ground undervoltage generator protection relay (27G)
ground undervoltage generator protection relay (27G)
(OP)
How do you connect the 27G relay and what is the difference between the undervoltage (27) and the ground undervoltage (27G) relays?






RE: ground undervoltage generator protection relay (27G)
RE: ground undervoltage generator protection relay (27G)
In "normal" operation a 3rd harmonic voltage exists between the neutral and ground and can be measured by the relay. When a ground fault occurs near the neutral point of the winding, the transformer primary is shorted out and the 3rd harmonic voltge disappears, picking up the 27G element. The 59G relay does not react to faults close to the generator neutral, there is not enough voltage.
Problem: 3rd harmonic N-G voltage varies from machine to machine and varies with load. You usually cannot calculate the setting. Have to measure the values and select a safe setting.
Some 27G relays take input from the generator VT's and/or CT's to develope blocking/permissive signals.
RE: ground undervoltage generator protection relay (27G)