Studies on the aging processes of polymers in electrical systems

After a definition of electrical systems in which polymers play the role of the insulating material, the macroscopic failures occurring in the polymer under working conditions are presented. Some aspects of aging, like electr ical or water treeing, are considered dependent on the morphology and the i nduced characteristics of the insulating material. The understanding of the aging process of LDPE and XLPE is achieved through the use of original tec hniques, e.g. electroluminescence, confocal laser scanning microscopy, ther mally stimulated creep. The slow degradation of the polymer characterized b y the break of bonds may lead to submicrocracks which coalesce to produce d efects of critical sizes. Indeed, it is shown how the presence of gas-fille d cavities in the insulating material is one of the causes of breakdown. Th e synergistic effect of the discharge species impinging on the polymer is p resented. The discharge activity is extended to new insulating materials li ke poly(ethylene 2,6-naphthalate) (PEN) films. An overview of the recent mo dels is given in conclusion to point out the needs for a better understandi ng of the aging mechanisms.