RU95107061A - Method of directional protection against single-phase ground fault in ac mains and device for its realization - Google Patents

Abstract

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 11and 11in channels 1,2 the first half-wave of HFIo and HFVo is separated. The threshold elements or 14(14), or 15(15) 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

Claims (1)

The inventive device contains identically made high-frequency channels 1.2 current (HFI ₀ ) and voltage (HFU ₀ ) zero sequence and channel 3 voltage zero sequence. When a circuit shorts in channels 1.2, the first half-wave of HFI ₀ and HFU _{0 is} allocated. The threshold elements 14 ₁ (14 ₂ ), or 15 ₁ (15 ₂ ) compare the half-wave amplitudes with the reference values. The phase-sensitive elements 4 or 5 fix the phase relationship between HFI ₀ and HFU ₀ at the moment of passage through zero of HFI ₀ . In channel 3, the low-pass filter 16 extracts from U _{0 a} component corresponding to the operating frequency. The threshold element 17 compares the value of its amplitude with a reference. When the phase angle is found in a given interval and if the amplitude U ₀ exceeds the reference value, the results are monitored for a time interval. When saving the results, an alarm is generated. The time interval is set by an adjustable delay circuit 7 in accordance with the duration of the transient processes, or increase it by the value of the compensation time of capacitive currents with a single-phase earth fault. Technical result achieved: increasing reliability, selectivity, reducing the likelihood of false positives, expanding functionality.