Abstract
Ionisation can occur in the soil when high impulse currents are subjected to grounding systems. This occurrence is generated by a difference in the dielectric strength value between the soil and air voids. Several published works investigating the ionisation process in soil have seen that the degree of ionisation is dependent on several factors, among them soil resistivity, ground electrode size and impulse polarity. The effects on soil resistivity, such as the moisture content in soil, soil grain size, type of soil and its temperature, have been studied; however, the effect of the size of air voids in soil has not been extensively presented. This study considered four rod electrodes—a conventional rod electrode, conventional electrode with porous concrete (PC), conventional electrode with concrete mixed with a foaming agent (FC) and conventional electrode with concrete (NC)—to provide variations in the size of air voids. Resistance values, RDC, were measured for all these electrodes, and we found that the conventional rod electrode had the lowest value. A detailed evaluation of these rod electrodes under high impulse conditions revealed that similar current rise and discharge times were seen in all electrodes; however, PC, with the largest size of air voids, had the lowest impulse impedance (Zimp value) for the current magnitudes below 2 kA.