Pertains 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 less than 5 kVA; - transformers, which have no windings with rated voltage higher than 1000 V; - instrument transformers; - traction transformers mounted on rolling stock; - starting transformers; - testing transformers; - welding transformers; - explosion-proof and mining transformers; - transformers for deep water (submerged) applications.