3 Installation and Commissioning
384
7UM62 Manual
C53000-G1176-C149-3
3.4.8
Checking the Sensitive Earth Fault Protection when Used
for Rotor Earth Fault Protection
If the sensitive earth fault protection is used for rotor earth fault protection, it must first
be set to
Block relay
under address
An earth fault is simulated via a resistor which is roughly equivalent to the desired trip
resistance. In generators with rotating rectifier excitation, the resistor is placed
between the measurement slip rings; in generators with excitation via slip rings
between one slip ring and earth.
Start up generator and excite to rated voltage. If applicable place measurement
brushes into operation. It is irrelevant in this context whether the sensitive earth fault
protection picks up or not. The earth fault current I
EE
that is flowing now can be read
out on the device among the operational measured values.
Check that this measured earth fault current is roughly equal to the pick-up value
for sensitive earth fault detection that has been set in address
. However, it must
not be set to less that the double value of the spill current that has been determined
in section 3.4.5 for healthy insulation.
For generators with excitation via slip rings, the test is repeated for the other slip ring.
Shut down generator. Remove earth fault resistor.
The sensitive earth fault detection used for rotor earth fault protection is then set to be
operative:
=
ON
in address
.
3.4.9
Checking the Rotor Earth Fault Protection During Operation
3.4.9.1
Rotor Earth Fault Protection (R, fn)
In Section 3.3.7, the rotor earth fault protection was checked with the machine at
stand-still. In order to exclude possible interference on the measurement circuit by the
running generator, an additional test during operation is recommended.
An earth fault is simulated via a resistor of approximately 90% of the trip resistance
(
, address
). In machines with rotating rectifier excitation (Figure 3-
19 left), the resistor is placed between the measurement slip rings; in machines with
excitation via slip rings (Figure 3-19 right) between one slip ring and earth.
Caution!
Make sure that the checked rotor circuit is completed isolated from the earth, to
avoid that the earthing resistor that is interposed for test purposes causes a
double earth fault!
Caution!
Make sure that the checked rotor circuit is completed isolated from the earth, to
avoid that the earthing resistor that is interposed for test purposes causes a
double earth fault!
