Nonlinear impulse current spreading and electrical breakdown in soil

Abstract

The results of laboratory experiments on the impulse current spreading from the spherical elec trodes and the breakdown occurring in quartz sand of various humidity at the impulse voltages of 20-40 kV are presented. It is shown that, at the current densities on the electrode above some critical value, a sharp non linear decrease of the impulse grounding resistance occurs, an ionization superheating instability develops, and thus the current contraction takes place and a plasma channel in the soil occurs. A method is proposed to determine the critical strength of the ionization electric field. It was discovered that, at long discharge gaps in humid sand, the breakdown develops with a long time delay, similarly to thermal breakdown.