The volt-time characteristics of oil-impregnated paper insulation in the submicrosecond and microsecond regime

The dielectric breakdown of oil-impregnated paper insulation was studied. Fast-front step voltages and standard lightning impulses were used to determine the breakdown volt-time characteristics of the insulation. Breakdown time lags in the submicrosecond range were obtained with the fast-front voltages. A model was proposed for the breakdown time lag probabilities. The model relies on charge injection from the cathode followed by the generation of intense local fields arising from structural fluctuations within the dielectric. The parameters for the probability functions were estimated from the fast-front measurements, and the limiting probability envelopes were derived for the standard lightning impulses. Satisfactory agreement was observed between the calculated probability envelopes and measured data, thus indicating that the physical processes leading to breakdown do not change substantially over the time regime investigated