Influence of radiation on the sparkover of sphere-plane gaps stressed with impulse voltages

The influence of ¿ radiation and some X radiation on the sparkover of sphere-plane gaps has been studied using spheres of 6.25, 15 and 25 cm diameter, under impulse voltages of both polarities up to 500 kV, and having wavefronts of 1 to 180 ¿s, all impulses having the same 1000 ¿s wavetail. In general, the use of the 100 mCi ¿-ray source slightly lowers the sparkover voltage V50 and fractional probability range for all impulses of positive polarity and wavefront duration of up to 13 ¿s. With longer wavefronts, radiation increases the sparkover voltage of some of the gaps. The effects on negative polarity are small. Circuit parameters have been found to have an important influence on some sparkover voltages.