[Hamid]

Operation group of an industrial network as illustrated figure below decide to replace one of incoming circuit breaker of main distribution switchgear which failed due to a problem in its control mechanism.
Operation group of an industrial network as illustrated figure below decide to replace one of incoming circuit breaker of main distribution switchgear which failed due to a problem in its control mechanism, they don't access to any reserve unit and replace it with one of switchgear outgoing circuit breaker with similar rated current; because they think continuous power supplying of network is important than having of all outgoings, but after a time operation switchgear front to a sever busbar fault current and all of incoming circuit breaker except mentioned replaced one trip successfully.
How do you can explain the reason of that breaker mal-function?

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[amir khashayar]

Isc(dynamic)/Isc(RMS)=? In general ? is selected as 2.5 for ordinary circuit breakers . But for points very close to generator and as GCB it will be 3.0 . It is probable this C.B. has had malfunction due to high peak of subtransient short circuit current . On the other hand these types of CBs has the advantage of current limiting ,namely , in case of short circuit the down stream CB will be fronted with less short circuit current . Probably , the designer has sized the outgoing feeders according to this phenomenon . But , now the function and duty of CB has changed and it is not outgoing feeder any longer . It is incoming breaker .

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