Research on Distribution Characteristics of DC Potential Near the UHVDC Grounding Electrode

The rated current of ±800kV Ultra High Voltage Direct Current (UHVDC) Transmission system can be up to 6250A, so that the influence of the DC grounding current of electrode is enormous. It is of great significance to understand the distribution characteristics of DC earth potential near the grounding electrodes and the influence of the grounding current to propose prevention and controlling schemes. According to the needs of Shanghaimiao-to-Shandong UHVDC terminal grounding electrode DC bias treatment project, a three-dimensional (3D) earth resistance model of 310km depth is established by the data of shallow earth resistance measurement and deep magnetotelluric data of 1°×1° longitude and latitude measurement point. The distribution of earth surface potential in the total area of 204.3 thousand square kilometers under 6250A DC is calculated by the finite element method. The results show that the larger the current entering the grounding electrode, the larger the influence range. Additionally, the distribution of equipotential lines were relatively dense in the area 80 kilometers away from coastline under the influence of coast effect and sparse in the area with high earth resistance.