A New Approach to Transmission Line Pilot Protection in the Presence of Inverter-Interfaced Distributed Generators

In recent decades, the penetration of inverter-interfaced distributed generators (IIDGs) in power systems has increased significantly due to the environmental and economic benefits. The increasing participation of IIDGs and the developments of power electronic technologies have raised the possibility of controlling the power injected by IIDGs for regulating the voltage level, especially during short-circuit fault conditions, following the regional grid codes. When a short-circuit fault occurs on the transmission line connected to the IIDGs bus, a dramatic voltage drop occurs. In this situation, the IIDG injects the reactive power fast that disrupts the performance of the distance relay as a result of which the operation of the relay in different operational conditions may either over reach or under reach. In this article, a comprehensive analysis is accomplished regarding the errors imposed on the estimated impedance of the distance relay, due to the voltage control of IIDGs, in single and double-circuit transmission lines. Then, an impedance-based pilot protection method is proposed to enhance the performance of the transmission line protection relays affected by the reactive power injected by the IIDGs.