Point-to-Plane Corona in Dry Air

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Abstract
A survey study has been made of point-to-plane corona in dried air for a range of pressures and point sizes. It has been found that negative points can be satisfactorily triggered by ultraviolet illumination and that the difficulties encountered in past attempts have probably been due to too intense illumination and possibly the presence of dust on the points. Under some conditions transitions from Trichel pulses to a pulseless Townsend-type discharge have been observed for negative points at high voltage. With positive points the occurrence of pre-onset streamers has been found to depend on higher pressures and the presence of water vapor to give sufficiently high photon absorbtion. Breakdown streamers are not observed with standard geometry for the usual points sizes, because the first one always closes the gap resulting in breakdown. For points of around 2-mm diameter the gap must be about twice standard length with room air, and about two and one-half times standard length with dried air, for breakdown streamers to be observed.