Affected by factors such as land acquisition and site selection difficulties, more and more HVDC projects selects common grounding electrode to be constructed. When HVDC system with the common grounding electrode are both in monopolar operations, one of them during the earth-to-metal loop conversions will cause the grounding grid of the converter station to form a parallel connection between the electrode by the fast grounding switch. The current is introduced into the grounding grid of the converter station, causing a risk of stepping voltage and contacting voltage of the grounding grid of the converter station, causing a DC bias magnetic of the converter transformer. This paper calculates and analyzes the safety risk of stepping voltage and contacting voltage caused by the shunt of the common grounding converter station, and points out the safety risk of DC bias magnetic of the converter transformer.

electrode, converter station, shunt, DC bias