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 paper shows how and why series voltage
and shunt current change during power swing. Moreover, the admittance swing characteristic is
proposed in this paper and effects of series and shunt branches of UPFC on the admittance seen by
a distance relay during power swing have been examined.
keywords:Admittance, Distance relay, Power Swing, Unified Power Flow Controller (UPFC).