3 Mounting and Commissioning
276
7UM61 Manual
C53000-G1176-C127-3
3.3.10 Checking the Stator Earth Fault Protection
General 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 con-
nection. 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, it is appropriate to test 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.
Unit Connection In the event of an external (high-voltage side) short-circuit, an interference voltage is
transmitted via the coupling capacitance C
K
which induces a displacement voltage on
the generator side. To ensure that this voltage is not interpreted by the protection as
an earth fault within the generator, it is reduced by a suitable loading resistor RB to a
value which corresponds to approximately one half the pick-up voltage U0> (address
5002). On the other hand, the earth fault current resulting from the loading resistor in
the event of an earth fault at the generator terminals should not exceed 10 A, if possi-
ble.
Figure 3-16 Unit Connection with Earthing Transformer
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