Modified distance protection in presence of upfc on a transmission line

This paper presents a modified distance protection scheme in the presence of Unified Power Flow Controller (UPFC), one of the Flexible Alternating Current Transmission System (FACTS) devices. The presence of UPFC on a transmission line has a great influence on the measured impedance at the relaying point. The measured impedance itself depends on the power system structural conditions, pre-fault loading, and especially the fault resistance. In the presence of UPFC, its controlling and structural parameters as well as its installation point affects the measured impedance. Therefore, the conventional distance schemes might not fulfil the protective duties satisfactorily and new approaches are required.