I work at a power plant and had two separate occasions where a 3 phase 480VAC 150HP delta connected motor tripped on ground fault (valid). A 3 phase 480VAC 150HP wye connected motor also nuisanced tripped (not valid). Both motors are connected to a ITE/ABB Kline loadcenter with a 13.8KV/480VAC delta/wye neutral grounded 1000KVA transformer. Ground fault protection for both provided by a ITE GR-5 ground fault relay and type GS ground sensor (core balance or "window" type CT). Relay pickup is 50A and time delay is .033 seconds. Would like some suggestions on what is causing the wye connected motor to also trip on ground fault when the delta connected motor has a valid ground fault.
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