A Transformer is a static apparatus by means of which electric power in one circuit is transformed to electric power of the same frequency in another circuit.It can raise or lower the voltage in a circuit but with corresponding decrease or increase in current.The physical basis of a transformer is mutual induction between two circuits linked by a common magnetic flux.In its simplest form,it consists of two inductive coils which are electrically separated but magnetically linked through a low reluctance path.

The two coils possess high mutual inductance.If one coil is connected to a source of alternating voltage,an alternating flux is set up in the laminated core,most of which is linked with the other coil in which it produces mutually induced emf.If the second coil circuit is closed, a current flows in it and so electric energy is transferred from the first coil to the second coil.

The first coil in which electric energy is fed from the AC supply mains is called primary winding and the other from which energy  is drawn out is called secondary winding.In brief transformer is a device that :-

• transfers electric power from one circuit to another
• does so without change in frequency
• accomplishes this by electromagnetic induction
• where two electric circuits are linked by mutual induction.