transformer class 12 project

8/13/2019 transformer class 12 project

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They are so important in our lives

that without them even the electric

bells fitted in our homes wont

work.


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CertificateThis is to certify that , student of Class XII, KENDRIYA VIDYALAYA,

GOMTI NAGAR, LUCKNOW, has completed the project titled Transformers during

the academic year 2013-2014, and submitted satisfactory report, as compiled in the

following pages, under my supervision.

_________________

Department of Physics

Kendriya Vidalaya, Gomti Nagar, Lucknow

Acknowledgements


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"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, but only put a

veneer over true feelings, 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 andencouragement, without which this project would not have come forth. I would also like to express mygratitude to the staff of the Department of Physics at Kendriya Vidyalaya for their support during themaking of this project.

________________

INTRODUCTION___________


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The transformer is a device used for converting alow alternating voltage to a high alternating

voltage or a high alternating voltage into a low

alternating voltage. It is a static electrical devicethat transfers energy by inductive couplingbetween its winding circuits. Transformers range in

size from a thumbnail-sized coupling transformerhidden inside a stage microphone to huge unitsweighing hundreds of tons used in power plant

substations or to interconnect portions of the

power grid. All operate on the same basicprinciples, although the range of designs is wide.While new technologies have eliminated the needfor transformers in some electronic circuits,transformers are still found in many electronicdevices. 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, theelectrical energy transfer from one circuit toanother circuit takes place without the use of

moving parts. A transformer which increases thevoltages is called a step-up transformer.

A transformer which decreases the A.C.voltages is called a step-down transformer.

Transformer is, therefore, an essential piece of

apparatus both for high and low current circuits.


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Close-up of single-phase pole mount transformer.

PRINCIPLE___________


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It is based on the principle of mutual induction thatis 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 producevarying magnetic flux which induces e.m.f. in theneighboring circuit.

_ CONSTRUCTION___________


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A transformer consists of a rectangular shaft iron

core made of laminated sheets, well insulated from

one another. Two coils p1 & p2 and s1 & s2 arewound 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 p1p2, the primary coil and a

load resistance R is connected to s1 s2, the

secondary coil through an open switch S. thus

there can be no current through the sec. coil so

long as the 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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An ideal voltage step-down transformer. The secondary current arises from the

action of the secondary EMF on the (not shown) load impedance


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__________________________________________________________________

The ideal transformer as a circuit element

_______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 good-transformer, whole of the magnetic flux

linked with primary is also linked with the


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secondary, and then the induced e.m.f. induced in

each turn of the secondary is equal to that induced

in each turn of the primary. Thus if Ep and Es bethe instantaneous values of the e.m.f.s induced in

the primary and the secondary and Npand Nsare

the no. of turns of the primary secondary coils of

the transformer and, D / dt= rate of change of

flux in each turn of the coil at this instant, we have

Ep= -NpD/dt (1)

Es= -NsD/dt (2)

Since the above relations are true at every 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 p1, so the

instantaneous current in primary coil is due to the


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difference (E Ep) in the instantaneous values of

the applied and back e.m.f. further if Rp is the

resistance o, p1p2 coil, then the instantaneous

current Ip in the primary coil is given by

I =E Ep/ Rp

E Ep = IpRp

When the resistance of the primary is small, Rp Ip

can be neglected so therefore

E Ep = 0 or Ep= E

Thus back e.m.f = input e.m.f

Hence equation 3 can be written as Es/ Ep= Es/ E

= output e.m.f / input e.m.f = Ns/ Np= K


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Where K is constant, called turn or transformation

ratio.

In a step up transformer

Es> E so K > 1, hence Ns> Np

In a step down transformer

Es< E so K < 1, hence Ns< Np

If Ip=value of primary current at the same instant t

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 = EsIs

If there are no losses of power in the transformer,

then Input power = output power or

EpIp = EsIs Or


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Es/ Ep = Ip/ Is = K

In a step up transformer

As k > 1, so Ip> Isor 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.

BASIC IDEA OF STEP DOWN TRANSFORMER


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_______________________________________________________

BASIC IDEA OF STEP UP TRANSFORMER

EFFICIENCY_____________

Efficiency of a transformer is defined as the ratio of

output power to the input power i.e.

= output power / input power = EsIs/ EpIp

Thus in an ideal transformer, where there is no

power losses, = 1. But in actual practice, there

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 alwaysless than the input energy, because energy losses occur

due to a number of reasons as explained below.

1. Loss of Magnetic Flux: The coupling between the

coils is seldom perfect. So, whole of the magnetic flux

produced by the primary coil is not linked up with thesecondary coil.

2. Iron Loss: In actual iron cores in spite of lamination,


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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.

3. Copper Loss: 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.

4. Hysteresis Loss: The alternating current in the coil

tapes the iron core through complete cycle of

magnetization. So Energy is lost due to hysteresis.

5. Magneto restriction: 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 is used in almost all a.c. operations

In voltage regulator for T.V., refrigerator,computer, air conditioner etc.

In the induction furnaces. A step down transformer is used for welding

purposes.

A step down transformer is used for obtaininglarge current.


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A step up transformer is used for theproduction of X-Rays and NEON advertisement.

Transformers are used in voltage regulatorsand stabilized power supplies.

Transformers are used in the transmissions ofa.c. over long distances.

Small transformers are used in Radio sets,telephones, loud speakers and electric bells

etc.

__________________A BIG TRANSFORMER_______________


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Bibliography

The data used in this project was taken from thefollowing sources:www.google.comwww.wikipedia.comN.C.E.RT physics


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transformer class 12 project

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