Effects of SMES Equipped UPFC on Distance Relay Tripping Characteristic

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, which is equipped with a superconductor magnetic energy storage (SMES) system. The presence of SMES equipped UPFC on a transmission line greatly influences 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 SMES equipped UPFC, its structural and controlling parameters as well as its installation location affects the measured impedance. Here, the measured impedance at the relaying point is presented due to the mentioned affecting parameters.