vvvf drive-features, commissioning procedure and …125-132).pdf · m ramana rao 1*, p vinnarasi...

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Int. J. Elec&Electr.Eng&Telecoms. 2015 M Ramana Rao et al., 2015

VVVF DRIVE-FEATURES, COMMISSIONINGPROCEDURE AND CHALLENGES

M Ramana Rao1*, P Vinnarasi Ponnury1, V Parvathy1 and S Magesh1

*Corresponding Author: M Ramana Rao

INTRODUCTIONA VVVF drive is acronym of variable voltagevariable frequency drive. This is a solid stateunit having capability to deliver power withvariable voltage and variable frequency. Itshall be possible to run motors at differentspeeds.

The speed of the motor shall be varied asper the process/functional requirement. Thesame can be achieved by using VVVf drive.Number of Drives are used in SPP, mainly toachieve micro speed in EOT crane and inother application like speed control of pumps,blowers, etc.

This paper deals with the basics of VVVfDrive, its advantages, the commissioningprocedure and selected case studies whichenumerates the challenges and the solution.Also apart from presenting normal Driveapplication, the extended application like

• Using a single Drive for two roller standequipments,

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Int. J. Elec&Electr.Eng&Telecoms. 2015

1 Faculty of Engineering, University Malaysia Sarawak (UNIMAS), Kota Samarahan 94300, Sarawak, Malaysia.

• Utilizing communication capability of Drivefor controlling and acquiring data withoutmulti core cable, CT and transducers.

Since we are handling, large no drives ofvarious capacities and various makes, wehave gained significant experience in thesedrives and few case studies are described inthis paper.

BASICS OF VVVF DRIVEWhy both voltage and frequency needs to bevaried?

We know that, Speed N =120 x f/P

where

N is speed of the motor

f is frequency of the supply voltage

P is number of poles of the motor.

The speed is proportional to frequency. Bychanging the frequency, we can vary the speed.But flux Ø = v/f. If frequency alone is changedby keeping the voltage constant, flux Øvaries,Speed also varies along with flux. We

Research Paper

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know that Torque is proportional to product offlux (Ø) and armature current (Ia). Since flux ischanging, the torque also changes. This isundesirable in maqny applications.

And also, If the frequency alone is reduced,the inductance of the motor coil will be verylow. (XL = 2fl) and therefore the motor windingdraws excessive current which may result toburning of the motor.

Hence we have to vary both voltage andfrequency to maintain constant flux in turnconstant torque.

Conversion of AC voltage to DC voltage isdone by diodes.

Inversion from DC voltage to Ac voltage isdone by Insulated Gate Bipolar Transistor(IGBT) in a simple VVVf Drive.

FEATURES AVAILABLE INVVVF DRIVEThe following features are available in VVVFdrives.

• Speed control with encoder

• Speed control without encoder

• Free blocks like Logic gates, timers,counters, etc., available for making thedifferent types of logics.

• Communication capability

• Different operating stations for control, i.e.,VVVF drive Panel, Terminal and throughcommunication like Profibus, etc.

Advantages and Disadvantages of VVVFdrive:

Advantages• Variable speed at motor shaft

• Conservation of power (In case of pumploads)

• Quick reversal (contactor is not required).

• Reduced wear of brake liners due toapplication of brake at low speed using Drive.

• Smooth acceleration and decelerationusing Ramp Up and Ramp down time toavoid sudden load on mechanical systemand smooth handling of loads withoutJerk.

• Due to absence of contactors, pitting ofcontact tips is avoided and maintenance isreduced.

• Good reliability and availability

• Reduction of inrush current

• Inbuilt protection like OC/SC

Disadvantages• Initial cost

• Harmonics generation

Figure 1: Block Diagram of VVVf Drive

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• Expertise is required for programmingduring commissioning and for rectifyingfaults.

VVVF DRIVES AT SPP, SDSCSHARNearly 150 no’s of various capacity of drivesare being handled at Solid Propellant Plant fordifferent application like

1. Handling equipment like crane (majorportion)

2. Pumps

3. Blowers

4. A P grinding mill

5. Rollers stand for rocket motor hard warerotation

6. Small capacity mixer used for sampleprocessing

7. Vacuum driers

The Capacity of drives available at SPP isranging from 0.75 k W to 132 kW of differentmakes.

SELECTION OF VVVF DRIVEThe major parameters to be specified/considered for selection of drive is givenbelow.

PROGRAMMING, LOGICBUILDING ANDCOMMISSIONING OF VVVFDRIVES• Power and control connections are to be

established.

• Drive is to bepowered from normal power

1. Motor Capacity Equivalent or one stepupper side can beconsidered

2. Type of application • Crane

• Pump

• Blower

3. No. of Motors to be Single drive/multioperated drive

4. Motor voltage 3Ø 415 V

3Ø 220 V

5. Input Voltage 1 phase/3 phase

6. Control station of VVVF Drive Paneldrive Terminal

Profibus

7. No of Inputs and Number of DIs/Dos/outputs required for AIs/AOsoperation

8. Communication ProfibusCapability RS 485

9. Line filters This is to be consideredfor not allowing theharmonics to source

10. load side chokes To improve the sinewave

11. Semiconductor fuses Suitable rating to beconsidered for VVVFdrive protection

Table 1

S.No.

Parameter to beConsidered for

Selection

VVVF Drive SelectionCriteria

• Factory reset is to bedone to VVVf drive.

• Quick commissioning is to be carried outas per the procedure which involves thefollowing steps.

– Motor data is to be entered as per nameplate details

– Frequency source is be provided

– Minimum and maximum frequency is tobe provided.

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– On/off selection location to bementioned, i.e., Drive Panel, Terminal,Profibus communication (SCADA)

– Ramp up/ramp down time is to beselected

– Types of control to be selected based onthe application of the motor, i.e., SensorLess Vector Control (SLVC)

– Closed loop control

– V/f control

– If closed loop control is selected,encoder is to be enabled.

– Motor data identification to be carriedout, i.e., acquiring equivalent parametersvalues from the motor. This is achievedby giving power to Motor for few secondsand VVVF drive will acquire relevant dataof the motor like equivalent resistance,inductance, capacitance, etc., and storein the memory.

– End of quick commissioning.

Assignment of Digital/Analog Inputs in theProgramme: This is to be carried out correctlyfor proper operation of the total system. Thephysical inputs from push button station (DI)or potentiometer (AI) for on/off and frequencyset point are connected to VVV drive. This isread by drive and accordingly it delivers theoutput to motor.

Assignment of Digital/Analog Outputs:For example, Building up of logic forexecuting a digital output for opening ofbrake is demonstrated here for logic buildingof EOT crane application. As an example,one typical DO assignment was explainedbelow.

(Digital Output Assignment)Mechanical Brake is one of the importantdevices in EOT crane operation. This Fail safeMechanical brake ensures safe handling ofloads without slip during EOT crane operation/power failures.

In conventional crane the brake logic issimple. The brake supply is tapped from Motorsupply and whenever the motor is energizedbrake is also energized and open. DuringMotor Off condition or during power failure, thebrake deenergizes and due to spring tension(Fail safe) holds the brake drum.

However, when using VVVf drive, the brakesupply cannot be tapped from motor for thesimple reason that the motor gets variablevoltage depending on the speed requirementbut the brake needs constant voltage for itsoperation.

The brake supply is extended from mains(drive input) through a contractor. The contactoris switched on using Digital Output (DO)command of Drive. The brake logic is built onthis particular DO.

When brake is released, then only motor willoperate and when motor stops, break has tohold the shaft of the motor, otherwise shaft willrotate due to inertia and load will be moved.Hence brake logic has to be given importancein view of safety. Hence, the logic building forbrake is very important.

The brake shall release only when motordevelops sufficient torque and closes whenmotor reaches near zero speed or nearer tozero speed condition.

The brake logic is built as follows:

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After completion of the above steps theVVVf drive is ready for operation and showsstatus as “Drive ready for operationparameter”.

After this, if “On” command +Frequency setpoint is given, the drive starts feeding themotor.

LESSONS LEARNTExperience gained with VVVF drives:

Incorporation of Micro Speed for3.2t EOT Crane with the Help ofVVVf Drive in AP Drying Facility atSPPThe creep operation for 3.2t crane wasincorporated in house with available spareVVVf drive of micro master of Siemens make.The drive was kept in FLP panel and all powerconnections were established. Programmingof VVf drive was carried out as per theprocedure. No load trials were carried outsuccessfully.

When Load testing was planned and ratedload was lifted, VVVf drive was workingnormal, But when down operation wasperformed; drive tripped on “DC link voltagehigh”. This had happened due to less value ofdynamic braking resistor connected to theDBU.

Remedial Action: The DBR of correct ratingwas provided by trial and error method bymaking series and parallel combinationdynamic braking resistor, it could able toperform the Down motion without any trip. Theapproximate resistance value used is 2.5.

Checks are to be Done DuringTaking Over of the VVVf DriveBased Cranes/SystemsDuring handing over of the crane at verticalmixer-3, the functioning of encoder was erraticand was not working. The crane erectionengineer has disabled the encoder and shownthe operations of all motions.

Figure 2: Logic Building for Brake Opening

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We have checked the encoder parametersand found that the encoder was disabled andshown him. Then he replaced with new one.Encoder enabling parameters in master driveof Siemens make are as follows.

input power to drive was interrupted andrestored and the hoist up command wasexecuted, drive got tripped under parameterNo. F008 which is “DC link voltage low” butVVVf drive has given command for brake toopen.

This type of problems can be eliminated ifproper care is taken during commissioning.This problem was rectified by providing theproper parameter in the drive logicprogramme.

Compatibility Checks were CarriedOut for Various Types of VVVfDrives to Suit with Siemens makeDrivesWe have different capacities and differentmakes of VVVf drives like Siemens, ABB.Yaskawa, and Allen Bradley, etc.

Out of the above brands, 90% of VVVfdrives are of Siemens make and others are10%. We have procured spare drives ofSiemens make. To eliminate the investmentof capital on maintaining spare drives for 10%of other brands, we have carried outcompatibility checks with Siemens drives.

During failure of any of the above drives,we can use Siemens make drives as spareand put the system in normal operation.

This we could achieve by makingcompatibility checks with Siemens VVVfdrives.

• The steps to achieve the same are

• Power rating is to be checked.

• Number of Control inputs (DI) and controlout puts (DO) are to be checked.

P65 5 Setting mode

P100 4 Speed control mode

P130 11 Pulse encoder

P151 1020 No. of pulses

P60 7 User mode

Table 2

ParameterNumber

Setting ofIndices

Description of theSetting

P65 5 Setting mode

P100 1 V/f mode

P130 10 Without encoder

P60 7 User mode

Table 3: Encoder Disabling Parameter

ParameterNumber

Setting ofIndices

Description of theSetting

By making the encoder disable, the erectionengineer has run the crane. Since encoder isphysically connected to the motor shaft androtates along with the motor, we assume thatencoder is in line. If we are aware of theencoder enabling parameters, this type ofproblems can be eliminated.

Assignment of Brake LogicParameter not Proper DuringCommissioningIn one of EOT cranes, brake logic programmewas not properly assigned by thecommissioning engineer of VVVf drive. Eventhough the DO was not assigned properly, dueto other hardware interconnections the logicwas functioning normal. During T&E, when the

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• Number of AI (from potentiometer) and AO(for meters) to be checked.

• Weather the required logics can be builtwith available Drive.

Using the above steps, the programme wasgenerated with Siemens make drives,compatibility of I/Os have been checked andprocedure has been generated and kept ready.

The advantages of above exercise are asfollows.

• Elimination of capital cost on the investmentof spare drives for all models/makes.

• Time required for replacement of drive willbe minimized since we have laid down theproper procedure.

• Confidence level of maintenance personnelwill be improved.

The following compatibility checks ofvarious drives have been carried at differentfacilities of SAPP.

Two Rollers Stand Needs to beRun with One VVVf Drive at HILFacilityS200 roller stand is having a VVVf drive ofcapacity 9.3 kW at HIL Facility, SPP. RecentlyS139 roller stand has been added to the facilityto make rubber lining to S139 segments. Bothmotors are of 9.3 kW capacity but having

different speeds. But this Roller stand was nothaving Drive to have variable speed.

As variable speed was the processrequirement to achieve better results, it isplanned to utilize the existing drive withoutresorting to procurement.

The available Drive is having capability tostore the logics in two different indices. Bothindices can be operated as per the selection.Using this feature.

For each motor we have generated aprogramme according to name plate detailsof the motor, process requirement and storedthe programme in different indices.

By using a selection bit, the respectiveprogramme will be loaded to VVVf drive asper selection. This is achieved with the help ofdigital inputs combination.

Data Acquisition and ControlThrough Communication Capabilityof VVVf DriveThe data related to VVVf drive can be retrievedby utilizing communication provision betweenVVVf drive and PLC, SCADA. The control ofVVVf drive can also be done by this provision.With this, parameters like current, voltage,frequency, DC link voltage, etc., of VVVf drivecan be monitored and logged without runningcontrol cable and without CT, transducer and

1. AP Grinding Feed motor 0.75 kW ABB 1.1 kW Siemens2.2 kW

2. HIL Roller stand 9.3 kw ABB 9 kW Siemens 18.5 kW

3. ISPF 100 L mixer 9.3 kW Yaskawa-11 kW Siemens 18.5 kW

4. ISPF 4 L mixer 0.75 KW Allen Bradley Siemens1.1 kW

Table 4: For Example

S. No. Facility Name Equipment Name Motor Capacity VVVF Drive makeand Capacity

Compatibility Checkwith make of

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control cable. This is useful in analyzing themotor/VVVf drive performance.

Maintenance of Spare Drives-Proper Care Needs to be TakenIf we have spare VVVf drive, we need to putthe spare drives in operation periodically, i.e.,the spare drive has to be kept in operation andthe removed VVVf drive can be kept as spare.This will ensure the health of the drive. If thispractice is not followed, and the drive is storedfor long time (more than a year), the drive needsFORMING which is applying the AC voltagegradually from zero to till it reaches ratedvoltage.

CONCLUSIONVVVf drives are having many advantages. Butproper care needs to be taken duringcommissioning as well as operation andmaintenance. Improper parameterization and

mishandling causes malfunctioning of the VVVfdrive and in turn damage/accident may occurto the equipment, personnel, properties, etc.Proper care needs to be taken while buildingthe logics for brakes, etc., which shall supportfor safe operation since we are handlinghazardous/explosive nature of materials.

VVVf drives of various capacities havebeen commissioned in all SPP facilities,successfully. In the last 5 years duringprocessing/production of solid rocket motor inSPP, the drives have been effectively used forsafe handling of propellant materials,segments, etc. Also capability of VVVf drivehave been optimally utilized during troubleshooting analysis of its systems.

Electrical team of SPP is fully conversantwith and tackle any problem associated withVVVf drives in SPP.

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