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Transformers
ISRA NAZIR
* Overview 2
Need of transformer
Introduction
History
Principle
Construction and Working
Types of transformers
Applications
Auto transformer
Bibliography
* Need of transformer 3
In most cases, appliances are manufactured to work at
some specific voltages. Transformers are used to adjust
the voltages to a proper level.
The transformers are the basic
components for the transmission of
the electricity.
Transformer is used to increase the
voltage at the power generating
station(Step up) and used to decrease
the voltage(Step down) for house
hold purpose.
By increasing the voltages the loss of the electricity in
the transmission is minimized.
* Transformer
Introduction
is a static device.
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It transfer electrical energy from one part of the electrical
or electronic circuit to other part of circuit without
changing the frequency.
It works on the Michal Faraday's law of Electromagnetic
Mutual Induction.
* History
The first transformer was
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developed by Ottó Bláthy, Miksa
Déri, Károly Zipernowsky (Z.B.D
Transformer) in 1885.
Further In 1885 William
Stanley made the transformer
more practical with some
design changes and developed
a three phase transformer.
The design of William Stanley
was first commercially used in
the U.S.A in 1886.
* Principle 6
* It works on the principle of Electromagnetic Mutual
Induction.
Electromagnetic Mutual Induction:
When the current is provided to the Primary Winding it
behaves as electromagnet due to this the EMF is induced in
the Secondary winding as it comes in the area having
magnetic field lines due to primary Winding.
Vs = Ns.dΦ/dt
Vs = Secondary Winding Voltage
Ns = Secondary Winding Turns .
* Construction 7
Laminated • Cores are designed not to have current in it. But still there is a
leakages current Or the eddy current present in it. To minimize
Core these current the cores are laminated.
• Made up of copper or aluminum coated with very
Winding
Winding thin layer of insulation.
• The main function of conservator tank of transformer is to
Tank
Tank provide adequate space for expansion of oil inside the
transformer. It is usually Cylindrical or cubical.
Isolation • It is provided by using Synthetic Oil between Core
and Tank.
• When the temperature changes occur in Transformer insulating oil, the oil
Breather expands or contracts and there an exchange of air also occurs when
transformer is fully loaded. When transformer gets cooled, the oil level
goes down and air gets absorbed within.
* Types of Transformers 8
Transformer
Basis of Basis of coolant
Construction Basis of Winding material used
Core type Step up Oil filled self
transformer transformer cooling
Shell type Step down Oil filled
transformer transformer water cooling
Spiral core Isolation
transformer transformer Air blast
* Basis of construction 9
Core type transformer: Its core has two limbs
.The windings are wounded on two limbs of the
core material.
Shell type transformer: Its core has three
limbs and two windows. Both the windings
are wounded on the central limb.(one over
the other)
Spiral core transformer:
The core constructed is
similar to wheels of
spokes. The windings are
wounded these spokes
like structure.
* Basis of Windings 10
* Step up Transformer: The no of
windings on Primary side is less than
the no. of windings on the secondary
side.
Np < Ns
* Step down Transformer: The no. of
winding on Primary side are more
than the no. of windings on the
secondary side.
Np > Ns
* Isolation Transformer: The no. of
winding on Primary side are equal to
the no. of windings on the secondary
side.
Np = Ns
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* Basis of coolant
*Oil filled self cooling:
Oil filled self cooled type uses small and
medium-sized distribution
transformers. The assembled windings
and core of such transformers are
mounted in a welded, oil-tight steel
tanks provided with a steel cover.. The
oil helps in transferring the heat from
the core and the windings to the case
from where it is radiated out to the
surroundings.
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*Oil filled water cooled: This type
is used for much more economic
construction of large transformers. The
cooling coil is mounted near the
surface of the oil, through which cold
water keeps circulating. This water
carries the heat from the device.
*Air Blast: This type is used for
transformers that use voltages below
25,000 volts. The transformer is used
at houses.
* Applications 13
1. Transmitting electrical energy over long distances
through wires.
2. Transformers with several secondary's are used in
television and radio receivers where several different
voltages are required.
3. Used as voltage regulator
4. Used almost everywhere in daily life.
Magnetic 14
Connected To a Flux The Winding
Source Of Ac Connected To
Electric Power The Loads
Primary Secondary Load
Input Winding Output Winding
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Transformer Principle of Operation
An
alternatin Small
g voltage current Magnetic flux
V1 is called the in the core
applied to no-load
the current I0
primary
winding
Alternating flux links with
Induces in them both primary and
e.m.f.'s of E1 and E2 secondary coils
If N2 is less than N1 then V2 is less than V1 and the device is termed
a step-down transformer.
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If N2 is greater than N1 then V2 is greater than V1 and the device
is termed a step-up transformer. When a load is connected
across the secondary winding, a current I2 flows.
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Numerical
Example 1:
A transformer has 500 primary turns and 3000 secondary turns. If
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the primary voltage is 240 V, determine the secondary voltage,
assuming an ideal transformer.
Solution
For an ideal transformer, voltage ratio = turns ratio
V1/V2 = N1/N2 = a
240/V2 = 500/3000, V2 = 1440V
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Example 2:
An ideal transformer with turns ratio of 2:7 is fed from a 240V supply.
Determine its output voltage.
Solution
A turns ratio of 2:7 means that the transformer has 2 turns on the
primary for every 7 turns on the secondary (i.e. a step-up
transformer); thus a = (N1/N2) = (2/7). For an ideal transformer,
voltage ratio = turns ratio V1/V2 = N1/N2 = a
V2 = 7 × 240 /2 =840V
Example 3: 20
A 5 KVA single-phase transformer has a turn ratio of 10 : 1 and is fed from
a 2.5 KV supply. Neglecting losses, determine:
a) The full-load secondary current,
b) Minimum load resistance which can be connected across the
secondary winding to give full load KVA.
c) The primary current at full load KVA
a) Turns ratio a = N1/N2 = 10/1 and V1 = 2.5KV =2500 V.
Since N1/N2 = V1/V2
V2 = V1 (N2/N1)= 250V
The transformer rating in volt-amperes=V2I2(at full load) i.e. 5000 =
250I2
Hence full load secondary current:
I2 = (5000/250) =20A.
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b) Minimum value of load resistance,
RL = V2/I2 = 250/20 = 12.5Ω
c) The primary current, N1 / N2 = I2 / I1
I1 = I2(N2 / N1) = 20×0.1 = 2A
* Auto Transformer 22
The autotransformer has only one winding. The winding is
common to both the primary and the secondary one.
The working principle is same as that of normal transformer
difference is that it has one winding divided into primary and
secondary.
Advantages:
Less costly
Better regulation
Low losses as compared to ordinary two
winding transformer of the same rating.
Disadvantages;
An autotransformer does not provide
electrical isolation between its
windings.
The secondary winding is not insulated from the primary
winding. 23
Used only in the limited places where a slight variation of
the output voltage from input voltage is required.
Applications
It is used as a starter to give upto
50 to 60% of full voltage to the
stator of a squirrel cage induction
motor during starting.
It is used to give a small boost to
a distribution cable, to
reduce/increase the voltage
drop.
Changing fan speed over a
narrow range.
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www.wikipedia.org/wiki/transformers
www.cnet.com/transformers
www.electricalengineeringinfo.com/transformers
www.electrical4u.com/transformers
www.electronics-tutorials.ws/transformers
