CONTENTS
1. Acknowledgement
2. Introduction
3. Principle
4. Step Down Transformer
5. Construction
6. Theory
7. Energy Losses In Transformer
8. Bibliography
ACKNOWLEDGEMENT
Primarily I would thank God for being able to
complete this project with success. Then I would
like to thank my physics teacher Miss Anshu
Ma’am, whose valuable guidance has been the
one that helped me patch this project and make it
a full proof success. Her suggestions have served
as a major contributor towards the completion of
the project.
Then I would like to thank my parents and friends
who have helped me their valuable suggestions
and guidance has been helpful in various phases of
the completion of the project.
Last but not the least I would like to thank my
classmates who have helped me a lot.
INTRODUCTION
The transformer is a device used for converting a low
alternating voltage to a high alternating voltage or a high
alternating voltage into a low alternating voltage.
PRINCIPLE
It is based on the principle of mutual induction that is if a
varying current is set-up in a circuit, induced e.m.f. is
produced in the neighboring circuit. The varying current
in a circuit produce varying magnetic flux which induces
e.m.f. in the neighboring circuit.
STEP DOWN TRANSFORMER
In our project step-down transformer is used: This
transformer converts high voltage at alternating current
into a low voltage alternating current. In a step-down
transformer the number of turns in primary coil remains
more as compared to the secondary coil.
CONSTRUCTION
The transformer consists of two coils. They are insulated
with each other by insulated material, and wound on a
common core. For operation at low frequency, we may
have soft iron. The soft iron core has iron strips coated
on it, to insulate them to reduce energy losses by eddy
currents.
THEORY
Suppose, the number of turns in the primary coil in Np
and that in the secondary coil is Ns.
The resistance of the coil is assumed to be zero. Let
dф/dt be the rate of change of flux in each turn of the
primary coil.
If Vp be the induced e.m.f. in the primary coil then,
Vp = -Np dф /dt (1)
We suppose that there in no loss in flux between the
primary and secondary coils.
Then, the induced e.m.f. in the secondary coil will be :
Vs = -Ns dф /dt (2)
From equation (i) and (ii), we find:
Ns/Np = K is called transformer ratio or turn ratio.
For step up transformer K > 1
For step down transformer K < 1
That is for step-up transformer
Vs > Vp, Is < Ip so K > 1, hence Ns > Np
For the step-down transformer
Vs < Vp, Is > Ip so K < 1, hence Ns < Np
If, Ip = value of primary current
Is = value of secondary current
Input power = Vp Ip
Output power = Vs Is
If there are no losses of power in the transformer, then
Input power = Output power
Vp Ip = Vs Is
So, Vs / Vp = Ip / Is = K
Efficiency: the efficiency of the transformer is given by:
η = output power / input power = Vs Is / Vp Ip
For ideal transformer η = 1 = 100%
Therefore for the step-up transformer, voltage in the
secondary is more than in the primary coil ( Vs > Vp)
and in a step down transformer we have ( Vs < Vp)
ENERGY LOSSES IN
TRANSFORMER
In practice, the output energy of a transformer is always
less than the input energy, because energy losses occur
due to several reasons as explained below.
1. Loss of Magnetic Flux: the whole magnetic flux
produced by the primary coil is not linked up with
the secondary coil.
2. Hysteresis Loss : Each time the magnetic flux is
reversed (due to supply of alternating current), a
small amount of energy is lost due to hysteresis
within the core
3. Eddy Current Loss : Eddy currents are produced in
the metal transformer core and energy is lost
because of heat produced in the iron core. This can
be reduced by using laminated core
4. Copper Loss : The coils of the transformer possess
resistance. So some energy in los due to heat
produced in the resistance of the coil.
5. Vibrational Loss : Transformer may produce
vibrations and sound. It is called humming. Thus, a
part of energy may be lost due to humming.
PRECAUTIONS
1. Keep yourself safe from the high voltage.
2. While taking the readings of current and voltage, the
A.C. should remain constant.
3. Do not exceed the limit the alternating current
BIBLIOGRAPHY
1. Physics NCERT textbook class 12
2. NCERT physics Lab manual
3. Wikipedia
4. Google.com
