Theory, application of phase-shifting transformers, and the difference of specification and testing to standard system transformers are described in this guide. Various types of phaseshifting transformers and how to select the optimal design to achieve required control of power flow are covered. An understanding of the terminology, types, construction, and testing specific to phase-shifting transformers is provided.

This guide covers the application, specification, theory of operation, and factory and field testing of singlephase and three-phase oil-immersed, phase-shifting transformers (PSTs). This guide is limited to matters particular to PSTs and does not include matters relating to general requirements for power transformers covered in existing standards, recommended practices, or guides.

The terminology, function, application, theory of operation and protection, and design of PSTs are not covered by existing transformer standards and guides. The purpose of this document is to provide guidance to those specifying, designing, and using PSTs.