This guide provides recommendations for loading mineral-oil-immersed transformers and step-voltage regulators with insulation systems rated for a 65 °C average winding temperature rise at rated load. This guide applies to transformers manufactured in accordance with IEEE Std C57.12.00 and tested in accordance with IEEE Std C57.12.90, and step-voltage regulators manufactured and tested in accordance with IEEE Std C57.15. Because a substantial population of transformers and step-voltage regulators with insulation systems rated for 55 °C average winding temperature rise at rated load are still in service, recommendations that are specific to this equipment are also included.
- Standard Committee
- PE/TR - Transformers
- Status
- Active PAR
- PAR Approval
- 2017-09-28
- Superseding
- C57.91-2011
- Open Source
- IEEE SA Open Source Project
- Open Source CLA
- BSD 3-Clause
Working Group Details
- Society
- IEEE Power and Energy Society
- Standard Committee
- PE/TR - Transformers
- Working Group
-
InsLife-WGC57.91 - Insulation Life - Loading Guide Working Group
Learn More About InsLife-WGC57.91 - Insulation Life - Loading Guide Working Group - IEEE Program Manager
- Malia Zaman
Contact Malia Zaman - Working Group Chair
- David Wallach
Other Activities From This Working Group
Current projects that have been authorized by the IEEE SA Standards Board to develop a standard.
No Active Projects
Standards approved by the IEEE SA Standards Board that are within the 10-year lifecycle.
No Active Standards
These standards have been replaced with a revised version of the standard, or by a compilation of the original active standard and all its existing amendments, corrigenda, and errata.
C57.91-1981
IEEE Guide for Loading Mineral-Oil-Immersed Overhead and Pad-Mounted Distribution Transformers Rated 500kVA and Less with 65 C or 55 C Average Winding Rise
General recommendations for loading 65 degrees Centigrade-rise mineral-oil-immersed overhead and pad-mounted distribution transformers are covered. Recommendations for 55 degrees Centigrade-rise transformers are included because a substantial percentage of these transformers are still in service. The recommendations are based on winding hottest-spot calculations only. Other factors that may limit the permissible load to lower values are listed. A method to establish winding temperature and loss of life by nomographs is given.
C57.91-1995
IEEE Guide for Loading Mineral-Oil-Immersed Transformers
General recommendations for loading 65 C rise mineral-oil-immersed distribution and power transformers are covered.
C57.91-1995/Cor 1-2002
IEEE Guide for Loading Mineral-Oil-Immersed Transformers - Corrigendum 1
Errors identified in IEEE Std C57.91-1995 are addressed in this corrigendum.
These standards have been removed from active status through a ballot where the standard is made inactive as a consensus decision of a balloting group.
No Inactive-Withdrawn Standards
These standards are removed from active status through an administrative process for standards that have not undergone a revision process within 10 years.
C57.91-2011
IEEE Guide for Loading Mineral-Oil-Immersed Transformers and Step-Voltage Regulators
This guide provides recommendations for loading mineral-oil-immersed transformers and step-voltage regulators with insulation systems rated for a 65 u00b0C average winding temperature rise at rated load. This guide applies to transformers manufactured in accordance with IEEE Std C57.12.001 and tested in accordance with IEEE Std C57.12.90, and step-voltage regulators manufactured and tested in accordance with IEEE Std C57.15. Because a substantial population of transformers and step-voltage regulators with insulation systems rated for 55 u00b0C average winding temperature rise at rated load are still in service, recommendations that are specific to this equipment are also included.