Earticle

This paper presents a novel current differential protection scheme for UHV/EHV transmis-sion lines. This method is based on active current component extraction using instantaneous power theory, which is also called ip-iq method, and it has been widely used in APF (active power filter). Adopt three digital PLL (phase-locked loop) to get the positive voltage’s angle and active current containing DC and AC components can be obtained by using dq transfor-mation. The average filter is employed to filter the AC active current component out. This algorithm can eliminate the influence of distributed capacity current fundamentally. Com-pared to compensation methods, it requires no heavy computation, line parameters and volt-age information transmission. Compared to other differential protection methods, it has the advantages of clear physical meaning and simple operation. Simulation results show that the novel protection method is effective and robust, providing a new perspective on transmission lines’ protection.