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We have substation of 110KV/11KV of 8 MVA transformer (Dyn11) catering of nearly 4000KVA power. There is one 800A 11KV VCB in the secondary of this transformer. This 11KV vacuum circuit breaker has failed while it is working. Suddenly huge blasting with chattering sound heard from breaker. The operator gone to check it found the power supply was tripped from our supply grid, and severe fire occurred in the breaker. After fire extinguished, the breaker was checked and found completely damaged. When checked the trip history of 11KV VCB the over current amp was only 800A. Our optimum load current is only 220Amps.
All three vacuum interrupters were totally damaged and breaker assembly collapsed. There are melt holes found in copper flat above the Vacuum interrupters. The melt holes may be due to flashed metal from VIs, but it could not be concluded. But there are no arc damages found in finger contact stub and prong of the breaker incoming and out going.
If we suspect this is due to short circuit, again doubt comes. Because the breaker structure is has good plastic molded separators and bus bars are insulated.
So we couldn't find the root cause of this incident. We need your expertise to find the root cause of this incident.
All three vacuum interrupters were totally damaged and breaker assembly collapsed. There are melt holes found in copper flat above the Vacuum interrupters. The melt holes may be due to flashed metal from VIs, but it could not be concluded. But there are no arc damages found in finger contact stub and prong of the breaker incoming and out going.
If we suspect this is due to short circuit, again doubt comes. Because the breaker structure is has good plastic molded separators and bus bars are insulated.
So we couldn't find the root cause of this incident. We need your expertise to find the root cause of this incident.