METHOD OF DIRECTIONAL PROTECTION AGAINST SINGLE-PHASE GROUND FAULT IN AC MAINS AND DEVICE FOR ITS REALIZATION

摘要

FIELD: electrical engineering. SUBSTANCE: the device uses identical high-frequency current (HFIo) and voltage (HFVo) channels 1,2 of zerophase-sequence (Io,Vo) and zero phase-sequence voltage channel 3 (Vo). At a fault of circuit 11₁ and 11₂ in channels 1,2 the first half-wave of HFIo and HFVo is separated. The threshold elements or 14₁(14₂), or 15₁(15₂) compare the half-wave amplitudes with the standard quantities. Phase-sensitive elements 4 or 5 determine the phase relation between HFIo and HFVo at the instant of zero crossing of HFIo. Low-pass filter in channel 3 separates a component from Vo corresponding to the operating frequency. Threshold element 17 compares the magnitude of its amplitude with the standard one. Of the phase shift is within the preset range and the magnitude of amplitude of Vo exceeds the standard one, the results are being checked during a time interval. Of the results are unchanged, an emergency signal is produced. The time interval is determined by adjustable delay circuit 7 or in accordance with the duration of transients, or it is increased by the time of compensation of capacitive currents at a single-phase ground fault. EFFECT: enhanced reliability, selectivity, reduced probability of false operations, expanded functional capacities. 3 cl, 1 dwg