The role of negative ions in the propagation of discharges across insulating surfaces

Abstract

The relative importance of atmospheric negative ions in corona formation and breakdown in a radial electric field has been investigated, with special reference to effects occurring at an insulating surface of a cycloaliphatic polyurethane with dolomite filler. The inception times, corona charge, light emission (by UV photography) and sparkover voltages under lightning impulses have been recorded under natural atmospheric conditions and under the influence of negative ions introduced from an auxiliary corona. The presence of excess negative ions on the surface is shown to increase both the charge injected and the mean radius of the corona, attributable to an augmentation of streamer discharges. In similar experiments in air, the excess ions cause a transition to a `glow' discharge. Effects of negative ions on sparkover are not significant on the insulator surface, but they cause a small increase in air. Comparisons between the two cases lead to the conclusion that the most important effect of the ions on the surface is to provide `seed' electrons for streamer propagation, following ion detachment in the field of advancing streamer tips.

Study of the Development of Positive Streamers Along an Ice Surface

“…However when discharge is taking place over a gas/insulator interface results from previous investigations have shown that the critical volume as typically defined in air is not well appropriate to describe the conditions of streamer inception [36]. Moreover based on this present work, our camera recordings revealed that corona streamers on ice surface can be initiated midway of the surface, far from the HV rod electrode, as illustrated in Figure 5b.…”

Role of electronegative gas admixtures in streamer start, propagation and branching phenomena

“…The relative importance of atmospheric negative ions in corona formation and breakdown has been investigated many times (see, e.g. [32]). As already mentioned, the main negatively charged species in cold air plasmas is O − 2 , but only free electrons play a role in streamer propagation.…”

Effect of micro-fillers in polytetrafluoroethylene insulators on the characteristics of surface discharges in presence of SF6, CO2 and SF6-CO2 mixture

“…In addition, several mechanisms have been advanced to explain the mechanisms implicated in their initiation and development. Among these mechanisms the dynamic interaction between the discharge and the insulator surface [5 -7], the accumulation of electrical charge at the insulator surface [8][9][10][11][12][13][14], the modification of the ionisation and attachment coefficient [15,16] and the distortion of electric field [17,18]. Therefore the understanding of the initiation conditions of creeping discharges and the parameters characterising their development up to breakdown or flashover is very helpful for the design and the dimensioning of high-voltage components and systems (bushings, insulators, switchgears, gas insulating lines, gas circuit breaker .…”