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Transformer & its Operation, Characteristics & Applications

What is a Transformer | its Operation of Working, Characteristics & Applications

A transformer is a very common and widely used electrical device. It has applications from mini mobile devices that can fit into a pocket to heavy industrial machines. In this article, we are going to discuss the transformer, its principle operation, its characteristics & its applications. 

What is a Transformer, its Operation of Working, Characteristics & Applications


A transformer is a static Electrical device that transfers electrical energy from one circuit to another with increasing or decreasing voltage & current.

It is made up of two or more than two windings (coils) wounded around a stationary iron core. There are two types of windings i.e.

  • Primary Winding
  • Secondary Winding

Primary Winding

The input winding that is excited through the varying supply current is called the primary winding. The number of turns in the primary winding is denoted by Np.

Secondary Winding

The winding of the transformer, which is the output of the transformer & is connected with the load is called secondary winding. The number of turns in the secondary winding is denoted by Ns.

Transformer Turn Ratio

It is the ratio of a transformer’s number of turns in the secondary winding to the number of turns in primary windings.

It is very important in figuring out the input & output voltage & current of a transformer.

Principle of Transformer

Transformers operate according to the Faraday’s 2nd law of Electromagnetic induction. it means that if a coil is placed in a varying magnetic field, an EMF will be induced in the coil.

Transformer operates on varying supply current, also known as alternating current (AC). Due to varying AC current in the primary windings, a varying magnetic field is generated around it. This varying magnetic field induces an EMF in the secondary winding through the phenomenon of “Mutual Induction”. Hence the transfer of the electrical energy between the two windings occurs. The primary & secondary windings are connected magnetically but they are electrically isolated.

The output voltage & current levels of a transformer may vary depending on the numbers of turns in primary & secondary windings but the frequency remains the same.

Characteristics of Transformer

Some of the characteristics of a transformer are given below:

  • Variable Voltage

The input and output voltages of a transformer are variable. A transformer can increase or decrease the supply voltage.

Vout  = Vin (Ns/Np)

  • Variable Current

The current is also a variable quantity in a transformer which can be increased or decreased.

Iout  = Iin (Np/Ns)

  • Constant Frequency

A transformer is a constant frequency operating device. The frequency of the input voltage & the output voltage remains the same.

  • Constant Power

The power of the transformer remains constant. The power that is supplied to the transformer & the power delivered by the transformer remains the same.

Pin = Pout

Vin Iin = Vout Iout

Step-up & Step-down Transformer

According to the input and output voltage of a transformer, they are classified into these two types;

1) Step Up Transformer

A step-up transformer has a greater number of turns in secondary winding Ns than the primary winding Np. It increases the input voltage by the transformer turn ratio.

Ns > Np

Turn Ratio > 1

Vout  = Vin (Ns/Np)

The Turn ratio of a step-up transformer is greater than 1.

2) Step Down Transformer

The transformer whose number of turns of in primary winding Np is greater than that of the secondary winding Ns is called step down transformer.

It decreases its input voltage by the transformer turn ratio.

Ns < Np

Turn Ratio < 1

Vout  = Vin (Ns/Np)

The Turn ratio of a step-down transformer is lower than 1.

Applications of Transformer

A transformer is used in a wide variety of electrical & electronic devices. It is the most common electrical device. Some of its applications are given below:

  • It is used for increasing or decreasing the voltage in a circuit.
  • It is used for electrically isolating two circuits.
  • It is used in AC to DC rectifiers for reducing the High input AC voltages.
  • It is used for impedance matching
  • Current transformers are used for measurement purposes.
  • Distribution transformers are used for reducing the voltage levels for our domestic appliances.
  • Voltage stabilizer & regulators


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