Evaluation the Electrical Properties of XLPE Cable Insulation Material Aged Under the Combined Effects of Thermal Stress and UV-Radiation

Cross-linked polyethylene (XLPE) is widely used as insulation material for power cables. In spite of its outstanding mechanical and electrical characteristics, XLPE may undergo degradation under service conditions. It is well known that temperature and UV radiations are the most aggressive stresses inducing degradation in XLPE insulation, especially under oxidative conditions (air). In this paper, the combined effects of thermal and accelerated UV-radiation aging on the dielectric properties of XLPE specimen used as power cables insulation material have been investigated. The resulting structural deteriorations were quantified by measuring and evaluating the dielectric permittivity$(\varepsilon^{\prime})$, dielectric loss factor (tanδ) and dielectric loss index$(\varepsilon^{\prime\prime})$as function of aging time and frequency. Experimental results showed that the XLPE structure and related physical properties are considerably affected by the combined aging. Indeed, it was found that the dielectric parameters of XLPE are significantly changed as functions of aging time and frequency.