b hel editing

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ABOUT THE COMPANY: BHARAT HEAVY

ELECTRICALS LIMITED

Bharat Heavy Electrical Limited (BHEL) is today the largest engineering Enterprise of India with an

excellent track record of performance.

Its first plant was set up at Bhopal in 1956 under technical collaboration with M/s. AEI,UK followed by

three more major plants at Haridwar, Hyderabad and Tiruchirapalli with Russian and Czechoslovak

assistance.

These plants have been at the core of BHELs efforts to grow andDiversify and become Indias leadingengineering company.

The company now has 14 manufacturing divisions, 8 service centers and 4 power sector regional centers,

besides project sites spread all over India and abroad and also regional operations divisions in various

state capitals in India for providing quick service to customers. BHEL manufactures over 180 products

and meets the needs of core sectors like power, industry, transmission, transportation (including

railways), defense, telecommunications, oil business, etc.

Products of BHEL make have established an enviable reputation for high quality and reliability. BHEL

has installed equipment for over 62,000 MW of power generation for Utilities, Captive and Industrial

users.

Supplied 2,00,000 MVA transformer capacity and sustained equipment operating in Transmission &

Distribution network up to 400kVAC & DC, Supplied over 25,000Motors with Drive Control SystemPower projects.

Petrochemicals, Refineries, Steel, Aluminum, Fertilizer, Cement plants etc., supplied Traction electric and

AC/DC Locos to power over 12,000 Km Railway network. Supplied over one million Valves to Power

Plants and other Industries.


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This is due to the emphasis placed all along on designing, engineering and manufacturing to international

standards by acquiring and assimilating some of the best technologies in the world from leading

companies in USA, Europe and Japan, together with technologies from its-own R & D centers.

BHEL has acquired ISO 9000 certification for its operations and has also adopted the concepts of Total

Quality Management (TQM).

BHEL presently has manufactured Turbo-Generators of ratings up to 560 MW and is in the process of

going up to 660 MW.

It has also the capability to take up the manufacture of ratings unto 1000 MW suitable for thermal power

generation; gas based and combined cycle power generation as-well-as for 13 diverse industrial

applications like Paper, Sugar, Cement, Petrochemical, Fertilizers, Rayon Industries, etc.

The Turbo generator is a product of high-class workmanship and quality. Adherence to stringent quality-

checks at each stage has helped BHEL to secure prestigious global orders in the recent past from

Malaysia, Malta, Cyprus, Oman, Iraq, Bangladesh, Sri Lanka and Saudi Arabia. The successful

completion of the various export projects in are cord time is a testimony of BHELs performance.

Bharat Heavy Electrical Limited (BHEL) is, today, a name to reckon with in the industrial world. It is the

largest engineering and manufacturing enterprises of its kind in India and is one of the leading

international companies in the power field.

BHEL offers over 180 products and provides systems and services to meet the needs of core sections like:

power, transmission, industry, transportation, oil & gas, non-conventional energy sources and

telecommunication.

A wide-spread network of 14 manufacturing divisions, 8 service centers and 4 regional offices besides a

large number of project sites spread all over India and abroad, enables BHEL to be close to its customersand cater to their specialized needs with total solutions-efficiently and economically.

An ISO 9000 certification has given the company international recognition for its commitment towards

quality.

With an export presence in more than 50 countries BHEL is truly Indias industrial ambassador to theworld.


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BHEL

Haridwar units manufacture includes the following:

Gas turbines

Steam turbines

Compressors

Turbo generators

Heat Exchangers

Pumps

Pulverizers

Switch Gears

Oil rigs


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INTRODUCTION

TURBO GENERATOR

A turbo generator is a turbine directly connected to electrical generator for the generation of electric

power. An electrical generator is a machine which converts mechanical energy to electrical energy.

HISTORY OF TURBO GENERATORS:

Generators are based on the theory of electromagnetic induction, which was discovered by MichaelFaraday in 1831, a British Scientist. Faraday discovered that if an electric conductor, like a copper wire, ismoved through a magnetic field, electrical current will flow(be induced) in the conductor. So the

mechanical energy of the moving wire is converted into the electric energy of the current that flows in the

wire.

PRINCIPLE OF OPERATION:

Turbo generator or A.C. generators or alternators operates on the fundamental Principles of FARADAYS

LAWS OF ELECTROMAGNETIC INDUCTION. In them the standard construction consists of armature

winding mounted on stationary element called stator and field windings on rotating element called

rotor .

The stator consists of a cast-iron frame, which supports the armature core, having slots on its inner

periphery for housing the armature conductors. The rotor is like a flywheel having alternating north and

south poles fixed to its outer rim. The magnetic poles are excited with the help of an exciter mounted on

the shaft of alternator itself. Because the field magnets are rotating the current is supplied through two slip

rings. As magnetic poles are alternately N and S, they induce an e.m.f and hence current in armature

conductors. The frequency of e.m.f dependsupon the no. of N and S poles moving past a conductor in1 second and whose direction is givenby Flemings right hand rule.


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SYNCHRONOUS GENERATORS CLASSIFICATION

BASED ON THE MEDIUM USED FOR GENERATION

Turbo generators in Thermal, nuclear, Gas station are:

High speed3000 rpm

Min poles2 poles

Horizontal construction

Cylindrical rotor

Hydro generators in hydel plants are:

low speed1000 to 500 rpm

more poles6 or more

vertical construction

salient rotor


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COMPONENTS OF TURBO GENERATOR

STATOR

Stator Frame

Stator Core

Stator Windings

End Covers

INSULATION

ROTOR

Rotor Shaft

Rotor Windings

Rotor Retaining Rings

The following auxiliaries are required for operation:

Bearings

Cooling System

Oil Supply System

Excitation System


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STATOR CORE

Purpose of stator core:1. To support the stator winding

2. To carry the electromagnetic flux generated by rotor winding .So selection of material forbuilding up of core plays a vital role. The losses in the core are of two types:

Hysterysis Loss:Due to the residual magnetism in the core material. Hysterysis loss is given by

Wh (max )1.6

Eddy Current Loss:Due to the e.m.f induced in the core of the stator. Eddy current loss is given byWe 2max f2 t2.In order to reduce the hysterysis loss, silicon alloyed steel, which haslow hysterysis constant is used for manufacture of core. The composition of silicon steel

is Steel - 95.8%Silicon 4.0%Impurities - 0.2%.From the formula it is seen that eddycurrent loss depends on the thickness of the laminations. Hence to reduce the eddy

current loss core is made up of thin laminations which are insulated from each other. Thethickness of the laminations is about 0.5mm. The silicon steel sheets are of COLD

ROLLED NON-GRAIN ORIENTED (CRANGO) type as it provides the distribution of flux

throughout the laminated sheet.

PREPARATION OF LAMINATIONS

For high rating machines each laminations is build of 6 sectors (stampings), each of 60 cut according to

the specifications. Press tools are used in the manufacture of laminations. Press tools are mainly of twotypes.

Compounding tools.

Blanking and slot notching tools.


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LAMINATIONS ARE MANUFACTURED IN TWO

DIFFERENT WAYS:

1. COMPOUNDING OPERATION:In this method the stamping with all the core bolt holes, guiding slots and winding slots is manufactured

in single operation known as Compounding operation and the press tool used is known as Compounding

tool. Compounding tools are used for the machines rated above 40 MW.

2. BLANKING AND NOTCHING OPERATIONS:In case of smaller machines the stampings are manufactured in two operations. In the first operation the

core blot holes and guiding slots are only made. This operation is known as Blanking and the tools used

are known as Blanking tools. In the second operation the winding slots are punched using another toolknown as Notching tool and the operation is called Notching.

THE DIFFERENT OPERATIONS IN MANUFACTURE

OF LAMINATION

Deburring operation:

In this operation the burrs in the sheet due to punching are deburred. There are chances of short circuit

within the laminations if the burrs are not removed. The permissible is about 5micrometer. For deburring

punched sheets are passed under rollers to remove the sharp burs of edges.

Varnishing:

Then depending on the temperature withstand ability of the machine the laminations are coated by varnish

which acts as insulation. The lamination sheets are passed through conveyor, which has an arrangementto sprinkle the varnish is obtained. The sheets are dried by a series of heaters at a temperature of around260-350 C. Two coatings of varnish are provided in the above manner till 12-18mm thickness of coat is

obtained.


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Thepreparedlaminations are subjected to following tests:

Xylol test - To measure the chemical resistance.

Mandrel test - When wound around mandrel there should not be anycracks.

Hardness test - Minimum 7H pencil hardness.

IR value test - For 20 layers of laminations insulation.

ASSEMBLY OF CORE

The stator laminations are assembled as separate cage without stator frame. The entire core length is madein the form of packets separated by radial ducts to provide ventilating passages for the uniform cooling of

the core. The thickness of each lamination is 0.5mm and the thickness of lamination separating the

packets is about 1mm. The lamination separating each packet has trips of non-magnetic material that are

welded to provide radial ducts. The segments are staggered from layer to layer so that a core of high

mechanical strength and uniform permeability to magnetic flux is obtained. Stacking mandrels and boltsare inserted into the windings slot bores during stacking provide smooth slot walls.

Fig: assembly of core

To obtain the maximum compression and eliminate under setting during operation, the laminations are

hydraulically compressed and heated during the stacking procedure when certain heights of stacks are

reached. The complete stack is kept under pressure and located in frame by means of clamping bolts and

pressure plates. The clamping bolts running through the core are made of nonmagnetic steel and are

insulated from the core and pressure plates to prevent them from short circuiting the lamination sand

allowing the flow of eddy currents. The pressure is transmitted from the clamping plates to the core by


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clamping fingers. The clamping fingers extend up to the ends of the teeth thus, ensuring a firm

compression in the area teeth. The core building or assembling method depends on the insulation system

used.1. For resin rich insulation system the laminations are stacked in the frame itself.2. For resin poor

insulation system (VPI) cage core of open core design is employed.

STATOR WINDINGS:

Stator winding is the one which induces emf and supplies the load. Stator winding is placed in the slots

of stator core. Due to the advantages of generation and utilization of 3 phase power we use three phase

windings for generation. So number of slots must be a multiple of 3 (or 6 if two parallel circuits arerequired).

fig.: copper bar are used for stator winding in TURBOGENERATOR


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Generally two layer lap winding, chorded to about 5/6 pitch which practically eliminates 5th and 7th

harmonics from the flux wage or open circuit induced emf wave is used. The stator coil is made up of

number of strips instead of single solid piece to reduce the skin effect.

Copper material is used to make the coils. This is because:

i.Copper has high electrical conductivity with excellent mechanical properties.ii. Immunity from oxidation and corrosion.iii. These are highly mallable and ductile metal.

There are two types of coil :

Diamond pulled multi-turn coil (full coiled)

Roebel bar (half coiled)

Generally diamond pulled multi-turn coils are used for low capacity machine. In this coils are pulled in a

particular shape similar as diamond thats why they are called so. In large capacity machines we use

ROEBEL bars. These coils were constructed after considering the skin effect losses. In the straight slotportion, the conductors or strips are transposed by 360 degrees. The transposition is done to ensure that all

the strips occupy equal length under similar conditions of the flux.

High purity (99%) copper conductors/strips are used to make the coils. This results in high strength

properties at higher temperatures so that deformations due to the thermal stresses are eliminated. The high

voltage insulation is provided according to the resin poor mica base of thermosetting epoxy

system. Several half overlapped continuous layers of resin poor mica tape are applied over the bars. The

thickness of the tape depends on the machine voltage.

Fig: stator windings


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Slot Discharges:

Slot discharges occur if there are gaps within the slot between the surface of the insulation and that of the

core. This may cause ionization of he air in the gap, due to breakdown of the air at the instances of

voltage distribution between the copper conductor and the iron.

Within the slots, the outer surface of the conductor insulation is at earth potential, in the over-hanging itwill approach more nearly to the potential of the enclosed copper. Surface discharge will take place if the

potential gradient at the transition from slot to overhang is excessive, and it is usually necessary to

introduce voltage grading by means of a semi-conducting (graphite) surface layer, extending a short

distance outward from the slot ends.

MANUFACTURING OF STATOR COILS:

Various operations carried out during manufacture of stator coil are

1. Set the straightening and cutting machine using guide pilot.

2. Cut the conductor strips as per the requirement.

3. Set the press for Roebel Transposition.

4. Assemble strips with respect to template and transpose.

5.Assemble both halves of coil sides to from

1.One Roebel half bar

2. Insert insulation of halves between quarter bars matching the straight part zone as per drawing.(Fig:stator coils)

6.Cure half coil on hydraulic press. This process is known as Baking.

(a) Remove insulation at the ends of the strips.

(b) Test for inter-strip and inter-halves shorts.

7.Set the universal former as per standards. Check the setting of universal former for

(a)Length of straight part also mark diagonals/former walls inside for cross check.

(b)Check for marking made by template.


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MANUFACTURING OF STATOR COILS

8.(a) Place the bar on former.

(b) Form the overhang bends as per standards.

(c) Remove clamps and inserts overhand insulation to both roebel halves with an application of araldite

mixture.

(d) The bar is allowed to cure by giving supply to heating clamps.

9.(a)Remove heating clamps and take out the bar halves from former.

(b)Round off sharp edges of straight part and dress up overhang halves insulation of both halves without

damage to copper strip insulation and to copper stacks.

PROCESS OF TAPING:

Fig: mica taping machine

1.Tape the bar with Resin poor fine mica paper tape on straight part of bar taking copper foil outside the

tape.

2.Tape with one layer of conductive polyester fleece tape.a)Provide main insulation

b)OCP protection tape


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3.Tape the straight part of bar with conductive polyester fleece tape with starting and ending shall be on

straight part of bar.

4.Tape with mica splitting tape with accelerator taking OCP layer into and leaving.

5.Tape the straight part of bar with polyester Conductive fleece tape.

6.Provide End Corona protection taping.

7.Provide overhang with protective tape (Polyester glass tape).

8.Test for inter-strip shorts.

STATOR END COVERS:The stator end covers are attached to end flanges of stator frame and also rest on the foundation plate. The

end covers are made up of non-magnetic material (Aluminium castings) to reduce stray load and eddy

current losses.

PHASE CONNECTORS:The phase connectors consist of flat copper sections, which results in low specific current loading. Thephase connectors are wrapped with resin rich mica tape. After curing the connectors are attached to

the pressure plate with clamps and bolts.

RESISTANCE TEMPERATURE DETECTORS :The temperature measurements on the generator are made with RTDs. They are placed at various sections

of the core and winding. When making measurements with RTDs the resistance element is exposed to the

temperature to be measured. The RTD works on the principle of the change in electrical resistance of a

conductor due to temperature.

R= Ro (1+ T)Where Ro = reference resistance at room temperature

R=temperature coefficient of resistance

T = temperature difference in C.

WINDING HOLDER:Assemble the winding holder as per the drawing requirement and check all the winding hold with

template with respect to core.

ASSEMBLY OF HG RINGS:Assemble the HG rings on the both the side, turbine side as well as laminated side. Pass HGL gauge in allthe slots to detect laminations projection of the bottom surface if any lamination projection are noticed

then rectify the projection. Check prior operation completion.

IDENTIFICATION OF RTD SLOTS:Identify all the RTD slots with respect to the drawing and assemble the RTD slots as per the drawing

purposes required. Identify all the slots with slots number as per the drawing.


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BOTTOM BARS LAYING

Pressing of bottom bars:

Each individual bars subjected for pressing at 60 kg/cm2 horizontal & vertical in order to obtain

predetermine the dimensions up to 30 minutes.

This process is carried out for all the bottom bars before laying to the respective slots.

By following above procedure first bar is laid in to the respective slots when the bar is center to the core

centre by measuring pitch dimensions on both sides.

Similarly next bar is laid in to the respective bar by following procedure.

After laying the every two bars the over hangs are reinforced with glass mat at three different locations on

both sides and tying the bars with neoprene glass view.

Similarly the above procedure is following for all the eliminating bars.

After completion bottom bars laying the bars reinforced end wedges and middle wedges.

Then the bottom bars are subjected to D.C high voltage.

Inter layer inserts & RTDS assembles:

All the inter layer inserts & RTDS are assembled as per drawing required i.e. inter layer inserts are

assembled in each and every slots except RTDS slots. In RTDS slots only RTDS are assembled beforelaying top bars.

Stiffner assembles:

Stiffner are assembled on the winding layers on to the bottom bars by reinforcing & placing glass mat and

tieing with neip ring glass. Stiffeners are carried out on the both sides.


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TOP BARS LAYING

Pressing of top bars:

Each individual top bar is subjected to pressure 60kg/cm2 horizontally and vertically for duration of

30minutes in order to obtain pre determine dimensions.

The above operation for each top bar before laying in to their respective slots.

First top bar laying is carried out by centering the bar with respect to the stator core & check the pitchdimensions on both sides.

Similarly the next bar is assembled in to respective slots by following the above procedure.

After laying every two bars the over hangs are reinforced by inserting glass mat at 3different locations on

the both sides.

By following the above procedure all the top bars are laid in to the slots by full filling the drawing

requirements then the top bars are reinforced wedging with HGW over layer and placing glass mat under

the wedges.

All the respective wedges are driven by matching with respective ventilation holes of the pores.

Similarly all the wedges are driven in all respective slots by blocking the top bars.

After completion top bars laying top bars are subjected to D.C. high voltage.

Connecting rings assembly

All connecting rings assemble as per the drawing requirements, and then the phase groups are processed

by jointing, bracing and insulation. After completion of jointing bracing and insulation once again it is

subjected to D.C. high voltage. Termination of desired RTDSon one side for monitoring the post curing

temperature.


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VACUUM PRESSURE IMPREGNATION

INTRODUCTION TO VPI SYSTEM:

DR. MEYER brought the VPI system with the collaboration of WESTING HOUSE in the year 1956.

Vacuum Pressure Impregnation has been used for many years as a basic process for thorough filling of allinterstices in insulated components, especially high voltage stator coils and bars.

VPI is a process, which is a step above the conventional vacuum system. VPI includes pressure in

addition to vacuum, thus assuring good penetration of the varnish in the coil.

The result is improved mechanical strength and electrical properties. With the improved penetration, a

void free coil is achieved as well as giving greater mechanical strength.

With the superior varnish distribution, the temperature gradient is also reduced .

In order to minimise the overall cost of the machine & to reduce the time cycle of the insulation systemvacuum pressure Impregnated System is used.

The stator coils are taped with porous resin poor mica tapes before inserting in the slots of cage stator,

subsequently wounded stator is subjected to VPI process, in which first

thestator is vacuum dried and then impregnated in resin bath under pressure of Nitrogen gas.

Fig: VPI system

RESIN POOR RESIN RICH1.Epoxy resin content is about 8%. 1. Epoxy resin content is about 40%.2.This method follows Thermo Setting Process. 2. This method also follows Thermo Setting

Process.

3.There is a need for addition of resin from outside. 3. Further addition of resin is not required from

outside.

4.Time required for this cycle is less. 4. It is a very long process and time consuming.

5.Repairing is very difficult. 5. Repairing is easy.

6.Over all cost is less compared to resin rich. 6. Over all cost is more.


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Features and Benefits:

State-of-the-art process for completely penetrating air pockets in winding insulation.

The jobs that are entering tank for Vacuum Pressurised Impregnation shall not have any oil based

coatings. Any such, rust preventive/corrosion preventive viz., red oxide etc., shall be eliminated into the

tank.

Resin in the storage tank shall be stored at 10 to 12oC and measured for its viscosity, viscosity rise.

Proper functioning of the impregnation plant and curing oven are to be checked by production and

cleared for taking up of job for impregnation.

1.Preheating:

The job is to be loaded in the curing oven and heated. The temperature is to be monitored by the RTDelements placed on the job and the readings are logged by production. The time of entry into the oven,

time of taking out and the temperature maintained are to be noted. Depending on convenience of

production the jobs can be preheated in impregnation tank by placing them in tubs.

The impregnation tubs used for impregnation of jobs are to be heated in the impregnated tank itself,

when the jobs are preheated in the curing oven.

2. Impregnation:

Job insertion into preheated tub and insertion into tank By the time, the preheating of job is completed, it

is to be planned in such a way that the heating of tub and tank heating matches with the job. This is

applicable when the job is heated in the curing oven separately. The preheated job is to be transferred into

the tub by crane handling the job safely and carefully without damage to the green hot insulation.

Insertion of tub with job into the impregnation tank

The warm tub with job is inserted into impregnation tank by sliding on railing, in case of horizontal tank.

The thermometer elements are to be placed at different places on the job. The connection for inlet resin is

to be made for collection of resin into tub. After ensuring all these lid of the impregnation tank is closed.

In case of vertical tank the job along with tub is slinged and inserted carefully into impregnation tank

without damage to insulation.


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Fig: VPI Resin tub

Drying the job in vacuumThe job is to be dried under vacuum. Drain out the condensed moisture/ water at the exhausts of vacuum

pumps for efficient and fast vacuum creation. Also check for oil replacement at pumps in case of delay in

achieving desired vacuum.

Heating the resin in the storage tank

The completion of operations of drying and the heating of the resin in the storage tank are to besynchronized. The heating of resin in the tank and pipeline is to be maintained as at preheating

temperature.

Admission of resin into impregnation tank

The resin is allowed into the impregnation tank tub if required from various storage tanks one after the

other up to a level of 100mm above the job generally, after which the resin admission is stopped. After10mins of resin settling the tank is to be pressurized by nitrogen. While admitting resin from storage

tanks pressurize to minimum so that nitrogen will not affect resin to spill over into tank .

Pressurizing/gellingThe pressure cycle is to be maintained.

Withdrawal of resin from impregnation tank to storage tank

The resin that is pressurized as per pressure cycle through which the opening of relevant valves will

allow the resin to come back to the storage tank. The job also shall be allowed for dripping of residue of

resin for about 10min. After dripping, withdrawal of resin in various storage tanks is to be carried out.

Taking out the tub with job from impregnation tankThe lid is then opened after taking precautions of wearing mask and gloves for the operating personnel as

a protection from fumes. The job is withdrawn from impregnation tank by sliding on railing for horizontal

and slinging on to crane for vertical impregnation tanks.

3.Post curing:

The job is post heated. The time for raising from job temperature to this temperature as per relevant

annexure. The time at which the heating is started, achieved and maintained is to be logged.


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4.Electrical testing:

All jobs that are impregnated till above process, are to be tested for electrical tests. After ensuring that all

the temperature/vacuum conditions stipulated for drying, impregnation and curing operations have been

properly followed, the job is to be released for this operation.


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ROTOR

Rotor is the rotating part of alternator. It is used to support field winding placed in slots on the rotor.

FOR 2-POLE GENERATOR: Solid rotors are manufactured from forged alloy steel with suitable

alloying elements to achieve very high mechanical and superior magnetic properties. This type of rotor

can withstand even upto speed of 3000 rpm. Rectangular or trapezoidal rotor slots are accurately

machined to close tolerances on slot milling machine. For indirectly cooled generator rotors, ventilationslots are machined in the teeth.

FOR 4-POLE GENERATOR: For directly cooled rotors, sub slots are provided for cooling

Generator rotors of 1500 RPM are of round laminated construction. In this case rotor is made up of two

parts core AND lamination. The outer diameter of core and the inner diameter of laminations are equal.

So for inserting the core inside the laminations the laminations are first red heated at medium temperature

for 15 hours in BELL FURNACE. After that the core is shrunk fitted inside the laminations. Thus

punched and varnished laminations of high tensile steel are mounted over machined shaft and are firmlyclamped by end clamping plates.

ROTOR SHAFT :

Fig: rotor body

Rotor shaft is a single piece solid forming manufactured from a vacuum casting. It is forged from a

vacuum cast steel ingot. Slots for insertion or the field winding are milled into rotor body. Thelongitudinal slots are distributed over the circumference such that two solid poles are obtained. To ensure

that only a high quality product is obtained, strength tests, material analysis and ultrasonic tests are

performed during the manufacture of rotor. The high mechanical stresses resulting from the centrifugal

forces and short circuit torques call for a high quality heat treated steel. After completion, the rotor isbalanced in various planes at different speeds and then subjected to an over speed test at 120% of the

rated speed for two minutes.


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Approximately 60% of rotor body circumference has longitudinal slots which hold the field winding. Slot

pitch is selected so that the two solid poles are displaced by 180 degrees. The rotor wedges act as

damper winding within the range of winding slots. The rotor teeth at the ends of rotor body are provided

with axial and radial holes enabling the cooling air to be discharged into the air gap after intensive cooling

of end windings.

ROTOR WINDINGS:The rotor windings consist of several coils inserted into the slots and series connected such that two coil

groups form one pole. Each coil consists of several series connected turns, each of which consists of two

half turns connected by brazing in the end section. Thickness of each strip can be made upto 10.5 mm but

here in BHEL we make only upto 5.3 mm. The rotor bearing is made of silver bearing copper ensuring

an increased thermal stability. For ventilation purpose the slots are provided on the both coil and on inter

strip insulation layer .The individual turns of coils are insulated against each other by interlayer

insulation. L-shaped strips of laminated epoxy glass fiber fabric with nomex filter are used for slot

insulation.

The slot wedges are made of high electrical conductivity material and thus act as damper windings. At

their ends the slot wedges are short circuited through the rotor body. The inter space between the

overhang is called slot through.

CONSTRUCTIONThe field winding consists of several series connected coils inserted into the longitudinal slots of rotorbody. The coils are wound so that two poles are obtained. The solid conductors have a rectangular cross

section and are provided with axial slots for radial discharge or cooling air. All conductors have identical

copper and cooling duct cross section. The individual bars are bent to obtain half turns. After insertion

into the rotor slots, these turns are brazed to obtain full turns. The series connected turns of one slot

constitute one coil. The individual coils of rotor are connected in a way that north and south poles are

obtained.

CONDUCTOR MATERIAL:The conductors are made of copper with a silver content of approximately 0.1%. As compared to

electrolytic copper, silver alloyed copper features high strength properties at high temperatures so that

coil deformations due to thermal stresses are eliminated.

INSULATION:The insulation between the individual turns is made of layer of glass fiber laminate. The coils are

insulated from the rotor body with L-shaped strips of glass fiber laminate with nomex interlines. Toobtain the required leakage paths between the coil and the rotor body thick top strips of glass fiber

laminate are inserted below top wedges. The top strips are provided with axial slots of the same cross

section and spacing as used on the rotor winding. Insulation b/w overhang is done by blocks made of

HGL.

ROTOR SLOT WEDGES:


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To protect the winding against the effects of centrifugal forces, the winding is secured in the slots with

wedges. The slot wedges are made of copper alloy featuring high strength and good electrical

conductivity. They are also used as damper winding bars. The slot wedges extend beyond the shrink seats

of retaining rings. The wedge and retaining rings act on the damper winding in the event of abnormal

operations. The rings act as short circuit rings in the damper windings.

END WINDING BRACING:The spaces between the individual coils in the end winding are filled with insulated members that preventcoil movement. Two insulation plates held by HGL high glass laminate plates separate the different

cooling zones in the overhangs on either sides.

ROTOR RETAINING RINGS:The centrifugal forces of the rotor end winding are contained by single piece rotor retaining rings.Retaining rings are made of non-magnetic high strength steel in order to reduce stray losses. Each

retaining ring with its shrink fitted. Insert ring is shrunk on to the rotor body in an overhang position. The

retaining ring is secured in the axial position by snap rings. The rotor retaining rings withstand the

centrifugal forces due to end windings. One end of each ring is shrunk fitted on the rotor body while the

other end overhangs the end windings without contact on the rotor shaft. This ensures an unobstructed

shaft deflection at the end winding.

ROTOR FANS

Rotor fan


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The cooling air in generator is circulated by two axial flow fans located on the rotor shaft one at each end.

To augment the cooling of the rotor winding, the pressure established by the fan works in conjunction

with the air expelled from the discharge parts along the rotor. The blades of the fan have threaded roots

for being screwed into the rotor shaft. The blades are drop forged from an aluminium alloy. Threaded root

fastenings permit angle to be changed. Each blade is secured at its root with a threaded pin.

Fig: rotor fan

BEARINGS VENTILATION AND COOLING EXCITER SYSTEM:

BEARINGSThe turbo generators are provided with pressure lubricated self-aligning elliptical type bearings to ensure

higher mechanical stability and reduced vibration in operation. The bearings are provided with suitabletemperature element devices to monitor bearing metal temperature in operation. From inside the bearings

are made of very soft metal called Babbitt so that rotor doesnt get harmed even if it comes in contactwith Babbitt. Inside this Babbitt there is a very thin film of pressurized lubrication oil on which the shaft

rotates. The temperature of each bearing is monitored with two RTDs (Resistance Thermo

Detectors)embedded in the lower bearing sleeve such that the measuring point is located directly below

the babitt. To prevent damage to the journals due to shaft currents, bearings and oil piping on either side

of the non-drive end bearings are insulated from the foundation frame. For facilitating and monitoring the

healthiness of bearing insulation, split insulation is provided.

VENTILATION AND COOLINGTurbo generators are designed with the following ventilation systems:

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

Closed circuit hydrogen cooling with water or hydrogen coolers mounted axially on the stator frame.

The fan design usually consists of two axial fans on either made of cast aluminum with integral fan blades

or forged and machined aluminum alloy blades screwed to the rotor. In case of 1500 RPM

generators, fabricated radial fans are provided.

EXICTATION SYSTEM

The basic use of given exciter system is to produce necessary DC for turbo generator system .Principal

behind this is that PMG is mounted on the common shaft which generates electricity and that is fed to

yoke of main exciter. This exciter generates electricity and this is of AC in nature. This AC is that

converted into DC and is that fed to turbo generator via C/C bolt. For rectifying purpose we have RC

block and diode circuit. The most beautiful feature is of this type of exciter is that is automatically divides

the magnitude of current to be circulated in rotor circuit. This happens with the help of AVR regulator


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which means automatic voltage regulator. A feedback path is given to this system which compares

theoretical value to predetermine and than it sends the current to rotor as per requirement.

Fig: BLE exciter

The brushless exciter mainly consists of:-

1. Rectifier wheels

2. Three phase main exciter

3.Three phase pilot exciter4. Metering and supervisory equipment.The brushes exciter is an AC exciter with rotating armature and stationery field. The armature is

connected to rotating rectifier bridges for rectifying AC voltage induced to armature to DC voltage. The

pilot exciter is a PMG (permanent magnet generator). The PMG is also an AC machine with stationery

armature and rotating field. When the generator rotates at the rated speed, the PMG generates 220 V at 50

hertz to provide power supply to automatic voltage regulator.


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EVALUATION OF SHORT CIRCUIT RATIO:

From the test data Short Circuit Ratio is calculated using the formula.S.C.R= Field current at 100% Rated

voltage from OCC/Field current at 100% rated current from SCC.


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CONCLUSION AND FUTURE SCOPE

CONCLUSION :

The Vocational training at BHEL Hyderabad helped us in improving our practical knowledge andawareness regarding Turbo Generator to a large extent. Here we came to know about the technology and

material used in manufacturing of turbo generators. Besides this, we also visualized the parts involved or

equipments used in the power generation. Here we learnt about how the electrical equipments are being

manufactured and how they tackle the various problems under different circumstances. At least we

could say that the training at BHEL Hyderabad is great experience for us and it really helped us in making

or developing our knowledge about turbo generator and other equipment used in power generation.

FUTURE SCOPE:

The technology research and investigations division of BHEL is currently investigating the technical and

logistical merit of performing offline quadratic-rate partial discharge tests on the stator winding insulationof its hydro & turbo generators. A series of laboratory based insulation research studies on stator barshave been conducted to gain a better understanding of the various partial discharge phenomena involved.

Results thus far obtained from these tests have provided valuable insight into the discharge activity of

operation.


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BIBLIOGRAPHY

1. www.indiamart.com

2. www.eriks.co.uk

3. www.seimens.com

4. www.bhel.com

5. A text book of electrical technology by B.L.THERAJA

6. A text book of electrical machines by P.S.BIMBRA
http://www.indiamart.com/http://www.eriks.co.uk/http://www.seimens.com/http://www.bhel.com/http://www.bhel.com/http://www.seimens.com/http://www.eriks.co.uk/http://www.indiamart.com/

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