Fault impedance calculation algorithms for transmission line distance protection

Abstract

Two algorithms are proposed to calculate the apparent impedance of a transmission line fault. They calculate the apparent impedance using the integral and difference operations from sampled data sets. The data window of the proposed basic algorithm requires only two samples. The modified algorithm can eliminate the second-, third-, fourth- and their multiple-order harmonics. Simulated fault data generated by a transmission line model are used for testing the proposed algorithms. The test results show that they have the advantages of a small amount of calculation and short data window, and are suitable for high speed digital distance relays.