IEEE Draft Guide for Loading Mineral-Oil-Immersed Transformers and Step-Voltage Regulators

The contents of this guide describe the assumptions, techniques, and methods for estimating the effects of loading above nameplate of mineral-oil-immersed distribution and power transformers as well as step voltage regulators. Consequences due to loading above nameplate ratings are discussed including damage to insulation, production of gases in oil, and ultimately loss of life effects. In addition, effects of loading on auxiliary equipment are presented. Different types of loading scenarios as well as variations in ambient temperature and altitude are described. Effects due to different cooling techniques and their impacts on transformer capacity are reviewed. Transformer temperature criteria are also provided. Finally, calculation methods with and without consideration to duct oil effects are provided and with sample temperature calculations.