A transformer consists of two important components, the winding and the core. The winding of a transformer is basically composed of several coils, largely produced from electrolytic copper and as an insulator, receive a layer of synthetic varnish. Already the core, is generally projected from a ferromagnetic material, being the major responsible for effecting the transferred induced current in the primary winding for the secondary winding.
These two elements found in the transformer are considered as the active part, in this way, the other elements of the transformer are part of the complementary components.
Considering transformers with two windings, it is common to call them as primary and secondary winding. However, three winding transformers can be found, considering that the third is tertiary. There are also transformers that only rely on a winding, that is, the primary winding has a connection to the secondary winding, so that there is no insulation between them, these transformers are known as autotransformers.
A three-phase transformer has three transformers that can be operated in different ways. By activating the primary windings in triangle and the secondary windings in star, one obtains a set in which the primary receives three-phase current and in the secondary, three phases and neutral.