New Methodology for Representing Soil Ionization in FDTD Simulations of Grounding Electrodes

Soil ionization has been represented in finite-difference time-domain (FDTD) simulations by the variation in resistivity in the cells depicting the soil. This approach represents the dynamics of soil ionization and its effect on the resistance of grounding electrodes, but it has a high computational cost as it requires discretizing the working volume into small cells. This article proposes a new method for representing the soil ionization effect on grounding electrodes in FDTD simulations. The electrode resistance is calculated based on the injected current using a dynamic soil ionization model, considering equipotential surface patterns and analytical expressions of the variation in soil resistivity. The resistance variation is then represented in FDTD by an equivalent radius. The method allows the use of coarse meshes and therefore fast simulations, while still considering the dynamics of soil ionization. Application examples with unipolar and bipolar injected current, single vertical rods of different lengths, and four parallel rods are used to validate the proposed method and compare it with the existing one. Results show good accuracy in all cases and a gain of up to 539 times in computing speed compared to the existing method, proving to be an efficient alternative for representing the phenomenon.