BREAKDOWN VOLTAGE CHARACTERISTICS OF AIR BY C7F16O4 VAPOUR-MIST SUSPENSION AND INFLUENCE OF MIST CONCENTRATION, ELECTRON IMPACT IONIZATION AND ATTACHMENT COEFFICIENTS OF VAPOUR ON ENHANCEMENT OF THE BREAKDOWN VOLTAGE

摘要

The AC and impulse breakdown voltages (V-s) of C7F16O4 (HT90) vapour-mist suspended in atmospheric air are measured far a sphere-sphere and a needle-plane gap. A significant enhancement of V-s by the vapour-mist suspension is observed. The mechanism of the enhancement is discussed in terms of data of the mist droplet diameter distribution, electron impact ionization alpha and attachment coefficient eta of the vapour, the measurements of which we also report. The V-s enhancement by the vapour suspension can be explained by the fact that the vapour has a high limiting (E/p(20)) value at which alpha/p(20)=eta/p(20) (p(20) is the gas pressure at 20 degrees C); 320 V cm(-1) Torr(-1). The effect of the mist on V-s values is found to be most pronounced for the impulse voltage case. [References: 16]