3.4 Primary Commissioning Tests with the Generator
373
7UM62 Manual
C53000-G1176-C149-3
F.No.
„
“ must appear. When performing the test, keep in
mind that the zero voltage is calculated from the three phase voltages and converted
on the secondary side to the phase-to-phase voltage (equivalent to
√
3 U0). The value
thus obtained is the same as for a broken delta winding.
Blocking by
Overcurrent
If the above measurement have been successfully performed, and the measured
phase currents were plausible, it can be assumed that the current measurement works
correctly. You only need to check the correct setting in the protection function (address
=
). The pickup values are checked by injecting a current by
means of some secondary test equipment (CTs need not be disconnected).
•
After completion of the tests, disconnect the test source and the protected object
(shut down generator)
•
If parameters have been changed for the tests, restore the settings required for op-
eration.
•
After completion of the earth fault protection tests, switch the earth current differen-
tial protection to be operative.
3.4.5
Checking the Voltage Circuits
General
The voltage circuits of the machine are checked to ensure the correct cabling, polarity,
phase sequence, transformer ratio etc. of the voltage transformers - not to check
individual protection functions of the device.
Earthing of the
Voltage
Transformers
When checking the voltage transformers, particular attention should be paid to the
open delta windings because these windings may only be earthed in one phase.
Preparation
Set the overvoltage protection function to about 110 % of the rated generator voltage
and give the trip on excitation.
Switch frequency protection (address
4201
) and overflux protection (address
)
to
Block relay
.
Check in the unexcited condition of the machine with the help of remanent voltages,
that all short-circuit bridges are removed.
Note on Testing
The checks of all voltage transformer circuits (protection, measuring, metering etc.)
are carried out with about 30 % of the rated transformer voltage. Tests with generator
voltages of more than 30 % are only required when the idle characteristic is measured
for the first time.
The measuring circuit supervision of the rotor earth fault protection (see below) can be
checked when testing the voltage circuits, or after the synchronization.
Amplitudes
Read out voltages in all three phases in the operational measured values. They can
be compared with the actual voltages. The voltage of the positive sequence system
U
1
must be approximately the same as the indicated phase voltages. If this is not, the
voltage transformer connections are incorrect (crossovers).
Phase Rotation
The phase rotation must conform with the configured phase sequence (address
under
Power System Data 1
); if it does not, an indication “
Fail Ph.
