Surface profile effect on streamer propagation and breakdown in air

In a uniform field arrangement, under direct voltage, positive streamer pro pagation and breakdown are investigated along cylindrical insulators with d ifferent profiles, inserted perpendicularly between two parallel plane elec trodes. The basic properties of streamer propagation and breakdown, namely the electric field required for a stable propagation together with the asso ciated velocity and the breakdown field together with time to breakdown, ar e measured as influenced by the pulse voltage amplitude used for the stream er initiation and by the insulator profile. It is shown that a strong relat ion between streamer propagation and breakdown exists, because the insulato r profile exerts a similar influence on the breakdown and propagation field s. The effect of a shed on an insulating surface, forming an 'obstruction' to streamer progress, is to increase the stability for propagation and brea kdown fields, and to reduce the propagation velocity at all applied fields compared with those in the case of a smooth insulator. Along the surface of a smooth insulator, a streamer system propagates with a 'surface' and an ' air' component; however, a shed on an insulating surface modifies this syst em, resulting in only one component reaching the cathode.