Variation of UPFC controllable parameters during power swing and their impacts on distance relay

Unified power flow controller (UPFC) has impact on the performance of distance relay during power swing. Generally, power system's parameters oscillate during power swing and since UPFC operation depends on some of these parameters (bus voltage, active and reactive power), the UPFC injects oscillated series voltage and draws oscillated shunt current. These oscillating series voltage and shunt current influence distance relays, as the impedance seen by a distance relay during power swing changes in UPFC-compensated lines. This study shows how and why series voltage and shunt current change during power swing. Moreover, the admittance swing characteristic is proposed in this study and effects of series and shunt branches of UPFC on the admittance seen by a distance relay during power swing have been examined.