generator differential
generator differential
(OP)
hi,
we have a problem about current angles for generator differential protection-REG670 relay.
Between generator and transformer there is no CB. CB is after transformer.
And for synchronizing with grid, they did replace B and C phases on the primary side(grid side) of transformer.
Does this effect generator differential protection.
I can not see the angles reverse, between two side of generator.
Can you help me?
we have a problem about current angles for generator differential protection-REG670 relay.
Between generator and transformer there is no CB. CB is after transformer.
And for synchronizing with grid, they did replace B and C phases on the primary side(grid side) of transformer.
Does this effect generator differential protection.
I can not see the angles reverse, between two side of generator.
Can you help me?






RE: generator differential
The transformer phase shift, if present, must be accounted for. In a delta-wye transformer, there will be 30 degree phase shift one way or the other.
I'm not sure what was replaced, but if the CTs or CT wiring was involved, the CT polarity could be off, which would cause the current to be 180 degrees from where it should be, or the phasing could be off, or both.
By looking at the current phasors coming into the relay, you should be able to get an idea about where the problem might be.
RE: generator differential
RE: generator differential
Please see what dpc has said. If the CTs were replaced (is that true) then the polarities of the new CTs are probably reversed or otherwise wrong and the relay will not balance when load current is flowing. You may be getting a false trip.
You may have to run a new primary test to sort this out, that means running the unit on short-circuit on the HV side. This was probably done on the original commissioning, and now may have to be repeated.
Since the CTs will have each several socondaries (likely) then possibly other circuits, protections, and metering may now also be wrong.
rasevskii
RE: generator differential
Traditionally, CTs on the Y side were connected delta and on the Delta side were connected wye to correct phase shift and handle the zero sequence current. With new digital relays, both sides are normally connected wye and the relay does the math. But you have to tell the relay how the CTs are physically wired.
But if you replaced CTs, my first guess is that the polarity is backwards.
RE: generator differential
generator differntial is generator differntial, no phase shift and is not suitble for block protection.
what is a code of your REG670?
C30 or A20, or B30. C30 and B30 types are included transformer differntial protection, you can used it.
why only phases B and C was replaced?
RE: generator differential
RE: generator differential
RE: generator differential
But REG670 is special relay, is included a few differntial protections in one box with lot of current inputs ( for example, version C30 is included 87G, 87T and 87UT).
RE: generator differential
Thanks for the info - I am not really familiar with this relay. It's hard to keep up with all of the relays these days.
Cheers,
David
RE: generator differential
I solved the problem today.
Polarities has changed, so I do the correct wiring.
Now relay sees the correct values and angles.
thanks all of you