Implementation of Multifunction Relay for Three Zone Protection of Transmission Line

Abstract

The multifunction relay includes quadrilateral relay, overcurrent relay, under/over voltage relay and under/over frequency relay and has been implemented at the generating end of a 5 bus system in Simulink. The three phase voltage and current signals have been sampled at 20 kHz for LG, LL and LLG faults with varying distance, fault resistance and inception angle. The DC offset has been filtered from the current signal using full cycle window. The fundamental component of voltage and current signals has been extracted using FFT algorithm full cycle window. The fault resistance (R) and reactance (X) have been calculated using sine and cosine coefficients of voltages and currents for LG, LL and LLG faults. These values of R and X have been used for implementation of three zone protection scheme of transmission line. The effect of arc resistance and power swing on the quadrilateral relay has also been analyzed. The impedance seen by the relay has been calculated for location of the fault after its classification.