Which IEC or ASTM transformer oil testing standards are commonly used?

Utilities typically reference IEC and ASTM methods for comparable, repeatable oil quality data. Common IEC documents include IEC 60296 for mineral insulating oil specifications, IEC 60422 for supervision and maintenance guidance, IEC 60156 for breakdown voltage testing, and IEC 60567 plus IEC 60599 for sampling and interpreting dissolved gas analysis (DGA). On the ASTM side, widely used methods include ASTM D1816 or D877 for dielectric breakdown voltage, ASTM D3612 for DGA, ASTM D974 for acidity, and ASTM D924 for dissipation factor.