In the case of transformers having two windings, they are referred to as primary and secondary windings. In the case of transformers that contain three windings, the third is tertiary. There are also transformers that rely on only one winding. This means that the primary winding has a connection to the secondary winding, so that there is no insulation between them, so these transformers are called autotransformers.
It is important to note that the three-phase transformer has 3 internal transformers that can be connected in different ways. Activating the primary triangle windings and the secondary star windings, resulting in a set in which the primary receives three-phase current and in the secondary, three-phase and neutral, considering that the neutral becomes the center of the star.
In this way, simple stresses are obtained, as well as compound stresses. In the case of the distribution of electric energy, it has 400 volts between phases, and three ways can be found, they are, between the phases R and S; S and T; And R and T, and 230 volts between any of the phases and the neutral.