A new differential protection scheme for fixed series-compensated transmission line

This paper proposes an improvement of a new differential protection technique for three-phase transmission line together with series compensation using a hybrid technique based on discrete Fourier transform (DFT) and discrete Haar wavelet transform (DHWT). The proposed technique relies on the three-phase currents of the series compensation-based transmission line at the sending and at the receiving ends, respectively. Initially, the measured three-phase line currents at both the relaying buses are processed using DFT to get the matrix of fundamental components of three-phase fault currents. Subsequently, the acquired fundamental components are decomposed into five levels of approximate coefficients decomposition using the DHWT. Consequently, the maximum amplitude of spectral energy-index of the fifth level approximate coefficients of the fundamental components at both the buses is computed, and then the differential spectral energy (DSE)-index is calculated to detect the fault and categorize the faulty phase in series compensation-based transmission line. The proposed technique is extensively tested using the model of a 400-kV, 200-km transmission line with series compensation at mid-point of line and simulated in MATLAB/Simulink. The proposed technique is far and wide assessed against near-in relay faults, far-end relay faults, evolving faults, multi-location faults, forward faults, reverse faults, open-circuit faults, internal faults, and external faults. Furthermore, the proposed hybrid technique is tested for different feasible fault switching, with sources of different power ratings, sudden load switching events, with varying degree of series compensation, and with varying fault resistance between 0.5 and 500 ohms. The simulation outcomes represent that all types of abovementioned faults, faulty zone, and the fault phase can be exemplarily recognized within a full cycle time and the proposed hybrid technique is flexible to the modification of faulty type, fault switching time, fault location, fault resistance, ground resistance, degree of series compensation, and power ratings of both sources and loads.