Power Swing Detection in UPFC-Compensated Line by Phase Angle of Current

Power swing blocker (PSB) is a complementary part of distance relay protection, that detects power swing, in order to prevent unintended operation of a distance relay. Unified power flow controller (UPFC) is used in power system to control both active and reactive powers and its operation during power swing influences the performance of PSB. In this paper, two traditional methods for detecting power swing are analyzed in UPFC-compensated condition to show how UPFC influences the performance of these methods. The indices proposed for the above-mentioned methods are examined in compensated condition. The results show that these indices may no longer work in systems with UPFC. In addition, this paper proposes a new method for detecting power swing based on the phase angle of current at relay point and compares it with two other methods. The new method distinguishes power swing from a fault through the trend of the phase angle of current. Finally, intensive studies are performed and simulations demonstrate the merits of the proposed method.