Transformer Basics And Working Principle

What is a Transformer?

Transformer is a static device which transfers electrical energy from one circuit to an another circuit without altering the frequency.The transfer of energy in the transformer is done through electromagnetic induction process. The transformer raise or lower the voltage according to supply voltage requirement and current also gets changed proportionally to the voltage to maintain the same power.

Why voltage is required to be raised or lowered?

The beauty of the alternating voltage is that it can easily be generated,transmitted, and raised or lowered by a transformer. The voltage is raised for long transmission to reduce the line losses. 

The line loss depends on the current and resistance of the conductor. The line loss varies proportionally to the current in the circuit. By raising the voltage the current gets reduced for transfer of the same amount of electrical power and as a result, the line loss reduces.

At receiving end, the voltage is lowered to the utilization level through step down transformer. 

Working Principle of Transformer:

The transformer functions on the principle of Faraday's Law of Electromagnetic Induction. The law states that if a conductor is placed in a varying magnetic field the voltage is induced in the conductor. When the alternating voltage is fed to the primary, the flux varying in magnitude and direction gets linked to the primary and the secondary winding of the transformer.

The magnitude of induced EMF depends on the rate of change of the flux and number of turns in a coil. According to the Lenz's Law the induced EMF in a coil always opposes the applied voltage. The induced EMF in a coil can be expressed as;

e = - N dФ/dt

The transformer has primary and secondary winding which is wound on the magnetic core.When the primary winding is fed alternating voltage the transformer draws magnetizing current to set up magnetic flux in the core. The varying flux gets linked to the primary and the secondary winding of the transformer. 

Ideally, the flux produced in the primary must get linked to the secondary without any leakage. However, practically all the flux produced in the primary does not link to the secondary and the some parts of the flux is lost. The magnetic core made of Cold Rolled Grain Oriented (CRGO) is more efficient for transferring the flux to the secondary winding. Also, the hysteresis loss of CRGO  core is less.

If the transformer is ideal, the flux generated by the primary winding gets linked to the secondary and primary and there is no leakage flux. However, this is an ideal condition and practically some of the flux gets leaked and links to the other parts of the transformer.The flux links in the core material induce emf which further cause heat loss in the core because of eddy current. The loss is called the eddy current loss. The magnetic core is laminated to reduce the eddy current loss.

The primary winding is fed sinusoidal voltage.The sinusoidal voltage is alternating voltage and the current flowing in the primary set up magnetic flux in the core. The flux travels through the core and gets linked to the secondary and primary. The varying flux induce EMF in the primary and secondary. The magnitude of the EMF induced in the primary and secondary is as given below.

Ep = 4.44 Np fФm

Es = 4.44 Ns fФm

Where,

Ep     = Induced EMF in primary winding
ES     = Induced EMF in secondary winding
Np     = Number of turns in primary winding
Ns     =  Number of turns in the secondary winding
f        =  Frequency
Фm   =  Flux in the core

The transformer core can carry the flux up to its maximum rated capacity. The CRGO core can carry flux up to 1.9 Tesla. If the flux increases above 1.9 Tesla the core may get saturated and the output voltage may get distorted.

The transformer functions pretty well as long as the flux remains constant. The flux density depends on the ratio of voltage/ frequency.

Turns ratio and voltage transformation ratio of  Transformer :


EMF equation of the transformer is as given below.

Ep = 4.44 Np fФm  -------(1)

Es = 4.44 Ns fФm ---------(2)

Dividing equation (2) By (1) we get,

Es/Ep =  Ns/ Np ---------(3)

Es and Ep is almost equal to the primary and secondary terminal voltage if the winding resistance and the leakage reactance is ignored. 

Es= Vs and Ep= Vp

Vs/Vp =  Ns/ Np = K  ----(4)

Where, 

K is the voltage transformation ratio. 

The input power of the transformer is almost equal to the output power.

Vs x Is  = Vp x Ip

Vs/Vp   = Ip/Is  ---------(5)

From equation (4) and (5) we get

Vs/Vp = Ns/Np = Ip/Is = K

The turns ratio is defined as the ratio of primary turns to secondary turns. 

Turns ratio = Np/Ns= 1/K

The transformer  is used to raise and lower the voltage. The transformer which raise the primary voltage is called the step-up transformer and the transformer which lowers the voltage is called step down transformer.

In a step-down transformer, the numbers of turns in the primary is more than the numbers of turns in the secondary.

In a step-up transformer, the numbers of turns in the primary(Np) is less than the numbers of turns in the secondary(Ns).

The transformer  is used to raise and lower the voltage. The transformer which raise the primary voltage is called the step-up transformer and the transformer which lowers the voltage is called step-down transformer.