PC57.91 - Guide for Loading Mineral-Oil-Immersed Transformers and Step-Voltage Regulators

Project 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 C57.12.00 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.

Standards Committee	PE/TR - Transformers
PAR Approval	2017-09-28
PARs	Approved PAR

Additional Resources Details

Historical Base Standard

C57.91-2011

Working Group Details

Working Group	InsLife-WGC57.91 - Insulating Life - Loading Guide Working Group
Standards Committee	PE/TR - Transformers
Society	IEEE Power and Energy Society
IEEE Program Manager	Malia Zaman
Existing Standards	Superseded IEEE C57.91-1981 - IEEE Guide for Loading Mineral-Oil-Immersed Overhead and Pad-Mounted Distribution Transformers Rated 500kVA and Less with 65 C or 55 C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	Superseded IEEE C57.91-1995 - IEEE Guide for Loading Mineral-Oil-Immersed Transformers General recommendations for loading 65 C rise mineral-oil-immersed distribution and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	Superseded IEEE C57.91-1995/Cor 1-2002 - IEEE Guide for Loading Mineral-Oil-Immersed Transformers - Corrigendum 1 Errors identified in IEEE Std C57.91-1995 are addressed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.
	Active IEEE 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 ?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.