POWER-MAINS DIRECTIONAL GROUND-FAULT PROTECTIVE DEVICE Russian patent published in 1998 - IPC

FIELD: insulated-neutral power mains. SUBSTANCE: device has zero-sequence current and voltage sensors, two amplifiers, two relay members, two period measuring units, phase comparison unit, two one-shot multivibrators, two comparison units, five-input AND gate, NOT gate, timer, NOR gate, and series element. Upon occurrence of single-phase ground fault, signals across outputs of zero-sequence current and voltage sensors rise with the result that relay members switch over their contacts. When phase shift between zero-sequence current and voltage is within protective gear operating range and current frequency and voltage equal rated value, logic one signals are set up across all five inputs, and protective device operates. EFFECT: improved selectivity of power mains protective gear in case of single-phase ground faults at transients accompanied by subharmonic oscillations. 1 dwg