Explain the working principle of transformer and also its construction - Physics

You all must have seen a transformer in your area and you must have seen a transformer in many places. You must be wondering why transformers are installed in every area. Does the transformer make any electricity or is it installed like this? Nor does it generate electricity, so what is its function, why is it visible in every area? So today we will know how a transformer works and we study the working principle of transformer.

A Transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit or multiple circuits. 

                                                     Or

A Transformer is an electrical device that transfers energy from one electrical circuit to another using the principle of electromagnetic induction.

It is a device used to change or transform an alternating voltage from one to another of greater or smaller value.

This may also be defined as the device used to obtain high AC voltage from a low AC voltage AC source or to obtain a low AC voltage from a high voltage AC source.

A varying current in one of the coils of the transformer produces a varying magnetic flux in the core of the transformer, which produces a different electromotive force in any other coils wound around the same core.

Working Principle of transformer:

The working principle of transformer or Transformer works on the principle of mutual induction. Mutual Induction is the phenomenon by which when two coils are brought close to each other, the magnetic field of one coil tends to join with the other. This further leads to the generation of voltage in the second coil. This property of the coil that affects or changes the current and voltage in the secondary coil is called mutual inductance.

Construction:-

A transformer is made up of a rectangular iron core. The main elements of the transformer are the primary and secondary windings and the steel core. The core of the transformer is made of silicon steel to provide a continuous magnetic path.
Two coils are wounded separately on a laminated soft iron core(the coils of the transformer are laminated to reduce the loss of eddy current). one of the coils is called primary and the other is called Secondary. Both these coils are insulated with a ferromagnetic iron core.

The Original source of alternating voltage is connected across the primary. An induced EMF appears across the ends of the secondary which is used to drive current in the desired circuit.

The Coils are insulated from one another. Np is the number of turns in the primary. Ns are the number of turns in the secondary. The primary coil is the input coil and the secondary coil is the output coil of the transformer.

Types of Transformer

There are two types of transformers are:

1. Step-up transformer.

2. Step-down transformer

The transformer which converts low voltage into higher ones is called a step-up transformer.

Transformers while those which convert high AC voltage into lower ones are called step-down transformers.

In a step-up transformer, the coil of thick copper wire having a smaller number of turns is the primary coil and the coil of thin wire having a larger number of turns is the secondary coil.

In step down transformer, the order is reversed. 

Theory and Working

The given source of AC is connected to the primary coil.

when alternating current flows through the primary then in each cycle of current once in one direction and one in the opposite direction and alternating magnetic flux is produced in the core. 

The magnetic flux linked with the secondary coil also changes continuously as it is bounded on the same iron core. 

Therefore by mutual induction, an alternating EMF of the same frequency is induced in the secondary coil. 

The induced EMF depends on the ratio of a number of turns in the coil and is given by Faraday's law of induction: 

${\displaystyle V_{\text{P}}=-N_{\text{P}}{\frac {\mathrm {d} \Phi }{\mathrm {d} t}}}$                                 

                                 

                  

                  

        where k is Transformation ratios.

                              Input Power = Output Power

                       

                        

From the above equations, we conclude that

                       

The above relation is based on three assumptions

1. The secondary circuit is very small.
2. The primary resistance and the primary current are small.
3. The flux of both the primary and the secondary coil is the same with very little flux escape through the core. 

Above we are talking about the theory and working principle of transformer.

Energy losses in a transformer: 

Generally, the power output of a transformer is less than the power input because of unavoidable energy losses.

1. Copper loss:-  As AC flows through a primary and secondary coil, heat is developed inside the copper turns, this waste of energy is known as Copper loss. This is due to the resistance of the windings. They are minimised by using thick wire.

2. Eddy current losses:- The alternating magnetic flux induces Eddy currents in the iron core and causes heating. It is reduced by having a laminated core. This is done by making it of a number of thin sheets insulated from each other.

3. Flux losses:- The coupling of the primary and secondary is never perfect. Therefore the whole of the magnetic flux generated in the primary does not pass through the secondary.

    The air gaps in the core are also the cause of flux loss. It can be reduced by winding the primary and the secondary coil over one another.

4. Hysteresis loss:- During each cycle of AC, the core undergoes a complete cycle of magnetization. The energy in this process is converted into heat and wasted.

It is minimised by using a magnetic alloy for which area of the hysteresis loop is minimum.

There is one more energy loss in the transformer which is called Hamming loss that is the loss of energy in the form of vibration and sound.

These are the losses in the working principle of the transformer.

Application of Transformer

1. It can raise or lower the level of Voltage or Current in an AC Circuit.

2. It can isolate the two circuits electrically.

3. The transformer is used in the rectifier.

4. It can increase or decrease the value of a capacitor, an inductor or a resistance in an AC circuit.

5. It is used in voltage regulators, voltage stabilizers, power supplies etc.