Impulse breakdown characteristics of dry sand: Effect of sand grain size

Soil ionization, that is, electrical discharges developing in ground, occurs due to the high electric field associated mainly with lightning currents. Despite having attracted a great interest among researchers from the beginning of the 20th century, soil ionization is far from being completely understood owing to the complex nature and structure of soil. This study investigates breakdown of several dry natural silica sand samples in a quasi-uniform electric field electrode arrangement under standard lightning impulse voltages. The dependence of sand breakdown gradient and time delay on the grain size is assessed. Corona inception, thus also breakdown, is favored by the sand grains as compared with the case of air alone.