Adaptive α ‐plane line differential protection

Abstract

Alpha plane ( α -plane)-based differential relay protecting a transmission line uses the ratio of the current phasors of both ends and has numerous advantages. Such an approach either uses phase or sequence components of currents. For a normal operating condition and external fault, the ratio remains within restraining region in the α -plane. During high resistance internal fault, the computed ratio at times lies inside the restraining region resulting misoperation of the technique. The scheme which uses sequence components of the currents has limited performance for single pole tripping and line impedance unbalance conditions. In this study, two features: phase angle between voltage and current and magnitude of change in currents of both ends of the line supplement the relay in identifying an internal fault. This improves the performance of phase current-based α -plane relay. The proposed method is tested for Western Electricity Coordinating Council (WSCC) 9-bus and two source equivalent system and results for various cases show improved performance.