Examination of the risk of flash X-ray induced breakdown in pressurised electrical enclosures

Disruptive breakdown in gas triggered by flash X-rays is studied. For relevant electrode geometries found in electrical and electronic boxes, filled with air, nitrogen or SF₆ under a pressure between 1 and 1000 millibars, is noticed a drop in the breakdown threshold voltage when the dose rate is higher than 1E8 rad (Si)/s. The maximum drop appears at about 1E10 rad (Si)/s but is never higher than half of the static BV. For higher dose rates (1E11-1E12) the breakdown voltage tends to increase, due to the higher charge density created in the gas, which precludes to the filament formation. The impact of solid dielectrics on the phenomena is evaluated, and a protection strategy is proposed