Study of visible discharge onset and development on ice surfaces

This paper reports the results of a laboratory study on the first visible discharges developed on ice surfaces with micro air-gaps, using ultra high-speed photography. Two metallic hemispherical capped rods, 12 mm in diameter and half submerged in ice, were used. A relatively short air-gap was made at different locations in the ice, between the electrodes. The development of visible discharges, under lightning impulse voltage as well as the 50% impulse lightning breakdown voltage were determined as a function of air-gap position and voltage polarity. The results found will contribute to a better understanding of combined air-gap and ice surface flashover, and could help for the design of insulators destined to cold climate regions.