Which IEC standards govern transformer oil quality and testing?

IEC standards commonly referenced include IEC 60296 for requirements of unused mineral insulating oils, IEC 60156 for determination of breakdown voltage, and IEC 60422 for supervision and maintenance guidance for mineral insulating oils in electrical equipment. Additional IEC documents can apply to specific tests such as moisture and dielectric loss depending on the program and oil type. Utilities typically reference a set of IEC test methods and acceptance criteria in procurement and maintenance specifications to ensure consistent quality and comparable results over time.