Terminology and definitions for transformers, regulators, reactors, associated apparatus and for power system and insulation terms which are commonly involved in transformer technology. Cross-references are made to certain terms that appear in IEC 50, the international standard for International Electrotechnical Vocabulary. These terms can be identified when "(IEC)" follows the term To review and update IEEE Std C57.12.80 which was last issued in 1978. Revision Standard - Superseded. This standard is a compilation of terminology and definitions primarily related to electrical transformers and associated apparatus included within the scope of C57, Transformers, Regulators, and Reactors standards. It also includes similar data relating to power systems and insulation,which is commonly involved in transformer technology.