which grade oil is used in transformer?

Transformers typically use mineral oil, specifically classified as either “naphthenic” or “paraffinic” oil, with a grade that meets the standards of ASTM D3487. The most common grade is “Insulating Oil,” which has excellent dielectric properties and thermal stability. This oil serves as both an insulator and a coolant, ensuring efficient operation and longevity of the transformer by dissipating heat generated during electrical processes.