A New Fault-Impedance Algorithm for Distance Relaying on a Transmission Line

This paper describes a new algorithm to calculate the per phase impedance between the measurement and fault points on a transmission line, featuring robustness to the uncertainties in load current and fault path resistance. The algorithm, which is ideal for distance relaying, is derived based on a justifiable assumption of the fault path being purely resistive, implying that the unmeasured fault point voltage and fault path current are in phase with each other. This paper illustrates the characteristics of the proposed algorithm and evaluates its performance by using PSCAD/EMTDC simulation.