Evaluation Of The Impact Of Initial Thermal Aging On The Performances Of The Methyl Ester/Paper Composite Insulation

Oil immersed transformers are essentially used for electric power transmission. In order to improve the current safety level of distribution and power transformers, natural esters have been proposed as a reliable solution. According to various recent studies, the use of natural esters can extend the operating time of the solid insulation as compared to the use of mineral oils (MO). To reduce their viscosity, natural esters are transesterified to produce methyl esters with a kinematic viscosity below 50 centistokes. Up to date, very few literature data is available on the aging of the methyl ester/paper insulation. Hence, the aim of this work is the improvement of the understanding of the influence of thermal aging on the performances of the monoesters/paper mixed insulation. Firstly, we explain the elaboration and performance analysis processes of monoesters of palm kernel and castor oils. Then we present the aging procedure; the oil/paper composite insulation was aged during 100 hours at 110°C. Finally, we show the results of the analyses performed. Three analyses were realized, namely the determination the Total Acid Number (TAN) based on the standard ASTM D974, UV-visible spectroscopy according to the standard ASTM D6802 and finally the Breakdown Voltage (BDV) of the insulation paper based on the standard ASTM D149. For comparison, the same analyses were performed on the mineral oil/paper complex. In view of the results obtained, the excellent dielectric of monoglycerides can be confirmed.