A treatment of the substation grounding grids in multilayer earth by using FEM with irregular hexahedron element

Based on finite-element method of 1-dimensional conductor element coupled with 3-dimensional soil element, a coordinate transformation is carried out. The irregular hexahedron domain of element is mapped onto a cube domain. Considering the frequency dependent characteristic of the discretized elements, the grounding performance of the substation grounding grids in multilayer earth is analyzed, and the influencing factors such as grounding resistance and earth surface potential are calculated. Compared with the results of the measurement, the presented method is proved to be correct. It reduces the number of units and speeds up the calculation obviously under the precondition that the accuracy of the calculation is adequately ensured.