Transient Potential Power Based Supervisory Zone-1 Operation During Unstable Power Swing

Unstable power swing (UPS) may cause unwanted zone-1 tripping. This is caused due to presence of electrical center within the reach of zone-1 of distance relay. Fast detection of unstable swing can assist distance relay in taking reliable decision. This paper suggests a new coordinate system with transient potential power as they-coordinate and angular difference of positive sequence voltage phasors across the transmission line (δ
_SR
) as the x-coordinate. We observed that this coordinate system can be useful to successfully differentiate an UPS from stable power swing (SPS) and three phase fault. The prediction is fast enough to prevent an unwanted zone-1 operation of distance relay. IEEE-39 bus New England test system is used to validate the proposed scheme. The suggested method showed improved and fast unstable swing detection accuracy under different pre-disturbance and fault conditions.