Electrical transformers continue to be designed to suit the needs of the transfer of electrical energy from one circuit to another through a shared magnetic field. These devices are made for the basic function of changing current by the creation of a changing magnetic field that takes place in the primary or first circuit. The magnetic field in turn induces a changing voltage in the secondary or second circuit. The current flows in the transformer with the addition of a load to the secondary circuit, and the transfer of energy from circuit to circuit takes place.
The scaling of the secondary induced voltage or VS from the primary voltage or VP takes place by a factor ideally equal to the ratio of the number of turns of the respective wire windings. By the satisfactory selection of numbers or turns, the transformer allows an alternating voltage to be stepped up or down with the number of turns in the secondary coil or NS either higher or lower than the number of turns in the primary or NP.
The reduction of current before transmission of electrical energy over long distances through wires to enable economic transmission of power from the source of generation to the location of consumption continues to be the main application of a transformer.