Studies of the diffusion of low molecular weight silicone fluids on polluted hv silicone insulators. I. use of diffuse reflectance FTIR

The process of hydrophobic recovery of surface-polluted silicone rubber weather sheds on high voltage (HV) composite insulators was studied by applying an artificial kaolin coating to a sample of clean silicone rubber surface. Quantitative analysis of the kaolin coating into which had diffused low molecular weight silicones (LMWS) was achieved using diffuse reflectance infra red spectroscopy (DRIFT). The results show that: the recovery of hydrophobicity is due to the diffusion of LMWS to the surface from the bulk of the insulator rather than the re-orientation of surface molecules; the LMWS concentration in the contaminant is dependent on its concentration in the bulk of the rubber; and at least 60% of the final surface concentration was reached within 24 hours and a plateau reached in 10-15 days. However, the diffusion rate was not affected by temperature in the range from 30 to 80 degC. The results also show that ageing may facilitate the diffusion process. Analysis of the LMWS concentration in the small amounts of real pollutants on insulators returned from service was also achieved using DRIFT by adding an internal standard. Electrostatic deposition of kaolin on rubber surfaces successfully mimics "real world" processes and is an aid in determining the condition of these materials