LV13922A - Method for determination of distance to fault place by phase-to-earth fault in distribution networks - Google Patents

Abstract

The invention object relates to electrical distribution networks the neutrals of which are not directly earthed, i.e. to networks with isolated, through arc suppressing coils or through resistors earthed neutrals, in the concrete - to single phase-to-earth faults in medium voltage power lines. The aim of invention is to determine the distance to single phase-to-earth fault using measurements at the monitoring point of the line. For this purpose, the real and imaginary component of apparent impedance Ýa by classical formula for single phase-to-earth fault are used. As a result, direct sequence reactance X1 to fault place is obtained. To enable it, not only specific reactance X1sp of protected line must be known but also several other specific quantities of the line: Xosp - specific zero sequence reactance, Rcsp - specific resistance of phase conductor, Rgsp - specific ground resistance; llin - length of the protected line grid. The faulty phase voltage , current ?ph, ground current ?g must be measured. To diminish the influence of resistance Rcsp instability, the ground current should not be less than sufficient fraction of maximum load current. To raise the accuracy, also temperature Tc of faulty phase conductor should be measured using which the resistance Rcsp can be determined more accurately. To raise the accuracy still more, capacitive current phase-earth ?clin of the faulty line network and specific capacitive currents of the faulty line - current phase-to-earth ?csp and phase-to-phase ?cssp must be taken into account; in the classical formula, the voltage should be used, instead of faulty phase voltage , which is the difference between measured voltage and the voltage, the last being calculated by iteration procedure using faulty line capacitive currents. The distance to fault place is calculated using obtained reactance X1 and the specific one X1sp.