Analysis of Surface Degradation of Silicon Rubber Insulators after 30 Years in-Service

Abstract

In recent years, polymeric insulators have been increasingly used for high voltage overhead transmission lines. The industry has replaced the insulators from ceramic to polymeric due to its lightweight and hydrophobic materials, not to mention the performance against pollutant contamination. In this study, an analysis of two 70 kV silicone rubber insulators is performed. The insulators had been in service for 30 years on transmission networks in volcanic area, exposed to intense UV solar radiation in midday, but also high precipitation occur throughout the year. The urge to understand better of polymeric aging behavior is important to improve the quality of the polymeric type insulators. In this study, these aged samples were then compared with virgin samples to identify the endurance and quality of polymer material. The surface deterioration and the change of chemical content were evaluated using advanced techniques, including Spectroscopy and Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Analysis (EDX), Thermo-Gravimetric Analysis (TGA), and Fourier Transform Infrared (FTIR). Meanwhile, the hydrophobic and visual inspection were also conducted. The hydrophobicity was evaluated by measuring the contact angle and assessed using IEC62073. The aged samples are categorized as hydrophobic class 1 due to the angle value of more than 60o. Physicochemical results showed that the aged sample compared with the virgin simple did not differ significantly given that the aged samples have been in-service for 30 years. Based on TG/DTA result, the percentage difference of weight loss between virgin and aged sample only lower than 4%. Then, from EDX result, the atomic percentage differences of C and O component compared with virgin sample are 4%-10%. Furthermore, the FTIR spectra indicates a normal aging condition of the silicone rubber, the difference in peak value of Si-(CH3)2 and OH compared with virgin sample is 10%.