High-speed photography of prebreakdown phenomena in dielectric liquids under highly non-uniform field conditions

Abstract

The electrical breakdown process in dielectric liquids for a point-to-plane gap configuration has been studied, using an image converter camera in conjunction with an image intensifier and a schlieren system. It is shown that the positive streamer has a tendency to keep its propagation velocity constant across the gap. The constant streamer velocity in benzene and toluene is equal to that of the accompanying shock wave. Discrete transition from primary streamer to fast secondary is occasionally observed for positive polarity. The aspect of negative streamer propagation in carbon tetrachloride is similar to that of the positive one. The development of the actual breakdown channel has also been observed in carbon tetrachloride. The results are consistent with models of a breakdown mechanism based on a field ionization process for positive polarity and an Auger-like electron emission process for negative polarity.

A survey of streamer and diffuse glow dynamics observed in sprites using telescopic imagery

“…[14] Studies of breakdown phenomena in liquids have shown that shock waves can be created by streamers forming rings of ripples emanating from the streamer tips. These shock waves have been found to have slower velocities than the causative streamers [Devins et al, 1981;Yamada et al, 1990]. A similar phenomenon may be present in the atmospheric breakdowns such as that observed in this example.…”

“…Models of positive and negative streamers in air have shown that positive streamers have a higher electric field in their head and a higher electron density, but a lower channel electric field [ Babaeva and Naidis , 1997]. It has been found in studies of breakdown in dielectric liquids that positive streamers appeared with a lower crest voltage, lower light emission and higher velocity than negative streamers [ Yamada et al , 1990; Massala and Lesaint , 2001]. It is possible that the more slowly propagating negative streamer with a higher channel field allows for a greater enhancement of the electric field surrounding dust microspires and thus accounts for the asymmetry of bead formation.…”

Streamers in water and other dielectric liquids

“…For n-hexane they found an average positive streamer velocity of 2.7 km s −1 while negative streamers were only moving forward at 0.15 km s −1 . The difference is smaller in transformer oil, where positive streamers are slower (2.2 km s −1 ) but negative streamers much faster (1.1 km s −1 ) [140,141]. As a result, the propagation velocity of positive streamers, in particular, seems to be independent of the liquid and for hydrocarbon liquids has the same value as for water.…”

“…In particular, Hebner and Devins also gave accounts of the propagation velocities of positive streamers in n-hexane, finding a linear increase with gap lengths from 1 to 2 km s −1 [136,138,139]. Yamada reported on the same dielectric liquid but obtained higher values of up to 7 km s −1 and associated these high velocities with a 'fast mode' of streamer propagation [140]. Yamada and, independently, Yoshino had earlier compared measurements between different dielectric liquids.…”

Untitled

“…On the experimental side, dielectric breakdown can be difficult to study due to its short time scales and high energies. Despite this, several studies illustrate breakdown with high-speed photography [Yamada et al 1990;Auckland et al 1975;Budenstein 1980;Auckland et al 1981]. Breakdown in solids has been studied in detail in single crystals in [Neusel et al 2012].…”