High Speed Differential Protection of Series-Shunt Compensated Transmission Line Using Phaselet

A phaselet approach for the real-time differential protection of the series-shunt compensated transmission line is proposed here. Phasors of the signal using phaslet approach can be obtained at 0.4 sub cycle. The measured input currents from both ends of the transmission line are fed to the phasor estimation algorithm where both current signals are reconstructed by using the phaselet approach. An index namely, Moving Average Error (MAE) is calculated using the errors between the actual and estimated current signals taken from Current Transformers (CTs). The Rate Of Change Of Mean Average Error (ROCOMAE) of both signals is calculated and the difference of ROCOMAEs is taken, which is Trip Decision Index (TDI) for the proposed method. The operation of differential relay based on the TDI is investigated. For validation, two area system with midpoint compensation along with series compensation is also considered and simulated in Real Time Digital Simulator (RTDS) platform. Different test cases like internal fault, external fault, high impedance fault, CT saturation and series-shunt compensation are generated to test the efficacy of the proposed approach.