IEEE C57.12.70:2020

Revision Standard - Active.
Standard terminal markings and connections are described for single-phase and three phase distribution, power, and regulating transformers. For terminal markings, it covers sequence designation, external terminal designation, neutral terminal designation, grounded terminal designation, and marking of full and tap winding terminals. Additive and subtractive polarity and parallel transformer operation are described. Connections of single-phase transformers in various configurations and angular displacement of three-phase transformers to connect to various system phase displacements are covered.

This standard defines the terminal markings and connections for distribution, power, and regulating transformers covered in the IEEE C57(TM) series of standards, guides, and recommended practices.
The standard provides a consistent method for terminal markings and connections for single-phase and three-phase distribution, power, and regulating transformers. It designates terminal markings for interchangeability showing the sequence, external terminations, neutral terminations, grounded terminations, and marking of full and tap winding terminations. It also puts forth the connections of single-phase transformers in various configurations and describes the angular displacement of three-phase transformers when connected to various system phase displacements.