Bucholtz relay (ANSI 63)
Bucholtz relay (ANSI 63)
(OP)
Situation: Oil filled power transformer fed through a fused combination starter (fuse + MV contactor)
Question: In case of heavy fault ( 63 trip signal) is it correct to trip the MV contactor?
Thanks
Question: In case of heavy fault ( 63 trip signal) is it correct to trip the MV contactor?
Thanks





RE: Bucholtz relay (ANSI 63)
I'd think the device to be tripped must be capable of interrupting the available fault current (the same devices that are tripped by your 87 relay).
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RE: Bucholtz relay (ANSI 63)
It doesn't really matter what type of relay it is. However, considering a "heavy fault" would suggest an internal arc has formed it's quite likey the current will be above the rated contactor breaking current.
RE: Bucholtz relay (ANSI 63)
But Buchholz relay operation implies possible major internal transformer fault so it would be unwise to use the contactor unless it is certain that the contactor has adequate interrupting rating. Which is not likely.
Best engineering solution is to replace the contactor and fuse with a circuit breaker.
David Castor
www.cvoes.com
RE: Bucholtz relay (ANSI 63)
Buchholz(german inventor) relay is connected between oil tank and conservator and detects, in case of major faults, sudden surge of pressure.Here in my country, a fuse+MV contactor combination is frequently used as a cheap transformer feeder option(up to 1,0MVA).
Sometimes, contactor breaking capacity is eight or more times smaller than network short circuit capacity.
So, is there a possibility,even remote,of contactor be tripped under short circuit condition by Buchholz actuation?
Thanks.
RE: Bucholtz relay (ANSI 63)
Fault has to be cleared by a fuse or a breaker. Contactor are for normal load or overload interrupting duties, within its rating.
Rafiq Bulsara
http://www.srengineersct.com
RE: Bucholtz relay (ANSI 63)
We don't know. We didn't design the protection scheme. Is the protection scheme wired so the Buchholz relay trips the contactor?
All I can tell you is that you should not open the contactor when the network fault current is eight or more times higher than the contactor breaking capacity.
RE: Bucholtz relay (ANSI 63)
If the transfomer is 1 MVA standard distribution transformer where you have a spare available within a few hours the fuse/contactor option may be suitable.
If you have to protect a one-of-design rectifier transformer where you might have to wait 3 month for a replacement unit built new, the combination of Buchholtz and breaker may be advisable.
RE: Bucholtz relay (ANSI 63)
Additionally, I have found fused combination starters applied to feed transformers up to 1,0MVA.
My question it was:Is there a short circuit condition where Buchholz actuation can be faster than fuse actuation?
Summarizing, how fast can be Buchholz?
If yes, I will not wire Buchholz trip signal to the contactor.I will wire it to the first circuit breaker located upstream.
That is it.
Thanks
RE: Bucholtz relay (ANSI 63)
Yes, definitely.
David Castor
www.cvoes.com
RE: Bucholtz relay (ANSI 63)
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