Fault clearing
Fault clearing
(OP)
Gents,
I just want a sanity check. Say I have a 3ph bolted fault on the secondary of a unit substation ahead of it's secondary main. The primary is protected by a current limiting fuse. Will the fault be cleared by the primary fuse(this is assuming of course there is enough fault current beyond the fuse's clearing curve)? I'm just checking some worst case scenarios. I am thinking it will clear, even if the fault was on the load side of the secondary main, as typically, the main has maximum time delay built in for downstream coordination.
Thanks in advance,
Mike
I just want a sanity check. Say I have a 3ph bolted fault on the secondary of a unit substation ahead of it's secondary main. The primary is protected by a current limiting fuse. Will the fault be cleared by the primary fuse(this is assuming of course there is enough fault current beyond the fuse's clearing curve)? I'm just checking some worst case scenarios. I am thinking it will clear, even if the fault was on the load side of the secondary main, as typically, the main has maximum time delay built in for downstream coordination.
Thanks in advance,
Mike






RE: Fault clearing
RE: Fault clearing
If it is downstream of the secondary breaker, it just depends on the coordination between the fuse and main breaker protection. There is no assurance that the breaker will trip first unless someone has made sure this will happen. For very high fault currents, it is difficult to fully coordinate with fuses.
RE: Fault clearing
RE: Fault clearing
Your assumption is correct as to where the fault is on the secondary. That's exactly what I was thinking, but wanted to be 100% sure.
Thanks guys,
Mike
RE: Fault clearing
For secondary faults in front of or behind secondary overcurrent protection, wouldn't IEEE Std C57.109-1993 {Liquid-Immersed Transformer Through-Fault-Current Duration} usually apply?
RE: Fault clearing
If this is an existing installation, a check of the short-circuit & co-ordination study for your installation will indicate whether the fuse will clear before the main protective device operates. This should be apparent from the co-ordination curves for the transformer feeder.
RE: Fault clearing
RE: Fault clearing