Performance analysis of transformer oil/paper insulation with ester and mixed dielectric fluids

In this work, thermal aging aspects of mineral oil, ester oils (synthetic and natural), mixed oil have been reported. All the samples were thermally stressed at 110°C, 140°C, 160°C, and 185°C for 2 weeks each. Concentration of dissolved decay contents in oil, flash point of insulation oil, and linear thermal expansion coefficients of solid insulation with aging have been studied using ultraviolet visible spectroscopy, flash point and dilatometry analysis respectively. Change in functional groups of the insulation oils with aging have been understood by Fourier Transform Infrared Spectroscopy analysis. Additionally, diffusion of oil-moisture mixture into paper with aging and corresponding effect on dielectric strength of paper has been also examined. Further, design and monitoring aspects of ester and mixed oil filled transformers have been also emphasized. It is observed that ester dielectric fluids and ester content as an additive in mineral oil improves the performance of solid insulation. Importantly, blended oil offer an advantage of retarding the degradation of oil as well as solid insulation accompanied by reduced cost of oil when compared to pure synthetic esters.