A Novel Traveling-Wave Directional Relay Based on Apparent Surge Impedance

A novel directional relay, which is based on apparent surge impedance acquired from initial traveling waves, is proposed in this paper. The phasor of initial voltage and current traveling waves extracted by the S-transform are employed to calculate the apparent surge impedance. The criteria to determine the fault direction consist of two $mho$ circles. One is the forward $mho$ circle which is set according to the backside busbar surge impedance. The other one is the reverse $mho$ circle which is set according to the forward line surge impedance. The fault direction is determined per the relationship between the apparent surge impedance and the $mho$ circles. The proposed algorithm was verified using PSCAD/EMTEDC software. The simulation results allow us to draw a conclusion that the proposed algorithm has the ability to reliably discriminate between the forward faults and the reverse faults under various conditions.