Synchronization of power station generator and power system – Testing the accuracy of a synchronizing deviceusing special EnerLyzer features

Boris Bastigkeit, OMICRON

Introduction

Is the synchronizing device set correctly? Are thegenerator voltage and frequency sufficiently adjusted tothe corresponding quantities of the power system? Is thesynchronization performed precisely at the ideal moment?How much is the deviation of the voltage, frequency andthe angle when the circuit breaker closes? What aboutthe values of the active and reactive power transients andthe compensation processes after the close occurs?Which harmonics are caused by this process?

These are possible questions occurring in context with thecommissioning of a synchronizing device. The quality ofthe synchronization process has a positive influence onthe generator lifetime. Conversely, malfunctions can resultin tremendous defects. [1], [2]

The new test module OMICRON Synchronizer isdedicated for testing of synchronizing devices. Thetransient recording feature of the OMICRON EnerLyzer,which is integrated in OMICRON's CMC 256 can helpanswer the questions mentioned above. This is pointedout by the following report dealing with thecommissioning of a synchronizing device for asynchronous machine in the power station Tavanasaoperated by NOK in Switzerland.

Figure 1: Engine room in the power station Tavanasa

Situation

Each of the four engine groups installed in the Tavanasapower station consists of a water-powered Pelton turbinehaving 2 runners with 2 nozzles each (head 479m, power45,000kW) and one generator (nom. power 60MVA,nom. voltage 13.5kV).The task was to upgrade the synchronizing devices. Perengine group one dual-channel system Synchrotact 4from ABB Industrie AG was used as the synchronizingdevice. The power system voltage (measured on thecorresponding generator bus bar) and the generatorvoltage were supplied to the synchronizing device usingpotential transformers. The synchronizing device wascontrolled by the station's automation.

Test and measurement tasks

The following test and measurement tasks wereperformed as part of the commissioning for thesynchronizing device for engine group 4 using the test set(transient recorder feature of the) OMICRON CMC 256.

• Secondary testing of the synchronizing devices.For more details refer to the chapter "First step ofcommissioning".

• Primary trials and quality assessment of thesynchronization For more details refer to the chapter"Third step of commissioning".

First step of commissioning:Secondary testing of synchronizing devices

The goal is to check the correct function of thesynchronizing devices and to determine possiblemalfunctions or parameterization (settings) errors. Thesynchronizing devices contain different sets ofparameters. One set of parameters is available for eachoperating mode of the engine group (normal mode,power system start up, stand-alone system).Each set of parameters must be checked separately.

For this purpose, NOK uses the test module OMICRONSynchronizer.

The test object (the synchronizing device) is connected tothe OMICRON test set as shown in figure 2. For dual-channel synchronizing devices the second channel of thesynchronizing device is driven in parallel.

Figure 2: Test set-up

The corresponding parameter settings (e.g. for parameterset 1: ±U=2V, ±f=100mHz, ∆Phi=15°el., CB residualtime=60ms) are entered as shown in figure 3.

Figure 3: OMICRON Synchronizer, parameter settingsfor parameter set 1

Then an "adjustment test" is performed using the testsoftware. This means that the OMICRON test systemreceives the control commands, which are normally sentfrom the synchronizing device to the voltage or speedregulator, and simulates the generator's response(controller characteristics du/dt and df/dt). Thus thesynchronizing device is tested under conditions as real aspossible.

In the V/f plane (refer to figure 4) for each quadrant onetest point was pre-determined outside of thesynchronizing window (±U>2V, ±f>100mHz).

Default Result

Quadrant U>, f< passedQuadrant U>, f> passedQuadrant U<, f< passedQuadrant U<, f> passed

It is only possible to pass these tests if the following twoconditions are fulfilled:

• The synchronizing device puts out sufficient controlcommands with a correct time period to thecorresponding actuating elements (this way thegenerator is lead into the permissible range of thesynchronizing window).

• The CB close command is put out by thesynchronizing device within the permissible range ofthe synchronizing window.

Figure 4: OMICRON Synchronizer with the 4 passed testpoints

The most important results are the voltage, frequency andangle differences of the 2 systems for the 4 test points.The following results were calculated by the OMICRONSynchronizer test module for the moment when thegenerator is connected to the power system, taking intoaccount the CB residual time:

Calculated test results when switching on the CB:

Testpt. ∆U ∆f −{}−∆ϕ

Quadrant U>, f< 480mV 27mHz 0,83°Quadrant U>, f> 390mV 70mHz 0,46°Quadrant U<, f< 360mV 68mHz 0,45°Quadrant U<, f> 870mV 33mHz 0,70°

Second step of commissioning:Further tests

During these tests the generator is not yet connected tothe power system (the CB is in disconnected position).The following tests were performed (the most importantitems are listed in short form, no claim to completeness;the OMICRON test set was not required for these tests):• Check of the entire wiring and signaling.• Generator bus bar disconnected on the primary side,

connected through, nominal voltage, check of thesecondary differential voltages (nominal voltage 0V)and the rotating field.

• Check of the values measured by the synchronizingdevice and the instruments.

• Circuit breakers for the potential transformer:Check of locking mechanisms when they are tripped.

• Check whether the synchronizing device is controlledcorrectly.

• Checks of the control commands and controllercharacteristics, behavior of the engine groupregarding this. Possibly required optimizations for theparameter settings.

• Repeated switching on of the CB in disconnectedstate in several initial situations as well as checks ofthe connection moments and the sequences in thecontrol.

Third step of commissioning:Primary trials and quality assessment of thesynchronizations

Up to now, all tests were passed. The actualsynchronization of the generator to the power system canbe performed.

In order to assess the quality of the first synchronizationwith the power system (primary trials) various measuringvalues are recorded using a transient recorder. Here, thefollowing is of particular importance:

• Level of the differential voltage when switching on(nominal value = 0V).

• Level of the reactive and active power transient afterswitching on.

• Power behavior after switching on.

Remark:Up to now, NOK created the power behavior recordsusing an old UV paper graph plotter together with specialtransducers. (Advantage: high measurement precision.Disadvantages: very time-consuming measuringarrangement, many devices required, high volume andweight of the UV paper graph plotter, UV paper isexpensive and fades, measured values are not available asdigital data, thus no evaluation on the PC possible, nospare parts.)

Now, this measurement task can be considerablyimproved and simplified using the OMICRON EnerLyzer(10 channel transient recorder integrated in theCMC 256) in conjunction with OMICRON TransViewwhich enables directly calculating the power from therecorded currents and voltages. In addition, the secondarytesting and the recording of the primary trial can now beperformed using one single device, the OMICRONCMC 256. Due to the automatic power calculation of theanalysis program OMICRON TransView, specialtransducers are also no longer needed. The recordedtransients can be stored to COMTRADE files and areagain available for analysis at any later point in time.

When setting up the test, please note that the powercalculation of OMICRON TransView always assumes a 3-phase system. Therefore it is necessary to additionallyrecord V2, V3, I2 and I3 apart from the following desiredsignals

CB close (binary signal, potential free)VR-E (voltage, secondary)VR-R (voltage, secondary)IR (current, secondary)

These additional channels are indeed parameterized in theOMICRON EnerLyzer but for recording they are short-circuited at the device. Therefore, during themeasurement V2, V3, I2 and I3 are zero. The powercalculated by OMICRON TransView corresponds exactlyto the power for phase R.

Figure 5: Connection diagram for recording the primarytrials

Figure 6: Test set-up for primary testing / The OMICRONCMC 256 used as a 10-channel transient recorder

The transient recording mode settings in the OMICRONEnerLyzer were as follows:

Figure 7: Settings in the OMICRON EnerLyzer

Sampling rate 3 kHzRecording time (pre-trigger) 5 secRecording time (after trigger) 20 secTrigger CB close command

A total of 4 synchronization’s were recorded. Below, anexact analysis of the first synchronization is described.

Display of the recorded voltages and currents as well asthe CB close command using OMICRON TransView:

Figure 8: OMICRON TransView, voltages, currents andCB close command

Calculation of the power behavior for the firstsynchronization using OMICRON TransView:

Figure 9: OMICRON TransView, power behavior of P, Qand S

The maximum value of the active power transient is0.35 MW. The value of the reactive power transient is 0.6MVAr and the apparent power transient is 0.7 MVA. Thiscorresponds to approx. 1 % of the rated generator power.Consequently the synchronization quality is high.

Measurement of the circuit breaker residual time andthe differential voltage when switching on thegenerator to the power system using OMICRONTransView:

Figure 10: OMICRON TransView, measurement ofcircuit breaker residual time and differential voltage

The measured circuit breaker residual time is 55.3 ms.

The peak value of the differential voltage when switchingon is approx. 2 V secondary. This corresponds to approx.170 V primary or 2 % of the nominal voltage.Consequently the synchronization quality is high.

The analysis of the synchronization is finished. Theanalysis of the other synchronization’s was performedsimilar to the described procedure.

Conclusions

The secondary testing using the OMICRONSynchronizer test module shows that thesynchronization device is able to bring the generator fromvarious non-synchronous conditions very close to thesynchronous point (the maximum measured differentialangle is 0.8°).

The recording of the synchronization’s using the 10-channel transient recorder OMICRON EnerLyzer in theCMC 256 can confirm the result from the secondarytesting.The very high synchronization quality is confirmed by theanalysis of the recorded transients and the calculationsfrom the analysis software OMICRON TransView.

The procedure described in this document used inconjunction with the commissioning of a synchronizingdevice provides high reliability for an optimum adjustmentand correct function of the synchronizing device.

Literature:

[1] VGB Technische Vereinigung derGroßkraftwerkbetreiber e.V: Fachkunde für denKraftwerkbetrieb, Elektrotechnik, Teil 1 und 2

[2] K.Albert, O.Apelt, G.Bär, H-J. Koglin: ElektrischerEigenbedarf, Energietechnik in Kraftwerken undIndustrie; VDE Verlag