TRANSFORMER

TRANSFORMER DEFINITION:

Transformer is a static machine, which is used to step up or step down the electrical energy (Voltage) without changing the frequency. it works on the Faraday's Law of ELECTROMAGNETISM.

FARADAY'S FIRST LAW:

When magnetic flux linking with the coil changes, the EMF (Voltage) is induced in the coil.

FARADAY'S SECOND LAW:

The magnitude of EMF induced in the coil depends on rate of changes of flux linking with the coil.

EMF OF SELF INDUCTION:

Whenever flux linking with the coil changes due to change of current of the coil itself then EMF induces in the coil which is called as self induced EMF.

This EMF opposes the supply voltage and hence called back EMF.

Es = N . dΦ/dt 

Where, 

N - Number of turns of coil.

dΦ/dt - Rate of change of flux.

EMF OF MUTUAL INDUCTION:

If there are two coils kept near to each other or one over the other and if one coil is connected to AC supply so that AC flux is produced, the changing flux links with the turns of the second coil and hence EMF produced in the second coil due to change of current in the first coil is called Mutually Induced EMF.

Em = N₂. dΦ₁/dt 

or

N₂ =  dI₂/dt

Where,

N -  Number of turns of second winding coil.

dI₂/dt - Rate of change of flux (or current) due to first coil.

Es = EMF of self induction is produced in the coil when it is connected to AC supply. The value of Es will depend on turns N_{1 and on rate of change of flux. If rate of change of flux is same then this EMF depends on number of turns of the coil. More the turns more is the EMF.}

_{Instead of AC, if DC is connected to the coil then there will be a 'steady flux' produced. Thus flux linking the coil will not change and hence there will not be any EMF produce in it.}

_{Now take the case of two coils A & B. If A is connected to AC supply then it produces AC (changing) flux,This links with coil A and produces in it EMF of self induction Es =}  N_{1 .} dΦ1/dt. At the same time the same AC (changing) flux also links with coil B which has N_{2  number of turns. Hence in coil B also EMF is produced. This EMF is called as Mutually induced EMF (Em), and Em =} N₂. dΦ1/dt. Hence its magnitude depends on number of turn of coil B.

In the above case if instead of coal A connected to AC supply, coil B is connected to AC supply and A is kept near to it, then there will be self induced EMF in coil B {Es = N₂. dΦ₂/dt} and manually induced EMF in coil A { Em = N₁. dΦ₂/dt }.

In short, self and manually induced EMF depends on number of turns of the respective coils. More the number of turns more is the EMF and vice versa. If DC is connected there will not be any self or mutually induced EMF in the coils.

The above theory helps in understanding the working principle of the "TRANSFORMER" The transformer works on the principle of Mutual Induction.