The Effect of Wave Shape on the Electric Breakdown of Nitrogen Gas

The electric breakdown of nitrogen gas is determined using direct and 60-Hz voltage and impulse waves of both positive and negative polarity over the range of ½ × 10 to 550 × 9000 microseconds. The electrode system is composed of a 1-inch diameter brass sphere and a 1¾-inch-diameter square-edged brass plane with a spacing between them of ½ inch. The voltages are adjusted in small increments to give breakdown occurrences from 0 to 100 percent of the time. The change in voltage breakdown level for nitrogen gas as a function of time to voltage crest is shown to be markedly different from the generally accepted voltage-time curve for solid insulations. In the latter case the longer times to voltage crest invariably show lower voltage levels. By contrast, the voltage breakdown level for nitrogen gas for impulse waves of the order of switching surge length is even greater than that for an impulse wave reaching a crest around 0.5 us. In some cases the level of the 10 percent incidence of the voltage breakdown of nitrogen is found to be as low as one-half of that for the 90 percent incidence.