Introduction to the Generator II

The method of earthing the neutral end of each of the generator windings allows earth faults to be detected and the generator tripped. The neutral end of each winding is taken out separately, through a current transformer, to the high-voltage neutral bushings. The three neutral bushings are connected in parallel externally and taken through the primary of the neutral earthing transformer to earth. The secondary of the transformer is connected across the neutral earthing resistor.

Under normal conditions no current flows to ground. However, if a fault such as a ground short, occurs in one of the stator windings of the generator, there will be an imbalance between the three phases causing a large loop current to pass through the primary of the neutral earthing transformer.

This will result in a voltage appearing across the neutral earthing resistor. The stator earth fault relay, wired in parallel with the neutral earthing resistor, will detect this voltage and operate the generator protection Class 2 trip circuits.