All About Transformer

Do you know all about the transformer? 

The transformer is a piece of static apparatus that converts an electrical power with the desired change in current and voltage from one alternating-current circuit to another without any change in frequency.

Transformer Working Principles:

As we all know the principle of mutual induction that the current changing in one coil induces an alternating emf in the other coil which drives the load. So that our transformer works on that same principle. Generally, it consists of two inductive coils having high mutual inductance and common magnetic circuit but is separated electrically. One of the two coils is connected to the alternating power source which is to be transformed, is primary winding having a number of turns N1. and the second one on which the emf gets induced and if the load is connected to it, the induced emf will drive the current through the load; is secondary winding having a number of turns N2.


There are basically two parts of a transformer.

  1. Magnetic Core: It is of square or rectangular shape in which vertical portion is called limb while the top and bottom which is horizontal is called yoke of the core. It is made up of laminations and due to this eddy currents losses are minimized and they insulated from each other by using insulation like varnish and they are overlapped to avoid the air gap at the joints.
  2. Winding or Coils: The coils are wound on the limbs of a transformer and wound adjacent to each other to get high mutual inductance while they are divided into a large number of coils and insulation is applied between them to increase the performance of a transformer.


There are three types of transformer on the basis of their construction.

  • Core Type:

This type contains a single magnetic circuit. The shape of the core is of the rectangular type having two limbs upon which the windings are wound encircling the limbs and the winding used are of cylindrical type. The coils are wound in helical layers with different layers insulated from each other by paper or mica. The low voltage coils placed first on the limb near the core while the high voltage coil surrounds it. Due to this, windings are uniformly distributed and they can easily be removed from the top yoke for maintenance. It is preferred for low voltage applications.

  • Shell Type:

This type contains a double magnetic circuit. The core contains three limbs and the windings are wound on the center limb and the winding is of sandwich-type coils. Each high voltage coil is placed in between two low voltage coils and these low voltage coils arrangement is such that they are near to the top and bottom of the yoke. If we require maintenance for the windings, the removal of a large number of windings lamination will be required. It is preferred for high voltage applications.

  • Berry Type:

This type contains more than two magnetic circuits. The core looks like the spokes of a wheel but internally, it is symmetrical to that of shell type. As the windings used is of sandwich-type and their arrangement is similar to shell-type transformers. Their maintenance is difficult than shell type as the removal of yokes is difficult. It is preferred for both low and high voltage applications. 

E.M.F. Equation:

We know the working of a transformer as emf generated in primary coil E1 due to input electrical power which is sinusoidal in nature and due to its emf is induced in the secondary coil which is E2. From Faraday’s law of electromagnetic induction, the average induced emf in each turn is proportional to the average rate of change of flux.


Average emf per turn = 4*f*Øm  volts    

As the input power is of sinusoidal nature then the output will also be of sinusoidal nature. Therefore,

RMS value = 1.11*Average value

And hence the          

RMS value of emf induced per turn = 1.11*4*f*Øm = 4.44*f*Øm

Hence the emf equations for primary and secondary coil turns N1 and N2­ respectively will be

E1 = 4.44*f*Øm*N1

E2 = 4.44*f*Øm*N2

Voltage Ratio:

                      Dividing the secondary emf equation by the primary emf equation, we will get the voltage transformation ratio denoted by K.

E2/E1 =  N2/N1 = K

Current Ratio:

                      There are no losses in an ideal transformer and due to this, the input power is equal to the output power. Therefore, we can write

V1I1 = V2I2


V2/V1 = I1/I2 = K

We can see that the currents are in an inverse ratio than that of the voltage transformation ratio.


Volt-Ampere Rating:

                             When power is produced at the output, it varies with the load depending on the output power factor. Due to this, transformers power is not rated in Watts or kilo-Watts but it is rated in volt-ampere as the product of voltage and current called VA Rating which is generally expressed in kVA (kilovolt amperes rating).

We know that

V2/V1 = I1/I2 = K

V1I1 = V2I2


kVA Rating of a transformer = V1I1/1000 = V2I2/1000

All About Transformer Applications:

It is used:

  • For Impedance matching.
  • For isolating two circuits electrically.
  • For increasing or decreasing alternating voltages in electric power applications.
  • For voltage, current, and power measuring instruments.
  • For stepping up low voltages for measurement.
  • For stepping down high voltages for safety precautions.
  • For the Rectification process.
  • For voltage regulation and stabilization.
  • For power supplying instruments.

Related Topics;

  1. Equivalent circuit of the transformer
  2. Characteristics of an ideal transformer
  3. Parallel operation of Transformer
  4. Efficiency and losses of a transformer
  5. 3-phase transformer