Analysis of soil ionization behaviors under impulse currents

Abstract

This paper presents the characteristics of soil ionization for different water contents, and the parameters associated with the dynamic properties of a simple model grounding system subject to lightning impulse currents. The laboratory experiments for this study were carried out based on factors affecting the soil resistivities. The soil resistivities are adjusted with water contents in the range from 2 to 8% by weight. A test cell with a spherical electrode buried in the middle of the hemispherical container was used. As a result, the electric field intensity Ec initiating ionization is decreased with the reduction of soil resistivities. Also, as the water content increased, the pre-ionization resistance R1 and the post-ionization resistance R2 became lower with increasing current amplitude. The time-lag to ionization t1 and the time-lag to the second current peak t2 at high applied voltages were significantly shorter than those of low applied voltages. It was found that the soil ionization behaviors are highly dependent on the water content and the applied voltage amplitude.