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Transformer
VAISHNAV GAURAV
YADAV SHALU
GHARIA ISHA
MATARIYA RAHISHA
PINJARI SADIK
130450112037
130450112038
140453111002
140453111004
140453111013
Introduction
 The transformer is a static device(i.e. the one which
does not contain any rotating or moving parts) which
is used to transfer electrical energy from one ac
circuit to another ac circuit, with increase or
decrease in voltage/current but without change in
the frequency.
Introduction
 Input and output of the transformer are alternating quantity.
 The electrical energy is generated and transmitted at an
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extremely high voltages.
The voltage level can be reduced and increased using
transformer.
To reduce voltage the transformer is used which is then called
as the step down transformer.
To increase voltage the transformer is used which is then
called as the step up transformer.
When the transformer changes the voltage level, it changes
the current level also.
Types of transformer
 On the basis of the supply transformers are designed
and they are of two types:1.
2.
Single phase transformer with single phase supply.
Three phase transformer with three phase supply.
 However the principle for both the types is same.
Principle of the transformer
 Single phase transformer consists of two highly
inductive coils(windings)wound on an iron or steel
core.
 The winding connected to the ac supply is called as
the primary winding whereas the other one which is
connected to the load is called as the secondary
winding.
 The primary and secondary winding are isolated
from each other as well as from the iron core.
 There is no physical connection between primary
and secondary windings.
Elementary transformer
Symbol of transformer
1
2
The ac primary
current produces an
alternating flux ø in
the core
When the primary
winding is connected
to the single phase ac
supply, an ac current
starts flowing
through it.
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Operating Principle of a
transformer
The varying flux will
induce voltage into
the secondary
winding according to
the faraday’s laws of
electromagnetic
induction
Most of the changing
flux linked with the
secondary winding
through the core.
3
 Thus due to the primary current, there is an induced
voltage in the secondary winding due to the mutual
induction.
 Hence the emf induced in the secondary winding is
called as the mutually induced emf.
 Can the transformer operate on DC?
Ans. no
Construction of a transformer
 The most important part of transformer is winding
and core.
 However for the large capacity transformers, some
other parts such as
Suitable tanks
conservator
 Buchhloz relay
bushings
 Breather
explosion vent,etc
Are also used alongwith the core and windings.
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1. Laminated steel core
 The material used for the construction of the transformer core
is silicon steel. It is used for its high permeability and low
reluctance. Due to this the magnetic field produced in the core
is very strong.
 The core is in the form of stacks of the laminated thin steel
sheets which are electrically isolated from each other. The
laminations are typically 0.35 to 0.5 mm thick.
 The various ways of the construction of the core are as
follows:

Core construction using l-shaped laminations.
Core construction using I-Shaped laminations.
 The arrangement is in such a manner that there is the
continuous path for the magnetic flux, with a minimum air
gap
2. cross-sections of the transformer limbs.
 The cross-section of the limb of the core of small
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transformer is rectangular and the windings wound are
also rectangular.
But as the size increases circular cross-section windings
are preferred.
The cross section of such type of the transformer is either
square or stepped.
With the increase in the number of steps, the crosssection of the windings will be more and more closer to
the circular cross-section and less copper is used to wind
these coils.
But due to the stepped structure of the limb of the core
the labour charges to construct the core increases.
Windings of the transformer
 If we are practically dealing with this arrangement
then a part of the flux produced in the core will not
be linked with the secondary winding. This is called
as the leakage flux.
 In order to avoid this, the primary and secondary
windings are mounted on the same limb of the core.
Types of windings
 Concentric cylindrical type of winding
 Sandwiched type of winding
Concentric cylindrical type of winding
 The cylindrical coils are placed in the concentric way
around the same limb with the low voltage winding
placed onside and high voltage windings are placed
outside it with the proper insulation between the
windings.
 Both the windings are insulated from the core as
well.
Sandwiched type winding
 Here the high and low voltage windings are divided
into number of small coils and then these small
windings are interleaved
 The top and bottom windings are low voltage coils
because they are close to the core
Transformer tank
 The whole assembly of large size transformer is
placed in a sheet metal tank. Inside the tank the
whole assembly is immersed in oil which act as the
insulator as well as the coolant.
 the oil will take out the heat produced by the
transformer windings and core and transfer it to the
surface of the transformer tank.
Conservator
 In transformers, some empty space is always provided
above the oil level because due to the change in the
temperature the oil tends to contract or expand.
 When the oil temperature increases and decreases , it
expands and the air will be expelled out from the
conservator and it contracts and the air gets sucked
inside the conservator. This process is called as the
breathing of the transformer.
 Due to this process the air comes in contact with the oil
and because of the moisture oil will lose the insulating
power and it can be prevented by the conservator.
 Conservator is a cylindrical shaped air tight metal
drum placed on the transformer tank. It is connected
by a pipe to the tank.
 The oil level in the conservator is such a way that,
always some empty space is available above the oil.
Due to the use of the conservator, the main tank will
be always full with oil and the surface of oil in the
tank will not be exposed directly to the air.
Breather
 The apparatus through which breathing of the
transformer take place is known as “Breather”.
 The air goes in or out through the breather. To
reduce the moisture content of this air, some drying
agent such as silica gel or calcium chloride is used in
the breather.
 The dust particles present in the air are also removed
by the breather.
Explosion Vent
 The explosion vent consists of the diaphragm or
aluminium foil.
 When the transformer becomes faulty, the oil gets
decomposed and various gases are liberated
 If the gas pressure reaches a certain level then the
diaphragm in the explosion vent will burst to release
the pressure. This will save the main tank from
getting damaged.
Transformer types
 Core type transformer
 Shell type transformer
 Berry type transformer
Core type transformer
Shell type
transformer
Core and Shell type transformer
Core type transformer
Shell type transformer
 The core has only one
 The core has two window.
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window.
Windings encircle the core
Cylindrical windings are used.
It is easy to repair.
Better cooling since more
surface is exposed to the
atmosphere.
Less mechanical protections
to the coil.
The construction is preferred
for low voltage transformers.
 Core encircles the windings.
 Sandwich windings are used.
 It is not so easy to repair.
 Cooling is not very effective.
 Better mechanical protection to
the coils.
 The construction is preferred
for high voltage transformers.
Berry type transformer
 The berry type of the transformer has a distributed
magnetic circuit.
 The low voltage windings are placed inside and the
high voltage windings are placed outside.
EMF Equation of transformer
 For deriving the emf equation of a transformer
 The primary winding is connected across the ac supply
 This forces an alternating current through the primary
winding to produce an alternating flux(ø) in the core.
 The varying flux gets linked with the secondary and primary
winding to induce the mutually induced and self induced emfs
in the secondary and primary windings respectively.
Expressions for the induced voltages
 Step 1 Expression for the instantaneous flux(ø):
The instantaneous flux changes in a sinusoidal
manner with respect to time. Its frequency “f” is
same as that of the ac voltage applied to the primary
winding.
Therefore, ø= øm sinωt
(1)
Where,
øm = Maximum value of the instantaneous flux.
ω = 2Πf where f is the frequency of the flux
waveform
 step 2 Obtain the expression for induced voltage:
According to the faraday’s law of
electromagnetic induction, then induced emf due to
varying flux is given by
e= - N volts
(2)
e= emf induced due to varying flux.
 Step 3 Obtain the maximum value of “e” per turn
The value of the induced emf per turn can be
obtained by substituting N=1 in equation (2)
e= Substitute ø=øm sinωt
e= therefore e= - øm ωcosωt
(3)
the max. value of induced voltage per turn is
given by substituting cosωt=1
e= - øm ω2Πf volts
 Step 4 Obtain the rms value of “e” per turn
RMS value of “e” per turn
=
=4.44 f øm
(4)
 Step 5 Obtain the expressions for induced voltages E1 and E2
 Let E1 be the rms induced voltage in the primary winding with
N1 and E2 be the rms induced voltage in the secondary
winding with N2 turns.
Therefore, RMS value of the induced voltage in primary
is,
E1= RMS value of “e” per turn * number of primary turns
E1= 4.44 f øm*N1 volts
(5)
Similarly rms value of induced voltage in the secondary
winding is
E2= RMS value of “e” per turn * number of secondary
turns
E2= 4.44 f øm*N2 volts
(6)