scope:

This guide provides recommendations for loading mineral-oil-immersed transformers and step-voltage regulators, with insulation system 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. Since a substantial population of transformers and step-voltage regulators with insulation systems rated for a for a 55 °C average winding temperature rise at rated load are still in service, recommendations that are specific to this equipment are also included.

This standard incorporates open-source code hosted on the IEEE Open-Source Platform.

Purpose

This guide provides recommendations on loading and loading beyond nameplate of mineral-oil-immersed transformers and step-voltage regulators, considering prescribed current and temperature limits and their effect on insulation life. This guide is intended for use by equipment end-users in planning and operating transformers and voltage regulators, utilizing the equipment's loading capability to its maximum extent while understanding the impacts of utilizing this capability. This guide also provides a practical and theoretical basis for the development of transformer and step-voltage regulator thermal models and end-user continuous and emergency ratings.

¹ Information of references can be found in Clause 2.