BHEL Haridwar Vocational Training Program

BHEL Haridwar Vocational Training Program

Submitted by:

S Azhar Madar

12212011

EPE IV

Electrical Department

DECLARATIONI hereby declare that this summer training report submitted to the Department of Electrical Engineering, IIT Roorkee is a record of an original work done by me under the guidance of Mr. Raj Mani Jaiswal, BHEL, Haridwar, and this report is submitted in the partial fulfillment of the requirements for hte award of the degree of Bachelor of Technology in Electrical Engineering. The resilts embodied in this report have not benn submitted to any other University of Institute fo the award of any degree.

Contents

Introduction BHEL

Turbo-generators

TheoryComponents of a Turbo Generator

Rotor

Stator

Ventilation and Cooling System

Exciter System

Bay-4 (Miscellaneous components)

LSGT Test Stand

Testing

Helium Leak Test

Hydrogen Testing and Pneumatic testing

Conclusion

References

Abstract- This report presents a technical study of Stator, Rotor & Exciter assembly of Turbo Generator or Alternator (500MW) at Bharat Heavy Electrical Limited (BHEL) Haridwar. Various constructional features of Stator, Rotor and Exciter system are employed during manufacturing process of Turbo Generator. Different types of turbo generator and their essential components are highlighted in this report. Role of insulation and methods of insulation are an important aspect of stator and rotor winding. A wide range of facilities comprising small and medium size machine tools like centerlathes, milling, radial drilling, cylindrical grinding, slotting, copy turning lathe, internal grinding andsurface grinding machines used in various section of BHEL Haridwar are briefly discussed. Methods of testing namely HELIUM LEAK TEST and HYDRAULIC TESTING AND PNEUMATIC TESTING are considered in the report.

1.Introduction

Bharath Heavy Electricals Limited (BHEL) is a hugely profitable enterprise established by the Government of India in 1964 with headquarters located at New Delhi, India. With over 180 products under 30 major product groups, BHEL is the largest engineering and manufacturing enterprise in India. Its influence can be definitively observed in core sectors of the Indian Economy like Industry, Transportation, Power Generation and Transmission, Telecommunication, etc. Its recent involvement in Solar Power generation has been essential and productive step towards a renewable energy power sourced country. BHEL has already commissioned 70 MW of solar plants in the country.

Bharath Heavy Electricals Limited (BHEL) is a vast company with a network of 17 manufacturing units to supply various core branches of India, 2 repairing units, 4 regional offices, 8 service centers, 8 overseas offices, 15 regional centers, 7 joint ventures, and infrastructure. With this huge resources at hand, it executes more than projects both in our country and abroad.

BHEL has been a leading company with more than 70% market share in Power Sector. The company has provided the country the capability to deliver 20,000 MW per anum. This enabled the country to satisfy the growing demand for power generation equipment and decreasing the amount of imports being taken by the country. So far, more than 1.24 lac MW has been added to our nations power generation.

Exporting power and industry segment products and services has been a common practice by BHEL for over 40 years. BHEL manufactured many power plants to 21 countries like Egypt, New Zealand, Bhutan, etc, whose power generation has exceeded 9000 MW. BHEL continues doing multinational projects, global references, sales services and many other things.

BHELs Units

Manufacturing units of BHEL across the country

BHEL Haridwar

Heavy Electricals Equipment Plant of BHEL is located in Ranipur near Haridwar. It has two large plants with various shops for different purposes viz. CFFP (Central Foundry Forge Plant) and HEEP (Heavy Electrical Equipment Plant).

CFFPs various shops:

Forge Shop

Machine Shops

Steel Melting Shop

Steel Foundry

Pattern Shop

Cast Iron foundry

2. HEEP is divided into following blocks:

Block-1 Turbo Generators, AC Machines

Block-2 Fabrication (Steam, Hydro & Gas Turbine)

Block-3 Gas & Steam Turbine

Block-4 Coil & Insulation Manufacturing, Apparatus Control Gear

Block-5 Heat exchangers, Forging and Fabrication

Block-6 Stamping

Block-7 Wooden Patching works

Block-8 Fabrication, seamless tubes and heat exchangers

Turbo Generators

Turbo Generators are manufactured in Block-I. The Block-I is mainly divided into 4 Bays each of area of approximately 12,960 sq. meters. For transporting and handling the various components, overhead crane facilities are available. Trolleys that are self-propelled and electrically driven are also available for the inter bay movement of the components.

Theory

Turbo Generator works on the principle of Electromagnetic induction. Basic standard construction consists of armature winding which is placed on a stationary element called stator. The field winding's are mounted on a rotating element called rotor. Stator is an assembly of a cast iron frame, which provides support to the core of the armature which has slots on its inner periphery for housing the armature conductors. The rotor has alternating south and north poles during rotation. Exciter is mount on the shaft of alternator to excite the magnetic poles. Current is supplied through the slip rings as the field magnets rotate. The alternating magnetic poles induce an emf thereby a current in armature conductors. The frequency of emf depends upon the number of poles moving past a conductor in a second and their direction is given by Fleming,s right hand rule.Functioning of Turbo Generator

Prime mover drives the generator which is a steam turbine in this case.The other side of generator is provided by a rotating armature of an exciter whichproduces A.C. voltage. Its rectification toD.C. is done by using a rotating diode wheel.The rearend of above exciter armature is mounted by a permanent magnet generator rotor. During operation, the Permanent Magnet Generator (PMG) produces A.C. voltage.The thyristor circuit rectifies the voltage to D.C.The rectified supply is fed to the exciter field which is also regulated by feedback taken from main generators voltage terminal. Feedback is taken so that automatic voltage regulator can be used to control exciter field variation. The rectified supply out of the exciter is fed to turbo generator rotor winding. The connection can be direct or through brushes depending on what the type of exciter is used.

The main A.C. voltage is finally available at the stator of Turbo Generator.

The Turbo Generators manufactured in BHEL Haridwar are Large Size Turbo Generator (LSTG). In these types of generators steam turbine does the function of prime mover which rotates the rotor of LSTG and the field windingis supplied D.C. by an exciter. Main types of T.G manufactured in BHEL are:-

#PhaseGenerator CoolingRotor CoolingStator

Cooling

1THRI

2TARI

3THDI

4THDD

5THFF

6THDF

1st Letter (here-T): it denotes 3-phase turbo generator

2nd Letter (here- H/A):

H- Medium present for generator cooling is Hydrogen

A- Medium present for generator cooling is Air

3rd Letter(here-R/D/F):

R- type of rotor cooling employed is radial

F- type of rotor cooling employed is direct water cooling

D- type of rotor cooling employed direct axial gas cooling.

4th Letter (here- I/D/F): I- type of stator winding cooling employed is indirect gas cooling D- type of stator winding cooling employed is direct gas cooling

F- type of stator winding cooling employed is direct water cooling

Components of a Turbo Generator

Rotor: Rotor winding, Rotor shaft, Rotor retaining rings

Stator: Stator core, Stator frame, Stator winding, and the End

cover

Bearings

Excitation System

Cooling System

Rotor

Rotor is the moving or rotating part of generator. The axial length ofshaft of the rotor is very large as compared to its diameter in case of turbo generators. It is coiled heavily (field coils) as it has to support largeamount of current and voltage. Rotor revolving speed of generators is mostly of 3000rpm. Field coils are wound overit to make the magnetic poles. In order to maintain the magnetic strength, the winding mustcarry a very large value of current. As current flows heat is generated,but the temperature has to bemaintainedbecause as temperature rises, the problem with insulation becomes morepronounced.ROTOR SHAFT:-

The rotor shaft is cold rolled forging 26N1 or MOV116 grade and it is imported from Japan and Italy. Rotor shaft is a single piece. Thelongitudinal slots are distributed over its circumference. After the process is complete, the rotor is balanced at several speeds and in various planes. It is then exposed to over speedtest at 120% of speed of rotor. Nearly 60 % of the circumference of the rotor body has longitudinal slots which hold the field winding. The selection of slots pitch is such that the 2 solid poles are shifted by 180 degrees. The damper winding is provided by rotor wedges. The rotorteeth at the body of the rotor are providedin radial and axial poles. This enables discharge of cooling air.

Various Steps Involved In Rotor Machining:-

SHAFT MACHINING:-

It involves finishing of shaft by machining it with a centrallathe machine. It is done in accordance to the engineering drawing design. Special care is taken to maintain the tolerance level.

SLOTTING:-

Two types of machines do slotting, air cooledand liquid cooled. Slotting is done diametrically. First the shaft is made to rest on two horizontal plates andis firmly attached to them with the help of chains which exerts load and with thehelp of jack so that it handles the vibrations produced during the slotting process.Now the Centre is marked andslotting is done. After slotting is done through one side the shaft is rotated to the diametrically opposite end of the slotted portion and then again slotting of that portion is done. It is done in diametrically opposite ends so as toprevent bristling of slot due to mechanical vibrations.

ROTOR WINDING :-

Rotor winding involves coiling of rotor. It is atwo pole rotor. Rotor coils are made of pure copper + 0.2% silver, which has high tensile as well as temperature bearing properties. The coil doesnt deform even at high temperatures as on adding silver the thermal stresses are eliminated. Rotor windingis also known asfieldwindingwhich is wound in longitudinal slots in rotor.

ROTOR SLOT WEDGES :-

In order to provide protection to the rotor windings from the effects of centrifugal forces, the windings are protected in slots with wedges. Copper-nickel-silicon alloy is used to make slot wedges. This provides high temperature resistance and high strength. There is retaining ring, which protects the rotor from theimpact of centrifugal force on end windings. Comprehensive tests such as ultrasonic examination and liquid penetration examination are carried out in thecoils.

To ensure low contact resistance, retaining rings are coated with nickel, aluminum and silver by three step flame-spraying process.

ROTOR WINDING:-

The winding of rotor consists of several series connected coils placed inside theslots. These are connected so that 2 coils group to form a single pole. Every coil is made up of many turns each of which are connected in series. Each turn consists of two half turns connected by brazing in end section. Inter layerinsulation is used to provide insulation to individual turns of a coil against each other. Slot insulation is provided by L-shaped strip of laminated epoxy glass fiber with nomexfilter. The slot wedges act as damper winding as they are made up of high electrical conductivity material. The slots wedges are short circuited at the ends through therotorbody. When rotor rotates at high speed, the centrifugal forces try to lift the winding out of slots. They are restricted with the help of wedges.

Construction of field windings:-

The field windings are made of many series connected coils into the longitudinal slots of body. The winding is done in such a manner such that two poles are obtained.The cross-section of solid conductors is rectangular. These coils are formed arranging together the14 strips which makes ahalfof the coil which meansthat total 28 strips are used to make singlecoil of the field winding.

Field winding of Turbo Generator

A phase has 7 conductors.

B phase have 9 conductors each coil.

They are transposed by 540o as itremoves air gap and improves crossover insulation.It increases mechanical strength and help in producing equal E.M.F across all the conductors.

The insulation is molding mica mite.

Testing involving the coils are thermal shock testing hotand cold.

This testing is done to checkthe strength of brazing so that there is no water leakage and as aresult it can bear thermal stresses easily.Nitrogen test is also performed for cleaning and leakagepurposes and finally impregnating it through vacuum impregnation technique.

The vacuum impregnation technique is the latest technique to insulate the windings ofstator and not used in rotors of any of the generators being used inthe power plants now a days. The process above is discussed is also known as transposition, which involves thebending of the strips used in forming the coil of either rotor or stator.

Material of Conductor:-

The conductors are mainly made up of copper with an approximate content of silver as 0.1%. Silver alloyed copper have high strength properties compared to electrolytic copper at high temperatures. So its ensured that there is no coil deformation due to thermal stresses.

Insulation:-

Glass fiberlaminate is used for insulation between the individualturns. The coils are insulated from the body of the rotor using strip of glass fiberlaminate which are L-shaped with nomex interlines. Thick top stripsof glass fiber laminate are placed below wedge so that required leakage path is obtained between the coil and the body of the rotor.

ROTOR RETAINING RINGS

Rotor retaining rings are used to confine the centrifugal forces of the endwindings. Non -magnetic high strength steel is used to make retaining rings so that stray losses can be reduced. The retaining rings are protected in the axialposition with the help of snap rings. Due to presence of endwindings, the rotor retaining rings are able to withstand the centrifugal forces. One end ofeach ring is shrunk fitted on the rotor body and the other overhangs the end winding ensuring no connection with the shaft of the rotor. Unobstructed deflection of the shaft is thus ensured at endwindings. On the endof the retaining ring, the shrunk on hub serves the purpose of reinforcing the retainingrings and serves the end winding in the axial direction. A snapring is also provided against displacement of the retaining ring in axial direction. In order to minimizethe stray losses and have high strength, non-magnetic cold worked material is used for making the rings.

ROTORFANSTwo axial flow fans ensure the cooling air inside the generator. There are located at each end of the rotor shaft. The blades of fan have threaded roots for screwed into the shaft of the rotor. Bladesare made from alloy of aluminum. Threaded root fastening enables the angle change of angle.

FIELD CURRENT LEAD IN SHAFTBASE

Leads are run in axialdirection through the radial bolt of the exciter coupling. These lead contains low semi-circular conductors. These conductors are insulated from each other andfrom the shaft by a tube. The field current leads are coupled with exciter leads through a multi contact plugin which allows unobstructed thermal expansion offield current

ROTOR ASSEMBLY:-Rotor winding assembly and rotor assembly and rotor assembly like rotorretaining ring fitting. All these four assemblies are carried out in a:ROTORASSEMBLY SECTIONPresent in BAY-1. This section is also in a dust-proof enclosure with no. of rotators, rotor bars laying facilities and MI heating and mounting of retaining rings

2.2.2 Stator

A generator stator is a heavy construction which gives support andencloses the statorwinding, hydrogencooling medium and the core. Gas of hydrogen is contained in aframe and fans are used for its circulation in the system. These fans are installed either of the two ends of the rotor. A steam turbine is used to drive the generator at the speed of 3000 rotations per minute. The design of the generator is for a continuous rated output.

STATOR FRAME

The stator frame is used for housing armature conductors. It is made of cylindrical section with two end shields which aregas tight and pressure resistant. The stator frame accommodates the electrically active parts of stator i.e. the stator core and the statorwinding. A stator frame is shown in ure 3.2.

STATOR CORE:-

The stacking of stator core is done from theinsulated electrical sheet steel lamination and mounted in supporting rings over the insulated dovetail guide bars. In order to minimize eddy current losses, the core is made of thinlaminations. Lamination layers are made ofindividual sections. Ventilation ducts are imposed sothat the distribution of gas can be done accurately over the core andan adequate support can be given tothe teeth .The main roles of core are

1. To provide the mechanicalsupport.

2. To carry the electric and magnetic flux efficiently.

3. To ensurethat the linkbetween the coreand rotor is perfect.

STATOR WINDING:-The windings of the stator are composed of 2 layers that are composed upof individual bars. The winding bars are made from copper strips which are wounded with insulated tape and then they are impregnated using varnish. They are then dried and hot pressed to form a bar. Thebars are then placed inthe slots of the stator and are held in with the help of wedges tomake the end turns, which are placed tightly and are packed with lumps of insulation material so as to bear heavy pressure. The stator bar consists of hollow (in case of 500 MW generators) solid strands distributed over the entire bar cross-section, so that goodheat dissipation is ensured. The strands are transposed in the straight slot portion by 540o. Mutual neutralization of the inducedvoltage is caused by the transposition in each individual strand because of the slot cross field and end winding flux leakage and ensures the existence of minimum circulating currents. The current that flows through the conductors is hence uniformly distributed over the entire cross section of the conductor and thus reduction in losses is ensured. The alternate arrangement of onehollow strand and two solid strands ensures optimum heat removal capacity and minimum losses. The electrical connection between top and bottom bars is made by connecting sleeve. Class F insulation is used. The number of insulation layers depends on the voltage of the machine. The bars are brought undervacuum and impregnated with epoxy resin, which has very good penetration property due to low viscosity. After impregnation bars are subjected to pressure with nitrogen being used as pressurizing medium (VPI process). The impregnated bars areformed to the required shape on molds and cured in an oven at high temperatures to minimize the corona discharge between theslot wall and insulation. Finally a coating of varnish which is semiconducting in nature is applied to the surface of thebars that are within the slot range. The barsarefurther provided with an endcorona protection so as to control the electric field atthe transition from the slot to end winding. Thebars consist of a number of strands that are separately insulated, which are transposed to reduce the skin effect.

Stator frame

INSULATION OF BARS:-Vacuum pressed impregnated micalastic high voltage insulation:-The insulation for voltage protection is provided according to the resin poor mica base ofthermosetting epoxy system. The bars are applied over with several continuous layers ofresin poormica tape. The thickness or no. oflayers of insulating material is decided by the voltage of machine.

CoronaProtection:-In order to prevent corona discharge between insulation and the slot wall, outer coronaprotection is provided to the section of bars. The protection consists of polyester fleece tape impregnated in epoxy resin with carbon and graphite as fillers. a semiconductor tapeis impregnated at thetransition from the slot to the end windingportion of the stator bars.Resistance Temperature Detector (RTD):-The slots of the stator are equipped with platinum resistance thermometer for observing and recording the temperature of toothregion, stator core and between the coil sides of the operating machine. All the machines (AC) that are rated for more than 5 MVA have to beequipped with at least 6 resistance thermometers. The thermometer should be placed in the slot butoutside the insulation of the coil but thermometer is to be fixed between the insulated coil sides when the winding has more than one coil side per slot. The length of armature decides the length ofresistance thermometer. For connection onto temperature meter or relays the leads from the detector are connected to the terminal board. Working of RTD isbased on the fact thatfor a given temperature range the electric resistance of metallic conductor varies almost linearly with temperature.END COVERS:-They are mostlymade up of aluminumcastings or fabricated steel. They are provided with guide vents on innerside. These guides ensure the uniform distribution of air orgas. End cover is shown in ure 3.3.

Stator End CoverMANUFACTURING OF VARIOUS PARTS OF STATOR:-

Stator CoreAssembly Section:-

This section is presentin BAY-1.Two no. core pits with core building andpressing facilities are available in this section. The section is also equipped with optical centering device, core heatinginstallation and core loss testing facilities.

Iron Assembly Section:-In BAY-2 this section has facilities for stator core assembly of Turbo-generators and Heavy Electric Motors.

Stator Winding Section:-

This section is present in BAY-1. The sectionis located in a dust-proof enclosure with winding platform and with rotating installation for assembly ofwinding. Resistance brazing machines andhigh voltage transformers are also available in this section.

Bar Preparation Section:-

This section is present in BAY-1. This section consists of milling machine forlong preparation, installation for insulation of tension bolts for stator and preparationofstator winding before assembly. The three phase winding is a fractional pitch, two layertype winding consisting of individual bars.

Armature Section:-

This section is equipped with installations like bandaging machines, tensioning devices, magnetic putty application machine and 45 KW MF brazing machinesfor laying windings in large size DC armatures.

Cooling:-

Heat losses arising in the generator are dissipated throughhydrogen. The heat dissipating capacity of hydrogen is eight times to that of air.BEARINGS Turbo generators have bearing of pressure lubricated self-aligning type. This is to ensure reduced vibration and better mechanical stability during operation. Suitable temperature element is provided to the bearings tomonitor metal temperature of bearing during operation. The temperature monitoring of each bearing is done with the help of 2 Resistance Thermo Detectors (RTDs). These RTDs are embedded in thebearing sleeve such that the measuringpoint is located directlybelow Babbitt. To monitor the shaft vibrations, the bearing have provision for vibration pickup. Shaft current can cause damage to the journal. So to prevent this, coil piping on either side of the non-drive andbearings are insulated from the foundation frame.

2.4 VENTILATION AND COOLING SYSTEM:-

VENTILATION SYSTEM-Ventilation system is designed for every machinehaving the rated pressure. The circulation of hydrogen gas is ensured with axial fans that are fitted on either of the sides ofthe rotor. Thedesign of rotor is for radial ventilation. Special ventilation system is used for ensuring that the temperature of stator core and rotor windings remains uniform.

COOLING SYSTEM STATOR COOLING SYSTEM Distillate water is used for cooling of the stator winding. The water is supplied through one end of the machine using Teflon tube. It then drifts through the upper bar and then proceeds back through the lower bar of a slot. Arrangement of cooling water is required by Turbo generator over and above the normal cooling arrangement of hydrogen.In this system, the cooling of stator is ensured by circulating demineralized water via hollow conductors. It is very important to have a cooling system for the stator winding but for it very high quality of cooling water is required. Accordingly demineralized water of proper specifying resistance is chosen. The design of the system is such that the rate of flow of cooling water flow through the winding of stator is maintained at a nominal inlet temperature of40o centigrade. Thecooling water is again cooled by water which is also demineralized to avoid contamination with any impure water in case of cooler tube leakage. The secondary DM cooling water is in turn cooled by Clarified water taken from clarified water header.

ROTOR COOLING SYSTEM Gap pickup cooling method is used for cooling the rotor. In this method of cooling, gas of hydrogen which is present in the air gaps is drawn throughthe scoops on the rotor. It is made to flow through the ventilating canals which are grinded on the rotor coil sides, to the foot of the slot. Therethe gas takes a bend and then appears on the similar channel made on theother side of the rotor coil to the hot zone of therotor. Apositive section and a discharge are formed because to the rotation of the rotor. As a result this, a certain quantity of a gasis able to flow and cools the rotor. The method of coolingensures that temperature distribution is uniform. An inherent advantage of this method is that it has property of eliminating the copper deformation due to wavering temperature.

HYDROGEN COOLING SYSTEM Low density and high heat capacity of hydrogen makes it a suitable choice for cooling medium in turbo generators. Oil sealing system is used to prevent leaking of hydrogen from generators. The system can perform the following

Safely filing in and purging of hydrogen without bringing air in contact with it.

Keeping the pressure of gas at a desired value all thetimes.

Indicating temperature, purity and pressure of the gas to the operator.

Removing any water vapors present inside the gas, by circulating it through a drier continuously inside the machine.

Monitoring the level of liquid in thegenerator and alarming in case above preset value.

GENERATOR SEALING SYSTEM Seals are employed to prevent theleakage of hydrogen from the stator atthe point of rotor exit. A continuous film between a rotor collar and the seal liner is maintained by measurement of the oil at pressure above the casing hydrogen gas pressure.

2.5 Exciter SystemEXCITER ROTOR: The exciter system is used for production of DC field, needed for the working of turbo generator system. The main principle behind it is that Permanent Magnet generator is mounted on acommon shaft which is used to generate electricity, which is fed toyoke of the main exciter. This generated electricity and is AC in nature. This generated ACis first converted into DC andis then fed to turbo generator. For rectification we usediode bridges and RC circuits. The most beautiful feature of this type

Exciter Rotor

of exciteris that it automatically divides Magnitude of current to be circulated in the circuit of rotor is automatically divided by this exciter. This is performed with the aid of AVR. A feedback path is given to this system which compares theoretical value to predetermine and then it sends the current to rotor as per requirement. An rotor exciter is shown in figure above.The brushless exciter mainly consists of Rectifier wheels, 3- main exciter, 3- pilot exciter, metering and supervising equipment. The brushless exciter has a stationery field and a rotating armature. There is a connection made between armature and rotating rectifier bridges, used for rectifying voltage (AC) induced in armature to DC. PMG (permanent magnet generator) acts as a pilot exciter. PMG is an AC machine with rotating field and stationery armature. When the generator rotates at the rated speed, 220 V is generated by PMG at 50hertz to providepower supply to AVR (automatic voltage regulator). There is a common shaft that carries the rectifier wheels, thepermanent magnet rotor of the pilot exciter and the rotor ofmain exciter. This shaft is supported on the bearings. It is coupled rigidly to the exciter rotors and generator rotor. 2.6 BAY IV (SMALLAND MISCELLANEOUS COMPONENTS)Facilities available in the various sections are as follows:-MACHINE SECTION:-The machine section of Bay-4 is equipped with small and medium size CNC& conventional machine tools like centerlathes, milling, radial drilling, cylindrical grinding, slotting, internal andsurface grinding machines. Small-size and miscellaneous components for Turbo-generators, Hydro generators and Motors are machined in this section.POLE COIL SECTIONThickness of the profiled copper is checked with the gauge. Grinding is uniform & of smooth finish.

Sharp edges are rounded. Coil is pressed. PICKLING:-Coil is sent for pickling to block4 & quality of pickling is checked.

Coil is pressed again after pickling. Brazing is done with brazing alloy Ag 40 Cd.

Extra material is removed, cleaned and checked with gauge.FINISHING:-Coil is hanged on stand and turns are separated out.

Black spots are removed, sharpedges are burred and coil turns are cleaned with cotton dipped in thinner.

Coil is pressed again and height is checked of the coil under press to checkdimensions. Coil is sent for insulation.

INSULATION:-Coil is hanged on stand and turns are separated out.

Each turn is cleaned with cotton dipped in thinner.

Epoxy varnish is applied on both sides ofeach turn uniformly with brush all over the turn leaving top & bottom turn.

Strips of Nomax paper are cut as percontour of coil with technological allowance3to 5 mm on either side.

Two layers of Nomax strips are sticked between each turn.

Varnish layer is coated between two layers of Nomax.

Excess varnish is left to flow out for some time.BAKING AND PRESSING OF COIL:-Coil is placed on mandrelputting technological washer at top & bottomof the coil.

Coil is heated by DC up to 100 +/-5deg.C, and maintained for 30 to 40 minutes.

Supply is switched off and thecoil is elongated and pressing blocks are tightened from sides.

Heating of coil is started again and temperature is raised gradually in steps up to 130 +/- 5deg. within 10+/- 10 minutes.

110 tones pressure is applied and maintained for 20to 30 minutes. Then after everyhalfan hour, the pressure andtemperature is increased according to product requirement.

Heating is stopped and then coil is allowed to cool under pressure,below 50o C.

CLEANING AND DRYING:-

Outer and innersurface of projected insulation are cleaned by means of shop made scrubber.

Dry compressed air is flown after cleaning.

Height and window dim0102.ensions are checked.

Check no gap between the turns.

TURBO ROTOR COIL SECTION:-

This section is equipped with copper straightening and cutting machines, edgebending machines, installation for forming and brazing,10-block hydraulic press and installation for insulation filling. Rotor coils for water cooled generators (210 /235 MW) are manufactured in this section.IMPREGNATION SECTION:-This section is equipped with electric drying ovens, Air drying booths, Bath forarmature / rotor impregnation. Rotors / armatures of AC and DC motors are impregnated in this section.BABBITING SECTION:-This section is equipped with alkaline degreasingbaths, hot and coldrinsingbaths, pickling baths, tinning bath, and electric furnaces and centrifugal babbittingmachines. Babbitting ofbearing liners forTurbo generators,Turbines, Hydro generators,ACmotors andDC motorsis carriedout inthis section.

2.7 LSTG TEST STANDS:-

Turbo-generators Test Bed -The Test Bedfor Turbo-generators and Heavy motors is equipped with a drive motor and atest pit for carrying out testing of Turbo-generators and Heavy motors. Open circuit,short circuit, temperature rise.

Hydraulic and hydrogen leakage test etc., are carried out here for Turbo-generators. AC motors up to 11 MVA capacity and DC machines up to 5000 amps and 850 volt can alsobe tested. Two DC drive motors of 2200 KW and one of 1500 KW are available for type testing of motors. Data logging equipment is also available.

3 LARGE SIZE TURBO GENERATOR TESTSTAND (LSTG)3.1 HELIUM LEAK TEST

It is used to check any leakageof gas from stator and rotor. If there is anyleakage of gas, used for cooling such as hydrogen then it may cause an explosion.

Testing of stator frame involves two types of testing:

3.2 HYDRAULIC TESTING AND PNEUMATIC TESTING

Hydraulic testing involves an empty stator frame with attached end shields and terminalbox is subjected to ahydraulic test at 10 bar to ensure thatit will be capable ofwithstanding maximum explosion pressure. The pneumatic testing involves filling of hydrogen inthe sealed stator frame and then soap water is used to check the leakage of welding.

ConclusionThe Vocational training at BHEL Hardwar improved mypractical knowledge and awareness regarding Turbo Generator to a large extent. Here I came to know about the technology and material used in manufacturing of turbo generators. Being able to look at the parts and construction of various components of Turbo Generator had a profound effect on my learning. Here I learnt about how the electrical equipments are being manufactured and how they tackle the various problems under different circumstances. Time spent training at Bhel helped me acquire a great experience allowing me to expand my knowledge of making Turbo Generators used in Power Generation.

Referenceshttp://economictimes.indiatimes.com/bharat-heavy-electricals-ltd/infocompanyhistory/companyid-11831.cmshttp://www.bhel.com/about.phphttp://www.moneycontrol.com/news/business/bhel-commissions-10-mw-solar-power-plantkarnataka_1901701.html[Book] Nagrath I. J. and Kothari D. P., Electrical Machines, 3rd Ed., Tata McGraw-Hill Publishing Company Limited (2004).[Book] Fitzgeraid A. E., Kingsley C. and Kusko A., Electric Machinery,6th Ed., McGraw-Hill International Book Company (2008)