Impact of UPFC on Power Swing Characteristic and Distance Relay Behavior

This paper analyzes the distance relay performance during power swing conditions for an uncompensated and compensated transmission line with a unified power-flow controller (UPFC). UPFC can control voltage and power flow of the transmission line independently; hence, it has an impact on the apparent impedance seen by the distance relay. To analyze the case, the apparent impedance seen by the distance relay during a power swing is extracted, and the results are synopsized graphically. The impact of UPFC on different transmission-line parameters from an impedance point of view is investigated. Moreover, the impact of different operation modes of UPFC and their reference values on the apparent impedance seen by concentric$mho$circles as a power swing detection method are also evaluated by detailed simulations.