Manoj

SEMINAR
POWER TRANSFORMER
Submitted in partial fulfilment of the requirements
Bachelor of Technology in Electrical Engineering of
Rajasthan Technical University, Kota
Submitted to:
Dr. HARSHVARDHAN PUROHIT
HOD (ELECTRICAL ENGINEERING)
DEPARTMENT OF ELECTRICAL ENGINEERING
JAIPUR ENGINEERING COLLEGE
RAJSTHAN TECHNICAL UNIVERSITY, KOTA
A
SEMINAR REPORT
ON
POWER TRANSFORMER
Submitted in partial fulfilment of the requirements
For the degree of
Bachelor of Technology in Electrical Engineering of
Rajasthan Technical University, Kota
Submitted by:
Dr. HARSHVARDHAN PUROHIT MANOJ KUMAR RAY
(ELECTRICAL ENGINEERING) ROLL NO:14EJEEE0
JAIPUR ENGINEERING COLLEGE
RAJSTHAN TECHNICAL UNIVERSITY, KOTA
(AUGUST, 2017)
Submitted by:
MANOJ KUMAR RAY
ROLL NO:14EJEEE020

STUDENT’S DECLARATION
I hereby, certify that the work, which is being presented in the Project/Seminar Report, entitled
“POWER TRANSFORMER At BHARAT HEAVY ELECTRCAL LIMITED” in partial fulfilment of
the requirement for the award of Degree of B.TECH in Electrical Engineering, submitted in the Department
of Electrical Engineering of Jaipur Engineering College, kukas, Affiliated to Rajasthan Technical
University, Kota, Rajasthan, is an authentic record of my work under the supervision of VIKASH KUMAR
YADAV.
The results embodied in this report have not been submitted by me or anybody else to any other
University or Institute for the award of Degree.
MANOJ KUMAR RAY
ROLL NO. 14EJEEE020
CERTIFICATE
This is to certify that the above statement made by the Student is correct to the best of our knowledge.
LAKSHMI RATHORE Dr. HARSHVARDHAN PUROHIT
Assistant Prof. HOD, Electrical Department
DEPARTMENT OF ELECTRICAL ENGINEERING. (I)

ACKNOWLEDGEMENT
I express my sincere thanks to my Project/Seminar guide, MISS. LAKSHMI RATHORE (Assistant Prof.),
Department of Electrical Engineering, for guiding me right from the inception till the successful completion of
the project/seminar. I sincerely acknowledge him for extending his valuable guidance, support for literature,
critical reviews of project/seminar and this report and all above all for the moral support he provided me at all
stages of training.
.
MANOJ KUMAR RAY
DEPARTMENT OF ELECTRICAL ENGINEERING. (II)

ABSTRACT
Practical knowledge means visualization of the knowledge which we read in our course for this we perform
experiment and get observation .Practical knowledge is very important in every field .One must be familiar
with the problem related to that field ,So that he may solve them and become a successful person. After
achieving the proper goals in life an engineer has to enter in professional life. According to this life, He has to
serve an industry, may be public or private sector or self-own for the efficient work in the field, he must be
well aware of the practical knowledge as well as the theoretical knowledge.
To be a good engineer one must be aware of the industrial environment and must know about management,
working in such an industry, labour problem etc. so that he can tackle them successfully.
Due to all the above reason and to bridge the gap between theory and practical, our engineering curriculum
provides practical training of 4 weeks. During this period a student work in the industry and gets all type of
experience and knowledge about the working and the maintenance of various type of machinery.
I have undergone my 4 week training at BHEL, BHOPAL. This report is based on the knowledge which I
acquired during my 4 weeks training period at the plant.
DEPARTMENT OF ELECTRICAL ENGINEERING. (III)

Index
CHAPTER TITLE PAGE
1. ABOUT BHARAT HEAVY ELECTRICAL LIMITED 1
2. TRANSFORMER 6
3. TRANSFORMER MANFACTURING 9
4. CORE PUNCH AND BUILDING 13
5. CORE BUILDING 17
6. INSULATION SHOP 19
7. WINDING 22
8. COIL ASSEMBLY 25
9. POWER ASSEMBLY 26
10. TECHNICAL DIVISION 29
11. TESTING UHV LAB 32
DEPARTMENT OF ELECTRICAL ENGINEERING. (IV)

List of Figure
FIGURE TITLE PAGE
Fig. 1.1 Overview of BHEL 1
Fig. 1.2 Ac Motor And Alternator 3
Fig. 1.3 Steam Turbine 3
Fig. 1.4 Transformer 4
Fig. 1.5 Traction Motor and Alternator 4
Fig. 2.1 Circuit Arrangement of Transformer 6
Fig. 2.2 Ideal Transformer 6
Fig. 2.3 Eddy Current Phenomenon 7
Fig. 2.4 Magnetostriction 8
Fig. 3.1 Instrument Transformer 9
Fig. 3.2 Reactor 10
Fig. 3.3 Capacitor Bank 10
Fig. 3.4 Drawing of Transformer Core 11
Fig. 3.5 Transformer Manufacturing Process 12
Fig. 4.1 Lamination Layout 13
Fig. 4.2 Laminated Transformer Core 14
Fig. 4.3 Process of Core Manufacturing 15
Fig. 4.4 Slitting Machine 16
Fig. 4.5 CRGO Material 16
Fig. 5.1 Core Manufacturing Process 17
Fig. 5.2 Limbs of Core 18
Fig. 5.3 Completely Manufacturing Core 18
Fig. 6.1 Press Board 19
DEPARTMENT OF ELECTRICAL ENGINEERING. (V)

Fig. 6.2 Crepe Paper Cutting 20
Fig. 6.3 Power Press 20
Fig. 6.4 Glass Tape 21
Fig.6.5 Heat Shrink Tape 21
Fig.7.1 Helical Winding 22
Fig. 7.2 CTC 23
Fig. 7.3 Flow Chart of Coil Winding 23
Fig. 7.4 Winding of Coil on Frame 24
Fig. 7.5 Complete Coil Structure 24
Fig. 9.1 Complete Power Assembly 26
Fig. 9.2 Tap Changer 27
Fig. 10.1 Flow Chart of Vapour Phase Drying Process 30
Fig. 11.1 Ultra High Voltage Transformer 32
Fig. 11.2 Impulse Generator 33
Fig. 11.3 Impulse Discharge 33
Fig. 11.4 Cascade Transformer 34
Fig. 11.5 Bushing Testing 35
DEPARTMENT OF ELECTRICAL ENGINEERING. (VI)

Chapter-1.
ABOUT BHARAT HEAVY ELECTRICAL LIMITED.
B.H.E.L. is an integrated power plant equipment manufacturer and one of the largest engineering and
manufacturing companies in India in terms of turnover. They were established in 1964, 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. The company has been earning profits continuously since 1971-
72 and paying dividends since 1976-77.
They are engaged in the design, engineering, manufacture, construction, testing, commissioning and servicing
of a wide range of products and services for the core sectors of the economy, viz. Power, Transmission,
Industry, Transportation (Railway), Renewable Energy, Oil & Gas and Defence . They have 16 manufacturing
divisions, two repair units, four regional offices, eight service centres and 15 regional centres and currently
operate at more than 150 project sites across India and abroad.
They place strong emphasis on innovation and creative development of new technologies. They have been
exporting our power and industry segment products and services for over 40 years. BHEL’s global references
are spread across over 75 countries.
The cumulative overseas installed capacity of BHEL manufactured power plants exceeds 9,000 MW across
21 countries including Malaysia, Oman, Iraq, the UAE, Bhutan, Egypt and New Zealand. Our physical
exports range from turnkey projects to after sales services.
Fig 1.1 Bharat Heavy Electrical Limited
DEPARTMENT OF ELECTRICAL ENGINEERING. 1

1.1 POWER GENERATION
Power Generation sector comprises thermal, gas hydro and nuclear power plant business. BHEL supplies sets
account for nearly 65% of the total installed capacity in the country.
1.2 TRANSMISSION AND DISTRIBUTION
BHEL offers wide-ranging products and systems for T&D applications. Products manufactured includes
power transformers, Instrument Transformers, Dry type transformers, Series and Shunt Reactors, Capacitor
banks, Vacuum & SF6 circuit breakers, Gas-insulated switchgears and insulators.
1.3 INDUSTRIES
BHEL is a major contributor of equipment and systems to industries, cement, sugar, fertilizer, refineries,
petrochemicals, paper, oil and gas, metallurgical and other process industries. The range of system and
equipment supplied includes capacitive power plants, co-generation plants, industrial steam turbines,
industrial boilers, gas turbines, heat exchangers and valves, seamless steel tubes, electrostatic preceptors,
fabric filters, reactors, fluidized bed combustion boilers, chemical recovery boilers and process controls.
1.4 TRANSPORTATION
BHEL is involved in the development, design, engineering, marketing, production, installation and
maintenance and after sales service of rolling stock and traction propulsions systems. BHEL manufactures
electric locomotive up to 5000 HP, diesel electric locomotives from 350 HP to 3100 HP, for both main line
and shunting duty applications. It also produces rolling stock for applications viz. overhead equipment cars,
special well wagons and Rail-cum road vehicle.
1.5 RENEWABLE
Technologies that can be offered by BHEL for explaining non-conventional and renewable sources of energy
include: wind electric generators, solar photovoltaic systems, solar heating systems, solar lanterns and battery-
powered road vehicles.

1.6 MANUFACTURING UNITS OF BHEL:
1) Heavy Electrical Plant, Bhopal.
2) Heavy Electrical Equipment Plant, Haridwar.
3) Heavy Power Equipment Plant, Hyderabad.
4) Transformer & Locomotive Plant, BHEL Jhansi (Uttar Pradesh).
5) High Pressure Boiler Plant & Seamless Steel Tube Plant, Trichy (Tamil Nadu).
6) Boiler Auxiliaries Plant, Ranipet, Vellore (Tamil Nadu).
7) Power Plant Piping Unit, Thirumayam (Tamil Nadu).
8) Power Plant Fabrication Unit, Gondia.
9) Insulator Plant, Jagdishpur (Uttar Pradesh).
10) BHEL Electrical Machines Ltd., Kasargod (Kerala).
1.7PRODUCT’S OF BHEL BHOPAL
1.7.1POWER UTILISATION:-
1) Ac Motors and Alternator:
Fig 1.2 Ac Motor and Alternator.
1.7.2POWER GENERATION:-
1) Hydro Turbine.
2) Hydro Generator.
3) Steam Turbine.
Fig 1.3 Steam Turbine.

1.7.3POWER TRANSMISSION:-
1) Transformer
2) Steam Turbine
3) Tap Changer
4) Control And Relay Panels
Fig 1.4 Transformers.
1.7.4TRANPORTATION:-
1) Traction Motor And Alternator
Fig 1.5 Traction Motor and Alternator.

1.8 MAJOR CUSTOMER’S OF B.H.E.L:
Following are the major customers of BHEL at national & international arena.
National International
NTPC TNB, Malaysia
PGCIL PPC, Greece
NJPC MEW, Oman
NHPC OCC, Oman
NLC GECOL, Libya
NPCIL Trinidad & Tobago
NEEPCO New Zealand
APTRANSCO Tanzania etc
APGENCO
JPPCL
ALL State Electricity Boards

Chapter- 2.
TRANSFORMER.
A transformer is a device that transfers electrical energy from one circuit to another through inductively
coupled conductors the transformer's coils .A varying current in the first or primary winding creates a
varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary
winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the
secondary winding. This effect is called mutual induction.
Fig 2.1 Circuit Arrangement of Transformer.
2.1 BASIC PRINCIPAL
The transformer is based on two principles: first, that an electric current can produce a magnetic
field (electromagnetism), and, second that a changing magnetic field within a coil of wire induces a voltage
across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the
magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.
Fig 2.2 Ideal Transformer.
6

2.2 ENERGY LOSSES
An ideal transformer would have no energy losses, and would be 100% efficient. In practical transformers,
energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more
efficient, and those rated for electricity distribution usually perform better than 98%.Experimental
transformers using superconducting windings achieve efficiencies of 99.85%. The increase in efficiency can
save considerable energy, and hence money, in a large heavily loaded transformer. The trade-off is in the
additional initial and running cost of the superconducting design.
Losses in transformers (excluding associated circuitry) vary with load current, and may be expressed as "no-
load" or "full-load" loss. Winding resistance dominates load losses, whereas hysteresis and eddy
currents losses contribute to over 99% of the no-load loss. The no-load loss can be significant, so that even an
idle transformer constitutes a drain on the electrical supply and a running cost. Designing transformers for
lower loss requires a larger core, good-quality silicon steel, or even amorphous steel for the core and thicker
wire, increasing initial cost so that there is a trade-off between initial cost and running cost (also see energy
efficient transformer).
Transformer losses are divided into losses in the windings, termed copper loss, and those in the magnetic
circuit, termed iron loss. Losses in the transformer arise from.
2.2.1 HYSTERESIS LOSSES.
Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within
the core. For a given core material, the loss is proportional to the frequency, and is a function of the
peak flux density to which it is subjected.
2.2.2 EDDY CURRENT.
Ferromagnetic materials are also good conductors and a core made from such a material also
constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore
circulate within the core in a plane normal to the flux, and are responsible for resistive heating of
the core material. The eddy current loss is a complex function of the square of supply frequency and
Inverse Square of the material thickness. Eddy current losses can be reduced by making the core of
a stack of plates electrically insulated from each other, rather than a solid block; all transformers
operating at low frequencies use laminated or similar cores.
Fig 2.3 Eddy Current Phenomenon.

2.2.3 WINDING RESISTANCE
Current flowing through the windings causes resistive heating of the conductors. At higher
frequencies, skin effect and proximity effect create additional winding resistance and losses.
2.2.4 MAGNETOSTRICTION
Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and
contract slightly with each cycle of the magnetic field, an effect known as Magnetostriction. This
produces the buzzing sound commonly associated with transformers that can cause losses due to
frictional heating. This buzzing is particularly familiar from low-frequency (50 Hz or 60 Hz) mains
hum, and high-frequency (15,734 Hz (NTSC) or 15,625 Hz (PAL)) CRT noise.
Fig 2.4 Magnetostriction.
2.2.5 MECHANICAL LOSSES
In addition to magnetostriction, the alternating magnetic field causes fluctuating forces between the
primary and secondary windings. These incite vibrations within nearby metalwork, adding to the
buzzing noise and consuming a small amount of power.

Chapter- 3.
TRANSFORMER MANUFACTURING
3.1 TRANSFORMER’S
a) Power Transformers up to 420kV class, 50/60 Hz 930 MVA, 3-phase Bank.
b) Power Transformers up to 420kV class, 50/60 Hz 400 MVA, 3-phase Unit.
c) HVDC Converter Transformers and Smoothing Reactors.
d) 500 MVA, ± 500kVDC, 3 winding, 1- Phase. Convertor Transformer.
e) 254 MVAR, 360mH, 1568A, ±500KV DC 1–Phase Smoothing Reactor.
3.2 INSTRUMENT TRANSFORMER’S
a) Current transformers up to 400 kV.
b) Capacitor voltage Transformer up to 420 kV.
Fig 3.1 Instrument Transformer.
TRANSFORME
R
TRANSFORM
ER
CAPACITOR BUSHING

3.3 REACTORS
a) Gapped core Shunt Reactors up to 420 kV class, 125 MVAR 3 Phase Unit.
b) Series and Neutral Grounding Reactors.
c) Controlled Shunt Reactor up to 420 kV class, 80 MVAR 3 Phase Unit.
Fig 3.2 Reactor.
3.4 POWER BANK’S
a) Capacitor Bank from the range of 3.3kV to 500 kV.
Fig 3.3 Capacitor Bank.
10

3.5 PRODUCT’S AND APPLICATION
a) Power Transformers.
b) For Power Station.
c) Generator Transformer (Up to 500MVA. 400kV, 3-ph/400MVA, 400kV,1ph).
i. Application- Power Generation.
d) Autotransformers
i. (Upto1000MVA,400kV,3ph/600MVA,400kV,1ph/1000MVA,765kV,1ph/1000MVA,1
200kV,1ph).
e) Application- Power Transmission.
f) Shunt Reactors (Up to 150MVAr,420kV,3ph/110MVAr,765kV,1Ph).
g) Application – Controlling Reactive Power.
h) Bushings.
i) Oil impregnated paper (OIP) condenser bushings (52kV to 400kV).
j) Application – Transformer
k) 25kV bushings for locomotives.
l) Application – Transformer.
m) Special application bushings.
3.6 TRANSFORMER ENGINEERING
In Transformer Engineering Department Various Officials and Engineering work is done. It includes:-
1) Making a bit on available Tenders of the customers.
2) If sanctioned, it will create a descriptive copy of the jobs that will be done for making a product
which includes testing to be done, material used, etc.
3) It will create a drawing of the product with very precision and accuracy.
Fig 3.4 Drawing of Transformer Core.

Fig 3.5 Transformer Manufacturing Process.

Chapter- 4.
Core Punch and Building.
4.1 INTRODUCTION: -
Core of the Transformer serve the purpose of magnetic flux linkage path between primary and secondary
windings and are made up of highly permeable materials( e.g.: ferromagnetic material like “CRGO” cold
rolled grain oriented Steel).Generally transformer core is made up of thin laminated sheets. This thin
laminated sheet is prepared by the process of cropping and slitting. This is done so as to minimize the eddy
current losses. The physical orientation of grain oriented material is done in such a fashion that the magnetic
field lines are not suddenly interrupted and there exists a near smooth path for magnetic flux to be established
in the core. In practical transformers, we want to reduce magnetizing currents to almost negligible levels; it is
therefore important to eliminate all air gaps if possible.
One approach would be to make the core from a solid block of material. The circulating currents would
oppose the changing flux and effectively ‘‘short out’’ the transformer. A practical solution is to fabricate the
core from thin laminated steel sheets that are stacked together and to coat the surfaces of the laminations with
a thin film that electrically insulates the sheets from each other. Steel not only has excellent magnetic
properties but is also relatively inexpensive and easy to fabricate into thin sheets.
In a modern transformer plant, steel ribbon is cut into sections by acutting /punching machine commonly
called a Georg machine. The sizes and shapes of the sections are determined by the core design of the
individual transformer. The thickness of the sheets varies somewhat; core laminations operating at 60 Hz are
between 0.010 and 0.020 in. thick, with 0.012 in. being the most common thickness in use today.
Fig 4.1 Lamination Layout.
Grain-oriented steels a silicon-iron alloy that is rolled or ‘‘worked’’ during fabrication in such way that the permeability
is higher and the hysteresis losses are lower when the flux is in the direction of the ‘‘grain.’’ Unfortunately, the
properties of this steel for a flux that goes ‘‘against the grain’’ are much worse than then on-grain-oriented steel.
Therefore, the design of the core has to take this into account. The grain of the steels oriented along the length of the
laminations in the horizontal and vertical directions. The flux is at a 45° angle to the grain at the mitered edges.
Alternate layers are cut into slightly different lengths and their corners have slightly different shapes. The modern
multistep layer method uses up to five layers of differently shaped sections. The cross section of a transformer core
can either be square or rectangular; however, a round shape is used in most large transformers of the so-called core
form design, where the coils have a round cross section.

4.2 TYPES OF CRGO SILICON STEEL USED
4.4 LAMINATED TRANSFORMER CORE:-
The core of a laminated transformer consists of a stack of punched sheet alloy made of iron and nickel (the
laminations). The percentage of nickel is adjusted to give a reduced energy loss when the core is
magnetized by the magnetic field produced when the primary winding is energized. Further improvements
are made to the molecular structure by a rolling process. The typical flux density 0.5mm thick material is
1.3-1.5 tesla. For grain orientated material a higher flux density is used to minimize the size but incurs an
increased cost. A further process is carried out to insulate the surface of the sheet by heat treatment, either
gas or chemical. This is to reduce eddy currents that would flow from lamination to lamination. The
punching process causes a slight degradation in the performance and further heat treatment may be
required.
Generally three thicknesses of lamination are manufactured, 0.5mm and 0.35mm for 50Hz and up to
400Hz, 0.1mm up to 1000Hz. Higher frequencies can be used but the flux density would have to be
reduced to minimize core losses and reduce distortion.
Note: Because of the gaps in the magnetic circuit and the lamination material, the switch on in rush
current is lower than the equivalent power rated torridly transformer. The size of a laminated transformer
is typically larger than the equivalent power rated torridly transformer.
Fig 4.2 Laminated Transformer Core.
CRGO Type Lamination Size Losses (Watts per Kg)
M4 0.27 mm 1.00 W/Kg
MOH 0.27 mm 1.00 W/Kg
ZDKH 90 0.27 mm 0.90 W/Kg
ZDKH 85 0.23 mm 0.85 /Kg

4.5 FLOW CHART OF CORE MANUFACTURING STEPS:-
Fig 4.3 Process of Core Manufacturing .

4.6 SLITTING MACHINE (SEQUENCE OF OPERATION):
1) Drawing / Q plan.
2) Size / Grade CRGO.
3) Burr Level 20 micron.
4) Steel width within tolerance.
5) Every 500m width check Burr Gauge.
6) Scrap and Buckling.
Fig 4.4 Slitting Machine.
4.7 CROPPING MACHINE (SEQUENCE OF OPERATION):
1) Revised drawing / QA Plan checked
2) Every 100 sheet parameter check
4.7.1 After completion of assembly of core including curing of resin glass tape, 10 kv AC Test
between.
 Core and End-Frame.
 Core and Yoke-Bolts.
 End-Frame and Yoke-Bolts.
Fig 4.5 CRGO Material.

Chapter- 5.
CORE BUILDING
Fig 5.1 Core Manufacturing Process.

Fig 5.2 Limbs of Core.
Fig 5.3 Completely Manufacture Core.

Chapter-6.
INSULATION SHOP
6.1 INTRODUCTION:-
The service life of a distribution transformer is governed by the condition of the insulating material.
Deterioration of the transformer insulating material reduces the dielectric strength and also reduces the
ability of the transformer to withstand short-circuit events. Korea's domestic transformer manufacturers
use varnish to improve winding mechanical strength. However, the solidified varnish deteriorates over
time, which adversely affects the characteristics of the transformers. By improving insulation
performance and the short circuit withstand strength of distribution transformers, the cost of maintaining
and replacing these transformers can be reduced.
Many pole-type transformer failures could be avoided by using hybrid insulation, where layers of aramid
papers and cellulose papers are used. Additional design modifications include reducing the number of
cooling ducts between layers and reinforcing the frame of the transformer to improve short-circuit
withstand strength. Then, varnish impregnating process is not required when this hybrid insulation is used.
The higher reliability and longer life anticipated of hybrid-insulation manufactured transformers should
result in cost savings to the utility. Construction of oil-filled transformers requires that the insulation
covering the windings be thoroughly dried before the oil is introduced. There are several different methods
of drying.
Common for all is that they are carried out in vacuum environment. The vacuum makes it difficult to
transfer energy (heat) to the insulation. For this there are several different methods. The traditional drying
is done by circulating hot air over the active part and cycles this with periods of vacuum (hot-air vacuum
drying, HAV).
More common for larger transformers is to use evaporated solvent which condenses on the colder active
part. The benefit is that the entire process can be carried out at lower pressure and without influence of
added oxygen. This process is commonly called vapour-phase drying (VPD).
For distribution transformers, which are smaller and have a smaller insulation weight, resistance heating
can be used. This is a method where current is injected in the windings to heat the insulation. The benefit
is that 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
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.
6.2 MATERIALS USED:-
1) Press Board (1mm – 50mm).
2) Bakelite (2mm – 25mm).
3) Fibre Glass (0.5mm – 4mm).
4) Card Sheet / Gasket (for tanking) (3mm – 12.5mm).
5) GUM – Fevicol & Den droid.
Fig 6.1 Press Board.

6.3 LIST OF MACHINES USED IN INSULATION SHOP:
Power Press (T-Block). Listing m/c
Crepe Paper Cutting. Weighing Drill m/c
Embossing m/c . Bend Saw –Cutting m/c.
Plate Bending m/c. Angle Hot Press.
Cylinder Gumming m/c. Circular Saw.
Scraffing m/c. Hydraulic Press m/c (300T / 500T).
Press Board Impregnation Equipment. Pneumatic Platform.
Shield Ring Milling m/c. Structural Platform.
Guillitone m/c. Steam Oven.
RM62 / Drill m/c. Vacuum Drying Vessel.
Fig 6.2 Cylindrical Gumming Machine.
Fig 6.3 Power Press.

6.4 INSULATING MATERIALS USED ARE:
Kapton tape IsopathalateTerylene Tape
Epoxy Bonded Mica Paper Zinc Napthanate epoxy mica polyester tape.
Poly propylene tape. Zinc Napthanate epoxy mica glass tape.
Glass Tape. Heat Shrink tape
Mica Putty Nomex composite tape.
Conducting Fleece PGAM(polyester glass acrylene mica tape)
Stress Grading tape.
Red gel And Corona tape.
Mica is the most widely used naturally occurring insulating material and is brittle in nature and hence requires
a base either of polyester or raisin.
Fig 6.4 Stress Grading Tape.
Fig 6.4 Heat Shrink Tape.

Chapter-7.
WINDING
7.1 INTRODUCTION
The 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.
For small power and signal transformers, in which currents are low and the potential difference between
adjacent turns is small, the coils are often wound from enameled magnet wire, 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.
The transposition equalizes the current flowing in each strand of the conductor, and reduces eddy current
losses in the winding itself.
The stranded conductor is also more flexible than a solid conductor of similar size, aiding manufacture.
This is known as a stacked type or interleaved winding.Both the primary and secondary windings on
power transformers may have external connections, called taps, to intermediate points on the winding to
allow selection of the voltage ratio.
In distribution transformers the taps may be connected to an automatic on-load tap changer for voltage
regulation of distribution circuits. 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. This produces transformers more suited to damp or dirty environments, but at increased
manufacturing cost.
7.2 TYPES OF WINDING
1) Reverse section winding
2) Helical winding
3) Spiral winding
4) Interleaved winding
Fig 7.1 Type of Winding.

The type of winding depends upon the job requirement. Also, the width and thickness of conductors designed
and decided by design department.Winding of a transformer mainly consists of High Voltage (HV) winding
and Low Voltage (LV) winding. Four types of copper conductors are used for winding material at BHEL
Bhopal:
a) PICC (Paper Insulated Copper Conductor).
b) Bunch PICC.
c) Glue Bunch PICC.
d) CTC (Continuous Transposed Copper Conductor).
Fig 7.2 Paper Insulated Copper Conductor.
Copper conductors used for HV as well as LV winding is 99.99% pure Copper. Glue Bunch PICC has
advantage over PICC since it requires less amount of insulation and hence lesser the thickness.HV winding is
done vertically and is in disk type fashion (orientation) Whereas LV winding is done by horizontally and is in
helical fashion.HV and LV windings are done separately and mounted on the same legs of the core section,
LV winding is nearer to the leg of the core so as to reduce the insulation requirements.
Fig 7.3 Flow Chart of Coil Winding.
COIL WINDING
PICC/CT
C
MOULDED
COMP.
B.O
INSULATIO
N COMP.
IN HOUSE
INSUL.COM
P
WOUND COIL
TO PROCESS

Fig 7.4 Winding of Coil on Frame.
Fig 7.5 Complete Coil Structure.
7.3 COIL PRE-HEATING:
a) 100 o
C (min 95 o
C oven temperature).
b) Duration 3 Hours.

Chapter -8.
Coil Assembly
8.1 INTRODUCTION:
Winding design and manufacturing practices for power and distribution transformers has focused in the
differences between rectangular core and coils and layer windings common in the production of distribution
transformers and disc and helical windings and circular core designs common in power transformers. In the
small power transformer market defined as 5-15 MVA, ONAN, with primary winding voltages up through 69
kV class, both core and coil designs are commercially available. Rectangular core and coils and layer
windings offer the advantage of lower costs for manufacturing compared to power class circular core and coils
with disc and helical windings.
8.2 COIL WINDING IS OF TWO TYPES
The precise details of the winding arrangements will be varied according to the rating of the transformers.
The general principles remain the same throughout most the range of transformer. The copper or
Aluminum strips/wires used in winding are meticulously selected for its quality to give the best output.
8.2.1 L. V. COIL WINDING
The Low Voltage coil is designed to approximately match the current rating of the available low-voltage
(LV). The L.V. coil is normally wound on robust tube of insulation material and this is almost invariably of
synthetic resin-bonded paper. This material has high mechanical strength and is capable of withstanding the
high loading. Electrically it will probably have sufficient dielectric strength to withstand the relatively modest
test voltage applied to the L.V. winding during the repairing without any additional insulation.
8.2.2 H. V. COIL WINDING
The second process is H.V. Coil Winding, which are wound with strip conductor and it usually consists of
continuous disc type. The coils are usually created in layers and ideally all the joints are extremely well brazen
and insulated in order to withstand difficult service conditions and tests.The LV windings are made from
Paper covered Copper Strip and placed nearest to the core. The HV winding are wound with Super Enameled
Copper Wire or Aluminum wire or Paper covered Round wire or paper covered Strip depending upon the
rating of the transformers.The cross section of the conductor is also chosen to keep the thermal gradient in the
winding to a minimum and thus increase the life of transformer .The coils are assembled with the best
insulating material avail and they are adequately clamped by the use of perm wood rings where necessary to
give required mechanicalstrength. The tapping are provided o the external HV windings.
8.3 GENERAL WINDING ARRANGEMENT:
TAP LV HV
LV TAP HV
LV HV TAP

Chapter – 9.
Power Assembly
9.1 CORE AND COIL ASSEMBLY:
A part of the transformer manufacturing process, the core and coil assembly aspect plays a
significant role The limbs of the core are tightly wrapped with cotton tape and then varnished during
the manufacturing and even repairing process.
First, the individual windings are assembled one over the other to form the entire phase assembly.
The radial gaps between the windings are subdivided by means of solid transformer board barriers.
Stress rings and angle rings are placed on top and bottom of the windings to achieve a contoured end
insulation design for optimal control of the oil gaps and creep age stresses.
The complete phase assemblies are then carefully lowered over the separate core legs and solidly
packed towards the core to assure optimal short circuit capability.
The top core yoke is then repacked and the complete core and coil assembly is clamped.
The lead exits (if applicable) and the lead supports and beams are installed. All winding connections
and tap lead connections to the tap changer(s) are made before drying the complete core and coil
assembly in the vapor phase oven.
9.2 PROCESSING OF CORE AND COIL ASSEMBLY:
The completed core and coil assembly is thoroughly dried to pre-determined power factor readings
by the vapour phase drying process, providing the fastest, most efficient and most effective drying of
the transformer insulation available.
The vapour phase process uses the standard kerosene cycle method. In this system, kerosene is
vaporized and drawn by vacuum into a heated autoclave where the transformer has been placed.
Condensation of the vapour on the core and coil assembly rapidly causes the temperature to rise and
allows moisture to be drawn out of the insulation by the vacuum.
High temperature and pressure are used to accelerate the drying process. When the power factor
measurements and the removal rate of moisture have reached the required levels, the flow of
kerosene vapour is stopped and a high vacuum is used to boil off the remaining moisture and
kerosene.
Because so much water is removed in this process, the insulation physically shrinks in size. Follow-
ing removal from the autoclave, the transformer is repacked as required and then undergoes its final
hydraulic clamping to ensure maximum short-circuit strength in the finished product.
Fig 9.1 Complete Power Assembly.

9.3 TAP CHANGING:
The LTC can be installed in the transformer tank with the diverter switch in its own oil compartment,
so that no contamination of the transformer oil occurs due to arcing during switching, or can be
mounted on the main tank.
To prevent voltage surges on the tap changer during switching MOV surge suppressors can be
installed. A tap changer is a connection point selection mechanism along a power transformer winding
that allows a variable number of turns to be selected in discrete steps. A transformer with a variable
turn’s ratio is produced, enabling stepped voltage regulation of the output.
The tap selection may be made via an automatic or manual tap changer mechanism .BHEL Bhopal is
a leading On Load Tap Changer (OLTC) group involved in Design, manufacturing, commissioning
and services of Tap Changers. It is having latest Technology incorporating high speed resistor
switching of OLTCBHEL Bhopal is having capacity to supply 500 nos.
OLTC Complete system for parallel operation of transformers and remote Tap changer control panel.
An OLTC has mainly following parts: Tap selector, Diverter Switch, Drive- Mechanism, oil chamber.
Tap selector is a mechanical switch. Diverter maintains the continuity of current for avoiding
switching transients. Make before break phenomenon occurs in oil compartment. Drive mechanism
consists of squirrel cage induction motor.
Tap changers are always present in HV side because:
a) Regulation is smooth
b) Current is less.
Fig 9.2 Tap Changer.
.

9.4 DRYING OUT PROCESS
In order to ensure power supply is completely reliable it depends on high performance transformers
and in order to achieve that the drying out process is extremely important. Under this process, the
paper insulation and pressboard material, which make up a significant proportion by volume of
transformer winding, have the capacity to absorb large amounts of moisture from atmosphere.
9.5 TANK FABRICATION AND FITTINGS:
The tanks are made of high quality steel and can withstand vacuum and pressure test as specified in IS as well
as by the customers. All welds are checked ensuring 100 % leak proof seems and mechanical strength. All
tanks are pressure tested before tanking the active part.The Pressed steel radiators are used to dissipate heat
generated at rated load. The fin height and length are calculated according to the rating of transformers as well
as customers' specifications. The fins can be plain or embossed. The radiators are fitted variably according to
the rating of transformer.
9.6 TANKING:
After vacuum drying process the active part is removed from the Oven and all components subject to the
shrinkage are tightened again. The core & coil assembly is then placed into the tank and properly locked up
during the transformer manufacturing process. While in higher rating transformer, the vacuum is drawn for a
period of time dependent on the voltage of the unit and time for which the active part was exposed to the
atmosphere and the humidity at the time. The vacuum period is between 12 to 35 hours. Meanwhile the
external wiring and termination work to be completed as per customer requirements.
9.7 PAINTING
The outside surface of tank including all fittings and accessories are cleaned properly. Necessary chipping and
grinding applied for smooth surface and finishing. After cleaning of the tank, one coat of hoi oil resistance
pint is applied on the internal surface of the tank during the transformer manufacturing process. The outside
surface is painted with one coat of Red Oxide Primer and subsequently one coat of enamel paint as per
customer's requirement. The transformers are fitted with Bare Porcelain Bushings and metal parts conforming
to IS specification 3347 "Dimension for Porcelain transformer Bushings." The electrical characteristics of the
bushings conform to IS 2099 "Specification for High Voltage Porcelain Bushings". Alternatively transformers
are supplied, fitted with Cable Box either with Wiping type of glands suitable for PVC/XLP cables.

Chapter-10
TECHNICAL DIVISION
10.1 INTRODUCTION:
Capacity : 430 KW
Autoclave Size : 12500 x 6000 x 6000
Max Loading : 450 Ton
Transformer Rating : 750 MVA, 765 KV
10.2 PROCESS:
It is a process of proper drying of insulation of transformer by a perfectly controlled automatic process,
with lowest possible paper de-polymerization and energy consumption.
Basic Equipment of Vapor Phase Drying (VPD) plant:
1) Evaporator system.
2) Condensation system.
3) Autoclave.
4) Vacuum system.
5) Solvent Pumping system.
6) Heating system for evaporator and autoclave.
7) Heat recovery system.
8) Distillation equipment.
9) Special water extraction measuring equipment.
10) Computer aided process.
The whole process is carried out in % stages, which is as explained below:
10.2.1 R1: PREPARATION:
In this first stage, the oven is prepared for the process. The job is let inside the chamber by means of crane.
All the instruments and devices are checked for correct operation.
The oil filling pipe is placed in position. Thermocouple is attached to the core of the transformer for
temperature monitoring; drain plug is connected by steel pipe, etc... Finally, the door is closed and clamped by
hydraulic pump.
10.2.2 H1: HEATING UP:
The heating process is started after initial preparation. Pressure of 7mBar is maintained within the autoclave.
The capacity of solvent tank is 12,000 L and a minimum of 5,000-6,000L is maintained during the process.
The heating cycle is of 48-60 Hrs and 2-3 intermediate pressure lowering (IPL) of 1.5-2 Hrs is applied in
between. The job temperature is maintained between 105o
C – 125o
C.

Fig 10.1 Flow Chart of Vapour Phase Drying Process.

10.2.3 P1: Fine Pressure Reduction:
 V1: Fine Vacuum:
When water is obtained at 50mL/hour is obtained for three hours in three simultaneous reading at 105o
C –
125o
C temperature and 0.2 Torr pressure, the solvent is closed down through valves. The job is flooded with
oil and it is soaked for a minimum of 12Hrs.
 A1: Aeration:
The vacuum inside the clave is broken down and air is let inside. Oil is drained from the job and it is sent to
the assembly unit for servicing. Post servicing, the job is let in for P2 process.This is generally carried out by
conventional process only. The ob is heated to 100 +/- 5o
C 0.2 torr vacuum pressure. When simultaneous 3
reading of 50mL/hour of water is obtained for 3 hours, the job is sent to Testing department for further
process in oil-filled condition.
Transformer Oil Properties-
1) (Ascoryl / OM 16 / Pyroclor).
2) High insulating.
3) Low Viscosity.
4) Low Surface Tension.
5) Optimum Cooling Point.
6) Low Decomposition.
10.3 ADVANTAGES OF V.P.D:
1) Fast, uniform heating up of the material to be dried.
2) Substantial reduction in the drying cycle of the transformer compared to conventional process.
3) Little de-polymerization of insulating material.
4) Optimum and homogeneous during quality, since the heating process take
place in practically air free atmosphere, i.e. NO2
Process Conventional Process VPD Process
1st
Process 12 to 15 days 5 days
2nd
Process 07 to 08 days Days

CHAPTER -11.
TESTING UHV LAB
11.1 INTRODUCTION:
Ultra High Voltage Laboratory at BHEL, Bhopal the premier laboratory of its kind in India, offers most
modern and sophisticated testing facilities for a wide range of transmission and equipment and products. The
testing room is climatically controlled and is fully equipped with facilities for conducting all routine tests and
temperature- rise tests. The transformers are tested at various stages of manufacture and various rating
transformers are tested at independent institution to establish short circuit and insulatingcapacity of the
transformers and also the impulse withstanding capacity.Prior to shipment, all transformers manufactured
BHEL are tested in accordance with the latest applicable standards according to customer specifications. All
industry standard and optional tests with the exception of short-circuit tests; can be performed in-house by
trained personnel using accurate and modern test equipment.
Fig 11.1 Ultra High Voltage Transformer.
11.2 SALIENT FEATURES:
UHV Laboratory is one of the largest electromagnetically screened laboratories in the world.It offers very low
background level during PD and RIV measurements. The major test equipment are mobile on air cushion
transport system, which provides flexibility of placement of test objects and test equipment’s in the hall with
no space constraint up to the highest test voltages.
11.3 TEST RESOURCES:
11.3.1 Impulse Voltage:
a) 4.0 million –volt, 400 KW impulse generator.
b) 500 Kilo-Volt, 15 KW impulse generators
c) 3.6 million-volt, 400 Pf impulse voltage divider
d) 3 million volt multiple chopping gap.

Fig 11.2 Impulse Generator.
Fig 11.3 Impulse Discharge.
11.3.2 AC Voltage:
1.5 million volt, 1 a Cascade test transformer.
1.5 million volt, 200 pF AC voltage divider
1.0 million volt, 1000 pF coupling capacitor.
11.3.3 DC Voltage:
1.2 million volt, 30 mA DC voltage generator
1.2 million volt, 1250pF, 2400 M-Ohms DC voltage divider

Fig 11.4 Cascaded Transformer.
11.3.4 Power Sources
40 MVA, 0-11 KV, 3 phase MG set
9 MVA, 0-11 KV, 50-200 Hz, 3 phases MG Set
7 MVA, 0-11 KV, 3 phases MG Set
2 MVA, 0-11 KV, 30-180 Hz, 3 Phase MG Set
2000 Amps, 1200 volts DC Power source.
11.3.6 Standard Capacitors
800kV, 71.5 pF, SF6 – filled standard capacitor
600kV, 50 pF, SF6 – filled standard capacitor
.
11.4 THE TESTS ARE CLASSIFIED AS FOLLOWS:-
11.4.1 Routine Test
1) Measurement of voltage ratio, polarity, magnetic gap, magnetic balance & magnetizing
current.
2) Open ckt test/ No load test/ Core loss/ Iron loss
3) Separate source voltage resistant test.
4) Switching source voltage resistant test.
5) Switching impulse voltage resistant test.
6) Lightning impulse voltage resistant test.
7) Partial Discharge test
8) Winding resistance test
9) Short Circuit/ Full load/Cu loss/ Winding loss test
10) Insulation resistance measurement test
11) Capacitance & 10-Delta test
12) Isolation test
13) FRA: Frequency Response Analysis

11.4.2 TYPE TEST
1) Temperature rise / Heat run test
2) Zero Sequence Impedance test
3) Power testing by cooling circuit test
4) Measurement of Harmonics
5) Measurement of Sound Level
11.4.2 SPECIAL TEST:
This include extra demanded test by the customer as per their working condition.
12.6.1 TEST ON BUSHINGS
1. Tan-Delta and Capacitance measurements
2. Partial Discharge and RIV measurement
3. Dry and wet power frequency dielectric tests
4. Lightening and wet switching impulse tests
5. Thermal stability test
6. Dielectric test with DC application
.
Fig 11.5 Bushing Testing.

CONCLUSION
The training at BHEL was very useful. As it provide very useful information about transformer capacitor and
bushing. BHEL is manufacturing many equipment of power system. I request all 3rd year students visit any
industry or generating station and increase our practical knowledge. This report has discussed the role that
how electrical power is transmitted. The Substation may be defined as assembly of apparatus which
transforms the characteristics of electrical energy from one form to another, say for example, from A.C. to
D.C. and from one voltage to another.
A.C. electrical energy is generated at low voltage but for transmission the voltage is stepped up. Higher the
voltage, lesser is the current and lesser is the power loss (I²R) and lesser is the voltage drop (IR). Similarly the
consumers do not use high voltage and so the same must be stepped down to low voltage. The stepping up and
stepping down of voltage is done in the substations. There are various bays for Incoming Lines, Outgoing
Lines, Transformer, Bus-coupler and Bus transfer etc.
I express my sincere thanks to my Training Report guide, Miss LAKSHMI RATHORE (ASST.
PROFESSOR) for guiding me right from the inception till the successful completion of the Training Report.
I sincerely acknowledge him for extending his valuable guidance, support for literature, critical reviews of
Training Report and this report and above all for the moral support he provided me at all stages of the
training.

REFERENCES
1. “TRANFORMER MAGZINE” Bharat Heavy Electrical Limited.
2. Basic Electrical Engineering - By B.L. Thereja
3. Electrical Machines - By Ashfaq Hussain
4. Electrical Machines - By P.S. Bhimra
5. AC & DC Machines - By S.K. Bhattacharya

Manoj

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