Shockwave Characteristics of Streamer Propagation in Insulating Liquids under Positive Lightning Impulse

Abstract

This paper presents an experimental study focusing on the quantitative analyses of spatial characteristics of Mach-cone shaped shockwaves generated by streamers in a mineral oil and a synthetic ester in a fixed 12 mm needle-plane gap under positive lightning impulse. The influences of voltage level and liquid type are investigated. Results showed that Mach-cone shaped shockwaves are always observed ahead of actively propagating streamer channels. In the mineral oil, instantaneous streamer velocities undergo initial bursts before gradually decreasing and stabilizing at around 2 km/s. Shockwave pressures decrease from 6-8 GPa upon the streamer initiation to around 4 GPa as streamer propagates to a longer distance. Compared to the mineral oil, the initial bursts of instantaneous streamer velocities and shockwave pressures are lower in the synthetic ester. Investigated voltage levels from initiation to near breakdown do not impose significant effects on the observed shockwave parameters. In addition, the appearance of Mach-cone shaped shockwave is found to be an effective indicator of actively propagating streamer channel which can be used as a tool to quantify streamer main branches.