The transformer is a static device which converts the magnetic energy into electrical energy. It consists of two or more than two stationary circuits interlinked by a common magnetic circuit; the energy transfer takes place through this circuit without having any change in frequency from one circuit to another.
The transformer consists of two windings. The winding which is connected with the supply a.c. voltage is called the primary winding, and the winding which is connected to load and delivers the energy to load is called secondary winding.
E.M.F. Equation of a Transformer
Let the flux at any point is given by
φ = φm sin ω t
The instantaneous e.m.f. induced in a coil of T turns linked by this flux is given by Faraday's law as
The above equation can also be written as
Where Em = Tωφm = maximum value of e.
For sine wave, the r.m.s. value is given by
This is called as e.m.f. equation of transformer.
φm is the maximum flux in webers (Wb)
f is the frequency in hertz (Hz)
E is the voltage in volts
T is number of turns in winding
The primary r.m.s. voltage is
E1 = 4.44φm fT1
The secondary r.m.s. voltage is
E2 = 4.44φm fT2
Voltage Ratio and Turns Ratio
The ratio E/T is called voltage per turn.
As we know
Form equation 1 and 2
The ratio is called truns ratio.
Step - up transformer: These are the transformer in which the output voltage is higher than the input voltage.
Step - down transformer: These are the transformer in which the output voltage is less than the input voltage.