Tripped by Differential Rele (87)

You say it's a new generator - what do the suppliers have to say about it?

Check the polarity of the current transformers.

Check the setting of the relay.

Is that generator already tested by Load Bank during commisioning ?

Is the function test of the protection relay ok ?

is the Generator already tested by Load Bank during commisioning ?

is the function test of protection relays correct ?

how much ratio of CT that put in frontside & backside of generator winding ?

is the connection correct (wye-delta or delta-delta or delta-wye) ?

is all of wiring already meggered?to make sure there are no leakage current.

is the setting of its Digital Protection Relay correct?

Hi,

All of the function of protection relay was correct, CT's ratio frontside & backside, the connection (wye-delta,delta-wye or delta-delta), no leagake current were correct as well.

CT's polarity was correct, in my opinion if CT's polarity wasn't correct then the circuit breaker will trip if we close

Your kindly advice is highly appreciated

Thanks,

Kuncoro

Plz check relay setting used for o/P contactor

There have been cases where the manufacturer labeling on the CT was incorrect, both for polarity and/or ratio. Has the ratio and polarity of each CT been verified to match the markings? If the secondary amps are expected to be 1 amp at marked load, and in fact are 5 amp at rated load, this would give you the results you are experiencing. CJM

My Assume is :

may be there is already happen differential current. But still not detectable by Digital protection relay. may be because of wrong setting.because you only load 700KW . I dont know how muct your voltage system. but this load is only 16 % full load. so relay not yet detect the differential thing from your generator.

And then after you increase the load. Digital relay can detect the differential of current and command the breaker to trip.

That is MY ASSUME. For Further and Clearly information, please CONTACT your vendor as soon as possible.

dear,

Considering that the installation & wiring of the relay is error free,

Considering that you have already caliberated the relay with current injection kit,

& working OK,

then, if relay trips,

May I know the nature of load ? is it high frequency load like induction furnaces,

then May be due to Current Harmonics generated in the system due to load.

In this case, precautions are required to eliminate the same from sensing CTs.