UV degradation of polymers for outdoor HV equipment: Aging diagnostic test using FMIR techniques

Insulators with polymer weather sheds are finding increasing use in high-voltage overhead transmission lines. Compared to conventional ceramic insulators, they have several advantages: not only are they lightweight and easy to install but they have better insulation strength under certain contaminated conditions. Apart from the design or manufacturing process, the various types of polymer insulator commercially available also differ from the point of view of the rubber base: silicone rubber, ethylene-propylene rubber (EPM) or ethyl-ene-propylene-diene rubber (EPDM), as well as the fillers and additives used. Ranking the best polymer formulations is still a matter of discussion in the industry. Accelerated-aging tests are usually performed for that purpose, and a wide variety of aging criteria have been proposed to evaluate polymer degradation, such as tensile strength, elongation to break, tracking endurance [1], [2] hardness, swelling or surface oxidation by ATR infrared spectrometry [3]. However, dependable quantitative data allowing definite conclusions to be drawn about the long-term reliability of insulators in service cannot always be obtained by these techniques. The present work investigates a new method of evaluation of surface chalking of the insulators, using FMIR infrared techniques.