A three-phase transformer is made of three sets of primary and secondary windings, each set wound around one leg of an iron core assembly. ... Three phase transformer core has three sets of windings. Those sets of primary and secondary windings will be connected in either Δ or Y configurations to form a complete unit.

Three phase transformers are designed to supply electric power to three-phase systems. These electrical devices have three circuit conductors and may or may not have a neutral wire. Three phase power is used by electric power distribution grids and to power large motors and other large loads.