Adaptive Mho distance relay for combined transmission line: An optimization technique for charging current compensation

Abstract

The combined transmission system is expanding due to beatification and safety considerations and enhanced reliability in the distribution and transmission systems. It is expected to improve distance relay operation in presence of combined transmission system. Distance relay with Mho characteristics is simulated to mitigate the charging current effect of combined system with significant part of underground cable. The combined system is modelled mathematically based on the equivalent pi model to increase the accuracy. The distance relay is simulated based on the mathematical equation. The rate of charging current is compensation is extracted for single line to ground, line to line to ground and three-phase faults. The charging current compensation rate is extracted by direct search and the feasible solution is extracted by Utopia point approach. The findings show the fault with high resistance faces distance relay to mal-operation. The compensation of charging current can significantly mitigate the mis-operation rate of Mho distance relay. Due to the zone characteristics is constant, the selected value of charging current compensation required to have minimum overreach and underreach rates. By injecting the optimal charging current compensation rate at the relay point, the operation of Mho relay bounces to more than 99.5% for combined transmission system.