Influence of Control and Protection Characteristics on Insulation Coordination of MMC-HVDC System

The operating overvoltage of HVDC (high voltage direct current) system is closely related to control and protection characteristics. At present, the overvoltage and insulation coordination of the modular multilevel converter based high voltage direct current (MMC-HVDC) system is based on the simplified control strategy recommended by the simulation software PSCAD. There are some differences between the protection action sequence of simplified control strategy and that in reality, which will have a greater impact on the simulation results of overvoltage and arrester configuration. The article considers MMC-HVDC control protection and action characteristics of arrester to study the influence of MMC-HVDC control protection characteristics on the insulation coordination. Based on actual control and protection strategy of symmetrical unipolar MMC-HVDC system, the influence of different time delays of actual control and protection on the operating characteristics of arresters under three decisive overvoltage conditions, the single-phase grounding fault on secondary side of transformer, the valve bottom grounding fault of bridge arm reactor and HVDC unipolar grounding fault are studied by simulation. The study found that the insulation coordination parameter has a large margin and is not economical under simplified control strategy. Therefore, the refusal, misoperation and coordination of the control protection should be simulated in detail to ensure that insulation coordination parameter setting margin is reasonable.