Simulation on the time dependence of breakdown strength in insulating polymers

On the basis of the percolation model for electrical breakdown in insulating polymers, a simulation approach was put forward for the process of electrical aging. The deteriorated regions formed by bond scission are expressed as the sites with lower trap barriers, and the local deterioration rate is related to both the electrical field and the size of existing deteriorated regions. Then the reduction of breakdown strength (or the percolation threshold) with the increase of deteriorated sites can be simulated. Assuming a parameter β to reflect the effect of the size of existing deteriorated region, simulation results show two types of breakdown: percolationlike breakdown for β ≤ 2 (in which the percolation threshold is reduced due to the gradual global increase of deteriorated sites) and avalanchelike breakdown for β < 1 (in which breakdown occurs by the rapid growth of a filamentary structure). Moreover, it is indicated that the lifetime might not be in inverse proportion to the local deterioration rate in the case of percolationlike breakdown.