Working principle of transformer:
The transformer is based on induction (mutual induction) principle.
From the above figure shows circuit diagram of transformer
V1= Primary applied voltage
E1= Primary (self) induced emf
I1= Primary current
N1= Primary number of turns
V2= Secondary terminal voltage/Load voltage
E2= Secondary induced emf
I2 = Secondary current/Load current
N2= Secondary number of turns
∅= Alternating flux
When alternating voltage (v1) is applied to the primary winding a similar nature of current termed as exciting current flows through it. The exciting current produces an alternating flux (∅) in the core, which links with both the windings i.e primary and secondary.
According to Faraday’s laws of electromagnetic induction, there will be self-induced emf in the primary and mutually induced emf in the secondary winding. But according to Lenz’s law primary induced emf will oppose the applied voltage that is why some time it is referred to as back emf. In magnitude the primary induced emf (E1) is almost equal to the applied voltage (V1). Therefore, we can say emf induced in the primary winding is equal and opposite of the applied voltage. i.e.
When the load is connected across the secondary winding, the secondary emf (E2) will cause a current (I2) to flow through the load. Thus a transformer enables us to transfer a.c. power from one circuit to another i.e. primary to secondary winding through magnetic circuit by electromagnetic induction with a change in voltage level. This is the working principle of the transformer.
- Simple circuit for a 1-∅ transformer
E2>E1, Step-up transformer
E2<E1, Step-down transformer
V1=E1+ I1 (jX1+R1)
The magnitudes of E2&E1 depend upon the number of turns N2&N1 respectively. If N2 >N1, Then E2>E1 and we get a step-up transformer. If N2 <N1, Then E2<E1, we get a step-down transformer.