A study of the inception of positive streamers in cyclohexane and pentane

Abstract

This paper presents an experimental study of the inception of positive streamers in point-to-plane geometry under pulsed voltage. The different pre-breakdown events (slow and filamentary streamers) are characterized via sensitive transient current recordings, obtained using a new differential measurement technique described in the text. The roles of the tip radius, voltage pulse rise time, gap distance and hydrostatic pressure are systematically investigated in two liquids, cyclohexane and pentane. We found two parameters to characterize inception of both streamer types in a liquid: a unique initiation field for slow and filamentary streamers (depending slightly on the point tip radius of curvature); and a threshold propagation voltage for filamentary streamers (depending on the gap distance). There is also a critical point-tip radius above which no slow streamers are observed. It is shown that the initiation field and the propagation threshold can be accurately determined only in very specific conditions, namely below the critical point-tip radius and with fast rise time voltage impulses (about 10 ns). The presence of a gaseous phase in the initiation process is identified via the influence of hydrostatic pressure. Finally, the significance of the critical point-tip radius and that of the propagation voltage of filamentary streamers are discussed by comparison between the streamer and a conducting filament.