Research on Grounding Current Distribution in HVDC System Operating in Monopolar Mode

With the comprehensive promotion of HVDC project, the electromagnetic effect in the power system became more complicated than ever. During monopolar operation of HVDC system with ground return, there exists a DC loop between the earth and AC system, and the grounding current returned may enter into neutral points of transformers. It causes DC bias of transformers and influences the operation of transformers. To solve this problem, typical grounding electrode model and earth model have been built in the ANSYS simulation environment in this paper. Then, using the finite element method, the surface potential distribution and the influence of resistivity on it have been studied. Simultaneously, the potential field and the zero sequence current flowing into AC system have been solved with field-circuit coupled method. In addition, the interaction between adjacent transformers and the impact of the distance between the grounding pole and the converter station on the zero-sequence current calculation have been studied. Finally, combined with the experimental phenomenon, some practical suggestions and viewpoints have been put forward in this paper.