Mho relay for protection of series compensated line

Mho distance relays are widely used for the protection of uncompensated and series compensated transmission lines in order to determine the presence and location of faults. This paper investigates a Mho relay model and its compensation algorithm. The residual current compensation algorithm is used to compensate the error in the impedance measurement and detect correct fault location under earth fault conditions. The Mho relay model is used for the protection of a 270 kV, 326 km long 40% series compensated transmission line using the EMTP-RV simulation package. The relay model detects faults by measuring and comparing phase angles between voltage and current signals through a phase comparator, using four impedance circles characteristics. The paper presents the simulation results under various fault types, fault locations, fault resistances and MOV reference voltages.