ZSCT Pickup
ZSCT Pickup
(OP)
I'm hoping someone can provide some insight into ground fault pickup settings.
Motor info:
1. 2400 volt;
2. Solidly grounded;
3. Fuse/vacuum contactor starter;
4. 1.15 SF
5. ~8k amps ground fault current
6. Zero sequence 50:5 CT for ground fault protection;
7. 300Hp
I've read through the Buff book as well as many many online resources and can't find a resource which provides an explanation on how to choose the ground fault pickup current setting for a solidly grounded mv motor. With a time delay of 0.1 seconds, the fuse will clear a fault.
Any insight would be appreciated.
Thanks.
Motor info:
1. 2400 volt;
2. Solidly grounded;
3. Fuse/vacuum contactor starter;
4. 1.15 SF
5. ~8k amps ground fault current
6. Zero sequence 50:5 CT for ground fault protection;
7. 300Hp
I've read through the Buff book as well as many many online resources and can't find a resource which provides an explanation on how to choose the ground fault pickup current setting for a solidly grounded mv motor. With a time delay of 0.1 seconds, the fuse will clear a fault.
Any insight would be appreciated.
Thanks.






RE: ZSCT Pickup
A zero-sequence CT on a solidly grounded system is not a good idea if you have a fused vacuum contactor (as opposed to a circuit-breaker). This has to do with the IC of a vacuum-contactor. IC of a typical vacuum contactor is approx 5ka, with fuses is approx 50ka. With your 8ka of GF current, you could smoke the contactor if it were called upon to interrupt the full 8ka. However, you might get lucky and have the fuse clear the fault prior to the contactor opening.
To summarize, do use the ZSCT on a vacuum-contactor on a solidly grounded system.
Regards,
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: ZSCT Pickup
RE: ZSCT Pickup
Sorry, I made a mistake in the last line of my tirade above. What I meant to say was:
To summarize, do NOT use the ZSCT with a vacuum-contactor on a solidly grounded system.
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: ZSCT Pickup
RE: ZSCT Pickup
Frankly, i would remove the ZSCT from the starter. That will prevent anyone in the future form trying to hook it up.
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: ZSCT Pickup
You could set some arbitrary lower level pickup point with enough time delay so the fuses can clear any fault that exceeds the contactor breaking capacity. You have a 50:5 CT so you can set it to say 25A or 50A. The likelihood of this setup being useful and actually tripping on a "low level" ground fault vs the ground fault blowing fuses is quite low.
RE: ZSCT Pickup
RE: ZSCT Pickup
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". û Nikola Tesla
RE: ZSCT Pickup