Thermal Aging Performance of Cellulose Insulation in Natural Ester Liquid

Natural esters have the capability to enhance the life expectancy of the insulating cellulose paper used in oil-filled transformers. This work presents the aging behavior of an insulating paper when it is combined with a new natural ester (based on soybean oil) and compared with an industry-proven system according to the latest version of the standard IEEE Std. C57.100 (2011). The temperatures for the candidate system (natural ester + cellulose paper) are 160, 175, and 190 degrees C. Experimental results show that the average mechanical tensile retention from the industry-proven system aging system is 44.2%, which is used as reference to evaluate the candidate system. According to this investigation, the insulation system with the new natural ester liquid shows an improvement in the behavior of the aging performance compared to the mineral oil system. The Arrhenius life plots demonstrate that the system of natural ester-thermally upgraded Kraft paper shows a life expectancy higher than for the industry-proven system. Therefore, this alternative could be considered either to increase the lifetime of a transformer or to improve its overload capacity during operation.