ESTIMATING THE LOCATION OF A TRANSMISSION LINE SHUNT FAULT FROM DIGITAL IMPEDANCE RELAY MEASUREMENTS

Abstract

Analog type distance relays used for transmission line protection identify the faulted zone but do not provide any information concerning the exact location of the fault. Fault locators, that estimate the distance to a fault point on a transmission line, conventionally measure the apparent impedance to the fault from a line terminal. This impedance is then converted to the line length. The fault location estimates are adversely affected by the presence of a fault resistance. The advent of microprocessor-based relays has made it possible to estimate the location of a transmission line fault with reasonable accuracy. The interest in fault location algorithms has, therefore, increased consideraby among the utility engineers and researchers. This thesis presents a technique that is suitable for estimating the location of a transmission line shunt fault. The technique uses the fundamental frequency voltage and current phasors measured at the line terminals. The estimation procedure is independent of the type of fault and the identity of the faulted phases. In addition to estimating the fault location, the proposed technique identifies the type of fault and identifies the faulted phases independent of the relay targets. The estimation procedure does not require that the measurements taken at the line terminals be synchronised. Source impedances, distribution factors and pre-fault currents are not used by the proposed technique. Results from computer simulations of faults on a two machine model and a six bus model of the transmission network of the Saskatchewan Power Corporation are presented. The results indicate that the proposed technique is capable of accurately estimating the location of a transmission line shunt fault even if the fault resistance is numerically comparable to the line impedances. Results also indicate that the proposed technique is suitable for determining the type of fault and identifying the faulted phases independent of the relay targets.