A directional comparison pilot protection scheme for hybrid HVDC transmission lines

The hybrid high-voltage direct current (HVDC) transmission system comprising a line commutated converter (LCC) at the sending end and a voltage source converter (VSC) at the receiving end combines the advantages of both LCC and VSC and compensates their drawbacks. In order to guarantee the safe operation of the hybrid HVDC system, a directional comparison pilot protection for hybrid HVDC transmission lines is proposed in this paper. Fault direction is discriminated based on the different characteristics of current fault component under forward fault and backward fault. The faulty pole is identified based on the different variation trends of voltages at faulty pole and non-faulty pole. Simulation results show that the proposed protection is able to distinguish the internal faults from the external faults, identify the faulty pole, and has enough sensitivity to high transition resistance fault as well.