Influence of impulse waveshape on breakdown voltage of a nonuniform-​field gap in compressed gases

The effects were studied of the pulse wave-​shapes, gas pressure (p)​, and polarity on the breakdown voltage (Vs) of a sphere-​plane gap in compressed air and N. The pressure was 0-​150 lb​/in2 gage, the gap spacing was 6.35-​102 mm, and the risetimes of the pulsed voltage was 2.1-​189 μsec. For a pulsed voltage of either polarity, certain gap lengths exhibited a crit.-​pressure effect, and the gap lengths and the pressure at which this effect was obsd. depended on the risetime of the pulsed voltage. Observations of the dependence of Vs on the risetime showed that Vs decreased with increasing risetimes, for risetimes of 16 μsec or 40 μsec, beyond which it increased again to reach a max. at risetimes of the order of 100 μsec. For risetimes >100 μsec, Vs again decreased with increasing risetime. This behavior was similar for both N and air. Possible mechanisms are suggested to explain this behavior