bhel training report
DESCRIPTION
bhel vt training ffileTRANSCRIPT
TRAINING REPORT ON
Manufacturing process of 600 MW stator bars
Six Weeks INDUSTRIAL TRAINING AT
BHARAT HEAVY ELECTRICALS LIMITED RANIPUR , HARIDWAR (UTTARAKHAND)
Submitted To: Submitted By:Er. Satish Kumar Singh VikashBLOCK-1BHEL HARIDWAR
DeenBandhu Chhotu Ram University of Science & TechnologyMurthal, Sonepat, Haryana
ACKNOWLEDGEMENT
“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.
CONTENTS:
INTRODUCTION.
BHEL - A Brief Profile.
BHEL - An Overview.
HEAVY ELECTRICAL EQUIPMENT PLANT (HEEP).
TURBO-GENERATOR
COIL AND INSULATION(BLOCK-4)
PROJECT UNDERTAKEN (DETAILS) -
MANUFACTURING PROCESS OF 600MW STATOR
BARS.
REFERENCES
INTRODUCTION
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 manufacture of electrical equipments.
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 “Forbes Asia Fabulous 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 transportation.
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 complete power stations on turnkey basis.
BHEL - A BRIEF PROFILE
BHEL is the largest engineering and manufacturing enterprise in India in the energy related infrastructure sector today. The wide network of BHEL's 14 manufacturing division, four power Sector regional centers, over 150 project sites, eight service centers and 18 regional offices, enables the Company to promptly serve its customers and provide them with suitable products, systems and services - efficiently and at competitive prices. While the company contributes more than 75% of the national grid, interestingly a share of 45% comes from its single unit. And this is none other than BHEL-HARIDWAR
BHEL has:-
Installed equipment for over 90,000MW of power generation--- for utilities captive and industrial users.
Supplied over 2, 25,000 MVA transformer capacity and other equipment operating in transmission and distribution network up to 400 kV (AC & DC).
Supplied over 25,000 motors with drive control systems to power projects, petrochemicals, refineries, steel, aluminum, fertilizers, cement plants etc.
Supplied Traction electrics and AC/DC locos to power over 12,000 kms railway network.
Supplied over one million valves to power plants and other industries.
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 1971-72.
BHEL's vision is to become a world-class engineering enterprise, committed to enhancing stakeholder value. The company is striving to give shape to its aspirations and fulfill the expectations of the country to become a global player.
BHEL business operations cater to core sectors of Indian Economy.
Power
Industry
Transportation
Transmission
Defenses etc.
The greatest strength of BHEL is its highly skilled and committed 60,000 employees. Every employee is given an equal opportunity to develop himself and grow in his career. Continuous training and retraining, career planning, a positive work culture and participative style of management all these have engendered development of a committed and motivated workforce setting new benchmarks in terms of productivity, quality and responsiveness.
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 capacity of 1,38,175 MW in the country , as against nil in 1969 -70. As part of India’s largest Solar Power-based Island Electrification Project in India, Bharat Heavy Electricals Limited (BHEL) has successfully commissioned two Grid-Interactive Solar Power Plants of 100 KW each in Lakshadweep. With this, the company has commissioned a total of eleven Solar Power Plants in the Lakshadweep islands, adding over 1 MW of Solar Power to the power generating capacity of the coral islands in the Arabian Sea.
BHEL has proven turnkey capabilities for executing power projects from concept to commissioning and manufactures boilers, thermal turbine generator sets and auxiliaries up to 500MW.
It possesses the technology and capability to procure thermal power generation up to 1000MW.
Co- generation and combined cycle plants have also been introduced.
For the efficient use of high ash content coal BHEL supplies circulating fluidized boiler.
BHEL manufacturers 235MW nuclear sets and has also commenced production of 500MW nuclear turbine generator sets.
Custom made hydro sets of Francis, pelton and kaplan types for different head discharge combination are also engineering and manufactured by BHEL.
In, all 700 utility sets of thermal, hydro, gas and nuclear have been placed on the company as on date. The power plant equipment manufactured by BHEL is based on contemporary technology comparable to the best in the world and is also internationally competitive.
The Company has proven expertise in Plant Performance Improvement through renovation modernization and up rating of variety of power plant equipment besides specialized know how of residual life assessment, health diagnostics and life extension of plants.
POWER TRANSMISSION AND DISTRIBUTION (T&D) ---
BHEL offer wide-ranging products and systems for T & 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 switch gears 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 Transmission System) project under execution.
INDUSTRY SECTOR -
BHEL is a major contributor of equipment and system to important industries like -
Cement Petrochemicals Fertilizers Steel papers Refineries Mining and telecommunication
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 Transmission System) projects is under execution.
The range of system and 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 Heat exchangers Process control etc.
TRANSPORTATION—
BHEL is involved in the development design, engineering, marketing, production, installation, and maintenance and after-sales service of Rolling Stock and traction propulsion systems. In the area of rolling stock, BHEL manufactures electric locomotives up to 5000 HP, diesel-electric locomotives from 350 HP to 3100 HP, both for mainline and shunting duly applications. BHEL is also producing rolling stock for special applications viz., overhead equipment cars, Special well wagons, Rail-cum-road vehicle etc., Besides traction propulsion systems for in-house use, BHEL manufactures traction propulsion systems for other rolling stock producers of electric locomotives, diesel-electric locomotives, electrical multiple units and metro cars. The electric and diesel traction equipment on India Railways are largely powered by electrical propulsion systems produced by BHEL. The company also undertakes retooling and overhauling of rolling stock in the area of urban transportation systems. BHEL is geared up to turnkey execution of electric trolley bus systems, light rail systems etc. BHEL is also diversifying in the area of port handing equipment and pipelines transportation systems.
TELECOMMUNICATION-
BHEL also caters to telecommunication sector by way of small, medium and large switching system.
HEAVY ELECTRICAL EQUIPMENT PLANT (HARIDWAR)
At Haridwar, against the picturesque background of Shivalik Hills, 2 important manufacturing units of BHEL are located viz. Heavy Electrical Equipment Plant (HEEP) & Central Foundry Forge Plant (CFFP). The hum of the construction machinery working started under Shivalik Hills during early 60s and sowed the seeds of one of the greatest symbol of Indo Soviet Collaboration - Heavy Electrical Equipment Plant. Consequent upon the technical collaboration between India and USSR in 1959, BHEL’s prestigious unit, Heavy Electrical Equipment plant (HEEP), was established in October, 1963, at Hardwar. It started manufacturing thermal sets in 1967 and now thermal sets of 210, 250 and 500 MW, including steam turbines, turbo-generators, condensers and all associated equipments, are being manufactured. This unit is capable of manufacturing thermal sets up to 1000 MW. HEEP-manufactured gas turbines, hydro turbines and generators, etc., are not only successfully generating electrical energy within and outside the country, but have also achieved a historic record of the best operational availability.
VISION
World-class , innovative, competitive and profitable engineering enterprise providing total global business solutions.
MISSION
The leading Indian engineering enterprise providing quality products systems and services in the fields of energy, transportation, infrastructure and other potential areas.
VALUES
Meeting commitments made to external and internal customers.
Foster learning creativity and speed of response.
Respect for dignity and potential of individuals.
Loyalty and pride in the company.
Team playing
Zeal to excel.
Integrity and fairness in all matters.
ESTABLISHMENT AND DEVELOPMENT STAGES:
Established in 1960s under the Indo-Soviet Agreements of 1959 and 1960 in the area of Scientific, Technical and Industrial Cooperation.
DRR - prepared in 1963-64, construction started from October '63
Initial production of Electric started from January, 1967.
Major construction / erection / commissioning completed by 1971-72 as per original DPR scope.
Stamping Unit added later during 1968 to 1972.
Annual Manufacturing capacity for Thermal sets was expanded from 1500 MW to 3500 MW under LSTG. Project during 1979-85 (Sets up to 500 MW, extensible to 1000/1300 MW unit sizes with marginal addition in facilities with the collaboration of M/s KWU-Siemens, Germany.
Motor manufacturing technology updated with Siemens collaboration during 1984-87.
Facilities being modernized continually through Replacements / Reconditioning-Retrofitting, Technological / operational balancing.
CLIMATIC AND GEOGRAPHICAL CONDITIONS:
Haridwar is in extreme weather zone of the UTTARAKHAND and temperature varies from 2oC in Winter (December to January) to 45oC in Summer (April-June); Relative humidity 20% during dry season to 95-96% during rainy season.
Longitude 78o3' East, Latitude 29 o55'5" North.
Height above Mean Sea 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 Factory area.
HEEP is located around 7 KMs on the Western side of Hardwar city.
POWER & WATER SUPPLY SYSTEM:
40 MVA sanctioned Electric Power connection from UPC Grid (132 KV / 11KV / 6.6 KV) (Connected load - around 185 MVA)
26 deep submersible Tube Wells with O.H. Tanks for water supply.
A 12 MW captive thermal power station is located in the factory premises.
MAIN PRODUCTS:
Steam Turbines Hydro Turbines Gas Turbines Turbo Generators Medium Size Motors.
DIFFERENT BLOCKS AT HEEP-PLANT FACILITES:
S.No. Area/ Block Major Facilities Products
1. Block -I
(Electrical
Machines)
Machine Shop.,
Windings bar
preparation assembling,
painting section,
packing& preservation,
over speed balancing,
test bed test stand,
babbiting, micalastic
impregnation etc.
Turbo
Generator,
Generator
exciters, motors
(AC& DC)
2. Block - II
(Fabrication
Block)
Markings, welding
,Cutting, straightening,
gas cutting press, ,
grinding, assembly, heat
treatment, cleaning &
Shot blasting,
machining, fabrication
of pipe coolers, painting
Large size
fabricated
assemblies/
components for
power
equipments
3. Block -III
(Turbines &
Auxiliary Block)
Machining, facing wax
melting, broaching,
assembly preservation &
packing, test stands/
station, painting
grinding, milling,
polishing etc.
Stem turbines,
hydro turbines,
gas turbines,
turbine bladders,
special tooling.
4. Block -IV
(Feeder Block)
5. Block - V
Bar winding, mechanical
assembly, armature
winding, sheet metal
working marching,
copper profile drawing
electroplating,
impregnation,
machining & preparation
of insulating
components plastic
molding, press molding
Fabrication, pneumatic
hammer for forgings,
gas fired furnaces,
hydraulic manipulators
Windings for
turbo
generators,
hydro
generators
insulation for AC
& DC motors,
insulating
components for
TG, HG & Motors
control panel,
contact relays
master control
etc.
Fabricated parts
of steam
turbine, water
box, storage
tank hydro
turbine parts,
hydro turbines
assemblers &
Components
6. Block - VI
(Fabrication)
7. Block- VI
(Stamping & Die
Manufacturing)
8. Block- VII (wood
working)
9. Block - VIII
Welding, drilling, shot
blasting, CNC flame
cutting ,CNC deep
drilling, Shot basting,
sheet metal work,
assembly
Machining, turning,
grinding, jig boring
stamping presses, de
varnishing, degreasing
& de rusting, varnishing
sport welding, painting.
Wood Cutting,
machines, grinding ,
packing
Drilling ,turning, saw,
cutting, welding, tig
welding
Fabricated parts
of steam turbine
water box,
stronger tanks,
hydro turbine
parts, Hydro
turbines
assemblies &
components,
Wooden packing,
spacers etc.
Wooden packing,
spacers etc.
LP Heater
ejectors glad,
steam cooler oil
coolers, ACG
collers, oil tanks,
bearing covers.
10. Services plat TPS : Power generation Power
equipment & auxiliaries generation
plat capacity 12 MW
PGP Plat : Boiler Type Producer gas
gas generators
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
compressors
Acetylene gas
Compressed air
Oxygen gas
Nitrogen gas
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
allied equipment
11. Motor transport
12. Telecommunication
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
communication
3 no Satellite exchange
13. Hydro Turbine Lab 3 test beds with Testing of
electronic turbine models
instrumentation. It
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
electrical work
carpentry work
15. Engineering
16. Computer Center
17. CPL (Central plant
Lab.)
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
etc.
Testing Lab for new Testing of
materials & sample components
components
ELECTRICAL MACHINES BLOCK (BLOCK-I)
INTRODUCTION---
Block-I is designed to manufacturing Turbo Generators, Hydro generators and large and medium size AC and DC Electrical machines.
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 components /assemblies.
Conventional bay -wise broad distribution of products is as
BAY-
1
BAY-
2
follows :
ROTORSHAFTMACHINING
EXCITERSHAFTMACHINING
ROTOR SHAFTSLOTTING
STATOR BODY MACHINING
ROTOR OVER SPEEDWINDING AND
BALANCINGTUNNEL
STATOR TOTALWINDING IMPREGNATION
LARGE SIZETURBOGENERATORS
TEST BED
BAY—
3
ROTORSUPPORTBEARING
SHAFT SEAL BODY
DCMOTOR WINDING (EARLIER)
BAY—
4COOLINGFANSMACHINING
ARRANGEMENTAND OTHER PARTS
BASIC TURBO GENERATOR DEPARTMENTS: -
MACHINE SHOP. T/G ROTOR WINDING. H/G IRON ASSEMBLY. EXCITER. 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. TEST BED.
TURBO GENERATOR
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 A.C. voltage.
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 Generator.
LSTG AREA
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:-
1. THRI 2. TARI 3. THDI 4. THDD 5. THDF 6. THFF
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
R= radial,
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. :-
STATOR -
1. Stator frame
2.Stator core
3.Stator winding
4.End covers.
ROTOR -
1. Rotor shaft 2. Rotor windings 3. Rotor retaining rings
BEARINGS
COOLING SYSTEM
EXCITATION SYSTEM
STATOR
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.
STATOR FRAME
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.
STATOR CORE:-
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.
STATOR WINDING:-
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 turns. 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 sleeve.
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 skin effect.
INSULATION OF BARS:-
A. Vacuum pressed impregnated micaclastic high voltage insulation:-
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 overhang.
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 temperature”
END COVERS:-
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 individual bars.
Armature Section:-
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.
Cooling:-
Heat losses arising in the generator are dissipated through hydrogen. The heat dissipating capacity of hydrogen is eight times to that of air.
ROTOR
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.
ROTOR SHAFT:-
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:-
SHAFT 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.
SLOTTING:-
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.
ROTOR WINDING:-
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
Coils separated.
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 slots.
Then the coils placed in the slots and tighten up to prevent the loosening by tightening rings.
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 turbogenerators.
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 and cold.
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 or stator.
Conductor material:-
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.
Insulation:-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 threaded pin.
BEARINGS -
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 operation.
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 current.
ROTOR ASSEMBLY:-
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.
MACHINE SECTION:-
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:-
VENTILATION 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 high level.
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.
BLK-I
EXCITATION SYSTEM:-
EXCITER:-
EXCITER ROTOR
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 shaft end.
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 exciter.
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.
RECTIFIER WHEELS
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 diode fails. 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.
COOLING SYSTEM
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 detection.
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 current
BAY IV (SMALL AND MISCELLANEOUS COMPONENTS)
Facilities available in the various sections are as follows:-
MACHINE SECTION:-
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
COILING 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 poles.
1. ANNEALING PROCESS:-
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 to winding.
This process is carried out in the annealing furnace.
2.WINDING PROCESS:-
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.
NOTE:-
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.
3.BRAZING:-
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.
4. PRESSING:-
Pressing of coil is done by hydraulic pressure of 800 tons. This process is carried out in order to remove wrinkles from the
coil. 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.
5. FIXING:-
Fix the accessory on the stretching machine. Put the coil on the stretching machine& pull the coil to the
drawing dimensions. Dress the conductors along periphery & take out the coil. Check window dimensions as per drawing.
6. SEPARATION:-
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.
7. PICKLING:-
Send the coil for pickling to block 4 & check the quality of pickling.
Press the coil again after pickling then remove pressure and take out.
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
joint. Remove extra material and check thickness of the gauge. Check the distance from center axis of pole coil as per drawing.
8. FINISHING:-
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.
9. 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 40 minutes.
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.
IMPREGNATION 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.
BABBITING SECTION:-This section is equipped with alkaline degreasing baths, hot and cold rinsing baths, pickling baths, tinning bath, and electric furnaces and centrifugal
Shot Blasting babbitting machines, Babbitting of bearing liners for Turbo generators, Turbines, Hydro generators, AC motors and DC motors is carried out in this section.
TEST STAND:
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 -
PURPOSE -
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 explosion.
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 pressure.
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 of motor stator coil, DC armature coil, main pole
Coil , inter-pole coil, equalizer coil etc. BAY-3: Insulating detail shop: Manufacturing of hard insulation &
machining of hard insulation part such as packing, washer, insulation box, wedges etc.
Bar Shop: This shop is meant for manufacturing of stator winding coils of generator that may be turbo-generator or hydro-generator.
Why do we call it bar: It is quite difficult to manufacture, handle and wind the coil in stator slot of generator of higher generation capacity because of its bigger size and heavy weight. That is why we make coil in two parts. One part is bottom part of coil called bottom or lower bar and other part of coil is called top bar or upper bar.
HG bars: The manufacturing of bars of different capacity as required by the consumer depends upon the water head available at site. The Hydro generator is air cooled generator of lesser length in comparison to 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 technology to manufacture 800MW and 1000MW generators.
Insulation Classification: Thermal classification of insulation depends upon the temperature withstand capacity of the insulation. 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- H upto 180’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 generator such as:
THRI TARI THDI THDD THDF THFF
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
R= radial,
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
Resin system: a) Rich resin or Thermoreactive insulation system: In this type of
insulation system the bond content in resin is 35-37%. The raw materials are ready to use and require preservation and working on temperature 20-25’c. its shelf life is one year when kept at temperature 20’c which could be increased when kept at temperature of 5’c.
b) Poor resin or Micalastic insulation system: In this type of insulation
the bond content in the resin is 5-7% and insulation material is prepared with accelerator treatment. The temperature control need not required. The insulating material is applied on job and then the same is impregnated in the resin.
TURBO GENERATOR
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.
STATOR WINDING IN TURBO GENERATOR
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 turns. 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 sleeve. 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 skin effect.
PROJECT:
MANUFACTURING PROCESS OF 600 MW TURBO-GENERATOR STATOR WINDING BAR-:-
FLOW CHART OF THE PROCESS:
Conductor Draw from Store.
Conductor cutting and end cleaning.
Transposition of conductor.
Assembly of all conductors to be used in stator Bars.
Cross over insulation.
Consolidation if slot portion of Bar.
I.S. Test (i.e. inter strand test).
Forming or Bar (to shape overhang portion).
Pickling of bar ends (1)
Mounting of Contact sleeve & bottom part of water box.
Brazing of Contact sleeve & bottom part of water box.
Pickling of bar ends (2)
Mounting of water box leak test.
Repickling.
Water flow and N2 test.
Thermal Shock Application.
Helium Leak Test.
Reforming of Bar. (i.e. overhang portion).
Insulation of bar on CNC machine.
Impregnation an curing of bar insulation.
Surface finishing of stator bar.
OCP on stator Bar.
Preparation of bar for HV and TanQ Test.
If O.K. Dispatch to Block-1 for laying in the generator.
CONDUCTOR BARS
MFG PROCESS:
CUTTING:
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 both ends of the conductor cut.
Cutting size of conductor :
Set type Conductor length Dimension No. of Sharingconductors
210 MW
500 MW
upper: 7000 mm
lower: 7300 mm
upper: 10050 mm
lower: 10200 mm
solid: 7.4*2.1
hollow: 7.4*5*1.5Lower : 8*2.8
solid: Upper: 8*1.3
hollow: 8*4.6*1.5
solid: 28
hollow: 14
Lower:Solid: 10hollow: 10Upper:solid:20hollow:10
300 bothends
500 both ends
600 MW upper: 10887 mm
lower: 11053 mm
solid: 9.5*1.2
hollow: 9.5*4.4*1.3
solid: 28
hollow: 14
250 MW(THRI) 8200 mm Solid : 10.5*1.8 conductors:
80
Exciter500 MW
upper: 1680 mm
lower: 1620 mm
Solid: 4.6*1.6110 both
conductors: ends24
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 are given to the conductors with the help of bending die at required distance. Then the conductors are taken out from the comb and die and placed with their ends in a line and transposition is carried out. This process is repeated for making another half of the bar which would be mirror image of the first half. The two halves of the bar are overlapped over each other and a spacer is placed between the two -halves. 1-Equalize the voltage generator. 2-To minimize skin effect of ac current so small cross section of conductor is used and also hollow conductor are used to effect colling by D.M. water. 3-To reduce the eddy current loses.
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
stack pressing.
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 stack is 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 short circuit between conductors.(300 A/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
duration.
9. Thermal shock test:
The cycles of hot (80C) and cold (30°C) water are flew through the bar to ensure the
thermal expansion and contraction of the joints.
10. Helium leakage test:
After thermal shock test bar is tested for any leakage with the help of helium gas.
11. Insulation:
The bar is insulated with the given number of layers to build the wall thickness of
insulation subjected to the generating voltage of the 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 for a given period.
b) Micalastic system: In case of poor 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 under pressed condition in closed box fixture.
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 for given 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 temperature for given duration.
13. Finishing:
The baked and dimensionally correct bars are sanded-off to smoothen the edges and
the surface is calibrated, if required, for the dimension.
14. Conducting varnish coating:
i) OCP (Outer Corona Protection) coating: The black semi-conducting
varnish coating is applied on the bar surface on the core length.
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.
15. Testing:
a) Tan@ test: This test is carried out to ensure the healthiness of dielectric
(Insulation) i.e. dense or rare and measured the capacitance loss.
b) H.V. Test: Each bar 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
Generators) for winding.
REFERENCES
B.H.E.L. MANUALS
B.H.E.L. Websites
Electrical machines – P.S. BIMBHRA.