On the growth rate of instabilities occurring during the electrical breakdown of silicone fluids

Abstract

The initiation and development of discharges from a point cathode has been studied as a function of viscosity. The initial growth rate and the transition from a small roughly spherical region to a multi-branched geometry have been recorded for a wide range of viscosities using a CCD camera and Framestore. fleasurements are reported on the development of the instabilities. D U C T I ONSeveral stages are discernible in the development of the negative discharge from a point cathode. Following the initial charge injection (of a sufficient magnitude to produce a spheroidal cavity) this cavity expands, develops an instability leading to the growth of branches and the branches extend across the gap ultimately leading to the breakdown arc. Watson has proposed that the transition from spheroid to branched structure is governed by a process analogous to the gravity driven Rayleigh-Taylor instability. In this case the instability is driven by the electrical force on charge at the interface. EXPERIMENTAL . . . . , . , . Single-flash shadow photographs of the development of the negative discharge as a function of time. applied single stage Capacitor (Marx) Voltage pulse generator. Store. The results have allowed the growth of the velocity-growth plots can be made. The effective width measurement [figure 11 using a photo-diode. It is approximately one third of a micro-second under the conditions of use. The finite width of the light flash is evident on the shadow photographs [figure 21 of the flash produces a "fuzzy" edge.