Modified Protection Algorithm for Shunt Compensated Doubly-fed Line against Phase-to-ground Fault

Abstract

Traditional digital distance relaying scheme is used to protect the transmission lines against various abnormal conditions/faults. In this paper, the authors have discussed the adverse effects of fault and system parameters, such as fault resistance, fault location, power transfer angle etc., on the performance of the protection scheme. Further, a modified protection algorithm is developed to mitigate the effect of weak sources/non-homogeneous network on the protection of shunt-compensated doubly-fed transmission line. It also improves the performance of the protection scheme during all the aforesaid variations in system and fault parameters. The modified protection scheme is based on the mathematical analysis of the sequence components of voltage, current and impedance of the network components. An equivalent impedance vector for each of the above-stated fault and system parameters is obtained and the relationship between these vectors is represented in vectorial form. With the help of this vector diagram and the mathematical analysis, the actual impedance of faulted part of the line is calculated. Since the algorithm is derived mathematically, it is simple to understand and user-friendly. A negligible error is observed while simulating the modified protection algorithm considering all the severe variations in fault and system parameters. MATLAB/Simulink software is used to verify the developed algorithm using 50 Hz frequency of the power system.