A transformer is a static machine used for transforming
power from one circuit to another without changing
II.TYPES OF TRANSFORMER:
Transformers can be classified on the basis, like types of
construction, types of cooling, etc.
On the basis of construction, transformers can be
classified into 2 types:-
Core type transformer:
The primary and secondary coils are wound on separate
limbs of the core so that the core is largely surrounded by
the coils. Many of the modern transformers are of the
closed core type.
Shell type transformer:
The primary and secondary coils are wound one over
another on the same limb of the iron core. The coils are
very largely surrounded by the iron core. Transformers
used in radio and TV transmitters and receivers are of
On the basis of purpose:
STEP UP TRANSFORMER
step-up transformer is the direct opposite of a step-down
transformer. There are
many turns on the
secondary winding than in
the primary winding in the
Thus, the voltage supplied
in the secondary
transformer is greater than the one supplied across the
primary winding, Because of the principle of conservation
of energy, the transformer converts low voltage, high-
current to high voltage-low current. In other words, the
voltage has been stepped up.
STEP DOWN TRANSFORMER:
In a step-down transformer is one who secondary windings
are fewer than the primary
windings. In other words,
secondary voltage is less than
the primary voltage
transformer is designed to
convert high-voltage, low-
current power into a low-voltage, high current power and it
is mainly used in domestic consumption.
III. Working principle of Transformer
The working principle of transformer depends upon
Faraday's law of electromagnetic induction. Actually,
mutual induction between two or more winding is
responsible for transformation action in an
According to these Faraday's laws, "Rate of change of flux
with respect to time is directly proportional to the induced
EMF in a
conductor or coil.
Consider a situation when no load is connected to the
secondary, i.e., its terminals are open. Let N1 and N2 be
the number of turns in the primary and secondary
Induced emf in the primary coil, E1 =-N1d /dt
Induced emf in the secondary coil, E2 =-N2d /dt
Where is the magnetic flux linked with each turn
of the primary or secondary at any instant. Thus
Let E be the emf applied to the primary .By Lenz’s law,
self-induced emf E1 opposes E in the primary coil.
Hence resultant emf in the primary = E-E1
This emf sends current I1, through the primary coil of
resistance R. E-E1 = RI1
But R is very small, so the term RI1 can be neglected.
Thus E1 may be regarded as input emf and E2 as the output
E1/E2= Output/Input = N2/N1
The ratio of the number of turns in the secondary to that
of the primary is called the turn’s ratio of the
CURRENTS İN PRIMARY AND SECONDARY COIL
Assuming the transformer to be ideal one so that there
are no energy losses, then no energy losses, then Input
powers output power or E1I1 = E2I2, where I1, and I2 are
the currents in the primary and secondary, respectively
Hence I1/I2 = E2/E1 = N2/N1
thus the step up transformer steps up the voltage, but
steps down the current exactly in the same ratio.
Similarly, a step down transformer steps down the current
exactly in the same ratio. The efficiency of a transformer
is defined as
η = [Power output/ Power input] X 100%
the efficiency of real transformers is high [90-99] %
though not 100%
IV. CONSTRUCTIONAL PARTS OF A TRANSFORMER
These are the basic components of a transformer:
A transformer essentially consists of two coils of insulated
copper wire having different number of turns and wound on
the same soft iron core. The coil P to which electric energy
is supplied is called the
primary and the coil from
which energy is drawn or
output is obtained is called
the secondary. To prevent
energy losses due to eddy
currents a laminated iron
the entire magnetic flux due to the current in the primary
coil practically remains in the iron core and hence passes
fully through the secondary. This also prevents the stray
current being generated in the conductor lying around and
the consequent power loss.
ENERGY LOSSES IN TRANSFORMER
The main causes for energy loss in transformers are as
1.Copper loss: Some energy is lost due to heating of
copper wires used in the primary and secondary windings.
This power loss (-I'R) can be minimized by using thick
copper wires of low resistance.
2. Eddy current: The alternating magnetic flux induces
eddy currents in the iron core which leads to some energy
in the form of heat. This loss can be reduced by using
laminated iron core.
3. Hysteresis loss: The alternating current carries the
iron core through cycles of magnetization and
demagnetization. Work is done in each of these cycles and
is lost as heat. This is called hysteresis loss and can be
minimized by using core material having narrow hysteresis
4.Flux Leakage: The magnetic flux produced by the
primary may not be fully associated with the secondary.
Some of the flux may leak into the air. This loss can be
minimized by winding primary and secondary coils over one
5. Humming Loss: In this case the transformer gives rise
to humming sound by a phenomenon called magnetosriction.
V. Uses of transformer
1. Small transformers are used in radio receivers,
Telephones, loud speakers, etc.
2. In voltage regulators for TV, refrigerators, air
conditioners, computers, etc.
3. In stabilized power supplies.
4. A step down transformer is used for obtaining large
current for electric welding.
5. A step down transformer is used in induction furnace
for melting metals.
6. A step up transformer is used for the production of X-
Thus the above discussed project work gives the
detailed study of construction, working, uses of
This to certify that PRATYUSH KUMAR OF
CLASS XII-C has successfully completed his
project entitled ‘POWER TRANSFORMER’
under our guidance and supervision during
academic year 2019-2020.
Sign of Internal Sign of External
This is to certify that PRATYUSH KUMAR of
: class XII-C has successfully completed his
project entitled 'POWER TRANSFORMER
: under our guidance and supervision
during academic year 2019-2020
Dr. BK MISHRA
Delhi Public School
Nalco Nagar, Angul
I express deep sense of gratitude to my guide
Mrs K.Panda, physics teacher and Mr N.R.
Pattnaik lab asst. For their kind guidance,
supervision and encouragement for the timely
and successful completion
Types of transformers
Working principle of transformers
Constructional parts of
Uses of transformers
NCERT CLASS 12th
Physics reference book by S.L.ARORA
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