3 Installation and Commissioning
374
7UM62 Manual
C53000-G1176-C149-3
Seq.
“ will be output. The allocation of measuring quantities to phases must be
checked and corrected, if necessary. If signification deviations are found, check, and
if necessary correct, the voltage transformer circuits and repeat the test.
It is also possible to use for this check the operational measured value of positive-
sequence component U
1
of the voltages: U
1
≠
U
L-E
indicates a wiring error.
Measuring Circuit
Supervision of the
Rotor Earth Fault
Protection
If the sensitive earth fault protection is used for rotor earth fault protection, the
measuring circuit supervision of that protection function can be checked with the
generator under voltage:
−
Start up the generator and excite it to rated voltage. Apply measurement brushes
if necessary. Inject a test voltage between the rotor circuit and the earth by
interposing the additional source device 7XR61. The earth current I
EE
that is
flowing now can be read out on the device among the operational measured
values. The value obtained is the capacitive spill current flowing in fault-free
operation.
−
(address
) should be set to about 50 % of this capacitive spill current.
It should also be checked that the set value
(address
) is at least twice
this measured spill current. Correct the set value if necessary.
Frequency
Protection
The frequency protection function is verified by a plausibility check of the instantane-
ous machine speed and the associated operational measured value that is indicated.
Overexcitation
The frequency protection function is verified by a plausibility check of the
instantaneous machine speed and the associated operational measured value that is
indicated.
The voltage tests are completed after the generator has been shut-down. The required
voltage and frequency protection functions are switched to be operative (address
:
=
ON
or
OFF
), (address
:
=
ON
or
OFF
),
(address
=
ON
or
OFF
) and (address
=
ON
or
OFF
). Partial functions can be switched to be inoperative by appropriate
limit value settings (e.g. f* set to rated frequency).
3.4.6
Checking the Stator Earth Fault Protection
The procedure for checking the stator earth fault protection depends mainly on
whether the generator is connected to the network in unit connection or in busbar
connection. In both cases correct functioning and protected zone must be checked.
In order to check interference suppression of the loading resistor, and in order to verify
the protected zone of the earth fault protection, primary tests are suggested, once with
an earth fault at the machine terminals (e.g. with 20 % of the rated transformer
voltage) and once with a network earth fault.
Instant. overexcitation
U
f
----
f
N
U
N
--------
⋅
=
U
Instantaneous machine voltage
U
N
Rated primary voltage of the
protected object
f
Instantaneous frequency, in
accordance with the machine
frequency in Hz
f
N
Rated frequency
