An Improved Pilot Relaying Scheme for Shunt Compensated Transmission Line Protection Based on Superimposed Reactive Power Coefficients

The fault component power and energy based relaying schemes have limitation during double-phase to ground fault due to the mutual coupling effect. This article presents a superimposed reactive power coefficient (SRPC) based pilot relaying scheme for the protection of shunt compensated transmission line. SRPC of a phase is defined as the ratio of integrated superimposed reactive power (SRP) of that phase to the maximum magnitude of integrated SRPs among all three phases. If SRPC of any phase is found less than ?0.5, an internal fault is detected and that phase is considered as a faulty phase. If no phase possesses SRPC less than ?0.5, the fault is an external fault. The algorithm will start only if the superimposed differential current of any phase is found more than 50% of pre-fault differential current. The results are obtained using PSCAD/EMTDC software for different conditions, such as different fault resistances, fault locations, static VAR compensator locations, and source impedances. The proposed scheme is found robust and accurate for all the cases considered. The performance of the proposed scheme is superior to the recently proposed similar type of scheme and is unaffected from capacitive coupled voltage transformer and current transformer measurement errors and synchronization error.