Research on protection block strategy of grounding faults in HVDC converter station

摘要

DC grounding fault is a typical fault for HVDC system. In order to obtain smoother, faster, and more secure transient process, the DC protection block strategy is used to remove and isolate the converter to prevent the accident enlargement and reduce the impact on devices and power grid when the grounding fault is detected. Two main strategies are commonly taken in this situation: the X block for not >±500 kV and the S block for ±800 kV. There is no specific principle on the strategy choosing for ±1100 kV UHVDC system with hierarchical connection mode. Changji–Guquan ±1100 kV UHVDC transmission project adopting hierarchical connection mode at receiving end. In this study, the effects of different DC block strategies when grounding faults occurred in both converter stations are compared based on PSCAD simulation. The simulation results indicate that the overvoltage at rectifier side has two stages while the overvoltage at inverter side has only one. Taking S block strategy can cause lower overvoltage but longer oscillation duration on grounding current. The proper block strategy for ±1100 kV UHVDC grounding faults is adopting S block at rectifier side and X block at inverter side.