Abstract:

The grounding methods for multi-terminal voltage source converter based high voltage direct current （VSC-HVDC） transmission system in Zhoushan were researched, and the grounding method for each converter station was determined, in which star ground reactance with neutral grounding resistor were recommended for Dinghai and Daishan converter station, while Y/Y converter transformer with neutral grounding resistor were recommended for Qushan, Yangshan and Sijiao converter station. On this basis, the overvoltage and insulation levels of converter station equipments were calculated. For Dinghai and Daishan converter station, the rated voltage of equipment at the ac side of the converter transformer is 220 kV, the lightning impulse insulation level for equipments at this zone are 950 kV. For the other three stations, the rated voltage is 110 kV, the lightning impulse insulation level is 450 kV; the insulation level of lightning impulse and that of switching impulse for AC equipment at the valve side of the transformer are 650 kV （or 750 kV） and 550 kV; insulations for 200 kV DC polar line are suggested to 650 kV （or 750 kV） and 550 kV respectively. 

Key words: modular multi-level converter （MMC）, multi-terminal voltage source converter based high voltage direct current （VSC-HVDC）, converter station, grounding method, overvoltage, insulation level