Cable Surge Arrester Operation Due to Transient Overvoltages Under DC-Side Faults in the MMC-HVDC Link

The dc cables of the voltage-sourced converter-based HVDC link, including the modular multilevel converter (MMC) configuration, must be protected by surge arresters against transient overvoltages. The selection of the appropriate surge arresters requires a comprehensive understanding of the phenomena that cause the overvoltages and accurate calculation of energy discharged in the arresters. This paper investigates the mechanism that causes transient overvoltages, due to dc-side line-to-ground faults, in a cable-connected MMC-HVDC link. This paper also evaluates the impacts of various system parameters, for example, the prefault power transfer level, the MMC arm inductance, the transformer leakage inductance, the fault location, the ac system short-circuit capacity, the cable inductance, and the MMC blocking delay, on the peak transient overvoltages and the amount of energy discharge in the cable surge arresters. The transient overvoltage studies are also conducted when the dc cable is replaced by an overhead line. The studies are performed in the PSCAD platform. The studies conclude that the prefault power transfer level and the MMC blocking delay have the most significant impacts on the surge arrester energy discharge under dc-side line-to-ground faults in the MMC-HVDC link. The study results also provide essential information for the design of the MMC-HVDC link components.