Introduction
The transformer is a device used for converting a low
alternating voltage to a high alternating voltage or a high
alternating voltage into a low alternating voltage. It is a
static electrical device that 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 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 which
increases the voltages 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.
Principle
The electric transformer works on the fundamental
principle of electromagnetic induction, a concept first
discovered by Michael Faraday in the 19th century. The
transformer consists of two coils of wire, known as the
primary and secondary windings, which are usually wound
around a common magnetic core. When an alternating
current (AC) flows through the primary winding, it
generates a changing magnetic field around the coil.
According to Faraday’s law of electromagnetic induction,
this changing magnetic field induces an electromotive
force (EMF) or voltage in the secondary winding. The key
principle here is that the transformer relies on the mutual
induction between the primary and secondary windings
through the magnetic flux linkage.
Construction
A transformer consists of a rectangular shaft iron core
made of laminated sheets, well insulated from one
another. Two coils
& and & 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 , the primary coil and a load resistance R is
connected to , 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.
Theory
When an altering e.m.f. is supplied to the primary coilp1p2
,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
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
be the instantaneous 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 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 = -NpDфь/dt (1)
Es = -Ns Dфь/dt (2)
Since the above relations are true at every instant, so
bydividing 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 difference (E–Ep ) in the
instantaneous values of the applied and back e.m.f. further
if Rp is the resistance, p1p2 coil, then
the instantaneous current Ip in the primary coil is given by
I =E– Ep / Rp
E– Ep = Ip Rp
When the resistance of the primary is small, Rp Ip
Ca n 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/ E
p = Es/ E = output e.m.f / input e.m.f = Ns/ Np = K
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 = Es Is
If there are no losses of power in the transformer,
thenInput power = output power or
EpIp = Es Is Or
Es / Ep= Ip / Is = 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
incurrent 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.
Working
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 that is if a varying current is set-up in a
circuit induced e.m.f. is produced in the neighbouring
circuit. The varying current in a circuit produce varying
magnetic flux which induces e.m.f. in the neighbouring
circuit.
The transformer consists of two coils. They are insulated
with each other by insulated material and wound on a
common core. 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.
Efficiency
Efficiency of a transformer is defined as the ratio of output
power to the input power i.e.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.
Material Required
Iron Rod
Voltmeter
Ammeter
Copper wire
Diagram
Procedure
1. Take thick iron rod and cover it with a thick paper and
wind a large number of turns of thin Cu wire on thick
paper (say 60). This constitutes primary coil of the
transformer.
2. Cover the primary coil with a sheet of paper and
wound relatively smaller number of turns (say 20) of
thick copper wire on it. This constitutes the secondary
coil. It is a step-down transformer.
3. Connect p1,p2 to A.C main and measure the input
voltage and current using A.C voltmeter and ammeter
respectively.
4. Similarly, measure the output voltage and current
through s1 and s2
5. Now connect s1 and s2 to A.C main and again
measure voltage and current through primary and
secondary coil of step up transformer.
6. Repeat all steps for other self-made transformers by
changing number of turns in primary and secondary
coil.
Energy Loss
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.
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 the
secondary coil.
Iron Loss: 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.
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.
Hysteresis Loss: The alternating current in the coil
tapes the iron core through complete cycle of
magnetization. So, Energy is lost due to hysteresis.
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.
Application of Transformer
1. Electric Power Transmission: Transformers are
crucial in power transmission networks to step up
voltage for efficient long-distance transmission and
step-down voltage for distribution to end-users.
2. Voltage Regulation: Transformers help maintain a
stable voltage level by adjusting the voltage as
needed, ensuring consistent and reliable electrical
supply.
3. Power Distribution: They are used in power
distribution systems to provide various voltage levels
suitable for residential, commercial, and industrial
applications.
4. Power Supply Units: Transformers are employed in
power supply units of electronic devices, converting
AC power from outlets to the DC power needed by
devices like computers and chargers.
5. Voltage Transformation: Transformers change the
voltage levels, allowing electricity to be transmitted at
high voltages to reduce energy losses and then be
distributed at lower voltages for use.
6. Industrial Applications: Transformers power various
industrial machinery and equipment by adapting
electrical voltage to meet specific operational
requirements.
Electrical Appliances: Many electronic devices and
appliances use transformers to convert electricity to the
required voltage for their operation.
Conclusion
The output voltage of the transformer across the
secondary coil depends upon the ratio (Ns/Np) with
respect to the input voltage.
The output voltage of the transformer across the
secondary coil depends upon the ratio (Ns/N p) with
respect to the input voltage.
There is a loss of power between input and output coil
of a transformer.
