IEEE C57.115-1991

C57.115-1991 is a technical standard for immersed power transformers rated in excess of 100 MVA with a 65C winding rise. It addresses design and rating considerations for large oil-immersed transformers used in power, energy, and industrial applications, where thermal performance and dependable operation are critical. As an inactive document, C57.115-1991 remains useful for understanding the historical basis of transformer requirements and for evaluating legacy equipment or earlier procurement specifications.

About C57.115-1991

This standard focuses on immersed power transformers that operate above 100 MVA and are built for a 65C winding rise. Its technical context centers on how these large units are specified, rated, and assessed for temperature-related performance. The document is relevant to transformer engineering because winding rise affects insulation life, loading capability, and thermal margins. For buyers and engineers, C57.115-1991 helps define a clear reference for comparing transformer design assumptions and compliance expectations.

Where is C57.115-1991 used?

C57.115-1991 is most relevant in utility transmission and substation projects, as well as heavy industrial power systems that use large immersed transformers to step voltage levels up or down. It may also appear in plant engineering, equipment procurement, and refurbishment work when legacy transformer specifications need to be reviewed against older rating practices. The standard is particularly useful where large MVA transformers must be matched to thermal limits, loading profiles, and installation requirements.

Importance in practice

In practice, C57.115-1991 matters because transformer rating and winding temperature rise directly affect reliability, service life, and operating safety. For procurement and design teams, it provides a defined technical basis for checking whether a large immersed transformer aligns with the expected duty and thermal performance. It can also support consistent documentation during specification review, factory testing coordination, and asset management of older equipment. Using the standard helps reduce ambiguity when comparing legacy transformer requirements.

• Immersed power transformers
• Ratings above 100 MVA
• 65C winding rise context
• Legacy specification reference
• Utility and industrial power systems