A Comprehnensive Traning Report On112 - Copy

8/10/2019 A Comprehnensive Traning Report On112 - Copy

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A Comprehensive report on the Study ofManufacture & Assembly of Turbo Generator

Project Incharge: Submitted By: Mr. Rajendra kumar Prabhakar singhPost: SDGM B.tech (3 rd yr)BHEL,Haridwar


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ACKNOWLEDGEMENT

An engineer with only theoretical knowledge is not a completeengineer. Practical knowledge is very important to develop and applyengineering skills . It gives me a great pleasure to have an opportunityto acknowledge and to express gratitude to those who were associatedwith me during my training at BHEL, Haridwar.

Special thanks to Mr. .. for providing me with anopportunity to undergo training under his able guidance and offeringme a very deep knowledge of practical aspects of industrial workculture...

I express my sincere thanks and gratitude to BHEL authorities forallowing me to undergo the training in this prestigious organization. Iwill always remain indebted to them for their constant interest andexcellent guidance in my training work, moreover for providing mewith an opportunity to work and gain experience

CONTENTS

1. Overview on BHEL

2. Coil & Insulation Manufacturing Shop(Block-4)

3. Electrical Machines Block(Block-1)


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4. Manufacturing process of Turbo Generators

5. Introduction to 500MW Turbo Generators

6. Constructional Features of Stator Body

7. Constructional Features of Stator Core

8. Constructional Features of Stator Winding

9. Constructional Features of Rotor

10. Cooling System

11. Excitation System

12. Electrical Generator Protection

13. Salient Design Features


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BHEL: AN OVERVIEW

Bharat Heavy Electricals Ltd . has emerged as the largest engineering andmanufacturing enterprise of its own kind in India with an excellent trackrecord of performance. The Company is engaged in engineering,development and manufacturing of a wide variety of electrical andmechanical equipment for generation, transmission and utilization ofenergy and electrical power. The company today enjoys national andinternational presence featuring in the "Fortune International 500" and isranked among the top 10 companies in the world manufacturing powergeneration equipment.BHEL has now thirteen manufacturing divisions, eight service centersand four power sector regional centers, besides a large number of projects

sites spread all over India and abroad. This enables prompt service to thecustomers with state-of-art products, systems and services that meet theneeds of energy, industry, transportation and other key sectors.HEAVY ELECTRICAL EQUIPMENT PLANT BHEL's Heavy Electrical Equipment Plant (HEEP) was set up intechnical collaboration with USSR, for the manufacturing of power plantequipment, AC/DC motors of various with associated control equipmentand started production in January 1967. In 1976, BHEL entered into acollaboration agreement with M/s Kraftwerk Union, AG of Germany for

design, manufacturing, erection and commissioning of large size steamturbines. More than 40 percent of the country's electrical energy isgenerated from the power equipment supplied by BHEL, Haridwar.The products, which are manufactured in HEEP, are: - Steam Turbines,Turbo Generators, hydro turbines, Gas turbines, etc..


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(BLOCK-IV) COIL & I NSUL ATI ON M ANUFACTURING SH OP

BAY-I: Bar winding shop manufacturing of stator winding bars ofgenerator.

BAY-II: Manufacturing of heavy duty generator stator bars with New CNC M/c No. 3-464 i.e. Robol bar centre.

BAY-III: Insulation detail shop. Manufacturing of hard insulation &

machining of hard insulation part (Glass textolite) such as packing, washer,insulation box, wedges etc.

Bar Shop: This shop is meant for manufacturing of stator winding coilsof turbo-generator

Why do we call it bar:It is quite difficult to manufacture, handle and wind in the stator slot ofgenerator 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 andother 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.

Type of generators: The generator may be classified based upon thecooling system used in the generators such as: THRI, TARI, THDI,THDD, THDF, THFF, THW.

T = First alphabet signifies the type of generator i.e. turbogeneratoror Hydro-generator

H/A = Second alphabet stands for the cooling media used for thecooling 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,


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forced, direct etc.I/D/F = Last alphabet stands for the type of cooling of stator e.g.indirect cooling, direct cooling, forced cooling.

W = Cooling media used for cooling of stator coil e.g. water.

Resin System :

a) Rich resin or Thermo reactive insulation system : In this type ofinsulation system the bond content in resin is 35-37%. The rawmaterials are ready to use and require preservation and working ontemperature 20-25 0C. Its shelf life is one year when kept attemperature 20 0C which could be increased when kept at temperature

of 5 0C.

b) Poor resin or Micalastic insulation system : In this type of insulationthe bond content in the resin is 5-7% and insulating material is

prepared with accelerator treatment. The temperature control neednot required. The insulating material is applied on job and then the

same is impregnated in the resin.

M anuf actur ing process of Bars :

Some points of mfg. process are in brief as below ---

Conductor cu ng :

This process is done by automatic CNCmachine. In this process the pre-insulated copper conductor is cutinto number of pieces of required length (length given in drawingas per design) insulation is removed from both ends of the copperconductor out.

2. Transposition :

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

conductors with the help of bending die at required distance. Thenthe conductors are taken out from the comb and die and placed


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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 twohalves.

3. Crossover insul ation :

The pre insulation of the copper conductormay get damaged due to mechanical bending in die duringtransposition, hence the insulating spacers are provided at thecrossover portion of the conductors. A filler material (insulating

putty of moulding micanite) is provided along the height of the barto maintain the rectangular shape and to cover the difference oflevel of conductors.

4. Stack Consoli dation :

The core part of the bar stack is pressed in press (closed box) under pressure (varies from product to product)and temperature of 160 0 C for a given period. The consolidatedstack is withdrawn from the press and the dimensions are checked.

5. I nter Strand Short test :

The consolidation bar stack is tested forthe short between any two conductors in the bar, if found then ithas to be rectified.

6. F orming :

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

7. Br azing of coil lugs :


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For water cooled generator bars, the electricalconnection contact and water box for inlet and outlet of water are

brazed.

8. Ni trogen l eak test :

The bar is tested for water flow test, nitrogenleak test and pressure test for given duration.

9. Thermal shock Test :

The cycles of hot (80 0C) and cold (30 0C)water are flew through the bar to ensure the thermal expansion andcontraction of the joints

10. H elium l eakage test :

After thermal shock test bar is tested for anyleakage with the help of helium gas.

11. I mpregnation and baking :

a) Th ermo reactive System: In case of rich resin insulation the baris pressed in closed box in heated condition and baked under

pressure and temperature as per requirement for a given period.

b) M icalastic System : In case of poor resin system the insulated

bars are heated under vacuum and the impregnated (dipped) inheated resin so that all the air gaps are filled, layer by layer,


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with resin. Then extra resin is drained out and bars are heatedand baked under pressed condition in closed box fixture.

VPI M icalastic System :- The bars already laid in closed fixture and

full fixture is impregnated (dipped) in resin and then fixture with boxis baked under given temperature for given duration.

VI P Micalastic System :- The individual (Separate) bar is heated invacuum and impregnated in resin. Then bar is taken out and pressedin closed box fixture and then baked at given temperature for givenduration.

12. I nsulation :

The bar is insulated with the given number of layersto build the wall thickness of insulation subjected to the generatingvoltage of the machine.

F ini shing :-

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

Conducting varni sh coating :

(i) OCP (Outer Corona Protection) Coating : - The black semiconductingvarnish coating is applied on the bar surface onthe core length.

(ii) ECP (End Corona Protection) Coating: The grey semiconductingvarnish is applied at the bend outside core end of

bars in gradient to prevent from discharge and minimize theend corona.

Testing :


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(a)Tano Test : - This test is carried out to ensure the healthiness of dielectric(Insulation) i.e. dense or rare and measured the capacitance loss.

(b) H .V.Test: - The each bar is tested momentarily at high voltage

increased gradually to three times higher than rated voltage.

Di spatched for winding :

The bars preserved with polythenesleeves to protect from dust, dirt, oil, rain etc. are send to block-1for winding .

(BLOCK I)ELECTRICAL MACHINES BLOCK

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*360meters) and Bay-III and Bay-IV (Of size 24*360 meters each).

3. For handling and transporting the various components over-head cranefacilities are available, depending upon the products manufactured ineach Bay. There are also a number of self-propelled electrically driventransfer trolleys for the inter-bay movement of components /


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assemblies.

4. Testing facilities for Turbogenerator are available in Bay-II.

5. There is a special test bed area for testing of T.G. of capacity of 500MW Unit sizes.

MANUFACTURING PROCESS

Fabricated components are received in respective machine sections fromFabrication blocks (Block II, V, VI, VIII), while castings and forgingsare received from sister unit CFFP and other indigenous and foreignsources for Turbo Generators. Stampings are received from stampingsmanufacture block, block VI and coils, bars, insulating details and sheetmetal components are received from coils and insulation manufacture andapparatus and control gear box (block IV).

1. Turbo Generators

a) Making of blanks is done for checking the availability ofmachining 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 boringmachine using a rotary table. The shaft is turned on lathe havingswift 2500 mm and the rotor slots are milled on a special rotor slotmilling machines.

c) In case of large size Turbo Generators core bars are welded tostator frame with the help of telescopic centering device. Thecentering of core bar is done very precisely. Punchings are


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assembled manually and cores are heated and pressed in number ofstages depending on the core length.

d) Stator winding is done by placing stator on rotating installation.

After laying of lower and upper bars, these are connected at theends, with the help of ferrule and then soldered by resistancesoldering.

e) Rotor winding assembly is carried out on special installation wherecoils are assembled in rotor slots. The pressing of overhang portionis carried out on special ring type hydraulic press, whereas slot

portion is pressed manually with the help of rotor wedges. Coilsare wedged with special press after laying and curing. The dynamic

balancing of rotors is carried out on the over speed balancinginstallation. 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, bearingsetc. are carried out to make generators ready for testing. Prior totest 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:-

Direct cooling of stator winding with water.Direct hydrogen cooling for rotor.Micalastic insulation systemSpring 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


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Rated frequency : 50 Hz Rated power factor : 0.85 Lag Efficiency : 98.55%

I mportant dimensions & weights

Heaviest lift of generator stator : 255 Tons Rotor weight : 68 Tons Overall stator dimensions [LxBxH] : 8.83Mx4.lMx4.02M Rotor dimensions : 1.15M dia x 12.11 M length Total weight of turbo generator : 428 Tons

Unique install ations

Heavy Electrical Equipment Plant, Haridwar is one of the best equippedand most modern plants of its kind in the world today. Some of theunique manufacturing and testing facilities in the plant are:

TG Test Bed

New LSTG [Large Scale Turbo Generator] Test Bed has been put up withindigenous know- how in record time for testing Turbo generators ofratings 500 MW and above up to 1000 MW. It caters to the mostadvanced requirement of testing by employing on-line computer fordataanalysis.Other major facilities are as follows

Major facilities like stator core pit equipped with telescopic hydrauliclift, micalastic plant for the manufacture of stator bars, thermal shockstest equipment, rotor slot milling machine etc. have been speciallydeveloped by BHEL.

12 MW/10.8 MW, 6.6 KV, 3000 RPM AC non salient pole,synchronous motor has been used for driving the 500 MW Turbogeneratorat the TEST Bed. The motor has special features to suit therequirement 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 invacuum for ratings up to 1,000 MW, an over speed and balancing tunnel


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has been constructed indigenously. This facility is suitable for all types ofrigid 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 wagonspecially designed indigenously and manufactured at Haridwar.

The wagon has been used successfully for transporting one generator-from Calcutta Port to Singrauli STPP.

CONSTRUCTIONAL FEATURES OF STATOR BODY

Stator F rame

Stator body is a totally enclosed gas tight fabricated structure made upof high quality mild steel and austenitic steel. It is suitably ribbed with


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annular rings in inner walls to ensure high rigidity and strength .Thearrangement, location and shape of inner walls is determined by thecooling circuit for the flow of the gas and required mechanicalstrength and stiffness.

The natural frequency of the stator body is well away from any ofexiting frequencies. Inner and sidewalls are suitably blanked to housefor longitudinal hydrogen gas coolers inside the stator body.

Pipe Connection

To attain a good aesthetic look, the water connection to gas cooler isdone by routing stainless steel pipes; inside the stator body; whichemanates from bottom and emerges out of the sidewalls.These stainless steel pipes serve as inlet and outlet for gas coolers.From sidewall these are connected to gas coolers by the means ofeight U-tubes outside the stator body. For filling the generator withhydrogen, a perforated manifold is provided at the top inside the stator

body.

3) Terminal Box

The bearings and end of three phases of stator winding are brought outto the slip-ring end of the stator body through 9 terminal brushing inthe terminal box. The terminal box is a welded construction of (nonmagnetic) austenitic steel plates. This material eliminates stray lossesdue to eddy currents, which may results in excessive heating.

4) Testing Of Stator Body

On completion of manufacture of stator body, it is subjected to a


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hydraulic pressure of 8 kg/cm for 30 minutes for ensuring that it will be capable of withstanding all expansion pressure, which might ariseon account of hydrogen air mixture explosion. Complete stator body isthen subjected to gas tightness test by filling in compressed air.

CONSTRUCTIONAL FEATURES STATOR CORE

Core

It consists of thin laminations. Each lamination made of number ofindividual segments. Segments are stamped out with accuratelyfinished die from the sheets of cold rolled high quality silicon steel.Before insulation on with varnish each segment is carefully debarred.Core is stacked with lamination segments. Segments are assembled inan interleaved manner from layer to layer for uniform permeability.Stampings are held in a position by 20 core bars having dovetail

section. Insulating paper pressboards are also put between the layer ofstamping to provide additional insulation and to localize short circuit.Stampings are hydraulically compressed during the stacking procedureat different stages. Between two packets one layer of ventilatingsegments is provided. Steel spacers are spot welded on stamping.These spacers from ventilating ducts where the cold hydrogen fromgas coolers enter the core radialy inwards there by taking away theheat generated due to eddy current losses. The pressed core is held in

pressed condition by means of two massive non-magnetic steelcastings of press ring. The press ring is bolted to the ends of core bars.The pressure of the pressure ring is transmitted to stator core stampingthrough press fringes of non-magnetic steel and duralumin placedadjacent to press ring. To avoid-heating of press ring due to endleakage flow two rings made of copper sheet are used on flux shield.The ring screens the flux by short-circuiting. To monitor the formationof hot spots resistance transducer are placed along the bottom of slots.To ensure that core losses are with in limits and there are no hot spots

present in the core. The core loss test is done after completion of coreassembly.


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2) Core Suspension

The elastic suspension of core consist of longitudinal bar type spring

called core bars. Twenty core bars are welded to inner walls of stator body with help of brackets. These are made up of spring steel having arectangular cross section and dove-tail cut at tap, similar type of dovetailis also stamped on to stamping and fit into that of core bar dovetail.Thus offering a hold point for stamping core bars have longitudinalslits which acts as inertial slots and help in damping the vibrations.The core bars are designed to maintain the movement of stator corewith in satisfactory limits.

CONSTRUCTIONAL FEATURES OF STATORWINDING

1) General

The stator has a three phase, double layer, short pitched and bar typeof windings having two parallel paths. Each slots accommodated two

bars. The slot lower bars and slot upper are displaced from each other by one winding pitch and connected together by bus bars inside thestator frame in conformity with the connection diagram.

2) Conductor Construction

Each bar consist of solid as well as hollow conductor with coolingwater passing through the latter. Alternate arrangement hollow andsolid conductors ensure an optimum solution for increasing currentand to reduce losses. The conductors of small rectangular cross sectionare provided with glass lapped strand insulation.A separator insulates the individual layers from each other. Thetransposition provides for mutual neutralization of voltage induced inthe individual strands due to the slots cross field and end windingfield. The current flowing through the conductor is uniformlydistributed over the entire bar cross section reduced.To ensure that strands are firmly bonded together and give


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dimensionally stability in slot portion, a layer of glass tape is wrappedover the complete stack. Bar insulation is done with epoxy micathermosetting insulation. This insulation is void free and posses bettermechanical properties. This type of insulation is more reliable for high

voltage.This insulation shows only a small increase in dielectricdissipation factor with increasing test voltage. The bar insulation iscured in an electrically heated process and thus epoxy resin fill allvoids and eliminate air inclusions.

M ethod Of I nsulation

Bar is tapped with several layers of thermosetting epoxy tape. Thisis applied continuously and half overlapped to the slot portion. The

voltage of machine determines the thickness of insulation. Thetapped bar is then pressed and cured in electrical heated pressmould for certain fixed temperature and time.

Corona Preventi on

To prevent corona discharges between insulation and wall of slots,the insulation in slot portion is coated with semiconductor varnish.The various test for manufacture the bar are performed which areas follows (a) Inter turn insulation test on stuck after consolidation to ensureabsence of inter short.

(b)Each bar is subjected to hydraulic test to ensure the strength ofall joints.

(c) Flow test is performed on each bar to ensure that there is noreduction in cross section area of the ducts of the hollowconductor.

(d)Leakage test by means of air pressure is performed to ensuregas tightness of all joints.(e)High voltage to prove soundness of insulation.

(f) Dielectric loss factor measurement to establish void free

insulation.


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Laying Of Stator Winding

The stator winding is placed in open rectangular slots of the statorcore, which are uniformly distributed on the circumference. A semiconducting spacer is placed in bottom of slots to avoid any damageto bar due to any projection. Driving in semi conducting fillerstrips 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.

Ending Winding

In the end winding, the bars are arranged close to each other. Anygaps due to design or manufacturing considerations are fitted withcurable prepag with spacer in between. The prepag material is also

placed between the brackets and binding rings. Lower and upperlayers are fixed with epoxy glass ring made in segment and flexiblespacer put in between two layers.Bus bars are connected to bring out the three phases and sixneutrals. Bus bars are also hollow from inside. These bus bars areconnected with terminal bushing. Both are water-cooled. Brazingthe two lugs properly makes connection.

CONSTRUCTIONAL FEATURES OF ROTOR

The rotor comprises of following component:1) Rotor shaft2) Rotor winding3) Rotor wedges and other locating parts for winding4) Retaining ring5) Fans6) Field lead connections


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Rotor Shaft

The rotor shaft is a single piece solid forging manufactured from a vacuum casting. Approximately 60 % of therotor body circumference is with longitudinal slots, which hold thefield winding. The rotor shaft is a long forging measuring morethan 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 toeach 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) Boroscope examination

On 2/3 of its circumference approximately the rotor body is providedwith longitudinal slot to accommodate field winding. The slot pitch isselected in such a way that two solid poles displaced by 180 o C areobtained. For high accuracy the rotor is subjected to 20% over speedingfor two minutes.The solid poles are provided with additional slots in short lengths of twodifferent configurations.One type of slots served as an outlet for hydrogen which has cooled theoverhang winding and other type used to accommodate finger of dampersegments acting as damper winding.

Rotor Winding

After preliminary turning, longitudinal slots are milled on sophisticatedhorizontal slot milling machine. The slot house the field winding consistsof several coils inserted into the longitudinal slots of rotor body .

Copper Conductor


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The conductors are made of hard drawn silver bearing copper. Therectangular cross section copper conductors have ventilating ductson the two sides thus providing a channel for hydrogen flow. Twoindividual conductors placed-one over the other are bent to obtain

half turns. Further these half turns are brazed in series to form coilon the rotor model.

Insulation

The individual turns are insulated from each other by layer of glass prepag strips on turn of copper and baked under pressure andtemperature to give a monolithic inter turn insulation. The coils areinsulated from rotor body by U-shaped glass laminate module slotthrough made from glass cloth impregnated with epoxy varnish.At the bottom of slot D-shaped liners are put to provide a planeseating surfaces for conductors and to facilitate easy flow of gasfrom one side to another. These liners are made from moldingmaterial. The overhang winding is separated by glass laminated

blocks called liners. The overhang winding are insulated fromretaining rings segments having L-shape and made of glass clothimpregnated by epoxy resin.

Cooling Of Winding

The rotor winding are cooled by means of direct cooling method ofgap pick-up method. In this type of cooling the hydrogen in the gapis sucked through the elliptical holes serving as scoop on the rotorwedges and is directed to flow along lateral vent ducts on rotorcooper coils to bottom of the coils. The gas then passes into thecorresponding ducts on the other side and flows outwards andthrown into the gap in outlet zones.In this cooling method the temperature rise becomes independentof length of rotor. The overhang portion of the winding is cooled

by axial two systems and sectionalized into small parallel paths tominimize temperature rise. Cold gas enters the overhang fromunder the retaining rings through special chamber in the endshields and ducts under the fan hub and gets released into the airgap at rotor barrel ends.

1) Rotor Wedges


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For protection against the effect of centrifugal force the winding issecured in the slots by slot wedge. The wedges are made fromduralumin, an alloy of copper,

magnesium and aluminum having high good electrical conductivityand high mechanical strength.The wedges at the ends of slot are made from an alloy of chromiumand copper. These are connected with damper segments under theretaining ring for short circuit induced shaft current. Ventilation slotwedges are used to cover the ventilation canals in the rotor so thathydrogen for overhang portion flows in a closed channel.

2) Retaini ng Ring The overhang portion of field winding is held by non-magnetic steelforging of retaining ring against centrifugal forces. They are shrinkfitted to end of the rotor body barrel at one end; while at the other sideof the retaining ring does not make contact with the shaft.The centering rings are shrink fitted at the free end of retaining ringthat serves to reinforce the retaining ring, securing, end winding inaxial direction at the same time. To reduce stray losses, the retainingrings are made of non-magnetic, austenitic steel and cold worked,resulting in high mechanical strength.

3) F ans

Two single stage axial flow propeller type fans circulate the generatorcooling gas. The fans are shrink fitted on either sides of rotor body.Fans hubs are made of alloy steel forging with three peripheralgrooves milled on it. Fan blades, which are precision casting withspecial alloy, are machined in the tail portion so that they fit into thegroove of the fan hub.

4) F ield L ead Connections

Sl ip Rings

The slip ring consists of helical grooved alloy steel rings shrunk onthe body shaft and insulated from it. The slip rings are provided

with inclined holes for self-ventilation. The helical grooves cut onthe outer surfaces of the slip rings improve brush performance by


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breaking the pressurized air pockets that would otherwise getformed between the brush and slip rings.

F ield L ead

The slip rings are connected to the field winding through semiflexible copper leads and current-carrying bolts placed in the shaft.The radial holes with current carrying bolts in the rotor shafts areeffectively sealed to prevent the escape of hydrogen.A field lead bar, which has similar construction as, does theconnection between current carrying bolt and field winding that ofsemi flexible copper leads (they are insulated by glass clothimpregnated with epoxy resin for low resistance and ease ofassembly).

COOLING SYSTEM:

Heat losses arising in generator interior are dissipated to secondarycoolant (raw water, condensate etc.) through hydrogen and Primarywater. Direct cooling essentially eliminates hot spots and differentialtemperature between adjacent components, which could result inmechanical stresses, particularly to the copper conductors, insulation,rotor body and stator core.

H ydrogen Cooling Cir cuit :

The hydrogen is circulated in the generator interior in a closed circuit byone multistage axial flow fan arranged on the rotor at the turbine end. Hotgases is drawn by the fan from the air gap and delivered to the coolerswhere it is recooled and then divided into three flow paths after eachcooler:F low path I :Flow path I is directed into the rotor at the turbine end below the fan hubfor cooling of the turbine end half of the rotor.

F low path II :Flow path II is directed from the cooler to the individual framecompartments for cooling of the stator core.

Fl ow path II I :Flow path III is directed to the stator end winding space at the exciter endthrough guide ducts in the frame of cooling of the exciter end half of therotor and of the core end portion.


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The three flow paths miss the air gaps. The gas is then returned to thecoolers via the axial flow fan.The cooling water flow through the hydrogen coolers shouldautomatically control to maintain a uniform generator temperature level

for various loads and cold-water temperature.

Cooling Of Rotors :

For direct cooling of rotor winding cold gas is directed to the rotor endwedges at the turbine and exciter ends. The rotor winding is symmetricalrelative to generator centerline and pole axis. Each coil quarter is dividedinto two cooling zones consists of the rotor end winding and the secondone of the winding portion between the rotor body end and the midpointof the rotor. Cold gas is directed to each cooling zone through separateopenings directly before the rotor body end. The hydrogen flows througheach individual conductor is closed cooling ducts. The heat removingcapacity is selected such that approximately identical temperature isobtained for all conductors. The gas of the first cooling zone isdischarged from the coils at the pole center into a collecting compartmentwithin the pole area below the end winding from the hot gases passes intoair gap through the pole face slots at the end of the rotor body. The hotgas of the second cooling zone is discharged into the air gap at the midlength of the rotor body through radial openings in the hollow conductorsand wedges.

Cooling of stator core:

For cooling of the stator core, cold gas is passes to the individual frame

compartment via separate cooling gas ducts.From these frames compartment the gas then flow into the air gapthrough slots and the core where it absorbs the heat from the core. Todissipate the higher losses in core ends the cooling gas section. To ensureeffective cooling. These ventilating ducts are supplied from end windingspace. Another flow path is directed from the stator end winding space

paste the clamping fingers between the pressure plate and core sectioninto the air gap along either side of flux shield.All the flows mix in the air gap and cool the rotor body and stator bore

surfaces. The air gap is then returned to the coolers via the axial flow fan.To ensure that the cold gas directed to the exciter end cannot be directly


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discharged into the air gap. An air gap choke is arranged with in the statorend winding cover and the rotor retaining rings at the exciter end.

Primary Cooling Water Cir cuit I n The Generators :

The treated water used for cooling of the stator winding, phase connectorsand bushings is designated as primary water in order to distinguish itfrom the secondary coolant (raw water, condensator etc.). The primarywater is circulated in a closed circuit and dissipates the absorbed heat tothe secondary cooling in the primary water cooler. The pump is suppliedwith in primary water cooler. The pump is supplied with in the primarywater tank and delivers the water to the generator via the following flow

paths:

F low path I :Flow path I cools the stator winding. This flow path passes through watermanifold on the exciter end of the generator and from there to the stator

bars via insulated bar is connected to the manifold by a separate hose.Inside the bars the cooling water flows through hollow strands. At theturbine end, the water is passed through the similar hoses to another watermanifold and then return to the primary water tank. Since a single passwater flow through the stator is used, only a minimum temperature rise is

obtained for both the coolant and the bars. Relatively movements due tothe different thermal expansions between the top and the bottom bars arethus minimized.

F low Path II :Flow path II cools the phase connectors and the bushings. The bushingand the phase connectors consist of the thick walled copper tubes throughwhich the cooling water is circulated. The six bushings and phaseconnectors arranged in a circle around the stator winding arehydraulically interconnected so that three parallel flow paths are obtained.The primary water enters three bushings and exits from the threeremaining bushings. The secondary water flow through the primary watercooler should be controlled automatically to maintain a uniform generatortemperature level for various loads and cold-water temperatures.


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EXCITATION SYSTEM:

In large synchronous machines, the field winding is always provided onthe rotor, because it has certain advantages they are:

It is economical to have armature winding on the stator and fieldwinding on the rotor.

Stationary armature windings can be insulated satisfactorily for highervoltages, allowing the construction of high voltage synchronousmachines.

Stationary armature winding can be cooled more efficiently.Low power field winding on the rotor gives a lighter rotor and

therefore low centrifugal forces. In view of this, higher rotor speedsare permissible, thus increasing the synchronous machine output forgiven dimensions.Design features

The excitation system has a revolving field with permanent magnet poles.The three-phase ac output of this exciter is fed to the field of the mainexciter via a stationary regulator & rectifier unit. Three-phase acinduced in the rotor of the main exciter is rectified by the rotatingRectifier Bridge & supplied to the field winding of the generator rotorthrough the dc lead in the rotor shaft.A common shaft carries the rectifier wheels, the rotor of the main exciter& PMG rotor. The shaft is rigidly coupled to the generator rotor. Thegenerator & exciter rotors are supported on total three bearings. .

Three Phase Pilot Exciter

It is a six-pole revolving field unit. The frame accommodates thelaminated core with the three-phase winding. Each pole consists of


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separate permanent magnets that are housed in a non-magnetic metallicenclosure.

Three phase main exciter

The three phase main exciter is a six-pole armature-revolving unit. Thefield winding is arranged on the laminated magnetic poles. At the poleshoe, bars are provided which are connected to form a damper winding.Between the two poles, a quadrature-axis coil is provided for inductivemeasurement of the field current. After completing the winding &insulation etc., the complete rotor is shrunk on the shaft.

Rectifier wheels

The silicon diode is the main component of the rectifier wheels, whichare arranged in a three-phase bridge circuit. With each diode, a fuse is

provided which serves to cut off the diode from the circuit if it fails. Forsuppression of the momentary voltage peaks arising from commutation,R-C blocks are provided in each bridge in parallel with each set of diodes.The rings, which form the positive & negative side of the bridge, areinsulated from the rectifier wheel which in turn is shrunk on the shaft.The three phase connections between armature & diodes are obtained viacopper conductors arranged on the shaft circumference between therectifier wheels & the main exciter armature.

Voltage regulator

The voltage regulator is intended for the excitation and control ofgenerators equipped with alternator exciters employing rotatinguncontrolled rectifiers. The main parts of the regulator equipment aretwo closed-loop control systems including a separate gate control set andthyistor set each, field discharge circuit, an open loop control system forexchanging signal between the regulator equipment and the control room,and the power supply circuits.

Voltage regulation

The active and reactive power ranges of the generator ve require a wideexcitation setting range. The voltage regulator in the restricted sense, i.e.

the control amplifiers for the generator voltage controls via the gatecontrol set the thyristors so as they provide quick correction of the


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generator voltage on changing generator load. For this purpose the gatecontrol set changes the firing angle of the thyristors as a function of theoutput voltage of the voltage regulator. The main quantities acting on theinput of the voltage regulator are the setpoint and the actual value of the

generator voltage. The setpoint is divided into a basic setpoint (e.g. 90%rated voltage) and an additional value (e.g. 0 to 20%), which can beadjusted from the control room. In this case the setting range is 90 to110%. With operation at the respective limits of the capability curve,further, influencing variable are supplied by the under and over excitationlimiters. To partly compensate the voltage drop at the unit transformer, asignal proportional to the reactive current can be added to the input, thecontrolled voltage level then rising together with the reactive current(overexcited) thereby increasing the generator degree of activity incompensating system voltage functions. Further, signals can be added ifnecessary via free inputs.

BRUSHLESS EXCITOR STATOR

The various schemes, for supplying D.C. excitation to the field winding to large turbo generators are given below:

The Pilot Exciter and the main exciter are driven by the turbogenerators main shaft. The pilot Exciter, which is a small D.C.shunt generator, feeds the field winding of main exciter is given tothe field winding of the main alternator, through slip-rings and

brushes. The function of the regulator is to keep the alternatorterminal voltage constant at a particular value.

In this second scheme it consists of main A.C. exciter andstationary solid-state rectifier. The A.C. main exciter, which iscoupled to shaft of generator, has rotating field and stationaryarmature. The armature output from the A.C. exciter has afrequency of about 400 Hz. This output is given to the stationarysolid-state controlled rectifier. After rectification, the power is fedto the main generator field, through slip rings and brushes.

In third scheme the A.C exciter, coupled to the shaft that drives themain generator, has stationary field and rotating 3-phase armature.The 3-phase power from the A.C exciter is fed, along the main

shaft, to the rotating silicon-diode rectifiers mounted on the sameshaft. The output from these rectifiers is also given, along the main


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shaft, to the man generator field, without any slip rings and brushes. In the other words, the power flows along the wiresmounted on the main shaft, from the A.C. exciter to the silicondiode rectifiers and then to the main generator field. Since the

scheme does not require any sliding contacts and brushes, thisarrangement of exciting the turbo generators has come to be calledas Brush less Excitation system .For large turbo generators of 500 MW excitation systems, the directcooling required by the rotating field winding increases considerably (upto 10 kA or so). In such cases, the brush gear design becomes morecomplicated and reliability of turbo generator operation decreases. Theonly promising solution of feeding the field winding of large turbogenerator is the brush less excitation system. In view of its manyadvantages, the brush less excitation system is employed in almost alllarge turbo generators being designed and manufactured now days.Here are some merits of Brush less Exciters.

Eliminates slip rings, brush gear, field breaker and excitation bus/cables.

Eliminates all the problems associated with transfer of current viasliding contacts.

Simple, reliable and ideally sited for large sets.Minimum operation and maintenance cost.Self-generating excitation unaffected by system faults or

disturbances of shaft mounted pilot exciter.

ELECTRICAL GENERATOR PROTECTION

Generator may be endangered by short circuit, ground fault, over voltage,under excitation and excessive thermal stresses.The following protective equipment is recommended1) Differential protection

2) Stator ground fault protection3) Rotor ground fault protection4) Under excitation protection5) Over current protection6) Load unbalance protection7) Rise in voltage protection8) Under-frequency protection9) Reverse power protection10)Over voltage protection

SALIENT DESIGN FEATURES


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1) Air Cooled Turbo Generators Up To 200 MW Range (Type.- TARI) Stator core and rotor winding direct air cooled Indirect cooling of stator winding Horizontally split casing design of stator Vertically side mounted coolers in a separate housing Micalastic bar type insulation system Separately assembled stator core and winding for reducing themanufacturingcycle Brush less/static excitation system1) Hydrogen & Water-Cooled Turbo Generators Of 200-235 MW range(Type: THW) Stator winding directly water cooled Rotor winding directly hydrogen cooled by gap pick up method Resiliently mounted stator core on flexible core bars Thermo reactive resin rich insulation for stator winding Top ripple springs in stator slots Enclosed type slip rings with forced ventilation Ring/thrust type shaft seal Two axial fans for systematic ventilation and four hydrogencoolers Static excitation1) Hydrogen Cooled Turbo Generators Of 140-260 MW range (Type:THRI) Stator core and winding directly hydrogen cooled Indirect cooling of stator winding Rigid core bar mounting Micalastic insulation system End shield mounted bearings

Top ripple springs in stator slots Ring type shaft seals Symmetrical ventilation Brush less/ static excitation Integral coupling of rotor1) Hydrogen & Water-Cooled Turbo Generators Of 500 MW range(Type: THW) Stator winding directly water cooled Rotor winding direct hydrogen cooled (axial) Leaf spring suspension of stator core


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Micalastic insulation system End shield mounted bearings Support ring for stator over hang Magnetic shunt to trap end leakage flux Ring type shaft seals with double flow Multistage compressor and vertical coolers on turbine end Brush less/static excitation Integral coupling of rotor

CONCLUSION

Bharat Heavy Electrical Limited is the largest engineering and

Manufacturing enterprise of is kind in the public sector in India.

The sector is an important part in Turbo generators. The stator Core

is assembled by the laminated sheets. We use the UNIVERSAL FORM

FICTURE type bar which assembles all the straight part and the over

hang at a time. The universal form facture type bar is more flexible

and its life time more. We use the BAR Transposition for stator

winding which is more advantageous. BHEL has acquired the latest

technology in the insulation system, the VACCUM IMPREGNATION

system of insulation, which has various advantage like cost

reduction with improved quality. Thus designed and manufactured


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start of turbo generator is used mostly in paper, Sugar, Cement,

Petrochemical, Fertilizers, Reyon, industries.

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 has allowed us an opportunity to get an exposure of the practicalimplementation of theoretical fundamentals.

Documents

A Comprehnensive Traning Report On112 - Copy