Electrical aging test and accelerated water tree aging test for physicochemical properties of XLPE insulation

To reveal the effects of electrical aging test (ETA) and accelerated water tree aging test (AWTT) on physicochemical properties of XLPE insulation, the actual cable samples of ETA and AWTT were tested by infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TG), and the changing rule with aging of physicochemical properties was analyzed. A microscopic structure model of AWTT was established, and aging mechanism was deeply discussed from the aspects of morphology and the formation of traps. It is found that R₁R₂C=CH₂ and -OH in ETA and AWTT samples tend to increasing. The growth rate of -OH in AWTT samples is higher than that in ETA samples, while the growth rates of double bond in both ETA and AWTT samples are almost the same. The crystallinity of ETA samples increases first and then decreases, while that of AWTT samples becomes smaller, and the thermal stability of ETA and AWTT samples gets worse. Peak separation in DTG curves of ETA samples is not found, but multiple peaks can be found in the DTG curves of AWTT samples and more peaks are found after a longer aging period. The results suggest that the established model combing with the change of charge traps well explains the change of the physicochemical properties during aging, and the traps exert obvious effect on insulating properties of XLPE.