Laboratory Measurement of the Impulse Characteristics of Wet Sand

Electrical discharges occurring in the ground, commonly called soil ionization, may have a significant impact on the lightning impulse behavior of grounding systems causing a large reduction of the impulse ground impedance. The effects of soil ionization have not been fully clarified yet due to the dependence on excitation current characteristics, ground electrode configuration, as well as on soil characteristics and conditions. This study presents an experimental setup and measurement procedure for the investigation of the impulse behavior of soil. Experiments are performed on wet sand under lightning impulse voltages of negative polarity. Results are analyzed and discussed considering soil ionization inception, soil breakdown and impulse impedance. A preliminary attempt is made to develop a simulation model suitable for EMTP-type software so as to reproduce the temporal variation of the impulse impedance obtained through experiments.