Transformer: What Is It? (Definition And Working Principle)

Contents

• What is a Transformer?
• Working Principle of Transformer
  • Transformer Theory
• Transformer Parts And Construction
  • Primary Winding of Transformer
  • Magnetic Core of Transformer
  • Secondary Winding of Transformer

💡Key learnings:

• Transformer Definition: A transformer is a passive device that transfers electrical energy from one circuit to another using electromagnetic induction.
• Working Principle: The working principle of a transformer involves mutual induction between coils to transfer electrical energy.
• Core Function: The core of a transformer provides a path with low reluctance, essential for efficient flux linkage between the windings.
• Voltage Conversion: Depending on the turns ratio between the primary and secondary windings, a transformer can either step up or step down the voltage.
• Inrush Current Impact: The inrush current is the initial surge of electricity experienced when a transformer is switched on, affecting its immediate performance.

What is a Transformer?

A transformer is defined as a passive electrical device that 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 a 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 is explained in further detail below.

Transformer Theory

Say you have one winding (also known as a coil) 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 another winding is brought close to this winding, some portion of this alternating flux will link with the second winding. 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 will be an EMF induced in the second winding. If the circuit of this secondary winding is closed, then a current will flow through it. This is the basic working principle of a transformer.

Let us use electrical symbols to help visualize this. The winding which receives electrical power from the source is known as the ‘primary winding’. In the diagram below this is the ‘First Coil’.

The winding which gives the desired output voltage due to mutual induction is commonly known as the ‘secondary winding’. This is the ‘Second Coil’ in the diagram above.

A transformer that increases voltage between the primary to secondary windings is defined as a step-up transformer. Conversely, a transformer that decreases voltage between the primary to secondary windings is defined as a step-down transformer.

Whether the transformer increases or decreases the voltage level depends on the relative number of turns between the primary and secondary side of the transformer.

If the primary coil has more turns than the secondary coil, the voltage decreases, known as step down.

If the primary coil has fewer turns than the secondary coil, the voltage increases, known as step up.

Although the diagram above represents an ideal transformer, it is impractical because only a small portion of the flux from the first coil links with the second coil in open air. So the current that flows through the closed circuit connected to the secondary winding will be extremely small (and difficult to measure).

The rate of change of flux linkage is governed by the amount of flux linked with the second winding, ideally linking almost all the primary winding’s flux 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.

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 initially 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:

Transformer Parts And Construction

The three main parts of a transformer:

• Primary Winding of Transformer
• Magnetic Core of Transformer
• Secondary Winding of Transformer

Primary Winding of Transformer

Which produces magnetic flux when it is connected to an 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.