COMPATIBILITY TEST OF GASKETS AND COATINGS WITH ESTER INSULATING LIQUIDS AT ELEVATED TEMPERATURE

Compatibility test provides recommendations for different electrical equipment to screen appropriate construction materials in different liquids. However, the unique compatibility evaluation standard, ASTM D3455, focusing on mineral-oil-filled transformers is challenged by newly adopted liquids at higher operation temperature. In this paper, the compatibility test method has been modified at elevated temperature in compliance with the thermal class of insulation system. The compatibility tests have been conducted for four types of gaskets, inner surface coating, coating of silicon steel sheet, and enamelled wire with natural ester, synthetic ester and modified ester. After the 168-h heating process, not only the insulating liquids but also the construction materials were analysed and discussed. The results showed that dielectric dissipation factor, breakdown voltage, interfacial tension and acidity of insulating liquids can be determined as critical parameters to judge compatibility, while kinematic viscosity is not sensitive to potential compatibility risks. In addition, properties of construction materials, mass, volume, hardness, tensile strength and elongation of gaskets, are also critical to determine compatibility. It is necessary to raise the test temperature to the thermal class of the electric insulation system. The study is of great significance for transformer manufacturers to determine appropriate compatible materials with ester liquids.