13.8KV DISTRIBUITION CIRCUIT NEUTRAL CONNECTION QUESTION
13.8KV DISTRIBUITION CIRCUIT NEUTRAL CONNECTION QUESTION
(OP)
Gents,
I work for a small town electric utility that has 4 distribution circuits at 13.8kv GRDY. Each circuit has at least one tie point where it can be tied with another circuit. These tie points only connect or disconnect the phase conductors, the neutral runs right through these points. The substation breakers and system reclosers monitor phase and ground currents, and react to fault conditions as programed. My question is: how accurate is the ground current readings at these points when the neutral is interconnected at so many points throughout the circuits?
thanks,
Chris
I work for a small town electric utility that has 4 distribution circuits at 13.8kv GRDY. Each circuit has at least one tie point where it can be tied with another circuit. These tie points only connect or disconnect the phase conductors, the neutral runs right through these points. The substation breakers and system reclosers monitor phase and ground currents, and react to fault conditions as programed. My question is: how accurate is the ground current readings at these points when the neutral is interconnected at so many points throughout the circuits?
thanks,
Chris






RE: 13.8KV DISTRIBUITION CIRCUIT NEUTRAL CONNECTION QUESTION
David Castor
www.cvoes.com
RE: 13.8KV DISTRIBUITION CIRCUIT NEUTRAL CONNECTION QUESTION
RE: 13.8KV DISTRIBUITION CIRCUIT NEUTRAL CONNECTION QUESTION
After further research, I believe you are correct. The neutal and ground currents at the recloser control (SEL 351) are calculated, as there is no CT physically measuring either paths.
Thanks
Chris
RE: 13.8KV DISTRIBUITION CIRCUIT NEUTRAL CONNECTION QUESTION
RE: 13.8KV DISTRIBUITION CIRCUIT NEUTRAL CONNECTION QUESTION
As this is a single point, there is no easy way to allocate a measured transformer neutral current to each circuit. And a CT on each circuit neutral would be 'fooled' by the portion of the unbalance returning through the ground in parallel with the neutral.
In the final analysis, ground current trip levels have to be set with some margin above the greatest anticipated unbalance current to prevent nuisance tripping. Keep in mind such factors as normal unbalance (as pointed out by Jebb) as well as unbalances that arise from single phase fuses blowing.