An Electrical instrument which is used to
alternating emf in to larger or smaller alternating
emf or to render a current earth-free.
Working Principle: It works on principle of
Construction: It is made up of two coil
1. Primary Coil:
Is in which input alternating emf is
2. Secondary Coil: From which output emf is
4. Working of
Two coils are magnetically
connected. There is no electrical
An alternating current is passed
through the primary coil and this
setsup a varying magnetic field,
which passes to secondary coil
by electromagnetic induction and
5. Ns/Np = Vs/Vp
On basis of numbers of turns transformer is
divided into two types.
1. Set up Transformer
2. Set down Transformer
Set up Transformer:
Ns> Np .then Vs > Vp.
Set Down Transformer:
Ns< Np . Then Vs<Vp
8. Power Loss of Tranformer:
Power is lost in two ways
1. Eddy Current
2. Hysteris Loss
9. Eddy Current:
Induced current set up perpendicular
to flux is eddy current. It causes
2.Heating core material.
It is energy to magnetic and
demagnetic the core material in
each cycle of A.c
10. Minimizing the power loss:
1.Insulation is provided.
2.Resistance between primary coil
and secondary coil should be
Efficiency of Transformer:
E= output power/Input power *100
11. Rendering a Current –Earth free:
Electricity produced by dynamo and
consumer supplied by live wire, it is
at high potential.
It is at zero potential
Supplies current to instrument.
12. If live earth wire accidently meet
,current will flow, and if person
touches that connection he will
Transformer reduces Earth shocks.
Other Types of Transformer
1. Auto Transformer
2. variable transformer
13. Auto Transformer
Consist of single coil of wire with four
contecting points coming to it.
Length of coil can be changed.