Analysis on insulating characteristics of natural high oleic ester and mineral oil based blended oil under accelerated thermal aging exposure

The service life of liquid insulation is influenced by various operational factors, particularly aging. This study investigates the suitability of high oleic natural esters and their blends with mineral oil as insulating liquids. The properties and thermal aging process of these liquids are examined. Natural esters containing high oleic fatty acids, such as canola oil and sunflower oil, are individually studied, as well as their blends and naphthenic mineral oil. From the proposed samples, the one with the best properties is selected for subsequent investigation into aging behavior in the presence of kraft paper insulation. Both the mineral oil and the chosen blended oil are subjected to accelerated thermal aging in separate closed vessels for 50 days at a temperature of 150 degrees C. Properties, including breakdown voltage, viscosity, flashpoint, density, acidity, and moisture content, are assessed according to international standards to ensure the samples possess suitable characteristics. The impacts of aging are analyzed by observing selected oil sample properties, the presence of dissolved gas, and the degree of polymerization of the kraft paper. The results of the aging tests indicate that the blended oil outperforms the mineral oil, and overall performance fluctuations are essentially the same for both types of oil. The findings suggest that natural ester and mineral oil-based blended oils could potentially be reintroduced as liquid insulation in the future.