What is a transformer?

Transformer is a static electrical device which transfers power from one circuit to another circuit without any physical contact. The main aim of this transformer is that the output power of the transformer is same as output power. The term static indicates that it does not contain any rotating part in it.



In addition to the power transfer it also acts as a parameter control device or parameter changing device. The above figure shows that the input and output are same where as cases the voltage and currents may not be same. i.e. the voltage and current at the output can be changed by varying output windings to get the desired parameter at the output. Like as in step up transformer the voltage is stepped up i.e. the output is high compared to input voltage but the power ratio is same.

What is transformer working principle?

Transformer works on the principle of Faraday’s electromagnetic induction principle where varying magnetic field produces an EMF in the electric coil. Basically it is the combination of two laws i.e. in primary side the varying current produces a varying magnetic field (electromagnetism) and this magnetic flux lines are cut by the adjacent secondary coil (induction principle) and EMF will be induced.

Es = Ns (dΦ/dt)

Ep = Np(dΦ/dt)

Electro Magnetic field introduction

Electro Magnetic field introduction

 What is an equivalent circuit of a transformer?

Transformer consists of two coils called primary and secondary which will have inductance and as well as small resistance.

transformer equivalant circuit

In the above equivalent circuit

R1= Primary coil resistance

X1= Primary coil inductance

R2’= Secondary equivalent coil resistance

X2’= Secondary equivalent coil inductance

Rm = Magnetizing resistance

Xm= Magnetic inductance.

The magnetizing components in the transformer indicate the losses of power to magnetize the core which acts as a magnetic flux transmission media. To simplify the circuit the secondary components brought to primary side which are R2’ and X2’ where

R2’= R2/N2

X2’= X2/N2

Where N is the turns ration between primary and secondary.

N= N1/N2

N1= primary Inductor coil number of turns

N2 = Secondary number of turns.  

What is a transformer core?

Transformer core is an important component of an amplifier as it acts a bridge for the magnetic flux between primary and secondary coils. There are two types of cores air and iron. In air core transformer the reluctance offered for the flow of magnetic flux is high compared to iron core so more flux transmission from primary to secondary hence more efficiency. The cost is a bit high because of the iron in iron core transformer.

What is the difference between transformer and amplifier?

Amplifier:  An electronic device which increases or boosts the power of the signal is called is an amplifier. I.e. both quantities of the signal (voltage and current), increases in amplifier. If it is voltage amplifier also there will not be decrease in current.

Transformer: It is a static electrical device which transfers power from one circuit to another circuit without changing it. Even though the signal quantities (voltage and current) can be boosted at the output, it cannot acts as amplifier because if one of the quantities is boosted at the output the other quantity is reduced. So the power is same.

What is difference between induction motor and transformer?

The main difference between induction motor and transformer is that transformer is a static machine and motor is an rotating machine. The secondary winding in induction motor is wounded on rotor to convert primary power in to rotational force. Where as in transformer there is no conversion of energy and hence no work done.

What is auto transformer?

Auto transformer is one type of transformer which shares one winding as primary and secondary coil. This is also called as single coil transformer where at the input and output leads are from same coil. It is designed to use for small voltage changing applications i.e. it can increase or decrease the output voltage a small bit because of one coil sharing.

What are the advantages and disadvantages of auto transformer?


  1. Smaller in size (consists of only one winding)
  2. Cost is less
  3. Better use in smaller applications


  1. There is no isolation between primary and secondary.
  2. Fault current can damage the entire circuit.


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