A distance protection relay for a 1000-kV UHV transmission line

A traditional distance protection relay uses a lumped parameter model of the transmission line. For a long 1000-kV UHV line with large distributed capacitance, such a simplified line model is inadequate and can cause malfunction of the relay due to large errors in the impedance measurement. This paper presents a new line model for a distance relay and the procedure of reliable fault impedance measurement and relay setting. It describes the proposed application of the relay developed to a 645-km 1000-kV UHV transmission line including shunt reactor compensation, which is currently being constructed in China. Tests are carried out on an RTDS (real time dynamic system) to evaluate the relay performance, showing significant improvement compared to a more traditional distance relay. The new distance relay is shown to satisfy the requirement of 1000-kV UHV transmission line protection