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1.

Scope

1.1 This Standard specifies energy efficiencies for dry-type transformers.

The Total Ownership Cost (TOC) methodology is re commended as the means for achieving these energy efficiencies, particularly for use by electric utilities.

This Standard also specifies an optimal method for nonutility users, based on a modified TOC methodology that meets the conditions of energy cost. Note:

Table 1 in this Standard provides minimum efficiency values.

1.2 The transformers to which this Standard applies are singleand threeself-contained units or components of larger assemblies, 60 Hz, ANN, rated at 15-833 kV A for single-phase and at 15-7500 kV A for three phase.

1.3 This Standard describes special features that influence efficiency and provides for the necessary modifications to the tabulated efficiency values.

1.4 This Standard addresses the test methods and procedures for determining the transformer efficiencies.

1.5 This Standard does not apply to sealed and unventilated transformers, autotransformers, testing transformers, welding transformers, furnace transformers, rectifier transformers, drive transformers, instrument transformers,

transformers with tap ranges greater than 10%, or transformers with nominal frequency other than 60 Hz.