Transformer Basics And Working Principle

Definition of Transformer

A transformer is a static device which transfers electrical energy from one circuit to another through the process of electromagnetic induction. It is most commonly used to increase (‘step up’) or decrease (‘step down’) voltage levels between circuits.

Working Principle of Transformer

The working principle of transformer is very simple. Mutual induction between two or more windings (also known as coils) allows for electrical energy to be transferred between circuits. This principle will be explained in further detail below.

Basic Theory of Transformer

Say you have one winding which is supplied by an alternating electrical source. The alternating current through the winding produces a continually changing and alternating flux that surrounds the winding. If any other winding is brought nearer to the previous one, obviously some portion of this flux will link with the second. As this flux is continually changing in its amplitude and direction, there must be a changing flux linkage in the second winding or coil.

According to Faraday’s law of electromagnetic induction, there must be an EMF induced in the second. If the circuit of the later winding is closed, there must be a current flowing through it. This is the most basic thing on which the working principle of transformer stands. The winding which takes electrical power from the source, is known as the primary winding. Here in our above example, it is first winding.

mutual induction

The winding which gives the desired output voltage due to mutual induction is commonly known as the secondary winding. Here in our example, it is second winding.

The form mentioned above of a transformer is theoretically possible but not practically, because in open air very tiny portion of the flux of the first winding will link with second; so the current that flows through the closed circuit of later, will be so small in amount that it will be difficult to measure.

The rate of change of flux linkage depends upon the amount of linked flux with the second winding. So, almost all flux of primary winding should link to the secondary winding. This is effectively and efficiently done by using a core type transformer. This provides a low reluctance path common to both of the windings.

transformer core winding

The purpose of the transformer core is to provide a low reluctance path, through which the maximum amount of flux produced by the primary winding is passed through and linked with the secondary winding.

The current that intially passes through the transformer when it is switched on is known as the transformer inrush current.

If you would prefer an animated explanation, below is a video explaining exactly how a transformer works:

Main Constructional Parts of Transformer

The three main parts of a transformer are,

Primary Winding of Transformer

Which produces magnetic flux when it is connected to electrical source.

Magnetic Core of Transformer

The magnetic flux produced by the primary winding, that will pass through this low reluctance path linked with secondary winding and create a closed magnetic circuit.

Secondary Winding of Transformer

The flux, produced by primary winding, passes through the core, will link with the secondary winding. This winding also wounds on the same core and gives the desired output of the transformer.


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