This Standard specifies efficiency values for dry-type transformers. The total ownership cost (TOC) methodology is recommended as the means for achieving these efficiencies, particularly for electric utilities. This Standard also specifies an optimal method for users other than utilities, based on a modified TOC methodology that meets the conditions of energy cost.

This Standard covers single-phase and three-phase self-contained units or components of larger assemblies, nominal frequency of 60 Hz, having a high-voltage winding of 35 kV or less, ANN, rated 15 to 833 kVA for single-phase and 15 to 7500 kVA for three-phase.

This Standard describes the special features that influence efficiency and provides modifications to the efficiency values specified in Table 1 where such modifications are necessary.