Friday, August 28, 2020


Transformer is a passive electrical device used to increase or decrease AC voltage. It is based upon principle of electromagnetic induction. There are two coils on transformer. The coil on which power in fed is called primary coil and that one from which output power is taken is called secondary coil. Both coils are wound on laminated iron to reduce loss of electric energy by heating due to eddy current. Transformer cannot change the voltage of DC current. There are two types of transformers regarding to voltage level

  • Step Up Transformer: It is used to increase voltage of AC current. In step up transformer number of turns on secondary coil is greater than that of primary coil.
  • Step down Transformer: It is used to decrease the voltage of AC current. In step down transformer number of turns in primary coil is greater tha that in secondary coil.


Transformer Formula

The value of the power for an electric circuit is the value of the voltage by the value of the current intensity. As in the case of a transformer, the value of the power in the primary is the same value for the power in the secondary we have:

(input voltage on the primary coil) × (input current on the primary coil ) = (output voltage on the secondary coil ) × (output current on the secondary coil)

This can be written as an equation:

Vp × Ip = Vs × Is

We can also work out the transformer output voltage if we know the input voltage and the number of turns on the primary and secondary coils.

inputvoltageontheprimarycoiloutputvoltageonthesecondarycoil                          = numberofturnsofwireontheprimarycoilnumberofturnsofwireonthesecondarycoil

This can be written as an equation:

VpVs = npns


Vpinput voltage on the primary coil.
Vsinput voltage on the secondary coil.
Ipinput current on the primary coil.


Isinput current on the secondary coil.
npthe number of turns of wire on the primary coil.
nsthe number of turns of wire on the secondary coil.


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