SINGLE-PHASE SELECTIVE GROUND FAULT PROTECTIVE GEAR FOR AC POWER MAINS AND ITS OPERATION Russian patent published in 1997 - IPC

FIELD: selective ground fault protection of supply mains with resistive, insulated, partially or fully compensated neutral. SUBSTANCE: protective gear has identical zero-sequence high-frequency current and voltage channels (HFI_o) and (HFU_o), respectively, and zero-sequence voltage channel (V). First half-wave is separated upon occurrence of ground fault. Threshold elements compare half-wave amplitudes with reference values. Phase sensing elements record phase relations between HFI_o and HFU_o as soon as HFI_o chooses zero. Low-frequency filter separates component corresponding to working frequency from U_o. Threshold element compares its amplitude with reference value. With phase shift angle in desired interval and U_o amplitudeticaeeding reference value, results are checked within time space. With result maintained, alarm signal is shaped. Time space is set by means of controlled delay circuit or according to duration of transients, or it is increased by time required to compensate for capacitive currents at single-phase ground fault. EFFECT: improved reliability, selectivity, reduced probability of unwanted operations. 3 cl, 1 dwg