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You have two 600 amp emergency generators ones almost maxed out at 570 amp and the other is at 200amp.It's decided that the load be balanced between the two and the job is done under a P.E stamp. Shortly there after occasionally and only during a load test the upstream 800 amp breaker before the t-switch will trip just as it transfers back to standard power. I know an inphase monitor will resolve the issue by delaying the transfer. I was thinking we have motors free wheeling that are generating power back into the buss work. Also we have 12 elevators some of which are emergency power and likely grouped to one MCC per wing. I wonder if these MCC’s are all fed from the same generator? I’ve seen this before on a single 320a stand-by system where either the 200a main circuit breaker for the emergency elevator MCC would trip or just like now the 800 amp circuit breaker before the t- switch. During the load test the t-switch transfers to emergency so fast that you can’t see it pick up the load but if you pay attention you can see I a flicker when it switches back. Eventually both breakers got weak .I think this is the same problem but would like to hear as many ideas as to why it could happening as possible

I think you are correct in your assumption that the generator output is out of phase with the utility. They could be anywhere from 0 degrees (in phase) to 180 degrees out of phase at the instant of reconnection, and that is the reason the breaker doesn't trip every time.

Are the generators supplying a common load (operating in parallel)?

Ed

Be well aware that unsynchronized transfer may seriously damage the gensets and switchgear, and be a very grave risk to personnel and connected loads.

I mean no offense, but you may be in over your head, and retaining someone that understands the complete system is due and significantly more cost effective from a liability {and reliability} standpoint.

Bjarney
no offense taken and that’s what Im sayin one day this breaker is going to get weak and fail or someone will throw it against a real permanent fault. As for the genset taking a beating would it not be isolated since the t-switch is open on that side at that time in the transfer.As for the t-switch I bet it can't be good.I was once told years ago that this is not an uncommon problem and an accepted remedy was an inphase monitor.This was a recommendation by the manufacturer of the t-switch.Almost forgot we had respected contractor who specializes in this come in and put in place test equipment to record the fault while doing the manditory CSA full load bank test.The system passed with no problems and we were given the green light to a building load test today.Guess what happened.


[This message has been edited by frank (edited 11-20-2002).]

[This message has been edited by frank (edited 11-20-2002).]

electric-ed
Thanks or the reply,im new to this building and will check it out on my next shift.Are there any other possibilies you think we should look for?