1. BHARAT HEAVY
ELECTRICALS LIMITED
JHANSI
ROTATION REPORT
AND PROJECT ON POWER
TRANSFORMER
PROJECT MANAGER-
MR. KRISHAN KUMAR
(Sr.Design Engineer)
(TRE)
SUBMITTED TO-
Dr. DHRUV BHARAGAV
D.G.M(H.R.D)
BHEL, JHANSI
2015
SUBMITTED BY-
SHIVAM DWIVEDI
B.Tech ( EE)
NIT AGARTALA
2015

2. BHARAT HEAVY ELECTRICALS LIMITED JHANSI
ROTATION REPORT
AND
PROJECT ON POWER TRANSFORMER
PROJECT MANAGER-
MR. KRISHAN KUMAR
(Sr.Engineer)
(TRE)
SUBMITTED TO- SUBMITTED BY-
Dr. DHRUV BHARAGAV SHIVAM DWIVEDI
D.G.M(H.R.D) B.Tech ( EE )
BHEL, JHANSI NIT AGARTALA
Acknowledgement
I am extremely thankful & indebted to the numerous BHEL engineers,

3. who imparted me vital information about the functioning of their
respective departments, thus helping me to attain an overall consideration about
the functioning of the organization. I am highly thankful to them for their
support, guidance and amicable behavior.
I am highly indebted to my project guide Mr. KRISHAN KUMAR
(Sr.Design Engineer) for finding some hours to guide me, from his busy
schedule and helping me to grasp various concepts ofpower transformer . I also
convey my special thanks to all senior executives and members of BHEL,
Jhansi.
Last but not the least, I would like to thank my parents & all my fellow
Trainees who have been a constant sourceof encouragement & inspiration
during my training here. And a special thank to the H.O.D of my college he
helped me so much giving leave from my session so that I can concentrate on
this project.
SHIVAM DWIVEDI
(13UEE063)
INTRODUCTION OF B.H.E.L

4. BHEL is the largest engineering and manufacturing enterprise in India in the
energy/infrastructure sector today. BHEL was established more than 40 years
ago when its first plant was set up in Bhopal ushering in the indigenous Heavy
Electrical Equipment industry in India, a dream that has been more than realized
with a well-recognized track record of performance.
BHEL caters to core sectors of the Indian Economy viz., Power Generation &
transmission, Industry, Transportation, Telecommunication, Renewable Energy,
Defense, etc. The wide network of BHEL’s 17 manufacturing divisions, four
Power Sector regional centers, over 100 project sites, eight service centers and
18 regional offices, enables the company to promptly serve its customers and
provide them with suitable products, systems and services-efficiently and at
competitive prices. BHEL has already attained ISO 9000 certification for
quality management, ISO 27000 for Information Technology and ISO 14001
certification for environment management.
(3) VARIOUS BHEL UNITS

5. FIRST GENERATION UNITS
Bhopal : Heavy Electrical Plant.
Haridwar : Heavy Electrical Equipment Plant.
Hyderabad: Heavy Electrical Power Equipment Plant.
SECOND GENERATION UNITS
Tiruchy : High Pressure Boiler Plant.
Jhansi : Transformer and Locomotive Plant.
Haridwar : Central Foundry and Forge Plant.
Tiruchy : Seamless Steel Tube Plant.
UNITS THROUGH ACQUISTION & MERGER
Bangalore : Electronics Division
Electro Porcelain Division.
NEW MANUFACTURING UNITS
Ranipet : Boiler Auxiliaries Plant.
Jagdishpur: Insulator Plant.
Govindwal : Industrial Valve Plant.
Rudrapur : Component and Fabrication Plant.
Bangalore : Energy Systems Division
BHARAT HEAVY ELECTRICALS LIMITED JHANSI (UNIT)

6. A BRIEF INTRODUCTION
By the end of 5th five-year plan, it was envisaged by the planning commission
that the demand for power transformer would rise in the coming years.
Anticipating the country’s requirement BHEL decided to set up a new plant,
which would manufacture power and other types of transformers in addition to
the capacity available in BHEL Bhopal. The Bhopal plant was engaged in
manufacturing transformers of large ratings and Jhansi unit would concentrate
on power transformer upto 50 MVA, 132 KV class and other transformers like
Instrument Transformer s, Traction transformers for railway etc.
This unit of Jhansi was established around 14 km from the city on the N.H. No
26 on Jhansi Lalitpur road. It is called second-generation plant of BHEL set up
in 1974 at an estimated cost of Rs 16.22 crores inclusive of Rs 2.1 crores for
township. Its foundation was laid by late Mrs. Indira Gandhi the prime minister
on 9th Jan. 1974. The commercial production of the unit began in 1976-77 with
an output of Rs 53 lacs since then there has been no looking back for BHEL
Jhansi.
The plant of BHEL is equipped with most modern manufacturing processing
and testing facilities for the manufacture of power, special transformer and
instrument transformer, Diesel shunting locomotives and AC/DC locomotives.
The layout of the plant is well streamlined to enable smooth material flow from
the raw material stages to the finished goods. All the feeder bays have been laid
perpendicular to the main assembly bay and in each feeder bay raw material
smoothly gets converted to sub assemblies, which after inspection are sent to
main assembly bay.

7. The raw material that are produced for manufacture are used only after thorough
material testing in the testing lab and with strict quality checks at various stages
of productions. This unit of BHEL is basically engaged in the production and
manufacturing of various types of transformers and capacities with the growing
competition in the transformer section, in 1985-86 it under took the re-powering
of DESL, but it took the complete year for the manufacturing to begin. In 1987-
88, BHEL has progressed a step further in under taking the production of AC
locomotives, and subsequently it manufacturing AC/DC locomotives also.
PRODUCT PROFILE OF BHEL JHANSI UNIT
1. Power transformer up to 400 KV class 250
MVA.
2. Special transformer up to 180 KV.
3. ESP transformer 95 KVp, 1400 mA.
4. Freight Loco transformer 3900 to 5400 KVA &
7475 . KVA for 3 phase.
5. ACEMU transformer up to 1000 KVA (1-
phase).
1385 KVA (3 phase).
.
6. Dry type transformer up to 6300 KVA 33 KV
class
7. Instrument transformer VT & CT up to 220 KV
class.
8. Diesel electric locomotives up to 2600 HP.
9. AC/DC locomotives 5000 HP.
10. Over Head Equipment cum Test Car

8. 11. Well wagon 200 tone.
12.Rail cum road vehicle
13. Dynamic track stabilizer
PLANT LAYOUT
It has two product categories:-
(1) Transformer shop:-
There are ten bays in this shop i.e. from bay 0 to 9. Its comprises of
fabrication of transformer, winding section, core and punch section,
winding work for power transformers, manufacturing of dry –type
transformer and assembly of transformers
(2) Locomotive shop:-
This shop contain LOCO and LOCO production shop. LOCO
assembly is mainly done here. further there is LOCO test section in
this unit.

9. VARIOUS DEPARTMENTS/FUNCTIONS AT BHEL JHANSI
TRANSFORMER COMMERCIAL (TRC)
The objective of the department is interaction with the customers. It brings out
tenders and notices and also responds to them. It is this department that bags
contracts of building transformers. After delivery regarding faults, this
department does failures and maintenance. All such snags are reported to them
and they forward the information to the concerning department.
One of the major tasks of this department is to earn decent profits over all
negotiations. Transformer industry has become very competitive. The company
offering the lowest price gets the contract but this process may continue does
the work on very low profits. To avoid such a situation, a bodyby the name of
India Electrical and Electronics Manufactures Association (IEEMA) was set up.
This association helps to maintain a healthy competitive atmosphere in the
manufacturing of electrical appliances.
TRANSFORMER ENGINEERING (TRE)
The transformer manufactured in BHEL Jhansi range from 10 MVA to 250
MVA and up to 400 KV. The various transformers manufactured in this unit
are:-
POWER TRANSFORMER
a) Generator transformer
b) System transformer.
c) Auto transformer.
SPECIAL TRANSFORMER
a) Freight loco transformer.
b) ESP transformer.
c) Instrument transformer.

10. d) Dry type transformer.
.
FABRICATION
Fabrication is nothing but production. It comprises of three bays i.e. Bay 0,Bay1,
Bay2.
BAY-00 & 0:
It is a sub part of Fabrication. It is the preparation shop while the other two
bays form the assembly shop. This section has the following machines:
 Planner machine – To reduce thickness
 Shearing machine
 CNC / ANC Flame Cutting machine – To cut Complicated shaft items
using Oxy-Acetylene flame
 Bending machine
 Rolling machine
 Flattening machine
 Drilling machine
 Nibbling machine
 Pantograph flame cutting machine
BAY-1
It is also a sub part of Fabrication. It is an assembly shop where different parts
of tank come from bay 0.Here welding processes are used for assembly, after
which a rough surface is obtained Grinder operating at 1200 rpm is used to
eliminate the roughness.
BAY-2

11. It is also a sub part of Fabrication It is an assembly shop dealing with making
different objects mentioned below.
1-Tank assembly 5-cross feed assembly
2-Tank cover assembly 6-core clamp assembly
3-End Frame assembly 7-pin and pad assembly
4-foot assembly
Before assembly, short blasting (firing of small materials i.e., acid pickling) is
done on different parts of jobs to clean the surface before painting.
NON DESTRUCTIVE TEST
1 Ultrasonic test to detect the welding fault on the CRO at the fault place
high amplitude waves are obtained.
2. Die Penetration test Red solution is put at the welding and then cleaned.
After some time white solution is mixed. Appearance of a red spot indicates a
fault at the welding.
3. Magnetic crack detection Magnetic field is created and then iron
powder is put at the welding. Sticking of the iron powder in the welding
indicated a fault.
4. X-Ray Test: It is same as human testing and the fault is seen in X-ray
film.
BAY-3
Here are basically three sections in the bay:
 Machine section
 Coppersection

12.  Tooling section
BAY 4
It is the winding section.
There are four types of coil fixed in a transformer, they are :
1. Low voltage coil (LV)
2. High voltage coil (HV)
3. Tertiary coil
4. Tap coil
The type of winding depends upon job requirement. Also, the width and
thickness of the conductors are designed particulars and are decided by design
department. Conductors used for winding is in the form of very long strips
wound on a spool, the conductor is covered by cellulose paper for insulation.
For winding first the mould of diameter equal to inner dia meter of required
coil is made .The specification of coil are given in drawing. The diameter of
mould is adjustable as its body is made up of wooden sections that interlock
with each other. This interlocking can be increased or decreased to adjust the
inner diameter of coil.
The moulds are of following types
1. Belly types
2. Link types
3. Cone type

13. BAY-5
It is core and punch section. The lamination used in power, dry, ESP
transformer etc for making core is cut in this section.
CRGO (cold rolled grain oriented) silicon steel is used for lamination, which
is imported in India from Japan, U.K. Germany. It is available in 0.27 and
0.28 mm thick sheets, 1mt wide and measured in Kg.The sheet s are coated
with very thin layer of insulating material called “carlites”.
For the purpose of cutting and punching the core three machines are installed
in shop
BAY-6
Single-phase traction transformer for AC locomotives is assembled in this
section. This Freight locomotive transformers are used where there is frequent
change in speed. In this bay core winding and all the assembly and testing of
traction transformer is done.
Three-phase transformers for ACEMU are also manufactured in this section.
The supply lines for this transformer are of 25 KV and power of the
transformer is 6500 KVA. The tap changer of rectifier transformer is also
assembled in this bay. Rectified transformer is used in big furnace like the
thermal power stations / plants (TPP).
BAY-7
1. This is the insulation shop. Various types of insulations are
2. AWWW - All Wood Water Washed press paper.
3. The paper is 0.2-0.5mm thick cellulose paper and is wound on the
conductors for insulation.

14. 4. PRE COMPRESSED BOARD: This is widely used for general
insulation & separation of conductors in the forms of blocks.
5. PRESS BOARD: This is used for separation of coils e.g. L.V. from
H.V. It is up to 38 mm thick.
6. UDEL(Un Demnified Electrical Laminated) wood or Permawood
7. This is special type of plywood made for insulation purposes.
8. FIBRE GLASS: This is a resin material and is used in fire pron areas.
9. BAKELLITE
10.GASKET- It is used for protection against leakage.
11.SILICON RUBBER SHEET- It is used for dry type transformer.
BAY 8
It is the instrument transformer and ESP transformer manufacturing section.
INSTRUMENT TRANSFORMER
These are used for measurement. Actual measurement is done by measuring
instruments but these transformers serve the purpose of stepping down the
voltage to protect the measuring instrument. They are used in AC system for
measurement of current voltage and energy and can also be used for
measuring power factor, frequency and for indication of synchronism. They
find application in protection of power system and for the operation of over
voltage, over current, earth fault and various other types of relays.
ESP TRANSFORMER
The Electrostatic Precipitator transformer is used for environmental application.
It is used to filter in a suspended charge particle in the waste gases of an

15. industry. They are of particular use in thermal power stations and cement
industry.
The ESP is a single-phase transformer. It has a primary and secondary. The core
is laminated and is made up of CRGOS. It is a step up transformer. An AC
reactor is connected in series with primary coil. The output of the transformer
must be DC the is obtained by rectifying AC using a bridge rectifier (bridge
rectifier is a combination of several hundred diodes). A radio frequency choke
(RF choke) is connected in series with the DC output for the protection of the
secondary circuit and filter circuit. The output is chosen negative because the
particles are positively charged. The DC output from the secondary is given to a
set of plates arrange one after the others. Impurity particles being positively
charged stick to these plates, which can be jerked off. For this a network of
plates has to be setup all across the plant. This is very costly process in
comparison with the transformer cost. A relive vent is also provided to prevent
the transformer from bursting it higher pressure develops, inside it. It is the
weakest point in the transformer body. An oil temperature indicator and the
secondary supply spark detector are also provided.
One side of the transformer output is taken and other side has an ‘marshalling
box’ which is the control box of the transformer.
BAY-9
In this bay power transformer are assembled. After taking different input from
different bays 0-9 assembly is done Power transformer is used to step and step
down voltages at generating and sub-stations. There are various ratings –11KV,
22KV, manufactured, they are

16. 1. Generator transformer.
2. System
3. Autotransformer.
A transformer in a process of assemblage is called a job. The design of the
transformer is done by the design deptt. & is unique of each job; depends on the
requirement of customer. The design department provides drawing to the
assembly shop, which assembles it accordingly.
The stepS involved in assembly are:
1. Core building
2. Core Lifting.
3. Unlacing.
4. Delacing and end-frame mounting.
5. High voltage terminal gear and low volt terminal gear mounting
6. Vapour phasing and oil soaking
7. Final servicing and tanking.
8. Case fitting.
STORE
There are three sections in store:
1. Control Receiving Section
2. Custody Section
3. Scrap Disposal Section
LOCOMOTIVE PRODUCTION(LMP)
There are following products are manufactured at Loco shops
 Alternating Current Locomotive (ac Loco)

17.  WAG-5H
 AC./D.C. Loco
 WCAM-2P
 WCAM-3
W-broad gauge A-running in AC mode
C-running in DC mode G-hauling goods train
P-hauling passenger train M-hauling passenger
& goods train
 Diesel Electric Locomotive Shunting (DESL)
 350 HP
 700 HP
 Single Power Pack (SPP): One 700 HP m/c
is made as a single
Unit. It is a meter gauge locomotive
 Twin Power Pack (TPP): 2 350HP m/cs are combined in 1 engine
& can be operated individually or in combination depending on
the load.
 450 HP
 1400 HP
 1150 HP
 1350 HP
 2600 HP
1150 HP and 1350 HP DESL s are non-standard locomotives and are
modified versions of 1400 HP DESL based on requirement of customer.
Under mention are the new non-conventional products designed and
developed for Indian Railways based on their requirement.
 OHE (Overhead electric) recording and testing cars

18.  UTV(Utility vehicle )
 RRV(Rail cum road vehicle)
 DETV( Diesel electric tower car)
 BPRV(Battery power road vehicle)
 BCM(Blast cleaning machine)
 200 T Well wagon for BHEL Haridwar
 Metro Rake-Kolkata Metro Railways
LOCOMOTIVE MANUFACTURING (LMM)
This section deals with manufacturing of locomotives. The main parts of the
locomotive are
Under frame: The frame on which a locomotive is built
Super structure: The body of locomotive is called superstructure
or Shell and is made of sheet of Mild steel
DC motor
Alternator
Compressor
Flower
Static Rectifier-MSR
Static Converter-SC
Exchanger
Bogie-The wheel arrangement of a loco is called a bogie. A bogie
essentially contains
1-wheel axle arrangement
2-Suspension
3-Brake rigging

19. Traction transformer: It is fixed on under frame and gets supply from
an overhead line by equipment called pantograph. The type of
pantograph depends on supply. This transformer steps down voltage and
is fitted with a tap changer. Different taps are taken from it for operating
different equipment. One tap is taken and is rectified into DC using
MSR and is fed to the DC motor.
Railways has two types of power supplies – 25 KV , 1 Phase ,50hz AC
-1500 V DC
An AC/DC loco is able to work on both of these supplies. For e.g.
WCAM-3.

20. POWER
TRANSFORMER
INTRODUCTION
A transformer is a static electrical device that transfers energy by inductive
coupling between its winding circuits. A varying current in the primary
winding creates a varying magnetic flux in the transformer's core and thus a
varying magnetic flux through the secondary winding. This varying magnetic

21. flux induces a varying electromotive force (emf) or voltage in the secondary
winding.
Transformers range in size from thumbnail-sized used in microphones to units
weighing hundreds of tons interconnecting the power grid. A wide range of
transformer designs are used in electronic and electric power applications.
Transformers are essential for the transmission, distribution, and utilization of
electrical energy.
DESIGN OF POWER TRANSFORMER
1.CORES
Laminated steel core

22. Transformers for use at power or audio frequencies typically have cores made
of high permeability silicon steel. The steel has a permeability many times that
of free spaceand the core thus serves to greatly reduce the magnetizing current
and confine the flux to a path which closely couples the windings. Early
transformer developers soonrealized that cores constructed from solid iron
resulted in prohibitive eddy current losses, and their designs mitigated this
effect with cores consisting of bundles of insulated iron wires. Later designs
constructed the core by stacking layers of thin steel laminations, a principle that
has remained in use. Each lamination is insulated from its neighbors by a thin
non-conducting layer of insulation.The universal transformer equation indicates
a minimum cross-sectionalarea for the coreto avoid saturation.
The effect of laminations is to confine eddy currents to highly elliptical paths
that enclose little flux, and so reduce their magnitude. Thinner laminations
reduce losses,butare more laborious and expensive to construct. Thin
laminations are generally used on high-frequency transformers, with some of
very thin steel laminations able to operate up to 10 kHz.
Laminating the core greatly reduces eddy-current losses
One common design of laminated core is made from interleaved stacks of E-
shaped steel sheets capped with I-shaped pieces, leading to its name of 'E-I
transformer. Such a design tends to exhibit more losses, but is very economical
to manufacture. The cut-coreor C-coretype is made by winding a steel strip
around a rectangular form and then bonding the layers together. It is then cut in
two, forming two C shapes, and the core assembled by binding the two C halves
together with a steel strap They have the advantage that the flux is always
oriented parallel to the metal grains, reducing reluctance.
A steel core's remanence means that it retains a static magnetic field when
power is removed. When power is then reapplied, the residual field will cause a
high inrush current until the effect of the remaining magnetism is reduced,
usually after a few cycles of the applied AC waveform. Overcurrent protection

23. devices such as fuses must be selected to allow this harmless inrush to pass. On
transformers connected to long, overhead power transmission lines, induced
currents due to geomagnetic disturbances during solar storms can cause
saturation of the core and operation of transformer protection devices.[48]
Distribution transformers can achieve low no-load losses by using cores made
with low-loss high-permeability silicon steel or amorphous (non-crystalline)
metal alloy. The higher initial costof the corematerial is offset over the life of
the transformer by its lower losses at light load.
Solid cores
Powdered iron cores are used in circuits such as switch-mode power supplies
that operate above mains frequencies and up to a few tens of kilohertz. These
materials combine high magnetic permeability with high bulk
electrical resistivity. For frequencies extending beyond the VHF band, cores
made from non-conductive magnetic ceramic materials called ferrites are
common.[46] Some radio-frequency transformers also have movable cores
(sometimes called 'slugs') which allow adjustment of the coupling
coefficient (and bandwidth) of tuned radio-frequency circuits.
Toroidalcores
Toroidal transformers are built around a ring-shaped core, which, depending on
operating frequency, is made from a long strip of silicon
steel orpermalloy wound into a coil, powdered iron, or ferrite. A strip
construction ensures that the grain boundaries are optimally aligned, improving
the transformer's efficiency by reducing the core's reluctance. The closed ring
shape eliminates air gaps inherent in the construction of an E-I core. The cross-
section of the ring is usually square or rectangular, but more expensive cores
with circular cross-sections are also available. The primary and secondarycoils
are often wound concentrically to cover the entire surface of the core. This

24. minimizes the length of wire needed, and also provides screening to minimize
the core's magnetic field from generating electromagnetic interference.
Toroidal transformers are more efficient than the cheaper laminated E-I types
for a similar power level. Other advantages compared to E-I types, include
smaller size (about half), lower weight (about half), less mechanical hum
(making them superior in audio amplifiers), lower exterior magnetic field (about
one tenth), low off-load losses (making them more efficient in standby circuits),
single-bolt mounting, and greater choice of shapes. The main disadvantages are
higher costand limited power capacity (see Classification parameters below).
Because of the lack of a residual gap in the magnetic path, toroidal transformers
also tend to exhibit higher inrush current, compared to laminated E-I types.
Ferrite toroidal cores are used at higher frequencies, typically between a few
tens of kilohertz to hundreds of megahertz, to reduce losses, physical size, and
weight of inductive components. A drawback of toroidal transformer
construction is the higher labor costof winding. This is becauseit is necessary
to pass the entire length of a coil winding through the core aperture each time a
single turn is added to the coil. As a consequence, toroidal transformers rated
more than a few kVA are uncommon. Small distribution transformers may
achieve some of the benefits of a toroidal core by splitting it and forcing it open,
then inserting a bobbincontaining primary and secondary windings.
Air core
A physical core is not an absolute requisite and a functioning transformer can be
produced simply by placing the windings near each other, an arrangement
termed an 'air-core' transformer. The air which comprises the magnetic circuit is
essentially lossless, and so an air-core transformer eliminates loss due to
hysteresis in the core material. The leakage inductance is inevitably high,
resulting in very poorregulation, and so such designs are unsuitable for use in
power distribution. They have however very high bandwidth, and are frequently
employed in radio-frequency applications, for which a satisfactory coupling
coefficient is maintained by carefully overlapping the primary and secondary
windings. They're also used for resonant transformers such as Tesla coils where
they can achieve reasonably low loss in spite of the high leakage inductance.
Windings

25. Windings are usually arranged concentrically to minimize flux leakage.
conducting material used for the windings depends upon the application, but in
all cases the individual turns must be electrically insulated from each other to
ensure that the current travels throughout every turn. Forsmall power and signal
transformers, in which currents are low and the potential difference between
adjacent turns is small, the coils are often wound from enamelled magnet wire,
such as Formvar wire. Larger power transformers operating at high voltages
may be wound with copperrectangular strip conductorsinsulated by oil-
impregnated paper and blocks ofpressboard.
High-frequency transformers operating in the tens to hundreds of kilohertz often
have windings made of braided Litz wire to minimize the skin-effect and
proximity effect losses. Large power transformers use multiple-stranded
conductors as well, since even at low power frequencies non-uniform
distribution of current would otherwise exist in high-current windings. Each
strand is individually insulated, and the strands are arranged so that at certain
points in the winding, or throughout the whole winding, each portion occupies
different relative positions in the complete conductor. Thetransposition
equalizes the current flowing in each strand of the conductor, and reduces eddy
current losses in the winding itself. The stranded conductoris also more flexible
than a solid conductorofsimilar size, aiding manufacture.

26. The windings of signal transformers minimize leakage inductance and stray
capacitance to improve high-frequency response. Coils are split into sections,
and those sections interleaved between the sections of the other winding.
Power-frequency transformers may have taps at intermediate points on the
winding, usually on the higher voltage winding side, for voltage adjustment.
Taps may be manually reconnected, or a manual or automatic switch may be
provided for changing taps. Automatic on-load tap changers are used in electric
power transmission or distribution, on equipment such as arc
furnace transformers, or for automatic voltage regulators for sensitive loads.
Audio-frequency transformers, used for the distribution of audio to public
address loudspeakers, have taps to allow adjustment of impedance to each
speaker. A center-tapped transformer is often used in the output stage of an
audio power amplifier in a push-pull circuit. Modulation transformers
in AM transmitters are very similar.
Dry-type transformer winding insulation systems can be either of standard
open-wound 'dip-and-bake' construction or of higher quality designs that
include vacuum pressure impregnation (VPI), vacuum pressure
encapsulation (VPE), and cast coil encapsulation processes. In the VPI process,
a combination of heat, vacuum and pressure is used to thoroughly seal, bind,
and eliminate entrained air voids in the winding polyester resin insulation coat
layer, thus increasing resistance to corona. VPE windings are similar to VPI
windings but provide more protection against environmental effects, such as
from water, dirt or corrosive ambients, by multiple dips including typically in
terms of final epoxy coat.

27. COOLING-
To place the cooling problem in perspective, the accepted rule of thumb is that
the life expectancy of insulation in all electric machines including all
transformers is halved for about every 7°C to 10°C increase in operating
temperature, this life expectancy halving rule holding more narrowly when the
increase is between about 7°C to 8°C in the case of transformer winding
cellulose insulation.
Small dry-type and liquid-immersed transformers are often self-cooled by
natural convection and radiation heat dissipation. As power ratings increase,
transformers are often cooled by forced-air cooling, forced-oil cooling, water-
cooling, or combinations of these. Large transformers are filled
with transformer oil that both cools and insulates the windings. Transformer oil
is a highly refined mineral oil that cools the windings and insulation by
circulating within the transformer tank. The mineral oil and paper insulation
system has been extensively studied and used for more than 100 years. It is
estimated that 50% of power transformers will survive 50 years of use, that the
average age of failure of power transformers is about 10 to 15 years, and that
about 30% of power transformer failures are due to insulation and overloading
failures. Prolonged operation at elevated temperature degrades insulating
properties of winding insulation and dielectric coolant, which not only shortens
transformer life but can ultimately lead to catastrophic transformer failure. With
a great bodyof empirical study as a guide, transformer oil
testing including dissolved gas analysis provides valuable maintenance

28. information. This can translate in a need to monitor, model, forecastand
manage oil and winding conductorinsulation temperature conditions under
varying, possibly difficult, power loading conditions.
Building regulations in many jurisdictions require indoor liquid-filled
transformers to either use dielectric fluids that are less flammable than oil, or be
installed in fire-resistant rooms. Air-cooled dry transformers can be more
economical where they eliminate the costof a fire-resistant transformer room.
The tank of liquid filled transformers often has radiators through which the
liquid coolant circulates by natural convection or fins. Some large transformers
employ electric fans for forced-air cooling, pumps for forced-liquid cooling, or
have heat exchangers for water-cooling. An oil-immersed transformer may be
equipped with a Buchholz relay, which, depending on severity of gas
accumulation due to internal arcing, is used to either alarm or de-energize the
transformer. Oil-immersed transformer installations usually include fire
protection measures suchas walls, oil containment, and fire-suppression
sprinkler systems.
Polychlorinated biphenyls have properties that once favored their use as
a dielectric coolant, though concerns over their environmental persistence led to
a widespread ban on their use. Today, non-toxic, stable silicone-based oils,
or fluorinated hydrocarbons may be used where the expense of a fire-resistant
liquid offsets additional building costfor a transformer vault. PCBs for new
equipment was banned in 1981 and in 2000 for use in existing equipment in
United Kingdom Legislation enacted in Canada between 1977 and 1985
essentially bans PCB use in transformers manufactured in or imported into the
country after 1980, the maximum allowable level of PCB contamination in
existing mineral oil transformers being 50 ppm.
Some transformers, instead of being liquid-filled, have their windings enclosed
in sealed, pressurized tanks and cooled by nitrogen or sulfur hexafluoride gas.
Experimental power transformers in the 500-to-1,000 kVA range have been
built with liquid nitrogen or helium cooled superconducting windings, which,
compared to usual transformer losses, eliminates winding losses without
affecting core losses.
Insulation drying
Construction of oil-filled transformers requires that the insulation covering the
windings be thoroughly dried of residual moisture before the oil is introduced.
Drying is carried out at the factory, and may also be required as a field service.

29. Drying may be done by circulating hot air around the core, or by vapor-phase
drying (VPD) where an evaporated solvent transfers heat by condensation on
the coil and core.
For small transformers, resistance heating by injection of current into the
windings is used. The heating can be controlled very well, and it is energy
efficient. The method is called low-frequency heating (LFH) since the current is
injected at a much lower frequency than the nominal of the power grid, which is
normally 50 or 60 Hz. A lower frequency reduces the effect of the inductance in
the transformer, so the voltage needed to induce the current can be reduced. The
LFH drying method is also used for service of older transformers.
TYPE OF TRANSFORMER
A wide variety of transformer designs are used for different applications, though
they share several common features. Important common transformer types
include:
 Autotransformer: Transformer in which part of the winding is common to
both primary and secondary circuits.
 Capacitor voltage transformer: Transformer in which capacitor divider is
used to reduce high voltage before application to the primary winding.
 Distribution transformer, power transformer: International standards make a
distinction in terms of distribution transformers being used to distribute
energy from transmission lines and networks for local consumption and
power transformers being used to transfer electric energy between the
generator and distribution primary circuits.
 Phase angle regulating transformer: A specialised transformer used to
control the flow of real power on three-phase electricity transmission
networks.
 Scott-T transformer: Transformer used for phase transformation from three-
phase to two-phase and vice versa.
 Polyphase transformer: Any transformer with more than one phase.
 Grounding transformer: Transformer used for grounding three-phase circuits
to create a neutral in a three wire system, using a wye-delta transformer, or
more commonly, a zigzag grounding winding.
 Leakage transformer: Transformer that has loosely coupled windings.
 Resonant transformer: Transformer that uses resonance to generate a high
secondaryvoltage.
 Audio transformer: Transformer used in audio equipment.
 Output transformer: Transformer used to match the output of a valve
amplifier to its load.

30.  Instrument transformer: Potential or current transformer used to accurately
and safely represent voltage, current or phase position of high voltage or
high power circuits.
APPLICATION
Transformers are used to increase voltage before transmitting electrical energy
over long distances through wires. Wires have resistance which loses energy
through joule heating at a rate corresponding to square of the current. By
transforming power to a higher voltage transformers enable economical
transmission of power and distribution. Consequently, transformers have shaped
the electricity supply industry, permitting generation to be located remotely
from points of demand. All but a tiny fraction of the world's electrical power
has passed through a series of transformers by the time it reaches the consumer.
Transformers are also used extensively in electronic products to step-downthe
supply voltage to a level suitable for the low voltage circuits they contain. The
transformer also electrically isolates the end user from contactwith the supply
voltage.
Signal and audio transformers are used to couple stages of amplifiers and to
match devices such as microphones and record players to the input of
amplifiers. Audio transformers allowedtelephone circuits to carry on a two-way
conversation over a single pair of wires. A baluntransformer converts a signal
that is referenced to ground to a signal that has balanced voltages to ground,
such as between external cables and internal circuits.

31. Testing of Power Transformer
The structure of the circuit equivalent of a practical transformer is
developed earlier.
The performance parameters of interest can be obtained by solving
that circuit for any load
conditions. The equivalent circuit parameters are available to the
designer of the transformers
from the various expressions that he uses for designing the
transformers. But for a user
these are not available most of the times. Also when a transformer is
rewound with different
primary and secondary windings the equivalent circuit also changes.
In order to get the
equivalent circuit parameters test methods are heavily depended upon.
From the analysis of
the equivalent circuit one can determine the electrical parameters. But
if the temperature
rise of the transformer is required, then test method is the most
dependable one. There are
several tests that can be done on the transformer; however a few
common ones are discussed
here.
Winding resistance test
This is nothing but the resistance measurement of the windings by applying a
small
d.c voltage to the winding and measuring the current through the same. The
ratio gives
the winding resistance, more commonly feasible with high voltage windings.
For low voltage
windings a resistance-bridge method can be used. From the d.c resistance one
can get the
a.c. resistance by applying skin effect corrections.

32. Polarity Test
This is needed for identifying the primary and secondaryphasorpolarities. It is
a must for poly phase connections. Both a.c. and d.c methods can be used for
detecting the polarities of the induced emfs. The dotmethod discussed earlier is
used to indicate the polarities. The transformer is connected to a low voltage a.c.
sourcewith the connectionsmade as shown in the fig. 18(a). A supply voltage
Vs is applied to the primary and thereadings of the voltmeters V1, V2 and V3
are noted. V1 : V2 gives the turns ratio. If V3 readsV1−V2 then assumed dot
locations are correct(for the connection shown). The beginning and
end of the primary and secondarymay then be marked by A1 −A2 and a1 −a2
respectively.If the voltage rises from A1 to A2 in the primary, at any instant it
does so from a1 to a2 inthe secondary. If more secondary terminals are present
due to taps taken from the windingsthey can be labeled as a3, a4, a5, a6. It is the
voltage rising from smaller number towardslarger ones in each winding. The
same thing holds good if more secondaries are present.Fig. 18(b) shows the d.c.
method of testing the polarity. When the switch S is closed if thesecondary
voltage shows a positive reading, with a moving coil meter, the assumed
polarityis correct. If the meter kicks back the assumed polarity is wrong.

33. OPEN CIRCUIT TEST
As the name suggests, the secondary is kept open circuited and nominal value
of the input voltage is applied to the primary winding and the input current and power are
measured. In Fig. 19(a) V,A,W are the voltmeter, ammeter and wattmeter respectively.
Let these meters read V1, I0 and W0 respectively.Fig. 19(b) shows the equivalent circuit of
the transformer under this test. The no load current at rated voltage is less than 1 percent of
nominal current and hence the loss and drop that take place in primary impedance r1 +jxl1
due to the no load current I0 is negligible. The active component Ic of the no load current I0
represents the core losses and reactive current Im is the current needed for the magnetization.
Thus the watt meter reading
The parameters measured already are in terms of the primary. Sometimes the
primary voltage required may be in kilo-Volts and it may not be feasible to
apply nominalvoltage to primary from the point of safety to personnel and
equipment. If the secondaryvoltage is low, one can perform the test with LV
side energized keeping the HV side opencircuited. In this casethe parameters
that are obtained are in terms of LV . These have tobe referred to HV side if we
need the equivalent circuit referred to HV side.

34. Sometimes the nominal value of high voltage itself may not be known, or in
doubt, especially in a rewound transformer. In such cases an open circuit
characteristics is first obtained, which is a graph showing the applied voltage as
a function of the no load current. This is a non linear curve as shown in Fig. 20.
This graph is obtained by noting the current drawn by transformer at different
applied voltage, keeping the secondary open circuited. The usual operating
point selected for operation lies at some standard voltage around the knee
point of the characteristic. After this value is chosenas the nominal value the
parameters are calculated as mentioned above.
SHORT CIRCUIT TEST
The purpose of this test is to determine the series branch parameters of the equiv-
alent circuit of Fig. 21(b). As the name suggests, in this test primary applied voltage, the
current and power input are measured keeping the secondary terminals short circuited. Let
these values be Vsc, Isc and Wsc respectively. The supply voltage required to circulate rated
current through the transformer is usually very small and is of the order of a few percent
of the nominal voltage. The excitation current which is only 1 percent or less even at rated
voltage becomes negligibly small during this test and hence is neglected. The shunt branch
is thus assumed to be absent. Also I1 = I2 as I0 ≃ 0. Therefore Wsc is the sum of the
copper losses in primary and secondary put together. The reactive power consumed is that
absorbed by the leakage reactance of the two windings.

35. If the approximate equivalent circuit is required then there is no need to separate
r1and r2 or xl1 and x′l2. However if the exact equivalent circuit is needed then
either r1 or r′2 is determined from the resistance measurement and the other
separated from the total.As for the separation of xl1 and x′l2 is concerned, they
are assumed to be equal. This is a fairly valid assumption for many types of
transformer windings as the leakage flux paths are through air and are similar.
Load Test
Load Test helps to determine the total loss that takes place, when the transformer
is loaded. Unlike the tests described previously, in the present case nominal voltage is applied
across the primary and rated current is drown from the secondary. Load test is used mainly
1. to determine the rated load of the machine and the temperature rise
2. to determine the voltage regulation and efficiency of the transformer.
Rated load is determined by loading the transformer on a continuous basis and observ-
ing the steady state temperature rise. The losses that are generated inside the transformer

36. on load appear as heat. This heats the transformer and the temperature of the transformer
increases. The insulation of the transformer is the one to get affected by this rise in the
temperature. Both paper and oil which are used for insulation in the transformer start get-
ting degenerated and get decomposed. If the flash point of the oil is reached the transformer
goes up in flames. Hence to have a reasonable life expectancy the loading of the transformer
must be limited to that value which gives the maximum temperature rise tolerated by the
insulation. This aspect of temperature rise cannot be guessed from the electrical equivalent
circuit. Further, the losses like dielectric losses and stray load losses are not modeled in the
Electrical Machines I Prof. Krishna Vasudevan, Prof. G. Sridhara Rao, Prof. P. Sasidhara Rao
Indian Institute of Technology Madras
equivalent circuit and the actual loss under load condition will be in error to that extent.
Many external means of removal of heat from the transformer in the form of different cooling
methods give rise to different values for temperature rise of insulation. Hence these permit
different levels of loading for the same transformer. Hence the only sure way of ascertaining
the rating is by conducting a load test.
It is rather easy to load a transformer of small ratings. As the rating increases it
becomes difficult to find a load that can absorb the requisite power and a source to feed the
necessary current. As the transformers come in varied transformation ratios, in many cases
it becomes extremely difficult to get suitable load impedance.
Further, the temperature rise of the transformer is due to the losses that take place
‘inside’ the transformer. The efficiency of the transformer is above 99% even in modest sizes
which means 1 percent of power handled by the transformer actually goes to heat up the
machine. The remaining 99% of the power has to be dissipated in a load impedance external
to the machine. This is very wasteful in terms of energy also. ( If the load is of unity power
factor) Thus the actual loading of the transformer is seldom resorted to. Equivalent loss
methods of loading and ‘Phantom’ loading are commonly used in the case of transformers.
The load is applied and held constant till the temperature rise of transformer reaches a
steady value. If the final steady temperature rise is lower than the maximum permissible
value, then load can be increased else it is decreased. That load current which gives the
maximum permissible temperature rise is declared as the nominal or rated load current and
the volt amperes are computed using the same.
In the equivalent loss method a short circuit test is done on the transformer. The
short circuit current is so chosen that the resulting loss taking place inside the transformer
is equivalent to the sum of the iron losses, full load copper losses and assumed stray load
losses. By this method even though one can pump in equivalent loss inside the transformer,
the actual distribution of this loss vastly differs from that taking place in reality. Therefore
this test comes close to a load test but does not replace one.

37. In Phantom loading method two identical transformers are needed. The windings
are connected back to back as shown in Fig. 22. Suitable voltage is injected into the loop
formed by the two secondaries such that full load current passes through them. An equiv-
alent current then passes through the primary also. The voltage source V1 supplies the
magnetizing current and core losses for the two transformers. The second source supplies
the load component of the current and losses due to the same. There is no power wasted
in a load ( as a matter of fact there is no real load at all) and hence the name Phantom
or virtual loading. The power absorbed by the second transformer which acts as a load is
pushed back in to the mains. The two sources put together meet the core and copper losses
of the two transformers. The transformers work with full flux drawing full load currents and
hence are closest to the actual loading condition with a physical load.

38. Use of Power Transformer
Generation of electrical power in low voltage level is very much cost effective. Hence
electrical power is generated in low voltage level. Theoretically, this low voltage level
power can be transmitted to the receiving end. But if the voltage level of a power is
increased, the current of the power is reduced which causes reduction in ohmic or I2R
losses in the system, reduction in cross sectional area of the conductor i.e. reduction in
capital cost of the systemand it also improves the voltage regulation of the system.
Because of these, low level power must be stepped up for efficient electrical power
transmission. This is done by stepup transformer at the sending side of the power
systemnetwork. As this high voltage power may not be distributed to the consumers
directly, this must be stepped down to the desired level at the receiving end with the
help of stepdown transformer. These are the uses of electrical power transformer in the
electrical power system. Two winding transformers are generally used where ratio
between high voltage and low voltage is greater than 2. It is cost effective to use auto
transformer where the ratio between high voltage and low voltage is less than 2. Again
three phase single unit transformer is more cost effective than a bank of three single
phase transformer unit in a three phase system. But still it is preferable to use than the
later where power dealing is very large since such large size of three phase single unit
power transformer may not be easily transported from manufacturer's place to work site.

39. Transformer Basics – Efficiency
A transformer does not require any moving parts to transfer energy. This means that there
are no friction or windage losses associated with other electrical machines. However,
transformers do suffer from other types of losses called “copper losses” and “iron losses”
but ge.
Copper losses, also known as I2R loss is the electrical power which is lost in heat as a result
of circulating the currents around the transformers copper windings, hence the name. Copper
losses represents the greatest loss in the operation of a transformer. The actual watts of power
lost can be determined (in each winding) by squaring the amperes and multiplying by the
resistance in ohms of the winding (I2R).
Iron losses, also known as hysteresis is the lagging of the magnetic molecules within the core,
in response to the alternating magnetic flux. This lagging (or out-of-phase) condition is due to
the fact that it requires power to reverse magnetic molecules; they do not reverse until the
flux has attained sufficient force to reverse them.
Their reversal results in friction, and friction produces heat in the core which is a form of
power loss. Hysteresis within the transformer can be reduced by making the core from special
steel alloys.
The intensity of power loss in a transformer determines its efficiency. The efficiency of a
transformer is reflected in power (wattage) loss between the primary (input) and secondary
(output) windings. Then the resulting efficiency of a transformer is equal to the ratio of the
power output of the secondary winding, PS to the power input of the primary winding, PP
and is therefore high.
An ideal transformer is 100% efficient because it delivers all the energy it receives. Real
transformers on the other hand are not 100% efficient and at full load, the efficiency of a
transformer is between 94% to 96% which is quiet good. For a transformer operating with a
constant voltage and frequency with a very high capacity, the efficiency may be as high as
98%. The efficiency, ? of a transformer is given as:
Transformer Efficiency
where: Input, Output and Losses are all expressed in units of power.
Generally when dealing with transformers, the primary watts are called “volt-amps”, VA to
differentiate them from the secondary watts. Then the efficiency equation above can be
modified to:

40. It is sometimes easier to remember the relationship between the transformers input, output
and efficiency by using pictures. Here the three quantities of VA, W and ? have been
superimposed into a triangle giving power in watts at the top with volt-amps and efficiency at
the bottom. This arrangement represents the actual position of each quantity in the efficiency
formulas.
Transformer Efficiency Triangle
and transposing the above triangle quantities gives us the following combinations of the same
equation:
Then, to find Watts (output) = VA x eff., or to find VA (input) = W/eff., or to find Efficiency,
eff. =W/VA, etc.

41. Conclusion
Transformer design and manufacturing techniques have remained similar for
many years .over time, improvements have been made in materials, design
programs and testing technique to allow for lighter and more efficient units to
be produced. Properprocedureand handling for filed installation has proven to
be very critical in reducing moisture content and maximizing the life span of an
installed unit.
Power in a Transformer
Where: FP is the primary phase angle and FS is the secondary phase angle.
Note that since power loss is proportional to the square of the current being transmitted, that
is:I2R, increasing the voltage, let’s say doubling ( ×2 ) the voltage would decrease the current
by the same amount, ( ÷2 ) while delivering the same amount of power to the load and
therefore reducing losses by factor of 4. If the voltage was increased by a factor of 10, the
current would decrease by the same factor reducing overall losses by factor of 100
So if you increase the voltage the voltage out ,then the current decrease.
If you step up the voltage, so that voltage out is double the voltage input, you
can see from basic algebra that the output current must be half what the output
current is.
Transformer transform the power(p=voltage*current ) from one value to desired
value what we require and does not regulate the voltage.
SHIVAM DWIVEDI
13UEE063