WORKING PRINCIPLE OF TRANSFORMER

 Working Principle of a Transformer

A transformer is a static device which transfers electric energy from one circuit to another circuit without changing the frequency of the system. It works on principle of Faraday’s law of electromagnetic induction. According to this principle, an e.m.f. is induced in a coil if it links with a changing flux.

Symbolic representation

Arrangement of a simple transformer

Transformer consists of two windings insulated from each other (i.e.electrically separated) and wound on a common core made up of magnetic material of low reluctance as show in figure (3.1). The winding which is connected to the supply is known as primary winding and the other winding to which the load is connected is called secondary winding. When the primary winding is connected to an AC supply, an alternating current flow through it. This current in the primary winding sets up an alternating flux (Ф) in the core, which completes its path in the

common magnetic core as shown in the figure. This flux links with both the windings and it produces self-induced e.m.f. in the primary winding and mutual induced e.m.f. in the secondary winding (according to Faraday’s law of electromagnetic induction). If the secondary winding circuit is closed through the load, the mutually induced e.m.f. in the secondary winding circulates current through the load. Thus, the electrical energy is transferred from primary winding to secondary winding with the help of a magnetic core.

The symbolic representation of a two winding transform is shown in figure

The two vertical lines are used to represent magnetic core, which signify the tight magnetic coupling between the windings.

Transformer on DC Supply

A transformer cannot operate on DC supply. If rated DC supply is applied to

the primary winding of a transformer, the flux produced in the transformer core will

not vary but remains constant in magnitude and therefore no e.m.f. will be induced

in both primary and secondary windings. So, there is no induced e.m.f. in the

primary winding, to oppose the applied voltage. Practically the winding resistance

is very low; therefore, a heavy current will flow through the primary winding which

may result in damage of the winding. Thus, DC supply should not be applied to the Transformer