Ultra‐high voltage/extra‐high voltage transmission‐line protection based on longitudinal tapped impedance

Abstract

Longitudinal current differential protection is often used as the main protection of ultra-high voltage (UHV)/extra-high voltage (EHV) transmission lines. It's sensitivity and selectivity will be severely influenced by the considerably increased distributed capacitive current with the increase of voltage level and transmission distance. In this study, a novel UHV/EHV transmission line protection is proposed based on longitudinal tapped impedance. For sound transmission line or transmission line with external faults, the calculated impedance is approximately equal to the capacitive reactance of the line. If internal faults occur on the line, the computed impedance of the faulty phase is approximately equal to the parallel value of the line capacitive reactance and the fault resistance. The proposed protection does not require the compensation of capacitive current and is not affected by load current and system impedance. This new protection principle has an improved selectivity and natural phase selection ability, and very high sensibility for high resistance faults. The correctness and effectiveness of the proposed protection have been verified by simulation tests.