Hi all,
First time poster. We recently had a tree branch cause a 3 phase fault on an overhead tap line aprroximately 2000’ away from our substation. The fault caused 1 of 2 MAIN CIRCUIT BREAKERS to open at the substation. It should have opened the feeder on the tap only. I haven’t got the event report from the relay, but my feeling is either the SEL651 on the feeder is set incorrectly or the SEL351 is set incorrectly at the MAIN BREAKER. Thx.
1 Like
Did the 351 isolate the fault with that one CB it tripped? If so, the 361 could of tried to isolate but the fault lasted longer than the delay on the 351 that allows for relay coordination, due to a failed feeder breaker/switch or 361 failure, CT saturation could also be a factor. I would look at the SERs for both and go from there.
2 Likes
Sounds like a coordination problem, but I would not assume settings only until you see the event report.
If the fault was on the tap, I would expect the feeder device to clear first, so I would start by checking which element actually tripped on the main and whether the feeder relay saw the fault correctly at all. Could be bad coordination between the SEL-651 and SEL-351, but it could also be CT ratio/polarity issues, logic, instantaneous settings, or the main just being set too fast for a close-in fault.
My first move would be to pull the event report and compare the trip element, fault current seen, and timing on both relays. That should narrow it down pretty quickly.
3 Likes
Depends if there is a high current lockout situation. If the relay is configured for HCL then the station would operate and lockout instead of recloser. Depends on risk tolerance philosophies.
