2. Introduction
Transformer is a device used to convert low
alternating current at high voltage into high alternating
current into low voltage and vice versa.
It is designed to step up or step down the voltage or
current.
3. • Transformer works on the principle of mutual induction i.e.
When the magnetic flux linked with a coil is changed emf is
induced to the near coil.
• According to Faraday’s Law of Electromagnetic Induction.
• When an AC source is connected across the primary coil of a
transformer , the alternating current across it changes
continuously and periodically due to change in current in the
primary magnetic flux linked with the secondary coil also
changes continuously and periodically.
• Rate of change of flux linkage with respect to time is directly
proportional to the induced EMF in a conductor or coil .
Principle of Transformer
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4. 4
Construction
• It consist of an iron core on which two separate coils
of insulated copper wire are wound .
• The first coil to which AC source is applied in
primary coil.
• The other coil from which output is taken is
secondary coil.
5. Cont…..
It has three main parts :-
1. Primary winding : It produce magnetic flux when it is
connected to AC source.
2. Magnetic core of Transformer :- The iron core on which
primary winding and secondary winding are wound a close
magnetic circuit.
3. Secondary winding :- The flux produced by the primary
winding passes through the core will link with the
secondary winding it gives desire output of the transformer.
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7. THEORY
◎ Let Np and Ns be the no. of turns in the primary and secondary coil
of transformer respectively.
◎ When an AC source of Ep is applied to the primary coil an
alternating magnetic flux is produced .
◎ Thus changing magnetic flux will be induced in the secondary coil
result in an alternating emf “Es” in it.
◎ According to Faraday’s Law of Electromagnetic induction the
induced emf in the primary coil ,Ep = -Np dФ/dt
◎ Induced emf in the secondary coil ,Es = -Ns dФ/dt
On dividing above equation , we get
Es/Ep = Ns/Np
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8. 8
Cont…..
The ratio of Ns/Np is called transformer ratio or turn ratio
(K).
The ratio of Es/Ep is called voltage ratio i.e. K = Ns/Np =Es/Ep.
K>1, Ns>Np and Es>Ep
i.e. primary voltage is greater than the secondary voltage so,
transformer is called step down transformer. Hence ,K
determines whether the transformer is step or step down.
9. Cont…..
If there is no loss if energy power in secondary coil must be
equal to power in primary coil.
i.e.Pp=Ps
or, Ep.Ip=Es.Is
Hence , Es/Ep = Ip/Is
Hence , voltage step up transformer is current down
transformer and vice versa.
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10. Efficiency of Transformer
In ideal transformer there is no power loss. But in reality
there is always some loss of energy in primary and
secondary coil.
The greater is the energy transform from primary to
secondary the better is the transformer .
Thus , efficiency of transformer is defined as ratio of out
put to input power.
we have,
Pin = Ip.Ep
Pout = Is.Es
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11. Energy losses in Transformer
Efficiency of a transformer is always less than input power . So some
power is lost in the form of heat .
◎ So we can say the loss as copper loss and iron loss .
But in both case loss is due to electric current and general we can say
it as current loss.
◎ Another types of loss which arises due to the magnetization by
means of magnetizing field. The energy loss arises here is called
hysteresis loss.
◎ So in total ,transformer loss can be summarized in two form :
◎ Current loss- iron loss
◎ Copper loss -hysteresis loss
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12. Hysteresis Losses
◎ It is caused because of the friction of the molecules against the
flow of the magnetic lines of force required to magnetize the
core, which are constantly changing in value and direction first
in one direction and then the other due to the influence of the
sinusoidal supply voltage.
◎ This molecular friction causes heat to be developed which
represents an energy loss to the transformer . Excessive loss can
overtime shorten the life of the insulating materials used in the
manufacture of the windings and structures . Therefore ,
cooling of transformer is important.
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13. Contd…
• Also , transformers are designed to operate at a particular
supply frequency of the supply will result in increased
hysteresis and higher temperature in the iron core . So
reducing the supply frequency from 60 hertz to 50 hertz
will raise the amount of hysteresis present , decreased the
VA capacity of the transformer.
• This loss can be minimize by using steel thin plates to
construct the transformer . Steel have high retentivity.
14. Eddy Current Losses
• Transformer Eddy Current losses on the other hand are caused
by the flow of circulating currents induced into the steel caused
by the flow of the magnetic flux around the core . These
circulating current are generated because to the magnetic flux
the core is acting like a single loop of wire . Since the iron core is
a good conductor , the eddy currents induced by a solid iron core
will be large .
• Eddy currents do not contribute anything towards the usefulness
of the transformer but instead they oppose the flow of the
induced current by acting like a negative force generating
resistive heating and power loss within the core.
• Laminating the iron core. 14
15. Contd…
• Eddy current losses with in a transformer core can not
be eliminated completely , but they can be greatly
reduced and controlled by reducing the thickness of the
steel core. Instead of having one big solid iron core as
the magnetic core material of the transformer or coil ,
the magnetic path is split up into many thin pressed
steel shapes called Laminations.
• The lamination used in a transformer construction are
very thin strips of insulated metal joined together to
produce a solid but laminated core.
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16. Cont……
• These laminations are insulated from each other by a coat of
varnish or paper to increase the effective resistivity of the
core thereby increasing the overall resistance to limit the
flow of the eddy currents.
• The result of all this insulation is that the unwanted induced
eddy current power loss in the core is greatly reduced ,and it
is for this reason why the magnetic iron circuit of every
transformer and other electromagnetic machines are all
laminated . Using laminations in a transformer construction
reduces eddy current.
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17. 17
The losses of energy , which appears as heat due both to
hysteresis and to eddy currents in the magnetic path , is
known commonly known as “transformer core loss”.
Since these losses occur in all magnetic materials as a
result of alternating magnetic fields . Transformer core
losses are always present in a transformer whenever the
primary is energized , even if no load is connected to the
secondary winding .
Also these hysteresis and the eddy current losses are
sometimes reffered to as “Transformer iron losses “. As the
magnetic flux causing these losses is constant at all loads.
18. Copper Losses
◎ Transformer Copper losses are mainly due to the electrical
resistance of the primary and secondary windings. Most
transformer coils are made from copper wire which has
resistance in ohms(Ω). This resistance oppose the
magnetizing currents flowing through them.
◎ When a load is connected to the transformers secondary
winding , large electrical currents flow in both the primary
and the secondary windings ,electrical energy and power ( or
with the IR ) losses occurs as heat . Generally copper losses
vary with load current , begin almost zero at no load , and at
a maximum at full load when current flow is at maximum.
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19. Copper losses can be reduced by
using thick wires for winding .Then we can define an
ideal transformer as having :
-No hysteresis loops or hysteresis losses
-Infinite resistivity of core material giving zero Eddy
current losses
-Zero winding resistance giving zero IR copper loss.
20. Types of Transformer
• Step up transformer
• Step down transformer
• Auto transformer
• Variactor transformer
• Central tapped transformer
21. 1)Step up transformer
• The transformer which convert low AC voltage at high
current to high AC voltage at low current.
• This types of transformer is constructed by increasing the
no. of turns of coil in secondary winding greater than in
primary winding .So, we have :-
K>1
23. 2) Step down transformer :-
◎ It converts high AC voltage at low
current to low AC voltage at high
current .
◎ This type of transformer is
constructed by decreasing the no. of
turns of coil in secondary winding
less than in primary winding .
K< 1
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24. 3) Auto-transformer
• It consist of an iron core with only one winding of wire that
single winding is common to both primary and secondary
circuit.
• In this winding ,connections are made at different points on
the coil for both the primary and secondary sites.
• It is designed to the need of X-ray imaging device .
• Since ,there are different connection in the single winding
auto transformer can either be use in stepup or step down.
• The voltage it receives and the voltage it provides are directly
related to the no. of the transformer enclosed by the
respective connection.
26. 4) Variactor transformer
◎ It is a type of auto transformer that can be put out
different amounts of voltage from the same input.
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27. 5) Centre- tapped transformer
◎ It is more or less same as usual transformer .
◎ The only difference is that its secondary winding is divide
into two parts such that two line ends.
◎ Such transformer is constructed by connecting an
additional wire across the exact middle point of the
secondary winding of a transformer.
◎ The wire connected at the center is at zero volt .
◎ So, it forms a neutral point for the winding due to this
central-tapping we obtain two separate output voltage
which are equal in magnitude but opposite in polarity to
each other. 27
29. Difference between a Normal and a Center
tapped Transformer
• The primary difference that is evident here is that a
normal transformer provides you only one voltage , for
example say 240V .
• But a center tapped transformer will provide you with
two voltages each of 240/2 i.e.120V,so that we can drive
two independent circuits.
30. Application of transformer
• It can decrease or increase the level of voltage or current
in an AC circuit .
• It can be use to prevent DC from passing through one
circuit to the other.
• It is used in the production of X-ray because it provides
high voltage required filament current necessary for
thermo -ionic emission.
31. Cont……
In X-ray circuit , Transformer are used in the production of
x-rays. As it provides:
• High voltage to accelerate electrons from cathode to
anode
• Filament current to have thermo ionic emission by
producing heat to the filament .