A Novel Protection Scheme for HVDC Transmission Lines Based on DC-Filter Current and DC Line Current

HVDC effectively transmits large amounts of electrical energy using DC (direct current) over long distances by overhead transmission lines, underground cables, and submarine cables. HVDC system is also used to connect separate power systems with different characteristics and frequencies in which AC transmission is impossible [1]. HVDC transmission line protection is essential for the safety and reliability of the power grid due to the extensive use of the HVDC transmission line. Various faults can occur in the HVDC system, such as AC, internal converter, and DC faults. Failure may occur due to insulation failure due to short circuits, switching, and lightning, which imposes new challenges to protecting the HVDC transmission line. To address these challenges, a new protection scheme for HVDC transmission lines is proposed in this paper based on the flow characteristics of DC filters and DC line current. The flow characteristics of DC filters and the current passing through the DC line are theoretically analyzed for internal and external faults in a constant fault period. Moreover, this flow profile is used as a backup protection scheme to identify pole-to-ground faults, the worst of all. A 500 kV HVDC system built in PSCAD/EMTDC is used to verify the validity of the proposed protection scheme. The simulations show that the protection scheme proposed in this paper can not only accurately detect internal and external faults but is not sensitive to the amount of fault resistance and distance.