In electrical and electronic systems, the electrical transformer is one of the most useful electrical machine. An electrical transformer can increase or decrease the magnitude of alternating voltage or current. It is the major reason behind the widespread use of alternating currents rather than direct current. A transformer does not have any moving part. Therefore, it has very high efficiency up to 99% and very strong and durable construction.

Electrical Transformer

A transformer or electrical transformer is a static AC electrical machine which changes the level of alternating voltage or alternating current without changing in the frequency of the supply.

A typical transformer consists of two windings namely primary winding and secondary winding. These two windings are interlinked by a common magnetic circuit for transferring electrical energy between them.

Principle of Transformer Operation

The operation of the transformer is based on the principle of mutual inductance, which states that when a changing magnetic field of one coil links to another coil, an EMF is induced in the second coil.

When an alternating voltage V₁ is applied to the primary winding, an alternating current flows through it and produces an alternating magnetic flux. This changing magnetic flux flows through the core of the transformer and links to the secondary winding. According to Faraday’s law of electromagnetic induction, an EMF E₂ is induced in the secondary winding due to the linkage of changing magnetic flux of the primary winding. If the secondary winding circuit is closed by connecting a load, then this induced EMF E₂ in the secondary winding causes a secondary current I₂ to flow through the load.

Although the changing magnetic flux of primary winding is also linked with the primary winding itself. Hence, an EMF E₁ is induced in the primary winding due to its own inductance effect. The value of E₁ and E₂ can be given by the following formulae,

$$mathrm{mathit{E_{mathrm{1}}}:=:-mathit{N_{mathrm{1}}}frac{mathit{dphi }}{mathit{dt}}}$$

$$mathrm{mathit{E_{mathrm{2}}}:=:-mathit{N_{mathrm{2}}}frac{mathit{dphi }}{mathit{dt}}}$$

Where N₁ and N₂ are the number of turns in the primary winding and secondary winding respectively.

On taking the ratio of E₂ and E₁, we get,

$$mathrm{frac{mathit{E_{mathrm{2}}}}{mathit{E_{mathrm{1}}}}:=:frac{mathit{N_{mathrm{2}}}}{mathit{N_{mathrm{1}}}}}$$

This expression is known as transformation ratio of the transformer. The transformation ratio depends on the number of turns in primary and secondary windings. Which means the magnitude of output voltage depends on the relative number of turns in primary and secondary windings.

If N₂ > N₁, then E₂ > E₁, i.e., the output voltage of the transformer is more than the input voltage, and such a transformer is known as set-up transformer. On the other hand, if N₁ > N₂, then E₁ > E₂ i.e., the output voltage is less than input voltage, such a transformer is called step-down transformer.

From the circuit diagram of the transformer, we can see that there is no electrical connection between the primary and secondary instead they are linked with the help of a magnetic field. Thus, a transformer enables us to transfer AC electrical power magnetically from one circuit to another which a change in the voltage and current level.

Important Points

Note the following important points about transformers −

• The operation of transformer is based on the principle of electromagnetic induction.

• The transformer does not change the frequency, i.e. the frequency of input supply and output supply remains the same.

• Transformer is a static electrical machine, which means it does not have any moving part. Hence, it has very high efficiency.

• Transformer cannot work with direct current because it is an electromagnetic induction machine.

• There is no direct electrical connection between primary and secondary windings. The AC power is transferred from primary to secondary through magnetic flux.