Single-Phase Transformers | Electrical Machines for Electrical Engg. - Electrical Engineering (EE) PDF Download

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 = φ_m 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 E_m = Tωφ_m = 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.
Where,
φ_m 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 = 4.44φ_m fT₁
The secondary r.m.s. voltage is
E₂ = 4.44φ_m 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.