Date of Award


Publication Type

Doctoral Thesis

Degree Name



Electrical and Computer Engineering


Engineering, Electronics and Electrical.




Room temperature vulcanizing (RTV) silicone rubber protective coatings are applied to electrical insulators to improve their insulation strength under wet conditions. The electrical performance of RTV silicone rubber insulator coatings under accelerated aging in a salt-fog chamber for artificial testing has been investigated. Experimental and theoretical studies were carried out on RTV silicone rubber coatings to study the loss and recovery of hydrophobicity. The effect of the experimental conditions and the contaminants deposited during dry band arcing was studied with respect to the performance of RTV coatings. Five cleaning methods to remove the contaminants from the coated surface were examined using leakage current and contact angle measurements as indicators of their comparative effectiveness. Energy Dispersive X-ray Analysis (EDAX) was used to determine the composition of the elements of the scale near the surface and in the bulk of the RTV coating. The ability of RTV coatings to suppress leakage current in the presence of contamination thereby preventing power outages was extensively studied. The temporary loss of hydrophobicity and its recovery was studied in depth. The gradual loss of hydrophobicity as determined from the leakage current and the contact angle measurements is shown to be related to the physical and chemical changes to the coating brought about by dry band arcing. The suppression of leakage current by RTV silicone rubber coatings on porcelain suspension and post insulators was studied in a salt-fog chamber. To investigate the phenomenon of the loss and the recovery of hydrophobicity, the surface was subjected to various wetting conditions. Measurements of the contact and the sliding angles were used to determine the state of the surface. The surface free energies due to London dispersion ($\gamma\sb{\rm SD}$) and hydrogen bonding ($\gamma\sb{\rm SH}$) forces on the surface of RTV coatings were calculated from the contact angle measurements using both water and methylene iodide. Good agreement was obtained with the literature values for a virgin RTV surface. In order to study the chemical changes due to dry band arcing on the surface of RTV coatings, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and Electron Spectroscopy for Chemical Analysis (ESCA) was employed. A study of the diffusion of silicone fluid using ATR-FTIR spectroscopy is carried out. The results of ATR-FTIR spectroscopy and ESCA measurements are discussed from which a suppression mechanism of leakage current is suggested. The chemical derivative analysis is also carried out to elucidate the chemical changes on the surface of RTV coating. Several mechanisms are suggested with regard to the formation of water film, the suppression of leakage current on RTV coatings, development of dry band arcing, the temporary loss and recovery of hydrophobicity, heat transfer in the presence of dry band arcing, and chemical reactions and changes at the surface due to dry band arcing. A theoretical model to elucidate the mechanisms is presented.Dept. of Electrical and Computer Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1992 .K555. Source: Dissertation Abstracts International, Volume: 54-05, Section: B, page: 2660. Thesis (Ph.D.)--University of Windsor (Canada), 1992.