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 electrical or water treeing, are considered dependent on the morphology and the induced characteristics of the insulating material. The understanding of the aging process of LDPE and XLPE is achieved through the use of original techniques, e.g. electroluminescence, confocal laser scanning microscopy, thermally stimulated crcep. The slow degradation of the polymer characterized by the break of bonds may lead to submicrocracks which coalesce to produce defects of critical sizes. Indeed, it is shown how the presence of gas-filled cavities in the insulating material is one of the causes of breakdown. The synergistic effect of the discharge species impinging on the polymer is prescnted. The discharge activity is cxtended to new insulating materials like poly(ethylene 2,6-naphthalate) (PEN) films. An overview of the rccent models is given in conclusion to point out the needs for a better understanding of the aging mechanisms.