Finite-Element Model of the Grounding Electrode Impulse Characteristics in a Complex Soil Structure Based on Geometric Coordinate Transformation

This paper presents a finite-element method (FEM) based on Maxwell differential equations to analyze the impulse characteristics of the grounding system in a complex soil structure. The geometric coordinate transformation is leaded into the FEM and the soil parameters in the transformation domain are determined by comparing the original coordinates without drawing the geometric construction of the soil. The unit smoothing function with continuous partial derivative is adopted to solve the convergent difficulty caused by the resistivity jumping on the medium interface. The model is validated by comparing the results with the classic methods combined with field-circuit and simulation experiments. The simulation results show that the current dispersal proportion from the external conductors of the grounding grid, especially from the four corner points, is higher than that of the internal conductors. The resistivity of the soil that surrounds the grounding electrodes reduces under impulse current and the resistivity of the soil that surrounds the external conductors is lower than the resistivity of the soil that surrounds the internal conductors. These situations change more drastically under higher injected current.