Thermal Aging Effects on the AC Breakdown Voltage of Mineral Oil Containing TiO₂ Nanoparticles

Mineral oil is the most widely used liquid in transformers because it functions as a coolant and an electrical insulator. However, while transformers are operating under higher temperatures, insulation efficiency of oil will reduce. Therefore, electrical properties of mineral oil must be developed and improved. A larger number of research studies mainly focus on increasing electrical efficiency by adding nanoparticles into mineral oil. In this research, properties of mineral oil were improved by adding TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> nanoparticles (TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>) with 0.01% concentration of mineral oil volume. However, adding nanoparticles as a solid into oil that appeared as a liquid was not easy because nanoparticles tended to show poor dispersion. Therefore, a dispersant that functioned as a surfactant was required to facilitate efficient nanoparticles dispersion in mineral oil. In this article, a surfactant called "Span 80" was used at 90 % of particle volume for testing electrical degeneration of liquid insulators in accordance with ASTM D1934. The temperature used for degeneration was 115 °C for 96 hours. Degeneration was analyzed by testing AC voltage in accordance with ASTM D 877. The testing results revealed that mineral oil that went through thermal aging contained higher withstand voltage than regular oil because heat could reduce moisture in oil. As a result, liquid insulators contained higher density, which finally led to better withstand voltage efficiency of oil.