Effects of UPFC on measured impedance by distance relay in double-circuit lines

This paper presents the measured impedance at the relaying point in the presence of unified power flow controller (UPFC), one of flexible alternating current transmission system (FACTS) devices, on a double circuit transmission line. The presence of UPFC on a 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 ground fault resistance. In the presence of UPFC, its structural and controlling parameters as well as its installation location affect the measured impedance. The measured impedance at relaying point is evaluated due to the concerning parameters.