Characteristics of impulse breakdown of standard rod gaps under controlled-atmosphere conditions

The effect of humidity, polarity and irradiation on the 1/50¿s impulse voltage breakdown and time lag of standard rod gaps has been determined for a range of spacings from 5cm to 30cm and a range of humidities from 1g/m3 to 24g/m3. An anomalous condition is reported for a 5cm unirradiated gap under positive impulses in which the slope of the humidity characteristic is opposite to that normally obtained. It is shown that, although the time lag is independent of humidity, the probability of breakdown in the sigmoid region is not independent of humidity.