Distance protection in the presence of unified power flow controller

The presence of an important flexible AC transmission systems (FACTS) device like unified power flow controller (UPFC) can drastically affect the performance of a distance relay in a two-terminal system connected by a double-circuit transmission line. The control characteristics of the UPFC, its location on the transmission system and the fault resistance, especially the high ones make this problem more severe and complicated. The fault location with respect to the UPFC position also greatly influences the trip boundaries of the distance relay. The paper presents apparent impedance calculations for relaying of a double-circuit transmission system with varying UPFC parameters and location. The study reveals the adaptive nature of the protection scheme that necessitates the use of an artificial neural network (ANN) based procedure for the generation of trip boundaries during fault conditions. (C) 2000 Elsevier Science S.A. All rights reserved.