Thermal Aging Performance of Enhanced Cellulose Insulation in Natural Ester Liquid

As natural ester dielectric liquids continue to be utilized in liquid-filled transformers understanding the thermal performance of such liquids becomes increasingly important. The ability for natural ester liquids to increase the thermal capabilities of transformers produced with thermally upgraded Kraft paper has been tested and published. However, additional increases in thermal class can be achieved by combining natural ester liquids with enhanced cellulose insulation (DPE). This work presents testing completed according to IEEE C57.100 (2011) with a candidate system consisting of DPE paper and a natural ester liquid (soybean based). According to the investigation the candidate system has improved aging performance over the industry proven system (thermally upgraded Kraft paper and mineral oil) as well as improved aging performance over an insulation system consisting of thermally upgraded Kraft paper and the same natural ester liquid. Such an improvement in aging performance, and in turn thermal class, could be considered to either increase the lifetime of a transformer or to improve the overload capacity during operation.