Affect of photo-oxidation products on electroluminescence emission and conduction current of LDPE

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Description/Abstract

There is great interest in understanding the effects of long term ageing and degradation of high voltage insulation in an effort to improve its lifetime and efficiency. One area of interest regards the movement and interaction of charge within the polymeric insulation. Under ac electric stress polymers give out a faint light known as electroluminescence (EL), this emission is thought to relate to the charge injection, trapping and recombination near the electrode-polymer interface. The ultraviolet (UV) ageing of low density polyethylene (LDPE) films has shown an increase in oxidation products (carbonyl and hydroxyl groups) which may act as extra charge trapping sites. Samples have been masked during ageing such that a direct comparison in EL intensity can be made between both the aged and virgin condition. Initial EL measurements on aged materials have shown an increasing intensity and shift in phase angle for short ageing times but reduced emission in heavily aged samples. This change in EL is thought to relate to the easier injection of charge carriers and extra availability of charge trapping sites after short ageing times but then increased conduction through the material after heavy ageing reducing the availability of charge for recombination. The full paper will compare increases in oxidation products due to UV ageing with EL emission and conduction current in LDPE samples.