Finite element model of impulse dispersing characteristics of grounding equipment in layered soil

The process of impulse current scattering into layered soil possesses obvious feature of nonlinear variation. Based on electromagnetic field theory a finite element model is established to analyze the impulse characteristics of grounding device in layered soil. In the analysis on the nonlinear process, both conduction current and displacement current are taken into account to reflect the physical process of impulse current scattering into layered soil accurately. To cope with the problem that the finite element computation is not easy to converge due to the sudden change of resistivity at the boundary surface between the grounding conductor and that between the interfaces of layered soil, a method, in which the smooth step function with continuous partial derivative is used for the transition, is adopted; to transform the infinitive scattering space into finite computational region, a geometric coordinate transform method for the soil with layered structure is proposed, thus the calculated amount is reduced while the computation accuracy can be ensured. Simulation results and experimental results are compared and analyzed, and it is shown that using the proposed model the non-linear variation due to non-uniform ionization of soil and the randomness of discharge channel in layered soil structure can be simulated well, thus the effectiveness of the proposed model is validated.