Undervoltage Conditions and Relay Settings

The normal setting for Undervoltage relay is about 80%, irrespective of the voltage level. But, you can go for a time-delayed relay and co-ordinate (time discrminate) the 132 kV relay with those of downstream U/V Relays.

normal setting of under voltage is 80 % and no volt is 40 %. Under voltage condition may be during fault also.you should give time for fault clearing but time delay in no voltage condition is not required.It depend on weather you are using in under voltage tripping or other application

tHANKS FOR A GUD REPLY, BUT WHETHER THE 11KV BREAKER SHOULD TRIP FIRST OR 415 VOLTS WHEN THERE IS A U/V ON 132 KV SIDE.CAN U TELL THE SINGLE LINE DIAGRAM OF RELAY SETTING AT EACH SUBSTATION.

It all depends upon whether you have any loads that are sensitive to voltage at the 11kV level. If not, I would prefer to have 415V trip first for any undervoltage, then co-ordinate such that 11kV and then 132kV.