1-Phase / 3-Phase

In principle, the study of n-phase systems is an interesting academic field. In our day-to-day practice – the dimensioning and production of transformers – we only deal with 1- or 3-phase transformers or voltage systems. 3-phase is also referred to as three-phase current.

Remarks:
A so-called core transformer, also called KT or UI transformer, i.e. a transformer with two coils, is also a 1-phase transformer. The primary windings of this transformer are connected either in series or in parallel. The term 2-phase transformer is not in use.
Similarly, a transformer connected between two outer conductors of a 3-phase supply network is a 1-phase transformer. (In the usual public low-voltage grid, this is then, for example, a 1-phase transformer, primary voltage 400V).
It is often desired to distribute a 1-phase load evenly over the 3 phases of a network. This is not possible with a single transformer.