Space Charge and Soil Ionization: An Electro-kinetic Approach

This paper proposes an electro-kinetic model of soil ionization for concentrated electrodes submitted to impulse currents. This approach allows a better understanding of the dynamic response of earth rods. Since current density attains a sufficient value around the electrode, ionization appears in the soil and produces a transient reduction of the grounding resistance. Experimental results, obtained under well-controlled conditions in laboratory, indicate that the injected energy is the most important parameter in the transient resistance reduction, rather than the crest value of impulse currents. The meaning of this resistance reduction is interpreted by the electro-kinetic model that calculates the resistance-time variation by computing the energy required to arrange a distribution of space charge around the electrode. A practical conclusion of this energy-depending interpretation for grounding electrodes, is that with ionization it would be attended a significant and durable reduction of the transient resistance for long impulse currents.