Measured impedance by distance relay in presence of UPFC on next line

This paper discusses the distance relay ideal tripping characteristic in the presence of unified power flow controller (UPFC), one of flexible alternating current transmission system (FACTS) devices on the next line and pays especial attention to the distance relay over-reaching problem. This is done by presenting the measured impedance at the relaying point in the presence of UPFC at the near end of the next line. The measured impedance at the relaying point is greatly influenced in the presence of UPFC on the protected line or even on the near end of the next line. The measured impedance depends on many factors including the power system structural conditions, pre-fault loading, ground fault resistance, UPFC structural and controlling parameters.