generator rotor earth fault

[nikhilgajjar]

Hello,
we have installed SEGC make , RWE type rotor earth fault relay for our 11 MW steam turbine generator.
Relay aux. supply is of 110 VAC and output of the relay is 49 Volt ac. Here we have a confussion:
1. From relay manual it is understood that for rotor earth fault measuring circuit, relay will impressed above 20 VAC.
Now with 20 vAC even with solid eath fault relay is not at all operating. So what could be the reason for?
So my question is :
1. What should be the relay output for rotor earth fault measurment.

pls. clear my confusion.
regards
nikhil

 

[sanvapat]

Nikhil,
The relay you are reffering seems to be similiar to siemens rotor e/f relay which works, basically on resistance measurment between winding and ground.

In your case ,At what resistance, 1st alarm will come and at what 2nd ?

You can go for decade resistance test, right at the terminals of relay. If than also, it want work,,hardware failure can be suspected ?

Regarding your question, 49 Vac is sufficient for such resistance measurement.Because the resistance at which alarm is provided is in the range of 30 to 40 K-ohm, whereas for trip, value is < 5 k-Ohm

 

[amanat]

I am also interested in the solution of this problem.