Modified Protection Algorithm for a Non-Homogeneous Shunt-Compensated Transmission Line Against Phase-to-Ground Fault

Traditional digital distance relaying scheme is used to protect the transmission lines against various abnormal conditions/faults. In this article, 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 PV integrated microgrid is considered at one end of a doubly-fed transmission line network to analyze the effect of weak source, thereby, incorporating the concept of non-homogeneity in the system. A modified protection algorithm is proposed to mitigate the effect of all the aforementioned variations on the protection of shunt-compensated transmission line. This protection algorithm 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. Modified DFT algorithm is used to improve the transient response and operating time of the relaying algorithm. MATLAB/Simulink software is used to verify the proposed algorithm using non-homogeneous power system.