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Certificate
This is to certify that Sh
Shas
ashi
hi Pr
Praaka
kash
sh,
student of Class XII, Sri Guru Nanak
Public
School, has completed the project
Transformers
titled
guidance
under
the
of
(physics teacher)during the academic
year
2015-2016
fulfillment
of
credit
towards
partial
for
Physics
the
practical evaluation of CBSE 2016, and
submitted satisfactory report, as compiled
in
the
following
pages,
under
my
supervision.
Signature of external examiner
_______________
_______________
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Acknowledgements
"There are times when silence speaks so much more
loudly than words of praise to only as good as belittle a
person, whose words do not express,
express, but only
only put a
veneer over true feelings, which
which are of gratitude at this
point of time."
I would like to express my sincere gratitude to my
physics mentor for his vital support, guidance and
encouragement, without which this project would not
have come forth. I would also like to express my
gratitude to the staff of the Department of Physics at
Sri Guru Nanak public School for their support
during the making
making of this project.
project.
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INDEX
1. CERTIFIC
IFICA
ATE OF EXCELLENCE
2. ACKNOWLEDGEMENT
3. INTRODUCTION
4. PRICIPLE
5. CONSTRUCTION
6. THEORY AND WORKING
7. EFFICIENCY
8. ENERGY LOSSES
9. USES OF TRANSFORMERS
10.
10. CONCL
ONCLUS
USIO
ION
N
11.
11. PRE
PRECAUT
CAUTIO
IONS
NS
12.
12. SOUR
SOURCE
CES
S OF
OF ERR
ERROR
OR
13.BIBILIOGRAPHY
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INTRODUCTION
The transformer is a device used for converting a low alternating
voltage to a high alternating voltage or a high alternating
alternating voltage into
a low alternating
alternating voltage. It is a static electrical device that transfers
transfers
energy by inductive coupling between its winding circuits. Transformers
range in size from a thumbnail-sized coupling transformer hidden inside
a stage microphone to huge units weighing hundreds of tons used in
power plant substations
substations or to interconnect portions of the power grid.
All operate on the same basic principles, although the range of designs
is wide. While new technologies have eliminated the need for
transformers in some electronic circuits, transformers are still found in
many electronic devices. Transformers are essential for high-voltage
electric power transmission, which makes long-distance transmission
economically practical. A transformer is most widely used device in
both low and high current circuit. In a transformer, the electrical
energy transfer from one circuit to another circuit takes place without
the use of moving parts.
A transformer
transfor mer which increases the voltages
is called a step-up transformer. A transformer which decreases the
A.C. voltages is called a step-down transformer.
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Transformer is, therefore, an
essential piece of apparatus
both for high and low current
circuits.
Close-up of single-phase pole mount
transformer.
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PRINCIPLE
It is based on the principle of mutual
induction that is if a varying current is set-up
in a circuit then 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.
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CONSTRUCTION
A tran
transf
sfor
orme
mer
r cons
consis
ists
ts of a rect
rectan
angu
gula
lar
r shaf
shaftt
iron
core
made
of
laminated
sheets,
well
insulated from one another. Two coils p1 & p2 and
s1 & s2 are wound on the same core, but are well
insulated with each other. Note that the both the
coils are insulated from the core, the source of
alternating e.m.f is connected to p 1p2, the primary
coil and a load resistance R is connected to s 1 s2,
the secondary coil through an open switch S. thus
there can be no current through the sec. coil so
long
as
th e
switch
is
open.
For
an
ideal
transformer, we assume that the resistance of the
primary
&
secondary
winding
is
negligible.
Further, the energy loses due to magnetic the iron
core is also negligible. For operation at low
frequency, we may have a soft iron. The soft iron
core is insulating by joining thin iron strips coated
with varnish to insulate them to reduce energy
losses by eddy currents. The input circuit is called
primary.
And
the
output
circuit
is
called
secondary.
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The ideal transformer as a circuit element
An ideal voltage step-down
transformer.
transformer. The secondary
secondary current
arises from the action of the secondary
EMF on the (not shown) load
impedance.
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THEORY AND WORKING
When an altering e.m.f. is supplied to the
primary coil p1p2, an alternating current
starts falling in it. The altering current in the
primary produces a changing magnetic flux,
which induces altering voltage in the primary
as well as in the secondary. In a goodtransformer, whole of the magnetic flux
linked with primary is also linked with the
secondary, and then the induced e.m.f.
induced in each turn of the secondary
s econdary is
equal to that induced in each turn of the
primary. Thus if Ep and Es be the
instantaneous values
values of the e.m.f.’s induced
in the primary and the secondary and Np and
Ns are the no. of turns of the primary
pr imary
secondary coils of the transformer and, Dфь
/ dt = rate of change of flux in each turn of
the coil at this instant, we have
Ep = -Np Dфь/dt
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Es = -Ns Dфь/dt
(2)
Sinc
Since
e the
the abov
above
e rela
relati
tion
ons
s are
are true
true at ever
every
y
instant, so by dividing 2 by 1, we get
Es / Ep = - Ns / Np
(3)
As Ep is the instantaneous value of back e.m.f
induced
in
the
primary
coil
p 1,
so
t he
instantaneous current in primary coil is due to
the
the diff
differ
eren
ence
ce (E – Ep ) in the
the inst
instan
anta
tane
neou
ous
s
values of the applied and back e.m.f. further if
Rp
is
is
the
resistance
o,
p1p2
co
coil,
then
the instantaneou
instantaneous
s current
current Ip in
in the primar
primary
y coil
is given by
I =E – Ep / Rp
E – Ep
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Ip Rp
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And Is =value of sec. current at this instant,
then Input power at the instant t = Ep Ip and Output
power at the same instant
=
Es Is
If there are no losses of power in the transformer,
then Input power = output power or
Ep Ip
Es / Ep
=
Es Is
=
Ip / Is
Or
=
K
In a step up transformer
As k > 1, so Ip > Is or Is < Ip
I.e. current in sec. is weaker when secondary voltage
is higher. Hence, whatever we gain in voltage, we lose
in current in the same ratio. Similarly it can be shown,
that in a step down transformer, whatever we lose in
voltage, we gain in current in the same ratio.Thus a
step up transformer in reality steps down the current &
a step down transformer steps up the current.
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BASIC IDEA OF STEP DOWN TRANSFORMER
BASIC IDEA OF STEP UP TRANSFORMER
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EFFICIENCY
Efficiency of a transformer is defined as the
ratio of output power to the input power i.e.
i .e.
output power
power / input
input power
power = Es Is / Ep Ip
η = output
Thus in an ideal transformer, where there is no
actuall practic
practice,
e, there
there
power losses, η = 1. But in actua
are many power losses; therefore the efficiency
of transformer is less than one.
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ENERGY LOSSES
In practice, the output energy of a transformer is always less than the
input energy, because energy losses occur due to a number of reasons as
explained below.
: The coupling between the coils is seldom
perfect. So,
So, whole of the magnetic flux produced by the primary coil is not
linked up with the secondary coil.
: In actual iron cores in spite of lamination,
Eddy currents are produced. The magnitude of eddy current may,
however be small. And a part of energy is lost as the heat produced in the
iron core.
: In practice, the coils of the transformer possess
resistance. So a part of the energy is lost due to the heat produced in the
resistance of the coil.
: The alternating current in the coil tapes the iron
core through complete cycle of magnetization. So Energy is lost due to
hysteresis.
: The alternating current in the
Transformer may be set its parts in to vibrations and sound may be
produced. It is called humming. Thus, a part of energy may be lost due to
humming.
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USES OF TRANSFORMER
A transformer
transformer is used in almost all a.c.
operations

In voltage regulator for T.V., refrigerator,
comput
puter, air con
ondi
dittio
ion
ner etc
etc.

In the induction furnaces.

A step down transformer is used for welding
purposes.

A
step
down
transformer
is
used
fo r
obtai
ain
ning
ing la
larg
rge
e curre
rrent.
nt.

A step up transformer is used for the
production
of
X-Rays
and
NEON
advertisement.

Transformers are used in voltage regulators
and stabiliz
ilize
ed power supplie
lies.

Transformers are used in the transmissions
of a.c. over long distances.

Small transformers are used in Radio sets,
telephones, loud speakers and electric bells
etc.
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CONCLUSION
1. The output voltage
voltage of the
transformer across the secondary
coil depends upon the ratio (Ns/Np)
with respect to the input voltage
2. The output voltage
voltage of the
transformer across the secondary
coil depends upon the ratio (Ns/N p)
with respect to the input voltage
3. There is a loss of power between
input and output coil of a
transformer.
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PRECAUTIONS
1. Keep safe yourself from high
voltage.
2. While taking the readings of
current and voltage the A.C
should remain constant.
SOURCES OF
ERROR
1. Values of current can be
changed due to heating effect.
2. Eddy current can change the
readings.
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A Big Transformer
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Bibliography
The data used in this project was
taken from the following sources:

www.google.com

www.wikipedia.com

www.scribd.com
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