TRAINING REPORT ON
Manufacturing process of 600 MW stator bars
Six Weeks INDUSTRIAL TRAINING
BHARAT HEAVY ELECTRICALS LIMITED
RANIPUR , HARIDWAR (UTTARAKHAND)
Submitted To: Submitted By:
Er. Satish Kumar Singh Vikash
DeenBandhu Chhotu Ram University of Science & Technology
Murthal, Sonepat, Haryana
“An engineer with theoretical knowledge is not complete engineer.
Practical knowledge is very important for an engineer to develop and apply
engineering skills”. It gives me a great pleasure to have an opportunity to
acknowledge and to express gratitude to those who were associated with
my training art BHEL.
First of all I am thankful to training coordinator Er. Satish Kumar Singh for
providing me with an opportunity to undergo my training at BHEL Haridwar.
I express my sincere thanks and gratitude to BHEL authorities' for allowing
me to undergo my training in this prestigious organization. My most thanks
to Mr. Lalit Chauhan (TG Assembly (THRI)), Mr. Sandeep Rawat (CIM,
BLOCK-4)), Mr. Vishal Kumar (EXCITER Section) without whose kind and best
benedictions my project work would have been impossible. I shall always
remain indebted to them for their constant interest & excellent guidance in
my project work. More over for providing me with an opportunity to work
& gain experience.
Special thanks to Mr. Rajendra Kumar (project coordinator) who has guided
me at every step & my discussion with them was truly enlightening. Their
dedication & sincerity towards the project helped me a lot in the
completion of project report & gave it the present attractive look.
Last but not the least I would again like to express my sincere thanks to all
project guides for there constant friendly guidance during the entire stretch
of this report. Every new step I took was due to their persistent enthusiastic
backing and I acknowledge that with a deep sense of gratitude.
BHEL - A Brief Profile.
BHEL - An Overview.
HEAVY ELECTRICAL EQUIPMENT PLANT (HEEP).
COIL AND INSULATION(BLOCK-4)
PROJECT UNDERTAKEN (DETAILS) -
MANUFACTURING PROCESS OF 600MW STATOR
BHEL was established more than 50 years ago when its first plant was setup in
Bhopal ushering in the indigenous Heavy Electrical Equipment Industry in India.
A dream which has been more than realized with a well recognized track record of
performance it has been earning profits continuously since 1971-72 and will
achieve a turnover of Rs 134,000 crore for the plan year 2012, showing a growth of
50% in the plan. Bharat Heavy Electricals Limited is country’s ‘Navratna’
company and has earned its place among very prestigious national and
international companies. It finds place among the top class companies of the world for
BHEL caters to core sectors of the Indian Economy viz., Power Generation's &
Transmission, Industry, Transportation, Telecommunication, Renewable Energy,
Defense, etc. BHEL has already attained ISO 9000 certification for quality
management, and ISO 14001 certification for environment management and
OHSAS - 18001 certification for Occupational Health and Safety Management
Systems. The Company today enjoys national and international presence featuring
in the “Fortune International -500” and is ranked among the top 10 companies in
the world, manufacturing power generation equipment. BHEL is the only PSU
among the 12 Indian companies to figure in “ForbesAsiaFabulous 50” list.
Probably the most significant aspect of BHEL’s growth has been its
diversification .The constant reorientation of the organization to meet the varied needs
in time with a philosophy that has led to total development of a total capability
from concepts to commissioning not only in the field of energy but also in industry and
In the world power scene BHEL ranks among the top ten manufacturers of power
plant equipments not only in spectrum of products and services offered, it is right
on top. BHEL‘s technological excellence and turnkey capabilities have won it
worldwide recognition. Over 40 countries in world over have placed orders with
BHEL covering individual equipment to completepowerstations on turnkey basis.
BHEL - A BRIEF PROFILE
BHEL is the largest engineering and manufacturing enterprise in India in the
energy related infrastructure sectortoday. Thewide network ofBHEL's 14
manufacturing division, four powerSectorregional centers, over 150 project
sites, eight service centers and 18 regional offices, enables the Companyto
promptlyserveits customers and providethemwith suitable products,
systems and services -efficiently and at competitive prices. While the
companycontributes morethan 75% ofthe national grid, interestingly a
share of45% comes fromits single unit. And this is none other than BHEL-
Installed equipment for over 90,000MW of power
generation--- for utilities captiveand industrial users.
Supplied over 2, 25,000 MVA transformercapacityand
otherequipment operating in transmissionand
distributionnetwork up to 400 kV (AC & DC).
Supplied over 25,000 motors with drive controlsystems
to powerprojects, petrochemicals, refineries, steel,
aluminum, fertilizers, cement plants etc.
Supplied Tractionelectrics and AC/DC locosto power
over12,000 kms railway network.
Supplied over one million valves to powerplants and
BHEL - An Overview
BHEL today is the largest Engineering Enterprise of its kind in India with
excellent track record of performance, making profits continuously since
BHEL's vision is to becomea world-class engineering enterprise, committed
to enhancing stakeholdervalue. The companyis striving to give shapeto its
aspirations and fulfill the expectations ofthe countryto becomea global
BHEL business operationscaterto coresectorsofIndian Economy.
The greatest strength of BHEL is its highly skilled and committed 60,000
employees. Every employee is given an equal opportunityto develop
himself and grow in his career. Continuous training and retraining, career
planning, a positive work culture and participative style of management all
thesehave engendered developmentofa committed and motivated
workforcesettingnew benchmarks in terms ofproductivity, quality and
POWER SECTOR -
Power generation sector comprises thermal, gas, hydro and nuclear power plant
business .BHEL supplied utility sets accounts to 87,646 MW 65% of the total
installed capacityof 1,38,175 MW in the country , as against nil in 1969 -70.
As part ofIndia’s largest Solar Power-basedIsland Electrification Projectin India,
Bharat Heavy Electricals Limited (BHEL) has successfully commissioned two
Grid-InteractiveSolar PowerPlants of 100 KW each in Lakshadweep.
With this, the companyhas commissioned a totalof eleven Solar PowerPlants in the
Lakshadweep islands, addingover1 MW ofSolar Powerto the power
generating capacityofthe coralislands in the Arabian Sea.
BHEL has proventurnkey capabilities for executing powerprojects
from conceptto commissioningand manufactures boilers, thermal
turbine generator sets and auxiliaries up to 500MW.
It possessesthetechnology and capability to procurethermal power
generation up to 1000MW.
Co-generation and combined cycleplants have also been
Forthe efficient use ofhigh ash contentcoalBHEL supplies
circulating fluidized boiler.
BHEL manufacturers 235MW nuclear sets and has also commenced
productionof500MW nuclear turbine generator sets.
Custom made hydro sets of Francis, pelton and kaplan types for different head
dischargecombinationare also engineering and manufactured by BHEL.
In, all 700 utility sets of thermal, hydro, gas and nuclear have been placed on the
companyas on date. The powerplant equipment manufactured by BHEL is based on
contemporarytechnologycomparableto the bestin the world and is also
The Companyhas provenexpertise in Plant PerformanceImprovement through
renovation modernization and up rating of variety of powerplant equipment
besides specialized know how of residual life assessment, health diagnostics and life
POWER TRANSMISSION AND DISTRIBUTION (T&D) ---
BHEL offer wide-ranging products and systems forT & D applications Products. They
manufactured include power transformers, instrument transformers, dry type
transformers, series - and shunt reactor, capacitor tanks, vacuum - and SF6 circuit
breakers gas insulated switchgears and insulators.
A strong engineering base enables the Company to undertake turnkey delivery of
electric substances up to 400 kV level series compensation systems (for increasing
power transfer capacity of transmission lines and improving system stability and
voltage regulation , shunt compensation systems (for power factor and voltage
improvement) and HVDC systems (for economic transfer of bulk power). BHEL
has indigenously developed the state-of-the-art controlled shunt reactor (for
reactive power management on long transmission lines). Presently a 400 kV Facts
(Flexible AC TransmissionSystem)projectunderexecution.
INDUSTRY SECTOR -
BHEL is a major contributor of equipment and system to important industries like
Mining and telecommunication
BHEL has indigenously developed the state-of-the-artcontrolled shunt reactor(for
reactive powermanagement on long transmissionlines). Presently a 400 kV
FACTS (Flexible AC TransmissionSystem)projectsis underexecution.
The range of systemand equipment supplied includes:-
Captive power plants
High speed industrial drive turbines
Industrial boilers and auxiliaries Waste
heat recovery boilers
Gas turbine pump, valves, seamless steel tubes
BHEL is involved in the development design, engineering, marketing, production,
installation, and maintenance and after-sales service ofRolling Stockand traction
propulsionsystems. Inthe area of rolling stock,BHEL manufactures electric
locomotives up to 5000 HP, diesel-electric locomotives from350 HP to 3100 HP,
bothfor mainline and shunting duly applications. BHEL is also producingrolling
stockforspecialapplications viz., overhead equipment cars, Specialwell wagons,
Rail-cum-road vehicle etc., Besides tractionpropulsionsystems forin-house use,
BHEL manufactures traction propulsionsystems forotherrolling stockproducers
of electric locomotives, diesel-electric locomotives, electrical multiple units and
metro cars. Theelectric and diesel traction equipment on India Railways are
largely powered byelectrical propulsionsystemsproduced byBHEL. The
companyalso undertakes retooling and overhauling of rolling stockin the area of
urban transportationsystems. BHEL is geared up to turnkey execution ofelectric
trolley bus systems, light rail systems etc. BHEL is also diversifying in the area of
porthanding equipment and pipelines transportationsystems.
BHEL also caters to telecommunication sector by way of small, medium and large
HEAVY ELECTRICAL EQUIPMENT PLANT
At Haridwar, against the picturesquebackground of Shivalik Hills, 2 important
manufacturing units of BHEL are located viz. Heavy Electrical Equipment Plant
(HEEP) & Central FoundryForgePlant (CFFP). Thehum of the construction
machinery working started under Shivalik Hills during early 60s and sowed the seeds
ofone ofthe greatestsymbolofIndo SovietCollaboration - Heavy
Consequentuponthetechnical collaboration between India and USSR in 1959,
BHEL’s prestigious unit, Heavy Electrical Equipment plant (HEEP), was
established in October, 1963, at Hardwar. Itstarted manufacturing thermalsets in 1967
and now thermal sets of210, 250 and 500 MW, including steam turbines,
turbo-generators, condensersand all associated equipments, arebeing
manufactured. This unit is capableof manufacturing thermal sets up to 1000 MW.
HEEP-manufactured gas turbines, hydro turbines and generators, etc., are not only
successfullygenerating electrical energy within and outsidethe country, buthave also
achieved a historic record of the bestoperationalavailability.
World-class , innovative, competitive and profitable engineering enterprise
providing totalglobalbusiness solutions.
The leading Indian engineering enterprise providing quality products systems and
services in the fields of energy, transportation, infrastructure and other potential
Meeting commitments made to external and internal customers.
Fosterlearning creativity and speed ofresponse.
Respectfordignity and potential of individuals.
Loyalty and pridein the company.
Zeal to excel.
Integrity and fairness in all matters.
ESTABLISHMENT AND DEVELOPMENT STAGES:
Established in 1960s under the Indo-SovietAgreements of1959 and
1960 in the area of Scientific, Technicaland Industrial Cooperation.
DRR - prepared in 1963-64, constructionstarted from October'63
Initial productionofElectric started from January, 1967.
Major construction/erection/ commissioningcompleted by1971-72
as per original DPR scope.
Stamping Unit added later during 1968 to 1972.
Annual Manufacturing capacityforThermalsets was expanded from
1500 MW to 3500 MW under LSTG. Projectduring1979-85 (Sets up
to 500 MW, extensible to 1000/1300 MW unit sizes with marginal
additionin facilities with the collaborationofM/s KWU-Siemens,
Motormanufacturing technologyupdated with Siemens collaboration
Facilities being modernized continually through Replacements /
Reconditioning-Retrofitting, Technological/ operationalbalancing.
CLIMATIC AND GEOGRAPHICAL CONDITIONS:
Haridwar is in extreme weather zoneof the UTTARAKHAND and
temperature varies from 2oC in Winter (December to January) to 45oC in
Summer (April-June); Relative humidity 20% during dryseason to 95-96%
during rainy season.
Longitude 78o3' East, Latitude 29 o55'5" North.
Height aboveMeanSea Level = 275 meters.
Situated within 60 to 100 KMs of Foot-hills of the Central Himalayan
Ranges;Ganges flows down within 7 KMs from the Factoryarea.
HEEP is located around 7 KMs on the Westernside of Hardwar city.
POWER & WATER SUPPLY SYSTEM:
40 MVA sanctioned Electric PowerconnectionfromUPC Grid (132
KV / 11KV / 6.6 KV) (Connected load -around 185 MVA)
26 deep submersibleTubeWells with O.H. Tanks forwater supply.
A 12 MW captive thermal powerstation is located in the factory
Medium Size Motors.
DIFFERENT BLOCKS AT HEEP-
S.No. Area/ Block Major Facilities Products
1. Block -I
over speed balancing,
test bed test stand,
2. Block - II
gas cutting press, ,
grinding, assembly, heat
treatment, cleaning &
of pipe coolers, painting
3. Block -III
Machining, facing wax
assembly preservation &
packing, test stands/
4. Block -IV
5. Block - V
Bar winding, mechanical
winding, sheet metal
copper profile drawing
machining & preparation
molding, press molding
hammer for forgings,
gas fired furnaces,
insulation for AC
& DC motors,
TG, HG & Motors
6. Block - VI
7. Block- VI
(Stamping & Die
8. Block- VII (wood
9. Block - VIII
Welding, drilling, shot
blasting, CNC flame
cutting ,CNC deep
drilling, Shot basting,
sheet metal work,
grinding, jig boring
stamping presses, de
& de rusting, varnishing
sport welding, painting.
machines, grinding ,
Drilling ,turning, saw,
cutting, welding, tig
of steam turbine
steam cooler oil
collers, oil tanks,
10. Services plat TPS : Power generation Power
equipment & auxiliaries generation
plat capacity 12 MW
PGP Plat : Boiler Type Producer gas
Acetylene Plat : A fully
automated plant for
acetylene generation &
filling in cylinder
Compressor House: 4
No. Compressors of
rating 100 m2 / min
Oxygen Plat : 3 air
separation unit 4 air
132 KV substation : 2 Power supply
Nose 16.7 MVA/ 11 KV,
one no. 20 MVA & one
no. 12.5 MVA 132/6.6
KV transformer & other
11. Motor transport
A fleet of vehicles Transport
comprising of cars, service
jeeps trekkers, buses,
mini buses motorcycles
, fire tenders trucks etc.
A 2000 line main Telephone
exchange for internal service
3 no Satellite exchange
13. Hydro Turbine Lab 3 test beds with Testing of
electronic turbine models
consists of cavitations
test bed for reactions
turbine & hydrodynamic
test bed for Impulse
turbines facilities for
carrying out filed test at
hydro power sets.
14. HRDC Class room with Training to
audiovisual facilities Employees, VTs
workshop with facilities Apprentices,
for turnings fitting Contractors &
machining, weeding, Customers
16. Computer Center
17. CPL (Central plant
CAD Work stations, Design and
personal computer drawings of all
reprographic facilities products
like ammonia printing,
semi dry printing
machine, Xerox process,
micro filming facilities
ICIM’s series 39 DX IT services
level 270-320 computer
system HCL magnum
mini compute system ,
ESPL SM - 32 mini
computer Nexus - 3500
CAE work station, PCs
Testing Lab for new Testing of
materials & sample components
ELECTRICAL MACHINES BLOCK (BLOCK-I)
Block-I is designed to manufacturing Turbo Generators, Hydro
generators and large and medium size AC and DC Electrical
The Block consist of 4 bays: Bay-1 (36*482 meters), Bay-2
(36*360 meters) and Bay-3 and Bay-4 of size 24 *360 meters each.
For handling and transporting the various components over-head
Crane facilities are available, depending upon the products
manufactured in each Bay. There are also a number of self-propelled
electrically-driven transfer trolleys for the interbay movement of
Conventional bay -wise broad distribution of products is as
ROTOR OVER SPEED
BASIC TURBO GENERATOR DEPARTMENTS: -
T/G ROTOR WINDING.
H/G IRON ASSEMBLY.
T/G STATOR WINDING.
TOTAL IMPREGNATION TECHNIQUE.
T/G IRON ASSEMBLY.
T/G MAIN ASSEMBLY.
L.S.T.G ROTOR WINDING.
L.S.T.G STATOR WINDING.
L.S.T.G MAIN ASSEMBLY.
Turbo generator or A.C. generators or alternators operates on
the fundamental principles of ELECTROMAGNETIC INDUCTION. In
them the standard construction consists of armature winding mounted on
stationary element called stator and field windings on rotating
element called rotor. The stator consists of a cast-iron frame , which
supports the armature core , having slots on its inner periphery for
housing the armature conductors. The rotor is like a flywheel having
alternating north and south poles fixed to its outer rim. The magnetic
poles are excited with the help of an exciter mounted on the shaft of
alternator itself. Because the field magnets are rotating the current is
supplied through two slip rings. As magnetic poles are alternately N
and S, they induce an e.m.f and hence current in armature
conductors. The frequency of e.m.f depends upon the no. of N and S
poles moving past a conductor in 1 second and whose direction is
given by Fleming ’s right hand rule.
SYNOPSIS OF THE FUNCTION OF T.G.:
1. The generator is driven by a prime mover which is steam turbine
in this case.
2. The other side of generator is provided by a rotating armature of
an exciter which produces A.C. voltage. This is rectified to D.C.
by using a rotating diode wheel.
3. The rear end of above exciter armature is mounted by a
permanent magnet generator rotor.
4. As the above system is put into operation, the PMG produces
5. The voltage is rectified by thyristor circuit to D.C.
6. This supply is given to exciter field. This field is also controlled
by taking feedback from main generator terminal voltage, to
control exciter field variation by automatic voltage regulator. The
rectified DC supply out of exciter is supplied to turbo generator
rotor winding either through brushes or central which will be
directly connected to turbo generator. This depends on the type of
exciter viz. DC commutator machines or brushes exciter.
7. The main A.C. voltage is finally available at the stator of Turbo
LARGE SIZE TURBO GENERATOR (LSTG)
In these types of generators steam turbine does the function of
prime mover which rotates the rotor of LSTG and the field winding is
supplied D.C. by an exciter.
Main types of T.G. are:-
1st LETTER = (here-T)
= 3-phase turbo generator
2nd LETTER = (here H or A)
=Medium present for generator cooling
(H= hydrogen, A or L=air)
3rd LETTER=type of rotor cooling employed
F= direct water cooling
D= direct axial gas cooling)
4th LETTER= type of as used for stator winding cooling
I= indirect gas cooling
D= direct gas cooling
F= direct water cooling
COMPONENTS OF T.G. :-
1. Stator frame
1. Rotor shaft
2. Rotor windings
3. Rotor retaining rings
The generator stator is a tight construction supporting and
enclosing stator winding, core and hydrogen cooling medium.
Hydrogen is contained within the frame and circulated by fans
mounted at either end of rotor. The generator is driven by a direct
coupled steam turbine at the speed of 3000 rpm.
The generator is designed for continuous rated output.
Temperature detector or other devices installed or connected within the
machine, permits the winding core and hydrogen temperature, pressure
and purity in machine.
The stator frame is used for housing armature conductors. It is
made of cylindrical section with two end shields which are gas tight
and pressure resistant. The stator frame accommodates the electrically
active parts of stator i.e. the stator core and the stator winding.
The fabricated inner cage is inserted in the outer frame after the
stator has been constructed and the winding completed.
The stator core is stacked from the insulated electrical sheet
steel lamination and mounted in supporting rings over the insulated
dovetail guide bars. In order to minimize eddy current losses core is
made of thin laminations. Each lamination layer is made of individual
sections. The ventilation ducts are imposed so as to distribute the gas
accurately over the core and in particularly to give adequate support
to the teeth.
The main features of core are -
1. To provide mechanical support.
2. To carry efficiently electric, magnetic flux.
3. To ensure the perfect link between the core and rotor.
Each conductor must be capable of carrying rated current
without over heating.
The stator winding consists of two layers made up of individual bars.
Windings for the stators are made of copper strips wound with
insulated tape which is impregnated with varnish, dried under vacuum
and hot pressed to form a solid insulation bar. These bars are then
placed in the stator slots and held in with wedges to form the end
These end turns are rigidly placed and packed with blocks of insulation
material to withstand heavy pressure.
The stator bar consists of hollow (in case of 500 MW generators) solid
strands distributed over the entire bar cross-section, so that good heat
dissipation is ensured. In the straight slot portion the strands are
transposed by 540 degrees. The transposition provides for mutual
neutralization of the voltage induced in the individual strands due to
slot cross field and end winding flux leakage and ensure that minimum
circulating current exists. The current flowing through the conductors is
thus uniformly distributed over the entire cross section so that the current
dependent losses will be reduced.
The alternate arrangement of one hollow strand and two solid
strands ensures optimum heat removal capacity and minimum losses. The
electrical connection between top and bottom bars is made by connecting
Class “F” insulation is used.
The no. of layer of insulation depends on machine voltage. The bars
are brought under vacuum and impregnated with epoxy resin, which
has very good penetration property due to low viscosity. After
impregnation bars are subjected to pressure with nitrogen being used
as pressurizing medium (VPI process). The impregnated bars are
formed to the required shape on moulds and cured in an oven at high
temperature to minimize the corona discharge between the insulation
and slot wall a final coat of semiconducting varnish is applied to the
surface of all bars within the slot range. In addition all bars are
provided with an end corona protection to control the electric field at
the transition from the slot to end winding. The bars consist of a large
no. of separately insulated strands which are transposed to reduce the
INSULATION OF BARS:-
A. Vacuum pressed impregnated micaclastic high voltage
The voltage insulation is provided according to the proven resin
poor mice base of thermo setting epoxy system. Several half
overlapped continuous layer of resin poor mica tape are applied
over the bars. The number of layers or thickness of insulation
depends on the machine voltage. To minimize the effect of radial
forces windings hold and insulated rings are used to support the
B. Corona Protection:-
To prevent the potential difference and possible corona discharge
between the slot wall and the insulation, the section of bars are
provided with outer corona protection. The protection consists of
polyester fluce tape impregnated in epoxy resin with carbon and
graphite as fillers. At the transition from the slot to the end winding
portion of the stator bars a semiconductor tape is impregnated.
C. Resistance Temperature Detector:-
The stator slots are provided with platinum resistant thermometer
to record and watch the temperature of stator core and tooth region
and between the coil sides of machine in operation. All AC machines
rated for more than 5 MVA or with armature core longer, the
machine is to be provided with at least 6 resistance thermometers.
The thermometer should be fixed in the slot but outside the coil
insulation. When the winding has more than one coil side per slot,
the thermometer is to be placed between the insulated coil sides.
The length of resistance thermometer depends upon the length of
armature. The leads from the detector are brought out and
connected to the terminal board for connection onto temperature
meter or relays. Operation of RTD is based on the prime factor that
the “electric resistance of metallic conductor varies linearly with
The end covers are made up of fabricated steel or aluminum
castings. They are employed with guide vans on inner side for
ensuring uniform distribution of air or gas.
MANUFACTURING OF VARIOUS PARTS OF STATOR:-
Stator Core Assembly Section:-
This section is present in BAY-1. Two no. core pits with core
building and pressing facilities are available in this section. The section is
also equipped with optical centering device, core heating installation and
core loss testing facilities.
Iron Assembly Section:-
In BAY-2 this section has facilities for stator core assembly of
Turbo-generators and Heavy Electric Motors.
Stator Winding Section:-
This section is present in BAY-1. The section is located in a dustproof
enclosure with one no. winding. Platform with two no. rotating installation
for assembly of winding. Resistance brazing machines and high voltage
transformers are also available in this section.
Bar Preparation Section:-
This section is present in BAY-1. This section consists of milling
machine for long preparation, installation for insulation of tension bolts for
stator and preparation of stator winding before assembly. The
three phase winding is afractional pitch two layer type consisting of
This section is equipped with installations like bandaging machines,
tensioning devices, Magnetic putty application machine and 45 KW MF
brazing machines for laying windings in large size DC armatures.
Heat losses arising in the generator are dissipated through hydrogen. The
heat dissipating capacity of hydrogen is eight times to that of air.
The moving or rotating part of generator is known as rotor. The axial length
of shaft of the rotor is very large as compared to its diameter in case of
turbo generators. It is coiled heavily (field coils) as it has to support large
amount of current and voltage. Rotor revolves in most generators at a speed
of 3000rpm. Field coils are wound over it to make the magnetic poles and to
maintain magnetic strength the winding must carry a very high current. As
current flows heat is generated, but the temperature has to be maintained
because as temperature raises problems with insulation becomes more
pronounced. With good design and great care this problem can be solved.
The rotor shaft is cold rolled forging 26N1 or MOV116 grade and it is
imported from Japan and Italy.
Rotor shaft is a single piece. The longitudinal slots are distributed over its
circumference. After completion, the rotor is balanced in the various planes
and different speed and then subjected to an over speed test at 120% of
rotor speed. The rotor consists of electrically active portion
and two shaft ends approximately 60 % of rotor body circumference
have longitudinal slots which hold the field winding. Slots pitch is
selected so that the two solid poles are displaced by 180 degree the
rotor wedges act as damper winding within the range of winding slots. The
rotor teeth at the rotor body are provided in radial and axial poles enabling
cooling air to be discharged.
Various Steps Involved In Rotor Machining:-
It involves finishing of shaft by machining it with a central lathe
machine. It is done in accordance to the engineering drawing design.
Special care is taken to maintain the tolerance level.
Two types of machines do slotting, air cooled and liquid cooled. Slotting is
done diametrically. First the shaft is made to rest on two horizontal plates
and is firmly attached to them with the help of chains which
exerts load and with the help of jack so that it handles the vibrations
produced during the slotting process.
Now the centre is marked and slotting is done. After slotting is
done through one side the shaft is rotated to the diametrically opposite end
of the slotted portion and then again slotting of that portion is
done. It is done in diametrically opposite ends so as to prevent bristling of
slot due to mechanical vibrations.
ROTOR WINDING :-
Rotor winding involves coiling of rotor. It is a two pole rotor.
Rotor coils are made of pure copper + 0.2% silver, which has high
tensile as well as temperature bearing properties. The coil doesn’t
deform even at high temperatures as on adding silver the thermal stresses are
eliminated. Rotor winding is also known as field winding which is
wound in longitudinal slots in rotor.
ROTOR SLOT WEDGES :-
To protect the rotor windings against the effects of centrifugal force and the
secured in slots with wedges.
Slot wedges are made of copper-nickel-silicon alloy featuring high
temperature resistance and high strength.
There is retaining ring, which protects the rotor from the impact of
centrifugal force on end windings.
Comprehensive tests such as ultrasonic examination and liquid penetration
examination are carried out in the coils.
To ensure low contact resistance, retaining rings are coated with nickel,
aluminum and silver by three step flame-spraying process.
The winding consist of several coils inserted into the slots and
the series connected such that two coils group to form one pole. Each
coil consist of several series connected turns each of which consist of
two half turns connected by brazing in end section. The individual turn of
coil are insulated against each other by interlayer insulation. L-
shaped strip of laminated epoxy glass fiber with nomex filter are used
for slot insulation.
The slot wedges are made up of high electrical conductivity
material and thus act as damper winding. At their ends, the slots wedges
are short circuited through the rotor body. When rotor is rotating at high
speed, the centrifugal forces tries to lift the winding out of slots, they are
contained by wedges.
Construction of field windings:-
The field winding consists of several series connected coils into the
longitudinal slots of body. The coils are wound so that two poles are
obtained. The solid conductors have a rectangular cross-section.
These coils are formed arranging together the 14 no. of strips which makes a
half of the coil which means that total 28 strips are used to make single coil of
the field winding.
Depending upon the type of cooling there are 8 solid and 6 hollow strips in each
half of the coil.
Let us understand it with help of the flow chart:
Coils placed together.
Then Teflon insulation is done on them.
A total of 13 layers are wrapped.
Then epoxy glass tape is wrapped around.
A card board of paper thickness is placed to keep the
Then a varnish of 7556 is wrapped on it.
Then kept free heating of about 6 hrs is done.
Then a free heating of about 1.5 hr is done at low pressure of
about 30 kg and 115*c temperature.
Then for 45 minutes it is heated at temperature of about 130*c
and pressure is increased to 200 kg.
Then keeping the pressure constant the temperature is raised to
around 160*c and coils are heated for around 3 hrs.
Then the coils are removed off the pressure gradually and cooled
by spraying water so now the temperature reaches 60*c then
left to cool slowly and the coils are ready to be wedged in the
Then the coils placed in the slots and tighten up to prevent the loosening by
There are 7 turns per pole per pitch and rotor of 210 MW is ready to
test.There is a slight difference in formation of coils 500 MW
In those generators the coils are arranged in the following manner.
Firstly they alternate hollow and solid conductors.
There are two solid conductors for every hollow strip and they
are marked as
A---- Which has 7 conductors.
B---G where they have 9 conductors each coil.
They are transposed by 540* as it removes air gap and
improves cross over insulation.
It increases mechanical strength and help in producing
equal E.M.F across all the conductors.
The insulation is molding mica mite.
Testing involving the coils are thermal shock testing hot
This testing is done to check the strength of brazing so
that there is no water leakage and as a result it can bear
thermal stresses easily.
Nitrogen test is also performed for cleaning and leakage purposes and
finally impregnating it through vacuum impregnation technique.
The vacuum impregnation technique is the latest technique to
insulate the windings of stator and not used in rotors of any of the
generators being used in the power plants nowadays.
The process above is discussed is also known as transposition, which
involves the bending of the strips used in forming the coil of either rotor
The conductors are made up of copper with silver content of approx.
0.1%. As compared to electrolytic copper silver alloyed copper
features high strength properties at high temperature so that coil
deformations due to thermal stresses are eliminated.
The insulation between the individual turns is made up of layer of glass fiber
laminate the coils are insulated from the rotor body with L-shaped strip of glass
fiber laminate with nomex interlines to obtain the required leakage path between
the coil and rotor body, thick top strips of glass fiber laminate are inserted below
wedge. The top strip are provided with axial slots of same cross-section and
spacing and used on the rotor winding.
ROTOR RETAINING RINGS -
The centrifugal forces of the end windings are contained by piece
rotor retaining rings. Retaining rings are made up of non-magnetic
high strength steel in order to reduce the stray losses. Ring so inserted is
shrunk on the rotor is an over hang position. The retaining ring is
secured in the axial position by snap rings. The rotor retaining rings
withstand the centrifugal forces due to end winding. One end of each
ring is shrunk fitted on the rotor body while the other hand overhangs
the end winding without contact on the rotor shaft. This ensures
unobstructed shaft deflection at end windings. The shrunk on hub on
the end of the retaining ring serves to reinforce the retaining ring and
serves the end winding in the axial direction. At the same time, a snap
ring is provided against axial displacement of retaining ring. To reduce
the stray losses and have high strength, the rings are made up of non-
magnetic cold worked material.
ROTOR FANS -
The cooling air in generator is cold by two axial flow fans located at
the rotor shaft one at each end augment the cooling of the winding.
The blades of fan have threaded roots for screwed into the rotor shaft.
Blades are drop forged from aluminum alloy. Threaded root fastenings
permit angle to be changed. Each blade is screwed at its root with a
The turbo generators are provided with pressure lubricated self
aligning type bearing to ensure higher mechanical stability and
reduced vibration in operation. The bearings are provided with suitable
temperature element to monitor bearing metal temperature in
The temperature of each bearing monitored with two RTD’s
(resistance thermo detector) embedded in the bearing sleeve such
that the measuring point is located directly below Babbitt. Bearing
have provision for vibration pickup to monitor shaft vibration.
To prevent damage to the journal due to shaft current, bearings and
coil piping on either side of the non-drive and bearings are
insulated from the foundation frame.
FIELD CURRENT LEAD IN SHAFT BASE
Leads are run in axial direction from the radial bolt of the exciter
coupling. They consist of low semi-circular conductors insulated from each
other and from the shaft by a tube.
The field current leads are coupled with exciter leads through a
multi contact plug in which allows unobstructed thermal expansion of field
Rotor winding assembly and rotor assembly and rotor assembly like
rotor retaining ring fitting. All these four assemblies are carried out in a
ROTOR ASSEMBLY SECTION present in BAY-1. This section is also in a
dust-proof enclosure with no. of rotators, rotor bars laying facilities and MI
heating and mounting of retaining rings.
This section is present in BAY-2 (Turbo- Generators and Heavy
Motors). This section is equipped with large size CNC and conventional
machine tools such as Lathes and Vertical Boring, Horizontal Boring
machine, Rotor slot milling and Radial drilling machines for machining
stator body, rotor shaft End shields, Bearing etc for Turbo-
generators. Same section is present in Bay-3 (Medium size motors)
equipped with Medium size machine tools for machining components for
medium size AC and DC machines and smaller components of
Turbo-generators and Hydro generators .
VENTILLATION AND COOLING SYSTEM:-
The machine is designed with ventilation system having rated
pressure. The axial fans mounted on either side of rotor ensure
circulation of hydrogen gas. The rotor is designed for radial ventilation by
stem. The end stator is packets and core clamping and is
intensively cooled through special ventilation system. Design of special
ventilation is to ensure almost uniform temperature of rotor windings
and stator core.
COOLING SYSTEM -
STATOR COOLING SYSTEM -
The stator winding is cooled by distillate water which is fed from
one end of the machine by Teflon tube and flows through the upper
bar and returns back through the lower bar of a slot. Turbo generator
requires water cooling arrangement over and above the usual
hydrogen cooling arrangement. The stator is cooled in this system by
circulating demineralized water trough hollow conductors. The cooling
was used for cooling of stator winding and for the use of very high
quality of cooling water. For this purpose DM water of proper
specifying resistance is selected. Generator is to be loaded within a
very short period. If the specific resistance of cooling DM water goes
beyond preset value. The system is designed to maintain a constant
rate of cooling water flow through the stator winding at a nominal inlet
with temperature of 40 degree centigrade, the cooling water is again
cooled by water which is also demineralized to avoid contamination
with any impure water in case of cooler tube leakage, the secondary
DM cooling water is in turn cooled by Clarified water taken from
clarified water header.
ROTOR COOLING SYSTEM -
The rotor is cooled by means of gap pickup cooling, where the
hydrogen gas in the air gap is sucked through the scoops on the rotor
and is directed to flow along the ventilating canals milled on the sides
of the rotor coil, to the bottom of slot where it takes a turn and comes
out on the similar canal milled on the other side of the rotor coil to the
hot zone of the rotor, Due to the rotation of the rotor, a positive
section as well as discharge is created due to which a certain quantity
of a gas flows and cools the rotor. The method of cooling gives uniform
distribution of temperature. Also this method has an inherent of
eliminating the deformation of copper due to varying temperature.
HYDROGEN COOLING SYSTEM -
Hydrogen is used as a cooling medium in large capacity
generators in views of highest carrying capacity and low density. Also in
order to prevent used hydrogen from generators, casing and sealing
system is used to provide oil sealing. The system is capable of
performing following system -
Filing in and purging of hydrogen safely without bringing in
contact with air.
Maintaining the gas pressure inside the machine at desired value
at all the times.
Providing indication to the operator about the condition of the
gas inside the machine I e the pressure, temperature and purity.
Continuous circulation of gas inside the machine through a drier
in order to remove any water vapors that may be present in it
Indication of liquid level in the generator and alarm in case of
GENERATOR SEALING SYSTEM -
Seals are employed to prevent the leakage of hydrogen from the
stator at the point of rotor exit. A continuous film between a rotor
collar and the seal liner is maintained by measurement of the oil at pressure
above the casing hydrogen gas pressure.
The basic use of given exciter system is to produce necessary DC for
turbo generator system. Principal behind this is that PMG is
mounted on the common shaft which generates electricity and that is
fed to yoke of main exciter. This exciter generates electricity and this
is of AC in nature. This AC is that converted into DC and is that fed to turbo
generator via C/C bolt. For rectifying purpose we have RC block and diode
circuit. The most beautiful feature is of this type of exciter is that is
automatically divides the magnitude of current to be circulated in rotor
circuit. This happens with the help of AVR regulator which
means automatic voltage regulator. A feedback path is given to this
system which compares theoretical value to predetermine and than it
sends the current to rotor as per requirement.
The brushless exciter mainly consists of:-
1. rectifier wheels
2. three phase main exciter
3. three phase pilot exciter
4. Metering and supervisory equipment.
The brushes exciter is an AC exciter with rotating armature and
stationery field. The armature is connected to rotating rectifier bridges
for rectifying AC voltage induced to armature to DC voltage. The pilot
exciter is a PMG (permanent magnet generator). The PMG is also an
AC machine with stationery armature and rotating field. When the
generator rotates at the rated speed, the PMG generates 220 V at 50
hertz to provide power supply to automatic voltage regulator.A common
shaft carries the rectifier wheels the rotor of main exciter and the
permanent magnet rotor of pilot exciter. The shaft is rigidly coupled to
generator rotor and exciter rotors are than
supported on these bearings.
The merits of brush-less excitation system are :-
(a) Completely eliminates brush gear, slip rings, field breaker and excited bus or cable.
(b) Eliminates the hazard of changing brushes and leads.
(c) Carbon dust is no longer produced and hence the operation is fully dust free.
(d) Brush losses are eliminated.
(e) Operating costs are reduced.
(f) The system is best suited for atmospheres contaminated with oil, salt, chemical etc.
and where sparking may be a fire hazard
(g) The system is simple and requires practically no maintenance except for an occasional
inspection. Maintenance costs are thus reduced.
(h) Ideally suited for locations where maintenance is likely to be rare due to continuous
demand on the m/c.
(i)Brush-less system with shaft mounted pilot exciter is of self generating type and the
excitation is unaffected by system faults and disturbances.
(j) Reliability is better.
(k) Ideally suited for large sets.
(l) Increasingly popular system the world over.
The various components of the brushless exciter are
(m) Permanent magnet pilot exciter
(n) Automatic voltage regulator
(o) Slip rings for field ground fault detection
(p) Three phase main exciter
(q) Rectifier wheels
(r) Cooling system
PERMANENT MAGNETIC PILOT EXCITER
The three phase pilot exciter is a 16 poles revolving-field unit. The frame
accommodates the laminated core with the three phase winding. The rotor consists of
hub with mounted Poles. Each pole consists of 12 separate permanent magnets which
are housed in a non-magnetic metallic enclosure. The magnets are braced between
the hub and the external pole shoe with bolts. The rotor hub is shrunk on to the free
AUTOMATIC VOLTAGE REGULATOR
Also known as thyristor voltage regulator. It converts the three phase ac generated by
the permanent magnet exciter in to the variable dc to excite the stator of the main
SLIP RINGS FOR FIELD GROUND FAULT DETECTION
The field ground fault detection system detects the high-resistance and low -resistance
ground fault in the exciter field circuit. It is very important for safe operation of a
generator, because a double fault causes magnetic unbalances with very high currents
flowing through the faulted part, resulting in its destruction with in a very short time.
The field ground fault detection system consists of two stages.
If the field ground fault detection system detect a ground fault, an alarm is activated
at R< 80 kΏ. If the insulation resistance between the exciter field circuit and ground
either drops to R< 5 kΏ the generator electrical protection is tripped. The generator is
automatically disconnected from the system and de-excited.
THREE PHASE MAIN EXCITER
The three phase main exciter is a six-pole revolving armature unit. Arranged in the
stator frame, the poles with field and damper winding. The field winding is arranged on
the laminated magnetic poles. At the pole shoe, bars are provided. Their ends being
connected so as to form a damper winding between two poles. A quadrature-axis coil
is fitted for inductive measurement of the exciter current. The rotor consists of
stacked laminations, which are compressed through bolts over compression rings. The
three-phase winding is inserted in the slots of the laminated rotor. The winding
conductors are transposed with in the core length, and the end turns of the rotor
winding are secured with steal bands. The connections are made on the side facing the
rectifier wheels. The winding ends are run to a bus ring system to which the three
phase leads to the rectifier wheels are connected. After full impregnation with
synthetic resin and curing, the complete rotor is shrunk onto the shaft. A journal
bearing is arranged between main exciter and pilot exciter and has forced oil
lubrication from the turbine oil supply.
The main component of the rectifier wheels are the silicon diodes which are arranged
in the rectifier wheels in a three-phase bridge circuit. The contact pressure for the
silicon wafer is produced by a plate spring assembly. The arrangement of the diodes is
such that this contact pressure is increased by centrifugal force during rotation. Two
diodes are mounted in each aluminum alloy heat sink and connected in parallel.
Associated with each heat sink is a fuse which serves to switch off the two diodes if one
For suppression of the momentary voltage peaks arising from commutation, each
wheel is provided six RC networks consisting of one capacitor and one damping
resistor each, which are combined in a single resin encapsulated unit.
The insulated and shrunken rectifier wheels serves as dc buses for the negative and
positive side of the rectifier bridge. This arrangement ensures good accessibility to all
components and a minimum of circuit connection. The two wheels are identical in their
mechanical design and differ only in the forward directions of the diodes.
The direct current from the rectifier wheels is fed to the leads arranged in the
center bore f the shaft via radial bolts. The three phase alternating currents is obtained
via copper conductors arranged on the shaft circumference between the rectifier
wheels and the three-phase main exciter. The conductors are attached by means of
banding clips and equipped with screw on lugs for the internal diode connections. One
three-phase conductor, each is provided for the four diodes of a heat sink set.
The exciter is air cooled. The cooling air is circulated in a closed circuit and recooled in two
cooling sections arranged along side the exciter. The complete exciter is housed in an
enclosure draw the cool air in at both ends and expels the warmed air to the compartment
beneath the base plate.The main exciter enclosure receives the cool air from the fan
after it passes over the pilot exciter. The air enters the main exciter from both ends and
is passes in to the ducts below the rotor body and discharged through radial slots in the
radial core to the lower compartment. The warm air is then returned to the main
enclosure via the cooler section
SUPERVISION OF EXCITER
The most essential measuring and supervisory devices at the exciter are:
Temperature monitoring system
Fuse monitoring system
Ground fault detection system
Excitation current measuring device
1. Temperature monitoring system: The exciter is provided with devices for monitoring
the temperatures of the cold air after the exciter cooler and the hot air leaving the rectifier
wheels and main exciter.
2. Fuse monitoring system: The indicator flags of the fuse on the rectifier wheels may be
checked during operation.
3. Ground fault detection system: Two slip-rings are installed on the shaft between the
main exciter and the bearing. One is connected to star point of the three-phase winding of
the main exciter and the other to the frame. These slip-rings permit ground fault
4. Excitation current measuring device: the excitation current is measured indirectly
through a coil arranged between two poles of the main exciter. The voltage induced in this
coil is proportional to the excitation current thus enabling a determination of the excitation
BAY IV (SMALL AND MISCELLANEOUS COMPONENTS)
Facilities available in the various sections are as follows:-
The machine section of Bay-4 is equipped with small and
medium size CNC & conventional machine tools like centre lathes,
milling, radial drilling, cylindrical grinding, slotting, copy turning lathe,
internal grinding and surface grinding machines. Small-size and
miscellaneous components for Turbo-generators, Hydro generators and
Motors are machined in this section.
POLE COIL SECTION
This section is equipped with baking oven , pneumatic shearing machines ,
semi-automatic winding machines , pole straightening installations , electric
furnace for bright annealing of copper , tinning installation and hydraulic
press (800 Ton capacity ) for manufacturing Pole Coils of DC motors , AC
synchronous motors and hydro generators . Pole assembly is also carried out
in this section.
Manufacturing of coils (hydro generators) taken in this section. German
copper coils are initially in the form of rolls. These rolls are then undergoes
following processes to change into copper coils which are then mounted with
This is the process of hardening or softening any metal.
Initially copper rolls are hard & if it undergoes annealing then it
may breaks so firstly to make it soft so that it can easily change
This process is carried out in the annealing furnace.
This process undergo following steps:
Take out the softened copper rolls for pole coil winding.
Winding is done with the help of change plate & winding
template so ensure major working dimensions of change plate &
winding template with respect to tool drawing.
Adjust & set the winding machine as per the product standards
using gear rack, change plate & winding template. Ensure
parallelity of winding template with respect to machine platform.
Maintain height of winding template with platform. Wind the coil
in anticlockwise direction.
The joint in the copper coil shall be located in the straight part
of longer side.
If required heating by gas torch of copper profile at corner
zone at temperature between 100-150 degree centigrade is
allowed. This is to make easier bending.
Braze the joint with brazing alloy Ag40Cd.
Remove the coil with machine with 2 to 3 turns extra than the
actual number of turns for preparation of end-half turns.
Carry out bright annealing of the coil. Take out the coil from the
oven after annealing.
Pressing of coil is done by hydraulic pressure of 800 tons.
This process is carried out in order to remove wrinkles from the
This process is carried out after every process. In this process,
set the coil on the mandrel for pressing then slide the coil under
press and press the coil.
Take out the coil from press.
Fix the accessory on the stretching machine.
Put the coil on the stretching machine& pull the coil to the
Dress the conductors along periphery & take out the coil.
Check window dimensions as per drawing.
Remove the buckling of each coil manually.
Grind the bulging of the copper at place of binding (inner side)
with pneumatic grinder.
Check the thickness of the profiled copper with the gauge.
Grinding shall be uniform & of smooth finish.
Round of sharp edges.
** Again press the coil as in pt.5 & take out the coil from the press.
Send the coil for pickling to block 4 & check the quality of
Press the coil again after pickling then remove pressure and take
Prepare end half turn as per drawing with template.
Braze item 2 & 3 corresponding to the variant with end half turn
with brazing alloy
Ag 40 Cd.
Remove extra material, clean and check with gauge.
Adjust the end half turn with top & bottom turn of coil braze the
Remove extra material and check thickness of the gauge.
Check the distance from center axis of pole coil as per drawing.
Hang the coil on stand and separate out turns
Remove black spots, burrs the sharp edges and clean the coil
turns with cotton dipped in thinner.
Press the coil again and check the height of the coil under press
to check dimensions as per drawing.
Take out the coil from the press and send for insulation.
Hang the coil on stand and separate out the turn.
Clean each turn with cotton dipped in thinner.
Apply Epoxy varnish on both sides of each turn with brush
uniformly all over the leaving top & bottom turn.
Cut strips of Nomax paper as per contour of coil with
technological allowance 3 to 5 mm on either side.
Stick two layers of Nomax strips between each turn.
Coat varnish layer between two layers of Nomax also.
Let the excess varnish to flow out some time
10. BAKING AND PRESSING OF COIL:-
Place the coil on mandrel putting technological washer at top &
bottom of the coil.
Heat the coil by DC up to 100 +/-5o C , and maintain for 30 to
Switch off the supply and elongate the coil and tight the pressing
blocks from sides.
Start heating coil again and raise temperature gradually in steps
up to 130 +/- 5o C , with in 10 +/- 10 minutes.
Apply 110 tones pressure and maintain for 20 to 30 minutes.
Then after every half an hour, increases the pressure and
temperature according to product requirement.
Stop heating and then allow cooling the coil under pressure
below 50o C, and taking out the coil from the press.
11. CLEANING AND DRYING:-
Clean outer and inner surface of projected insulation by means
of shop made scrubber.
Flow dry compressed air after cleaning.
Check height and window dimensions as per drawing.
Check no gap between the turns.
Test the coil from inter turn test at 116 volts AC at a pressure of
480 tons in 5 minutes.
Coat the coil with two layers of epoxy red gel.
TURBO ROTOR COIL SECTION:-
This section is equipped with copper straightening and cutting machines,
edge bending machines, installation for forming and brazing, 10-block
hydraulic press and installation for insulation filling. Rotor coils for water
cooled generators (210 /235 MW) are manufactured in this section.
This section is equipped with electric drying ovens, Air drying booths, Bath for
armature / rotor impregnation. Rotors / armatures of AC and DC motors are
impregnated in this section.
This section is equipped with alkaline degreasing baths, hot and cold rinsing
baths, pickling baths, tinning bath, and electric furnaces and centrifugal
babbitting machines, Babbitting of bearing liners for Turbo generators,
Turbines, Hydro generators, AC motors and DC motors is carried out in this
Turbo-generators Test Bed -The Test Bed for Turbo-generators and Heavy motors
is equipped with one no. 6 MW drive motor and a tests pit for
carrying out testing of Turbo-generators and Heavy motors. Open circuit, short
circuit, temperature rise, hydraulic and hydrogen leakage test etc., are carried
out here for Turbo-generators. AC motors up to 11 MVA capacity and DC
machines up to 5000 amps and 850 volt can also be tested. Two DC
drive motors of 2200 KW and one of 1500 KW are available for type testing of
motors. Data logging equipment is also available.
LARGE SIZE TURBO GENERATOR TEST STAND (LSTG):-
It is equipped with a 12 MW drive motor and two number test pits. Open
circuit ,short circuit , sudden short circuit , temperature rise , hydraulic &
hydrogen leakage tests are carried out here Large size Turbo-generators.
This test bed can presently test Tgs of unit capacity up to 500 MW. With
certain addition in facilities (Higher capacity Drive motor and EOT cranes and
modification in controls and auxiliary systems), Turbo-generators of unit size up
to1000 MW can be tested.
HELIUM LEAK TEST -
To check any leakage of gas from stator and rotor as if there is any
leakage of gas used for cooling such as hydrogen then it may cause an
Testing of stator frame involves two types of testing:
HYDRAULIC TESTING AND PNEUMATIC TESTING
Hydraulic testing involves in empty stator frame with attached end
shields and terminal box is subjected to a hydraulic test at 10 bar to
ensure that it will be capable of withstanding maximum explosion
The pneumatic testing involves filling of hydrogen in the sealed stator
frame and then soap water is used to check the leakage of welding.
BREIF SUMMARY OF C.I.M- BLOCK -4
BAY-1: Bar winding shop: Manufacturing of stator bars of generator.
BAY-2: Manufacturing ofmotorstatorcoil, DC armature coil, main pole
Coil , inter-pole coil, equalizer coiletc.
BAY-3: Insulating detail shop:Manufacturing of hard insulation &
machining of hard insulation part such as packing, washer,
insulation box, wedges etc.
BarShop: This shop is meant for manufacturing of statorwinding coils of
generator that may beturbo-generatororhydro-generator.
Why do we call it bar: It is quite difficult to manufacture, handle and wind the
coil in statorslot ofgenerator of higher generation capacitybecauseofits bigger
size and heavy weight. That is why we make coilin two parts. Onepart is bottom
part ofcoil called bottomorlower barand other part ofcoil is called top bar or
HG bars: The manufacturing ofbars of different capacityas required by the
consumer depends upon the water head available at site. The Hydro generator is air
cooled generatorof lesser length in comparisonto its bigger diameter.
Turbo-Generator: The manufacturing of bars of standard capacity such as
100MW,130MW, 150MW, 210/235MW, 500MW. The plant has capacity and
technologyto manufacture 800MW and 1000MW generators.
Thermal classification of insulation depends upon the temperature withstand
Class- Y upto 90’c
Class- A upto 105’c
Class- E upto 120’c
Class- B upto 130’c
Class- F upto150’c
Class-C > 180’c and upto 220’c
Type of generators:
The generator may be classified based upon the cooling system used in the
1st LETTER= (here-T)
= 3-phaseturbo generator
2nd LETTER= (here H orA)
=Medium present for generator cooling
(H= hydrogen, A orL=air)
F= directwater cooling
D= directaxial gas cooling)
4th LETTER=typeofas used forstatorwinding cooling
I= indirect gas cooling
D= directgas cooling
F= directwater cooling
a) Rich resin or Thermoreactive insulation system: In this type of
insulation systemthe bond contentin resin is 35-37%. The raw materials are
ready to useand require preservationand working ontemperature 20-25’c. its
shelf life is one year when keptat temperature 20’c which could be
increased when kept at temperature of5’c.
b) Poorresin or Micalastic insulation system: In this typeof insulation
the bond contentin the resin is 5-7% and insulation material is prepared with
acceleratortreatment. The temperature controlneed notrequired. The
insulating material is applied onjob and then the same is impregnated in the
Turbo generator or A.C. generators or alternators operates on the fundamental
principles of ELECTROMAGNETICINDUCTION.
In them the standard construction consists of armature winding mounted on
stationary element called stator and field windings on rotating element called
The statorconsistsofa cast-ironframe , which supportsthearmature core, having
slots onits inner periphery for housing the armature conductors.Therotoris like a
flywheel having alternating north and southpoles fixed to its outer rim.
The magnetic poles are excited with the help of an exciter mounted on the shaft of
alternator itself. Becausethe field magnets are rotating the current is supplied
through two slip rings. As magnetic poles are alternately N and S, they induce an
e.m.f and hencecurrent in armature conductors. The frequencyofe.m.fdepends upon
the no. of N and S poles moving past a conductor in 1 second and whose direction is
given byFleming ’s right hand rule.
STATOR WINDING IN TURBO GENERATOR
Each conductormustbecapableof carrying rated current without over heating.
The statorwinding consistsoftwo layers made up of individual bars. Windings forthe
stators aremade ofcopperstrips wound with insulated tape which is
impregnated with varnish, dried under vacuum and hot pressedto forma solid
insulation bar. These bars are then placed in the statorslots and held in with
wedges to form the end turns.
These end turns are rigidly placed and packed with blocks of insulation material to
withstand heavy pressure.
The statorbarconsists ofhollow (in caseof500 MW generators) solid strands
distributed over the entire bar cross-section, sothatgood heat dissipationis
ensured. In the straight slotportionthe strands are transposed by540 degrees. The
transpositionprovides formutual neutralization ofthe voltage induced in the
individual strands dueto slotcross field and end winding flux leakage and ensure that
minimum circulating current exists. The current flowing through the
conductors is thus uniformly distributed over the entire cross section so that the current
The alternate arrangement of one hollow strand and two solid strands ensures
optimum heat removal capacity and minimum losses. The electrical connection
between top and bottombars is madeby connectingsleeve.
Class “F”insulation is used.
The no. of layer ofinsulation depends onmachine voltage. The bars are brought
under vacuum and impregnated with epoxyresin, which has very good penetration
propertydueto low viscosity. After impregnation bars are subjected to pressure
with nitrogen being used as pressurizing medium (VPI process).Theimpregnated
bars are formed to the required shapeon moulds and cured in an oven at high
temperature to minimize the coronadischargebetween the insulation and slot wall
a final coatof semiconductingvarnish is applied to the surfaceof all bars within
the slotrange. In addition all bars are provided with an end coronaprotectionto
controlthe electric field at the transition from the slot to end winding. The bars
consistofa large no. of separately insulated strands which are transposed to reduce
the skin effect.
MANUFACTURING PROCESS OF 600 MW
TURBO-GENERATOR STATOR WINDING BAR-:-
FLOW CHART OF THE PROCESS:
ConductorDraw from Store.
Conductor cutting and end cleaning.
Assembly of all conductors to be used in stator Bars.
Consolidation if slot portion of Bar.
I.S. Test(i.e. inter strand test).
Forming or Bar (to shape overhang portion).
Pickling of barends (1)
Mounting of Contact sleeve & bottom part of water box.
Brazing of Contact sleeve & bottom part of water box.
Pickling ofbarends (2)
Mounting ofwater boxleak test.
Water flow and N2 test.
Helium Leak Test.
Reforming ofBar. (i.e. overhangportion).
Insulation of bar on CNC machine.
Impregnation an curing ofbar insulation.
Preparationofbar forHV and TanQ Test.
If O.K. Dispatch to Block-1 for laying in the generator.
This process is done by automatic 3-444CNC machine. In this process the pre
insulated copper conductor is cut into number of required length. Insulation is
removed from bothends oftheconductorcut.
Cutting size of conductor :
Settype Conductor length Dimension No. of Sharing
upper: 7000 mm
lower: 7300 mm
upper: 10050 mm
lower: 10200 mm
Lower : 8*2.8
solid: Upper: 8*1.3
600 MW upper: 10887 mm
lower: 11053 mm
8200 mm Solid : 10.5*1.8 conductors:
upper: 1680 mm
lower: 1620 mm
Transposition: Transposition means changing/shifting of position of each conductor in
active core(slot)part. After cutting the required number of conductors,the conductors are
arranged on the comb in staggered manner and then bends aregiven to the conductorswith the
help ofbending die at required distance. Then the conductorsaretaken out from the comb and
die and placed with their ends in a line and transpositionis carried out. This processis
repeated for making another half ofthe bar which would be mirror image of the first half. The
two halves ofthe bar are overlapped overeach other and a spaceris placed between the two -
1-Equalize the voltage generator.
2-To minimize skin effect of ac current so small cross section of conductor is used and also
hollow conductorareused to effectcolling by D.M. water.
3. Crossover Insulation :
The pre insulation of the copper conductor may get damaged due to mechanical
bending in die during transposition, hence the insulating spacers are provided at the
crossover portion of the conductors. A filler material (insulating putty or moulding
micanite) is provided along the height of the bar to maintain the rectangular shape
and to cover the difference of level of conductors.To eliminate inter turn short at
bends during edges wise bending and leveling of bars in slots portion for proper
4. Stack Consolidation :
The core part of the bar stack is pressed in press (closed box) under pressure
(varies from product to product) and temperature of 160 C for a given period. The
consolidated stackis withdrawn from the press and the dimensions are checked.
5. Inter Strand Short Test:
The consolidated oar stack is tested for the short between any two conductors in the
bar, if found then it has to be rectified.This is done to ensure that no local current is
flowing due to shortcircuit between conductors.(300A/C supply)
6. Forming :The straight bar stack is formed as per overhang profile (as per
design), The overhang portion is consolidated after forming.
7. Brazing of coil lugs :
For water cooled generator bars, the electrical connection contact and water box for
inlet and outlet of water are brazed.
8. Nitrogen Leak Test :
The bar is tested for water flow test, nitrogen leak test and pressure test for given
9. Thermal shock test:
The cycles of hot (80C) and cold (30°C) water are flew through the bar to ensure the
thermal expansionand contractionofthejoints.
10. Helium leakage test:
After thermal shocktestbaris tested forany leakage with the help ofhelium gas.
The bar is insulated with the given number of layers to build the wall thickness of
insulation subjected to the generating voltage ofthe machine.
12. Impregnation and baking:
a) Thermoreactive system: In case of rich resin insulation the bar is pressed in
closed box in heated condition and baked under pressure and temperature as per
requirement fora given period.
b) Micalastic system: In case ofpoor resin system the insulated bars are heated under
vaccum and the impregnated (dipped) in heated resin so that all the air gaps are filled,
layer by layer, with resin. Then extra resin is drained out and bars are heated and
baked underpressedconditionin closed boxfixture.
VPI Micalastic system: The bars already laid in closed fixture and full fixture is
impregnated (dipped) in resin and then fixture with box is baked under given
temperature forgiven duration.
VIP Micalstic system: The individual (separate) bar is heated in vaccum and
impregnated in resin. Then bar is taken out and pressed in closed box fixture and then
baked at given temperaturefor given duration.
The baked and dimensionally correct bars are sanded-off to smoothen the edges and
the surfaceis calibrated, if required, forthe dimension.
14. Conducting varnish coating:
i) OCP (Outer Corona Protection) coating: The black semi-conducting varnish
coating is applied on the bar surfaceonthe corelength.
ii) ECP (End Corona Protection) coating: The grey semi-conducting varnish is
applied at the bend outside core end of bars in gradient to prevent from discharge
and minimize the end corona.
a) Tan@ test: This test is carried out to ensure the healthiness of dielectric
(Insulation) i.e. denseor rare and measured the capacitanceloss.
b) H.V. Test: Eachbar is tested momentary at high voltage increased gradually to three
times higher than rated voltage.
16. Dispatched for Winding :
The bars preserved with polythene sleeves to protect from dust, dirt, oil, rain etc are
send to Block-I (Electric Machines Production Block - I, Turbo Generators and Hydro