Failure analysis of in-service aged 11 kV silicone rubber composite insulators

Composite insulators made of Silicone rubber (SiR) weather sheds have been deployed in power system networks due to their ability to offer exemplary insulation performance under wet and polluted environments. Aging of these insulators under various environmental conditions is one of the most important areas that has to be explored for understanding their performance. In the present work, the in-service failed/aged insulators are analyzed to understand their aging mechanism. Various experimental investigations including contact angle measurements, Scanning electron microscopy (SEM), energy dispersive X ray (EDAX) and Fourier transform infrared spectroscopy (FTIR) are performed on the affected locations of in-service failed 11 kV composite insulators. The surface structural changes are analyzed using contact angle measurements and SEM imaging techniques, elemental compositions are obtained using EDAX and optical properties of the shed material is studied using FTIR technique. Electric field computation along the insulators showed that the electric field magnitudes are within the limits (~ 3 kV/cm). SEM imaging showed changes in the SiR surface and reduction of contact angle up to 47% is also observed for failed insulators. EDAX and FTIR analysis revealed significant reduction of Si and Aluminum Trihydrate (ATH) in SiR material which led to the failure of these insulators. Contrastingly, an increment of oxygen content is observed due to oxidation. The possible reasons for the failures, suggestions to enhance the composite insulator life, and complexities to be addressed are also proposed.