GE 69kV Breaker - Trip Coils

[tefaber]

One of our clients had a Trip Coil burn up on one of their GE 69kV Circuit Breakers. They found it after a fault had occured on the breaker's line, causing the breaker failure relay to trip the sub offline.

The odd thing is that the prints for these breakers show them having two trip coils, so the protection logic utilized that fact in a way to make sure both coils were tripped before breaker failure would be initiated.

Well, we looked at the breaker and the "two" trip coils weren't what I expected...they were what appeared to be four leads coming out of the same coil. It didn't appear that the two coils were insulated from each other in any other way besides, perhaps, the conductor's insulation. In any case, either I'm missing something, or that design is less than what it should be.

Anybody seen or worked with these who could offer some insight?

Thanks

 

[NorthSlope]

What type of GE breaker? Oil? SF6?
What type, model, style?

 

[vtpower]

I have yet to see a breaker claiming dual trip coils but having one with four leads. That certainly defeats the purpose of redundancy.

As for the burn up, an issue I have had in the past was while utilizing digital relays. Check your Trip Duration timer to be sure it does not exceed the rating of the trip coil. I have had a coil burn due to an incorrect setting on this timer.

 

[ScottyUK]

Another way to burn up trip coils is for the normally closed auxiliary contact in the tripping coil circuit to fail in the closed position. In correct operation this contact cuts the coil current as the breaker opens.


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[davidbeach]

vtpower, on the other hand, if you use the relay output contact to interrupt the trip coil current before the breaker aux contact, you will likely weld the relay contact closed. Once energized, the trip coil needs to be interrupted by the breaker aux contact unless you have done something else to enable the relay to interrupt the current.

 

[tefaber]

Sorry for the delay...wife and I just had our first baby so been a bit busy.

Yes, the breaker is an oil circuit breaker, type fk-72.5-27000-10.

David, your comment brought up something I didn't think about. When we were commissioning the transmission relays for this breaker, we didn't have the aux contact interrupting the current, the relay was doing that...which did fuse the contacts on that relay output. We've since installed a aux relay inline, but I wonder if we did some damage to the coil in testing that caused it to fail later (The failure was noticed about 8 months after our commissioning work). I will have to check to see if that was the breaker we had that incident on or not..but it's something to look into...thanks.

 

[stevenal]

You sure your aux relay is suitable for this duty? Interrupting the highly inductive tripping current is pretty severe, and is generally done by big aux contacts on the breaker. If trying to interrupt tip current with a relay, or if aux contact wear is a concern, you might look into SEL's arc suppression devices. Congrats on the kid.