An alternating voltage can be raised or lowered as per requirements in the different stages of electrical network by using static device called as transformer.
The transformer works on the principle of mutual induction. It transfers an electric energy from one circuit to other when there is no electrical connection between the two circuits.
The transformer is a static device in which electric power is transformed from one alternating current circuit to another with desired change in voltage and current, without any change in frequency.
The principle of mutual induction states that when two coils are inductively coupled and if the current in one coil changed uniformly then an e.m.f gets induced in the other coil. This e.m.f can drive a current, when a closed path is provided to it. The transformer works on the same principle. In its elementary form, it consists of two inductive coils which are electrically separated but linked through a common magnetic circuit. The two coils have high mutual inductance. The basic transformer is shown in fig.
One of the two coils is connected to a source of alternating voltage. This coil in which electrical energy is fed with the help of source called primary winding (P). The other winding is connected to the load. The electrical energy transformed to this winding is drawn out to the load. This winding is called secondary winding (S). The primary winding has N1 number of turns while the secondary winding has N2 number of turns. Symbolically the transformer is indicated as shown in fig.
When the primary winding is exited by an alternating voltage, it circulates an alternating current. This current produces an alternating magnetic core as shown dotted in fig. thus an alternating flux links with secondary winding. As the
flux is alternating, according to faradays law of electromagnetic induction, mutually induced e.m.f gets developed in the secondary winding. If now the load is connected to the secondary winding, this e.m.f drives a current through it.
Thus though there is no electrical contact between the two windings, an electrical energy gets transferred from primary to the secondary.