Influence of Water, Acid Rain and Bentonite on Ionization Characteristics of Sand under Lightning Impulse Voltage

Change in soil ionization surrounding a ground rod electrode after impulse voltage application with addition of water, acid rain and bentonite to different sized sand is examined. Impulse voltage and current responses in a rod-plane configuration show a characteristic change in sand ionization and breakdown with addition of water and gap length but no effect from voltage polarity. Soil ionization voltage (V50) and time to ionization (tbd) of sand are found to be increasing with increase in its grain size. Increase in water content in sand decreases the V50 and tbd indicating increased ionization activity. Acid rain-sand mixture shows approximately the same V50 as water mixed with sand, but a lower tbd due to increased ion concentration and new functional groups formation, as observed through FTIR patterns. Bentonite-sand mixture shows lower V50 than sand, especially with large grain size due to filled voids. This is attributed to a decrease in permittivity and an increase in plasma temperature after addition of bentonite to sand, as verified by measurements. Modifications of the physico-chemical properties of sand and bentonite are also observed when the samples are subjected to successive impulse voltages; these changes are verified by XRD, FTIR, VSM, LIBS and DRS analyses.