonic problems. New power electron-ics technologies are resulting in products that can controlharmonic distortion with active control. These active filters,see Figure 8.3, provide compensation for harmonic com-ponents on the utility system based on existing harmonicgeneration at any given moment in time.

Figure 8.3 External active filter principle diagram.

The active filter compensates the harmonics generatedby nonlinear loads by generating the same harmonic com-ponents in opposite phase as shown in Figure 8.4. Externalactive filters are most suited to multiple small drives. Theyare relatively expensive compared to other methods.

Figure 8.4 External active filter waveforms and harmonics.


9.5 24-pulserectifierwith 23-windingtransformers

9.4 12-pulsewith doublewoundtransformer

9.3 12-pulserectifier withpolycontransformer

9.2 6-pulserectifier withinductor

9.1 6-pulserectifierwithoutinductor

Chapter 9 - Summary of harmonicsattenuation

There are many options to attenuate harmonics either insidethe drive system or externally. They all have advantagesand disadvantages and all of them show cost implications.The best solution will depend on the total loading, the supplyto the site and the standing distortion.In the following tables different internal actions are comparedto the basic system without inductor. The harmonic contentis given with 100% load. The costs are valid for small drives.For multidrive the 12-pulse solution is quite a lot cheaper.

Manufacturing cost 100%Typical harmonic current components.

Fundamental 5th 7th 11th 13th 17th 19th

100% 63% 54% 10% 6,1% 6,7% 4,8%

Manufacturing cost 120%. AC or DC choke addedTypical harmonic current components.


100% 30% 12% 8,9% 5,6% 4,4% 4,1%



100% 11% 5,8% 6,2% 4,7% 1,7% 1,4%



100% 3,6% 2,6% 7,5% 5,2% 1,2% 1,3%



100% 4,0% 2,7% 1,0% 0,7% 1,4% 1,4%


6

27

9.6 ActiveIGBT rectifier

Summary of harmonics attenuation

Manufacturing cost 250%. Not significant if electricalbraking is anyway needed.Typical harmonic current components.


100% 2,6% 3,4% 3,0% 0,1% 2,1% 2,2%


Chapter 10 - Definitions

S: Apparent power

P: Active power

Q: Reactive power

Rsc: Short circuit ratio is defined as the short circuitpower of the supply at PCC to the nominal apparentpower of the equipment under consideration.Rsc = Ss / Sn.

ω1: Angular frequency of fundamental componentω1 = 2*π*f1, where f1 is fundamental frequency(eg. 50Hz or 60Hz).

n: Integer n = 2, 3, ... ∞. Harmonic frequencies aredefined as wn = n*ω1.

In: RMS-value of n:th harmonic component of linecurrent.

Zn: Impedance at frequency n*ω1.

%Un: Harmonic voltage component as a percentage offundamental (line) voltage.

THD: Total Harmonic Distortion in the input current isdefined as:

where I1 is the rms value of the fundamental frequencycurrent. The THD in voltage may be calculated in a similarway. Here is an example for the 25 lowest harmoniccomponents with the theoretical values:

PWHD: Partial weighted harmonic distortion is defined as:


6

29

Definitions

PCC: Point of Common Coupling is defined in this text assuch a point of utility supply which may be commonto the equipment in question and other equipment.There are several definitions of PCC in differentstandards and even more interpretations of thesedefinitions in literature. The definition chosen hereis seen as technically most sound.

PF: Power Factor defined as PF = P/S (power / volt-ampere) = I1 / Is * DPF (With sinusoidal current PFequals to DPF).

DPF: Displacement Power Factor defined as cosφ1, whereφ1 is the phase angle between the fundamentalfrequency current drawn by the equipment and thesupply voltage fundamental frequency component.


Chapter 11 - Index

3-winding 265th harmonic 76-pulse rectifier 7, 18, 19, 206-pulse three phase rectifier 712-pulse rectifier 18, 19, 2024-pulse rectifier 18, 19

AABB 6, 10AC inductor 21active filter 5, 24, 25active power 14, 28American National Standard 14anti-parallel 20apparent power 28attenuation 5, 26

Ccalculation 5, 9, 11, 12, 15, 16, 23CE marking 12circuit breaker 8common DC-bus 19commutation notch 20compatibility limit 12, 13computer 8consumer's installation 14converter 6, 9, 12, 18, 20, 21converter load 6

DDC-capacitor 18DC-current 18displacement power factor 20, 29distortion calculation 5, 6distortion nomogram 23DriveSize 9, 10, 11

Eeffect 5, 6, 8, 17, 18, 21, 22electromagnetic compatibility(EMC) 22electronic device 8electronic display 8electronic lighting 8EMC product standard 12European Economic Area 12

evaluating of harmonic 16external filtering 17

Ffiltering 17, 18, 21, 24frequency 9, 12, 13, 14, 19, 24,28, 29fundamental frequency 7, 28, 29

Hharmonic component 7, 19, 22,24, 25, 28harmonic currents 6, 7, 9, 11, 12,13, 15, 20, 21, 22, 23, 26, 27harmonic distortion 6, 8, 9, 12,14, 15, 16, 19, 23, 25, 28harmonic limit 12, 13, 14, 15, 16harmonics reduction 17, 24, 25harmonic voltage 23, 28harmonics phenomena 6, 7

IIGBT bridge 20, 21inductance 17, 18, 22, 23inductor 5, 18, 21, 22, 23, 24, 26industrial installation 12installation 9, 12, 14, 15, 19, 24,25inverter selection 10inverter supply unit data 10

Llaboratory test 23line current 6, 18, 21low-pass filter 18

Mmains transformer 6manufacturing cost 26, 27metering 8motor load 9motor selection 10motor starter 8multiple arm passive filter 5, 24,25


6

31

Index

Nnetwork 10non-linear load 6, 8, 15, 16

Ooverheating 8

Ppassive filter 24, 25phase commutated rectifier 20PHD 12point of common coupling 15,29power distribution 6power drive system 12power factor 16, 20, 29power port 12public supply 12PWHD 14, 28

Rreactive power 21, 28rectifier 5, 6, 7, 17, 18, 19, 20,26, 27rectifying mode 20rectangular current 7regenerating mode 20report 11

Sshort circuit power 14, 16, 17,28short circuit ratio 22, 28source 6, 8, 9, 21source impedance 4, 9standard 12, 13, 14, 15, 18, 20,29structural modification 17, 18,19, 20, 21, 22, 23supply authority 14supply cable 18supply transformer 18supply voltage 6, 21, 29

TTDD 15THD 12, 14, 22, 23, 28three-winding transformer 19thyristor 17, 19, 20total demand distortion 15total harmonic distortion 10,15, 23, 28transformer 9, 10tuned arm passive filter 24two-winding transformer 19

Uuninterrupted power supply 8

Vvariable speed drives 8voltage 6, 9, 11, 12, 13, 14, 17,18, 19, 20, 21, 22, 23voltage boost 21

Wwelding supply 8

3AFE

642

9271

4 R

EV

B

EN

17.

5. 2

002

Spe

cific

atio

ns s

ubje

ct t

o ch

ange

with

out

notic

e.



Dimensioning of a Drive system

Technical Guide No.7 - Dimensioning of a Drive system2

Technical Guide No.7 - Dimensioning of a Drive system

7

3

Contents

1. Introduction .................................................... 5

2. Drive system ................................................... 6

3. General description of a dimensioningprocedure ....................................................... 7

4. An induction (AC) motor ................................. 9

4.1 Fundamentals ......................................................... 94.2 Motor current ........................................................ 11

4.2.1 Constant flux range .................................. 124.2.2 Field weakening range.............................. 13

4.3 Motor power ......................................................... 14

5. Basic mechanical laws ................................. 15

5.1 Rotational motion ................................................. 155.2 Gears and moment of inertia ............................... 18

6. Load types .................................................... 20

7. Motor loadability ........................................... 23

8. Selecting the frequency converterand motor ..................................................... 24

8.1 Pump and fan application (Example) .................. 248.2 Constant torque application (Example) ............... 278.3 Constant power application (Example) ............... 29

9. Input transformer and rectifier .................... 33

9.1 Rectifier ................................................................. 339.2 Transformer ........................................................... 34

10. Index ........................................................... 36


7

5

General


Dimensioning of a drive system is a task where all factorshave to be considered carefully. Dimensioning requiresknowledge of the whole system including electric supply,driven machine, environmental conditions, motors anddrives etc. Time spent at the dimensioning phase can meanconsiderable cost savings.


A single AC drive system consists typically of an inputtransformer or an electric supply, frequency converter, anAC motor and load. Inside the single frequency converterthere is a rectifier, DC-link and inverter unit.

Chapter 2 - Drive system

Figure 2.1 A single frequency converter consists of 1) rectifier,2) DC-link, 3) inverter unit and 4) electric supply.

In multi-drive systems a separate rectifier unit is commonlyused. Inverter units are connected directly to a commonDC-link.

Figure 2.2 A drive system which has 1) a separate supply section,2) common DC-link, 3) drive sections and 4) electric supply.


7

7

This chapter gives the general steps for dimensioning themotor and the frequency converter.

1) First check the initial conditions.In order to select the correct frequency converter andmotor, check the mains supply voltage level (380 V …690 V)and frequency (50 Hz … 60 Hz). The mains supply net-work's frequency doesn't limit the speed range of the ap-plication.

2) Check the process requirements. Is there a need forstarting torque? What is the speed range used? What typeof load will there be? Some of the typical load types aredescribed later.

3) Select the motor.An electrical motor should be seen as a source of torque.The motor must withstand process overloads and be ableto produce a specified amount of torque. The motor's ther-mal overloadability should not be exceeded. It is also nec-essary to leave a margin of around 30% for the motor'smaximum torque when considering the maximum avail-able torque in the dimensioning phase.

4) Select the frequency converterThe frequency converter is selected according to the ini-tial conditions and the selected motor. The frequency con-verter's capability of producing the required current andpower should be checked. Advantage should be taken ofthe frequency converter's potential overloadability in caseof a short term cyclical load.

Chapter 3 - General description of adimensioning procedure


Dimensioning phase Network Converter Motor Load

1) Chek the initialconditions of thenetwork and load

2) Choose a motoraccording to:• Thermal loadability• Speed range• Maximum needed torque

3) Choose a frequencyconverter according to:• Load type• Continous and

maximum current• Network conditions

fN=50Hz, 60Hz

UN=380...690V

Tload

T

n min n max

Tload

T

TS

n min n max

Imax

IN

n min n max

TS

General description of a dimensioning procedure

Figure 3.1 General description of the dimensioning procedure.


7

9

Induction motors are widely used in industry. In this chaptersome of the basic features are described.

An induction motor converts electrical energy into me-chanical energy. Converting the energy is based on elec-tromagnetic induction. Because of the induction phenom-enon the induction motor has a slip.The slip is often defined at the motor's nominal point (fre-quency ( fn ), speed ( nn ), torque ( Tn ), voltage ( Un ), cur-rent ( In ) and power ( Pn )). At the nominal point the slip isnominal:

4.1Fundamentals

Chapter 4 - An induction (AC) motor

(4.1)

where ns is the synchronous speed:

(4.2)

When a motor is connected to a supply with constant

voltage and frequency it has a torque curve as follows:

Figure 4.1 Typical torque/speed curve of an induction motor whenconnected to the network supply (D.O.L., Direct-On-Line). In the picturea) is the locked rotor torque, b) is the pull-up torque, c) is the maximummotor torque, Tmax and d) is the nominal point of the motor.


TORQUE

SPEED

An induction (AC) motor

A standard induction motor's maximum torque ( Tmax, alsocalled pull-out torque and breakdown torque) is typically2-3 times the nominal torque. The maximum torque isavailable with slip smax which is greater than the nominalslip. In order to use an induction motor efficiently the motorslip should be in the range - smax ... smax. This can beachieved by controlling voltage and frequency. Controllingcan be done with a frequency converter.

Figure 4.2 Torque/speed curves of an induction motor fed by afrequency converter. Tmax is available for short term overloads below thefield weakening point. Frequency converters, however, typically limit themaximum available torque to 70% of Tmax.

The frequency range below the nominal frequency is calleda constant flux range. Above the nominal frequency/speedthe motor operates in the field weakening range. In thefield weakening range the motor can operate on constantpower which is why the field weakening range is sometimesalso called the constant power range.

The maximum torque of an induction motor is proportionalto the square of the magnetic flux ( Tmax ~ ψ 2 ). This meansthat the maximum torque is approximately a constant atthe constant flux range. Above the field weakening pointthe maximum torque decrease is inversely proportional tothe square of the frequency

( Tmax ~ ).


7

11

Constant flux rangeSPEED

Field weekening range

Flux

Tmax

Voltage


4.2 Motorcurrent

Figure 4.3 Maximum torque, voltage and flux as a function of therelative speed.

An induction motor current has two components: reactivecurrent ( isd ) and active current ( isq ). The reactive currentcomponent includes the magnetizing current ( imagn )whereas the active current is the torque producing cur-rent component. The reactive and active current compo-nents are perpendicular to each other.

The magnetizing current ( imagn ) remains approximatelyconstant in the constant flux range (below the field weak-ening point). In the field weakening range the magnetizingcurrent decrease is proportional to speed.A quite good estimate for the magnetizing current in theconstant flux range is the reactive ( isd ) current at the motornominal point.

Figure 4.4 Stator current ( is ) consists of reactive current ( isd ) andactive current ( isq ) components which are perpendicular to each other.Stator flux is denoted as ψs.


Below the field weakening point the current componentscan be approximated as follows:

It can be seen that with zero motor torque the active cur-rent component is zero. With higher torque values motorcurrent becomes quite proportional to the torque. A goodapproximation for total motor current is:

4.2.1 Constantflux range

The total motor current is:

(4.5)

Example 4.1:A 15 kW motor's nominal current is 32 A and power factoris 0.83. What is the motor's approximate magnetizingcurrent at the nominal point? What is the total approximatecurrent with 120 % torque below the field weakening point.

Solution 4.1:At the nominal point the estimate for the magnetizingcurrent is:

(4.6)

The approximate formula for total motor current with 120 %torque gives:

The approximate formula was used because torque fulfilledthe condition 0.8 * Tn ≤ Tload ≤ 0.7 * Tmax

(4.3)

(4.4)


, when 0.8 * Tn ≤ Tload ≤ 0.7 * Tmax


7

13

4.2.2 Fieldweakeningrange

Above the field weakening point the current componentsalso depend on speed.

Total motor current is:

(4.8)

(4.7)

(4.10)

(4.9)

The motor current can be approximated quite accuratelywithin a certain operating region. The motor currentbecomes proportional to relative power. An approximationformula for current is:

Approximation can be used when:

and

(4.11)

(4.12)

In the field weakening range the additional current neededin order to maintain a certain torque level is proportionalto relative speed.

Example 4.2:The motor's nominal current is 71 A. How much current isneeded to maintain the 100 % torque level at 1.2 timesnominal speed (Tmax = 3 * Tn).

Solution 4.2:The current can be calculated by using the approximationformula:



4.3 Motorpower

The motor's mechanical (output) power can be calculatedfrom speed and torque using the formula:

Because motor power is most often given in kilowatts(1 kW = 1000 W) and speed in rpm revolutions per minute,

1 rpm = rad/s), the following formula can be used:

The motor's input power can be calculated from thevoltage, current and power factor:

The motor's efficiency is the output power divided by theinput power:

Example 4.3:The motor nominal power is 15 kW and the nominal speedis 1480 rpm. What is the nominal torque of the motor?

Solution 4.3:The motor's nominal torque is calculated as follows:

Example 4.4:What is the nominal efficiency of a 37 kW (Pn = 37 kW,Un =380 V, In =71 A and cos(ϕn) = 0.85) motor?

Solution 4.4:The nominal efficiency is:

(4.13)

(4.14)

(4.15)

(4.16)



7

15

Chapter 5 - Basic mechanical laws

5.1 Rotationalmotion

One of the basic equations of an induction motor describesthe relation between moment of inertia ( J [kgm2]), angularvelocity ( ω [rad/s]) and torque ( T [Nm]). The equation is asfollows:

(5.1)

In the above equation it is assumed that both the frequencyand the moment of inertia change. The formula is howeveroften given so that the moment of inertia is assumed to beconstant:

(5.2)

If the speed and moment of inertia are constants thedynamic component ( Tdyn ) is zero.

The dynamic torque component caused by acceleration/deceleration of a constant moment of inertia (motor's speedis changed by ∆n [rpm] in time ∆t [s], J is constant) is:

(5.3)

(5.4)

Torque Tload represents the load of the motor. The loadconsists of friction, inertia and the load itself. When themotor speed changes, motor torque is different from Tload .Motor torque can be considered as consisting of a dynamicand a load component:

(5.5)

The dynamic torque component caused by a variablemoment of inertia at constant speed n[rpm] is:


Basic mechanical laws

If the moment of inertia varies and at the same time themotor is accelerating the dynamic torque component canbe calculated using a certain discrete sampling interval.From the thermal dimensioning point of view it is howeveroften enough to take into account the average moment ofinertia during acceleration.

Example 5.1:The total moment of inertia, 3 kgm2, is accelerated from aspeed of 500 rpm to 1000 rpm in 10 seconds. What is thetotal torque needed when the constant load torque is50 Nm?

How fast will the motor decelerate to 0 rpm speed if themotor's electric supply is switched off?

Solution 5.1:The total moment of inertia is constant. The dynamic torquecomponent needed for acceleration is:

If the motor's electric supply is switched off at 1000 rpmthe motor decelerates because of the constant load torque(50 Nm). Following equation holds:

Total torque during acceleration is:

Time to decelerate from 1000 rpm to 0 rpm:

Example 5.2:Accelerating of a fan to nominal speed is done with nominaltorque. At nominal speed torque is 87 %. The fan's momentof inertia is 1200 kgm2 and the motor's moment of inertiais 11 kgm2. The load characteristics of the fan Tload is shownin figure 5.1.

Motor nominal power is 200 kW and nominal speed is991 rpm.


7

17

SPEED

TO

RQ

UE


Figure 5.1 Torque characteristics of a fan. Speed and torque are shownusing relative values.

Calculate approximate starting time from zero speed tonominal speed.

Solution 5.2:Motor nominal torque is:

The starting time is calculated by dividing the speed rangeinto five sectors. In each sector (198.2 rpm) torque is as-sumed to be constant. Torque for each sector is taken fromthe middle point of the sector. This is quite acceptablebecause the quadratic behaviour is approximated to belinear in the sector.

The time to accelerate the motor (fan) with nominal torquecan be calculated with formula:


Direction of energy

Acceleration times for different speed sections are:

0-198.2 rpm

198.2-396.4 rpm

396.4-594.6 rpm

594.6-792.8 rpm

792.8-991 rpm

The total starting time 0-991 rpm is approximately 112seconds.

Gears are typical in drive systems. When calculating themotor torque and speed range gears have to be takeninto account. Gears are reduced from load side to motorside with following equations (see also figure 5.2 ):

5.2 Gears andmoment ofinertia

Figure 5.2 A gear with efficiency η. Gear ratio is n1:n2.


(5.6)

(5.7)

(5.8)


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19

Also all the moments of inertia ( J [kgm2]) within the systemhave to be known. If they are not known they can becalculated which is rather difficult to do accurately. Typicallymachine builders can give the necessary data.

Example 5.3:A cylinder is quite a common shape for a load (rollers,drums, couplings, etc.). What is the inertia of a rotatingcylinder (mass=1600 kg, radius=0.7 m)?

Solution 5.3:The inertia of a rotating cylinder (with mass m [kg] andradius r [m]) is calculated as follows:

In the case of a gear, the moment of inertia to the motorshaft has to be reduced. The following example shows howto reduce gears and hoists. In basic engineering booksother formulas are also given.

Example 5.4:Reduce the moment of inertia to the motor shaft of thefollowing hoist drive system.

Figure 5.3 A Hoist drive system used in example 5.4.

Solution 5.4:The total moment of inertia consists of J1=10 kgm2,J2=30 kgm2, r=0.2 m and m=100 kg.The moment of inertia J2 and mass m are behind a gear-box with gear ratio n1:n2=2:1.

The moment of inertia J2 is reduced by multiplying withthe square of the inverse of the gear ratio. The mass m ofthe hoist is reduced by multiplying it with square of theradius r and because it is behind the gearbox it has to bemultiplied with the square of the inverse of the gear ratio,too.

Thus the total moment of inertia of the system is:



Certain load types are characteristic in the industrial world.Knowing the load profile (speed range, torque and power)is essential when selecting a suitable motor and frequencyconverter for the application.

Some common load types are shown. There may also becombinations of these types.

1. Constant torqueA constant torque load type is typical when fixed volumesare being handled. For example screw compressors, feed-ers and conveyors are typical constant torque applications.Torque is constant and the power is linearly proportionalto the speed.

Figure 6.1 Typical torque and power curves in a constant torque application.

2. Quadratic torqueQuadratic torque is the most common load type. Typicalapplications are centrifugal pumps and fans. The torque isquadratically, and the power is cubically proportional tothe speed.

Chapter 6 - Load types

Figure 6.2 Typical torque and power curves in a quadratic torqueapplication.


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21

3. Constant powerA constant power load is normal when material is beingrolled and the diameter changes during rolling. The poweris constant and the torque is inversely proportional to thespeed.

Figure 6.3 Typical torque and power curves in a constant powerapplication.

4. Constant power/torqueThis load type is common in the paper industry. It is acombination of constant power and constant torque loadtypes. This load type is often a consequence of dimen-sioning the system according to the need for certain powerat high speed.

Figure 6.4 Typical torque and power curves in a constant power/torqueapplication.

5. Starting/ breakaway torque demandIn some applications high torque at low frequencies isneeded. This has to be considered in dimensioning. Typi-cal applications for this load type are for example extrud-ers and screw pumps.

Load types


Load types

Figure 6.5 Typical torque curve in an application where starting torque isneeded.

There are also several other load types. They are howeverhard to describe in a general presentation. Just to men-tion a few, there are different symmetrical (rollers, cranes,etc.) and unsymmetrical loads. Symmetry/non-symmetryin torque can be for example as a function of angle ortime. These kinds of load types must be dimensioned care-fully taking into account the overloadability margins of themotor and the frequency converter, as well as the averagetorque of the motor.


7

23

T / Tn

Relative speed

Chapter 7 - Motor loadability

Motor thermal loadability has to be considered whendimensioning a drive system. The thermal loadabilitydefines the maximum long term loadability of the motor.

A standard induction motor is self ventilated. Because ofthe self ventilation the motor thermal loadability decreasesas the motor speed decreases. This kind of behaviour limitsthe continuous available torque at low speeds.

A motor with a separate cooling can also be loaded at lowspeeds. Cooling is often dimensioned so that the coolingeffect is the same as at the nominal point.

With both self and separate cooling methods torque isthermally limited in the field weakening range.

Figure 7.1 A standard cage induction motor's typical loadability in afrequency controlled drive 1) without separate cooling and 2) withseparate cooling.

An AC-motor can be overloaded for short periods of timewithout overheating it. Short term overloads are mainlylimited by Tmax (check the safety margin).

Generally speaking, a frequency converter's short termloadability is often more critical than the motor's. The motorthermal rise times are typically from 15 minutes (smallmotors) to several hours (big motors) depending on themotor size. The frequency converter's thermal rise times(typically few minutes) are given in the product manuals.


Chapter 8 - Selecting the frequencyconverter and motor

The motor is selected according to the basic informationabout the process. Speed range, torque curves, ventila-tion method and motor loadability give guidelines for mo-tor selection. Often it is worth comparing different motorsbecause the selected motor affects the size of the fre-quency converter.

When selecting a suitable frequency converter there areseveral things to be considered. Frequency convertermanufacturers normally have certain selection tables wheretypical motor powers for each converter size are given.

The dimensioning current can also be calculated when thetorque characteristics is known. The corresponding cur-rent values can be calculated from the torque profile andcompared to converter current limits. The motor's nomi-nal current gives some kind of indication. It isn't howeveralways the best possible dimensioning criteria becausemotors might for example be derated (ambient tempera-ture, hazardous area, etc.).

The available supply voltage must be checked before se-lecting the frequency converter. Supply voltage variationsaffect the available motor shaft power. If the supply volt-age is lower than nominal the field weakening point shiftsto a lower frequency and the available maximum torque ofthe motor is reduced in the field weakening range.

The maximum available torque is often limited by the fre-quency converter. This has to be considered already inthe motor selection phase. The frequency converter maylimit the motor torque earlier than stated in the motor manu-facturer's data sheet.

The maximum available torque is also affected by trans-formers, reactors, cables, etc. in the system because theycause a voltage drop and thus the maximum availabletorque may drop. The system's power losses need to becompensated also by the frequency converter rating.

Some stages in pump and fan application dimensioning:

- Check the speed range and calculate power with highestspeed.

- Check the starting torque need.- Choose the pole number of the motor. The most

economic operating frequency is often in the field

8.1 Pump andfan application(Example)


7

25

weakening range.- Choose motor power so that power is available at

maximum speed. Remember the thermal loadability.- Choose the frequency converter. Use pump and fan

rating. If the pump and fan rating is not available choosethe frequency converter according to the motor currentprofile.

Example 8.1:A pump has a 150 kW load at a speed of 2000 rpm. Thereis no need for starting torque.

Solution 8.1:The necessary torque at 2000 rpm is:

It seems that 2-pole or 4-pole motors are alternativechoices for this application.

Selecting the frequency converter and motor

Figure 8.1 Motor loadability curves in a pump and fan application.Comparison of 1) 2-pole and 2) 4-pole motors.

1) motor p=2For a 2-pole motor the loadability at 2000 rpm accordingto the loadability curve is about 95 %. The motor nominaltorque must be at least:


The corresponding nominal power must then be at least:

A 250 kW (400 V, 431 A, 50 Hz, 2975 rpm and 0.87) motoris selected. The nominal torque of the motor is:

The motor current at 2000 rpm speed (constant flux range)is approximately:

The minimum continuous current for the frequencyconverter is then 384 A.

2) motor p=4For a 4-pole motor the loadability at 2000 rpm is 75 %.The minimum nominal torque of the motor is:

The minimum power for a 4-pole motor is:

A 160 kW motor (400 V, 305 A, 50 Hz, 1480 rpm and 0.81)fulfills the conditions. The approximated current at a speedof 2000 rpm (66.7 Hz) is:

The exact current should be calculated if the selectedfrequency converter's nominal current is close to theapproximated motor current.

A 4-pole motor requires less current at the pump operationpoint. Thus it is probably a more economical choice thana 2-pole motor.


Figure 8.2 Motor loadability curves in a constant torque application.comparison of 1) 4-pole and 2) 6-pole motors.


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27

Some stages in dimensioning of a constant torqueapplication:

- Check the speed range.- Check the constant torque needed.- Check the possible accelerations. If accelerations are

needed check the moments of inertia.- Check the possible starting torque required.- Choose the motor so that torque is below the thermal

loadability curve (separate/self ventilation?). Typicallythe nominal speed of the motor is in the middle of thespeed range used.

- Choose a suitable frequency converter according to thedimensioning current.

Example 8.2:An extruder has a speed range of 300-1200 rpm. The loadat 1200 rpm is 48 KW. The starting torque requirement is200 Nm. Acceleration time from zero speed to 1200 rpm is10 seconds. The motor is self-ventilated and the nominalvoltage is 400 V.

Solution 8.2:The constant torque requirement is:

A suitable motor is a 4-pole or a 6-pole motor.


8.2 Constanttorqueapplication(Example)

Figure 8.2 Motor loadability curves in a constant torque application.comparison of 1) 4-pole and 2) 6-pole motors.


1) Motor p=4At 300 rpm speed the thermal loadability is 80 %.The estimated minimum nominal torque is:

The minimum motor nominal power is:

A suitable motor is for example a 75 kW (400 V, 146 A,50 Hz, 1473 rpm and 0.82) motor. The motor nominal torqueis:

Motor current is approximately (T/Tn ≈ 0.8):

According to the calculated motor current a suitablefrequency converter can be selected for constant torqueuse.

The starting torque requirement (200 Nm) is not a problemfor this motor.

If the motor's moment of inertia is 0.72 kgm2 the dynamictorque in acceleration is:

Thus the total torque during acceleration is 391 Nm whichis less than the nominal torque of the motor.

2) Motor p=6At speeds of 300 rpm and 1200 rpm the motor loadabilityis 84 %. Thus the minimum nominal torque of the 6-polemotor is:

The minimum value of the motor nominal power is:


Technical Guide No.7 - Dimensioning of a Drive system 29

A suitable motor could be for example a 55 kW (400 V, 110A, 50 Hz, 984 rpm and 0.82) motor. The motor nominaltorque is:

The dimensioning current can be approximated at a speedof 1200 rpm:

The nominal (continuous) current of the frequency convertermust be over 96 A.

The starting torque requirement is less than motor's nominaltorque.

If the inertia of the motor is 1.2 kgm2 the dynamic torque inacceleration is:

The total torque needed during acceleration is 397 Nmwhich is less than the nominal torque of the motor.

A 6-pole motor current is 19 A smaller than with a 4-polemotor. The final frequency converter/motor selectiondepends on the motor and frequency converter frame sizesand prices.

Some stages in dimensioning of a constant power appli-cation:

- Check the speed range.- Calculate the power needed. Winders are typical constant

power applications.- Dimension the motor so that the field weakening range

is utilized.

Example 8.3:A wire drawing machine is controlled by a frequencyconverter. The surface speed of the reel is 12 m/s and thetension is 5700 N. The diameters of the reel are 630 mm(empty reel) and 1250 (full reel). There is a gear with gearratio n2 :n1 =1:7.12 and the efficiency of the gear is 0.98.

Select a suitable motor and converter for this application.

8.3 Constantpowerapplication(Example)


7


Figure 8.3 Basic diagram of a winder.

In rectilinear motion the power is: P = Fv

In rotational motion the power is: P = Tω

The relation between surface speed and angular velocityis:

Torque is a product of force and radius: T = Fr

By using the above formulas the motor can be selected:

Solution 8.3:The basic idea of a winder is to keep the surface speedand the tension constant as the diameter changes.



7

31

The gear must be taken into account before choosing themotor. Speeds, torques and power have to be reduced:

1) Motor p=2If a 2-pole motor is selected loadability at a speed of 1305rpm is about 88 % and 97 % at 2590 rpm. The minimumnominal power of the motor is:

A 200 kW (400 V, 353 A, 50 Hz, 2975 rpm and 0.86) motor isselected. The motor nominal torque is:

The dimensioning current is calculated according to atorque of 511 Nm:

2) Motor p=4If a 4-pole motor is selected it can be seen from theloadability curve that loadability at a speed of 1305 rpm isabout 98 % and about 60 % at 2590 rpm. The minimumnominal power of the motor is:



A 90 kW (400 V, 172 A, 50 Hz, 1473 rpm and 0.83) is se-lected. The motor nominal torque is:

Dimensioning in this case is done according to the motorcurrent at 1305 rpm. The motor current is:

With a 2-pole motor the field weakening (constant power)range was not utilized which led to unnecessaryoverdimensioning. A 4-pole motor is a better choice forthis application.



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33

TORQUE

LINE CURRENT

Chapter 9 - Input transformer andrectifier

There are several types of input rectifiers. The rectifier typemight limit the operation.

A conventional rectifier is a 6 or 12 pulse diode rectifier.Diode rectifiers only support motoring loads where thepower flow is one way only.

In certain processes where the load can also be generat-ing, the energy needs to be absorbed. For short generat-ing loads the traditional solution has been a braking resis-tor where the power generated has been transformed intoheat losses. If however the load is generating all the time,a true 4-quadrant rectifier is needed.

Both the input transformer and the rectifier are dimen-sioned according to the motor shaft power and systemlosses. For example if high torque at low speed is deliv-ered the mechanical power is nevertheless quite low. Thushigh overloads do not necessarily mean high power fromthe rectifier point of view.

Figure 9.1 Line current in a constant torque application. Line current issmall at low speed.

Rectifiers are dimensioned according to motor shaft power.A single drive's input rectifier can be selected using theapproximation formula:

In drive systems where there is a common DC-link, therecan be motoring and generating power at the same time.Rectifier power is then calculated approximately as fol-lows:

9.1 Rectifier

(9.1)

(9.2)


An input transformer's power can be calculated as follows:

In the above formulas:

Ptotal is the total motor shaft power

k is the transformer loadability (k-factor)

1.05 stands for transformer voltage drop (impedance)

ηr is the rectifier efficiency

cos(α) is the rectifier control angle (=1.0 for dioderectifier)

ηc is the AC choke (if there is one) efficiency

ηi is the inverter efficiency

ηm is the motor efficiency

Typically total shaft power is multiplied by a coefficient1.2 - 1.35.

Example 9.1:In a constant torque application the maximum shaft powerneeded is 48 kW at a speed of 1200 rpm. A 55 kW motorand 70 kVA inverter unit was selected.

Specify the rectifier and input transformer. A 6-pulse diodesupply is used (efficiency 0.985), there is a DC-choke inthe DC-link, inverter efficiency is 0.97 and motor efficiencyis 0.95.

Solution 9.1:For the rectifier the estimated power is:

9.2Transformer

(9.3)

Input transformer and rectifier


7

35

Input transformer and rectifier

The choke efficiency is included in the inverter efficiency.Because of diode supply unit cos(α) =1. The power of theinput transformer (k=0.95) is:


Chapter 10 - Index

4-quadrant 33

AAC motor 6acceleration 18active current 11angular velocity 14

Bbreak down torque 10

Ccentrifugal pumps 20constant flux range 10constant power 10, 21constant torque 20coupling 19cubically 20cyclical load 7

DDC-link 6decelerate 16diode rectifier 33drum 19

Eefficiency 14electric supply 6

Ffan 16, 20friction 14field weakening range 10flux range 10frequency 7, 9frequency converter 6

Ggear 18gear box 19generating 33

Iinduction 9induction motor 9input transformer 6inverter 34,35

Kkilowatt 14

Lload 6load profile 20load type 20locked rotor torque 9

Mmotor 9maximum torque 10mechanical 14moment inertia 15motoring 33

Nnominal point 9, 12

Ooverloadability 7

Ppower 9, 14power factor 12pull-out torque 10pull-up torque 9

Qquadratically 20quadratic torque 20

Rreactive current 11rectifier 33rectifier unit 6roller 19

Sscalf ventilated 23separate cooling 23shaft power 24slip 9speed 9speed range 7starting/breakway torque 21starting torque 7supply 6, 7supply voltage 7, 24


7

37

Index

Tthermal loadability 23transformer 6torque 9, 10

Vvoltage 9

3AFE

64

3625

69

RE

V A

E

N 1

7.5.

200

2 S

peci

ficat

ions

sub

ject

to

chan

ge w

ithou

t no

tice.



Electrical Braking

Technical Guide No.8 - Electrical Braking2

Contents

Technical Guide No.8 - Electrical Braking

8

3

1. Introduction .......................................................... 5

1.1 General .................................................................... 51.2 Drive applications map according to speed and

torque ..................................................................... 5

2. Evaluating braking power ................................... 7

2.1 General dimension principles for electricalbraking .................................................................... 7

2.2 Basics of load descriptions ................................... 82.2.1 Constant torque and quadratic torque ...... 82.2.2 Evaluating brake torque and power ........... 82.2.3 Summary and Conclusions ........................ 12

3. Electrical braking solutions in drives .............. 13

3.1 Motor Flux braking ................................................. 133.2 Braking chopper and braking resistor ................... 14

3.2.1 The energy storage nature of thefrequency converter ................................... 14

3.2.2 Principle of the braking chopper ................ 153.3 Anti-parallel thyristor bridge configuration ........... 173.4 IGBT bridge configuration ...................................... 19

3.4.1 General principles of IGBT basedregeneration units ....................................... 19

3.4.2 IGBT based regeneration-control targets .. 193.4.3 Direct torque control in the form of direct

power control .............................................. 203.4.4 Dimensioning an IGBT regeneration unit ... 22

3.5 Common DC ........................................................... 22

4. Evaluating the life cycle cost of differentforms of electrical braking ................................. 24

4.1 Calculating the direct cost of energy .................... 244.2 Evaluating the investment cost ............................. 244.3 Calculating the life cycle cost ................................ 25

5. Symbols and definitions ..................................... 29

6. Index ..................................................................... 30



8

5

This guide continues ABB's technical guide series, describ-ing the practical solutions available in reducing stored en-ergy and transferring stored energy back into electricalenergy. The purpose of this guide is to give practical guide-lines for different braking solutions.

Drive applications can be divided into three main catego-ries according to speed and torque. The most commonAC drive application is a single quadrant application wherespeed and torque always have the same direction, i.e. thepower flow (which is speed multiplied by torque) is frominverter to process. These applications are typically pumpand fan applications having quadratic behaviour of loadtorque and thus often called variable torque applications.Some single quadrant applications such as extruders orconveyors are constant torque applications, i.e. the loadtorque does not inherently change when speed changes.

The second category is two-quadrant applications wherethe direction of rotation remains unchanged but the direc-tion of torque can change, i.e. the power flow may be fromdrive to motor or vice versa. The single quadrant drive mayturn out to be two quadrants for example if a fan is decel-erated faster than mechanical losses could naturallyachieve. In many industries also the requirement for emer-gency stopping of machinery may require two-quadrantoperation although the process itself is single quadranttype.

The third category is fully four-quadrant applications wherethe direction of speed and torque can freely change. Theseapplications are typically elevators, winches and cranes,but many machinery processes such as cutting, bending,weaving, and engine test benches may require repetitivespeed and torque change. One can also mention singlequadrant processes where the power flow is mainly frommachinery to inverter such as in a winder or an uphill todownhill conveyor.

It is commonly understood that from the energy savingpoint of view the AC motor combined with inverter is su-perior to mechanical control methods such as throttling.However, less attention is paid to the fact that many proc-esses may inherently include power flow from process todrive, but how this braking energy could be utilised in themost economical way has not been considered.

1.1 General

1.2 Driveapplicationsmap accordingto speed andtorque

Introduction


Figure 1.1 Drive applications map according to speed and torque.

Decelerating Accelerating

Accelerating Decelerating

Chapter 2 - Evaluating braking power


8

7

The evaluation of braking need starts from the mechanics.Typically, the requirement is to brake the mechanical sys-tem within a specified time, or there are subcycles in theprocess where the motor operates on the generator sideat constant or slightly varying speed.

It is important to note that devices used in electrical brak-ing are dimensioned according to braking power. The me-chanical braking power depends on braking torque andspeed, formula (2.1). The higher the speed the higher thepower. This power is then transferred at a certain speci-fied voltage and current. The higher the voltage the lesscurrent is needed for the same power, formula (2.2). Thecurrent is the primary component defining the cost in lowvoltage AC drives.

In formula (2.2) we see the term cosφ. This term defineshow much motor current is used for magnetising the mo-tor. The magnetising current does not create any torqueand is therefore ignored.

On the other hand, this motor magnetising current is nottaken from the AC supply feeding the converter, i.e. thecurrent to the inverter is lower than the current fed to themotor. This fact means that on the supplying side the cosφis typically near 1.0. Note that in formula (2.2) it has beenassumed that no loss occurs when DC power is convertedto AC power. There are some losses in this conversion,but in this context the losses can be ignored.

2.1 Generaldimensionprinciples forelectricalbraking

(2.1)

(2.2)

Evaluating braking power


2.2 Basics ofloaddescriptions

Typically loads are categorised as constant torque or quad-ratic torque type. Quadratic load torque means that theload torque is proportional to the square of the speed. Italso means that the power is speed to the power of three.In constant torque applications, the power is directly pro-portional to speed.

Constant torque:

C: constant

2.2.1 Constanttorque andquadratictorque

Quadratic torque:

2.2.2 Evaluatingbrake torqueand power

In the case of steady state operation (the angular acceler-ation α is zero) the motor torque has to make friction torquecorrespond proportionally to the angular speed and loadtorque at that specific angular speed. The braking torqueand power need in respect to time varies greatly in thesetwo different load types.

Let us first consider the case where the load is constanttorque type and the drive system is not able to generatebraking torque, i.e. the drive itself is single quadrant type.In order to calculate the braking time needed one can ap-ply the following equation. Please note that formula (2.7)underlines that the torque needed for inertia accelerating(or decelerating), friction and load torque is in the oppositedirection to the motor torque.

In practice, it is difficult to define the effect of friction ex-actly. By assuming friction to be zero the time calculated ison the safe side.

(2.3)

(2.4)

(2.5)

(2.6)

(2.7)

(2.8)



8

9

By solving t one ends up with the formula:

Assuming that the load inertia is 60 kgm2 and the loadtorque is 800 Nm over the whole speed range, if the load isrunning at 1000 rpm and the motor torque is put to zero,the load goes to zero speed in the time:

This applies for those applications where the load torqueremains constant when the braking starts. In the casewhere load torque disappears (e.g. the conveyor belt isbroken) the kinetic energy of the mechanics remainsunchanged but the load torque that would decelerate themechanics is now not in effect. In that case if the motor isnot braking the speed will only decrease as a result ofmechanical friction.

Now consider the case with the same inertia and loadtorque at 1000 rpm, but where the load torque changesin a quadratic manner. If the motor torque is forced tozero the load torque decreases in quadratic proportion tospeed. If the cumulative braking time is presented as afunction of speed, one sees that the natural braking timeat the lower speed, e.g. from 200 rpm to 100 rpm, increasesdramatically in comparison to the speed change from1000 rpm to 900 rpm.

Natural braking curve with constant load

Po

wer

[10

* k

W],

Tim

e [s

], To

rque

[10

0 *

Nm

]

Cumulative timeNatural brakingpower [kW] * 10

Natural brakingtorque [Nm] * 100

Speed [rpm]

(2.9)

(2.10)

(2.11)

Figure 2.1 Cumulative braking time, braking load power and torque as afunction of speed.



Figure 2.2 Natural braking curve for a 90 kW fan braking load power andtorque as a function of speed.

Figure 2.3 Cumulative braking time for, e.g., a 90 kW fan.

Let us now consider the case where the requirementspecifies the mechanical system to be braked in a specifiedtime from a specified speed.

The 90 kW fan has an inertia of 60 kgm2. The nominaloperating point for the fan is 1000 rpm. The fan is requiredto be stopped within 20 seconds. The natural braking effectcaused by the load characteristics is at its maximum atthe beginning of the braking. The maximum energy of inertiacan be calculated from formula (2.12). The average brakingpower can be calculated by dividing this braking energyby time. This value is, of course, on the very safe side dueto the fact that the fan load characteristics are not takeninto account.

A natural braking curve can easily be drawn based on thepower and speed at the nominal point applying the formulas(2.5) and (2.6).

Natural braking curve with quadratic load

Po

wer

[10

* k

W],

Tim

e [s

], To

rque

[10

0 *

Nm

]T

ime

[s]

Braking power[kW] * 10

Braking torque[Nm] * 100

Speed [rpm]

Braking time

Natural braking curve with quadratic load

Speed [rpm]


Technical Guide No.8 - Electrical Braking 11

When the braking chopper is dimensioned for this 16.4 kWvalue and the motor braking capability at a higher speed isfar more than 16.4 kW, the drive has to include a supervisionfunction for maximum regeneration power. This function isavailable in some drives.

If one wants to optimise the dimensioning of the brakechopper for a specific braking time one can start by look-ing at figure (2.3). The speed reduces quickly from 1000 to500 rpm without any additional braking. The natural brak-ing effect is at its maximum at the beginning of the brak-ing. This clearly indicates that it is not necessary to startbraking the motor with the aforementioned 16 kW powerin the first instance. As can be seen from figure (2.3) thespeed comes down from 1000 rpm to 500 rpm without anyadditional braking within less than 10 seconds. At that pointof time the load torque is only 25 % of nominal and thekinetic energy conserved in the fan is also only 25 % of theenergy at 1000 rpm. If the calculation done at 1000 rpm isrepeated at 500 rpm, it can be seen that the braking powerin order to achieve deceleration from 500 rpm to 0 rpm isappr. 8 kW. As stated in previous calculations this is alsoon the safe side because the natural braking curve causedby the load characteristics is not taken into account.

To summarise, the target for a 20 second deceleration timefrom 1000 rpm down to 0 rpm is well achieved with a brakingchopper and resistor dimensioned for 8.2 kW. Setting thedrive regenerative power limit to 8.2 kW sets the level ofbraking power to an appropriate level.

(2.12)

(2.13)

(2.14)

(2.15)

8



There are two basic load types: constant and quadraticload torque.

Constant torque application:

The load torque characteristic does not depend on thespeed. The load torque remains approximately the sameover the whole speed area.The power increases linearly as the speed increases andvice versa.Typical constant torque applications: cranes and convey-ors.

Quadratic torque application:

The load torque increases to speed to the power of two.When the speed increases, the power increases to speedto the power of three.Typical quadratic torque applications: fans and pumps.

Braking power evaluation:

The quadratic load characteristics mean fast natural de-celeration between 50-100 % of nominal speeds. Thatshould be utilised when dimensioning the braking powerneeded.The quadratic load torque means that at low speeds thenatural deceleration is mainly due to friction.The constant load torque characteristic is constant natu-ral deceleration.The braking power is a function of torque and speed atthat specified operating point. Dimensioning the brakingchopper according to peak braking power typically leadsto overdimensioning.The braking power is not a function of motor nominalcurrent (torque) or power as such.If the load torque disappears when braking starts thenatural braking effect is small. This affects the dimen-sioning of the braking chopper.

2.2.3 Summaryand conclusions

Chapter 3 - Electrical braking solutionsin drives


8

13

3.1 Motor fluxbraking

The modern AC drive consists of an input rectifier con-verting AC voltage to DC voltage stored in DC capacitors.The inverter converts the DC voltage back to AC voltagefeeding the AC motor at the desired frequency. The proc-ess power needed flows through the rectifier, DC bus andinverter to the motor. The amount of energy stored in DCcapacitors is very small compared with the power need-ed, i.e. the rectifier has to constantly deliver the powerneeded by the motor plus the losses in drive system.

Flux braking is a method based on motor losses. Whenbraking in the drive system is needed, the motor flux andthus also the magnetising current component used in themotor are increased. The control of flux can be easilyachieved through the direct torque control principle (formore information about DTC see Technical Guide No. 1).With DTC the inverter is directly controlled to achieve thedesired torque and flux for the motor. During flux brakingthe motor is under DTC control which guarantees that brak-ing can be made according to the specified speed ramp.This is very different to the DC injection braking typicallyused in drives. In the DC injection method DC current isinjected to the motor so that control of the motor flux islost during braking. The flux braking method based on DTCenables the motor to shift quickly from braking to motor-ing power when requested.

In flux braking the increased current means increased loss-es inside the motor. The braking power is therefore alsoincreased although the braking power delivered to the fre-quency converter is not increased. The increased currentgenerates increased losses in motor resistances. The high-er the resistance value the higher the braking energy dis-sipation inside the motor. Typically, in low power motors(below 5 kW) the resistance value of the motor is relativelylarge in respect to the nominal current of the motor. Thehigher the power or the voltage of the motor the less theresistance value of the motor in respect to motor current.In other words, flux braking is most effective in a low pow-er motor.

Electrical braking solutions in drives


The main benefits of flux braking are:

No extra components are needed and no extra cost, usingDTC control method.The motor is controlled during braking unlike in the DCinjection current braking typically used in drives.

The main drawbacks of flux braking are:

Increased thermal stress on the motor if braking is re-peated over short periods.Braking power is limited by the motor characteristics e.g.resistance value.Flux braking is useful mainly in low power motors.

Figure 3.1 Percentage of motor braking torque of rated torque as afunction of output frequency.

3.2 Brakingchopper andbraking resistor

3.2.1 Theenergy storagenature of thefrequencyconverter

In standard drives the rectifier is typically a 6-pulse or 12-pulse diode rectifier only able to deliver power from theAC network to the DC bus but not vice versa. If the powerflow changes as in two or four quadrant applications, thepower fed by the process charges the DC capacitorsaccording to formula (3.1) and the DC bus voltage startsto rise. The capacitance C is a relatively low value in an ACdrive resulting in fast voltage rise, and the components ofa frequency converter may only withstand voltage up to acertain specified level.

Braking torque (%)

No flux braking

Flux brakingRated motor power


Technical Guide No.8 - Electrical Braking 15

3.2.2 Principleof the brakingchopper

In order to prevent the DC bus voltage rising excessively,two possibilities are available: the inverter itself preventsthe power flow from process to frequency converter. Thisis done by limiting the braking torque to keep a constantDC bus voltage level. This operation is called overvoltagecontrol and it is a standard feature of most modern drives.However, this means that the braking profile of the ma-chinery is not done according to the speed ramp specifiedby the user.

The energy storage capacity of the inverter is typically verysmall. For example, for a 90 kW drive the capacitance val-ue is typically 5 mF. If the drive is supplied by 400 V AC theDC bus has the value of 1.35 * 400 = 565 V DC. Assumingthat the capacitors can withstand a maximum of 735 VDC, the time which 90 kW nominal power can be fed to theDC capacitor can be calculated from:

This range of values applies generally for all modern lowvoltage AC drives regardless of their nominal power. Inpractice this means that the overvoltage controller and its'work horse' torque controller of the AC motor has to be avery fast one. Also the activation of the regeneration orbraking chopper has to be very fast when used in driveconfiguration.

The other possibility to limit DC bus voltage is to lead thebraking energy to a resistor through a braking chopper.The braking chopper is an electrical switch that connectsDC bus voltage to a resistor where the braking energy isconverted to heat. The braking choppers are automatical-ly activated when the actual DC bus voltage exceeds aspecified level depending on the nominal voltage of theinverter.

(3.1)

(3.2)

(3.3) 8



The main benefits of the braking chopper and resistor so-lution are:

Simple electrical construction and well-known technol-ogy.Low fundamental investment for chopper and resistor.The chopper works even if AC supply is lost. Brakingduring main power loss may be required, e.g. in elevatoror other safety related applications.

The main drawbacks of the braking chopper and resistorare:

The braking energy is wasted if the heated air can not beutilised.The braking chopper and resistors require additionalspace.May require extra investments in the cooling and heatrecovery system.Braking choppers are typically dimensioned for a certaincycle, e.g. 100 % power 1/10 minutes, long braking timesrequire more accurate dimensioning of the braking chop-per.Increased risk of fire due to hot resistor and possibledust and chemical components in the ambient air space.The increased DC bus voltage level during braking causesadditional voltage stress on motor insulation.

When to apply a braking chopper:

The braking cycle is needed occasionally.The amount of braking energy with respect to motoringenergy is extremely small.Braking operation is needed during main power loss.

Figure 3.2 Circuit diagram example of braking chopper. UDC representsDC bus terminals and R the resistor terminals.

UDC+

UDC-

R+

R-

V1

C1ControlCircuit



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3.3 Anti-parallelthyristor bridgeconfiguration

In a frequency converter the diode rectifier bridges can bereplaced by the two thyristor controlled rectifiers inantiphase. This configuration allows changing the rectifierbridge according to the power flow needed in the process.

The main components of the thyristor supply unit are two6-pulse thyristor bridges. The forward bridge converts 3-phase AC supply into DC. It feeds power to the drives (in-verters) via the intermediate circuit. The reverse bridgeconverts DC back to AC whenever there is a need to passthe surplus motor braking power back to the supply net-work.

Figure 3.3 Line diagram of anti-parallel thyristor supply unit.

Only one bridge operates at a time, the other one isblocked. The thyristor-firing angle is constantly regulatedto keep the intermediate circuit voltage at the desired level.The forward/reverse bridge selection and intermediate cir-cuit voltage control are based on the measurement of thesupply current, supply voltage and the intermediate cir-cuit voltage. The DC reactor filters the current peaks ofthe intermediate circuit.

When to consider other solutions than braking chopperand resistor:

The braking is continuous or regularly repeated.The total amount of braking energy is high in respect tothe motoring energy needed.The instantaneous braking power is high, e.g. severalhundred kW for several minutes.The ambient air includes substantial amounts of dust orother potentially combustible or explosive or metalliccomponents.

Forward Reverse

L

Udc3



The main benefits of the anti-parallel thyristor bridge are:

Well known solution.Less investment needed than for an IGBT solution.The DC voltage can be controlled to a lower value thanthe network. In certain special applications this can bean advantage.

The main drawbacks of the anti-parallel thyristor bridgeare:

The DC bus voltage is always lower than AC supply volt-age in order to maintain a commutation margin. Thusthe voltage fed to the motor remains lower than the in-coming AC. However, this can be overcome by using astep-up autotransformer in the supply.If the supplying AC disappears a risk of fuse blowing ex-ists, due to the failure in thyristor commutation.The cosφ varies with loading.Total harmonic distortion higher than in IGBT regenera-tive units.The current distortion flows through other network im-pedance and can cause undesired voltage distortion forother devices supplied from the point where voltage dis-tortion exists.The braking capability is not available during main powerloss.

Figure 3.4. Example of anti-parallel bridge current and voltagewaveforms during braking.

Volta

ge

/ V,

Cur

rent

/ A

Sinusoidal phasevoltage

Distorted phasevoltage

Line current

Time / ms



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3.4 IGBT bridgeconfiguration

3.4.1 Generalprinciples ofIGBT basedregenerationunits

The IGBT based regeneration is based on the same princi-ples as power transmission within a power network. In apower network several generators and load points are con-nected together. One can assume that at the point of con-nection the power network is a large synchronous genera-tor having a fixed frequency. The input IGBT bridge of thedrive (later line converter) can be considered as anotherAC voltage system connected through a choke to the gen-erator. The principle of power transfer between two ACsystems having voltage U and connected to each othercan be calculated from figure (3.4).

The formula indicates that in order to transfer powerbetween these two systems there has to be a phasedifference in the angle between the voltages of the two ACsystems. In order to control the power flow between thetwo systems the angle has to be controlled.

Figure 3.5. Typical line current waveform and harmonics of an IGBT linegenerating unit.

3.4.2 IGBTbasedregeneration -control targets

There are three general control targets in IGBT basedregeneration units. The first one is to keep the DC busvoltage stable regardless of the absolute value of powerflow and the direction of power flow. This ensures thatinverters feeding AC motors can work in an optimum wayregardless of the operation point thanks to a stable DCbus voltage. The DC bus voltage is stable when the powerflow into the DC bus equals the power flow out of the DCbus. This control of appropriate power flow is achieved bycontrolling the power angle between the two AC systems.

Line generating unit Line generating unit

Harmonic order

(3.4)



The second control target is to minimise the supply currentneeded, i.e. to operate at cosϕ = 1.0. This is achieved bycontrolling the output voltage of the line converter. In someapplications it is desired that the IGBT line converter alsoworks as an inductive or as a capacitive load.

The third control target is to minimise the harmonic contentof the supply current. The main design criteria here are theimpedance value of the choke and an appropriate controlmethod.

Direct torque control (DTC) is a way to control an AC mo-tor fed by an inverter. The control principal turns IGBTswitches on and off directly based on the difference be-tween the actual AC motor torque and the user’s referencetorque (Technical Guide No. 1). The very same principlecan be applied in a line converter controlling the powerflow from power network to drive and vice versa. The poweris torque multiplied by angular frequency, which in the net-work is constant, i.e. controlling torque means also con-trol of power flow.

3.4.3 Directtorque controlin the form ofdirect powercontrol

Figure 3.6. Fast change from regenerating to motoring operation. Notehow stable the DC bus voltage is during this transition.

Times / ms

DC Measurement

Power

Po

wer

/ k

W, V

olta

ge

/ 10

*

V

Load step

Torque_REF Direct torque and fluxHysteresis controlFlux_REF

HysteresisTorque_BITSFlux_BITSControl_BITS

S1, S2, S3OptimalSwitchingLogic

ASICS

DC-Voltage

S1, S2, S3

Current

Flux_ACT Torque_ACT

Model of powertransmission

Calculateactual values

DC voltage control

L

(3.5)

Figure 3.7. Fundamental control diagram for DTC based IGBTregeneration unit.



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The DTC control method combined with IGBT technologycontributes to a low amount of current harmonics. For thatreason the IGBT supply unit can be used to replace singlequadrant 12-pulse or 18-pulse supply configurations, whichare typically used for reducing current harmonics on thesupply side. An IGBT supply unit is therefore also a solutionfor those cases where current harmonics rather than thehandling of braking energy is the issue.

The main benefits of an IGBT regeneration unit are:

Low amount of supply current harmonics in both motor-ing and regeneration.High dynamics during fast power flow changes on theload side.Possibility to boost the DC voltage higher than the re-spective incoming AC supply. This can be used to com-pensate for a weak network or increase the motor’s max-imum torque capacity in the field weakening area.Full compensation of system voltage drops thanks tovoltage boost capability.Possibility to control the power factor.Power loss ride through operation with automatic syn-chronisation to grid.DC bus voltage has approximately the same value dur-ing motoring or braking. No extra voltage stress on in-sulation of motor winding during braking.

Figure 3.8. Boosting capability of supplying voltage.

Times / ms

Actual DC voltage

Reference DC voltage

Volta

ge

/ V



The supply current dimensioning of the IGBT unit is basedon power needed. Let us assume that the motoring shaftpower needed is 130 kW and braking power 100 kW. Todimension the IGBT supply unit the maximum value ofmotoring or braking power is selected, in this case 130 kW.The motor voltage is 400 V. The minimum value for thesupplying network is 370 V.

In this case the voltage boost capability can be utilised;the DC bus voltage is raised to correspond to an AC volt-age of 400 V. However, the required supply current is cal-culated based on the 370 level. Assuming that there are5 % system losses in the motor and drive, the total powerneeded from the grid is 136.5 kW. The supplying currentcan be calculated from the formula:

3.4.4 Dimen-sioning anIGBT regenera-tion unit

The IGBT regeneration unit is selected based solely on thecalculated current value.

When a process consists of several drives where one mo-tor may need braking capability when others are operat-ing in motoring mode, the common DC bus solution is avery effective way to reuse the mechanical energy. A com-mon DC bus solution drive system consists of a separatesupply rectifier converting AC to DC, and inverters feedingAC motors connected to the common DC bus, i.e. the DC

3.5 CommonDC

The main drawbacks of an IGBT regeneration unit are:

Higher investment cost.The braking capability is not available during main powerloss.High frequency voltage harmonics due to high switchingfrequency. These several kilohertz voltage componentscan excite small capacitors used in other electrical de-vices. With appropriate design and arrangement of feed-ing transformers for different devices these phenomenaare eliminated.

When to use an IGBT regeneration unit:

The braking is continuous or repeating regularly.The braking power is very high.When space savings can be achieved compared to thebraking resistor solution.When network harmonics limits are critical.

(3.6)



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23

Figure 3.9. The basic configuration of the common DC bus solution.

The main benefits of the common DC bus solution are:

Easy way to balance power flow between drives.Low system losses in conversion of braking energythanks to common DC bus.Even if the instantaneous braking power is higher thanmotoring power the braking chopper and resistor do notneed to be dimensioned for full braking power.If braking power is likely to be needed for long periods acombination of rectifiers can be used.

The main drawbacks of the common DC bus solution withsingle quadrant rectifier are:

The instantaneous motoring power has to be higher thanor equal to braking power.The braking chopper and resistor are needed if instan-taneous braking power exceeds motoring power.If the number of motors is small the additional cost of adedicated inverter disconnecting the device from the DCbus raises the investment cost.

When to use common DC bus solution with single quadrantrectifier:

The number of drives is high.The motoring power is always higher than braking poweror only low braking power is needed by the braking chop-per.

bus is the channel to move braking energy from one motorto benefit the other motors. The basic configuration of thecommon DC bus arrangement can be seen from figure (3.9).

Supply section Braking sections Drive sections

Auxilliarycontrolunit

ACU ICU FIU

24 V

AC

Incomingunit

Filter unitwith IGBTsupply only

DSU/TSU/IGBTSupplyunit

Braking unit (optional)

Common DC bus

Supplyunit

Chopper

Res

isto

r

Inverter Inverter

Chapter 4 - Evaluating the life cycle costof different forms of electrical braking


It has become increasingly important to evaluate the totallife cycle cost when investing in energy saving products.The AC drive is used for controlling speed and torque. Thisbasic function of AC drives means savings in energyconsumption in comparison to other control methods used.In pump and fan type applications braking is seldomneeded. However, modern AC drives are increasingly beingused in applications where a need for braking exists.

Several technical criteria are mentioned above. Thefollowing examines the economic factors for differentelectrical braking approaches.

4.1 Calculatingthe direct costof energy

The direct cost of energy can be calculated based, forexample, on the price of energy and the estimated brak-ing time and power per day. The price of energy variesfrom country to country, but a typical estimated pricelevel of 0.05 Euros per kilowatt-hour can be used.1 Euro ~ 1 USD. The annual cost of energy can be calcu-lated from the formula:

For example, a 100 kW drive is running 8000 hours peryear and braking with 50 kW average power for 5 minutesevery hour, i.e. 667 hours per year. The annual direct costof braking energy is 1668 Euros.

The required investment objects needed for different brak-ing methods vary. The following investment cost compo-nents should be evaluated.

Braking chopper:

The additional investment cost of braking chopper andresistor plus the cost of additional space needed for thosecomponents.The investment cost of additional ventilation needed forthe braking chopper.

4.2 Evaluatingthe investmentcost

(4.1)

Evaluating the life cycle cost of different forms of electrical braking


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Thyristor or IGBT based electrical braking:

The additional investment cost of thyristor or IGBT re-generative braking in respect to the same power drivewithout electrical braking capability.

Common DC bus:

The additional investment cost of braking chopper andresistor including the space needed for those compo-nents if needed in a common DC bus solution.The investment cost difference between common DCbus solution and the respective single drive solution.

The life time cost calculation supports the purely economicdecision in making an investment. The price level of en-ergy as well as the price of drives varies depending on thecountry, utility, size of company, interest ratio, the time theinvestment is used and the overall macroeconomic situa-tion. The absolute values of prices given in the followingexamples are solely used to illustrate the calculation prin-ciples.

Case 1 - Occasional braking

Consider the following application case:The continuous motoring power is 200 kW at a shaft speedof 1500 rpm. In the event of an emergency stop commandthe application is required to ramp down within 10 sec-onds. Based on the experience of the process an emer-gency stop happens once every month. The inertia J ofthe drive system is 122 kgm2. When the emergency stop isactivated the load torque can be neglected.

Calculating the braking torque needed for the motor:

4.3 Calculatingthe life cyclecost

The typical torque value for a 200 kW, 1500 rpm motor isabout 1200 Nm. A normal AC motor instantaneously con-trolled by an inverter can be run with torque at 200 % ofnominal value. To achieve higher torque values a propor-tionally higher motor current is also needed.

(4.2)


The braking power is at its maximum at the beginning ofthe braking cycle.

The braking chopper and resistor have to withstandinstantenously the current for a power of 300 kW. The av-erage braking power is calculated below.

Cost of resistor braking:The braking chopper needed is for a maximum brakingpower of 300 kW. If the drive has a power limitation func-tion the braking resistor can be dimensioned according tothe 150.3 kW. The additional cost of the braking chopperand resistor is 4000 Euros.The braking resistor requires 0.4 m2 additional floor space.The cost of floor space is 500 Euros/m2.

Due to the small total heating energy and emergency useof braking, the cost of additional cooling is considerednegligible.

The total additional investment cost consists of:

Braking chopper and resistor in cabinet, 4000 Euros.Floor space 0.4 m2 * 500 Euros/m2, 200 Euros.

The total cost of wasted energy during one braking is:

In this case the cost of braking energy is negligible.

Cost of 4Q drive:The additional cost of a respective investment for electri-cal braking with anti-parallel thyristor bridge in compari-son with a drive with braking chopper is 7000 Euros. Asexpected, the energy savings cannot be used as an argu-ment to cover the additional investment required.

(4.3)

(4.4)

(4.5)

(4.6)

26 Technical Guide No.8 - Electrical Braking


(4.7) 8

Case 2 - Crane application

Consider following application case:Crane with hoisting power of 100 kW. The crane needs fullpower on both the motoring and generating side. The long-est hoist operation time can be 3 minutes. The average onduty time over one year for the hoist is 20 %.

Cost of resistor braking:The braking chopper and resistor have to be dimensionedfor continuous 100 kW braking due to the 3 minutes maxi-mum braking time. Typically the maximum braking chop-per dimensioning is made for a braking time of 1 minute in10 minutes.

Braking chopper and resistor in cabinet 7800 Euros.

The mechanical construction of the crane allows havingcabinets with braking chopper. No extra cost due to floorspace.

It is assumed that for 50 % of the duty time the craneoperates on the generator side, i.e. an average 2.4 h/day.The total cost of wasted energy is:

Cost of 4Q drive:The IGBT 4Q drive is recommended for crane applications.

The additional investment cost for electrical braking withIGBT input bridge in comparison to drive with braking chop-per is 4000 Euros.

The direct payback calculation indicates that an additional4000 Euros investment brings the same amount of energysavings during the first year of use.

Case 3 - Centrifuge application

Consider the following application case:Sugar Centrifuge with 6 pole motor 160 kW rating. Themotor needs full torque for a period of 30 seconds toaccelerate the charged basket to maximum speed of1100 r/min, centrifuge then spins liquor off the chargefor 30 seconds at high speed. Once the charge is drymotor decelerates the centrifuge as fast as possible toallow discharge and recharging.

27Technical Guide No.8 - Electrical Braking



In a batch cycle the charge, spin and discharge times arefixed, so the only opportunity to increase production is toincrease the rates of acceleration and deceleration. This isachieved by using an IGBT 4Q drive as the DC link voltagecan be boosted for operation in the field weakening range(1000 to 1100 r/min). This can save around 3 seconds percycle, therefore reducing cycle time from 110 seconds to107 seconds. This allows an increase in throughput mean-ing that the productivity of the process is improved. Thecost premium for IGBT is 10 %.

Chapter 5 - Symbols and Definitions

(5.1)


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29

AC: Alternating current or voltage

B: Friction coefficient

C: Constant or coefficient

cosφ: Cosine of electrical angle between the fundamentalvoltage and current

DC: Direct current or voltage

DPF: Displacement Power Factor defined as cosφ1, whereφ1 is the phase angle between the fundamentalfrequency current drawn by the equipment and thesupply voltage fundamental frequency component.

I: Current [Ampere, A]

J: Inertia [kgm2]

n: Rotation speed [revolutions per minute,rpm]

P: Power [Watt, W]

PF: Power Factor defined as PF = P/S (power/voltam-pere) = I1 / Is * DPF (With sinusoidal current PF isequal to DPF).

T: Torque (Newton meter, Nm)

t: Time

THD: Total harmonic distortion in the current is defined as

where I1 is the rms value of the fundamentalfrequency current. The THD in voltage may becalculated in a similar way.

U: Voltage [V]

W: Energy [Joule, J]

ω: Angular speed [radian/second, 1/s]

Chapter 6 - Index


AAC power 7

Bbraking chopper 11, 12, 15, 16,17, 23, 24, 25, 26, 27braking power 7, 11, 12, 13, 15,17, 22, 23, 26

Ccentrifuge 27common DC 22, 23, 25constant torque 8, 12conveyors 12cosφ 7, 18, 29crane 12, 27

DDC injection braking 13DC power 7direct torque control 13, 20

Eenergy storage 14, 15

Ffans 12flux braking 13, 14four-quadrant 5friction 8, 9, 12

Hharmonic distortion 18, 29

IIGBT 18, 19, 20, 21, 22, 24, 27, 28impedance 18, 20inertia 9, 10, 25, 29inverter 13, 15, 16, 19, 20, 23, 25

Lline converter 19, 20

Nnatural braking 10, 11, 12

Oover dimensioning 12overvoltage control 15

Ppumps 12

Qquadratic torque 8, 12

Rrectifier 13, 14, 17, 22, 23

Ssingle quadrant 5, 8, 21, 23

Tthyristor bridge 17, 18, 26two-quadrant 5


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