Generator Test Procedures

1. Determination of the transient open-circuit time constant τdo´
Table of Content:
1 Objective.............................................................................................................
2 Scope..................................................................................................................
3 Referenced Documents.......................................................................................
4 Definitions and Abbreviations..............................................................................
5 Voltage Recovery Test .......................................................................................
5.1 Preparation......................................................................................................
5.2 Conduction of voltage recovery test ................................................................
6 Field Current Decay Test....................................................................................
6.1 Preparation.......................................................................................................
6.2 Conduction of test.........................................................................................
7 Evaluation of test ................................................................................................
8 Proceeding in case of deviations ........................................................................
1 Objective
This procedure defines the tests to be performed for the determination of the following
machine quantities:
- direct-axis transient open-circuit time constant τBdoB´
- direct-axis open-circuit subtransient time constant τBdoB´´
2 Scope
This procedure applies to all types of synchronous machines during final testing in the
work shop or at site. This test is performed as a type test, i.e. only on one machine out of
two or more units with same or almost similar design.
Two measuring methods may be used as convenient:
− Voltage recovery test
This method is preferably used on site with HYDRO-generators. It must be used with
generators having brushless excitation and when no temporary slip rings are mounted.
− Field current decay test with armature winding open-circuited
This test requires either static excitation or mounting of temporary slip rings for separate
excitation, since external circuit elements (like the short-circuit breaker and an eventual
current limiting resistor) cannot be inserted into the rotor circuit.
3 Referenced Documents
IEC 34-4, 42, 43 or 58, 59
EN 60034-4, 42, 43 or 58, 59
IEEE 115, 11.10.5 (Method 4) or 11.10.1.1 (Method 1)
HTUP GEN QC3 6119DEUTH Sudden three-phase short-circuit test
4 Definitions and Abbreviations
None
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2. 5 Voltage Recovery Test
5.1 Preparation
The voltage recovery test is initiated after disconnection of a sustained three-phase
short-circuit.
It is usually performed immediately after the three-phase sudden short-circuit test, using
the plant circuit breaker to open the short-circuit.
In our work shop this test has to be carried out as an individual test, since the short-
circuit maker available in the Weiz test field cannot be reopened under load.
Preparatory work is similar to the procedure for the sudden short-circuit test (see also
P GEN QC3 6119DE).
Activities for work shop test only:
- disconnect the power cables between the line terminals and the short-circuit maker
- connect power cables between the line terminals and the circuit breaker used for this
test (Note: this c.b. must be capable of being reopened under load).
For site test only:
- connect power cables between the line terminals and the circuit breaker (this is not
necessary when the plant c.b. can be used)
For both work shop and site tests:
- install measuring devices. Recording instruments will be the same as used for the
sudden short-circuit test.
- connect output signals of armature p.t´s and one armature c.t. to the recorder
- calibrate and set trigger of the recording instruments to expected levels
5.2 Conduction of voltage recovery test
- operate the unit at rated speed in a sustained three-phase short-circuit condition, with
the excitation set according to approx. 0,5 Un no-load voltage
- reopen the circuit breaker to inititate the voltage recovery
- record one voltage and armature current until steady state has been reached (usually
after about 30 s).
- review the osilloscope data to make sure that data was captured correctly.
6 Field Current Decay Test
6.1 Preparation
The measuring circuit is set up according to fig. 1. Essential circuit elements are:
- Closing/opening contacts (S1/S2) of the switch activated by the same shaft.
- Slip rings (main or temporary)
- Measuring shunt for field current
- Static excitation equipment: The de-excitation resistor must be short-circuited for the
duration of this test. The test may be performed in current regulation mode.
6.2 Conduction of test
The machine is driven at rated speed with armature winding open-circuited and excited
to rated voltage. In normal operation, S1 is in closed position and S2 open. The
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3. excitation winding is then suddenly short circuited by closing first contact S2 and
immediately afterwards opening S1.
Decaying armature voltage, excitation current and slip ring voltage are recorded till
steady state.
Note: Activating EMERGENCY OFF of the static excitation equipment will trip the de-
excitation contactor and normally would insert the de-excitation resistor into the circuit.
However, this is shorted for this test and thus will also completely short-circuit the field
winding.
Since the excitation circuit must never come open, the de-excitation contactor will at the
same time bridge the excitation equipment for the short time element of the switch, so
that it will not take harm. The excitation will be automatically down regulated to zero.
7 Evaluation of test
− Mathematical or graphical evaluation follows the procedure given in the pertinent
standard.
− Evaluation procedure both for transient and subtransient time constants is analogous
to the evaluation of the sudden short-circuit test.
− Evaluation procedure is analogous for both measuring methods.
Note: After elapsing of 3 τBdoB´, the transient voltage component will have decreased to
approx. 0,05 of its initial value. When plotting the envelope of the decaying characteristic
against time on a semi-log scale, it may be more comfortable and accurate to use this
ordinate rather than the one after 1 τBdoB´ which must be interpolated to 0.368.
8 Proceeding in case of deviations
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4. Any nominal value, minimum value, maximum value, tolerance etc given in an instruction
is intended to serve for quality control purposes only. In the case of deviations, a
nonconformity report has to be written according to PNG Power Standard
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