Investigation of soil ionization propagation in two-layer soil samples

Abstract

High current lightning strikes into earthing systems can result in ionization in the soil surrounding the earthing electrode. Most of the published studies investigating this phenomenon have assumed uniform one-layer soil, but soil ionization propagation in a multilayered soil sample has not been extensively addressed. Practical soils may consist of several layers with different water contents, and hence soil resistivity will vary continuously with depth. This investigation considers several sand samples, consisting of two layers with different water contents subjected to standard lightning impulse voltages. A rod-plane electrode configuration was constructed inside a cylindrical plastic test rig, in order to house both wet and dry soil test samples. In order to quantify the propagation of ionization inside the test sample, voltage probes were installed along the tube at specific positions. Localized changes in the ionization zone potential could, therefore, be monitored in real time.

Investigations on the Performance of Grounding Device with Spike Rods (GDSR) with the Effects of Soil Resistivity and Configurations

“…It is also observed that the earth electrodes in high resistivity soil (site 4) have a significant reduction in Z impulse with increasing current magnitudes (for all configurations) and the reduction in Z impulse becomes less current-dependent for earth electrodes in low resistivity soil (site 3). This is similar to the results observed in References [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], which suggested that the decrease in Z impulse with current magnitudes is due to an ionisation process in the soil. In high resistivity soil, more field enhancement could have taken place due to more air voids, hence more non-linearity in Z impulse , in comparison to low resistivity soil.…”

“…Despite much research work [5][6][7][8][9][10][11][12][13][14] published on the impulse characteristics of grounding systems for different soil resistivities, the measurements are still important due to many variations in soil. Elzowawi et al [15] performed a series of tests, having a two-layer soil model with various thicknesses and percentages of water content for both layers. They [16] found that differences in soil resistivity affect the impulse characteristics of grounding systems.…”

Effect of high resistivity soil under high impulse currents

“…Reffin et al [1] found that a high percentage of impulse impedance reduction of grounding systems installed in high resistivity soil, in comparison to that grounding systems installed in low resistivity soil. It was also evident by Elzowawi et al [13] that, when the dry soil or low water content of sand soil was used as the upper layer, whereby the lower layer was filled with high percentage of water content, there was an initiation of ionization around the electrode at the upper layer, followed by further propagation to the lower layer, an indication that a larger degree of soil ionisation process in high resistivity soil.…”

Transient analysis of earthing electrodes considering soil ionization phenomenon under lightning impulse condition

“…Time-domain approach to study the transient behavior of earthing electrodes by considering the mutual inductance and capacitance are reported in [18]. The soil ionization and breakdown delay are investigated by researches in their experimental work for a two-layer soil model with different moisture contents [19,20]. Consideration of soil residual resistivity and soil dynamic behavior makes the soil ionization phenomenon more accurate during the breakdown period [21,22].…”