This standard applies to three-phase and single-phase power transformers (including autotransformers). Small and special transformers (such as: single-phase transformers with a rated capacity of less than 1kVA and three-phase transformers with a rated capacity of less than 5kVA; mutual inductors; converter transformers; electric locomotive traction transformers; starting transformers; test transformers; welding transformers) when there is no corresponding standard , can refer to this standard.