3BHE027632R0101 UCD216A ABB Excitation control of medium and high voltage frequency conversion board

Description

Ground fault protection function for detecting ground faults close
to the star-point of a generator. The scheme is based on the
principle of displacing 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. This protection in conjunction with the voltage function ‘Voltage’, which covers 95 % of the winding, achieves detection of ground faults over
100 % of the winding. Compensation is provided for the influence 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. In this
case the 95 % stator ground fault protection takes over the job of
clearing the fault on its own.
B. Features

protects the star-point and a part of the stator winding depending on the ground fault current

displacement of the star-point in relation to ground by injecting a signal generated by the injection unit REX 010

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 I/P’s)
II. Binary inputs:

blocking

2nd. parallel star-point

MTR adjustment

REs adjustment