Improved Physicochemical Properties of Electrically Aged-Heat Treated Silicone Rubber

This paper deals with the understanding of aging phenomenon of coated silicone rubber (SR) high voltage insulators in service. It is mainly focused on the physicochemical analyses of electrically aged and heat treated SR films. A complete characterization of SR in the virgin state, after electrical aging (with and without pollution), as well as the virgin heat-treated and electrically aged SR after heating, at 100°C for 100 hours, is performed. Accelerated electrical testing under AC (50Hz) high voltage under pollution conditions is first conducted on both thermally treated and untreated polymer. Dielectric strength, transverse and surface resistivities, capacitance, and loss factor to characterize their performance are subsequently measured. Different chemical analyses such as the Scanning Electron Microscopy (SEM), Infrared spectroscopy (FTIR), X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), Thermo-Gravimetric Analysis (TGA/DTG) and Differential Scanning Calorimetry (DSC) are also conducted to follow the evolution at microscopic scale. These analyses are carried out on virgin (Vg), electrically aged (EA), heat treated (HT) and electrically aged-heat treated (EAHT) samples. These latter highlight the material modifications leading to the deterioration of its electrical, physical and thermal properties resulting from the electrical stress and surface discharges worsened by conductive pollution deposits. However, a short-term heat treatment at 100 °C for 100 hours significantly improves these properties in both virgin and electrically aged states, effectively slowing the aging process and restoring values closer to those of the virgin state. The in-depth characterization of SR revealed the improvement of its properties and clarified the mechanisms behind it.