Coming to the classification of transformers, there are many types depending upon the core used, windings used, place and type of usage, voltage levels etc.

Single and three phase transformers

According to the supply used, the transformers are mainly classified as Single phase and three phase transformers.

·        A normal transformer is a single phase transformer. It has a primary and a secondary winding and it is operated to either decrease or increase the secondary voltage.

·        For a three phase transformer, three primary windings are connected together and three secondary windings are connected together.

A single three phase transformer is preferred to three single phase transformers so as to get good efficiency, where it occupies less space at low cost. But due to the transportation problem of heavy equipment, single phase transformers are used in most cases.

Another classification of these transformers is Core and Shell type.

·        In Shell type, the windings are positioned on a single leg surrounded by the core.

·        In Core type, they are wounded on different legs.

The difference is well known by having a look at the following figure.

The classification of transformers can also be done depending upon the type of core material used. These are actually RF transformers, which contain many types such as Air-core transformers, Ferrite core transformers, Transmission line transformers and Balun transformers. Balun transformers are used in RF receiver systems. The main types are the air core and iron core transformers.