Electrical aging of extruded dielectric cables: a physical model

A model is proposed to describe the electrical aging of polymeric cable insulation. It is based on simple thermodynamic concepts in the Eyring theory and supposes that the first step in electrical aging is essentially a molecular process. The authors´ model of electrical aging under AC fields supposes that the molecular-chain deformation which will generate submicrocavities in the amorphous region of the insulation, is essentially a fatigue process. Above a critical field F_c, there is an exponential relation between time and field, whereas below F _c, the breakdown strength of the insulation varies very little with time; in other words, there is very limited aging. The model confirms that there is a relation between cable endurance and the insulation morphology, and that the size or submicrocavities is ultimately limited by the amorphous-phase thickness