BHEL project report by Kishore Kumar Patri

BHARAT HEAVY ELECTRICALS LIMITED
JHANSI
POWER TRANSFORMER LOCOMOTIVES
SUMMER TRAINING PROJECT REPORT
On
“SPECIAL TESTING OF POWER TRANSFORMER”
PROJECT GUIDE: SUBMITTED TO:
Mr. D.N. YADAV Mr. DHRUVA BHARGAV
DY. MANAGER Sr. D.G.M (H.R.D)
(TRFR. TESTING LABORATORY) B.H.E.L, JHANSI
B.H.E.L JHANSI
SUBMITTED BY:
KISHORE KUMAR PATRI
M.TECH DUAL DEGREE (ELECTRICAL ENGINEERING)
NIT ROURKELA

CERTIFICATE
This is to certify that the project entitled “SPECIAL TESTING OF POWER TRANSFORMER’’
has been submitted by Mr. KISHORE KUMAR PATRI ,bearing Roll no: 713EE3085 of
Department of Electrical Engineering, NIT Rourkela under supervision of Mr. D.N.YADAV
for partial fulfilment of summer internship during 16th
May to 9th
July 2016(8 Weeks). His
performance was excellent during the training period. We wish good luck in their future
endeavor.
Mr. DHRUVA BHARGAV Mr. D.N. YADAV
Sr. D.G.M (H.R.D) Dy. Manager
B.H.E.L JHANSI (Transformer Testing Laboratory)
B.H.E.L JHANSI

ACKNOWLEDGEMENT
I am extremely thankful & indebted to the numerous BHEL Engineers, who provided vital
information about the functioning of their respective departments thus helping me to gain
an overall idea about the working of organization. I am highly thankful for the support &
guidance of each of them.
I am highly indebted to my project guide, Mr. D.N.YADAV (Dy. Manager-Transformer
Testing Laboratory) for giving me his valuable time and helping me to grasp the various
concepts of power transformer and their processes of manufacturing. Special thanks to
Mr. Dhruva Bhargava (Sr. Manager-HRD) , has it not been for his kind cooperation this
project would not have seen the light of the day.
I would like to express my gratitude towards Mr. B. N. NAIK, D.G.M, LMM for
his kind cooperation and encouragement which helped me in completion of this
project.
Last but not the least, I would like to express my sincere thanks to all the employees of
B.H.E.L JHAN“I who devoted their precious attention and time.

DECLARATION
I hereby declare that the project work entitled "SPECIAL TESTING OF POWER
TRANSFORMER” submitted to B.H.E.L JHANSI, is a record of original work done by
me .The facts, tables, pictures and information are based on my own experience and study
during training period.
Mr. KISHORE KUMAR PATRI
M.TECH DUAL DEGREE
ELECTRICAL ENGINEERING
NIT ROURKELA

[1]
CONTENT
SL NO. NAME Page No
1 About B.H.E.L. 2
2 Manufacturing Units of BHEL 4
3 Introduction to BHEL Jhansi 5
4 Product Profile of BHEL Jhansi 6
5 Rotation Report 8
6 TRM Bay-3 11
7 TRM Bay-4 13
8 TRM Bay-5 14
9 TRM Bay-6 15
10 TRM Bay-7 &8 16
11 TRM Bay-9 17
12 Various Departments 20
13 Power trfr. introduction 26
14 Testing of power trfr. 27
15 Preliminary tests 28
16 Final testing 29
17 Routine tests 30
18 Type tests 37
19 Special tests 39
20 Impulse test 42
21 Conclusion 56
22 References 57

[2]
ABOUT B.H.E.L.
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 a share of 57% in India’s total installed generating capacity contributing 69% (approx.)
to the total power generated from utility sets (excluding non-conventional capacity) as of March 31,
2013.
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.
Most of our manufacturing units and other entities have been accredited to Quality Management
Systems (ISO 9001:2008), Environmental Management Systems (ISO 14001:2004) and
Occupational Health & Safety Management Systems (OHSAS 18001:2007).
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.
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.

[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.
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.
TELECOMMUNICATION
BHEL also caters to Telecommunication Sector by way of small, medium and large switching
systems.
RENEWABLE ENERGY
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.
OIL AND GAS
BHEL’s products range includes Deep Drilling Oil Rigs, Mobile Rigs, Work Over Rigs, Well Heads
and X-Mas trees, choke and Kill Manifolds, full Bore Gate valves, Mud line Suspension system,
Casting support system, Sub-Sea well heads, Block valves, seamless pipes, Motors, Compressor,
Heat exchangers etc.
INTERNATIONAL OPERATIONS
BHEL is one of the largest exporters of engineering products & services from India, ranking among
the major power plant equipment suppliers in the world.

[4]
MANUFACTURING UNITS OF BHEL
 Heavy Electrical Plant, Bhopal
 Heavy Electrical Equipment Plant, Haridwar
 Heavy Power Equipment Plant, Hyderabad
 Transformer & Locomotive Plant, BHEL Jhansi (Uttar Pradesh)
 High Pressure Boiler Plant & Seamless Steel Tube Plant, Trichy (Tamil Nadu)
 Boiler Auxiliaries Plant, Ranipet, Vellore (Tamil Nadu)
 Power Plant Piping Unit, Thirumayam (Tamil Nadu)
 Power Plant Fabrication Unit, Gondia
 Insulator Plant, Jagdishpur (Uttar Pradesh)
 BHEL Electrical Machines Ltd., Kasargod (Kerala)
First Generation Units :
BHOPAL (Heavy Electrical Plant)
HARIDWAR (Heavy Electrical Equipment Plant)
HYDERABAD (Heavy Electrical Power Equipment Plant)
TIRUCHY (High Pressure Boiler Plant)
Second Generation Units :
JHANSI (Transformer and Locomotive Plant)
HARIDWAR (Central Foundry and Forge Plant)
TIRUCHY (Seamless Steel Tube Plant)
Unit through Acquisition and Merger :
BANGALORE (Electronic Porcelain Division)
New Manufacturing Units :
RANIPAT (Boiler Auxiliaries Plant)
JAGDISHPUR (Insulator Plant)
RUDRAPUR (Component and Fabrication Plant)
BANGALORE (Industrial System Group)
Repair Shop :
BOMBAY (Motor Repair Shop)
VARANASI (Heavy Repair Shop)

[5]
BHARAT HEAVY ELECTRICALS LIMITED , JHANSI
A BRIEF INTRODUCTION
By the end of the fifth year plan, it was envisaged by the planning commission that the demand for
the power transformer would raise in the coming years. Anticipating the country’s requirement, in
1974, BHEL started a new plant in Jhansi which would manufacture power and other type of
transformer in addition to the capacity available at BHEL in Bhopal. The Bhopal plant was engaged
in the manufacture transformers of large rating and Jhansi unit would concentrate on power
transformers, instrument transformers, 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.
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.

[6]
PRODUCT PROFILE OF B.H.E.L., JHANSI
A. PRODUCT PROFILE OF TRANSFORMER DIVISION :
PRODUCTS RATINGS
1. Power Transformer upto 400KV, 315MVA
2.Rectifier Transformer upto 132KV/120KA
3.Furnace Transformer upto 33KV/60MVA
4.High Voltage Rectifier
Transformer For ESP
upto 95KVp/1400mA
5. Voltage Transformer upto 220 KV
6. Current Transformer upto 400 KV
7.Traction Transformer
Single Phase Freight Loco
Three Phase Freight Loco
upto 25KV/5400 KVA
upto 25KV/7475KVA
8.Transformer for ACEMU upto 25KV/1500 KVA
9. Cast Resin Dry Type Transformer upto 33KV/15MVA

[7]
B. PRODUCT PROFILE OF LOCOMOTIVE DIVISION :
1.ELECTRIC LOCMOTIVES
 WAG-5 HB AC
 WCAM-2 AC-DC
 WCAM-3 AC-DC
 WCAG-1 AC-DC
 WAG- 7 AC
2.DEISEL ELECTRIC SHUNTING LOCOMOTIVES
 350HP
 450HP
 700HP-SPP
 700HP-TPP
 1400HP
 800HP-DH LOCO
3.TRACK MAINTENANCE EQUIPMENTS
 OHE CAR
 RAIL CUM ROAD VEHICLE
 DIESEL ELECTRIC TOWER CAR
 UTILITY VEHILCE
 DYNAMIC TRACK STABILISER
 BALLAST CLAENING MACHINE
4.OTHER NEW PRODUCTS
 WELL WAGON
 BATTERY LOCOMOTIVE
 ELECTRICS OF DG SET FOR DLW / NPCIL
 HOIST ASSEMBLIES FOR SYNCROLIFT
 BATTERY TROLLEYS
 BPRV - Discontinued

[9]
MAIN AIM OF ROTATION
Main aim behind the rotation of various departments is that one can understand the working
of each and every department and to see that how people (workers, middle level executives,
top officials) work in corporate environment.
Main departments of BHEL Jhansi are
 Production
 Administration
CLASSIFICATION OF SHOPS
FABRICATION
Fabrication is nothing but production. It comprises of 3 bays i.e. Bay-0, Bay-1, Bay-2.
BAY-0
It is the preparation shop. There are different machines available to perform different types
of function. This section has the following machines:
● Planner machine - To reduce thickness.
● Shearing machine - To shear the metal sheet according the required dimensions.
● CNC Flame cutting machine - To cut complicated shaft items using Oxy-Acetylene flame.
The other cutting machine, which uses oxy-acetylene are listed below:
▪ Pantograph machine
▪ Hand torch cutting machine
● Bending machine - To bend the any item.
● Rolling machine - In this machine three rollers are used to roll any metal sheet.
● Flattening machine - In this machine hammer is used for flattening operation.
● Drilling machine - To make the small hole by drill.

[10]
BAY-1
It is an assembly shop where different parts of tank come from bay 0. Here welding process
such as arc welding , co2 welding ,TIG & MIG welding are used for assembly, after which a
rough surface is obtained, Grinder operating at 1200 rpm is used to eliminate the roughness.
BAY-2
It is an assembly shop dealing with making different objects mentioned below:
1-Tank assembly
2-Tank cover assembly
3-End frame assembly
4-Core clamp assembly
5-Pin & Pad assembly
Before assembly, SHOT BLASTING (firing of small iron particles with compressed air) is
done on different parts of job to clean the surface before planning.
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 while solution is put, 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 fault is seen in X-ray film.

[11]
TRM BAY-3
Here are basically three sections in this bay:
1- Machine section
2- Copper section
3- Tooling section
1. MACHINE SECTION:
The operations to form small components of power and traction transformer are made in this
section. The shop consists of following machines:
a.) CENTRAL LATHE: It consists of tailstock, headstock & cross slide. In this machine job
rotates and tool is fed through cross slide. On this machine facing, turning and threading is
done.
b.) TURRET LATHE: Its function is same as central lathe but it is used for mass production.
Here turret head is used in place of tailstock because turret head contains many tailstocks
around six.
c.) CAPSTAN LATHE: Its function is also same as central lathe.
d.) RADIAL ARM DRILLING MACHINE: It is used for drilling operation. In this machine
drills are used to make hole into metal.
e.)HORIZONTAL BORING MACHINE: It is computerized and used for making bore & for
facing etc.
f.)MILLING MACHINE: It is of two types:
 Horizontal milling machine
 Vertical milling machine
The first is used for making gear and cutting operations and second one is used for facing
and T-slot cutting.

[12]
2. COPPER SECTION:
All the operations related to copper are done here. The machines used in this section are
given below:
a.) TUBE SLITING MACHINE: It is used for cutting the tube along its length and across its
diameter. Its blade thickness is 3mm.
b.) SHEARING MACHINE: It is operated hydraulically and its blade has V shape and a
thickness of 15mm.
c.) DIE AND PUNCHING MACHINE: It is also hydraulically operated and has a die and
punch for making holes.
d.) BENDING MACHINE: It is used for bending the job. It is also hydraulically operated.
e.) SHOLDER POT MACHINE: It has a pot that contains solder. Solder has a composition
of 60% Zn & 40% Pb.
3. TOOLING SECTION:
In this section the servicing of tools is done.
a.) BLADE SHARP MACHINE: It sharpens the blade using a circular diamond cutter. Blade
of CNC cropping line machine is sharpened here.
b.) MINI SURFACE GRINDER: It serves grinding purpose. It has a grinding wheel made of
Aluminium oxide.
c.) DRILL GRINDING MACHINE: To grind the drills.

[13]
TRM BAY-4
It is the winding section.
Types of winding:
1-Reverse section (RS) winding: This type of winding is
done to maintain the resistance same for both the inner and
outer conductor. Basically it is a special type of disc
winding in which multiple no. of conductors run at a time.
In this type of winding alternate layers are continuously
transposed. All HV coils are RS type.
Fig1: RS Winding
2-Helical winding: This is a special type of spiral winding
in which ducts are given in between two layers. LV coils
are helical type.
Fig2: Helical winding
3-Interleaved winding: This type of windings are used in
power transformer to increase the series capacitances. It is
done to protect the transformer from impulse stress.
Initial impulse voltage distribution can be represented as
E=A1exp(α) +A2exp(-α) - - - - - - - - - (1)
Where α=√
�
�
Cg=ground capacitance
Cs=series capacitance Fig3: Interleaved winding

[14]
If α is less then impulse withstand capacity is more.
As said before, the initial impulse voltage distribution is dependent on the magnitude of α
and the magnitude of α itself is dependent on the magnitude of Cs
& Cg, so that decreasing
Cg
or increasing Cs
modifies and decreases the magnitude of α. The interleaved winding
increases Cs
considerably compared to the previous windings and is used to reduce the severe
stresses. There are various methods to interleave windings. One of them is shown in Fig. 3.
Cs=
�� −
- - - - - - - - - - (2)
Where n=no. of turns in each disc
E=no of disc considered to be interleaved
Ct=capacitance between two turns in a disc.
The amount of series capacitance is increased in interleaved windings and this leads to the
more linearization of the voltage distribution along the winding.
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 types of winding depend upon job requirement. Conductor used for winding is in the
form of very long strips wound on a spool, the conductor is covered by cellulose paper for
insulation. The winding is done according the specification given in the drawing.
TRM 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 &
0.28mm thick sheets, 1m wide and measured in Kg. The
sheets are coated with a very thin layer of insulating
ate ial called ca itas . Fig4: cutting & punching of CRGO

[15]
For the purpose of cutting and punching the core,
three machines are installed in this shop.
a.) SLITTING MACHINE: It is used to cut CRGO sheets in different width. It has a circular
cutter whose position can be changed as per the requirement.
b.) CNC CROPPING LINE PNEUMATIC: It contains only one blade, which can rotate 900
above
the sheet. It is operated pneumatically.
c.) CNC CROPPING LINE HYDRAULIC: It is also used to cut the CRGO sheets. It contains two
blades, one is fixed and the other rotates 900
above the sheet. It is operated hydraulically.
TRM BAY-6
Single-phase traction transformer for AC
locomotives is assembled in this section. These
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 line for
this transformer is of 25 KV and power of the
transformer is 6500 KVA.
Fig5: Locomotive transformer
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.

[16]
TRM BAY-7
This is the insulation shop. Various types of insulations are:
1- AWWW: All wood water washed press paper. The paper is of 0.2- 0.5mm thick
cellulose paper and is wound on the conductors for insulation.
2- Pre-Compressed Board: This is widely used for general insulation & separation of
conductors in the form of the blocks.
3- Press Board: This is used for separation of coils e.g. L.V. from H.V. It is up to 36mm
thick.
4- UDEL: UNDEMNIFIED ELECTRICAL LAMINATED wood or Permawood. This is special
type of plywood made for insulation purposes.
5- Fiber Glass: This is a resin material & is used in fire prone areas.
6- Bakelite: A kind of plastic insulator highly resistive of heat.
7- Gasket: It is used for the protection against leakage.
8- Silicon Rubber Sheet: It is used for dry type transformer.
The machines used for shaping the insulation material are:
a. Circle cutting machine
b. Scarping machine
c. Punching machine
d. Drilling machine
e. Bench saw (spl for OD)
f. Jig saw(spl for ID)
g. Circular saw
TRM BAY-8
It is the Instrument Transformer & High Voltage Rectifier (HVR) transformer manufacturing
section.
1. 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 & energy and
can also be used for measuring power factor, frequency and for indication of synchronism.
They find application in protection of power system & for the operation of over voltage, over
current, earth fault and various others types of relays.

[17]
They are of two types:
1- Current Transformer(CT)
2- Voltage Transformer(VT)
 CURRENT TRANSFORMER: It is step down transformer. High current is not
directly measured by the CT but is stepped down to lower measurable voltages.
 VOLTAGE TRANSFORMER: This is also a stepped down transformer. The outer
construction is same is that of CT that is this also has top chamber, bushing and a
bottom chamber. The difference is only in the winding.
2. HVR TRANSFORMER: The Electro Static Precipitator transformer is used for
environmental application. It is used to filter in a suspended charge particle in the waste gases
of the industry. They are of particular use in thermal power stations and cement industry.
TRM 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 down voltage at generation and sub
stations. There are various ratings- 11 KV, 22 KV manufactured, they are:
(a) Generator Transformer System
(b) Auto transformer
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 upon the requirement of the
customer. The design department provides drawing to the assembly shop, which assembles
it accordingly.

[18]
The step involved in assembly are:
1.CORE BUILDING:
Initially laminations are cut at 450
.The punched core
is sent to this shop. Here it is assembled with the help
of drawing. A set of 4 lamination is called a packet.
The vertical portion of the core is called ‘leg’ and the
horizontal one is called as ‘yoke’ and packets of both
are interlinked. It is undesirable to keep the X section
of core circular to provide low reluctance part without
air space. Whatever spaces is left filled with thin
wooden rod. After core building the end frames are
bolted. The bolts are insulated.
Fig6: Core Building
2. CORE LIFTING:
The core is lifted by a crane and is placed vertical. The rest of assembly is done on the core
in this position.
3.UNLACING & CORE COIL ASSEMBLY:
The yoke of the core is removed using crane. Bottom
insulation in form of 50mm thick UDEL sheets is
placed. PCB, Press board are also used for filling the
gap and to provide a good base for the coil to rest. The
coil is then lowered primary, secondary, tertiary and
tap in that sequences.
Fig7: Unlaced core

[19]
4.RELACING AND END FRAME MOUNTING:
After lowering a coil, the top insulation similar to the
bottom one is provided. The removed yoke is placed
and end-frame bolted back into its position.
The connections are then made as per drawing. All the
conductors are insulated using crepe paper. The
following tests are done during Relaying:
1. Megger test
2. Ratio test
3. High voltage test
Testing at this stage is called pre-testing. Fig8: Relaced core
5.HIGH VOLTAGE TERMINAL GEAR & L.V.T.G.
The terminal gears are accessories provided at high voltage and low voltage terminals. Main
device used is tap changer. Tap changer can be on load of offload. In offload type the supply
has to be tripped, than the tapings changes but in on load type the tapings can be changed
while the supply is on.
6.VAPOUR PHASING & OIL SOAKING:
The process of moisture removal from the transformer is called vapour phasing. The job is
put in dummy type shell and then in a vacuum vessel. It is an air tight chamber with heating
facilities. The job is heated in vacuum. All the solvent vapours are sucked out with moisture.
After moisture removal tank is filled with transformer oil and soaked for at least three hours,
so that every part gets wet with oil.
7.FINAL SERVICING AND TANKING:
After tanking the job out of the dummy tank ,all the parts are retightened and any other defects
are rectified the job is reinserted in the mild steel tank after oil is filled.
8.CASE FITTING:
The accessories are fixed and final touches given to job. The accessories include tank cover,
fixing bushing, fixing valves etc. The terminals are marked R&D(rating and drawing) plate
is fixed by bolting. The bottom chamber is mild steel tank with a steel frame attached to its
base for earthing.

[20]
VARIOUS DEPARTMENTS
1. ENGINEERING (TRE):
TRANSFORMER
The transformer manufactured in BHEL Jhansi range from 10 MVA to 315 MVA and up to
400 KV. The various transformer manufactured in this unit are:
POWER TRANSFORMER
1. Generator Transformer
2. System Transformer
3. Auto Transformer
SPECIAL TRANSFORMER
1. HVR/ESP Transformer
2. Instrument Transformer
3. Cast Resin Dry Type Transformer
All above types are oil cooled except dry type, which is air cooled.
The generated voltages at the power station are 6.9 KV, 11 KV & 13.8 KV but due to certain
advantages like economical generation 11 KV is the most widely used. For this, voltage needs
to be stepped up. Transmission at high voltage is desirable because it results in lesser losses,
need thinner wire and hence is economical.
In certain cases the required voltage may be less than the output voltage, so in order to obtain
it we require a tapping circuit. The output voltage may have a certain percentage variation,
which may be tapped in 4 or 6 equal steps.
The type of tap changer depends on the application of the transformer. Where a continuous
power supply is not required an off circuit tap changer (OCTC) may be used. Where a
continuous power supply is must e.g. at a sub station in cities etc. on load tap changer (OLTC)
is used.

[21]
2. TECHNOLOGY:
This department analysis the changes taking place in the world and suggest changes and
upgrades accordingly. This is very important department because the product must not get
obsolete in the market otherwise they will be rejected by the customer.
FUNCTION:
Technology functions can be classified as:
 Processing Sequence: The sequence of process of manufacturing is decided for timely
and economic completion of the job.
 Operation Time Estimate: It includes incentive scheme management.
 Allowed Operation Time: It includes incentive amount.
 Facilities Identification: It includes looking for new equipment or plant or tools to
increase productivity.
 Special Process Certification: special processes are the ones requiring expertise for
example identifying errors, cracks, air bubbles in the welding.
 Special Tools Requirement: special tools are allotted, if possible, when required else
the design has to be reconsidered.
 Productivity Projects compilation: It includes the initial analysis of the problem and
their appropriate solution to enhance productivity.

[22]
3.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.
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 body by the name of India Electrical Manufactures Association (IEMA)
was set up. This association helps to maintain a healthy competitive atmosphere in the
manufacturing of electrical appliances.
The main work of TRC is classified as:
 Tender and notices
 Interaction with design department
 Place of the work
 Approximate cost of the work
 Earnest money
 Place & time of viewing contract documents
 Place & time of obtaining tender documents
 Deciding time up to which tender documents will be sold
 The amount if any, to be paid for such documents
 The place, date and time of submission of tenders and opening of tenders
4. LOCOMOTIVE DEPARTMENT:
This unit was started in 1985. This department of Jhansi consists of two sections the first is
manufacturing & other is design. The diesel, AC, AC/DC locomotive are manufactured
here.

[23]
a. THE DIESEL LOCOMOTIVE:
Salient features:
a) Flat bed under frame.
b) All pneumatic valves provides in single panel.
c) All electrical Equipments provided in single panel.
d) Improved filtration system.
e) Brush less traction alternators.
f) Fault display on control desk with alarm.
g) Simple driving procedure.
h) Automatic wheel slip detection & correction.
i) Multiple unit operation up to three locomotives.
j) Air & vacuum brakes.
b. THE AC LOCOMOTIVE
Salient features:
a) Operate on 25 KV AC Single-phase lines.
b) Driving cab at both ends.
c) Corridors on both sides for maintenance.
d) All pneumatic valves at one place.
e) Automatic wheel slip detection & correction.
f) Multiple unit operation up to three locomotives.
g) Fault displa o d i e s desk.
h) VCB in AC circuit.
i) Air & Vacuum brakes.

[24]
c. THE AC/DC LOCOMOTIVE
Salient features:
a) Designed to operate both in 1500 V DC & 25 KV AC lines.
b) Driving cab at both ends.
c) High adhesion bogie.
d) Corridors on both sides for maintenance.
e) All pneumatic valves at one place.
f) Automatic wheel slip detection & correction.
g) Multiple unit operation up to three locomotives.
h) Fault display on driver s desk.
i) Static inverter for auxiliary supply.
j) FRP control desk.
k) VCB in AC circuit.
l) Air & Vacuum brakes.
m) Air dryer for brake system.
5. WORKS ENGINEERING & SERVICE:
As the name suggest this section deals with services maintenance. It has following
sections:
A) Plant equipment: This has electronics & elect/mech. maintenance.
B) Services: This section deals with air, steam & Power equipments.
C) Telephone Exchange.
D) Township Electrical Maintenance.
E) W.E. & S Planning.
This sections deals with stores & new machines procurement & other general things. There
are three maintenance centre at bay-2, substation 1 & Loco. This section is also responsible
for Power distribution in B.H.E.L.

[25]
The power distribution is of two types:
1) HT Power Distribution: - This is at 11 KV, OCB are used for protection. There are four
substations for this distribution.
2) LT Distribution: - This is for the auxiliary in each shop & other section of
B.H.E.L.
6. CENTRAL QUALITY SERVICES (CQX):
First we get acquainted with a few terms concerning this department.
Quality: It is the extent to which products and services satisfy the customer needs.
Quality Assurance: All those plants and systematic action necessary to provide adequate
confidence that a product or service will satisfy the given requirement is called quality
assurance.
Quality control: The operational techniques and activities that are used to fulfill
requirement for quality are quality controlled.
Quality Inspection: Activities such as measuring, testing, gauging one or more
characteristics of a product or service and comparing these with specified requirements to
determine conformity are termed as Quality Inspection.

[26]
POWER TRANSFORMER
INTRODUCTION:
Transformers is a static electrical device which changes one ac voltage level to other keeping
frequency and power constant. When an alternating current flows in a conductor, a magnetic
field exists around the conductor. If another conductor is placed in the field created by the
first conductor such that the flux lines link the second conductor, then a voltage is induced
into the second conductor. The use of a magnetic field from one coil to induce a voltage into
a second coil is the principle on which transformer theory and application is based.
Design of the transformer is based on the induced emf principle
E=4.44BAfN - - - - - - - - - - - - - - - - - (1)
Where E=induced emf
B=flux density (tesla)
A=net area of the core (m2
)
f=frequency (Hz)
N=no. of turns
So flux voltage induced in a single turn (Et) =4.44BAf - - - - - - (2)
This is the fundamental design factor.
ANSI/IEEE defines a transformer as a static electrical device, involving no continuously
moving parts, used in electric power systems to transfer power between circuits through the
use of electromagnetic induction. The term power transformer is used to refer to those
transformers used between the generator and the distribution circuits, and these are usually
rated at 500 kVA and above. Power systems typically consist of a large number of generation
locations, distribution points, and interconnections within the system or with nearby systems,
such as a neighbouring utility. The complexity of the system leads to a variety of transmission
and distribution voltages. Power transformers must be used at each of these points where
there is a transition between voltage levels.

[27]
STAGES OF POWER TRANSFORMER MANUFACTURING:
1. CORE BUILDING
2. UNLACING OF CORE
3. FITTING BOTTOM INSULATION
4. CORE COIL ASSEMBLY AS PER DRAWING / ELECTRICAL SPECIFICATION
5. FITTING OF TOP INSULATION
6. RELACING OF CORE
7. TERMINAL GEAR MOUNTING
8. VAPOUR PHASING PROCESSING
9. FINAL TANKING AND OIL FILLING
10.CASE FITTING
11.TESTING
12.DESPATCH
Testing of Power Transformer
Reliable delivery of electric power is, in great part, dependent on the reliable operation of
power transformers in the electric power system. Power transformer reliability is enhanced
considerably by a well written test plan, which should include specifications for transformer
tests. Developing a test plan with effective test specifications is a joint effort between
manufacturers and users of power transformers. The written test plan and specifications
should consider the anticipated operating environment of the transformer, including factors
such as atmospheric conditions, types of grounding, and exposure to lightning and switching
transients. In addition to nominal rating information, special ratings for impedance, sound
level, or other requirements should be considered in the test plan and included in the
specifications. Selection of appropriate tests and the specification of correct test levels, which
ensure transformer reliability in service, are important parts of this joint effort.
Transformers can be subjected to a wide variety of tests for a number of reasons, including:
• Compliance with user specifications
• Assessment of quality and reliability
• Verification of design calculations
• Compliance with applicable industry standards

[28]
Testing is an important activity in the manufacture of any equipment. While certain
preliminary tests carried out at different stages of manufacture provide an effective tool
which assures quality and conformation to design calculations, the final tests on fully
assembled equipment guarantee the suitability of the equipment for satisfactory performance
in service. The basic testing requirements and testing codes are set out in the national and
international standards.
Preliminary tests are carried out on the transformer before it is put into the tank. Final tests
are carried out on completely assembled transformer.
Preliminary tests
As part of the manufacturer’s QA system some testing will of necessity be carried out during
manufacture. These are:
Core-sheets checks: Incoming core sheets is checked for thickness and quality of insulation
coating. A sample of the material is cut and built up into a small loop known as an Epstein
Square from which a measurement of specific loss is made. (According to BS 6404-IEC 404)
Core-frame insulation resistance: This is checked by Megger and by application of a 2.5
kV r.m.s. test voltage on completion of erection of the core. These checks are repeated
following replacement of the top yoke after fitting the windings. A similar test is applied to
any electrostatic shield and across any insulated breaks in the core frames.
Core-loss measurement: If there are any novel features associated with a core design or if
the manufacturer has any other reason to doubt whether the guaranteed core loss will be
achieved, then this can be measured by the application of temporary turns to allow the core
to be excited at normal flux density before the windings are fitted.
Winding copper checks: If continuously transposed conductor is to be used for any of the
windings, strand-to-strand checks of the enamel insulation should be carried out directly the
conductor is received in the works.
Tank tests: The first tank of any new design should be checked for stiffness and vacuum-
withstand capability. For 132 kV transformers, a vacuum equivalent to 330 mbar absolute
pressure should be applied. This need only is held long enough to take the necessary readings
and verify that the vacuum is indeed being held for hours. After release of the vacuum, the

[29]
permanent deflection of the tank sides should be measured and should not exceed specified
limits, depending on length. Following this test, a further test for the purpose of checking
mechanical withstands capability should be carried out. Typically a pressure equivalent to 3
mbar absolute should be applied for 8 hours.
FINAL TESTING
Final works tests for a transformer fall into three categories:
Tests to prove that the transformer has been built correctly: These include ratio, polarity,
resistance, and tap change operation.
Tests to prove guarantees: These are losses, impedance, temperature rise, noise level.
Tests to prove that the transformer will be satisfactory in service for at least 30 years:
The tests in this category are the most important and the most difficult to frame: they include
all the dielectric or over voltage tests, and load current runs.
The completely assembled transformer is tested in accordance with the International
Standards/IEEE Standards. The tests comprise the following:
(a)Routine tests:
All transformers are subjected to the following tests:
1. Voltage/Turn ratio and polarity.
2. Winding resistance.
3. Insulation resistance & Polarization index
4. Magnetic balance
5. Magnetizing current
6. Vector group
7. No-load losses
8. Load losses
9. Dielectric tests.
(a) Separate source AC voltage.
(b) Induced over voltage.

[30]
(b)Type tests:
Type test is done only one job in a lot. Following tests are considered as type test.
1. Temperature rise test.
2. Noise level test.
3. Lightning impulse tests.
(c)Special tests:
Special tests are tests, other than routine or type tests, agreed between manufacturer
and purchaser, for example:
1. Partial Discharge (PD)
2. Tan-delta
3. Frequency response
4. Low voltage testing (for % impedance)
5. Test with lightning impulse chopped on the tail.
6. Zero-sequence impedance on three-phase transformers.
7. Harmonics on the no-load current.
8. Power taken by fan and oil-pump motors.
ROUTINE TESTS
1.Voltage/Turn ratio and polarity test
Measurements are made on every transformer to ensure that the turns ratio of the windings,
tapping positions and winding connections are correct. The tolerance as per relevant standard
at no-load on the principal tapping is:
±0.5% of the declared ratio
These measurements are usually carried out during assembly of both the core and windings,
while all the connections are accessible, and finally when the transformer is fully assembled
with terminals and tap changing mechanism. In order to obtain the required accuracy it is

[31]
usual to use a ratiometer rather than to energize the transformer from a low-voltage supply
and measure the HV and LV voltages.
Ratiometer method
The ratiometer is designed to give a measurement accuracy of 0.1% over a ratio range up to
1110:1. The ratiometer is used in a ‘bridge’ circuit where the voltages of the windings of the
transformer under test are balanced against the voltages developed across the fixed and
variable resistors of the ratiometer. Adjustment of the calibrated variable resistor until zero
deflection is obtained on the galvanometer then gives the ratio to unity of the transformer
windings from the ratio of the resistors. This method also confirms the polarity of the
windings since a zero reading would not be obtained if one of the winding connections was
reversed.
100V is applied on HV side and from LV side observations are taken by TRT tester.
Observation of a job (132/33KV, 40MVA, YnYn0 Trfr.)
Tap
No.
U Phase
(ratio)
V Phase
(ratio)
W Phase
(ratio)
1 4.1995 4.1996 4.1995
2 4.1526 4.1525 4.1525
3 4.1008 4.1007 4.1007
4 4.0538 4.0538 4.0538
5 N 4.0021 4.0021 4.0020
6 3.9551 3.9551 3.9550
7 3.9034 3.9034 3.9034
8 3.8517 3.8517 3.8516
9 3.8 3.8 3.7999
10 3.7530 3.7530 3.7529
11 3.7013 3.7013 3.7013
12 3.6544 3.6543 3.6543
13 3.6026 3.6026 3.6026
14 3.5557 3.5557 3.5557
15 3.5040 3.5040 3.5040
16 3.4523 3.4523 3.4523
17 3.4007 3.4006 3.4006
At normal tap N=5, ratio should be ⁄ 4.

[32]
2.Windings Resistance
The DC resistances of both HV and LV windings can be measured simply by the
voltmeter/ammeter method, and this information provides the data necessary to permit the
separation of I2
R and eddy-current losses in the windings.
This is necessary in order that transformer performances may be calculated at any specified
temperature. The voltmeter/ammeter method is not entirely satisfactory and a more accurate
method such as measurement with the Wheatstone or Kelvin double bridge should be
employed. It is essential that the temperature of the windings is accurately measured;
remembering that at test room ambient temperature the temperature at the top of the winding
can differ from the temperature at the bottom of the winding. Care also must be taken to
ensure that the direct current circulating in the windings has settled down before
measurements are made.
For star connection R winding=R measured.
For delta connection R winding=1.5×R measured value.
As in delta winding equivalent Resistance=
�
All the measurements are done in ambient tempr
then it is converted to resistance at 750
C
For copper winding:
R75=RA×
+
+��
(for Aluminium 235 is replaced by 225)
Where RA=resistance measured at ambient temp.
Ta=ambient tempr
3.Insulation resistance test & Polarization Index Test
Insulation resistance tests are carried out on all windings, core and core clamping bolts.
The standard Megger testing equipment is used, the ‘line’ terminal of which is connected to
the winding or core bolt under test. When making the test on the windings, so long as the
phases are connected, together, either by the neutral lead in the case of the star connection or
the interphase connections in the case of the delta, it is only necessary to make one connection
between the Megger and the windings.

[33]
Polarization Index Test (PI Value Test) are conducted on HV machine to determine service
condition of the insulation. In HV machines and winding are likely to be affected by moisture
and contamination. PI test is conducted specially to determine the dryness and cleanliness of
winding insulation.
Polarization Index=
I a i e i a ce a i .
I a i e i a ce a i
Polarization index must be greater than 2.0
Resistance at
15sec
Resistance at
60 sec
Resistance at
600sec
PI value
HV-E . GΩ . GΩ . GΩ 2.19
HV-LV . GΩ . GΩ . GΩ 2.16
LV-E . GΩ . GΩ . GΩ 3.38
4.Magnetic Balance Test
Magnetic balance test of transformer is conducted only on three phase transformers to check
the imbalance in magnetic circuit.
Test procedure:
a. First keep the tap changer at normal position.
b. Now disconnect the transformer neutral from ground.
c. Then apply single phase 245V ac supply across one of the HV winding terminals and
neutral terminal.
d. Measure the voltage in two other HV terminals in respect of neutral.
e. Repeat the test for each of three phase.
U Phase (v) V Phase (v) W Phase (v)
Voltage applied at
U phase
245 232 17
Voltage applied at
V phase
118 244 122
Voltage applied at
W phase
17 232 244

[34]
5.Magnetizing Current Test
It is performed to locate any defects in the magnetic core str., failure in turn to turn insulation
shifting of windings or problem in tap changers. These conditions increase the effective
reluctance of the magnetic ckt. So current requirement increases for establishment of flux in
the core.
Test procedure:
a. First of all keep the tap changer in normal position and open all the HV & LV
terminals.
b. Then apply 3ph 415V supply on the line terminals of 3ph transformers.
c. Measure the supply voltage and current in each phase.
Normally magnetizing current is too small.it is in the range of mA.
6.Vector group Test
In 3ph transformer, it is essential to carry out a vector group test of transformer. proper vector
grouping in a trfr. Is essential criteria for parallel operation of transformers.
Test procedure:
a. First keep the tap changer at normal position.
b. Short 1U and 2U terminals
c. Then apply 3ph 420V ac supply to LV side
d. Measure all the ph-ph and ph-n voltages.
Fig9:Vector group diagram for YnYn0, DYn1, DYn11

[35]
Fig.10 Vector relationship test for star-delta (YN, d11) connected
Step-down transformer.
Voltages between terminals 2U–1N, 2V–1N, 1U–1N, 2V–1V, 2W–1W and 2V–1W are
measured.
For YN, d11 vector relationship
2U–1N>2V–1N>1U–1N
2V–1W>2V–1V or 2W–1W
The vector relationship for any other group can be checked in a similar manner.
7.Measurement of no-load loss
The no-load loss and the no-load current shall be measured on one of the windings at rated
frequency and at a voltage corresponding to rated voltage if the test is performed on the
principal tapping, or to the appropriate tapping voltage if the test is performed on another
tapping. The remaining winding or windings shall be left open-circuited and any windings
which can be connected in open delta shall have the delta closed.
8.Measurement of load loss
Load losses is a combination of I2
R loss and stray loss. This test is done at rated current of
the transformer. Test is performed on HV side and LV side is shorted. Measurement of load
loss is done through CT and PT. Now power analysers are available for measurement of load
loss.
9.Dielectric tests
The insulation of the HV and LV windings of all transformers is tested before leaving the
factory. These tests consist of:
(a) separate-source voltage withstand test
(b) Induced over voltage withstand test

[36]
Separate source AC voltage:
This test is intended to check the adequacy of main insulation to earth and between windings.
The line terminals of the windings under test are connected together & the appropriate test
voltage is applied to them, while the windings & tank are connected together to the earth.
Winding with graded insulation, which have neutral intended for direct earthing, are tested
at 38 kv. The supply voltage should be nearly sinusoidal and the peak voltage is measured
from digital peak voltmeter associated with capacitive voltage divider. The duration of test
is 60 seconds.
Highest Voltage for equipment
(KVrms)
Rated short duration power
frequency withstand voltage
(KVrms)
1.1 3
3.6 10
7.2 20
12 28
17.5 38
24 50
36 70
Induce over voltage withstand test:
The test is intended to check the inter-turn and line end insulation as well as main insulation
to earth & between windings.
In order to avoid core saturation at the test voltage, it is necessary to use a supply frequency
higher than the normal. When frequency is chosen in the range of 100-200 Hz, capacitive
reactance is reduced, and in draws significant capacitive current at test voltage, which causes
heavy loading on the generator can be reduced by connecting a variable reactor across the
generator terminals.
Test duration is determined by the following formula-
Test duration in seconds=
× � �
�
but not less than 30 sec.

[37]
The test is applied to all the non-uniformly insulated windings of the transformer. The neutral
terminal of the winding under test is earthed. For other separate windings, if they are star
connected they are earthed at the neutral and if they are delta connected they are earthed at
one of the terminals.
TYPE TESTS
1.Temperature rise test:
When a test for temperature rise is specified it is necessary to measure the temperature rise
of the oil and the windings at continuous full load, and the various methods of conducting
this test are as follows:
(a) short-circuit equivalent test;
(b) back-to-back test;
(c) delta/delta test;
(d) open-circuit test.
Method (a)
One winding of the transformer is short-circuited and a voltage applied to the other winding
of such a value that the power input is equal to the total normal full-load losses of the
transformer at the temperature corresponding to continuous full load. Hence it is necessary
first of all to measure the iron and copper losses. As these measurements are generally taken
with the transformer at ambient temperature, the next step is to calculate the value of the
copper loss at the temperature corresponding to continuous full load.
Method (b)
In this method, known as the back-to-back (or Sumpner) test, the transformer is excited at
normal voltage and the full-load current is circulated by means of an auxiliary transformer.

[38]
Method (c)
This method, known as the delta/delta test, is applicable to single- as well as three-phase
transformers where the single-phase transformers can be connected up as a three-phase
group.
Method (d)
If it happens that a transformer possesses a low ratio of copper loss to iron loss it is generally
impossible to conduct a temperature rise test by the short-circuit method. This is because the
required power input necessitates an excessive current in the windings on the supply side of
the transformer, so that a prohibitively high current density would be reached. In such cases
it may be possible to test the transformer on open circuit, the normal losses being dissipated
in the iron circuit. If a supply at a frequency considerably below the normal rated frequency
of the transformer is available, a condition may be obtained whereby the total losses are
dissipated at a test voltage and current in the neighbourhood of the normal rated voltage and
current of the transformer. If, however, a lower frequency supply is not available, the
transformer may be run at the normal rated frequency with a supply voltage greater than the
normal rated voltage, and of such a value that the total losses are dissipated in the iron circuit.
The iron loss varies as the square of the voltage, the required voltage under these conditions
is given by the formula: Normal voltage×(1+
. ×
� �
)
2.Noise Level Test:
This test is done in no load condition. As noise is due to the core vibration so rated voltage
is applied to measure the noise level. It is measured in decibel (dB).
For a power transformer noise level must be less than 76dB at ambient condition.

[39]
SPECIAL TESTS
1.Partial Discharge (PD) test:
Partial discharge occurs due to presence of void in insulation medium. Supply is given in LV
side and measurement is taken from power factor point or tan delta point of HV side bushing.
It is measured in pico Coulomb (pC). Test duration is one hour.
For power transformer PD must be less than 100pC.
For dry type or instrument transformer PD must be less than 10pC.
This test is carried out on the windings of the transformer to assess the magnitude of
discharges. If the apparent measured charge exceeds 104
pC, the discharge magnitude is
severe.
(a) Partial discharge in the insulation system may be caused by insufficient drying or oil
impregnation. Reprocessing or a period of rest, followed by repetition of the test, may
therefore be effective.
(b) A particular partial discharge gives rise to different values of apparent charge at different
terminals of the transformer and the comparison of simultaneous indications at different
terminals may give information about the location of the partial discharge source.
(c) Acoustic or ultrasonic detection of the physical location of the source within the tank.
2.Tan-delta Test:
Whenever there is a capacitive ckt, we have to test
tanδ for (dielectric dissipation factor) quality of
the instrument. Capacitance that is formed in
transformer is not ideal and it has some resistive
component.
Schering Bridge concept is used for measurement
of tanδ or dissipation factor (DF).
DF=tanδ=ωCR=
�
��
Fig11: Vector diagram representing IC & IR

[40]
For power transformer tanδ must be less than 0.002.
Better tanδ means resistive component is less, hence insulation quality is good.
3.Frequency Response Analysis Test:
This test is also known as signature test and it is performed in open ckt condition. Generally
Frequency response test is performed two times.
First one is at company after completion of job.
Second one is at the time of installation in field.
Test procedure:
1. The test equipment has two terminal.one is called as source and other is known as
receiver.
2. For star connected winding, connect source to a phase and receiver to the neutral point.
3. For delta type winding, connect source to one phase and receiver in another phase.
4. Take the observations (magnitude vs frequency and phase vs frequency plot) from
CRO screen.
5. Repeat the test for each and every phase of HV and LV windings.
If observations at company and observations at installation time are same then transformer
has no defect at time of transportation.
4.Low Voltage Test (% Impedance):
Low voltage test is performed to obtain the % impedance of the transformer. This is also an
important test.
Test Procedure:
1. First of all keep the tap changer in
normal
2. Short all the three phases of LV side
and connect neutral to ground.
3. Then apply 3ph 430V ac supply to
HV side.
4. Measure the voltage and current in
HV side. Fig12: For LV Test

[41]
Percentage Impedance must be less than 12%.
V=430V (applied voltage)
I=4.8amp
Z=
�
√ ×�
=
√ × .
= 51.72 Ω/phase
ZB=VB
2
/PB=1322
/40=435.6 Ω/phase
% Impedance = (Z/ZB)× = 11.8%
5.Measurement of zero sequence impedance of 3-phase transformer
This test is measured on Y-connected windings, which have an earth neutral, to determine
the current which will flow in the event of line-to-earth fault. The value of zero sequence
impedance depends upon type of core used in transformer. Since, reluctance path for zero
sequence flux is different in 3-phase 3-limb core and 3-phase 5-limb core.
Line terminals of star connected winding are joined together & 1-phase supply is applied
between these & the neutral point & delta terminals being left floating during this test.

[42]
IMPULSE TEST
Dielectric Withstand
In actual operation on a power system, a transformer is subjected to both normal and
abnormal dielectric stresses. For example, a power transformer is required to operate
continuously at 105% of rated voltage when delivering full-load current and at 110% of rated
voltage under no-load for an indefinite duration. These are examples of conditions defined
as normal operating conditions. The voltage stresses associated with normal conditions as
defined above, although higher than stresses at rated values, are nonetheless considered
normal stresses.
A transformer may be subjected to abnormal dielectric stresses, arising out of various power
system events or conditions. Sustained power-frequency over voltage can result from Ferranti
rise, load rejection, and ferroresonance. These effects can produce abnormal turn-to-turn and
phase-to-phase stresses. On the other hand, line-to-ground faults can result in unbalance and
very high terminal-to-ground voltages, depending upon system grounding. Abnormal
transient over voltages of short duration arise out of lightning-related phenomena, and longer
duration transient over voltages can result from line-switching operations.
Even though these dielectric stresses are described as abnormal, the events causing them are
expected to occur, and the transformer insulation system must be designed to withstand them.
To verify the transformer capability to withstand these kinds of abnormal but expected
transient and low-frequency
dielectric stresses, transient and low-frequency dielectric tests are routinely performed on all
transformers.
The general IEEE transformer standard identifies the specific tests required. It also defines
test levels for each test. The IEEE test code [2] describes exactly how the tests are to be made;
it defines pass-fail criteria; and it provides valid methods of corrections to the results.

[43]
Transient Dielectric Tests
Transient dielectric tests consist of lightning-impulse tests and switching-impulse tests. They
demonstrate the strength of the transformer insulation system to withstand transient voltages
impinged upon the transformer terminals during surge-arrester discharges, line-shielding
flashovers, and line-switching operations.
Power transformers are designed to have certain transient dielectric strength characteristics
based on basic impulse insulation levels (BIL). The general IEEE transformer standard [1]
provides a table listing various system voltages, BIL, and test levels for selected insulation
classes. The transient dielectric tests demonstrate that the power transformer insulation
system has the necessary dielectric strength to withstand the voltages indicated in the tables.
a)Lightning-Impulse Test
Impulse tests are performed on all power transformers. In addition to verification of dielectric
strength of the insulation system, impulse tests are excellent indicators of the quality of
insulation, workmanship, and processing of the paper and insulating-oil system. The
sequence of tests, test connections, and applicable standards is described below.
Lightning-impulse voltage tests simulate traveling waves due to lightning strikes and line
flashovers. The full-wave lightning-impulse voltage waveshape is one where the voltage
reaches crest magnitude in 1.2 µs, then decays to 50% of crest magnitude in 50 µs. Such a
wave is said to have a waveshape of 1.2 × 50.0 µs. This is shown in fig 13 The term
waveshape is used in to refer to the test wave in a general way. The term waveform is used
when referring to detailed features of the test voltage or current records, such as oscillations,
“mismatches,” and chops.
Fig 13: Standard full-wave lighting impulse.

[44]
In addition to the standard-impulse full wave, a second type of lightning-impulse wave,
known as the chopped wave, or sometimes called the tail-chopped wave, is used in
transformer work. The chopped wave employs the same waveshape as a full-wave lightning
impulse, except that its crest value is 10% greater than that of the full wave, and the wave is
chopped at about 3 µs. The chop in the voltage wave is accomplished by the flashover of a
rod gap, or by using some other chopping device, connected in parallel with the transformer
terminal being tested. This wave is shown in Figure 14. The chopped wave test simulates the
sudden external flashover (in air) of the line insulation to ground.
When the voltage applied to a transformer terminal suddenly collapses, the step change in
voltage causes internal oscillations that can produce high dielectric stresses in specific
regions of the transformer winding. The chopped-wave test demonstrates ability to withstand
the sudden collapse of instantaneous voltage.
In addition to the full-wave test and the chopped-wave test, a third type of test known as
front-of-wave test is sometimes made. (The test is sometimes called the steepwave test or
front-chopped test.) The front-of-wave test simulates a direct lightning strike on the
transformer terminals. Although direct strokes to transformer terminals in substations of
modern design have very low probabilities of occurrence, front-of-wave tests are often
specified. The voltage wave for this test is chopped on the front of the wave before the
prospective crest value is reached. The rate of rise of voltage of the wave is set to about 1000
kV/µs. Chopping is set to occur at a chop time corresponding to an assigned instantaneous
crest value. Front-of-wave tests, when required, must be specified.
Fig14: Standard chopped-wave lighting impulse.

[45]
Lightning-impulse tests, including full-wave impulse and chopped-wave impulse test waves,
are made on each line terminal of power transformers.
The recommended sequence is:
1. One reduced-voltage, full-wave impulse, with crest value of 50 to 70% of the required full-
wave crest magnitude (BIL) to establish reference pattern waveforms (impulse voltage and
current) for failure detection.
2. Two chopped-wave impulses, meeting the requirements of crest voltage value and time to
chop, followed by:
3. One full-wave impulse with crest value corresponding to the BIL of the winding line
terminal
When front-of-wave tests are specified, impulse tests are carried out in the following
sequence: one reduced full-wave impulse, followed by two front-of-wave impulses, two
chopped-wave impulses, and one full-wave impulse.
Generally, impulse tests are made on line terminals of windings, one terminal at a time.
Terminals not being tested are usually solidly grounded or grounded through resistors with
values of resistance in the range of 300 to 450 ohm. The voltage on terminals not being tested
should be limited to 80% of the terminal BIL.
b) Switching-Impulse Test
Man-made transients, as opposed to nature-made transients, are often the result of switching
operations in power systems. Switching surges are relatively slow impulses. They are
characterized by a wave that:
1. Rises to peak value in not less than 100 µs
2. Falls to zero voltage in not less than 1000 µs
3. Remains above 90% of peak value, before and after time of crest, for no
less than 200 µs.
This is shown in Fig15. Generally, the crest value of the switching-impulse voltage is
approximately 83% of the BIL.

[46]
Voltages of significant magnitude are induced in all windings due to core-flux buildup that
results from the relatively long duration of the impressed voltage during the switching-
impulse test. The induced voltages are approximately proportional to the turns ratios between
windings. Depending upon the transformer construction, shell-form versus core-form, three-
leg versus five-leg construction, etc., many connections for tests are possible. Test voltages
at the required levels can be applied directly to the winding under test, or they can be induced
in the winding under test by application of switching impulse voltage of suitable magnitude
across another winding, taking into consideration the turns ratio between the two windings.
The magnitudes of voltages between windings and between different phases depend on the
connections.
Figure 15: Standard switching impulse wave
Because of its long duration and high peak-voltage magnitude, application of switching
impulses on windings can result in saturation of the transformer core. When saturation of
the core occurs, the resulting waves exhibit faster-falling, shorter-duration tails. By
reversing polarity of the applied voltages between successive shots, the effects of core
saturation can be reduced. Failures during switching-impulse tests are readily visible on
voltage wave oscillograms and are often accompanied by loud noises and external
flashover.
Switching-impulse tests are generally carried out with impulse generators having adequate
energy capacity and appropriate wave-shaping resistors and loading capacitors.

[47]
Impulse Test Equipment — The generation, measurement, and control of impulse voltage
waves is a very specialized subject. In this section, only a very brief general introduction to
the subject is provided. Most impulse-generator designs are based on the Marx circuit.
Fig18 shows a schematic diagram of a typical Marx-circuit impulse generator with four
stages. In principle, voltage multiplication is obtained by charging a set of parallel-
connected capacitors in many stages of the impulse generator to a predetermined dc
voltage, then momentarily reconnecting the capacitor stages in series to make the
individual capacitor voltages add. The reconnection from parallel to series is accomplished
through the controlled firing of a series of adjustable sphere gaps, adjusted to be near
breakdown at the dc charging voltage. After the capacitors are charged to the proper dc
voltage level, a sphere gap in the first stage is made to flash over by some means. This
initiates a cascade flashover of all the sphere gaps in the impulse generator. The gaps
function as switches, reconnecting the capacitor stages from parallel to series, producing a
generator output voltage that is approximately equal to the voltage per stage times the
number of stages.
The desired time to crest value on the front of the wave and the time to half-crest value on
the tail of the wave are controlled by wave-shaping circuit elements.
Fig16:12-stage Impulse generator having an open-circuit test voltage of 2.4 MV and store
energy of 180 KJ. Each of the 12 stages has an output of 200 kV

[48]
These elements are indicated as Rc, Rp, and C Loading in Figure 18.
Generally, control of the time to crest on the front of the wave is realized by changing the
values of series resistance, the impulse-generator capacitance, and the load capacitance
.Control of the time to 50% magnitude on the tail of the wave is realized by changing the
values of parallel resistors and the load capacitance. Control of the voltage crest magnitude
is provided by adjustment of the dc charging voltage and by changing the load on the
impulse generator. The time of flashover for chopped waves is controlled by adjustment of
gap spacings of the chopping gaps or the rod gaps.
Fig17: Working procedure of Marx Circuit

[49]
Fig18: Marx generator with four stages. Fig19: Charging the capacitors of an impulse
generator.
The capacitor-charging current path for the impulse generator is shown in Fig19. At steady
state, each of the capacitors is charged to a voltage equal to the dc supply voltage. After
the cascade firing of the sphere gaps, the main discharging current path becomes, in
simplified form, that of Fig20. The RC time constants of the dc charging resistors, Rc as
defined in Fig17, have values typically expressed in seconds, while the wave shape control
elements, Rp and Rs as defined in Fig18, have RC time constants typically expressed in
microseconds. Hence, for the time period of the impulse-generator discharge, the relatively
high resistance values of the charging resistors represent open circuits for the relatively
short time period of the generator discharge. This is indicated by dotted lines in Figure 20.
The discharge path shown in the figure is somewhat simplified for clarity: Significant
currents do flow in the shunt wave-shaping resistors, Rp, and significant current also flows
in the loading capacitor, C Loading. These currents, which are significant in controlling the
wave shape, are ignored in Figure 20.

[50]
Fig20: discharging the capacitors of impulse generator
The measurement of impulse voltage in the range of a million volts in magnitude requires
the use of voltage dividers. Depending upon requirements, either resistive, capacitive, or
optimally damped (RC) types of dividers, having stable ratios and fast response times, are
utilized to scale the high-voltage impulses to provide a suitable input for instruments. Most
impulse-test facilities utilize specially designed impulse oscilloscopes or, more recently,
specially designed transient digitizers, for accurate measurement of impulse voltages.
Measurement of the transient currents associated with impulse voltages is carried out with
the aid of special non inductive shunts or wideband current transformers included in the
path of current flow. Usually, voltages proportional to impulse currents are measured with
the impulse oscilloscopes or transient digitizers.

[51]
Impulse Test Setup — For consistent results it is important that the test setup be
carefully made, especially with respect to grounding, external clearances, and induced
voltages produced by impulse currents. Otherwise, impulse-failure detection analysis could
be flawed. One example of proper impulse-test setup is shown in Figure 21 This figure
illustrates proper physical arrangement of the impulse generator, main circuit, chopping
circuit, chopping gap, test object, current shunt, voltage measuring circuit, and voltage
divider. High voltages and currents at high frequencies in the main circuit and the chopping
circuit can produce rapidly changing electromagnetic fields, capable of inducing unwanted
noise and error voltages in the low-voltage signal circuits connected to the impulse-
recorder inputs. The purpose of this physical arrangement is to minimize these effects.
Fig21: Impulse test set-up.
MEASUREMENT AND RECORDING OF IMPULSES
To measure the amplitude and shape of the applied impulses which have values ranging
from a few tens to over thousands of kV and duration 0.2 to 250 µs for the peak, special
measuring equipment are used. Oscillographs with high writing speeds and good accuracy
and voltage dividers with response time suitable for extremely fast transients are required.

[52]
OSCILLOGRAPHIC RECORDING
1.Lightning impulse test: The applied voltage wave and one other parameter, whose choice
depends on the selection of method of method of failure detection are recorded. For best
comparison, oscillograms taken and full test levels should be recorded to give equal
amplitude by the use of attenuators at the oscilloscope.
Recording of voltage
(a) wave shape recording- The preferred sweep time for the wave front record is 5-10 µs
and for wave tails 50-100 µs.
(b)Test wave recording- For full waves, the sweep time should not be less than 50 µs and
the chopped wave should be recorded at 10-25µs sweep.
Recording of current
The impulse currents are normally the most sensitive parameters in the failure detection
and the record of current waves are the main criteria of the test result.
2.Switching impulse test: During switching impulse test, only the recording of applied
voltage is required. The voltage record will indicate any fault developed on winding under
test or other non-tested windings.
Recording of voltage
(a) wave shape recording-For the wave front record ,a sweep time 100-200 µs is used. For
wave tail record, by which the time above 90% is determined, a sweep time of 1000-2000µs
is adequate.
(b)Test wave recording- the sweep time for test wave recording should be long enough to
encompass the first zero passage, generally a sweep time of 1000-3000µs is used.
Recording of current
A switching impulse current comprises of three parts:an initial current pulse,a low and
gradually rising value of current coincident with the tail of applied voltage and a peak of
current coincident with any saturation.

[53]
Fig22: comparison of lightning impulse 50% with 100% showing both impulses and
deviations numerically.
Fault detection during impulse tests
Detection of a breakdown in the major insulation of a transformer usually presents no
problem as comparison of the voltage oscillograms with that obtained during the calibration
shot at reduced voltage level gives a clear indication of this type of breakdown. .
Measurements of the voltages and currents in various parts of the transformer under test
can aid in location of dielectric defects. These schemes are summarized in Figure 23.
The principal indications are as follows:
1. Any change of wave shape as shown by comparison with the full-wave voltage
oscillograms taken before and after the chopped-wave shots.
2. Any difference in the chopped-wave voltage oscillograms, up to the time of chopping, by
comparison with the full-wave oscillograms.
3. The presence of a chopped wave in the oscillogram of any application of voltage for which
no external flashover was observed.

[54]
Fig23: Impulse-current measurement locations.
Audible noise
There is one another completely different method of fault detection known as the electro
acoustic probe, which records pressure vibrations caused by discharges in the oil when a
fault occurs. The mechanical vibration set up in the oil is detected by a microphone
suspended below the oil surface. The electrical oscillation produced by the microphone is
amplified and applied to an oscilloscope, from which a photographic record is obtained.
Alternatively acoustic devices may be attached to the external surfaces of the tank to detect
these discharges.
Fault location
The location of the fault after an indication of breakdown is often a long and tedious
procedure which may involve the complete dismantling of the transformer and even then
an inter turn or interlayer fault may escape detection. Any indication of the approximate
position in the winding of the breakdown will help to reduce the time spent in locating the
fault. Current oscillograms may give an indication of this position by a burst of high-
f e ue c oscillatio s o a di e ge ce f o the o-fault a e shape.

[55]
Fig24: example of fully automatic test.

[56]
CONCLUSION
To conclude po e t a sfo e s a e e te si e de ice i toda s o ld fo t a s issio a d
distribution systems. A device which could take the high-current, relatively low-voltage
output of an electrical generator and transform this to a voltage level which would enable
it to be transmitted in a cable of practical dimensions to consumers. BHEL is o e ho s
manufacturing the transformers. Power transformer undergoes several stages for
manufacturing process. Tests are done to ensure the status and reliability of the power
transformer during as well as after manufacturing.
These include some major tests like:
1. Impulse Tests
2. Temperature Rise Tests
3. Partial Discharge Test
4. Polarization Index Test
5. Ta δ Test
These eight weeks helped me a lot in gaining the knowledge of power transformer .It helped
me to learn the manufacturing as well as the testing process of power transformer.

[57]
REFERENCES
[1] www.bheljhs.co.in
[2] “Transformers” by Bharat Heavy Electricals Limited.
[3] The J&P Transformer Book by Johnson & Phillips Ltd.
[4] “Electrical Machines” by P.S. Bhimbra.

BHEL project report by Kishore Kumar Patri

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to BHEL project report by Kishore Kumar Patri

Similar to BHEL project report by Kishore Kumar Patri (20)

BHEL project report by Kishore Kumar Patri