Ring Bus Breaker LockOut(86) Control Circuit

[Thriggen]

I'm in the process of modifying a ring transmission sub with 3 lines. I am currently working on the the breaker lockout circuit. My idea is to energize the lockout of a breaker if an adjacent breaker is in Lockout(breaker failure) and is still seeing fault current. This means two failed breakers in a row. While this case is rare, I think you still need to protect against it happening. I would follow this scheme around the ring. Basically, if a breaker fails and gets locked out, the adjacent breaker should trip, if that one sees fault current, then it will get lockout out. Where a transmission line comes in between two breakers I would add the 62X and 62Y contacts from that line as a condition in the lockout circuit as well.

We are replacing a primary side normally closed tie switch with a tie breaker and while looking at the prints, my idea is not what the previous designer had in mind.

This scenario may be tough to envision without an actual print but I am wondering if this is normally how ring subs are designed. I worry that this is considered over tripping.

Any input will be greatly appreciated. Thanks.

 

[dpc]

In a ring bus, two breakers must be tripped to clear any line fault, assuming the ring is closed.

The lockout relay should trip the appropriate two breakers for that line position. If you are talking about breaker failure, that's a different issue.

David Castor

http://www.cvoes.com

 

[Thriggen]

Yes, the ring is closed and we do trip the two breakers with the lockout relay to clear the fault. But what happens if one of those breakers fail. This would be sensed by:

86 of the original failed breaker and 50 of the breaker that was asked to trip. That would indicate, after an appropriate delay, that this breaker has also failed. I want to put this condition in for every breaker around the ring. This sort of cascades protection around the ring. Is that a standard practice?

 

[davidbeach]

Yes, standard practice. I thought I had already answered this one. For each relay doing BF protection, the local 86 should be a BFI input. If the breaker doesn't open in response to the lockout, the next lockout around the ring should be tripped, etc. Also, if there is a transfer trip circuit, the breaker failure signal should be sent to the other end of the line.