FDTD surge analysis of grounding electrodes considering soil ionization

• Validity of Ala et al.’s soil-ionization model is tested against several electrodes.
• Values of adjustable constants for this model are determined.
• Progressions of soil ionization around grounding electrodes are visualized.

Recently, Ala et al. (2008) [7] have proposed a soil ionization model, on the basis of the dynamic soil-resistivity model of Liew and Darveniza (1974) [16], for finite-difference time-domain (FDTD) computations, and tested the validity of the model against experiments on a single vertical grounding conductor. In the model, the resistivity of each soil-representing cell is controlled by the instantaneous value of the electric field there and time. In this paper, in order to test the validity of this model more thoroughly, it has been applied to analyzing the surge responses of different grounding electrodes: a horizontal grounding conductor of lengths 8.1 m and 34 m, a vertical grounding conductor of lengths 1 m and 1.5 m, and four parallel vertical conductors of length 3.05 m, buried in different-resistivity soils. The FDTD-computed responses agree reasonably well with the corresponding ones measured by Sekioka et al. (1998) [17], Asaoka et al. (2005) [19], Geri et al. (1992) [23], and Bellaschi et al. (1942) [24].