transformers electrical enginnering

1. TOPICS
1.TRANSFORMERS
2. TRANSFORMERS LOSSES &
EFFICIENCY
3.THREE PHASE TRANSFORMER
PRESENTED BY JUSTIN VARGHESE
S5 F
ROLL NO 28
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2. FIRST TRANSFORMERS ??
The original 1885 Stanley prototype transformer at the Berkshire Museum.
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3. OTTO BLATHY
Ottó Bláthy
Ottó Tituss Bláthy (11 August 1860 – 26
September 1939) was a Hungarian electrical
engineer. In his career, he became the co-
inventor of the modern electric transformer
the tension regulator the AC watt-hour
meter. Motor capacitor for the single-phase
(AC) electric motor,
[citation needed]
the turbo
generator, and the high-efficiency turbo
generator
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4. TRANSFORMER
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5. WHAT IS INSIDE A TRANSFORMER ?
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6. TRANSFORMERS A transformer is a static electrical device that transfers electrical energy
between two or more circuits. A varying current in one coil of the transformer
produces a varying magnetic field, which in turn induces a
varying electromotive force (emf) or "voltage" across a second coil. Electric
power can be transferred between the two coils, without a metallic connection
between the two circuits. Faraday's law of induction discovered in 1831
described the effect of induced voltage across the secondary coil.
Transformers are used to increase or decrease the alternating voltages in
electric power applications.
Since the invention of the first constant-potential transformer in 1885,
transformers have become essential for the transmission, distribution, and
utilization of alternating current electrical energy.[3] A wide range of
transformer designs is encountered in electronic and electric power
applications. Transformers range in size from RF transformers less than a cubic
centimeter in volume to units interconnecting the power grid weighing
hundreds of tons.
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7. 7

8. Basic Principle Of Transformers
Faraday’s Principle of Mutual Induction
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9. So the Basic principle of transformers is that emf is induced in a coil due to the rate of change of flux linkage by it
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10. HOW A TRANSISTOR WORKS ?
Transformer is a static machine .
Transformer has main Three parts
1.Primary Winding
2.Secondary Winding
3. Metallic Core -on which the
windings are wound
Windings behave as an inductor .Windings are in the
form of good conductors of current the windings
of a transformer play a main role in the
machine the winding coils behave as an
inductor
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11. When an alternating current is allowed
to flow through any winding there will be an
alternating flux produced surrounding the
winding.
This Flux is proportional to the magnitude of
current flowing .Direction of the current can
be found by Right hand grip rule .
This rule states
that when we grip a right hand with
stretching the thumb along the axis of
coil or winding and other four figures
along the direction of current in the
coil then the thumb indicates the
direction of produced flux inside the
coil along the axis this
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12. This flux will become maximum in magnitude
when current reaches its maximum for one
half cycle of the alternating current wave .The
flux will become 0 when current in the coil
reaches 0 axis .Again for the next cycle the
current become max but in opposite direction
to its reverse maxima . in this way
alternating current produces continually
varying flux surrounding the winding the
flux lines link the winding itself and
the flux is varying so they will be self
induced EMF across the winding.
This phenomenon is due to Faraday's laws of
electromagnetic induction this induced
EMF or voltage whatever you say is same
in magnitude and opposite in polarity of
supply voltage supplied alternating
voltage causes alternating current in
the winding which produces continually
varying flux inside and outside the
winding this continually varying flux
produces induced EMF across the winding
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13. A
Alternating current produces continually varying flux
surrounding the winding the flux lines link the winding itself
and the flux is varying so they will be self induced EMF
across the winding this phenomenon is due to Faraday's
laws of electromagnetic induction
This induced EMF or voltage whatever you say is same in
magnitude and opposite in polarity of supply voltage
supplied alternating voltage causes alternating current in
the winding which produces continually varying flux inside
and outside the
winding this continually varying flux produces induced EMF
across the winding so we can say that the supply voltage is
Caused an induced voltage the winding is an effect of this
cause hence
According to lenses law this induced voltage will be in
opposite polarity of supply voltage since according to Lenz's
law effect always opposes cause this self induced voltage
across the winding does not depend upon the number of
turns in the winding but depends on the supply
voltage but the voltage induced per turn depends on the
number of turns in the winding this is nothing but induced
EMF divided by the number of turns in the winding
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14. now we are coming to second winding in the transformer supposing
one separate winding is brought nearer to the first winding then this
second winding gets kinked with a portion of varying flux of first
winding due to this varying flux linkage there will also be an induced
EMF across it t
This induced EMF would be quite small as because the flux linkages
is small hence rate of change of flux linkage is also small and
according to Faraday’s laws induced EMF across a coil is directly
proportional to the rate of change of flux linkage if now we connect
a closed circuit across the second winding we will get a very tiny
current through the circuit provided the second winding is placed
much nearer to the first so we have seen that some portion
of the input power is transformed to output through the second
winding this is because some portion of generated
flux of first winding is linked with second now if we want to
transform
maximum electric power from first
winding to second winding we have to
link maximum flux of first winding to
second winding.
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15. This is done by placing a low reluctant
magnetic core in between these windings
Steel is a well-known low reluctant
magnetic material so we'd normally use
steel for making low reluctant magnetic
core in the transformer as soon as we
place a steel core in between these
windings nearly the entire flux which
was surrounding the first winding will
be concentrated inside the core and
linked with the second winding as nearly
the same flux links with second winding
now the rate of change of flux with
respect to time is equal in both
windings since as laws of
electromagnetic induction induced EMF
across a conductor is directly
proportional to the rate of change of
flux linkage the voltage induced per
turn in both windings will be the same
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16. we have already explained that voltage induced across the first
winding is the same as a supply voltage actually here
we consider that there is no voltage drop between supply terminals
and the first winding this is an ideal case for
Theoretical purposes we will consider that condition as this first
winding is connected with supply it is referred to
as primary winding now if this primary winding has n1 number of
turns and supply voltage or adduced voltage across
primary winding is v1 that voltage per turn in the primary winding is
v1 by n1 so far we have understood that exactly
this V 1 by n1 voltage will appear across each turn of second winding
so if this second winding has n2 number of
turns then total voltage across the second winding is n2 into V 1 by
n1 and let us say this is v2 if now any closed circuit is connected
across the second winding it will provide voltage V to across the
circuit and due to the voltage there will be current flowing through
the circuit normally in a transformer the second winding is
connected with load circuit
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17. CONSTRUCTION
It may be noted that the transformer is placed inside an iron tank
filled with oil .The tank has some radiating tubes and fines so that
oil inside the tank gets circulated and the heat from the
transformer is radiated to atmosphere
The transformer consists of a core made up of magnetic material
Around which two coils are placed .
One coil is connected to supply voltage .This coil is called primary
windings .The other coil is called the secondary winding .Supply is
taken from the secondary winding by connecting load like fan
,tube light etc .
Transformer core is made up of thin sheets called laminations This
is done to reduce power loss in the core due to circulating current
flowing in the core and producing undesirable heating of the core
as well as windings which are wound on the core.
The laminated sheets are tightly fastened to form the core .If the
laminations are not tightly fastened ,they will vibrate in the
magnetic field and give rise to a humming noise .This magnetic
vibrations is known as Magnetostriction which is not desirable .
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18. CONSTRUCTION TYPES OF TRANSFORMERS
CORE TYPE Construction
• Primary & Secondary windings are placed
around the limbs of the transformer core .
• The windings are made in cylindrical form & are
placed around the core limbs
• Used in Power Transformers
SHELL TYPE Construction
• Primary & Secondary windings are placed in
central limb
• The windings are wound in the form of a
number of circular discs
• Used in Distribution Transformers
• Magnetic coupling is better than the core type
construction
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19. TYPES OF TRANSFORMERS (MANUFACTURED)
Single phase transformers Three phase transformers
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20. ADVANTAGES AND DISADVANTAGES OF
TRANSFORMER
Advantages
• *High efficiency.(comparison)
• *No moving parts.
• *Less capital cost.(comparison)
• *Less maintenance cost.(comparison)
• *Easy to move.(comparison)
• *Easy to add and remove.
• *Easy to increase or decrease voltage.
• *Less monitoring required.
• *No starting time.
Disadvantages
• *Emits heat and requires a cooling system.
• *Works only for ac supply.
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21. COOLING OF TRANSFORMERS
The Transformer is a device used to convert the energy at one voltage level to the energy at
another voltage level. During this conversion process, losses occur in the windings and the core
of the transformer. These losses appear as heat. The transformer’s output power is less than its
input power. The difference is the amount of power converted into heat by core loss and
winding losses. The losses and the heat dissipation increases with increase in the capacity of the
transformer.
The temperature rise of a transformer can be estimated by the following formula:
ΔT = (PΣ/AT)0.833
Where:
ΔT = temperature rise in °C
PΣ = total transformer losses (power lost and dissipated as heat) in mW;
AT = surface area of transformer in cm2.
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22. TYPES OF COOLING
• For Dry Type Transformers
Air Natural or Self Air Cooled Transformer
Air Blast
• For Oil Immersed Transformer
Oil Natural Air Natural
Oil Natural Air Forced
Oil Forced Air Forced
Oil Forced Water Forced
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23. COMPARISON
IDEAL TRANSFORMER
• An ideal transformer is an
imaginary transformer which has
- no copper losses (no winding resistance)
- no iron loss in core
- no leakage flux
In other words, an ideal transformer gives
output power exactly equal to the input power.
The efficiency of an idea transformer is 100%.
Actually, it is impossible to have such
a transformer in practice, but ideal transformer
model makes problems easier.
PRACTICAL TRANSFORMER
• It has 100% below efficiency.
• It has losses. It has I2R losses. It has iron loss.
• There is ohmic resistance drop.
• It has leakage drop.
• In it practical condition.
• It is used in practical condition.
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24. TRANSFORMATION RATIO
The transformation ratio is defined as the ratio of the secondary voltage to primary voltage. It is denoted by the letter K.
N is number of turns of the respective coils
V is the voltage in the respective coil
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25. EQUIVALENT CIRCUIT
Transformer Equivalent Circuit in Phasor Form
In phasor form, the transformer equivalent circuit takes the form shown in Fig.3. The reactances are derived
by multiplying the inductances by the radian frequencyω=2πfω=2πf, where f is the frequency. The turns
ratio a= N1/N2 is approximately equal to the voltage ratio V1/V2, the ratio of the rated primary voltage to the
rated secondary voltage provided by the manufacturer.
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26. PHASOR DIAGRAM OF PRACTICAL
TRANSFORMER
Phasor Diagram of Transformer:
1) Transformer when excited at no load, only takes excitation current which leads the working Flux by Hysteretic angle
α.
2) Excitation current is made up of two components, one in phase with the applied Voltage V is called Core
Loss component (Ic) and another in phase with the working Flux Ø called Magnetizing Current (Im).
3) Electromotive Force (EMF) created by working Flux Ø lags behind it by 90 degree.
4) When Transformer is connected with a Load, it takes extra current I’ from the Source so thatN1I’ = N2I2 where I’ is
called load component of Primary Current I.
Two Types of Practical Transformer Combination can be
1.PRACTICAL TRANSFORMER ON NO LOAD
2. PRACTICAL TRANSFORMER ON LOAD
2 cases
• When the Transformer has no winding Resistance and Leakage Flux
• When the Transformer has winding Resistance and Leakage Flux
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27. 1.PHASOR DIAGRAM OF PRACTICAL TRANSFORMER ON NO
LOADTransformer on load means that the secondary winding is open and no electrical load is connected across its terminal
for supply of electrical power.
Since the transformer on no load is not doing any useful work except that it remains energized and is ready to supply
electricity when required, its output =0
If the winding is purely inductive one ,I0 will lag the voltage v1 by 90
degree
However there will be hysterias and eddy current losses in the core .Thus I0
should have a component Ic in phase with V1 .The core loss is equal to V1
Ic Watts .Therefore ,I0 will lag v by an angle somewhat less than 90 degree
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28. PHASOR DIAGRAM OF PRACTICAL TRANSFORMER ON LOAD
CONDITION
When an electrical load is connected to the secondary winding of a transformer and the transformer loading is
therefore greater than zero, a current flows in the secondary winding and out to the load. This secondary current is due
to the induced secondary voltage, set up by the magnetic flux created in the core from the primary current.
The secondary current, IS which is determined by the characteristics of the load, creates a self-induced secondary
magnetic field, ΦS in the transformer core which flows in the exact opposite direction to the main primary field, ΦP.
These two magnetic fields oppose each other resulting in a combined magnetic field of less magnetic strength than the
single field produced by the primary winding alone when the secondary circuit was open circuited.
This combined magnetic field reduces the back EMF of the primary winding causing the primary current, IP to increase
slightly. The primary current continues to increase until the cores magnetic field is back at its original strength, and for a
transformer to operate correctly, a balanced condition must always exist between the primary and secondary magnetic
fields. This results in the power to be balanced and the same on both the primary and secondary sides
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29. INTERESTING QUESTIONS
Why Transformer can work only on AC ?
A constant dc cannot produce a time varying flux. But since ac changes with time, it produces a varying magnetic flux
while flowing through the primary winding which induces emf in the secondary coil. It can be tested by connecting
the secondary of a transformer to a voltmeter and primary to a dc supply.
What are the main types of Transformers ?
Transformers Based on Voltage Levels
Step-Up Transformer
Step-Down Transformer
Transformer Based on the Core Medium Used
Iron Core Transformer
Air Core Transformer
AutoTransformer
Transformers Based on Usage
Power Transformer
Distribution Transformer
Measurement Transformer
Transformers Based on Winding Arrangement, Transformers Based on the Place of Use
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