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

The initiation and development of discharges from a point cathode have been studied as a function of viscosity. The initial growth rate and the transition from a small roughly spherical region to a multibranched geometry have been recorded for a wide range of viscosities using a CCD (charge-coupled device) camera and Framestore. Measurements are reported on the development of the instabilities. It is deduced that electrical forces predominate in the cavity expansion. The instabilities are a natural consequence of growth. As viscosities rise to 100 cSt and above, the form of the breakdown instability changes. A pointed protrusion from the cavity begets another cavity to produce a sausagelike thick filament or thick-filament tree. The basic instability then looks like that described by C.G. Garton and Z. Krasucki (1964)