
Contact Nos. : +918398957646, Email ID : bhushanmehta245@yahoo.co.in


Project Report on Transformer
This project report is on Transformer, Introduction of Transformer, Principle of Transformer, Construction of Transformer, Stepup Transformer, Stepdown Transformer, Theory and Working of Transformer, Efficiency of Transformer, Energy Loss, Uses of Transformer
Introduction of Transformer
Transformer Introduction :
A transformer is an electrical device which is used for changing the A.C.
voltages. A transformer is most widely used device in both low and high current
circuit. As such transformers are built in an amazing strength of sizes. In
electronic, measurement and control circuits, transformer size may be so small
that it weight only a few tens of grams where as in high voltage power circuits,
it may weight hundred of tones.
Principle of Transformer : A Transformer based on the Principle of mutual induction according
to this principle, the amount of magnetic flux linked with a coil changing, an e.m.f is induced in the neighbouring coil.
Transformer
Construction : A transformer consists of a rectangular shaft iron core made of
laminated sheets, well insulated from one another. Two coils p_{1} & p_{2}
and s_{1} & s_{2} 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_{1}p_{2},
the primary coil and a load resistance R is connected to s_{1} s_{2},
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.
Electrical Energy Transfer : In a transformer, the
electrical energy transfer from one circuit to another circuit takes place
without the use of moving parts.
StepUp Transformer : A transformer which increases the
voltages is called a stepup transformer.
StepDown Transformer : A transformer which decreases the
A.C. voltages is called a stepdown transformer.
Transformer is, therefore, an essential piece of apparatus both for high and low
current circuits.
Theory and Working of Transformer
Theory and Working of Transformer :
When an altering e.m.f. is supplied to the primary coil p _{1}p _{2},
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, 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 E _{P} and E _{S} be the instantaneous values
of the e.m.f.’s induced in the primary and the secondary and N _{P} and N _{S}
are the no. of turns of the primary secondary coils of the transformer and
Dфь / d_{t} = rate of change of flux in each turnoff the coil at this
instant, we have
E_{P} = Np dфь/d_{t} (1) And
E_{S} = Ns dфь/d_{t}  (2)
Since the above relations are true at every instant, so by dividing 2 by 1, we
get
E_{s} / E_{p} =  N_{s} / N_{p}
(3)
As E_{P} is the instantaneous value of back e.m.f induced in the primary
coil p_{1}, so the instantaneous current in primary coil is due to the
difference (E – E_{P}) in the instantaneous values of the applied and
back e.m.f. further if R_{P} is the resistance o, p_{1}p_{2}
coil, then the instantaneous current I_{P} in the primary coil is given
by
I_{p} = E – E_{p} / R_{p}
E – E_{p} = I_{p} R_{p}
When the resistance of the primary is small, R_{p} I_{p} can be
neglected so therefore
E – E_{p} = 0 or E_{p} = E
Thus back e.m.f = input e.m.f
Hence equation 3 can be written as
E_{s} / E_{p} = E_{s} / E = output e.m.f / input e.m.f =
N_{s} / N_{p} = K
Where K is constant, called turn or transformation ratio.
In a step up transformer
E_{s} > E so K > 1, hence N_{s} > N_{p}
In a step down transformer
E_{s} < E so K < 1, hence N_{s} < N_{p}
If I_{p} = value of primary current at the same instant t
And I_{s} = value of sec. current at this instant, then
Input power at the instant t = E_{p} I_{p} and
Output power at the same instant = E_{s} I_{s}
If there are no losses of power in the transformer, then
Input power = output power Or
E_{p} I_{p} = E_{s} I_{s} Or
E_{s} / E_{p} = I_{p} / I_{s} = K
In a step up transformer
As k > 1, so I_{p} > I_{s} or I_{s} < I_{p}
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.
Efficiency of Transformer : Efficiency of a transformer is defined as the ratio of output power
to the input power. i.e.
η = output power / input power = E_{s} I_{s} / E_{p} I_{p}
Thus in an ideal transformer, where there is no power losses, η = 1. But in
actual practice, there are many power losses, therefore the efficiency of
transformer is less than one.
Energy Losses of Transformer:
Following are the major sources of energy loss in a transformer:
 Copper loss is the energy loss in the form of heat in the copper coils of
a transformer. This is due to joule heating of conducting wires.
 Iron loss is the energy loss in the form of heat in the iron core of the
transformer. This is due to formation of eddy currents in iron core. It is
minimized by taking laminated cores.
 Leakage of magnetic flux occurs inspite of best insulations. Therefore,
rate of change of magnetic flux linked with each turn of S_{1}S_{2}
is less than the rate of change of magnetic flux linked with each turn of P_{1}P_{2}.
 Hysteretic loss is the loss of energy due to repeated magnetization and
demagnetization of the iron core when A.C. is fed to it.
 Magneto striation i.e. humming noise of a transformer.
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 obtaining large current.
 A step up transformer is used for the production of XRays and NEON
advertisement.
 Transformers are used in voltage regulators and stabilized power supplies.
 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.
BIBLIOGRAPHY




