What is neutral earth compensator?

Answer 1

For earth fault protection on the windings of a delta connected transformer. Used in MV distribution. An earth fault current return path is provided by connecting a Neutral Earthing

Compensator (NEC) between the three phases of the power system and the earth

system. This is done at the source of the supply.

The NEC transformer winding has a Zig-zag configuration with no secondary winding. The

impedance of the winding is high when there is no fault on the system resulting in only a

small magnetising current in the transformer windings. The Zig-zag winding configuration

results in a low impedance when an earth fault condition occurs. By inserting resistance

between the neutral of the Zig-zag transformer and earth, the earth fault currents can be

limited to any desired value. The resistance value and rating has been standardised to

allow an earth fault current of 300 amp for 10 seconds, although some older installations

may still operate at the old standard of 600 amps.