Theoretical analysis on the internal discharge in gas-filled voids in insulating media

When an alternating stress is applied across an insulating medium containing a gas-filled void so that ionization occurs within the void, a partial discharge may ensue via multiplication of electrons in the void (Townsend avalanche). The “state” of the ionized gas is considered by the techniques of the classical kinetic theory. The Boltzmann transport equation which describes the time evolution of the density of charged particles is taken as the basis of the analysis. After considering the mechanisms of collision, drift, acceleration, absorption, and particle creation, an expression describing the partial discharge is obtained. Solutions of the expression, for the time intervals before and after a partial discharge, give the average kinetic energy and shape of the discharge pulse. The results are correlated with published experimental findings on the degradation of solid dielectric media: in particular accelerated frequency and hydrogen atmosphere degradation.