ServiceGenerators

Power Generation

SIPOLTransistorized Excitation Systemsfor Synchronous Generators

Excitation Systems

Operating Characteristics Standard circuit

SIPOL

SIPOL fitted in a cubicle

High availabilityReliabilityDigital control facilitiesVery good control characteristicsCompact design and easy installationLow maintenanceShort delivery timesSmall space requirements

SIPOL is an excitation system for synchronous generators with exciters androtating-rectifier diodes. It can also be connected directly to the sliprings ofthe generator. Thanks to its versatile usability and easy installation, thisexcitation system is suitable for use in small industrial-, steam- and hydropower plants and lends itself especially to the modernization of existing plant.

The power part exists of a transistorized chopper and is connected to the fieldwinding of the exciter or the generator sliprings. The rotor circuit is protectedagainst overvoltage with a protection feature connected in parallel to the rotor.

The excitation power of the standard excitation systems is supplied either froma permanent-field pilot exciter (AC or DC), from a separate excitation transformeror from an auxiliary winding. The clamping bolts of the laminated stator coreform the auxiliary winding, e.g. .The excitation transformer may be connectedeither to the terminals of the synchronous generator or to the station servicesystem. Further redundant incoming feeders are possible, e.g. through stationbattery or an uninterrupted power supply.

The low mounting space and the various standard software functions of thedigital open- and loop control make the SIPOL system particularly suitable forthe modernization of existing excitation systems.

That is how the modernization of existing excitation systems can be done veryquickly.

Mechanical Design

The SIPOL excitation system is completely wired, fully tested and fitted on ametal mounting plate ready for installation in a suitable cubicle. Optionallypossible is an installation in a standard cubicle specially designed for equipmentcomprising open loop and closed-loop controls and power electronics devices.

Modular design and easy accessibility of all components facilitate all settingand optimizing operations. The dimension of the mounting plate is 580 mmwide by 350 mm deep, at a height of 700mm.

2

SIPOL mounted on a metal sheet

SIPOL Standard Components

SIPOL

Transistor chopper (1) Automatic voltage regulator (2) for controlling the voltage at thegenerator terminals and the field current regulator (3) for themanual channel.The station battery can provide the excitation power (E) by thestation service system, by an auxiliary winding, by a separateexcitation transformer or by a permanent-magnet pilot exciter.Optional redundant feeders, e.g. from the station battery to theexcitation system ensure high availability of the excitation system.

Main components:

3

The excitation system SIPOL is suitable for various types of engines:brushless exciter with rotating-rectifier diodes (5) and (7), directcurrent exciter (6) and for direct excited engines (8).The input power for the transistor chopper regulator comes froma rectifier and DC link.De-excitation of the generator is by means of the integral fielddischarge resistor.

8

GE

7

G6

2/3 1

E

E

E G5

Mode of operation

SIPOL

Closed-loop controlAutomatic Voltage Regulator(Automatic control system)The actual value of the generator voltage is compared with anadjustable generator voltage setpoint. The resulting signal iscompared with the output of the excitation limiter and taken tothe input of the PI voltage controller. The PI voltage controllerwith adjustable gain and time response provides an output signalwhich is applied to the setpoint input Iref of the secondary fieldcurrent controller. The output of this controller governs thegeneration of the frequency-modulated driving pulses for thepower transistors of the associated output stage, which is operatedwith a clock frequency of about 2,5 kHz. The DC current flowsthrough the phase U and W of the transistor power circuit.

Automatic cos ϕ or reactive power regulator at the generator leads(Automatic control system)The cos ϕ regulator compares the actual value with an adjustablecos ϕ reference value. In case of a deviation the reference valueof the voltage regulator is adjusted until the deviation is reducedto zero. In isolated or no-load operation of the generator theoperation mode of the automatic control system is switched overfrom cos ϕ regulation to voltage regulation.

Manual control system(Excitation current regulator)The P-action control amplifier of this regulator receives a filteredsetpoint signal that is compared with the actual value of the fieldcurrent. The output signal controls the frequency-modulationdrive circuit for the power transistors of the associated outputstage.

Of the three control systems the automatic one is normally inoperation, even during starting and stopping of the electric set.The automatic control system includes the measuring and setpointdevices and the control and monitoring circuits for the followingfunctions:

Generator voltage regulationFast secondary control and limitation of the output current ofthe field current chopper regulator and/or field-forcing limiter.Limiting controller for the under-excited range (minimum-excitation limitation)Delayed high limiting control for the over-excited range(maximum excitation limitation)Delayed generator current limiter(stator current limitation)

OptionsRedundant power supplyMounting in a cubicleCos - ϕ - or reactive power regulator at the supply pointReactive Power Joint Control of several generatorsDiode failure detection

Commissioning modeThe manual control system is designed as excitation currentregulator which permits generator characteristics to be recordedduring commissioning and inspections, and also short-circuitoperation of the generator to be carried out for setting theprotective relays. When the automatic voltage regulator isfaulted, it can also be used for the operational adjustment of thegenerator excitation.

Follow-up controlThe setpoint value of the field current controller is continuallyupdated during operation on the automatic control system, thusensuring rapid and nearly bumpless changeover to manualcontrol in the event of a fault. Automatic switchover takes placewhen the internal excitation supervision operates or on cases ofa fault in the generator voltage aquisition.

4

PMU operator control andparameterizing unit of the powercircuit

SIPOL

During generator operation, it is necessary to observe thepermissible combinations of active and reactive power, whichcan be seen from the capability diagram.

LMO Limit characteristic of the underexcited rangeOP Limit set by the stator temperature risePQ Limit set by the rotor temperature rise

Similar characteristics with reversed active-power flow apply tomotor operation of the generator.

For ensuring the operation of the generator within the limits thefunction over- and underexcitation limiter can define 10 pairs ofvalue. This pairs (X= reactive power actual value and Y= associatedpermissible active power value) reproduce the characteristic dataof the generator.

Limiting controllers

Limit characteristics of a synchronous machine in generator operation

Minimum excitation limiting

Overexcitation limiting and secondary field current limiting

5

The underexcitation limiter corrects the reactive power by raisingthe machine voltage as necessary to ensure that, in case of anexcursion beyond the limit characteristic L-M-O, the operatingpoint is returned to that characteristic before the machine istripped by the underexcitation protection.

The overexcitation limiter ensures that, in the overexcited range,the operating point always keeps within capability curve sectionP-Q of the generator. In response to system voltage drops causedby high reactive power requirements, switching manipulationsor faults, the voltage regulator raises the excitation level so as tokeep the generator voltage constant. The overexcitation limitingdevice acts as a safeguard against thermal overloading of therotor.

The overexcitation limiter admits excitation current values betweenthe maximum continuous current and the maximum excitationcurrent (field forcing) for a limited period of time so that thegenerator can back up the system in response to short-time systemvoltage dips.

The secondary excitation current limiter (field-forcing limiter),in contrast, has the task of limiting the excitation current to themaximum permissible value as quickly as possible.

The stator current limiter ensures the delayed limitation ontoworking points, within the N-P range of the generator powerdiagram. The main task of the stator current limiter is to preventthe generator stator from thermical overload, which can be causedby a high reactive power at increased active power. The statorcurrent limiter also permits increased excitation values for alimited period so that the generator can back up the system.

Max. turbine-output

Overexcited

Active Power

Underexcited

Reactive Power

O

PN

M

L

Q

Active Power

Max. turbine-output

Reactive Power

Underexcited

M

L

O

N

Excitation current IE(Rated Value)

40

30

20

10

1 1.1 1.5

Subordinate excitationcurrent limitation

Overexcitationlimitation with failoverto MANUAL

t(s)

Automatic control

Each operating condition of the excitation system are all supervisedand indicated.

The internal monitoring routine makes the following signalsavailable at the cubicle terminals:

Fault with Protective Off commandFault in automatic control system and switchover to manual control systemGroup alarm triggered by various internal fault signals causingstarting lockout.

Additionally following operating signals are available for externalindication.

Excitation is onExcitation is offAutomatic Voltage Regulator is onExcitation Current Regulator is onCos ϕ – or VAR Regulator is onLimiters are active

Further more detailed signals are optionally possible.

SIPOL6

When driven to maximum output, the chopper regulators providea voltage higher than required for exciting the generator to itsceiling current. This overvoltage on the field winding shortensthe time required for reaching the ceiling current in that itsubstantially accelerates the excitation build-up.

The output current of the chopper regulator for the manual controlsystem is limited by the maximum value of the setpoint setter.

The output current of the chopper regulator for the automaticcontrol system is influenced by the integration limit of the PIvoltage controller. This reference variable corresponds to thevoltage that gives the required field current.

Driving the transistor chopper to a high output voltage in order to obtainfaster exciter response.UE = Chopper output voltage (equivalent to excitaiton voltage)lE = Chopper output current (equivalent to excitation current)lEO = No-load excitation currentlEN = Rated-load excitation currentlEmax = Ceiling current1 = Output current without field-forcing limitation2 = Output current without overdriving

Overexcitation and field-forcing limiter

IE UE

IEmax

IEN

IEO

UE

IE

Time in s

2

1

SIPOL

Power circuitThe power circuit uses transistor chopper regulators,which provides the necessary excitation power viaa DC link.

The field voltage is adjusted by varying thepulse/pause ratio and the field circuit resistancecauses the field circuit to vary accordingly. Thefield current is measured in the output stage andthe signal is converted for the field currentcontroller.

De-excitationDe-excitation of the synchronous generator isnecessary for shutdown and when a protectivedevice of the machine itself or of the unit trans-former operates. Therefore the transistor chopperis blocked. The magnetic energy stored in the fieldis returned to the DC link via the diodes in thechopper circuits. Additionally the power circuit isdisconnected from the power supply. This ensuresvery rapid de-excitation of the generator.

7

Principle connection of the transistor power part

Clock frequency about 2,5 kHz. Variable pulse/pause ratio. Chopper output voltage asaffected by the driving pulses.Excessively high voltages are prevented by parallel-connected varistors.

Rectifier Smoothing Adjuster

Output

Control

P

N

L1

L2

L3

+ + + + + + + + +

positive zero negative

-220 V

0

+220 V

- - -------

meters can be changed easily by selecting the correspondingparameter in the parameter list. It is possible to choose betweena complete parameter list, pre-defined parameter lists withselection of parameter for a special application (e.g. input/ out-put) or a user defined parameter list by entering the interestingparameter numbers. A complete upread of parameters allowseasy documentation.

SIPOL

PC Tools

8

The operator friendly software tool SIMOVIS/DriveMonitorguarantees simply commissioning of the SIPOL. Through a serialinterface the voltage regulator can be connected with the PC foreasy configuration.

Customer friendly ConfiguringThe SIMOVIS/DirveMonitor software for Microsoft Windows9x/2x/NT allows the complete parameterization of the SIPOL.Actual values can be monitored in the parameter list and para-

The trace recording function contains followingfeatures:

Monitoring of up to 8 analog signalsMonitoring of 16 binary signals per unused analog signal (e.g. 32 binary and 6 analog signals)Maximum recording time of 280s at a maximum sampling rate of 280ms or 1.4s at minimum sampling rate of 1.4ms Freely adjustable sampling rate between 1.4 and 280ms in stepps of 1.4msFault recording is automatically triggered by programmable fault signals (triggered by binary signals e.g. faults or by comparing an analog value (condition: </>/=/<>) with a predefined value)Adjustable pre-trigger between 0% (no pretrigger, only future)and 100% (only past, no future)

SIPOL

Trace

9

Trace is an add-on for SIMOVIS/Drive Monitor that permitsvisualization of recorded data. You can also store the data readout of the device and open it again later. It is also possible toimport such data into text processing programs, such as MicrosoftWord, or into spreadsheet programs, such as Microsoft Excel.

You can perform simple measurements of amplitudes and instantsusing two moveable cursors.

SIPOL10

Function Plan

Dimension Drawing

350

15

Side View

580

LKG50037

-A300 -U305

LKG50037

-L101

LKG

50

03

7

LKG

50

05

0

LKG50050

-X0 -X1 -X4 -X3 -X2

-U1

00

, -U

10

1, -

U1

02

-K1

01

-Q1

01

-Q2

01

-Q2

02

-U1

03

-V3

01

M2L+

32

03

20

560

700

600

500

400

300

100

200

0

0 10

0

20

0

30

0

40

0

60

0

50

0

70

0

23 23

30

9,2

Front View

LKG50037

Generatorvoltagesetpoint

Generatoractualvoltage

Static activeand reactivepower

LimiterVAR/PF-regulator

Generatorvoltagesetpointgeneration

Trackingof setpoint

Excitationcurrentsetpoint

SwitchoverAVR/ECR

Field currentregulator

TransistorcontrollerDeexcitation

U>>

24V DCBattery

Mainexciter

Generator protection

Control room

Power supplyPilot exciter (DC/AC)Power plant batteryor station service

Current transformer

Voltage transformer

UG

IG

L1 L2 L3Control room

Automaticvoltageregulator (AVR)

Control room

Excitationcurrentregulator(ECR)

Controlroom

AutomaticSwitchover

Transistor chopper

DC-intermediatecircuit PG scope of supply

Technical Data

SIPOL11

Gersthofen hydroelectric power plant; Lech Elektrizitätswerke AG:5 x 3MVA generators. Although the space was very restricted, the SIPOLtechnology was integrated without any problems into the existingfacility.

SIPOL

Auxiliary Power

DC voltage 24VDCMaximum power consumption < 100 W

Insulation test voltage 500 V/1 min

Main Power

AC voltage 1- or 3 phase approx. 90...400 VACRange of frequenz up to 400 HzDC voltage approx. 90...300 VDCInsulation test voltage 1500-2500 V/1 min

Measuring input

Generator voltage, 3-phase 100...120 VPower consumption max. 3 VA

Generator current, 1-phase 1 AMax. power consumption 0,5 VAGenerator current, 1-phase 5 AMax. power consumption 1,5 VAInsulation test voltage 2500 V/1min

Current output

Continuous current 15 ADC Short time (10s) 20 ADC

11 digital inputs Input voltage 24VDC

8 digital outputsMax. switching voltage 250 V AC/DCMax. switching current 8 A

Analog output

Output range 0...10 V oder0/4...20 mA

Control accuracy

Voltage regulation 0,5%

Customs tarif no.: 8537 10 10AL: N; ECCN: N

Maximumambient temperature

During operation 0°C bis +40°C

During storage / transport -25°C bis +70°C

Site altitude ≤ 1000m above NNwithout power reduction possible

Standards The SIPOL excitation systemis rated and designed according to IEC-, EN-, DIN-, VDE-, IEEE-421- standards. Service and maintenance of the excitation system SIPOL can be executed according the VGB4- instructions.

Published by and copyright 2004:Siemens AGPower GenerationFreyeslebenstrasse 191058 Erlangen, Germanyfax: 0049-9131-18-4369www.siemens.com/powergeneration

Subject to change without prior notice

The information in this document contains generaldescriptions of the technical options available whichdo not always have to be present in individual cases.The required features should therefore be specified ineach individual case at the time of closing the contract.

Excitation Systems