The Transformer

It is a device for converting a low alternating voltage at high current into a high alternating voltage at low current and vice-versa. It is an electrical device based on the principle of mutual induction between the coils.

Construction. A transformer consists of two coils, called the primary P and secondary S, which are insulated from each other and wound on a common soft-iron laminated core.

The alternating voltage to be transformed is connected to the primary while the load is connected to the secondary. Transformers which convert low voltages into higher voltages are called step-up transformers. Transformers which convert high voltages into lower voltages are called step-down transformers.

In a step-up transformer, the primary coil consists of a few turns of thick insulated copper wire of large current carrying capacity and secondary consists of a very large number of turns of thin copper wire. In a step-down transformer, the primary consists of a large number of turns of thin copper wire and the secondary of a few turns of thick copper wire.

Now when an ac is applied to the primary coil, it sets up an alternating magnetic flux in the core which also gets linked with the secondary. This change in flux linked with the secondary coil induces an alternating emf in the secondary coil. Thus the energy supplied to the primary is transferred to the secondary through the changing magnetic flux in the core.

Theory

(i)    Transformer on no load
(ii)    Transformer on load