We have applied infrared, Raman and UV-VIS spectroscopy to measure spatially resolved chemical composition and structure of cross-linked polyethylene insulated cables used in the EC-funded Artemis project, both before and after electrical and thermal stressing. The work shows that diffusion of the primary products of chemical crosslinking changes the quasi-parabolic concentration radial profile present in new cables to an almost flat distribution in stressed cables. There is also evidence for loss of these products and some level of incorporation with the polymer due to thermal conditioning. The UV data suggest that these compounds are attached to the polyethylene, providing quite large chromophores consisting of aromatic rings, carbonyl groups and unsaturation that can act as trapping centers.
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