A novel method to differentiate a fault from power swing using impedance angle rate

Proper discrimination of a fault from power swing is a challenge due to the similar variations in impedance observed by a distance relay in transmission lines. This article proposes a novel scheme to differentiate a fault from power swing using impedance angle and rate of change of impedance angle. A simple power system was chosen to understand the locus of impedance angle and rate of change of impedance angle. The situations considered include normal operation, stable swings for different power factor, stable swing for different swinging amplitude/frequency, unstable swing and faults during power swing. Based on the variation in impedance angle, regions were demarcated to indicate tripping region, restraining region, marginal stability and unstable regions.