Table of Contents

1. Overview
2. Normative references
3. Definitions
4. Effect of loading beyond nameplate rating
5. Transformer insulation life
6. Ambient temperature and its influence on loading
7. Calculation of temperatures
8. Loading of distribution transformers and step-voltage
   regulators
9. Loading of power transformers
Annex A (normative) - Thermal evolution of gas from
        transformer insulation
Annex B (normative) - Effect of loading transformers above
        nameplate rating on bushings, tap changers, and
        auxiliary components
Annex C (informative) - Calculation methods for determining
        ratings and selecting transformer size
Annex D (normative) - Philosophy of guide applicable to
        transformers with 55 degrees C average winding rise
        (65 degrees C hottest-spot rise) insulation systems
Annex E (normative) - Unusual temperature and altitude
        conditions
Annex F (normative) - Cold-load pickup (CLPU)
Annex G (informative) - Alternate temperature calculation
        method
Annex H (normative) - Operation with part or all of the
        cooling out of service
Annex I (informative) - Transformer insulation life

Abstract

Presents recommendations for loading mineral-oil-immersed transformers and step-voltage regulators with insulation systems rated for a 65 degrees C average winding temperature rise at rated load.

General Product Information

Published
Document Type	Standard
Status	Current
Publisher	Institute of Electrical & Electronics Engineers
Pages
ISBN
Supersedes	IEEE DRAFT C57.91 : D11.3 OCT 94