A STUDY OF THE INCEPTION OF POSITIVE STREAMERS IN CYCLOHEXANE AND PENTANE

This paper presents an experimental study of the inception of positive streamers in point-to-plane geometry under pulsed voltage. The differ ent pre-breakdown events (slow and filamentary streamers) are characte rized via sensitive transient current recordings, obtained using a new differential measurement technique described in the text. The roles o f the tip radius, voltage pulse rise time, gap distance and hydrostati c pressure are systematically investigated in two liquids, cyclohexane and pentane. We found two parameters to characterize inception of bot h streamer types in a liquid: a unique initiation field for slow and f ilamentary streamers (depending slightly on the point tip radius of cu rvature); and a threshold propagation voltage for filamentary streamer s (depending on the gap distance). There is also a critical point-tip radius above which no slow streamers are observed. It is shown that th e initiation field and the propagation threshold can be accurately det ermined only in very specific conditions, namely below the critical po int-tip radius and with fast rise time voltage impulses (about 10 ns). The presence of a gaseous phase in the initiation process is identifi ed via the influence of hydrostatic pressure. Finally, the significanc e of the critical point-tip radius and that of the propagation voltage of filamentary streamers are discussed by comparison between the stre amer and a conducting filament.