Setting Considerations of Distance Relay for UHV/EHV Long Transmission Lines

UHV/EHV long transmission lines have large distributed capacitance and small shunt reactors, both of which have comparable impedance with the line impedance, therefore have significant effects on the operation of a distance relay. To set the distance relay without considering any of the above two factors will cause serious overreaching or underreaching. This paper analyzes the effect of distributed capacitance and shunt reactors on the apparent impedance of a distance relay, and therefore points out the setting principles of distance relay for UHV/EHV long transmission lines. Plenty of EMTDC simulations have proved that the analysis results are correct and the setting principles can ensure the reliability and selectivity of the distance relay for UHV/EHV long transmission lines.