A transformer is a static electrical machine (it contains no moving parts) belonging to the broader category of converters.
In particular, a transformer makes it possible to convert the voltage (symbol V, the unit of measure for volts) and current (symbols: I, the unit of measure, Amperes [A]) parameters at input with respect to those at output, while maintaining constant the amount of electrical power (unless losses occur due to hysteresis and eddy currents).
A transformer is a machine capable of operating only on alternating current because it exploits the principles of electromagnetism relating to variable fluxes.
A transformer is not able to change the frequency value, therefore the input frequency is always equal to output frequency.
Transformers have a fundamental importance in today’s world. Without them large electricity transmission networks connecting power stations to millions of homes and industrial facilities and systems would not be able to operate.
Until 1965 the general scientific opinion was that it would be impossible to produce DC transformers. In that year a group of researchers at the General Electric company led by Nobel prize winner (1973) Ivar Giaever succeeded in producing such a device as a result of studies on superconductivity at a very low temperature.
In any case the practical and large-scale application of this discovery has not yet been achieved, and in the meantime scientific studies are continuing in the field of superconductivity at high temperature..
The technical references provided here are used to facilitate a correct choice for the use of transformers, auto-transformers, and inductive reactors in the various fields of use.