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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 12-01-2016
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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. 12-01-2016
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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. 12-01-2016
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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 R p 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 / R p E – Ep
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=
Ip R p
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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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