Test method and minimum efficiency values for dry-type transformers

1.1
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.

Note: See Table 1 for minimum efficiency values.

1.2
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.

1.3
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.

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

1.5
This Standard does not apply to

a) autotransformers;
b) grounding transformers;
c) rectifier transformers;
d) sealed transformers;
e) non-ventilated transformers (including encapsulated transformers);
f) testing transformers;
g) furnace transformers;
h) welding transformers;
i) drive (isolation) transformers with two or more output windings or a rated low-voltage line current greater than 1500 A;
j) special impedance transformers;
k) transformers with a nominal low-voltage line current of 4000 A or more;
l) on-load regulating transformers;
m) resistance grounding transformers;
n) transformers with two or more independent secondary windings for more than one independent output voltage for main power transformation. Any independent windings used to provide either single-phase or three–phase power to auxiliary devices are not included in the count of the number of independent windings when determining the type of transformer, and are completely excluded from the kVA rating, testing, and calculations for energy efficiency purposes. Secondary windings designed to be reconfigured in either series or parallel in order to provide two different voltages are not considered independent windings.
o) transformers with a low-voltage winding BIL above 30 kV; and
p) transformers that are in a voltage class greater than 1.2 kV and that have a BIL of less than 20 kV or more than 199 kV.

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.