What requirements does ASTM D3487 define for transformer oil quality and performance?

ASTM D3487 is a specification for mineral insulating oil used in electrical apparatus. It defines quality requirements and classification for new oils, including limits and test methods related to dielectric properties, oxidation stability, acidity, moisture, interfacial tension, and other performance indicators. Utilities use it to ensure delivered oil meets baseline properties for transformer service and to maintain consistency across suppliers. In practice, many projects reference ASTM D3487 alongside IEC standards and internal utility acceptance criteria.