Dielectric Aging and Dielectric Degradation (Breakdown) of Polymer Films in AC Electric Fields

Resumo

An explanation is proposed for the difference of the electric-strength properties of polymers in dc and ac electric fields. The energy release upon the recombination of electrons and holes injected into a polymer dielectric is considered as a factor accelerating the processes of electric aging of these dielectrics in an ac electric field. It is shown that the nonradiative relaxation of electron excited states, which causes the bond scission in macromolecules and the formation of free radicals, leads to the formation of deep electron traps in the polymer dielectric; as a result, the macromolecule ionization in an electric field is accelerated due to the transition of electrons into these traps. In the solid-state plasma, screening effect, which decreases the molecule ionization potential, appears. As a result, the macromolecule ionization rate, i.e., the rate of charge carrier formation, increases, which leads to a decrease in the lifetime of a polymer dielectric in an ac electric field as compared to the polymer lifetime in a dc electric field.