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X-former Secondary Fault Clearing Time

X-former Secondary Fault Clearing Time

X-former Secondary Fault Clearing Time

(OP)
Hi All – I have now experienced this a few times and have seen some literature on it which does not all match so I thought I would seek clarification. I have a small branch cct Xformer (15kVA) with only primary breaker protection (30A Molded Case). According to ETAP, the secondary bus fault clearing time is 2.4s! By changing the breaker type, I get clearing time as low as 0.3s. The results are even better with fuse protection.
Q1: Can someone help clarify why this is?
Q2: Am I correct in saying clearing time beyond 2 sec is unacceptable? I believe this is the value IEEE gives as the max clearing time but I have not seen it in the CEC... I am in Canada

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