The residual resistivity in soil ionization region around grounding system for different experimental results

The residual soil resistivity at peak of injection current with lightning current wave shape in soil ionization region around the grounding system is analyzed based on different experimental results in the literature by E.E. Oettle (1988), P.L. Bellaschi et al. (1942) and A.C. Liew and M. Darveniza (1974) and the recent experimental results in the high voltage laboratory at Uppsala University. The results show that the residual resistivity in soil ionization region is changing largely versus different soil resistivity ranging from 50 Ωm to 827 Ωm. Combining all the data, the geometric mean of the residual soil resistivity in ionization region is approximately 7% of the original soil resistivity. This value of 7% can be used in modeling of the transient behavior of grounding system under the lightning strike including non-linear soil ionization phenomenon.