Effect and influence of residual current compensation on earth-fault distance relays

For residual compensation of an earth-fault distance relay, a compensation method using only a reactive compensation factor (X0/X1) for the transmission line or a compensation method using both a reactive compensation factor (X0/X1) and a resistive compensation factor (R0/R1) which are widely used in Japan. In this paper, we present the reason why measuring distance errors of earth-fault distance relays occur even when these two residual current compensation methods are used. Furthermore, with the compensation method that uses both reactive and resistive compensation factors, we have shown that depending upon whether the ratio, (RG/RA) of the line to earth resistance (RG) to line to line resistance (RA) is larger or smaller than the resistive compensation factor (R0/R1) that an earth-fault distance relay will respectively either overreach or underreach for a double line to earth fault.