Applicable to three-phase and single-phase power transformers (including auto-transformers) with the exception of certain categories of small and special transformers such as single-phase transformers with rated power less than 1 kVA and three-phase transformers of less than 5 kVA; instrument transformers; transformers for static convertors; traction transformers mounted on rolling stock; starting transformers; testing transformers; and welding transformers.