Optimization of distance protection algorithm for double-circuit series-compensated transmission line

Distance protection still faces problems in application to parallel lines with series compensation (SC). Present practice relies on using traditional distance relays but with modified settings. As a result of that the firs zone reach is shortened to 30-40% of the line length instead of 75-80%. This paper presents optimized distance protection algorithm for double-circuit series-compensated transmission line. The algorithm considers the SC effect and can protect with first zone as much of the line as without SC. Consideration of the SC effect is done by reconstruction of three-phase voltage drops across series-capacitors bank. For this purpose a nonlinear differential equation is solved on-line, applying comparatively low sampling frequency. In order to assure high fidelity of the waveforms reconstruction using the up resampling procedure has been introduced. The other interest of this paper is in impedance calculation based on optimal solution of the fault loop model. Two methods for fault loop resistance and reactance calculation are taken for comparison. The developed algorithms have been tested and evaluated using signals taken from ATP-EMTP versatile simulations of faults on a double-circuit series-compensated transmission line. The sample results of the evaluation are presented and discussed.