What is the name of transformer oil commonly used in power systems?

The most common generic name is mineral insulating oil for transformers, often specified as inhibited mineral oil or uninhibited mineral oil depending on design. In many grids, natural ester fluids and synthetic ester fluids are increasingly used for fire safety and environmental reasons. Silicone transformer fluid is used for high fire resistance applications. In procurement and engineering, the key identifier is usually the standard classification such as IEC compliant mineral insulating oil or ASTM compliant mineral oil, plus confirmed test results for the delivered batch.