Sustainable natural ester dielectric liquid for power transformers: Thermo-oxidative performance and kraft paper compatibility

Natural ester-based insulating liquids have gained significant interest as sustainable alternatives to mineral oils in transformers due to their biodegradability, low toxicity, and favorable dielectric properties. However, their susceptibility to oxidation limits their application, particularly in free-breathing transformers. This study presents the formulation of a novel insulating liquid using canola oil and palm kernel oil methyl ester, enhanced with Tert-butylhydroquinone and 2,6-Di‑tert‑butyl‑4-methyl-phenol antioxidants to improve oxidation stability. The thermal and dielectric performance of the formulated liquid was evaluated through accelerated thermal aging, alongside its compatibility with cellulose insulating paper. Key properties analyzed included density, viscosity, acidity, dielectric dissipation factor, and AC breakdown voltage using Weibull statistical analysis. The synthesized insulating liquid demonstrated superior cooling efficiency, with a viscosity of 12.15 cSt, significantly lower than commercial insulating oil (37.96 cSt). After 40 days of aging, it exhibited a lower density increase (0.22 %) and oxidation rate (66.61 %) compared to commercial oil (0.44 % and 85.72 %, respectively), confirming its improved stability. AC breakdown voltage remained higher than commercial oil, with 54.7 kV after aging. Dielectric spectroscopy of impregnated insulating paper showed no significant variation in dielectric loss and permittivity, confirming the compatibility of the synthesized oil with cellulose insulation. FTIR analysis further validated the structural preservation of kraft paper in the formulated oil. These findings highlight the formulated liquid's enhanced oxidation stability, dielectric performance, and potential as an alternative insulating liquid for industrial transformer applications.