A Pilot Protection Scheme for HVDC Transmission Lines Based on Simultaneous Existence of Forward and Backward Voltage Travelling Waves

A pilot protection method that uses the forward and backward voltage travelling waves to identify DC line faults is proposed in this paper. This method is based on the idea that under internal faults forward and backward travelling waves are observed at both sides of the line within a specific time period. However, under external faults and depending on their direction, backward voltage travelling wave is not observed at one of the terminals. Therefore, a transient-based criterion based on simultaneous existence of line-mode forward and backward voltage travelling waves is proposed. It is shown that the proposed protection method is able to identify internal faults at any location along the line with fault resistance up to 1000 Ω with fast response and high sensitivity and selectivity. Performance evaluations of the proposed protection method is performed using a bipolar MMC-HVDC transmission line, simulated in PSCAD/EMTDC.