manufacturing process of 500MW turbo generator

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PREFACE

Practical knowledge means the visualization of the knowledge, which we read in our books. For this, we perform experiments and get observations. Practical knowledge is very important in every field. One must be familiar with the problems related to that field so that he may solve them and become a successful person. After achieving the proper goal in life, an engineer has to enter in professional life. According to this life, he has to serve an industry, may be public or private sector or self-own. For the efficient work in the field, he must be well aware of the practical knowledge as well as theoretical knowledge. To be a good engineer, one must be aware of the industrial environment and must know about management, working in the industry, labor problems etc. so he can tackle them successfully. Due to all the above reasons and to bridge the gap between theory and practical, our engineering curriculum provides a practical training of 30 days. During this period, a student works in the industry and gets all type of experience and knowledge about the working and maintenance of various types of machinery.

I have undergone my summer training (after 3rd yr.) at BHARAT HEAVY ELECTRICALS LIMITED. This report is based on the knowledge, which I acquired during my training period at the plant.

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ACKNOWLEDGEMENT

With a sense of great pleasure and satisfaction I present this industrialI ItrainingI IreportI IentitledI IasI I“I ,LCSCUIKILRCNOK ELECTRICALS LIMITED (GtE6aLtE) (or(AO83WXMSO1(OU(MDSN( reportI IisI InoI IdoubtI IaI IproductI IofI IinvaluableI IsupportI Iand contribution of a number of people.

present my sincere gratitude to Mr. S.N.Luthra (DGM) , MR. U.K.Singh (MGR), Mr.M.S.Rawat(Technical Head of Block 1) of BHEL for being a constant guide, inspiration and a source of illumination throughout this entire period. Without their support this would not have been possible.

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INDEX

S.NO 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

PARTICULARS

PAGE

CHAPTER 1 INTRODUCTION CHAPTER 2- BHEL ,A BRIEF PROFILE CHAPTER 3-BHEL,AN OVERVIEW CHAPTER 4-BHEL BLOCKS CHAPTER 5-BHEL LAYOUT CHAPTER 6-ELECTRICAL MACHINES(BLOCK 1)

4-5

CHAPTER 7-TURBOGENERATORS CHAPTER 8-BAR WINDINGS CHAPTER 9-FAILURE OF GENERATOR STATOR CONDUCTOR S CHAPTER 10-FEATURES AND SPECIFICATION S CHAPTER 11-GENERATOR STAMPING CONCLUSIO N

16-25

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26-32 33-37 38-40 41-43 44

NOS.

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CHAPTER 1 INTRODUCTION

In 1956, India took a major step towards the establishment of its heavy engineering industry when Bharat Heavy Electrical Ltd., the first heavy electrical manufacturing unit of the country was setup at Bhopal. It progressed rapidly and three more factories went into production in 1965. The main aim of establishing BHEL was to meet the growing power requirement of the country. B.H.E.L appeared on the power map of India in 1969 when the first unit supplied by it was commissioned at the Basin Bridge Thermal Power Station in Tamil Nadu. Within a decade, BHEL had commissioned the 100th unit at Santaldih. West Bengal. BHEL had taken India from a near total dependence on imports to complete self-reliance in this vital area of power plant equipment BHEL has supplied 97% of the power enerating equipment. BHEL has already supplied generating equipment to various utilities capable of generating over 18000 MW power. Today BHEL can produce annually; equipment capable of generating 6000MW. This will grow further to enable BHEL to meet all of India.s projected power equipment requirements. As well as sizeable portion of export targets. 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 time a philosophy that has led to the development of a total capability fromconcepts to commissioning not only in the field of energy but also in industry transportation and . SRMCEM,LUCKNO W

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In the world power scene, BHEL ranks among the top ten manufactures of power plant equipment and in terms of the spectrum o0f 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 the world over have placed orders with BHEL coverin individual equipment to complete power stations on a turnkey basis. In 1978-79 export earnings reached Rs. 122 crores, the highest for any one-year. BHEL has its headquarters at New Delhi. Its operations are spread over 11 manufacturing plants and number of engineering and service divisions located across the country/ the service divisions includes a network of regional branch offices throughout India.

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CHAPTER 2 BHEL-A BRIEF PROFILE BHEL is the largest engineering and manufacturing enterprise in India in the energy-related/infrastructure sector, today. BHEL is ushering in the indigenous Heavy Electrical Equipment industry in India-a dream that has been more than realized with a well-recognized track record of Performa A widespread network comprising of 14 manufacturing companies, which have international recognition for its commitment towards quality. With an export presence in more than 60 countries, BHEL is truly India.s industrial ambassador to the world. BHEL.s vision is to become a world class engineering enterprise, committed to enhancing stakeholder value.

BHEL has: Installed equipment for over 90,000MW of power generation.for Utilities, captive and Industrial users.   Supplied over 25000 Motors with Drive Control System to powe r projects, Petrochemicals Refineries, Steel, Aluminum, Fertilizer, Cement plant, etc.   Supplied Traction electrics and AC/DC locos over 12000 kms Railway network.   Supplied over one million Values to Power Plants and other Industries.\ 

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CHAPTER 3 BHEL-AN OVERVIEW

The first plant of what is today known as BHEL was established nearly 40 years ago at Bhopal & was the genesis of the Heavy Electrical Equipment industry in India. BHEL is today the largest Engineering Enterprise of its kind in India with excellent track record of performance, making profits continuously since 1971-72. BHEL business operations cater to core sectors of the Indian Economy like:Power Industry Transportation Transmission Defenses etc.. Today BHEL has • 14 Manufacturing Divisions • 9 Service Centers • 4 Power Sector Regional Centers • 150 Project sites

BHEL. vision is to world-class engineering enterprise, committed to enhancin stakeholder value. The greatest strength of BHEL is its highly skilled and committed 44,000 employees. Spread all over India & abroad to provide prompt and effective service to customers.

3.1 BUSINESS SECTOR BHEL operations are organized around business sectors to provide a stron market orientation. These business sectors are Power Indus and International operations.

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3.2 POWER SECTOR Power sector comprises of thermal, nuclear, gas and hydro business. Today BHEL supplied sets account for nearly 65% of the total installed capacity in the country as against nil till 1969-70. • BHEL has proven turnkey capabilities for executing power projects from concept to commissioning and manufactures boilers, thermal turbine generator set and auxiliaries up to 500MW. • It possesses the technology and capability to procure thermal power generation equipment up to 1000MW. • Co-generation and combined cycle plants have also been introduced. • For efficient use of the high ash content coal-BHEL supplies circulating fluidized boiler.

BHEL manufactures 235MW nuclear sets and has also commenced production of 500MWnuclear set. Custom-made huge hydro sets of Francis, Elton and Kaplan types for different headdischarge combinations are also engineered and manufactured by BHEL.

3.3 INDUSTRY SECTOR BHEL is a major contributor of equipment and system to important industries like • Cement • Petrochemicals • Fertilizers • Steel paper • Refineries • Mining and Telecommunication •

The range of system and equipment supplied including captive power stations

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•

High speed industrial drive turbines

•

Industrial boilers and auxiliaries

•

Waste heat recovery boilers

•

Gas turbines pump, valves, seamless steel tubes

•

Heat exchangers

•

Process control etc.

3.4 TRANSPORATION :BHEL supplies a wide equipment and system to Indian Railways. • Electric locomotive • Traction electric and traction control equipment

3.5 TELECOMMUNICATION:BHEL also caters to Telecommunication sector by way of small, medium and large switching system.

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CHAPTER 4 BHEL-BLOCKS BHEL has divided into many blocks:-

1). Block1:-

In block one turbo generator, generator, exciter motors (A.C & D.C) manufactured & are assembled

2). Block2:-

In block two large size fabricated assemblies\component for power equipment manufactured & are assembled.

3) BlockIn 3:-block -3 steam turbine, hydro turbines, and gas turbines, turbines blade manufactured & are assembled

4) Block4:-

In block -4winding for turbo generator, hydro generator, insulation of motors insulating component for turbo generator, hydro generator motors A.C&D.C manufactured & are assembled

5) Block5:-

In block -5 fabricated parts of steam turbine water box, hydro turbine parts are manufactured & turbines assembled

6) Block6:-

In block -6 fabricated oil tanks hollow guide blades, rings, stator frames spiders are manufactured & rotor assembled

7) Block7:In block -7all types of dies including stamping dies, stamping for &motors are manufactured & generators assembled

8) Block8:-

In block -8 LP heaters, ejectors, steam coolers, oil coolers, ACG coolers, oil are manufactured & tanks assembled. SRMCEM,LUCKNO W

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CHAPTER 5 BHEL-LAYOUT

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CHAPTER ELECTRICAL MACHINES BLOCK 1(BL1)

6.1 INTERODUCTION 1. Block-1 is designed to manufacture hydro-generators and large and medium size AC and DC Electrical machines. Equipment layout plan is as per drawing No.003 appended in section lll. 2. The Block consists of 3 Bays: Bay-1(36*482 meters), Bay- 2, (36*360 meters) and Bay-3 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 inter-bay movements of components/assemblies

3. Conventional Bay-wise broad distribution of products is as Follows:

LSTG Area Generators

Large Size Turbo

BAY-1

hydro generators, their exciters;PMG and Large size turbo generators

BAY-2

Turbo-generators, their exciters and Heavy Electrical Motors

BAY-3

Medium size Electrical Motors

4. Testing facilities for turbo generators and heavy motors are available in bat-2 and for medium size motors in bay-3 5. There is a special test bed for testing of T.G. of capacity of 500 MW units sizes and above.

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There are three BAY in BLOCK 1 BAY-I [Hydro Machine Section Generator]    Assembly Section   Stator windin 

BAY-II [Turbo Machine Section Generator]                

Iron Assembly Heavy Rotor Assembly Section Stator winding Section Armature/Rotor Section Armature/Rotor Impregnation Section General Assembly Section Test Stands

BAY-III [Medium Size Motors]  Machine Section                 

Iron Assembly Section Commutator Section Pole Core Section Painting Section Bus bar & filling Section Winding Section General Assembly Section Test Stand

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6.2 Bay-1 (A) LARGE SIZE TURBO GENERATORS (LSTG AREA) Following facilities are available in different sections of this area:a. Stators core assembly section: - Two number 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. b. Stator winding section: - The section is located in dust-proof enclosure and equipped with one number-winding platform with two number rotatin installations for assembly of winding. Resistance brazing machines and high voltage transformer are also available in this section. c. Rotor assembly section: - This section is also in a dust-proof enclosure with number of rotators, rotors bar laying facilities and MI heating and mounting of retaining rings, rotor winding assembly and rotor assembly like retaining rin fitting, four assemblies are carried out in this section. d. Bar preparation section: - This section consist of milling machine for lon preparation, installation for insulation of tension bolts for stator and preparation of stator winding before assembly. e. Test bed section: - This section this section is equipped with bedplates, height blocks, supporting blocks and 12MW drive motors. Large size turbo generators and exciters are assembled and tested in this section.

6.3 Bay-2 (B)Heavy Electrical Motors:The following are the main sections:(a.)Machine section: -

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 machinin stator body, rotor shaft end shields, bearing etc. for turbo-generators. SRMCEM,LUCKNO W

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(b.) Iron assembly section: This section has facilities for stator core assembly of turbo-generators and heavy electrical motors. 1000T and 250T umbrella type presses for pressing the cores and transformers for induction heating of the armature core of large size electric motor are available in this section. (c.) Armature section: This section is equipped with installations like bandaging m//c, tensioning devices, and magnetic putty application machine and 45KW MF brazing m/c for laying windows in large size DC armatures. (d.) General assembly section: General assembly of large size AC and DC motors is carried out in this section.

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CHAPTER 7 TURBO-GENERATOR

Bharat Heavy Electrical Limited (BHEL) is the largest Engineering and manufacturing Enterprise of it kind in the Public Sector in India. It ranks among the top twelve organizations in the world, engaged in the manufacture of power generation equipment.

BHEL, Haridwar manufactured turbo generators of ratings upto 210MW or even 250MW for industrial applications and for power generation. Now Turbo generators of rating as high as 500MW are being manufactured for the power generation purpose. The 500MW turbo generator being manufactured is the project given by the Reliance Power. These turbo generators are supplied together with the turbines and matching excitation systems, and are used mostly in paper, sugar, cement, petrochemical, fertilizers, rayon industries etc, and thermal power stations.

The general components of a turbo generator are SRMCEM,LUCKNOW

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•

Stato r

 Stator Frame  Stator Core  Stator Windings  End Covers

•

Rotor  Rotor Shaft  Rotor Windings  Rotor Retaining Rings

•

Bearing s

•

Cooling System

•

Excitation

STATOR Stator Frame

The stator frame is of welded steel single piece construction. It supports the laminated core and winding. It has radial and axial ribs having adequate strength and rigidity to minimize core vibrations and suitably designed to ensure efficient cooling. Guide bars are welded or bolted inside the stator frame over which the core is assembled. Footings are provided to support the stator foundation.

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Stator Core The stator core is made of silicon steel with high permeability and low hysteresis and eddy current Losses. The sheets are suspended in the stator frame from insulated guide bars. Stator laminations are coated with synthetic varnish; are stacked and held between sturdy steel clamping plates with non-magnetic pressing fingers which are fastened or welded to the stator frame.

In order to minimize eddy current losses of rotating magnetic flux which interact with the core is built of thin laminations. Each lamination layer is made of individual segments. The segments are punched in one operation from electrical sheet steel lamination having a high silicon content and are carefully deburred. The stator laminations are assembled as separate cage core without the stator frame. The segments are staggered from layer to layer so that a core of high mechanical strength and uniform permeability to magnetic flux is obtained. On the outer circumference the segments are stacked on insulated rectangular bars which hold them in position.

To obtain optimum compression and eliminate looseness during operation the laminations are hydraulically compressed and heated during the stacking procedure. To remove the heat, spaced segments are placed at intervals along the core length which divide the core into sections to provide wide radial passages for cooling air to flow.

Stator Winding Construction

The stator windings consist of two layers made of individual bars. To minimize losses, bars are composed of separately insulated strands which are transposed by 360 degrees. To minimize stray losses in end windings, strands of top and bottom bars are separately brazed and insulated from each other.

Each bar consists of a large number of separately insulated strands to reduce the skin effect losses. In straight slot portion, the strands are transposed by 360 degrees. The transposition provides for mutual neutralization of voltages induced in the individual strands due to slot cross field and ensures that no or small circulating currents exist in the bar interior. The current

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flowing through the bar is thus distributed uniformly over the entire cross section of a bar so that the current dependent losses will be reduced.

INSULATION OF BARS High voltage insulation is provided with thermosetting system. A voltage insulation obtained by vaccum press impregnation is particularly void free with excellent electrical, mechanical and thermal properties. To prevent corona discharge between the insulation and slot wall, a final layer of conductive tape is applied to the surface of all bars within the slot range. All bars are conditionally provided with an end corona protection to control the electric filed at the transition from slot to the end winding portion and to prevent the formation of creepage sparks.

(A) Vaccum Press Impregnated Micalastic High Voltage Insulation

The high voltage insulation is provided according to the proven resin poor mica base of thermosetting epoxy system. Several half overlapped continuous layer of resin poor mica type are applied over the bars. The number of layers or thickness of insulation depends on machine voltage.

The bars are inserted into the slots with very small lateral clearance and wedged with packers. To prevent moment of end windings in circumferential direction, spacer blocks are arranged between the bars and firmly with treated glass tapes. To minimize the effect of radial forces, winding holders and insulated rings are used to support the overhang.

The stator is impregnated in a tank under vaccum and pressure with low viscosity epoxy resin that penetrates the winding thoroughly. After impregnation, the stator is cured at at appropriate temperature in an oven.

The high voltage insulation thus obtained is characterized by its excellent electrical, mechanical and thermal properties. Its moisture absorption is extremely low and it is oil resistant. The behavior of the insulation is far superior to any other conventional mica tape insulation system.

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(B) Corona Protection

To prevent a potential difference and possible corona discharges between the insulation and slot wall, the slot sections of bars are provided with an outer corona protection. This protection consists of polyester fleece tape impregnated in epoxy resin with carbon and graphite as filters.

At the transition from slot to the end winding portion of stator bars a semiconductive tape made of polyester fleece is impregnated with silicon carbide as filler is applied for a specific length. This ensures uniform control of the electric field and prevents the formation of corona discharge during operation and performance of HV tests.

End Covers

The end covers are made of fabricated steel or aluminum alloy castings. They are employed with guide vanes on inner side for ensuring uniform distribution of cooling air or gas.

ROTOR Solid rotors are manufactured from forged alloy steel with suitable alloying elements to achieve very high mechanical and superior magnetic properties. Rectangular or trapezoidal rotors slots are accurately machined to close tolerances on slot milling machine. For indirectly cooled enerator rotors, ventilation slots are machined in the teeth.

For directly cooled rotors, Sub slots are provided for cooling Generators rotors of 1500 RPM are of round laminated construction. Punched and varnished laminations of high tensile steel are mounted over machined shaft are firmly clamped by end clamping plates.

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Rotor Shaft Rotor shaft is a single piece solid forming manufactured form a vaccum casting. It is forged from a vaccum cast steel ignot. Slots for insertion or the field winding are milled into rotor body. The longitudinal slots are disturbed over the circumference such that two solid poles are obtained.

To ensure that only a high quality product is obtained, strength tests, material analysis and ultrasonic tests are performed during the manufacture of rotor. The high mechanical stresses resulting from the centrifugal forces and short circuit torque call for a high specified mechanical and magnetic properties as well as homogeneous forging. After completion, the rotor is balanced in various planes at different speeds and then subjected the rotor is balanced in various planes at different speeds and then subjected to an over speed test at 120% of the rated speed for two minutes.

The rotor consists of electrically active portion and two shaft ends. Approximately 60% of rotor body circumference has longitudinal slots which hold the field winding. Slot pitch is selected so that the two solid poles are displaced by 180 degrees. The rotor wedges act as damper winding within the range of winding slots. The rotor teeth at the ends of rotor body are provided with axial and radial holes enabling the cooling air to be discharged into the air gap after intensive cooling of end windings

Rotor Winding The windings consist of several coils inserted into the slots and series connected such that two coil groups form one pole. Each coil consists of several series connected turns, each of which consists of two half turns connected by brazing in the end section. The rotor bearing is made of silver bearing copper ensuring an increased thermal stability. The individual turns of coils are insulated against each other by interlayer insulation.

The slot wedges are made o high electrical conductivity material and thus act as damper windings. At their ends the slot wedges are short circuited through the rotor body.

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 Constructio n The field winding consists of several series connected coils inserted into the longitudinal slots of rotor body. The coils are wound so that two poles are obtained . The solid conductors have a rectangular cross section and are provided with axial slots for radial discharge or cooling air. All conductors have identical copper and cooling duct cross section. The individual bars are bent to obtain half turns. After insertion into one slot constitute one coil. The individual coils of rotor are connected in a way that one north and one south pole is obtained.

 CONDUCTOR MATERIAL

The conductors are made of copper with a silver content of approximately 0.1%. As compared to electrolytic copper, silver alloyed copper features high strength properties at high temperatures so that coil deformations due to thermal stresses are eliminated.

 INSULATIO N The insulation between the individual turns is made of layer of glass fiber laminate. The coils are insulated from the rotor body with L- shaped strips of glass fiber laminate with nomex interlines. To obtain the required leakage paths between the coil and rotor body thick top strips of glass fiber laminate are inserted below top wedges. The top strips are provided with axial slots of the same cross section and spacing as used on the rotor winding.

 ROTOR SLOT WEDGES

To protect the winding against the effects of centrifugal forces, the winding is secured in the slots with wedges. The slot wedges are made of copper alloy featuring high strength and good electrical conductivity. They are also used as damper winding bars. The slot wedges extend beyond the shrink seats of retaining rings. The wedge and retaining rings act on the damper winding in the event of abnormal operations. The rings act as a short circuit rings in the damper windings.

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Rotor Reatining Rings

The centrifugal forces of the rotor end winding are contained by single piece rotor retaining rings. Retaining rings are made of non-magnetic high strength steel in order to reduce stray losses. Each retaining ring with its shrink fitted. Insert ring is shrunk on the rotor in an overhang position. The retaining ring is secured in the axial position by snap rings.

The rotor retaining rings withstand the centrifugal forces due to end windings. One end of each ring is shrunk fitted on the rotor body while the other end overhangs the end windings without contact on the rotor shaft. This ensures an unobstructed shaft deflection at end winding.

The shrunk on hub on the end of the retaining ring serves to reinforce the retaining ring and secures the end winding in the axial direction at the same time. A snap ring is provided against axial displacement of retaining ring. The shrunk seat of currents. To reduce the stray losses and have high strength, The rings are made of non magnetic, cold worked materials.



ROTOR FANS

The cooling air in generator is circulated by two axial flow fans located on the rotor shaft one at each end. To augment the cooling of the rotor winding, the pressure established by the fan works in conjunction with the air expelled from the discharge parts along the rotor. The blades of the fan have threaded roots for being screwed into the rotor shaft. The blades are drop forged from aluminium alloy. Threaded root fastenings permit angle to be changed. Each blade is secured at its root with a threaded pin.

BEARINGS The turbo generators are provided with pressure lubricated self - aligning elliptical type bearings to ensure higher mechanical stability and reduced vibration in operation. The bearings are provided with suitable temperature element devices to monitor bearing metal temperature in operation.

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The temperature of each bearing is monitored with two RTDs (Resistance Thermo Detectors) embedded in the lower bearing sleeve such that the measuring point is located directly below the babbit. These RTDs are monitored a temperature scanner in the control panel and annunciated if the temperature exceeds the prescribed limits. All bearings have provisions for fitting vibration pickups to monitor shaft vibrations.

To prevent damage to the journals due to shaft currents, bearings and oil piping on either side of the non-drive end bearings are insulated from the foundation frame. For facilitating and monitoring the healthiness of bearing insulation, split insulation is provided.

VENTILATION AND COOLING Turbo generators are designed with the following ventilation systems: •

Closed circuit air cooling with water or air coolers mounted in the pit.

• Closed circuit hydrogen cooling with water or hydrogen coolers mounted axially on the stator frame. The fan design usually consists of two axial fans on either made of cast aluminum with integral fan blades or forged and machined aluminum with integral fan blades or forged and machined aluminum alloy blades screwed to the rotor. In case of 1500 RPM generators, fabricated radial fans are provided.

EXCITER The exciter is brushless mainly consisting of:

The brushless exciter is an AC exciter with rotating armature and stationary field. The armature is connected to rotating rectifier bridges for rectifying AC voltage induced in the armature to DC voltage.

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The pilot exciter is a PMG (Permanent Magnet Generator). The PMG is also an AC machine with stationary armature and rotating field (the permanent magnets).When the generator rotates at the rated speed, the PMG generates 220v at 150 Hz to provide power supply to automatic voltage regulator.

A common shaft carries the rectifier wheels the rotor of the main exciter and the permanent magnet rotor of the pilot exciter. The shaft is rigidly coupled to the generator rotor and exciter rotors are then supported on three bearings.

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CHAPTER 8 BAR WINDING

BAR WINDINGS

Bar winding is carried out in separate shop in BHEL factory, Haridwar .This shop is meant for manufacturing of stator winding coils of generator that may be Turbo-generator or Hydroenerator. Bars manufactured are of standard capacity such as 100MW, 130MW, 210/235MW, 500MW.

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Stator

It is quite difficult (rather impossible) to manufacture, handle and wind the coil in slot of enerator of higher generation capacity because of its bigger size and heavy weight.

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gVERVIEW OF GENERATOR STATOR

That is why we make coil in two parts. They are: •

Bottom part (called as lower bar)

•

Top part (called as upper part)

Manufacturing process of Bars The manufacturing procedure for bars can be classified as follows-



Conductor cutting

:

This process is done by automatic CNC machine In this process the pre insulated copper conductor is cut into number of pieces of required length (as per given design).Insulation is removed from the both ends of copper conductor cut.

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 Transposition : Transposition means changing/shifting of position of each conductor in active core (slot) part. After cutting the required number of conductor ,the conductors are arranged on the comb in staggered manner and then bends are given to the conductor 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.

 Crossover insulation: The pre insulation of the copper conductor may get damaged due to mechanical bending in die during transposition, hence the insulation spacers are provided at the crossover portion of the conductors .A filler material ( insulating putty of moulding micanite ) is provided along the height of the bar to maintain the rectangular shape and cover the difference of level of conductors.

 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 1600C for a given period .The consolidated stack is withdrawn from the press and the dimensions are checked.

 Inter strand short test:

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The consolidated bar stack is tested for the short between any two conductors in the bar. If found then it has to be rectified.

 Forming : The straight bar stack is formed as per overhang profile (as per design). The overhanging portion is consolidated after forming.

 Brazing of coil lugs: For water cooled generator bars, the electrical connection contact and water box for inlet and outlet of water are brazed.

 Nitrogen leak test: The bar is rested for water flow test , nitrogen leak test and pressure test for given duration.

 Thermal Sock Test:

The cycles of hot (800C) and cold (300C) water are flew through the bar to ensure the thermal expansion and contraction of the joints.

 Helium Leakage Test: After thermal shock test bar is tested for any leakage with the help of Helium gas.

 Insulation : SRMCEM,LUCKNO W

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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.

Impregnation and Baking:

Thermoelectric system:

•

In case of rich resin insulation the bar is pressed in closed box in heated condition and baked under pressure and temperature for a given period.

Micalastic Sytem:

•

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 draied and bars are heated and baked under pressure condition in closed box fixture. 

The bars already laid in closed fixture and full VPI Micalastic fixture is System: impregnated (dipped) in resin and then fixture with box is baked under given temperature for given duration.



: The individual (separate) bar is heated in vaccum VIP Micalastic and impregnated System in resin. Then bar is taken out and pressed in closed bx fixture and then baked at given temperature for given duration.

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Finishing :

The baked and dimensionally correct bars are sanded-off to smoothen the edges and the surfaces is calibrated, if required, for the dimension.

Conducting Varnish Coating: • OCP (Outer Corona Protection) Coating: The black semi conducting varnish coating is applied on the bar surface on the core length • ECP (End Corona Protection) Coating: The gray semi conducting varnish is applied at the bent outside core end of bars in gradient to prevent from discharge and minimize the end corona.

Testing: • Tan TestCoThis test is carried to ensure the healthiness dielectric (insulation) i.e. then or rare and measure the capacitance loss. • HV Test:o/fgogrfo(rohWodgWdgo''gdrh*ordofhfo)drgo increased gradually to three times higher than rated voltage.

Dispatched for Winding: The bar preserved with polythene sleeves to protect from dust, dirt, oil, rain, etc are send to block 1 for winding.

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CHAPTER 9 Failure of generator stator conductor NTRODUCTION Reliable operation of generator is highly dependent on the electrical and mechanical integrity of stator winding. Failure of generator stator conductor due to electrical or mechanical problems will lead to long force outage of the unit resulting into huge revenue loss. As per our experience, most of the epoxy mica insulated generator stator conductor failure occurs due to loss of mechanical integrity of either overhang conductor or core looseness.

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CASE STUDY The Generators of 200MW units are designed by M/S Electrosila, Russia and manufactured by BHEL. The stator winding of generators are directly cooled by de-mineralized water passing through hollow conductors of the stator winding. Stator core and rotor are cooled by pressurized hydrogen gas. The rating of the generator is 235MVA, 15.75KV, 0.85lag, 3-phase, double star connection and 3000rpm. The generators are having 60 slots with 2 nos. stator windings per slot. Each stator winding conductor is made of both hollow and solid conductors. DM water passes through hollow conductors for conductor cooling. DM water pressure is maintained less than casing hydrogen pressure to prevent entry of water into the generator in case of hollow conductor leakage. For detecting hydrogen gas leakage through stator conductor, gas trap device has been provided.

The stator winding conductors are insulated by ‘F’ class epoxy based mica insulation. Overhang conductors of stator winding are supported on stator casing by fiber glass ring and fiber glass blocks. Conductors at overhang are tied with the fiber glass ring by polyester cord. Near the exit point of the conductor from core, one epoxy putty ring was made to reduce overhang conductor vibration. Top and side ripple spring has been provided in the slot to further reduce conductor vibration.

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After removing the insulation, crack was detected in the first bend of copper conductor. L shaped Aluminum support bracket just below the defective bar at 5 O’ clock position supporting phase connector 55B-C5 was found broken .Some blocks of supporting bracket at 11 O’ clock position was found loose .Black paste was found at the slot exit in top and bottom part of overhang .Paste like fretting product was found in the putty ring area and overhang support area.

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Minor cracks were also observed in the overhang support brackets. After replacement of defective bends, machine was taken into service.

ANALYSIS OF PROBLEM To detect the root cause of repeated failure fractography analysis of the cracked surface of copper conductor was carried out. The analysis indicates that the crack has developed due to fatigue. Fatigue has developed due to repetitive loading caused by conductor vibration at the overhang region. No sign of overheating or corrosion was observed. Failure of aluminum support bar also indicates presence of vibration in the overhang region. The fractography analysis of the fracture surface of the aluminum support indicates presence of beach mark caused by fatigue. The above observation indicates presence of high overhang conductor vibration. The presence of fretting product also indicates overhang conductor support looseness and subsequent vibration of the overhang conductor.

During shut down of the machine in June-05, natural frequency testing of overhang conductors revels that at 4 places natural frequency was near 100HZ particularly at the places where failure has taken place. The matching of natural frequency with core vibration frequency i.e. 100HZ resulted in excessive conductor vibration due to resonance when the generator is in service. The presence of excessive overhang conductor vibration has caused repeated failure of overhang conductor.

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Overhang conductor of these types of generators are supported by fiberglass ring and blocks. Gaps between fiberglass ring and overhang conductors are filled by glass webbing soaked in epoxy resin. But when the support blocks are tightened, some micro gaps exist in tangential direction. Secondly epoxy resin shrinks when it is cured. Due to this property of resin, micro gaps are formed between conductors and its support after prolong operation.

So when machine is in operation, due to presence of micro gaps between conductor and support, the support and conductor will not vibrate as a monolithic mass. This will cause further looseness of conductor and subsequent increase of amplitude of vibration. Conductor vibration will become severe when natural frequency of conductor approaches to 100HZ (core vibration frequency) and will result into failure.

CONCLUSION Looseness of overhang conductor (where overhang conductor is supported by fiber glass blocks, rings and tied by lacing) will occur after prolong operation of the machine. By measuring natural frequency of overhang conductor during overhaul, this type of problem can be detected at a very early stage and corrective action can be taken to avoid premature failure of stator winding conductor.

BHEL carries out the measurement of natural frequency of epoxy mica insulated overhang conductor (where overhang conductor is supported by fiber glass blocks, rings and tied by lacing) of generators during generator overhaul and corrective actions were taken on the basis of natural frequency of conductor.

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INDUSTRIAL TRAINING REPORT

CHAPTER 10 FEATURES AND SPECIFICATION

1. TURBO GENERATORS

(a)Air Cooled Generators Upto 200 Mw Range (Type: Tari) Salient Design Features • Stator core and rotor winding direct aircooled • Indirect cooling of stator winding SRMCEM,LUCKNO W

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Horizontally split casing design of stator.

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Vertically side mounted coolers in a separate housing.

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Micalastic bar type insulation system

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Separately assembled stator core winding for reducing the manufacturing cycle.

•

Brushless/static excitation system

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(b) Hydrogen Cooled Turbogenerators Of 140-260 Mw Range (Type: Thri) Salient Design Features

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 Stator core and rotor winding directly hydrogen cooled  Indirect cooling of stator winding.

 Rigid core bar mountin  Micalastic insulation system  End shield mounted bearings  Top ripple springs in stator slots  Ring type shaft seals  Symmetrical ventilation.

Salient Technical Data: Rated output : 588 MVA, 500 MW Terminal voltage : 21 KV Rated stator current : 16 KA Rated frequency : 50 Hz Rated power factor : 0.85 La

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Efficiency : 98.55%

Important Weights: Heaviest lift of generator stator : 255 Tons Rotor weight : 68 Tons Total weight of turbo generator : 428 Tons

CHAPTER 11 GENERATOR STAMPING

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In BHEL:210MW 250MW 500MW Generator is made by stamping. Stamping used to protects stator body

8.1 Assembly:It is divided in a point (1) Base: - All the stator parts and stamping is placed by base .it is made by hard iron plat. (2) End Packet :- Four or more stamping is joined together & made a ring is called stamping ring or end packet. It is depend upon size of motor or enerator.

No of ring are joined together and made of a packet. It is differ the finger plates. It is placed on the finger plat. It is fixed and of rotor. No of packets are joined together and made a rotor as shown in fig.

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(3) Finger plate: - It is fixed on the end plate. It is also made by a steel plate. It enerally used for supported all the parts of rotor winding.

(4) Insulating stamping: - it is placed in middle of two main stamping. It is used to absorb heat. Insulation stamping is placed above & below of the packet of

stamping. SRMCEM,LUCKNO W

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(5) Pressing process: - All the stamping packets are joint together. But some losses are occur (gap etc) so we use pressing process by the help of many types of hydraulic machines

Pressure required:-

Min pressure: - 50 Max pressure:-250-300

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