transformer electrical symbol || operation

A transformer is an electrical equipment which is used for raising or lowering the AC voltage supply. Also it is a static device which can transfer power by changing the supply voltage. It consists of two or more stationary electrical circuit which is interlinked by magnetic circuit for power transfer. While transferring electrical power, its supply power and supply frequency aren't changed. Only system voltage and current are changed. Transformer electrical symbol is drawn below:-

Transformer electrical symbol

Let's draw transformer electrical symbol that is consistently used in circuit.

If you see these symbols in any electrical circuit, you can easily identify it as a transformer. Let's describe more about single phase transformer which is similar for 3 phase transformer also. For a single phase transformer, there are two winding or coils which is wound on the laminated core. On the laminated core which is made of high grade silicon steel.

Operation of transformer

Let T₁ be the coils in primary winding and T₂ be the coils in secondary winding. The coil which receives energy from source is called primary coil and the coil which receive energy from flux, connected to load and delivers energy is called secondary winding. These windings are responsible for increasing or decreasing voltage. From primary winding, alternating voltage V₁ is applied and I₁ current will flow on it. This current will produces alternating flux ∅_m in the core. The mean path for magnetic flux is shown in the figure. This alternating flux links the turn T₁ of the coil and E₁ is the induced voltage by self induction in these turn. The voltage ratio of the transformer is determined by the ratio of the number of turns in the primary and secondary windings. If the number of turns in the secondary winding is greater than the number of turns in the primary winding, the transformer is called a step-up transformer and it increases the voltage. If the number of turns in the secondary winding is less than the number of turns in the primary winding, the transformer is called a step-down transformer and it decreases the voltage.

By the help of core, it create the magnetic path for electrical energy transfer. So by the help of flux, it produce E₂ voltage on secondary turn which process is called mutual induction. 

The relationship between primary winding, primary voltage, secondary winding, and secondary voltage is given by,

E₁ / N₁ = E₂ / N₂

This equation can be proved by below process:-

Flux is given by,

∅ = ∅_m sinωt

Instantaneous emf induced in a coil of N turns, From Faraday's law,

e = - d(∅N) / dt = -N d∅ / dt = -N d(∅_m sinωt) / dt = -N ω ∅_m cosωt = N ω ∅_m sin(ωt - π/2)

For sine wave, the rms value of emf is given by,

Erms = E = Em / √(2)

so, E =  Nω∅_m / √(2) = 4.44 N f ∅_m [∵ ω = 2πf ]

Hence, the primary rms voltage is,

E₁ =  4.44 N₁ f ∅_m 

The secondary rms voltage is,

E₂ =  4.44 N₂ f ∅_m 

Let's take the ratio of voltage and number of turn, which is known as voltage per turn.

For primary side,

E₁ / N₁ = 4.44 f ∅_m 

E₂ / N₂ = 4.44 f∅_m

 As we can see on both equation, same quantity on right hand side. So,

E₁ / N₁ = E₂ / N₂ 

It can be also write as,

E₁/E₂ = N₁  / N₂ 

Here, N₁  / N₂ is known as turns ratio. Also,

α = E₁ / E₂ = N₁ /  N₂ 

where α is known as transformation ratio.