REF/STAND BY EARTH FAULT
REF/STAND BY EARTH FAULT
(OP)
Hallo guys,
I have a scheme whereby the neutral of a 23MVA 33/11kV trafo has only one neutral CT (BUSHING) of class X. The incomer breaker too has class X CTs. I want to use ICT to be able to use the single bushing CT for both SBEF and REF.
Is it safe to use the ICT or is the REF alone sufficient for protection of the Trafo windings and the cable to the incomer breaker.
I have a scheme whereby the neutral of a 23MVA 33/11kV trafo has only one neutral CT (BUSHING) of class X. The incomer breaker too has class X CTs. I want to use ICT to be able to use the single bushing CT for both SBEF and REF.
Is it safe to use the ICT or is the REF alone sufficient for protection of the Trafo windings and the cable to the incomer breaker.






RE: REF/STAND BY EARTH FAULT
Regards
Marmite
RE: REF/STAND BY EARTH FAULT
RE: REF/STAND BY EARTH FAULT
The SBEF CT doesn't need to be anything special and you should have enough adjustment on the relay to allow a fair choice of CT ratio. Are you saying that you can't find any CT at all? If you have an NER then you could use a metering CT as the CT will never see high current under fault conditions.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: REF/STAND BY EARTH FAULT
I'm not sure if it's a good idea use series connection for the REF function. It not seems. Are the REF HI or LI?
Actually, you have a solidly trafo grounding..
REF is good function, but not must here. 87T is enough sensetive in such confuguration. You can use REF no problem and SBEF with residual connection. In first case you can add neutral CT and reconnect SBEF relay.
Just opinion.
Best Regards.
Slava.
BTW, why PUNGLU is name of drw, one of our members is PUNGLU
RE: REF/STAND BY EARTH FAULT
i would like to point the following:
1. REF is used because 87T doesn't cover 100% of Xfmr winding.
2. if the REF is high impedance type, deticated CTs shall be used for this function.
Best Regards
SMB
RE: REF/STAND BY EARTH FAULT
RE: REF/STAND BY EARTH FAULT
RE: REF/STAND BY EARTH FAULT
Best Regards.
Slava