The ubiquitous positive streamer

It is argued that the positive streamer mechanism in liquid insulators can be considered as a natural progression from the streamer process occurring in high-pressure gases. The streamer tip propagates under the influence of the applied Laplacian field and the Coulomb field of the tip charge and its image. The streamer will only propagate if the initial discharge at the anode is of sufficient magnitude. An increase in tip charge with streamer growth is required to account for branching. This increase is occasioned by charge movement within the conducting filament. The model suggests a limiting tip charge of approximately 5 pC, and photographs show that rate at which branches form. Taken together with the derived values of tip velocity, minimum filament currents of approximately 200 mu A can be deduced. It is suggested that the streamer model proposed is consistent with most of the experimental evidence available relating to the positive discharge.