Distance relay ideal tripping characteristic for inter phase faults 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, in the case of inter phase, phase to phase and three phase, faults. Especial attention is paid to the 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 at relating point depends on many factors including the power system structural conditions, pre-fault loading, fault resistance, and UPFC structural and controlling parameters.