Principle and Construction of Transformer

  • Describe principle of working of an ideal transformer.
  • Analyze operation of such a transformer.

Transformer is a static device. It transfer electrical energy from one part of the electrical or electronic circuit to other part of circuit without changing the frequency. It works on the Michael Faraday’s law of Electromagnetic Mutual Induction.


When the current is provided to the primary winding it behaves as electromagnet due to this the EMF is induced in the secondary winding as it comes in the area having magnetic field lines due to primary Winding. \[V_s = N_s \dfrac{d\phi}{dt}\] where,
\(V_s\) = Secondary Winding Voltage
\(N_s\) = Secondary Winding Turns


  • Laminated Core: Cores are designed not to have current in it. But still there is a leakages current Or the eddy current present in it. To minimize these current the cores are laminated.

  • Winding: Made up of copper or aluminum coated with very thin layer of insulation.

  • Tank: The main function of conservator tank of transformer is to provide adequate space for expansion of oil inside the transformer. It is usually Cylindrical or cubical.

  • Isolation: It is provided by using Synthetic Oil between Core and Tank.

  • Breather: When the temperature changes occur in Transformer insulating oil, the oil expands or contracts and there an exchange of air also occurs when transformer is fully loaded. When transformer gets cooled, the oil level goes down and air gets absorbed within.

\[\mathrm{Turns\ Ratio} = \dfrac{\mathrm{No.\ windings\ in\ Secondary}}{\mathrm{No.\ Windings\ in\ Primary}} = \dfrac{\mathrm{Voltage\ in\ Secondary}}{\mathrm{Voltage\ in\ Primary}} = \dfrac{V_s}{V_p} = \dfrac{N_s}{N_p}\]

Solved Example:


A single-phase 111-V, 50-Hz supply is connected to a coil with 200 turns of a coil-core assembly. Find the magnitude of maximum flux in the core. (SSC JE EE March 2021 Morning)

Correct Answer: B