Transformer oil specifications and important properties for optimal in-service life

Insulation oil used in transformer need to have chemical and physical properties in line with the basic functions it needs fulfilling. There are three main functions which transformer oil must handle in the transformer; to be an electric insulation barrier, to be a heat transfer medium and to preserve the transformer over time. To secure these basic functions there are specifications that have been developed over time, based on experience and demands from different parties on the market. The leading transformer standard specifications are IEC 60296 and ASTM D 3487. The requirements in the standards are defined with minimum and maximum limits. There are requirements on physical and chemical properties which depending on the base fluid and its degree of refining, but other properties like dielectric insulation needed for this application are also specified. Transformer oil can have properties that are just passing specification limits or can have properties which exceeding the requirements. The understanding of transformer oil qualities is important when deciding which oil is best for your equipment in order to get potential long in-service life.