Research on Fast Conversion Method of Metallic Return to Earth Return Operation mode in HVDC System

The grounding current at monopolar ground retrun opertaion mode of the HVDC system will adversely affect the surrounding environment. In order to reduce the influence of the grounding current, it is necessary to reduce the conversion time from earth return to metallic return operation mode. The fast conversion method was studied in this paper, two technical methods using Bypass(BPS) switch and converter valve bypass pair were proposed. It is verified through simulation that these two methods can reduce conversion time to about 3s, and effectively reduce the impact of grounding current. At the same time, the proposed method has no effect on existing primary equipment and doesn’t require additional equipment.