Calculation of Earth Surface Potential and Neutral Current Caused by HVDC Considering Three-Dimensional Complex Soil Structure

In ground return mode of high-voltage direct current (HVDC) transmission, direct current is injected into the soil through a ground electrode, causing ground potential rise in different areas and direct current at the neutral point of transformers. Earth surface potential (ESP) and neutral current are closely related to the 3-D structure of soil, but few studies treat the soil three dimensionally when calculating these two parameters. In this article, a 3-D resistor network (RN) is developed to construct the soil model, and a soil–grid unified circuit model is proposed to simplify the calculation of neutral current. The RN method is verified by calculating ESP of a horizontal multilayer soil model and contrasting the result with that of CDEGS software. The feasibility and accuracy of the soil–grid unified circuit model is demonstrated through comparing neutral currents of two substations with the results calculated by finite-element method (FEM). The influence of resistivity changes in a water-bearing fault on ESP and neutral current is specifically analyzed using RN method and FEM to prove the necessity of considering the 3-D complex soil structure. The results of this article contribute to the simulation of DC distribution of wide-area HVDC transmission in complex soil structures.