Soil ionization of earth electrodes under high pulse transient currents

This paper proposes a numerical model of soil ionization phenomena that can occur when earth electrodes are injected by high pulse transient currents. The model is solved by a finite difference time domain numerical scheme. It has been developed from a thorough analysis of the available studies in technical literature about the peculiar physical dynamics of soil ionization phenomena. As already underlined, soil ionization can occur, for example, when the earth electrode has to drain a lightning current into the soil. In this case, the electric field can overcome the electrical strength and conductive plasma paths can locally grow. The dimension of these ionized air channels are strictly dependent upon the local temperature. So, a local heat balance is enforced in order to obtain the actual instant value of the conductivity of the medium. These heat balance is evaluated step by step in each lattice cell, if the actual electric field value overcomes the electrical strength. This model can be implemented both for concentrated and extended electrodes, since no hypothesis has to be enforced about the geometric shape of the ionized region. Validation of the proposed model is obtained by comparing simulation results with experimental data found in technical literature.