Single Phasing circuit breaker
Single Phasing circuit breaker
(OP)
I'm attempting to understand a problem we had several weeks ago. I'm a mechanical engineer, so I probably don't have some of the terminology straight either.
We had several failures in the circuit breakers on equipment fed from our 5B 480V bus during a startup on our power plant. In one of the breakers a control transformer was burned up, some relays powered from the 5B bus were melted. We found in the circuit breaker from the 5B station service transformer to the 5B 480 Volt bus, the "b" phase "stab" was bent down and was apparently not making good contact with the b phase "fingers" on the back of the breaker.
An electrician bent the stab back up into line with the other two and we were able to rack it back in with no problems. He said it was "single phasing". how does this relate to burned up control transformer and relays?
Is it recommended to inspect other equipment which is powered from this bus.
We had no problems on any of the other 480v busses.
Thanks in advance for your replies.
We had several failures in the circuit breakers on equipment fed from our 5B 480V bus during a startup on our power plant. In one of the breakers a control transformer was burned up, some relays powered from the 5B bus were melted. We found in the circuit breaker from the 5B station service transformer to the 5B 480 Volt bus, the "b" phase "stab" was bent down and was apparently not making good contact with the b phase "fingers" on the back of the breaker.
An electrician bent the stab back up into line with the other two and we were able to rack it back in with no problems. He said it was "single phasing". how does this relate to burned up control transformer and relays?
Is it recommended to inspect other equipment which is powered from this bus.
We had no problems on any of the other 480v busses.
Thanks in advance for your replies.






RE: Single Phasing circuit breaker
RE: Single Phasing circuit breaker
yours
RE: Single Phasing circuit breaker
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Single Phasing circuit breaker
The control power should of been fused so it should not have burned up any control power transformer if it had the correct protection. The relays would have had the same issue as a contactor mentioned above. However, the control power transformer fuse should have protected them as well if the theory of excessive current draw as a result of low voltage is valid, and I think it is but the fuse should of popped.
I can see some of those things happening but not all of them. I guess if I could see it, rather than rely on a few paragraphs, I would have a better idea and may agree 100% that it would be possible. Stil can't see the CPT burning. This is one of them things you have to see to evaluate.
RE: Single Phasing circuit breaker