An Advance Compensated Mho Relay for Protection of TCSC Transmission Line

This paper describes a new high speed Mho distance protection scheme for single line to ground faults in TCSC (Thyristor Controlled Series Compensator) line in which fault voltage and current at relay point and firing angle from the TCSC substation are taken as the input for the Mho relay. In this scheme compensated impedance inserted by TCSC in the fault loop is calculated in a separate unit which is then subtracted from the total fault impedance and the resultant impedance fed as input to the conventional Mho relay. The proposed Mho relay model is tested for the protection of 220 kV, 200 km long and up to 70 % series compensated transmission line in PSCAD/EMTDC simulation software. Upon extensive testing at different fault location with continuously varying compensation level, loading and fault resistances, the developed Mho relay is found to be quite promising. Simulation results indicate that the proposed Mho relay does not shows any over-reaching and under-reaching effects as shown by the conventional Mho relay and the operating time of Mho relay is less than one cycle.