Multi-Resolution Resistor Network-Driven 3D Forward Modeling of HVDC Monopolar Geoelectric Current

This study proposes a three-dimensional forward modeling framework for geoelectric current distribution under high-voltage direct current (HVDC) monopolar operation. The proposed approach is based on a multi-resolution resistor network (MR-RN) discretization, in which gradient fusion interpolation is employed to suppress flux discontinuities at coarse–fine interfaces, and exterior equivalent boundary resistors are introduced to approximate open boundaries, enabling efficient and stable large-scale three-dimensional forward modeling. Compared with the traditional structured grid and finite element method (FEM), the proposed MR-RN achieves comparable accuracy while reducing computation time by up to 96% and the number of degrees of freedom by two orders of magnitude. Case studies on layered Earth, boundary extension, and substation–field coupling demonstrate that the MR-RN model maintains errors within 1–3%, confirming its suitability for large-scale HVDC ground return simulations and geoelectric safety assessment.