A Novel Protection Based on Phase Difference of Voltage and Current for DC Lines in Hybrid Multi-terminal HVDC Transmission System

A novel protection based on phase difference between voltage and current for DC lines in hybrid multi-terminal HVDC system is proposed in this paper. On the basis of analysis on fault traveling wave propagation, the Peterson equivalent circuit is derived. Based on this, fault analysis demonstrates that for the three parallel DC lines which connect the LCC station and MMC stations on the receiving side of hybrid HVDC system, for faulty line, at high frequency, the phase difference between the fault voltage traveling wave at the bus and the fault current traveling wave at the measuring point is -90°. Whereas, for non-fault line, the phase difference between fault voltage and current traveling wave is 90°. Thus, the protection is constructed utilizing the phase difference. Simulations verify that the proposed protection can correctly distinguish the faulty line, and can detect the high-impedance faults sensitively. Besides, the proposed protection is immune to fault position and has no requirement for data synchronization.