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Anonymous Poster #1

Selection of Fast Tripping Relays

08/02/2012 6:31 AM

Dear Gurus,

In one project, our consultant have designed 65 KA, 415 vot synchrinising panel, 5 nos Diesel generator and 5 out going load feeders C.B. was connected through this synchronising panel.

Each generator was 2000 KVA, 415 volt cummins make with indivdual fault current of aproximate 18 KA.

So total fault current was 90 KA.

Will this arrangement work if a fault of 90 KA flows ( in case of bus fault! ) , provided we install high speed tripping relays for fault clearing much before damaging bus bars and other out going feeder breakers.

All circuit breakers are 65 KA rated, masterpact series of schnieder electric.

Regards,

santosh.
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PeterT
Guru

Join Date: May 2010
Location: Liverpool, NY
Posts: 961
Good Answers: 131
#1

Re: Selection of Fast Tripping Relays

08/02/2012 8:51 AM

Ask your consultant to prove to you that their design is adequate for the available fault current. That is what you are paying them for!

__________________
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3PhaseDesign-Craig
Associate

Join Date: Jul 2011
Posts: 48
Good Answers: 1
#2

Re: Selection of Fast Tripping Relays

08/02/2012 6:18 PM

I would say there could be some issues. ACB's are generally not current limiting even with their own protection relays, this is due to the speed of operation in the region of 35mS. External relays would not solve the problem If you are using IEC 61439-2 then you need to prove the design through both design and routine verification have you carried out any design verification on your equipment? The only thing I would say is that the gen will not produce 18kA for long, have you asked cummins for the fault curves? I don't believe the peak will be as high as 2.1x either, but need to get that confirmed
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muditmah
Commentator

Join Date: May 2011
Posts: 84
Good Answers: 1
#3

Re: Selection of Fast Tripping Relays

08/03/2012 9:52 AM

you are right .!!

ask them for the reason for 65 kA switchgear which you are purchasing.

bcoz 90 kA rated switchgear are hard to find. that might be the reason.

So ask them what they are proposing for reducing the fault level from 90 kA to 65 kA .?
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3PhaseDesign-Craig (1); muditmah (1); PeterT (1)

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