A transformer operates on the principle of mutual inductance, between two (and sometimes more) inductively coupled coils. It consists of two windings in close proximity as shown in Fig.1. The two winding are coupled by magnetic induction. (There is no conductive connection between the windings). One of the windings called primary is energised by a sinusoidal voltage. The second winding, called secondary feeds the load. The alternating current in the primary winding sets up an
alternating flux (Φ) in the core. The secondary winding is linked by moat of this flux and e.m.f.s are induced in the two windings. The e.m.f, induced in the secondary winding drives a current through the load connected to the winding. Energy is transferred from the primary circuit to the secondary circuit through the medium of the magnetic field.
In brief, a transformer is a device that:
(i) transfers electric power from one circuit to another ;
(ii) it does so without change of frequency; and
(iii) it accomplishes this by electromagnetic induction (or mutual inductance)