Artificial rain accelerated aging test of HDPE pin insulators for medium voltage distribution in Brazil

High density polyethylene (HDPE) is a polymer commodity widely used in manufacturing of polymer pin insulators (PIN) for medium voltage distribution. The major problem to be faced in the use of HDPE by PIN manufacturers is their low resistance to oxidative degradation in the processing step and/or the prolonged exposure of HDPE-PIN to weathering and operation voltage for a long time. This work presents the experimental results on artificial ageing test of 15 kV commercial HDPE-PIN specimens for distribution system application in Brazil. Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR/ATR) for chemical analysis, UV-visible diffuse reflectance spectroscopy (DRUV-Vis) for band-gap (Eg) evaluation, contact angle (CA) for determination of polar surface tension (γΡ) components and scanning electron microscopy (SEM) for morphological surface analysis were conducted on aged and unaged specimens. Chemical analysis results of ATR/FTIR confirmed the occurrence of oxidation reactions with significant increase of polar groups C=O at tested HDPE-PIN specimens. It was also observed a significantly increase on the contribution of γp to the surface energy for all HDPE-PIN after 500 hours of accelerated aging time. The experimental values of Eg for aged commercial HDPE-PIN samples suggest that the accelerated aging test produces structural defects in commercial HDPE-PIN samples. The SEM micrographs reveal cracks, pinholes and degradation in the form of crystals and cavities after 3,500 hours of accelerated aging test in all HDPE-PIN specimens. The physicochemical performance of the aged commercial HDPE-PIN specimens analyzed in this work indicates that the HDPE resin was not formulated to be suitable for performing in tropical medium voltage environments.