Minimum efficiency values for liquid-filled distribution transformers

1.1
This Standard specifies energy efficiencies for liquid-filled distribution transformers. The total ownership cost (TOC) methodology is recommended 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.

1.2
The transformers to which this Standard applies are single-phase and three-phase, 60 Hz, liquid-filled distribution transformers, rated at 10-833 kVA for single-phase and at 15-3000 k/VA for three-phase, insulation class 34.5 kV and less. Minimum low voltage ratings are shown in Table 1.

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 autotransformers, testing transformers, welding transformers, furnace transformers, rectifier transformers, network transformers, or grounding transformers. Also excluded are transformers with special core/coil designs required by dimensional constraints, transformers with tap ranges greater than 15%, transformers with frequencies other than 60 Hz, and step-voltage regulators.

1.6
In this Standard, shall is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with the standard; should is used to express a recommendation or that which is advised but not required; and may is used to express an option or that which is permissible within the limits of the standard.

Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material.

Notes to tables and figures are considered part of the table or figure and may be written as requirements.

Annexes are designated normative (mandatory) or informative (non-mandatory) to define their application.