Breakdown mechanisms in a pulse-charged spark gap

The breakdown strength of a highly overvoltaged gas spark gap operating in air has been extensively investigated. The switch, which operated in a self-breakdown mode, was used to discharge a water Blumlein charged to peak voltages of 250 kV. At a charging rate of 20 kV/μs, overvoltages greater than a factor of three were measured at a pressure of 1 atmosphere. With UV preionization, the overvoltage was substantially reduced. A comprehensive model has been developed that precisely relates the DC and pulse-charge breakdown voltage in terms of the statistical delay and the streamer transit time. The dependence of these contributions over a pressure range of 1 to 5.5 atmospheres was considered. The statistical delay, which was eliminated with preionization, was inversely proportional to pressure and could be related to an effective surface roughness