Full transformer

TRANSFORMER
PRATIK ANANDPARA
ELECTRICAL DEPARTMENT
EMAIL : pratikanandpara1994@gmail.com
PH NO : 7405492701

CONTENT
 What is transformer
 Structure and working principle
 Construction of transformer
 Losses in transformer
 Ideal v/s practical transformer
 Uses and application of transformer

INTRODUCTION
 A transformer is a device that changes ac electric power at one
voltage level to ac electric power at another voltage level
through the action of a magnetic field.
 There are two or more stationary electric circuits that are
coupled magnetically.
 It involves interchange of electric energy between two or more
electric systems
 Transformers provide much needed capability of changing the
voltage and current levels easily.
 They are used to step-up generator voltage to an appropriate
voltage level for power transfer.
 Stepping down the transmission voltage at various levels for
distribution and power utilization.

WHAT IS TRANSFORMER
 A transformer is a static piece of apparatus by means of
which an electrical power is transferred from one
alternating current circuit to another electrical circuit
 There is no electrical contact between them
 The desire change in voltage or current without any
change in frequency
 Symbolically the transformer denoted as
NOTE :
It works on the principle of mutual induction

STRUCTURE OF TRANSFORMER
 The transformer two inductive coils ,these are electrical
separated but linked through a common magnetic current
circuit
 These two coils have a high mutual induction
 One of the two coils is connected of alternating voltage .this
coil in which electrical energy is fed with the help of source
called primary winding (P) shown in fig.
 The other winding is connected to a load the electrical energy
is transformed to this winding drawn out to the load .this
winding is called secondary winding(S) shown in fig.

 The primary and secondary coil wound on a ferromagnetic
metal core
 The function of the core is to transfer the changing magnetic
flux from the primary coil to the secondary coil
 The primary has N1 no of turns and the secondary has N2 no of
turns the of turns plays major important role in the function of
transformer

WORKING PRINCIPLE
 The transformer works in the principle of mutual induction
 When the alternating current flows in the primary coils, a
changing magnetic flux is generated around the primary coil.
 The changing magnetic flux is transferred to the secondary coil
through the iron core
 The changing magnetic flux is cut by the secondary coil, hence
induces an e.m.f in the secondary coil
“The principle of mutual induction states that when the two coils are
inductively coupled and if the current in coil change uniformly then the
e.m.f. induced in the other coils. This e.m.f can drive a current when a
closed path is provide to it.”

 Now if load is connected to a secondary winding, this e.m.f
drives a current through it
 The magnitude of the output voltage can be controlled by the
ratio of the no. of primary coil and secondary coil
The frequency of mutually induced e.m.f as same
that of the alternating source which supplying to the
primary winding b

CONSTRUCTION OF TRANSFORMER
 These are two basic of transformer construction
 Magnetic core
 Windings or coils
 Magnetic core
 The core of transformer either square or rectangular type in
size
 It is further divided into two parts vertical and horizontal
 The vertical portion on which coils are wounds called limb
while horizontal portion is called yoke. these parts are
 Core is made of laminated core type constructions, eddy
current losses get minimize.
 Generally high grade silicon steel laminations (0.3 to 0.5mm)
are used

WINDING
 Conducting material is used in the winding of the transformer
 The coils are used are wound on the limbs and insulated from
each other
 The two different windings are wounds on two different limbs
 The leakage flux increases which affects the performance and
efficiency of transformer
 To reduce the leakage flux it is necessary that the windings
should be very close to each other to have high mutual
induction

CORE TYPE CONSTRUCTION
 In this one magnetic circuit and cylindrical coils are used
 Normally L and T shaped laminations are used
 Commonly primary winding would on one limb while
secondary on the other but performance will be reduce
 To get high performance it is necessary that other the two
winding should be very close to each other

SHELL TYPE CONSTRUCTION
 In this type two magnetic circuit are used
 The winding is wound on central limbs
 For the cell type each high voltage winding lie between two
voltage portion sandwiching the high voltage winding
 Sub division of windings reduces the leakage flux
 Greater the number of sub division lesser the reactance
 This type of construction is used for high voltage

LOSSES IN TRANSFORMER
 Copper losses :
It is due to power wasted in the form of I2Rdue to
resistance of primary and secondary. The magnitude of
copper losses depend upon the current flowing through
these coils.
The iron losses depend on the supply voltage while the copper depend
on the current .the losses are not dependent on the phase angle between
current and voltage .hence the rating of the transformer is expressed as
a product o f voltage and current called VA rating of transformer. It is
not expressed in watts or kilowatts. Most of the timer, is rating is
expressed in KVA.

Hysteresis loss :
During magnetization and demagnetization ,due to hysteresis
effect some energy losses in the core called hysteresis loss
Eddy current loss :
The leakage magnetic flux generates the E.M.F in the core
produces current is called of eddy current loss.

IDEAL V/S PRACTICAL TRANSFORMER
 A transformer is said to be ideal if it satisfies the
following properties, but no transformer is ideal in
practice.
 It has no losses
 Windings resistance are zero
 There is no flux leakage
 Small current is required to produce the magnetic field
While the practical transformer has windings resistance ,
some leakage flux and has lit bit losses

APPLICATION AND USES
 The transformer used in television and photocopy
machines
 The transmission and distribution of alternating power is
possible by transformer
 Simple camera flash uses fly back transformer
 Signal and audio transformer are used couple in
amplifier
Todays transformer is become an essential part of
electrical engineering

REFERENCE
 Electrical engineering by UA Bakshi
 Principal of electrical machine by VK Mehta
 Electrical machine by RK Rajput
 www.allaboutcircuit.com
 www.iiee.com

Features of Ideal Trasnformer






Winding resistance core is negligible
Core loss negligible
Core has constant permiability
Maximum efﬁciency(100%)
All the ﬂux setup by primary links the
sceondary winding purely inductive coils
wound on loss free core
Practically not possible

1.5 The Ideal Transformer.



An Ideal transformer is a lossless device with an input
winding and an output winding.
Zero resistance result in zero voltage drops between the
terminal voltages and induced voltages
Figure below shows the relationship of input voltage and
output voltage of the ideal transformer.
An Ideal Transformer and the Schematic Symbols.
3

 The relationship between voltage and the number of turns.
Np , number of turns of wire on its primary side.
Ns , number of turns of wire on its secondary side.
Vp(t), voltage applied to the primary side.
Vs(t), voltage applied to the secondary side.
where a is deﬁned to be the turns ratio of the transformer.
a
N
N
tv
tv
s
p
s
p

)(
)(
Cont’d…
4



The relationship between current into the primary side,
Ip(t), of transformer versus the secondary side, Is(t), of the
transformer;
In term of phasor quantities;
-Note that Vp and Vs are in the same phase angle. Ip and Is
are in the same phase angle too.
- the turn ratio, a, of the ideal transformer affects the
magnitude only but not the their angle.
)()( tINtIN sspp

Cont’d…
atI
tI
s
p 1
)(
)(

a
V
V
s
p

aI
I
s
p 1

5

1.5.1 Power in an Ideal Transformer.



Power supplied to the transformer by the primary circuit is given by ;
where, p is the angle between the primary voltage and the primary
current.
The power supplied by the transformer secondary circuit to its loads
is given by the equation;
where, s is the angle between the secondary voltage and the
secondary current.
Voltage and current angles are unaffected by an ideal transformer ,
p – s =  he primary and secondary windings of an ideal
transformer have the same power factor.
sssout
IVP cos
pppin
IVP cos
6

Open delta connection
Or V-V connection
of three phase
transformer

•Three phase power is supply by
only two transformer
It is employed
1.Load is too small
2.One of the transformer is
disabled
3.Fault in any on transformer

Delta-delta connection means-normal
condition 3 transformer
Power capacity=3 Vl*Is……………..(1)
open delta transformer means-One transformer
is removed
Power capacity= √3 * Vl*Is…………………(2)

Now take ratio of eq(1) & eq(2)
• V-V capacity/delta-delta capacity=
= √3 * Vl*Is/3 Vl*Is
= 1/√3
=0.577
Approx 58%

• Example : three phase transformer is made up
form three 10 KVA transformer
• Total capacity= 10+10+10=30 KVA
• One transformer is removed now
• Remaining capacity is 20 KVA now
• Now transformer needs to transfer 20 KVA but
is supplys only = 30*0.57=17.3 KVA
• Capacity is reduced in otherwise 66% Load is
supplied by both transformer but now only
57% load is carried

Disadvantages of OPEN DELTA
transformer
• efficiency of transformer is decrease
• Secondary voltage is become unbalanced due
to higher load not perform when load is
unbalanced
• Average power factor is reduced and both
transformer operate at different power
fACTOR

Major manufacturing companies for
Trasnformer
• ABB INDIA(1889, More than 14000
transformer madeup)
• ALSTOM T&D INDIA(1911, market
capitalization of Rs 3,099.86 crore)
• SIEMENS(1867)
• TRANFORMER & RECTIFIER INDIA
LTD(1994)
• Kirloskar Electric Company Limited

1
Instrument Transformers
• A transformer that is used in conjunction
with a measuring instrument
• It utilizes the current-transformation and
voltage transformation properties to
measure high ac current and voltage
• They also provide isolation

2
Where to use Instrument Transformers
• To measure high currents and high
Voltages
• Why can’t we use voltmeter with very
high series resistance and ammeter with
very low shunt resistance?

3
Disadvantages of Shunts & Multipliers
• Shunts
• Time constant should be same for
meter and shunt
• Power consumed increases
• Insulation problems (for high voltages)
• No Isolation
• Multipliers (Series resistance)
• Power consumption
• Leakage currents, so good insulators
used , hence costly
• No isolation

4
Types of Instrument Transformers
• Current transformer
• Potential (Voltage) transformer

5
Current Transformers
• Secondary is usually 5 A (Standard)
• 5 A is sufficient for a relay to operate and
for a meter to measure

6
Point to note about CT
• Primary current depends on load, but not
on the burden
• Current coil of Wattmeter or Ammeter is
connected across the terminal of the
secondary or Relay
• Secondary operates near short circuit
conditions
• One of the terminal of CT secondary
winding is earthed

8
Constructional Details of Window CT

9
Layer 2
Layer 1
Core
Constructional Details of Window CT

10
Primary Winding
Secondary
Winding
Primary
Connections
Constructional Details of wound CT

11
Care, while operating with CT

12
Usually current is measured in terms
of voltage across a standard resistor

16
Points to note about PT
• Secondary is connected voltmeter or
Potential coil of the Wattmeter or Relay
• Design is similar to Power Transformer,
but Potential Transformers are lightly
loaded
• Secondary is usually rated for 110 V
• Should not be shorted

17
Construction of PT
• For the same power rating, Voltage
transformer is costly than Power
transformer (large core & conductor size)
• Output is small (and accurate), but size
is large
• Can carry more load (2 to 3 times)
• Shell type core – Low voltage
• Co-axial windings

18
Construction of PT
• Insulation: Cotton tape and varnished
cambric as insulation for coil
• Oil immersed for more than 7 kV
• Oil filled bushing for oil filled transformer
• If one side of the primary winding is at
neutral, one bushing is sufficient

• Open circuit : Maximum voltage
Minimum current
• Short circuit : Maximum current
Minimum voltage
WHY???

• Ameter always connects--
Series with terminal
• Voltmeter always connect
parallel with terminal
Why????

Open circuit test : Use to find Out Iron
loss – Maximum voltage value
 Iron Loss/core loss is Constant loss
Short circuit test : Use to find out
Copper loss/Ohmic loss [(I^2)*R]
 Copper loss is variable loss in
transformer which is vary
according to load it gives maximum
temprutre rise value

NECESSITY OF TESTING
Performance of device and other
equipment
Find Particular losses like Iron loss,
copper loss
Check the withstand capacity of
terminal maximum and minimum
levels of device.

Open circuit test(oc test)
• Open circuit test always perform on HV
side of transformer
• HV side side kept open in this test
• Open circuit test is use to identify
maximum Voltage value of transformer
• copper loss is neglected in this test
because Currrent value is very Low

Short circuit test(Sc test)
• SHORT circuit test always perform on LV
side of transformer
• LV side side kept SHORT in this test
• SHORT circuit test is use to identify
maximum CURRENT value of
transformer
• Iron loss is neglected in this test
because Voltage value is very Low

THREE PHASE SYSTEM
BASICS
Line voltage VL= voltage between lines
Phase voltage Vph= voltage between a line
and neutral

THREE PHASE SYSTEM
BALANCED STAR
Line Voltage VL= √3
Vph
Line current IL = Iph

THREE PHASE SYSTEM
BALANCED DELTA
Line Voltage VL= Vph
Line current IL = √3
Iph

THREE PHASE TRANSFORMERS
Almost all major generation & Distribution
Systems in the world are three phase ac
systems
Three phase transformers play an important
role in these systems
3 phase transformers can be constructed from
(a) 3 single phase transformers
(b) 2 single phase transformers
(c ) using a common core for three phase
windings

3 phase Transformer connections
By connecting three single phase transformers
1. Star- Star connection
2. Delta- Delta connection
3. Star – Delta connection
4. Delta – Star connection

*
*The generation of an electrical power is usually three
phase and at higher voltages like 13.2 KV, 22 KV or
some what higher, Similarly transmission of an
electrical power is also at very high voltages like 110
KV, 132 KV, 400 KV. To step up the generated voltages
for transmission purposes it is necessary to have three
phase transformers.

*
*Less space
*Weight Less
*Cost is Less
*Transported easily
*Core will be smaller size
*More efficient
*Structure, switchgear and installation of single three
phase unit is simpler

*The three cores are arrange at 120° from each other.
Only primary windings are shown on the cores for
simplicity.
*The primaries are connected to the three phase
supply.
*The three fluxes is also zero at any instant.

*Hence the centre leg does not carry any flux.
*So if centre leg is removed, any two legs provide the
return path for the current and hence the flux in the
third leg.
*This is the general principal used in the design of
three phase core type transformers.

*
*The primary and secondary winding of three phase
transformers as three phase winding can be connected
in different ways such as in star or in delta. With
suitable connection the voltage can be raised or
lowered.
*In this section some commonly used connections for
three phase transformers are discussed.

*Star-Star connection
*Delta-Delta connection
*Star-Delta connection
*Delta-Star connection
*Open Delta or V connection
*Scott connection or T-T connection

*Advantages of Parallel
Transformer:
To maximize electrical power system
efficiency—Load demand fulfill
availability during Fault & maintenance
To maximize power system reliability-No
Interrupt during any disturbance
flexibility-future expansion

Necessary Condition for parallel Transformer
Both transformer have
1. Same voltage ratio/Rating
2. Same polarity
3. Same Phase sequence(RYB-ryb)
4. Same percentage Impedance &
Phase shift

1) Same Voltage Ratio
*. Now say the secondary of these transformers are
connected to same bus,
*What happen if voltage ratio is not same?
Apply KVL on secondary side :
Its result voltage difference created between two
transformer
Ea-Eb ≠ 0
small voltage difference may cause
sufficiently high circulating current causing
unnecessary extra I2R loss in primary and
secondary

2)Same polarity
•Both have different polarity than in
transformer
Can’t nullify(cancel out each others
effect)Circulating current
This current create ohmic loss in
transformer Primary and secondary and
efficiency is decrease
•So transformer needed to maintain same
polarity

*3) Same Phase sequence(RYB-ryb)
*Opposite phase sequence not give
result
Ea-Eb ≠ 0
 Phase shift create unequal voltage
difference in transformer and it results
circulating current
• small voltage difference may cause
sufficiently high circulating current
causing unnecessary extra I2R loss in
primary and secondary

*What is Impdedance?
the effective resistance of an electric circuit or component to
alternating current, arising from the combined effects of ohmic
resistance and reactance.
Z=R+j(Xl-Xc)

4)Same percentage Impedance & Phase
shift
Ea and Eb is out of phase
&
impedance of transformer are inversely proportional to
their MVA ratings
Ea-Eb ≠ 0
Phase shift create unequal voltage
difference in transformer and it results
circulating currentOhmic Loss create

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