The impacts of series compensated EHV lines on distance protection, and a proposed new mitigation solution

Abstract: Series compensation is extensively applied to the transmission lines to increase the power transfer capability of transmission lines, reduce transmission losses, improve voltage profiles, and improve power oscillation damping and transient stability of power systems. But it modifies the apparent impedance of the transmission lines during fault conditions and might cause the distance protection of transmission lines to encounter directional discrimination issues and reach problems. The non-linear characteristic of metal oxide varistor in series compensation model creates further complexity to the fault analysis and might affects the performance of conventional distance protection scheme. The distance protection issues in the series compensated lines need to be addressed for the reliable and sustainable operation of power system.The directional discrimination issues related to current inversion and voltage inversion phenomenon, and reach problems related to sub-synchronous oscillation phenomenon are addressed in this thesis report. This report aims to analyse the impacts of series compensation on the performance of conventional distance relays, and proposes a new protection solution to mitigate the shortcomings of distance relays in the series compensated lines. The proposed new protection solution includes: new tripping characteristic of quadrilateral distance relays to cope with the steady-state reach problems due to current or voltage inversion, and a new high-pass filtering technique to handle the transient reach problems due to SSO.The proposed new protection algorithm is developed in MATLAB. The performance of new protection algorithm is evaluated by simulating a 500 kV two-source power system with a 200 km series compensated line in EMTDC/ PSCAD (Manitoba Hydro). The proposed new protection solution is found to be beneficial.