Compatibility of Construction Materials with Synthetic Esters in Fluid-filled Transformers

The compatibility of construction materials with insulating liquids not only affects the selection of materials but also the reliability of fluid-filled transformers after refilling with alternative insulating liquids. With the application of alternative insulating liquids for environmentally friendly and high-temperature insulation systems, the industry requires compatibility testing standards. Thus, in this study, the compatibility between different coatings and gasket materials with synthetic esters in fluid-filled transformers was investigated. To approximate the operation status, the testing conditions were upgraded by raising the temperature to the thermal class of insulation systems as suggested by IEC 63177 (committee draft as FDIS stage). Moreover, several tests were conducted to assess the performance of insulating liquids and construction materials for different durations, including 168, 336, 672 and 1008 hours. The results revealed the necessity of extending the test duration to 672 h and evaluating the performance of the insulating liquid and construction material in the compatibility test. In particular, the compatibility of polyesterimide, two-component epoxy resin, nitrile rubber, acrylic rubber, fluorosilicone rubber, and fluorine rubber with synthetic esters was examined. The results showed potential risks of incompatibility between the synthetic ester and the nitrile rubber, acrylic rubber and two-component epoxy resin selected in the experiment.