Development of a Novel Protection Device for Bipolar HVDC Transmission Lines

A novel nonunit transient-based protection scheme for bipolar high-voltage direct current (HVDC) lines is proposed. The protection scheme is composed of a starting unit, a boundary unit, a directional unit, a faulty pole identification unit, and a lightning disturbance identification unit. The prototype based on the proposed scheme is developed and its performance is evaluated through a hardware-in-the-loop test using real-time digital simulator (RTDS) and real HVDC control devices. Better than the presently used line protection, the proposed protection not only can detect faults on HVDC lines more rapidly and accurately in different HVDC operation modes, but is also more effective in detecting high-impedance grounding faults. In addition, the novel protection is designed to identify lightning disturbances from short-circuit faults correctly, which avoids the unnecessary restart of HVDC systems due to protection misjudgment.