C57.91-2011 - IEEE Guide for Loading Mineral-Oil-Immersed Transformers and Step-Voltage Regulators

Standard Details

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 C57.12.001 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 °C average winding temperature rise at rated load are still in service, recommendations that are specific to this equipment are also included.

Sponsor Committee	PE/TR - Transformers
Status	Active
Board Approval	2011-12-07
History	Published Date:2012-03-07

Additional Resources Details

PAR	Approved PAR

Working Group Details

Working Group	InsLife-WGC57.91 - Insulating Life - Loading Guide Working Group
Working Group Chair	David Wallach
Sponsor Committee	PE/TR - Transformers
Society	IEEE Power and Energy Society
IEEE Program Manager	Malia Zaman
Active Projects	Active PC57.91 - 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 ?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.
Existing Standards	Superseded C57.91-1981 - IEEE Guide for Loading Mineral-Oil-Immersed Overhead and Pad-Mounted Distribution Transformers Rated 500kVA and Less with 65 C or 55 C Average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.
	Superseded 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.
	Superseded 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.