Potentials'' Distribution in high resistivity soil around extended grounding electrodes

The potential distribution in high resistivity soil around extended grounding electrodes has been described in the paper. The high-voltage polygon has been developed for experimental investigation. It is well known that direct or indirect lightning discharges could produce dangerous conditions for human body, as well as unwanted electromagnetic interferences among electrical and electronic systems. Therefore the electromagnetic characterization of earth electrodes under high pulse transient currents is an important highpoint in the design of a grounding system. The Marx generator was developed to generate impulse similar to lightning impulse. The potentials have been measured by the probe measurement system previously developed. Grounding resistance is the main characteristic of the grounding systems. From the literature analysis and experimental data it has been shown that steady state grounding resistance can differ from impulse grounding resistance. This phenomenon is caused by the ionization process and sparking occurring in the surrounding soil. Channel spark resistance is much less soil resistivity, therefore the soil resistivity and grounding resistance decrease. Calculations of potentials in the soil have been carried out using the finite element method. The experimental data have been compared with the results of the potential distribution calculation. It has been shown that the resulting spark channels in soils significantly affect the potential distribution. Accordingly, the sparking channels are to be considered while calculating the step voltage.