Transformer, Working Principle of Transformer, Transformer Construction (For CBSE, ICSE, IAS, NET, NRA 2022)

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Transformers are electrical devices consisting of two or more coils of wire used to transfer electrical energy by means of a changing magnetic field

About Transformer

  • Transformers are used for the transmission of electrical energy.
  • At a different voltage level, transformers can change the electrical energy of a given voltage.
  • The reason for transforming the voltage to a much higher level is that higher distribution voltages imply lower currents for the same power and therefore lower losses along the networked grid of cables.
  • These higher AC transmission voltages and currents can then be reduced to a much lower, safer, and usable voltage level where it can be used to supply electrical equipment in our homes and workplaces, and all this is possible thanks to the basic Voltage Transformer.
  • It consists of two coils named as Primary coil and a Secondary coil which is wound on a soft iron core.
  • The soft iron core is laminated to minimize eddy currents.
  • The alternating current is applied across the primary coil and the output is obtained across the secondary coil.

Working Principle of Transformer

Working Principle of Transformer
  • The main working principle of transformer is based on the mutual inductance between the two circuits that are linked by a common magnetic flux.
  • A transformer consists of two coils that are electrically separated but magnetically linked through a path of reluctance.
  • There is no direct electrical connection between the two coil windings, thereby giving it the name also of an Isolation Transformer.
  • So, the primary winding of a transformer is connected to the input voltage supply and converts or transforms the electrical power into a magnetic field.
  • While the job of the secondary winding is to convert this alternating magnetic field into electrical power producing the required output voltage as shown.

Transformer Construction (Single-Phase)

Transformer Construction

Transformer turns ratio =


  • – is the Primary Voltage
  • – is the Secondary Voltage
  • – is the Number of Primary Windings
  • – is the Number of Secondary Windings
  • (phi) – is the Flux Linkage

Types of Transformers

  • Step-up Transformer
  • Step-down Transformer

Step-Up Transformer

  • A single-phase transformer can operate to either increase or decrease the voltage applied to the primary winding.
  • When a transformer is used to increase the voltage on its secondary winding with respect to the primary, it is called a Step-up transformer

Step-Down Transformer

  • A Step-down Transformer is a type of transformer, which converts a high voltage at the primary side to a low voltage at the secondary side.
  • If we speak in terms of the coil windings, the primary winding of a Step-down Transformer has more turns than the secondary winding.

Classification of Transformers

Based on Design

  • Core-type transformer
  • Shell-type transformer

Based on Cooling Method

  • Oil filled self-cooled type
  • Oil filled water cooled type
  • Air blast type

Applications of Transformer

  • To step up the current and voltage.
  • To step down the current and voltage.

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