Influence of humidity on the breakdown of sphere and rod gaps under impulse voltages of short and long wavefronts

Humidity-correction factors have been obtained for the breakdown of a 50 cm sphere gap, rod-rod gap and rod-plane gap using impulse voltages of both polarities up to 500 kV and having waveshapes of 1/50 ¿s 1/1000 ¿s and 80/1000 ¿s. The correction factor for all waves for the sphere-gap breakdown is 0.3% per g/m3. The factors for other gaps do not appear to depend much on gaplength over the voltage range 130 kV to 500 kV. Standard deviations of the scatter of results fall with increased spacing to about 2%, with one or two exceptions, and are not dependent on humidity for the range of 4¿18.6 g/m3 investigated.