Analysis of Ionization Phenomena in Soils under Impulse Voltages

초록

This paper presents characteristics of soil ionization when high currents such as lightning and switching surge currents are injected into a ground rod. In order to divert properly surge currents into the ground, it is necessary that grounding systems are designed with the low level grounding impedance. Thus, the laboratory experiments are carried out based on factors affecting the soil resistivities. The soil resistivities are largely changed by water contents. Ionization characteristics of soil are analyzed in different soil resistivities. The hemispherical test cell and an electrode were used to simulate the uniform electric field. As a result, a threshold electric field intensity Ec initiating ionization is decreased with reduction of soil resistivities. Also as the water content increase, the pre-ionization resistance R1 and post-ionization resistance R2 were getting lower with increasing current magnitude. Finally, the time to ionization t1 and the time to second current peak t2 at high applied voltages were significantly shorter than those of low applied voltages.