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Reply To: Switchgear Riddle No.8 – Replace of circuit breaker

#1933
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 .