Compatibility of ester oil with transformer components and comparison with mineral oil

Transformer insulation is a composite system made of insulating liquid and impregnable solid insulation. Generally, the mineral oil is used for insulating medium and cooling of transformers. Recently, the ester oil is becoming increasingly popular as a potential alternative to mineral oil for transformer applications. Insulating oil and impregnated solid insulation in service is subjected to heat, oxygen and electrical discharge, which may lead to its degradation. Hence, Compatibility between the materials which are used in the transformer manufacturing such as varnishes, insulation paper, paint, gasket, core etc., and ester oil must be taken into account for selection of suitable materials. It is also necessary for setting up the process guidelines for ester oil transformers in the real operation to maintain its reliable operation. In this study, material compatibility tests had been performed as per ASTM D3455-11 in order to evaluate the performance of materials with the ester oils of different types (natural ester and synthetic ester) in comparison to conventionally used mineral oil. The studies are of great interest for transformer manufacturers to decide a best compatible material with an insulating oil for a suitable transformer application.