It’s an electromagnetic device that transfers energy from one electrical circuit to another by magnetic coupling. It’s often used to convert between high and low voltages and accordingly between low and high currents.
The primary is fed with a varying alternating electric current that creates a varying magnetic field of voltage around the conductor. According to the principle of mutual inductance, which is a special case of electromagnetic induction applied to two coupled conductors, the secondary, which is placed in this varying magnetic field, will develop a potential difference called an electromotive force (EMF). If the ends of the secondary are connected together to form an electrical circuit this EMF will cause a current power fed into the primary is delivered to the secondary.
Power transformers convert power-level voltages from one level or phase configuration to another. They can include features for electrical isolation, power distribution, and control and instrumentation applications.