"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 Mr. Nizar, 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 Birla Public School for
their support during the making of this project.
The transformer is a device used for convertng a low alternatng voltage
to a high alternatng voltage or a high alternatng voltage into a low
alternatng voltage (transfers energy between two or more circuits
through electromagnetc inducton).
Transformers range in size from small RF transformers a cubic
centmeter in volume to large units interconnectng the power grid
weighing hundreds of tons. A wide range of transformer designs is
encountered in electronic and electric power applicatons. Since the
inventon in 1885 of the frst constant potental transformer,
transformers have become essental for the AC transmission,
distributon, and utlizaton of electrical energy.
It is based on the principle of mutual induction. A varying current
in the transformer's primary winding creates a varying magnetic
fux in the core and a varying magnetic feld impinging on the
This varying magnetic feld at the secondary induces a varying
electromotive force (EMF) or voltage in the secondary winding. The
primary and secondary windings are wrapped around a core of
infnitely high magnetic permeability[e] so that all of the magnetic
fux passes through both the primary and secondary windings. With
voltage source connected to the primary winding and load
impedance connected to the secondary winding, the transformer
currents fow in the indicated directions.
In our project step-down transformer is used: This
transformer converts high voltage at alternatng current
into low voltage alternatng current. Instep-down
transformer the number of turns in primary coil remains
large as compare to secondary coil.
Step down transformers are designed to reduce electrical
voltage. Their primary voltage is greater than their
secondary voltage. This kind of transformer "steps down"
the voltage applied to it. For instance, a step down
transformer is needed to use a 110v product in a country
with a 220v supply.
Step down transformers convert electrical voltage from
one level or phase confguraton usually down to a lower
level. They can include features for electrical isolaton,
power distributon, and control and instrumentaton
applicatons. Step down transformers typically rely on the
principle of magnetc inducton between coils to convert
voltage and/or current levels.
The transformer consists of two coils. They are insulated with each other by
insulated material and wound on a common core. For operaton at low frequency,
we may have a sof iron. The sof iron core is insulatng 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.
Suppose, the number of turns in the primary coil is NP and that in the secondary
coil is NS. The resistance of the coil is assumed to be zero. Let dq /dt be the rate of
change of fux in each turn of the primary coil. If Ep be the e.m.f. in the primary
EP = –NP (1)
We suppose that there is no loss of fux between the primary and secondary coils.
Then, the induced e.m.f. in the secondary coil will be:
ES= –NS (2)
From equatons (i) and (ii), we fnd: Ns/Np= K is called transformer rato or turn
For step up transformer K>1
For step down transformer K < 1
That is for step-up transformer NS> NP, therefore ES>EP.
For the step down transformer NS< NP therefore ES< EP
The efciency of the transformer is given by:
If Ip and Is be the currents in the primary and secondary circuits.
For ideal transformer = 1 = 100%.
Therefore ESIS = EPIP
Therefore, for step up, transformer current in the secondary is less than in the
primary (IS<IP). And in a step-down transformer we have IS > IP.
Energy Losses in Transformer
In practce, the output energy of a transformer is always less
than the input energy, because energy losses occur due to a
n u m b e r o f r e a s o n s a s e x p l a i n e d b e l o w .
1 . Loss of Magnetc Flux: The coupling between the coils is
seldom perfect. So, whole of the magnetc fux produced by the
primary coil is not linked up with the secondary coil.
2. Eddy Current Loss: In actual iron cores inspite of laminaton,
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 . Heat Loss: In practce, 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 alternatng current in the coil
tapes the iron core through complete cycle of
magnetzaton. So Energy is lost due to hysteresis.