Improved differential protection scheme for long distance UHVDC transmission line

This study concerns the misoperation of differential protection of long distance UHVDC transmission line under external faults. The two main factors that have effect on the sensitivity of differential protection long distance UHVDC transmission line are discussed in this study: transient harmonic currents and shunt branch currents. With the improved protection scheme presented in this paper, the two factors can be removed and the reliability and sensitivity of the differential protection can be improved.