Distribution Transformers

ANSI/IEEE defines a transformer as a static electrical device, involving no continuously moving parts, used in electric power systems to transfer power between circuits through the use of electromagnetic induction.

The term power transformer is used to refer to those transformers used between the generator and the distribution circuits, and these are usually rated at 500 kVA and above.

Power systems typically consist of a large number of generation locations, distribution points, and interconnections within the system or with nearby systems, such as a neighboring utility. The complexity of the system leads to a variety of transmission and distribution voltages. Power transformers must be used at each of these points where there is a transition between voltage levels.

Power transformers are selected based on the application, step – up transformer are used at generator site and step – down transformers are used at distribution systems.

 Any transformer that takes voltage from a primary distribution circuit and “steps down” or reduces it to a secondary distribution circuit or a consumer’s service circuit is a distribution transformer.

Although many industry standards tend to limit this definition by KVA rating (e.g., 5 to 500 KVA), distribution transformers can have lower ratings and can have ratings of 5000 KVA or even higher, so the use of KVA ratings to define transformer types is being discouraged (IEEE, 2002b).