Stator Ground Fault - ABB REG316 4 Series Operating Instructions Manual

REG 316*4 1MRB520049-Uen / Rev. F
3.5.24. Stator ground fault (Stator-EFP)
A. Application
Ground fault protection function for detecting ground faults close
to the star-point of a generator. The scheme is based on the
principle of biasing the potential of the generator star-point by
injecting a coded low-frequency signal. The injection signal is
generated by the injection unit REX 010 and fed into the stator
circuit by the injection transformer block REX 011. In conjunction
with the voltage function 'Voltage' that covers 95 % of the
winding, this protection completes detection of ground faults over
100 % of the winding. Compensation is provided for the in-
fluence of a second high-resistance grounded star-point in the
zone of protection.
Stator ground faults producing a current at the star-point > 5 A
cause the P8 contactor to reset which separates the injection
unit Type REX 010 from the injection transformer block REX 011
and interrupts injection in both stator and rotor circuits. The 95 %
stator ground fault protection then clears the fault on its own.
B. Features
· protects the star-point and a part of the stator winding de-
pending on the ground fault current. The entire winding is
protected when the generator is stationary.
· biases the star-point in relation to ground by injecting a signal
generated in the REX 010 unit
· computes the ground fault resistance
· monitors the amplitude and frequency of the injection signal
· monitors the measuring circuit with respect to open-circuit
and correct connection of the grounding resistor.
C. Inputs and outputs
I. C.t./v.t. inputs:
· voltage (2 inputs)
II. Binary inputs:
· blocking
· 2nd. parallel star-point
· MTR adjustment
· REs adjustment
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