Overcyrrent Relay Coordination for Double-Ended Industrial Substations

Overcurrent coordination details for phase, ground, and reverse current relays as applied to double-ended substations supplying three-wire low-resistance grounded medium-voltage industrial distribution systems with predominantly induction motor loads are discussed. Emphasis is on the National Electric Code (NEC) limitations to the pickup of phase overcurrent protective devices, the phase coordination of the double-ended substation with a normally closed bus tie breaker, and the ground-fault coordination of the four-wire solidly grounded low-voltage double-ended substation.