kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I've been looking at protection for MV switchgear (13.8kV) where the switchgear is ungrounded. In a nutshell; it is to avoid transfer of harmonics onto the utility side through the transformer, which is delta connected on the MV side.
We can add a zigzag transformer to create a ground on the MV bus, or utilize a relays, such as the SEL 351A with the optional Sensitive Earth Fault Function.
The 351A on the main would indicate a GF on the bus, but would not indicate which feeder, (28 Feeders). I would think it preferable to be able to isolate the feeder. Placing a 351A on each feeder is not out of the question other than it adds about $400 (x28) to the cost of the relay, (551C vs 351A).
Would be interested in feedback from others on how to address this issue in the most cost effective manner.
We can add a zigzag transformer to create a ground on the MV bus, or utilize a relays, such as the SEL 351A with the optional Sensitive Earth Fault Function.
The 351A on the main would indicate a GF on the bus, but would not indicate which feeder, (28 Feeders). I would think it preferable to be able to isolate the feeder. Placing a 351A on each feeder is not out of the question other than it adds about $400 (x28) to the cost of the relay, (551C vs 351A).
Would be interested in feedback from others on how to address this issue in the most cost effective manner.