Fault location and relay performance analysis by automatic oscillographs

The purpose of this paper is to describe a method developed for determining the location of ground faults on an extensive 140-kv grounded neutral transmission system. This method applies particularly to ground faults in a network of two or more parallel lines and is based on a comparison of the magnitude of ground currents in the faulted circuit and in the unfaulted circuits. Since the relative distribution of ground fault current in a network depends only on the zero sequence impedance of the system, an analysis of ground faults by comparison is independent of generation, fault resistance, or whether one or two phases are involved to ground. The paper also describes the use of ground fault current curves in determining the critical conditions for relay selectivity and summarizes the results of five years of satisfactory experience with automatic oscillographs used in the analysis of faults and relay operations on the system.