Travelling wave directional pilot protection for hybrid HVDC transmission line

Abstract As known, hybrid high-voltage direct current (HVDC) is wide applied in power system. Because two converter stations are line commutated converter based HVDC (LCC-HVDC) type and voltage source converter based HVDC (VSC-HVDC) type respectively, the HVDC transmission line (HVDC-TL) has special travelling wave (TW) propagation characteristic. Especially, due to the capacitance installed at VSC-HVDC station, the relay at VSC-HVDC side cannot detect voltage TW (VTW) signal. Meanwhile, TW protection is widely applied in HVDC transmission system, but it has no fault direction recognition ability. Hence, the paper proposes a novel TW directional pilot protection. Firstly, the paper analyzes the special propagation characteristics of TW along HVDC-TL. Secondly, the paper proposes novel fault direction discrimination criterions based on the integration of instantaneous power and current at LCC-HVDC side and VSC-HVDC side, respectively. Meanwhile, faulty pole selection criterion is also proposed based on the ratio of positive pole current to negative pole current. Thirdly, based on PSCAD/EMTDC, a simulation model of ± 400 kV LCC-VSC-HVDC transmission system is established. And the simulation results prove that the proposed protection method is immune to fault location, fault resistance and fault type.