TRAINING REPORT
ON INSULATION AND MANUFACTURING PROCESS OF 500MW TURBO GENERATOR BARS
Submitted By: ANIMESH VERMA rd
Electrical Engineering (3 Year) 074003 Dayalbagh Educational Institute (D.E.I) - Deemed University Dayalbagh Agra - 282005
Under the Guidance of Mr. A.K Dhiman (DGM) BHEL, HARIDWAR
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ACKNOWLEDGEMENT ―An engineer with only theoretical knowledge is not a complete engineer. Practical knowledge is very important 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 me during my training at BHEL, Haridwar. Special thanks to Mr. A.K Dhiman for providing me with an opportunity to undergo training under his able guidance and offering me a very deep knowledge of practical aspects of industrial work culture... I express my sincere thanks and gratitude to BHEL authorities for allowing me to undergo the training in this prestigious organization. I will always remain indebted to them for their constant interest and excellent guidance in my training work, moreover for providing me with an opportunity to work and gain experience.
ANIMESH VERMA Dayalbagh Educational Institute Electrical Engineering
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Table of Contents BHEL: AN OVERVIEW ......................... ...................................... .......................... ........................... ........................... .......................... ............... .. 4 Power Generation............................... Generation..................................................... ............................................ ............................................. ........................................ ................. 4 Heavy Electrical Equipment Plant .......................................... ................................................................ ............................................ ......................... ... 5
COIL & INSULATION MANUFACTURING SHOP (BLOCK-IV)...................... ...................... 7 Introduction............................................ .................................................................. ............................................ ............................................ .................................... .............. 7 Sections in Block IV .................................................... .......................................................................... ........................................... .................................... ............... 8 MFG. Process flow chart of 500MW TG stator bar ............................................. .............................................................. ................. 9
MANUFACTURING PROCESS OF BARS ........................... ........................................ .......................... .................... ....... 11 BAY-1 ......................................... ............................................................... ............................................ ............................................ ............................................. ....................... 11 Resin System................................................. ....................................................................... ............................................ ............................................. ........................... .... 22 Testing.................................. Testing........................................................ ............................................ ............................................ ............................................ .............................. ........ 22 Tan∆ Test ........................................... ................................................................. ............................................ ............................................ .................................. ............ 22 H.V. (High Voltage) Testing .......................................... ................................................................. ............................................. .......................... .... 23 23 BAY-2 ......................................... ............................................................... ............................................ ............................................ ............................................. ....................... 24 Introduction:........................................... ................................................................. ........................................... ............................................ ............................... ........ 24 Insulation Check ........................................... ................................................................. ............................................ ............................................ ........................ 24 Conductor Tapping ........................................... ................................................................. ........................................... ......................................... .................... 24 Winding Boat Coil .............................................................. .................................................................................... ............................................ ........................ 24 Boat Insulation .......................................... ................................................................ ............................................ ............................................. ........................... .... 25 Stack Pressing ........................................... ................................................................. ............................................ ............................................. ........................... ....25 Forming .......................................... ................................................................. ............................................ ............................................ ...................................... ............... 25 Insulation................................. Insulation....................................................... ............................................ ............................................ ............................................ ........................ 25 Impregnation .......................................... ............................................................... ........................................... ............................................. ............................... ........ 25 Curing ............................................ ................................................................... ............................................ ............................................ ...................................... ............... 26 Finishing ............................................ .................................................................. ............................................ ............................................ .................................. ............ 26 BAY -3 ............................................ .................................................................. ............................................ ............................................ ......................................... ...................27 Introduction:........................................... ................................................................. ........................................... ............................................ ............................... ........ 27
ELECTRICAL MACHINES BLOCK (BLOCK — I) ......................... ...................................... .................. ..... 28 Introduction............................................ .................................................................. ............................................ ............................................ .................................. ............ 28 Manufacturing Process................................... Process........................................................ ........................................... ............................................. ........................... .... 28 Turbo Generator........................................................... ................................................................................. ............................................ .................................. ............ 29 CONSTRUCTIONAL FEATURES OF STATOR WINDING ......................................... ........................................... 31 CONSTRUCTIONAL FEATURES OF ROTOR ............................................ ............................................................... ................... 32
CONCLUSION ......................... ...................................... .......................... ........................... ........................... .......................... .......................... ................ ... 36 Bibliography ......................... ....................................... ........................... .......................... ................ ... Error! Bookmark not defined. 3
Chapter 1 BHEL: AN OVERVIEW BHEL is the largest engineering and manufacturing enterprise on India in the energy related/infrastructure sector. BHEL was established more than 40 years ago, ushering in the indigenous Heavy Electrical Equipment industry in India, a dream which has been more than released with a well-recognized track record of performance. It has been earning profits continuously since 1971-72. BHEL caters to core sectors of India economy viz. Power Generation and Transmission, Renewable Energy, Energy , Defense etc. The wide network of BHEL’s 14 manufacturing divisions, 4 power sector regional centers, 8 service centers, 15 regional offices and a large number of projects sites spread all over India and abroad enables the company to promptly serve as customer and provide them with suitable products, systems and services- efficiently and at competitive prices. BHEL has attained ISO 9001:2000 certifications for quality management and all the manufacturing units divisions of BHEL have been upgraded to the latest ISO 9001:2000 version. All the major units divisions of BHEL have been awarded ISO 14001 certification for Environmental Management System and OHSAS-18001 certification for Occupational Health and Safety management System. BHEL become the first public sector Company in the country to win the coveted prize for in Haridwar unit under the CII Exim Award for the business excellence as per the globally recognized model of European Foundation for quality management. BHEL is the only PSU among the 12 Indian C ompanies to figure in ―Forbes Asia Fabulous 50‖ list. It has also won the ―Business standard star Public Sector Company Award 2006‖. The company received MoU Excellence award for 2004-2005 and Merit Certificate for MoU Excellence for 2005-2006.
Power Generation Power generation Sector comprises Thermal Gas, Hydrogen, Nuclear power plant business. As of 31.3.2007. BHEL supplied sets accounts for 80,781 MW or nearly 65% of the total install capacity of 1, 25,414 MW in the country. Significantly these sets contribute 73% of the total power generated in the country. BHEL has proven turnkey capabilities for executing power projects from concepts to commissioning. It possesses the technology and capability to produce Thermal sets with super critical parameters up to 1000 MW unit rating and gas turbine generator sets of up to 300 MW units rating. Co-generating and combined cycle plants have been introduced to achieve higher plant efficiencies. To make efficient use of the high-ash-content high- ash-content coal available in India. BHEL also supplies circulating Fluidized Bed Combustion (CFBC) boilers for thermal plants. 4
The company has proven expertise in Plant Performance Improvement through renovation, modernization and upgrading of a variety of Power plant equipment, besides specialized know-how of residual life assessment health diagnostics and life extension of plants. Overall, BHEL built Thermal sets achieved the highest ever PLH of 78.3% in 20062007 which is 2.5% higher than the National average. The combined operating availability of these sets was 84.7%.
Heavy Electrical Equipment Plant BHEL's Heavy Electrical Equipment Plant (HEEP) was set up in technical collaboration with USSR, for the manufacturing of power plant equipment, AC/DC motors of various rating with associated control equipment and started production in January 1967. In 1976, BHEL entered into a collaboration agreement with M/s Kraftwerk Union, AG of Germany for design, manufacturing, erection and commissioning of large size steam turbines. More than 40 percent of the country's electrical energy is generated from the power equipment supplied by BHEL, Haridwar. BHEL offer wide ranging products and systems for T & D applications. Products manufactured include power transformers, instrument transformers, dry type transformers, series – and stunt reactor, capacitor tanks, vacuum – and SF circuit breakers gas insulated switch gears and insulators. The products, which are manufactured in HEEP, are: - Steam Turbines, Turbo Generators, hydro turbines, Gas turbines, etc
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COIL & INSULATION MANUFACTURING SHOP (BLOCK-IV) Introduction As the complete one peace coil is not practicable so the coils are manufactured in two parts, upper and lower bars. Out of the various BLOCKS as mentioned before the coil and insulation manufacturing block is BLOCK-4. This block is known as the COIL AND INSULATION MANUFACTURING block. Block-4 is a feeder block for insulating items,
winding with class-B Bituminous insulation and sheet metal components for all the products of Block-1 i.e. Turbo-generators, Hydro-generators, A.C. and D.C. machines. There are three BAYS in this block each bay manufactures stator bars and coils for different machines as mentioned below: BAY-I:
Bar winding shop: manufacturing of stator winding bars of generator.
BAY-II:
Manufacturing of heavy duty generator stator bars with New CNC M/c No. 3-
BAY-III:
464 i.e. Roebel bar centre. Insulation detail shop: Manufacturing of hard insulation & machining of hares insulation part (Glass Textolite) such as packing, washer, insulation box, wedges etc. & CNC taping machine.
Bar Shop:
This shop is meant for manufacturing of stator winding coils of turbogenerator and hydro generator.
Why do we call it bar?
It is quite difficult (rather impossible) to manufacture, handle and wind in the 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 its bottom part of coil called bottom or lower bar and other part of coil is called top bar or upper bar. .Turbo-Generators: The manufacturing of bars of standard capacity such as 100MW, 130MW, 150MW, 210/235MW, 210/250MW, 500MW. The plant has capacity and technology to manufacture 800MW and 1000MW generators. Types of generators: The generator may be classified based upon the cooling system used in
the generators such as: THRI, TARI, THDI, THDD, THDF, THFF, and THW.
T => First alphabet signifies the type of generator i.e. turbo- generator or Hydro-
generator.
H/A => Second alphabet stands for the cooling media used for the cooling of rotor i.e.
hydrogen gas or air.
R/D/F/I => Third alphabet signifies the type of cooling of rotor e.g. radial, indirect,
forced, direct etc. 7
I/D/F => Last alphabet stands for the type of cooling of stator e.g. indirect cooling, direct
cooling, and forced cooling.
W => Cooling media used for cooling of stator coil e.g. water.
Sections in Block IV (a) Assembly Section
Mechanical Assembly Section: - It is equipped with small size drilling machines, welding sets and hydraulic testing equipment for manufacturing turbo-generator mechanical assemblies.
Close Cubical Assembly Section
(b) Stator Bar Winding Section
Conductor cutting, insulation and transposition section having facilities for transposing the bars.
Stack consolidation section, forming and lug brazing sections have block type hydraulic press, steel former and induction brazing installations respectively. respectively. Insulation taping sections with automatic taping facilities in air-conditioned temperature covering maximum slot portion each overhung ay both ends. Baking and pressing section having baking moulds for simultaneous curving of straight and overhead portion with electrical heating.
(c) Armature Winding, Rotor coil and Stator bar Section :Coils are diamond pulled type with Class-B (bitumen) and Class-F (conventional or resin rich discontinuous epoxy insulation) and Class-H Silicon insulation for machines ranging from 5 to 460 KW capacity. This section has the following work centers:
Conductors cutting, U- bending and terminal conductor cutting machines, U- bending machines and terminal baths.
Forming and Insulation of DC coils.
Main and Interpole Winding: - It is having semi-automatic winding machine.
Planking, boat pulling and diamond pulling machine.
Insulation and pressing of AC coils: - it is equipped with hydraulic presses of 608 T capacities.
(d) Impregnation Section :It is equipped with impregnation tank, ovens for impregnation of DC pole coils.
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(e) Insulation Section :
Insulating details, machining is equipped with small size lathes, milling and radial drilling machines and jet cutting saw. Press Molding Section: - It has electrical ovens, hydraulic presses, shearing and circular saw cutting machines for manufacturing press molded components of all the electrical machines.
Plastic Molding Section: - Is equipped with various presses for plastic molded parts.
Bitumen Mica Tape Manufacture: - Is equipped with mica tape manufacturing machine and lathe for slitting mica tape to the required size.
MFG. Process flow chart of 500MW TG stator bar 1. Conductor draws from store. 2. Conductor cutting and end cleaning. 3. Transposition of conductor. 4. Assembly of all conductors to be used in stator bars. 5. Cross over insulation. 6. Consolidation if slot portion of bar. 7. I.S Test (i.e. inter strand test). 8. Forming of bar (to shape overhang portion). 9. Pickling of bar ends (1). 10. Mounting of contact sleeve & bottom part of water box. 11. Brazing of contact sleeve & bottom part of water box. 12. Pickling of bar ends (2). 13. Mounting of water box leak test. 14. Re-Pickling. 15. Water flow and Nitrogen test. 16. Thermal Shock Application. 17. Helium leak test. 18. Reforming of bar (i.e. overhang portion). 19. Insulation of bar on CNC machine. 20. Impregnation & curing of bar insulation. i nsulation. 21. Surface finishing of stator bar. 22. OCP on stator bar. 23. Preparation of bar for HV and Tan δ test. 24. If O.K. Dispatch to Block-1 for lying in the generator.
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Figure 1 Main Products of CIM, Block-IV
Figure 2. Layout of CIM, Block-IV
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Chapter 2 MANUFACTURING PROCESS OF BARS BAY-1 Some points of manufacturing process is in brief as below – below – 1. Insulation Check
For the manufacturing of stator bars insulated copper conductors are brought from Bangalore, it’s of two type’s i.e. solid copper conductor & hollow copper conductors which are used in water cooled stator layer glass insulation.
Insulating materials and the conductors are ensured to be certified. If required the insulation is checked checked by the respective agencies.
2. 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 (length given in drawing as per design) insulation is removed from both ends of the copper conductor out.
Lower Bar: Conductor Size
Length
Number of conductors
8*4.6*1.5mm(Hollow) 8*4.6*1.5mm(Hollow)
10200mm
Hollow - 20
8*2.8mm(Solid)
10200mm
Solid - 20
Conductor Size
Length
Number of conductors
8*4.6*1.5mm(Hollow) 8*4.6*1.5mm(Hollow)
10500mm
Hollow - 20
8*1.3mm(Solid)
10500mm
Solid - 40
Upper Bar:
3.
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 11
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. Transposition is done in two ways:
Half Pitch Transposition: - In this transposition, the first conductor at one end of the bar becomes the last conductor at the other end of the bar. Full Pitch Transposition: - In this method of transposition, the first conductor at one end of the bar becomes the last conductor in the mid of the bar and then again becomes the first conductor at the other end of the bar. 1. To reduce eddy current losses. 2. Equalize the voltage generator.
3. To minimize skin effect of ac current, small cross section of conductor is used and also hollow conductors are used to effect cooling by D.M water. 4. 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 of molding 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 edge wise bending and leveling of bars in slots portion for proper stacking. 5. Stack Pressing:-
This process is basically done to consolidate the solid as well as the hollow conductors into a single bar, the insulating material provide at crossover positions which has gluing properties melts and helps helps in the proper consolidation consolidation of the bar. In this process process the bar is pressed both vertically and horizontally in the Pressing Machine. The pressing machines are also provided with the heaters Each bar is loaded on each tier of heating plate and it is then provided with an initial pressure of 35±5 kg per cm
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and an initial temperature of 100-110° C. then the
temperature is allowed to raise to the maximum of 160°C, this temperature is kept for at least one hour with a final pressure of 80±10 kg per cm2 vertically and 70±10 kg per cm2 horizontally. After pressing the bar at specified pressure and maximum temperature for one hour, the bars are then cooled placing them on cooling plates through which water is allowed to 12
follow below 50°C. The cooled bars are checked for their heights and widths at pressed portion of the bar. This complete process performed above is for one half of the bar. The same process is then repeated for the other half of the bar similarly and then checked for bar’s height and width at pressed portions as done before. Then the ends of both the bars are cleaned with rectified spirit and sand paper for the inter strand test 6. Inter Strand Short test : -
The consolidation bar 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. (300V A/C supply). For this test all the bare conductors at both the ends are separated from each other so that they do not short circuit. Then a live wire is connected to a conductor and received from it consecutive conductor to light a lamp. Hence if the lamp lights up it shows short circuit between the two conductors due to improper insulation between them. It shows insulation failure between the conductors, these conductors are then replaced and bar is followed through all the previous processes. Similarly all the conductors are checked for any short circuit. After passing both the half bars from I.S.T. the bars are combined together and pressed into a single bar. A sheet of mica glass insulation is provided between the two halves as the insulation also has some gluing property to consolidate the two halves into a single bar. All the steps of pressing are again followed for the complete bar and then it is allowed to cool.
7. Forming: -
In heavy generators each stator coil is very large in size and hence its manufacturing is difficult as it will be very difficult to handle and process the complete coil. So each coil is manufactured in two halves i.e. Upper half and Lower half. The bars which wh ich are processed till this process are straight and hence they are required to be formed into the upper half or the lower half. Hence this process of forming is very important as in this process the bars are bending from both the ends of the bar i.e. at exciter side and turbine side at specific angles and shape as per design. This process is done manually. First the former is set according to the design making different angles at different positions. Each bar of a variant is bent or formed at same angle. Once the former is set, the bar is mounted on it and formed manually by melleting it from both the ends. After forming the formed portion of the bars are assumed to get loose creating air gaps between the conductors due to such a heavy melleting. Thus the formed portion of the bar are clamped at different places and provided with heaters to reconsolidate the formed portion. After few hours the bar is then allowed to cool at room temperature.
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8. End Conductor Cutting:
Due to heavy malting of the bar for forming it from both the side i.e. exciter side and turbine side, the conductors of the bar are produced at the ends of the bar. Therefore to bring all the conductors of the bar in a plane End Conductor Cutting is required to be done. Both the solid and hollow conductors are cut and from both the sides of the bar. Also this process of cutting of the hollow conductors helps in opening of vents of hollow conductors from both the ends of the bar. 9. Pickling Process:
After the forming and cutting process of the bar and due to the transportation of the bar, there accumulate very minute particles of dust on the ends of the bar. These particles may cause hindrances at the time of brazing and may create some air gaps. So, in order to remove these unwanted particles, basically the oil particles pickling process is performed. The basic solution used for this process is called pickling solution. The constituents of the pickling solution are:
Sulphuric acid (H2SO4)-10%
Phosphoric acid (H 3PO4)-5%
Hydrogen peroxide (H2O2)-5%
Water (H2O)
There are many other solutions used in this process, these are:
Ammonia
Thinner
Water
Rectified spirit
Nitrogen
In this process the following steps are involved:
The end of the bar is dipped in thinner to remove the dust or oil particles.
The end is then dried with the help of N 2 gas.
Then the bar end is dipped in pickling solution for 5 to 10 minutes.
This is then followed with dipping in water.
As there is acid in the pickling solution, so accordingly to neutralize the acidic effect of the acid it has to be treated with some base, so the bar is then dipped in Ammonia (10%).
It is then followed with dipping in water.
As water takes a lot of time to evaporate, it may let the tiny chemical particles on the bar to react with it and leave spots on the bar, this may weaken the insulation at those particular points and thus damage it, further it may ma y lead to poor brazing. So in order to avoid such a damage the bar is dipped in rectified spirit to make the water contents evaporate as soon as possible.
The bar is then dried with N 2 gas. 14
Finally it is wrapped with cotton cloth to avoid any manual touch which may deposit any dust particle on it until it is ready for brazing. The same process of pickling is then preformed on the other end of the bar.
10. Contact Sleeve Mounting:
After the pickling process is complete, contact sleeve and water box bottom parts are mounted on both the ends of the bar. Contact sleeve, as clear from the name itself, it is a rectangular sleeve which is used to make contact between upper and lower bars when laid out in the generator to form a complete coil. All the solid conductors are cut from the ends of the bar after the contact sleeve except the outer solid conductors. None of the conductor is cut before the contact sleeve so that to make proper contact between the upper and the lower bars. The water box is mounted in two halves; first the water box bottom part is mounted after the contact sleeve keeping some distance between them. Both the ends of the bar are then again pickled along with contact sleeve and water box bottom part following the same procedure of pickling. 11. Brazing of coil lugs: -
For water cooled generator bars, the electrical connection contact and water box for inlet and outlet of water are brazed. The contact sleeves, which are used to make contact between the upper bar and the lower bar to form a complete coil and the water box bottom part, both together are called Coil Lug, so the brazing of these two parts at the end of a bar is called Coil Lug Brazing. Brazing is basically the process of fixation of both the contact sleeve and water box bottom part or we can say both are properly consolidated using brazing material at high temperatures. Consolidation is properly done so that no air gap is left which would adversely affect the conducting properties of the contact sleeve and the bar. The two types of brazing processes are:
Thermal brazing (using LPG)
Induction brazing
As induction brazing is more beneficial than thermal brazing as it does not requires any inflammable gas for heating. So now a day’s Induction brazing process is used. For brazing as we use very high temperature so that is possible due to carbon strips fixed on the brazer. Carbon has very high resistance and when the current is allowed to pass through it due to induction the material to be brazed i.e. Contact Sleeve gets super heated. Induction heating is hence faster and even more efficient than thermal t hermal heating.
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When the contact sleeve becomes red hot at 750ºC, the brazing material is then pushed to fill the air gaps and to consolidate the contact sleeve on the bar. It is then allowed to cool.
The types of brazing materials used are:
LAG 15P ( Alloy Silver 15 Phosphorous)
LAG 40Cd ( Alloy Silver 40 Cadmium)
Same process of brazing is then repeated for the water box bottom part. After the brazing of water box bottom part the bar is then allowed to cool at room temperature.
12. End Conductor Cutting
As is clear from the name itself this is the process of cutting of extra conductors i.e. the hollow conductors left after the water box bottom part are cut from both the ends of the bar. These conductors are required to be cut so that water box top part with a nozzle is to be mounted on the water box bottom part. The vents of the hollow conductors are visible from the ends of the water box bottom part. The openings of the vents of the hollow conductors are then checked to be uniform. After cutting of extra conductors from both the ends of the bar, pickling process is done. Same pickling process as mentioned before is then done at both the ends of the bar for removing the dust particles, oil particles and other unwanted impurities which we assume to be there after the brazing process of the contact sleeve and water box bottom part. After pickling the bar ends are then wrapped in cotton cloth until the water test is performed.
13. Water Test:
Water test is performed so that there not any blockage in the vents and also to check the flow of water. Flow should be uniform i.e. all the vents should have same water flow. In this test water is supplied from one side of the bar and is collected from the other side of the bar in a tank and is supplied back to the first end. Flow of the water is checked by measuring the distance of the flow of water. If there is any kind of blockage inside the hollow conductors of the bar then it is indicated by flow of water i.e. flow of water will be not uniform and the bar is assumed to be chocked. Then cocked conductors are changed or repaired and the bar is reformed and water test is again performed to check the flow of water.
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14. Brazing Of Water Box Top Part:
Brazing of water box box top part is done with water box bottom part in brazing section of Block-4.For this it should be kept in mind that water box bottom part should have same material as that of water box top part. The difference in previous brazing and this brazing is that, now flux is also introduced with brazing material and also flux is mixed with copper chips. Copper chips are added to make the electrical contact between the top and bottom part without the copper chips this will be not possible. In this brazing material is formed in the shape as that of water box side where it has to be brazed. Brazing material is formed in square shape for top and bottom part and in ring shape for the brazing of nozzle for water flow. Then both the parts are heated with induction brazer as done earlier. It is heated until they become red hot then the brazing material melts due to its low melting temperature then the melting temperature of the water box top and bottom part. Brazing material is also i ntroduced at the boundaries until it is completely consolidated that is the entire air gap is completely filled. After the brazing of water box top part the bar is then allowed to cool at room temperature. 15. Checking Of Threads and Pickling Process:
As mentioned earlier that water box top part has got nozzle for flow of water, it also has got threads which is provided for the proper fixation of water supply through water pipe to the bar. These threads are checked for its uniformity by fixing water pipe to the nozzle. If threads are not found found satisfactory than the nozzle is replaced replaced with new one one and again its threads are checked. Also the pickling process is again done for the removal of any dust particles and lubricants etc. the detail of this process is same as mentioned earlier in pickling process. 16. Nitrogen leak test: -
As the name suggests Nitrogen gas is the main constituent of the test. This test is similar to puncture test that is inflated tube is dipped in water for any leakage, the air bubbles gives us the exact position of the puncture. Similarly on the same steps this test is performed. Basically this test is performed to check any leakage in bar i.e. to check the brazing. In this test nitrogen at a pressure of 2
10Kg/Cm is forced from one end of the bar and other end of the bar is blocked then the 2
pressure of 10Kg/Cm is maintained and both the ends of the bar are dipped in water. The bubbles if there any tells us that brazing is weak or not done properly. So if bubbles appear then brazing is done again and same test is performed for the proper brazing of water box top and bottom part. Then both the ends of the bar wrapped in cotton cloth so that it is not disturbed i.e. to 17
avoid any manual touch which may deposit any dust particle on it until it is ready for brazing.
17. Internal Pickling
After various test performed on the bar the pickling process i.e. removal of any dust particles lubricants etc is done only on outer surface of the bar (ends). But from inside it is assumed that there must be some impurities, foreign material must be present. For this purpose inside pickling is done. As mentioned earlier same process is repeated but from inside of the hollow conductors this time. In this process the following steps are involved:
The thinner is passed through the bar to remove the dust or oil particles.
The dried with the help of N 2 gas.
Then the pickling solution is passed for 5 to 10 minutes.
Then water is flowed in the bar.
As there is acid in the pickling solution, so accordingly to neutralize the acidic effect of the acid it has to be treated with some base, so the bar is filled with Ammonia (10%).
It is then followed flowing of water again.
As water takes a lot of time to evaporate, it may let the tiny chemical particles in the bar to react with it and leave spots in the bar, this may weaken the insulation at those particular points and thus damage it, further it may lead to poor brazing. So in order to avoid such a damage the rectified spirit is flowed in the bar to make the water contents evaporate as soon as possible.
The bar is then dried with N 2 gas.
Finally it is wrapped with cotton cloth to avoid any manual touch which may deposit any dust particle on it until it is ready for brazing.
18. Baroscopic Testing
This test is performed to check the impurities or foreign material inside the bar. To look inside with naked eye is not possible so we use baroscopic for this purpose. So after internal pickling we use a baroscopic to look inside the bar. Baroscopic is having a probe probe having a LED (light emitting diode). diode). LED is used to provide provide light inside the bar. The probe of the baroscopic is inserted from one end of the bar and seen from a magnifying lens. The probe gives a light which is reflected by the sides of the bar (inside) and with the help of magnifying lens we get a clear image that what is there in the bar. If impurities are present then these are removed then only after the bar is send to next operation. 18
19. Water Test:
Here again water test is performed. In earlier water test water flow was checked without the water box top part . But now the top part is brazed to the bottom part and to check its flow this test is performed. Also to check the proper flow from the nozzle this test is performed. In this test water is forced or pushed from one end of the bar and flow of water is checked from other end of the bar. This test tells us the presence of any choke vents of water box top part. If any choke vent is present then it is repaired or whole of the water box top part is changed with new one. 20. Thermal Shock Test:
Thermal shock test is performed to check whether the bar can withstand extreme conditions i.e. when the generator is working or running at about 3000 Rpm. This is achieved by thermal shock test. Thermal shock test consist of series of hot water & cold water cycles c ycles alternatively. So firstly hot water at temperature of about 90ºC is passed through the bar and then cold water at about room temperature 27ºC approx. is i s flowed inside the bar alternatively. This process is repeated again and again. This process is repeated for about 26 times i.e. it has 26 cycles of hot and cold water. So this test tells us the strength of the bar so that it can withstand the working conditions of the generator. Temperature of the bar is taken in account according to the working 00
00
temperature of the generator. The cycles of hot (8 C) and cold (3 C) water are flown through the bar to ensure the thermal expansion and contraction of the joints. 21. Helium Leakage Test:
Helium test is the most important test of all, because helium test is performed to check any minute leakage within the bar and at the brazed portion. Any minute leakage which couldn’t be checked by water water test can easily be observed by helium test because helium is one of the lightest gases. So this is also the customers check point, before performing this test customer is by called and and they see themselves themselves the test being performed performed and if They find the test all right then only the bar is send send to next process. process. In helium test, whole of the bar is wrapped in the polythene excluding the end points. 2
The helium gas at pressure of 11Kg/Cm is passed through the bar and a probe connected to the gauge is inserted inside the polythene at different places. The gauge will show deflection if there is any helium atom present. Gauge will show reading even if 1 helium atom in 100000 atoms is present. This test checks the strength of brazing and insulation.
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22. Reforming:
After all the previous processes which had undergone on the bar it is assumed that the shape of the bar is deformed from its original shape due to handling handling of the bar from one place to another for different processes. So to keep the shape of the bar as per design, the bar is checked if it is found distorted then it is reformed in the previous former machine by placing the bar on the former and malleting. 23. 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. Insulation is basically done to prevent any kind of short circuit between the bar and the stator core when the bar is assembled in the stator of the machine. The stator bars are insulated with Micalastic
(trade name) insulation. High quality mica, selected epoxy resins and a
matching vacuum impregnation process are the characteristic features of the micalastic insulation for large turbo generators. The bar is provided with 14 layers of insulation. Out of these fourteen layers, 12 layers are provided by using a machine called CNC TAPPING MACHINE manufactured by a company named MICAMATION. The rest of the two layers are provided manually. The insulating material varies as according to the rating of the machines as follows:
For 500 MW : Mica Splitting Tape
For THRI
: Mica Glass
During machine taping in the slot portion the transition from machine to hand taping is adjusted at the start of the bend for a tape width for every layer from bar center. After about half the number of layers, the taping is to be started further at the bend. The mica tape consists of a thin high strength baking material to which the mica is bounded by synthetic resin. The number of layers i.e. the thickness of insulation is determined by the voltage of the t he machine. 24. Impregnation and baking :
a) Thermo reactive 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 of poor resin system system the insulated bars bars are heated under vacuum 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.
c) VPI Micalastic System: - The bars already lay in closed fixture and full fixture is impregnated (dipped) in resin and then fixture with box is baked under given temperature for given duration.
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d) VIP Micalastic System: - The individual (Separate) bar is heated in vacuum and impregnated in resin. resin. Then bar is taken out and pressed pressed in closed box fixture and and then baked at given temperature for given duration.
25. Micalastic Insulation and Impregnation
For insulation with micalastic, the conductor strands are arranged together to form a compact assembly and set to the required shape. This assembly is then baked with epoxy resin to give it mechanical strength required for further processing. The bars are then dried under vacuum and impregnated with synthetic resin, which by reason of its low viscosity penetrates the insulation thoroughly and eliminates all voids. After impregnation under vacuum, the bars are subjected to pressure, with nitrogen being used as pressurizing medium. The impregnated bars with direct conductor cooling are then brought to the required dimensions in moulds and cured in an oven at a high hi gh temperature. This complete process involves pressing of the bars, drying by heating, impregnation in resin and finally finall y curing. These processes are discussed briefly below:
Pressing: The bars are pressed to bring them back to the original dimensions.
Drying: The stator windings are to be dried under vacuum 0.1 m bar at (60±5) °C for
15 hours, minimum. The drying temperature is to be increased to (65±2) °C if the initial viscosity of the impregnating resin mixture is high. The temperature distribution should be as uniform as possible. The drying under vacuum can be stopped if the pressure rises, 10 minutes after closing of vacuum valve
is less than 0.06 m bar. Impregnation: The impregnation resin mixture is to be heated in the working tank, to (60±3) °C or in case of higher initial viscosity. At a temperature of 50ºC, the impregnating resin mixture is to be degassed with 1-5 m bar vacuum. Subsequently the stator windings are to be dipped continuously in resin hardener mix such that the highest locations of the windings are at least 100 mm below the resin level. After 10 minutes of resin stabilization, pressure is increased by application of nitrogen. Pressure is to be gradually increased in uniform stages within 80 minutes to 4 bars and to be maintained for 120 minutes in the impregnation tank. The impregnation of the stator winding is to be monitored continuously. Further it is to be b e decided whether to increase the pressure or to stop the impregnation process, however the total period of nitrogen pressure cycle shall in any case not exceed 4 hours. The impregnation tank during shut down is to be closed and kept
either filled with nitrogen (1.1bar) or low vacuum. Curing: To prevent heating in the overhang portion, the curing of the impregnated stator winding is to be done with a maximum 160°C hot air. The curing period is extended for such a long time till the measurement positions in the core indicate (140±5) ºC for minimum 8 hours. 21
26. Finishing: - The baked and dimensionally correct bars are sanded - off to smoothen the
edges and the surface is calibrated, if required, for the dimension. 27. 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.
Resin System a) Rich resin or Thermo reactive 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 0
preservation and working on temperature 20-25 C. Its shelf life is one year when kept at 0
0
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 insulating 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 (fully dipped) in the resin.
Testing When the bar is dried it is wrapped with aluminum sheet to make outer surface of the bar conducting so that tan δ and H.V. (High voltage test) can be performed. After these tests the coating of red gel is applied at both the ends of the bar.
Tan∆ Test Test is performed to find the capacitance of the bar because bar will act as capacitor when it is laid in the stator of the generator. In this test Schearing Bridge which works on the principle of wheat-stone bridge is used to find the unknown capacitance of the bar. For good efficiency, capacitance of the bar should be high but b ut we never approach pure capacitance. In this test also same bar which is wrapped with aluminum is used to make the bar conductive throughout the outer surface of the bar. The two conducting material i.e. the aluminum sheet and the conductors of the bar act as two plates of the capacitor and the insulation on the bar act as dielectric medium for the capacitor. The capacitance of the bar is found and of angle of deviation due to impurity in the insulation is obtained from the formula: -4 C4 * R4 * 10 = tan δ
For different ratings of the bar the acceptable value of tan δ is fixed according to their insulation requirement as per design considerations. 22
H.V. (High Voltage) Testing This test is also known as insulation test because this test is performed to check the insulation of the bar. In this test the bar which is already wrapped with aluminum is used. High voltage is applied to the bar using auto-transformer and it is increased in steps according to the working voltage of the generator. If the insulation is weak the bar will puncture at the place of weaker insulation. For 500 MW the working voltage of the bar is 64.5 KV & for 210 MW the working voltage of the bar is 63 KV. If any of the bar fails this test i.e. bar is punctured at any point then the bar is sent back for re-insulation and all the processes are repeated again.
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Chapter 3 BAY-2 Introduction: Bay 2 is the manufacturer of stator bars of hydro generators, stator coils of AC motors and stator coils of DC Exciter. The stator coils of AC motors of up to 11 KV, stator bars of Hydro generators of 200 MW and DC Exciters of all the 500 MW THRI generators are manufactured in this bay. The processes involved in the manufacturing of AC motors are as follows:
Insulation Check For the manufacturing of stator coils of AC motors, insulated copper conductors of specific dimensions rolled on the drums are brought from Bangalore. Before performing any process on that conductor, the insulation of the conductor is checked.
Insulating materials and the conductors are ensured to be certified.
If required the insulation is checked by the respective agencies.
Conductor Tapping The copper conductor is first provided with two layers of insulation, this is also known as double layer tapping. The insulation tape used in this is Micafabriglass Tape. In this process the copper drums are loaded on the stand and tapping rolls on taping heads of the Tapping machine. The copper conductor is insulated with two layer of tape in butt as per design and hence the insulated copper conductor is again rolled on the drum from other side of the machine. The insulation on the copper is checked, which is provided by the automatically moving tapping rolls with some tension. t ension.
Winding Boat Coil The next process is forming a boat shape coil with the insulated copper conductor. In this process the former of the boat shape coil, which is adjustable in length, is first set as per length of the coil required according to the design. The number of conductors per turn and the total number of turns in a coil are all set according to the design. The insulated copper conductor drums are loaded on stand on one side of the former, the former i s then rotated and hence a boat shaped coil of specified length and specific number of turns is formed. The boat coil is then checked for its length and number of turns.
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Boat Insulation The boat coil is then sending to the insulation block for its it s insulation. Here the complete boat coil is insulated with single layer of polythene and then the stack consolidation length of the coil is marked and the coil is send for the next process.
Stack Pressing In this process the press plank is first cleaned then the boat coil is loaded in the press. The boat coil is cured for 35 minutes at 155 ± 5 °C under high pressure (to ensure closing of box) after attaining the temperature. 0.1 mm filler gauge should not go inside the box. The stack length and width of the boat coil is checked at slot portions. The pressing of the boat coil is done for the consolidation of the coil. The length of heating plates should be approximately equal to the stack consolidation length of coil.
Forming The forming of the boat coil is done in an automatic machine i.e. Schumann Pulling Machine. The machine is first set, and then the forming plates are mounted for overhang on the machine. The forming plates mounted are according to the overhang design of the coil. The required variant of boat coil is pulled into the diamond shape. The loading of boat coil should be as per the variant of boat coil given in the design. The coil dimensions and geometry of the coil is then checked on the Universal Model. The terminals of the coil are set according to the design and also the first bends and the overhang portions are marked.
Insulation In this process the slot portion and the first bends of the coil are insulated with accelerator treated Mica Tape as per design. For the stator coil of 11 KV AC motor, total 8 layers of insulation tapping are provided i.e. three layers at the slot portion and the rest five layers all over the coil. Generally for the stator coils of low rating motors total five layers of insulation tapping is provided. The insulation tape used is Epoxy Mica Paper tape. Red tape is the finishing tape provided at the overhang portions of the coil. The black colored insulation tape in conducting in nature and it is provided at the slot portion of the coil. The insulation tape at the bend portions of the coil is grey in color and is semi conducting in nature. Then the perimeters and width of the insulated coil is checked at the slot portion of t he coil. A release film is to be provided on the entire coil including coil terminals. On slot portion two layers of release film is provided. The coil is now sending for the next process.
Impregnation For impregnation pressing strips are mounted on the coil. The pressing strips are checked to be closed properly. The coils are then impregnated in micalastic resin as per design. 25
The impregnation resin mixture is to be heated in the working tank, to (60±3) °C or in case of higher initial viscosity. At a temperature of 50ºC, the impregnating resin mixture is to be degassed with 1-5 m bar vacuum. Subsequently the stator windings are to be dipped continuously in resin hardener mix such that the highest locations of the windings are at least 100 mm below the resin level. After 10 minutes of resin stabilization, pressure is increased by application of nitrogen. Pressure is to be gradually increased in uniform stages within 80 minutes to 4 bars and to be maintained for 120 minutes in t he impregnation tank. The impregnation of the stator winding is to be monitored continuously. Further it is to be decided whether to increase the pressure or to stop the impregnation process, however the total period of nitrogen pressure p ressure cycle shall in any case not exceed 4 hours. The impregnation tank during shut down is to be closed and kept either filled with nitrogen (1.1bar) or low vacuum.
Curing After the impregnation of the coil , it is then cured at 140 ± 10 ºC for 18 hours after attaining the required temperature. Curing of the coil is done for the proper consolidation of the coil. The regime is then required to be checked. The pressing strips are disassembled after the curing of the coil. The dimensions of the coil are then checked.
Finishing In this process the release film is removed and the coil is finished with sand paper. The straight length of the coil is marked. The coil is then t hen coated with corona protection varnish as per design and then the coil is allowed to dry properly for 6 hours. The slot portion dimensions and the quality coating varnish are then checked. The coil is checked for its insulation using tan δ and H.V. (High Voltage) Test.
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BAY -3 Introduction: Bay 3 is the manufacturer of insulating material of different shapes and sizes as required according to the design. This bay is also called as I.D. Section (Insulation Design Section). For the manufacturing of insulations, different raw materials having insulating properties are brought by this section. The raw materials having different insulating properties are then processed in this section and molded to different shapes as per design. The raw materials used in this bay are:
Glass based Textolite Sheet
Cotton based Textolite Sheet
Paper based Textolite Sheet
Mica Glass sheet
Teflon Sheet
Mica Sheet
Nylon Sheet
Ebonite
Perpex Glass Sheet
Nomex Paper
Asbestos Sheet
Asbestos Paper
All the insulating raw materials mentioned above are in the decreasing order of their insulating property. The insulating materials used in the manufacturing of insulation moulds are categorized according to their laying requirement in the machine i.e. if an insulation mould is to be fixed in the place where the risk of fire is more then at those places moulds of Glass based Textolite sheet are preferred because cotton based or paper based textolite sheet could catch fire at those t hose places. Teflon Sheet has an important property and i.e. Teflon is non heat transferring material. So an insulating mould of Teflon is placed above the bearings of the rotor so that is any fault in the bearings of the rotor produces any heat then it is prevented by this material to get transferred to the rotor, and hence prevents the rotor of the machine. For the manufacturing of insulation moulds, the glass insulation raw material in fibers is first pressed into blocks in a pressing machine with the help of heaters and hydraulic pressure. Fibers are made into blocks because if fiber is used as it is then volume of the material will be very large. So blocks are placed on weighing machine and then weighed equal to the product required according to design. So then these blocks are placed in the mould and heated and molded in the shape as that of the mould by applying sufficient pressure and temperature.
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Chapter 4 ELECTRICAL MACHINES BLOCK (BLOCK — I) Introduction 1. Block-I is designed to manufacture Turbo Generators. 2. The block consists of 4 bays- Bay-I (36*482 meters), Bay-II (36*360 meters) and Bay-III and Bay-IV (Of size 24*360 meters each). 3. 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 movement of components / assemblies. 4. Testing facilities for Turbo generator are available in Bay-II. 5. There is a special test bed area for testing of T.G. of capacity of 500 MW Unit sizes.
Manufacturing Process Fabricated components are received in respective machine sections from Fabrication blocks (Block — II, — II, V, VI, VIII), while castings and forgings are received from sister unit CFFP and other indigenous and foreign sources for Turbo Generators. Stampings are received from stampings manufacture block, block — VI VI and coils, bars, insulating details and sheet metal components are received from coils and insulation manufacture and apparatus and control — IV). gear box (block — IV). 1. Turbo Generators –
a) Making of blanks is done for checking the availability of machining allowances. b) Machining of the major components is carried out in Bay - I & Bay - II and other small components in Bay - III and Bay - IV. The boring and facing of stators are done on CNC horizontal boring machine using a rotary table. The shaft is turned on lathe having swift 2500 mm and the rotor slots are milled on a special rotor slot milling machines. c) In case of large size Turbo Generators core bars are welded to stator frame with the 28
help of telescopic centering device. The centering of core bar is done very precisely. Punching is assembled manually and cores are heated and pressed in number of stages depending on the core length. d) Stator winding is done by placing stator on rotating installation. After lying of lower and upper bars, these are connected at the ends, with the help of ferrule and then soldered by resistance soldering. e) Rotor winding assembly is carried out on special installation where coils are assembled in rotor slots. The pressing of overhang portion is carried out on special ring type hydraulic press, whereas slot portion is pressed manually with the help of rotor wedges. Coils are wedged with special press after laying and curing. The dynamic balancing of rotors is carried out on the over speed balancing installation. 500 MW Turbo Generators are balanced in vacuum balancing tunnel. f) General assembly of Turbo Generators is done in the test bed. Rotor is inserted in the stator and assembly of end shields; bearings etc. are carried out to make generators ready for testing. Prior to test run the complete generator is hydraulically tested for leakages.
g) Turbo Generators are tested as per standard practices and customer requirements.
Turbo Generator 500 MW Turbo generators at a glance -
2-Pole machine with the following features:f eatures:
Direct cooling of stator winding with water.
Direct hydrogen cooling for rotor.
Micalastic insulation system
Spring mounted core housing for effective transmission of vibrations.
Brushless Excitation system.
Vertical hydrogen coolers
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 Lag
Efficiency
:
98.55% 29
Important dimensions & weights
Heaviest lift of generator stator
:
255 Tons
Rotor weight
:
68 Tons
Overall stator dimensions [L*B*H]
:
8.83m*4.lm*4.02m 8.83m*4.lm*4.02m
Rotor dimensions(Dia. and length)
:
1.15m and 12.11m
Total weight of turbo generator
:
428 Tons
Unique installations-
Heavy Electrical Equipment Plant, Haridwar is one of the best equipped and most modern plants of its kind in the world today. Some of the unique manufacturing and testing facilities in the plant are: TG Test Bed-
New LSTG [Large Scale Turbo Generator] Test Bed has been put up with indigenous knowhow in record time for testing Turbo generators of ratings 500 MW and above up to 1000 MW. It caters to the most advanced requirement of testing by employing on-line computer for data-analysis. Other major facilities are as follows –
Major facilities like stator core pit equipped with telescopic hydraulic hydraulic lift, micalastic plant for the manufacture of stator bars, thermal shocks test equipment, rotor slot milling machine etc. have been specially developed by BHEL.
12 MW/10.8 MW, 6.6 KV, 3000 RPM AC non salient pole, synchronous motor have been used for driving the 500 MW Turbo-generator at the TEST Bed. The motor has special features to suit the requirement of TG testing (500 MW and above). This is the largest 2-pole (3000 rpm).
Over speed balancing vacuum tunnel -
For balancing and over speeding large flexible Turbo generators rotors in vacuum for ratings up to 1,000 MW, an over speed and balancing tunnel has been constructed indigenously. This facility is suitable for all types of rigid and flexible rotors and also high speed rotors for low and high speed balancing, testing at operational speed and for over speeding. Generator transportation
Transport through300 Tons 24-Axle carrier beam railway wagon specially designed indigenously and manufactured at Haridwar. The wagon has been used successfully for transporting one generator -from Calcutta Port to Singrauli STPP. 30
CONSTRUCTIONAL CONSTRUCTIO NAL FEATURES OF STATOR WINDING 1) General –
The stator has a three phase, double layer, short pitched and bar type of windings having two parallel paths. Each slots accommodated two bars. The slot lower bars and slot upper are displaced from each other by b y one winding pitch and connected together by bus bars inside the stator frame in conformity with the connection diagram. 2) Conductor Construction –
Each bar consists of solid as well as hollow conductor with cooling water passing through the latter. Alternate arrangement hollow and solid conductors ensure an optimum solution for increasing current and to reduce losses. The conductors of small rectangular cross section are provided with glass lapped strand insulation. A separator insulates the individual layers from each other. The transposition provides for mutual neutralization of voltage induced in the individual strands due to the slots cross field and end winding field. The current flowing through the conductor is uniformly distributed over the entire bar cross section reduced. To ensure that strands are firmly bonded together and give dimensionally stability in slot portion, a layer of glass tape is wrapped over the complete stack. Bar insulation is done with epoxy mica thermosetting insulation. This insulation is void free and posses better mechanical properties. This type of insulation is more reliable for high voltage. This insulation shows only small increases in dielectric dissipation factor with increasing test voltage. The bar insulation is cured in an electrically heated process and thus epoxy resin fill all voids and eliminate air inclusions. 3) Method Of Insulation –
Bar is tapped with several layers of thermosetting epoxy tape. This is applied continuously and half overlapped to the slot portion. The voltage of machine determines the thickness of insulation. The tapped bar is then pressed and cured in electrical heated press mould for certain fixed temperature and time. 4) Corona Prevention –
To prevent corona discharges between insulation and wall of slots, the insulation in slot portion is coated with semiconductor varnish. The various test for manufacturing the bar are performed which are as follows(a) Inter turn insulation test on stuck after consolidation to ensure absence of inter short. (b) Each bar is subjected to hydraulic test to ensure the strength of all joints. 31
(c) Flow test is performed on each bar to ensure that there is no reduction in cross section area of the ducts of the hollow conductor. (d) Leakage test by means of air pressure is performed to ensure gas tightness of all joints. (e) High voltage to prove soundness of insulation. (f) Dielectric loss factor measurement to establish void free insulation. 5) Laying Of Stator Winding –
The stator winding is placed in open rectangular slots of the stator core, which are uniformly distributed on the circumference. A semi conducting spacer is placed in bottom of slots to avoid any damage to bar due to any projection. Driving in semi conducting filler strips compensates any manufacturing tolerances. After laying top bar, slot wedges are inserted. Below slots wedges, high strength glass texolite spacers are put to have proper tightness. In between top and bottom bars, spacers are also put. 6) Ending Winding –
In the end winding, the bars are arranged close to each other. Any gaps due to design or manufacturing considerations are fitted with curable prepag with spacer in between. The prepag material is also placed between the brackets and binding rings. Lower and upper layers are fixed with epoxy glass ring made in segment and flexible spacer put in between two layers. Bus bars are connected to bring out the three phases and six neutrals. Bus bars are also hollow from inside. These bus bars are connected with terminal bushing. Both are watercooled. Brazing the two lugs properly makes connection.
CONSTRUCTIONAL CONSTRUCTIO NAL FEATURES OF ROTOR The rotor comprises of following foll owing component: 1) Rotor shaft 2) Rotor winding 3) Rotor wedges and other locating parts for winding 4) Retaining ring 5) Fans 6) Field lead connections
32
1) Rotor Shaft – The rotor shaft is a single piece solid forging manufactured from a vacuum casting. Approximately 60 % of the rotor body circumference is with longitudinal slots, which hold the field winding. The rotor shaft is a long forging measuring more than 9m in length and slightly more than one meter in diameter. The main constituents of the steel are chromium, molybdenum, nickel and vanadium. The shaft and body are forged integral to each other by drop forging process. Following tests are done: (a) Mechanical test (b) Chemical analysis (c) Magnetic permeability test (d) Micro structure analysis (e) Ultrasonic examination (f) Baroscopic examination On 2/3 of its circumference approximately the rotor body is provided with longitudinal slot to accommodate field winding. The slot pitch is selected in such a way that two solid poles o
displaced by 180 C are obtained. For high accuracy the rotor is subjected to 20% over speeding for two minutes. The solid poles are provided with additional slots in short lengths of two different configurations. One type of slots served as an outlet for hydrogen which has cooled the overhang winding and other type used to accommodate accommodate finger of damper segments acting as damper winding.
2) Rotor Winding –
After preliminary turning, longitudinal slots are milled on sophisticated horizontal slot milling machine. The slot house the field winding consists of several coils inserted into the longitudinal slots of rotor body – 2.1. Copper Conductor –
The conductors are made of hard drawn silver bearing copper. The rectangular cross section copper conductors have ventilating ducts on the two sides thus providing a channel for hydrogen flow. Two individual conductors placed-one over the other are bent to obtain half turns. Further these half turns are brazed in series to form coil on the rotor model.
33
34
2.2. Insulation – The The individual turns are insulated from each other by layer of glass prepag strips on turn of copper and baked under pressure and temperature to give a monolithic inter turn insulation. The coils are insulated from rotor body by U-shaped glass laminate module slot through made from glass cloth impregnated with epoxy varnish. At the bottom of slot D-shaped liners are put to provide a plane seating surfaces for conductors and to facilitate easy flow of gas from one side to another. These liners are made from molding material. The overhang winding is separated by glass laminated blocks called liners. The overhang winding are insulated from retaining rings segments having L-shape and made of glass cloth impregnated by epoxy resin. 2.3. Cooling Of Winding –
The rotor winding are cooled by means of direct cooling method of gap pick-up method. In this type of cooling the hydrogen in the gap is sucked through the elliptical holes serving as scoop on the rotor wedges and is directed to flow along lateral vent ducts on rotor cooper coils to bottom of the coils. The gas then passes into the corresponding ducts on the other side and flows outwards and thrown into the gap in outlet zones. In this cooling method the temperature rise becomes independent of length of rotor. The overhang portion of the winding is cooled by axial two systems and sectionalized into small parallel paths to minimize temperature rise. Cold gas enters the overhang from under the retaining rings through special chamber in the end shields and ducts under the fan hub and gets released into the air gap at rotor barrel ends.
3) Rotor Wedges –
For protection against the effect of centrifugal force the winding is secured in the slots by slot wedge. The wedges are made from duralumin, an alloy of copper, magnesium and aluminum having high good electrical conductivity and high mechanical strength. The wedges at the ends of slot are made from an alloy of chromium and copper. These are connected with damper segments under the retaining ring for short circuit induced shaft current. Ventilation slot wedges are used to cover the ventilation canals in the rotor so that hydrogen for overhang portion flows in a closed channel. 4) Retaining Ring –
The overhang portion of field winding is held by non-magnetic steel forging of retaining ring against centrifugal forces. They are shrink fitted to end of the rotor body barrel at one end; while at the other side of the retaining ring does not make contact with the shaft. 35
The centering rings are shrinking fitted at the free end of retaining ring that serves to reinforce the retaining ring, securing, end winding in axial direction at the same time. To reduce stray losses, the retaining rings are made of non-magnetic, austenitic steel and cold worked, resulting in high mechanical strength. 5) Fans –
Two single stage axial flow propeller type fans circulate the generator cooling gas. The fans are shrinking fitted on either sides of rotor body. Fans hubs are made of alloy steel forging with three peripheral grooves milled on it. Fan blades, which are precision casting with special alloy, are machined in the tail portion so that they fit into the groove of the fan hub.
6) Field Lead Connections –
6.1 Slip Rings – The The slip ring consists of helical grooved alloy steel rings shrunk on the body shaft and insulated from it. The slip rings are provided with inclined holes for self-ventilation. The helical grooves cut on the outer surfaces of the slip rings improve brush performance by breaking the pressurized air pockets that would otherwise get formed between the brush and slip rings. 6.2 Field Lead – The The slip rings are connected to the field winding through semi flexible
copper leads and current-carrying bolts placed in the shaft. The radial holes with current carrying bolts in the rotor shafts are effectively sealed to prevent the escape of hydrogen. A field lead bar, which has similar construction as, does the connection between current carrying bolt and field winding that of semi flexible copper leads (they are insulated by glass cloth impregnated with epoxy resin for low resistance and ease of assembly).
CONCLUSION The second phase of training has proved to be quite faithful. It proved an opportunity for encounter with such huge machines like turbo-generator hydro generator etc. The architecture of B.H.E.L., the way various units are linked and the way working of whole plant is controlled make the students realize that Engineering is not just structural description but greater part is planning and management. It provides an opportunity to learn tech. Used at proper place and time can save a lot of labor. However, training has proved to be satisfactory. It has allowed us an opportunity to get an exposure of the practical implementation of theoretical fundamentals.
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BIBLIOGRAPHY
BHarat Heavy Electrical Ltd. BHEL Turbo Generators Manual. In BHEL, BHEL product technical Manual.
Bharat Heavy Electricals Limited. (2005). Bharat Heavy Electricals Ltd. Product Information. Retrieved May 2010, from http://www.bhel.com
Bharat Heavy Electricals Ltd. (1993). BHEL Pro/E Manuals. Haridwar: BHEL.
meena, A. (n.d.). electrical report at BHEL haridwar . Retrieved May 2010, from Scribd: http://www.scribd.com/do http://www.scribd.com/doc/31295276/e c/31295276/electrical-report-at-BHEL-haridwar lectrical-report-at-BHEL-haridwar
Verma, A. (2010, May). Daily Diary. Di ary. BHEL visiting notes . Haridwar, Uttrakhand, India.
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