Measured impedance by distance relay for inter phase faults in presence of UPFC

This paper presents the effects of unified power flow controller (UPFC), one of flexible alternating current transmission system (FACTS) devices, on the measured impedance at the relaying point in the case of inter phase, phase to phase and three phase, faults. The measured impedance at the relaying point is affected by several factors, including the line pre-fault loading, the line structural conditions, and specially the fault resistance. In the presence of UPFC, in addition to its structural and controlling parameters, its installation point also affects the measured impedance at the relaying point. The variation of the measured impedance for different UPFC installation points and controlling parameters would also be investigated.