Current differential protection principle of HVDC transmission system

Traditional high-voltage DC (HVDC) current differential protection has problems on identifying fault current and has long delay. In this study, a novel current differential protection principle for HVDC transmission lines is proposed. By the adoption of distributed parameter model, differential current criterion is formed at a selected point on the transmission line. When fault occurs on DC line, setting point differential current reaches a high value. When no fault occurs or fault occurs outside the DC line, setting point differential current reaches a small value. Comparing with the traditional current differential protection, the proposed principle eliminates the impact of distributed capacitive current and has no requirement of delay. Comparing with travelling wave protection, fault identification can be performed during both transient and steady states, and the proposed method has reasonable sampling frequency requirements and has high reliability. Simulation analysis shows that the proposed principle identifies faults reliably and rapidly. The proposed principle is theoretically novel and practically applicable.