Basic Components and Construction of Turbo Generators at

Bharat Heavy Electricals Ltd. Haridwar

A PROJECT REPORT Submitted in partial fulfillment of the

Summer Training Of

Bachelor of Technology(With Specialization in Electrical Engineering)

By

Gurtej Singh(12115044)

Under the Guidance of

Mr. Rajmani JaiswalSenior Engineer

Bharat Heavy Electricals Ltd. Haridwar, India

IIT ROORKEE, Uttarakhand,INDIA

1

ACKNOWLEDGEMENT

Design and manufacturing of electric generators, requires an

appreciation of multidisciplinary concept and in depth knowledge of

scientific analytical tools, geared to the solution of real life problems.

To acquaint me with such challenging situation, I was allowed to go to

BHEL, Haridwar by IIT Roorkee. During my training, I visited almost

all the departments. The training period was of one and half months

which was too short to find out an efficient feasible solution to the

problem of Electrical Engineering so, I have tried my best to collect all

relevant data and studied the details of turbo generators designed and

produced at BHEL.

I whole hearted appreciate the atmosphere provided to me by the staffs

of Electrical Engineering. The data has been collected at primary source

through discussions with officers of different sections. For this nice

gesture on their part, I shall ever remain obliged to them.

2

CONTENTS

1. INTRODUCTION

2. INSULATION

Insulation tape Insulation systems

3. STUDY ON TURBO GENERATORS

Technical data Construction features Stator Rotor

4. EXCITATION

Brushless Excitation for turbo generators Merits Construction features of brushless exciter various components of the brushless exciter PMG

5. CONCLUSION

6. REFERENCES

INTRODUCTION

3

In 1956, India took a major step towards the establishment of its heavy engineering industry and Bharat Heavy Electrical Ltd., the first heavy electrical manufacturing unit of the country was setup at Bhopal. It advanced rapidly and three more factories went into production in 1965. The main aim of establishing BHEL was to meet the growing power requirement of the country. BHEL appeared on the power map of India in 1969 when the first unit supplied by it was commissioned at the Basin Bridge Thermal Power Station in Tamil Nadu. BHEL had taken India from a near total dependence on imports to complete self-reliance in this vital area of power plant equipment.

BHEL has its headquarters at New Delhi. Its operations are spread over 11 manufacturing plants and number of engineering and service divisions located across the country/ the service divisions includes a network of regional branch offices throughout India. Bharat Heavy Electricals Ltd. has evolved as the largest engineering and manufacturing unit of its own kind in India with highest level of performance. BHEL is among one of the MAHA RATNA of India. BHEL manufactures over 180 products and 30 major project groups and supplies to core sectors of Indian economy like Power generation and transmission, transportation, telecommunication, renewable energy etc. Now BHEL has become the first company in India to make 1000 MW Turbo Generator.

BHEL has now thirteen manufacturing divisions, eight service centers and four power sector regional centers, besides a large number of projects sites spread all over India and abroad. Several products are manufactured in HEEP, such as: - Steam Turbines, Turbo Generators, hydroturbines, Gas turbines, etc.

4

INSULATION:INSULATION MATERIALS AND THEIR SPECIFICATIONS

CLASS TEMP MATERIAL

Y 900C Cotton, silk paper

A 1050C Cotton, silk paper with impregnation

E 1200C Synthetic material

B 1300C Mica, Asbestos, Glass fiber.

F 1550C- 1650C Mica, glass cloth base with epoxy resin

H 1800C Mica,porcelain,Quartz,glass

C >1800C Mica, porcelain, glass (without bending agent )

INSULATION TAPE

It consists of three materials:

1. BINDER (Resin or varnish e.g. epoxy resin of class-F)

2. Backing material to provide mechanical strength (e.g. glass tape or polyester tape).

3. MICA-poor mechanical strength in paper form

Mica and glass can withstand at temperature (700-8000C). As a whole it is class-F due to

binder. There are two types of tapes

RESIN RICH

RESIN POOR

RESIN RICH: Binder of the order of 40% by weight here during curing the resin should

flow and fill the voids and oozes out. Due to curing air voids are more and hence thickness

is more in it. Life of machine is 20-25 years. It has less life as there is flexible tape over the

overhang portion and therefore more moisture enters in it.

RESIN POOR: Binder is of the order of 6-8% by weight after curing the insulation we

need 34-35% of the binder. Before curing it is impregnated to resin to get the required

5

%age of the resin. Here we first remove all the air & thus penetration of resin is better &

voids are less and thickness is less. Also no effect of vibration.

INSULATION SYSTEMS:

The insulation of coils and winding bars is built by applying insulation materials in the

form of tapes and sheets. These tapes consist of electrical material (Generally mica

splitting or mica paper).

Depending upon the building materials insulation systems are classified in to two main

parts.

1. Thermoplastic insulation system

2. Thermo reactive or thermosetting insulation system.

Thermoplastic insulation system: In this system, the nature of resin is oil modified

electrical grade bitumen varnish. This system is not suitable beyond a temperature of

1300C. This is because the thermoplastic insulating materials exhibit a reversible change in

state with an increase in temperature. At room temperature the thermoplastic arte hard and

solid, while at elevated temperature these get softened and will melt at higher temperature.

Generally this system is used for class-b electrical machines. Due to this system machines

run at very high speeds and when temperature gets increase there is a risk of insulation risk

out.

Thermo reactive insulation system: In this system the insulation material gets harden

when heated and maintained at elevated temperature for sufficient period of time. This is

called curing. This is a non-reversible process meaning thereby that the insulation remains

hard after cooling and again heating. This is also called thermosetting system. The oil

bituminous bond is replaced by epoxy synthetic based resin which hardens under the effect

of heat. This system has superior thermal, mechanical and dielectric properties.

It has two types:-

1. Resin rich insulation system 2. Resin poor insulation system

6

STUDY ON TURBO GENERATOR (500MW):

Technical Data

Rated data &

Output

Turbo generator Main exciter Pilot exciter

Apparent Power 588 MVA - 65 kVA

Active Power 500 MW 3780 kW -

Current 1 6.2 kA 6300 A 195 A

Voltage 21 kV 600 V 220 V

Frequency 50 Hz 400 Hz

Power Factor 0.85 - -

Inner Connection of

S statator winding

YY

- -

H Hydrogen pressure 3.5 BAR - -

R Rated field current 4040 A - -

Rated field voltage 340 V - -

(General & Electrical data)

GENERATOR

Generators are the machines which converts mechanical energy into electrical energy or

the machine which are used to generate electricity.

The various types of generators manufactured in B.H.E.L.Hardwar are as follows:-

1) THDF (500 MW)

2) THRI (210/250 MW)

3) TARI (120-160 MW)

4) THW (210/235 MW)

The first three types are of Siemens Design and the last one is of Russian Design.

Stator cooling:

1) I Indirect cooling by H2

2) F Forced cooling by water

7

Rotor cooling:

1) R Radial cooling of rotor

2) D Direct cooling of rotor

Cooling gas in the casing:

1) H Hydrogen

2) A Air

CONSTRUCTIONAL FEATURES OF TURBOGENERATORS:

The two pole generator uses direct hydrogen and direct water cooling for the rotor winding

and stator winding respectively. The losses in the remaining generator components, such as

iron losses friction and windage losses and stray losses are also dissipated through

hydrogen.

The generator frame is pressure resistant, gas tight and equipped with end-shields at

each end. The hydrogen coolers are arranged vertically inside the turbine end stator end

shield

The generator consists of following components:

STATOR

Stator frame

Stator core

Stator winding

End shields

Terminal bushings

Phase connectors

Hydrogen coolers

Stator cooling system

Supervision of generator

End winding vibrations

8

ROTOR

Rotor shaft

Rotor winding

Rotor retaining rings

Field connection

Fans

Rotor Cooling System

BEARINGS

SHAFT SEALS

The following additional systems are required for generator operation:

1. Gas system

2. Excitation system

STATOR:

Stator Frame:

The stator frame with flexible core suspension components, core and stator winding is the heaviest

component of the entire generator .A rigid frame is required due to the forces and torque arising during

operation. In addition, the use of hydrogen for the generator cooling requires the frame to be pressure

resistant up to an internal pressure of approximately 10 bars.

The welded stator frame consists of cylindrical frame housing, two flanged rings and axial and radial

ribs. Housing and ribs with in the range of the phase connectors of the stator winding are made of non

magnetic steel to prevent eddy current losses, while the remaining frame parts are fabricated from

structural steel.

The arrangement and dimensionally of the ribs determine by the cooling gas passages and the

required mechanical strength and stiffness. Diminishing is also dictated by vibration considerations,

resulting partly in greater wall thickness than required, from the point of view of the mechanical strength.

The natural frequency of the frame does not correspond to any exciting frequency.

Two lateral supports for flexible core sustention in the frame are located directly adjacent to the

points where the frame is supported on the foundation; due to the rigid design of the supports and foot

portion the forces due to the weight and short circuits neither will nor result in any over stressing of the

frame.

9

Manifolds are arranged inside the stator frame at the bottom and top for filling the generator with

CO2 and H2. The connections of the manifolds are located side by side in the lower part of the frame

housing.

Additional openings in the housing, which are sealed gas tight by pressure resistant covers, afford

access to the core clamping flanges of the flexible core suspension system and permit the lower portion of

the core to be inspected. Access to the end winding compartments is possible through manholes in the end

shields.

In the lower part of the frame at the exciter end an opening is provided for bringing out the winding

ends, the generator terminal box is flanged to this opening.

Stator frame

Stator Core: In order to minimize the hysteresis and eddy current losses of the rotating magnetic flux

which interacts with the core, the entire core is built up of thin laminations. Each lamination layer is made

up from a number of individual segments. The segments are punched in one operation from 0.5 mm thick

electrical sheet-steel laminations having high silicon content, carefully debarred and then coated with

insulating varnish on both sides. The stator frame is turned on end while the core is stacked with

lamination segments in individual layers. The segments are staggered from layer to layer so that a core of

high mechanical strength and uniform permeability to magnetic flux is obtained.

On the outer circumference the segments are stacked on insulated dovetail bars which hold them in

position. One dovetail bar is not insulated to provide for grounding of the laminated core. Stacking guides

inserted in to the winding slots during stacking provide smooth slot walls.

To obtain the maximum compression and eliminates undue settling 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 the frame by means of clamping bolts

and pressure plates. The clamping bolts running through the core are made of non-magnetic steel and are

10

insulated from the core and the pressure plates to prevent the clamping bolts from short-circuiting the

laminations and allowing the flow of eddy currents.

The pressure is transmitted from the pressure plates to the core by clamping fingers. The clamping fingers

extend up to the ends of the teeth, thus ensuring a firm compression in the area of the teeth. The stepped

arrangement of the laminations at the core ends provides for an efficient support of the tooth portion and,

in addition, contributes to a reduction of a eddy current losses and local heating in this area. The clamping

fingers are made of non-magnetic steel to avoid eddy current losses.

The protection against the effects of stray flux in the coil ends, the pressure plates and the core end

portions are shielded by gas cooled rings of insulation bonded electrical sheet-steel.

To remove the heat, spacer segments, placed at intervals along the bore length, divide the core in to

sections to provide radial passages for cooling gas flow. In the core end portions, the cooling ducts are

wider and spaced more closely to account for the higher losses and to ensure more intensive cooling of the

narrow core sections.

The revolving magnetic field exerts a pull on the core, resulting in a revolving and nearly elliptical

deformation of the core which sets up stator vibration at twice the system frequency. To reduce the

transmission of these vibrations to the foundation, the generator core is spring mounted in the stator frame.

The core is supported in several sets of rings and two core clamping rings. The structural members to

which the insulated dovetail bars are bolted are uniformly positioned around the supporting ring interior to

support the core and to take up the torque acting on the core

Stator winding:

Manufacturing the stator bar

The stator bar consists of large number of separately insulated hollow and solid strands which are

distributed over the entire bar cross-sections so that good heat dissipation is insured. The manufacturing

process contains following operations.

1. Conductor cutting : The required size of conductor is cut by cnc conductor cutting machine. For the

lower bar length of conductors is 10.2m and for upper bar, length of conductors is 10.05m. The lower and

upper bar contains 20 conductors each. Total bar contains 20 hollow and 20 solid conductors.

2. Transposition : To minimize the stray losses, the bars are composed of separately insulated strands

which are transposed by 5400 in the slot portion the Tran positioning provides for a mutual neutralization

of the voltages induced in the individual strands due to the slot cross field and end winding flux leakage

and insures that minimum circulation currents exists. The current flowing through the conductor is

uniformly distributed over the entire bar cross section so that the current dependent losses will be reduced.

11

3. Bandaging : Between the lower and upper bar insulation is placed. The insulating material is epoxy

glass. The individual layers are insulated from each other by a vertical separator. This process is known as

bandaging.

4. Pressing and calibration: After bandaging the bars are pressed under the temperature of 1500 for

settlement of insulation.

5. Inter turn testing : This testing is done at 300volt .this is done to check whether the conductors are

short or not.

6. Forming : In forming bars are bended from each end by heating at 1800c for 35 min.

7. Coil lug brazing : at the bar ends, the solid strands are jointly brazed in to a connecting sleeve and

the hollow strands in to a water box from which the cooling water enter and exists via Teflon insulating

connection between top and bottom bars is made by a bolted connections at the connecting sleeve.

8. Pickling : in this process, the conductors ends are dipped in acid. Pickling solution contains

sulphuric acid, phosphoric acid, water, hydrogen peroxide in definite composition. The conductor ends are

dipped in this solution for 15 minute. Then the conductor ends cleaned with water and brass brush. For

neutralization we dipped conductor end in ammonia solution which consist of water and liquid ammonia.

After that the ends are dipped in ethyl alcohol and after that conductors are dried by nitrogen. This whole

processes are done for four times.

9. Testing :

Nitrogen leakage test : this is done to check the leakage in sleeves at pressure 11kg/sqcm

Helium leakage test : Helium gas is filled inside the bar at 11kg/sqcm. And the bar is covered with

polythene bag and locked on both sides. By helium leak detector probe, if any leakage at lug point

occurs, then the meter will show and it can be confirmed for a repair of bar joint.

Hydraulic test

Thermal shock test

12

10. Micalastic high voltage insulation : High voltage insulation is provided according to the micalastic

system. With this insulating system, several half over lapped continuous layers of mica tape are applied to

the bars. The mica tape is build up from large area mica splitting which are sandwiched between two

polyester backed fabric layers with epoxy as an adhesive. The number of layers, i.e. thickness of the

insulation depends on the machine voltage. In this machine the numbers of layers are 11. The bars are

dried under vacuum and impregnated with epoxy resin which has very good penetration properties due to

its low viscosity. After impregnation under vacuums, the bars are subjected to pressure, with nitrogen

being used as pressurizing medium (VPI process). The impregnated bars are formed to the required shape

in moulds and cured in an oven at high temperature. The high voltage insulation obtained is nearly void

free and is characterized by its excellent electrical, mechanical and thermal properties in addition to being

fully water proof and oil resistant.

11. Conductor varnishing coating : To prevent potential differences and corona discharges between the

insulation and slot wall, the slot sections of the bars are provided with an outer corona protection. This

protection consists of wear resistant, highly flexible coating of conductive alkyd varnish containing

graphite.

At the transition from the slot to the end winding portion of the stator bars, a semi conductive coating is

applied. On top of this, several layers of semi conductive end corona protection coating are applied in

varying lengths. This ensures uniform control of the electrical field and prevents the formation of corona

discharge during operation and during performance of high voltage tests.

12.Tan δ & high voltage test: To check the mechanical strength of stator bars high voltage testing is

done. After insulation and curing, the insulation of each stator bar is subjected to high voltage test at 150%

of the winding test voltage. (UT = 2* UN +1 KV). For assessment of the quality of the slot insulation the

dielectric dissipation factor tan δ is measured as a function of the voltage. The dissipation factor of the

stator winding is measured in the range of 0.2 to 1.4 UN.

13. Dispatch: after all the bars are dispatched to block one for assembling in stator frame.

Locating the bars:

The three phase stator winding is a fractional pitch two layer type consisting of individual bars. The

stator windings are placed in rectangular slots which are uniformly distributed around the circumference

of the stator core. Each stator slot accommodates two bars. Total slots are 48. The slot bottom bar & top

bar are displaced from each other by one winding pitch and connected at there ends to form coil groups.

The coil groups are connected together with phase connectors inside the stator frame shown in the

connection diagram.

13

Tp- pole pitch

Lap type winding:

Coil pitch = slots/pole = 48/2

= 24 i.e. full pitch

Short pitch = pole pitch = 24*(5/6)

= 20

Slot per pole per phase = 48/ (2*3)

= 8

The bars are protected by a cemented graphitize paper wrapper over the slot portion of the bars.

The bars fit tightly in the slots .manufacturing tolerances are compensated with semi conducting filler

strips along the bar sides which ensure good contact between the outer corona protection & the slot wall.

Radial positioning of the bar is done with slot wedges. To protect the stator winding against the effects

of magnetic forces due to load and to ensure permanent firm seating of the bars in the slots during

operation, the bars are inserted with a top ripple spring located beneath the slot wedge. The ripple spring is

made of semiconductor material performs following functions:

Provide mechanical strength

Absorb vibrations

Act as insulator

Protect from corona

14

Below the longitunally divided slot wedges fiber glass fabric is arranged between the filler and slide strip

which presses the bars against the slot bottom with the specific pre loading. An equalizing strip is inserted

at the slot bottom to compensate any unevenness in the bar shape and slot bottom surface during bar

insertion. The strip is cure after insertion of bars. These measures prevent vibrations. The specified

preloading is checked at each slot wedge.

With the winding placed in slots, the bar ends form a cone shaped end winding having particularly

favorable characteristics both in respect of its electrical properties and resistance to magnetically induced

forces. A small cone taper is used to keep the stray losses at a minimum. Any gaps in the end winding due

to the design or manufacturing are filled with curable plastic fillers, insuring solid sport of the cone shaped

top and bottom layers.

The two bar layers are brazed with clamping bolts of high strength fiber glass fabric against a rigid ,

tapered supporting rings of insulated material. Tight sitting is insured by plastic filters on both sides of the

bars which are cured on completion of winding assembly. Each end winding forms a compact, self

supporting arch of high rigidity which prevents bar vibrations during operation and can with stand short

circuit forces.

In addition, the end turn covering provides good protection against external damage. The supporting

rings rest on supporting brackets which are capable of moving in the axial direction. This allows for a

differential movement between the end winding and the core as the result of different thermal expansions.

The stator winding connections are brought out to six bushings locating in the compartment of welded non

magnetic steel below the generator at the exciter end. Current transformers for metering and relaying

purposes can be mounting on the bushings. The bars are subjected to numerous electrical and leakage test

for quality control

End Shield: The ends of the stator frame are closed by pressure containing end shields. The end

shields features a high stiffness and accommodate the generator bearings, shaft seals and hydrogen

coolers. The end shields are horizontally split to allow for assembly

Terminal Bushings: The cylindrical bushing conductor consists of high conductivity copper with a

bore central bore for direct primary water cooling. The insulator is wound directly over the conductor. It

consists of impregnated capacitor with conducting fillers for equalization of the electrical direct-axis and

quadrature-axis fields. The beginnings and ends of the three phase windings are brought out from the

stator frame through terminal bushings which provide for high voltage insulation and seal against

hydrogen leakage. The bushings are bolted to the bottom plate of the generator terminal box by the

mounting flanges

15

Phase connection: The phase connectors interconnect the coil groups and link the beginning and

ends of the winding to the bushings. They consist of thick-walled copper tubes. The stator bars are coupled

to the phase connectors. The phase connectors are provided with micalastic insulation

Hydrogen Cooler: The hydrogen cooler is a shell and tube type heat exchanger which cools the

hydrogen gas in the generator. The heat removed from the hydrogen is dissipated through the cooling

water. The cooling water flows through the tubes, while the hydrogen is passed around the finned tubes.

Stator Cooling System:

1. Cooling of Stator Core

2.. Cooling of Stator winding, Phase connectors and Bushings.

End Winding Vibration: Stator end windings are subjected to three different vibratory forces:

1. Pulsating forces during start-up , shut down and normal operation.

2. Forces resulting from the restrained thermal expansion, which depends upon generator load and

coolant temperature.

3. Electromagnetic forces arising from abnormal operating conditions especially during short-circuit

conditions during synchronization.

SUPERVISION OF GENERATOR:

Temperature Monitoring

Stator slot temperature: The slot temperatures are measured with resistance temperature detectors

(RTD'S). The platinum measuring wire is embedded in a molded plastic body which provides for

insulation and pressure relief

Cold and Hot Gas Temperatures: The temp of the hot and cold gasses is measured by RTD's upstream

and downstream of the hydrogen coolers, and the limit values are sensed with rod-type thermostats.

Separate RTD's are provided downstream of the coolers for use with the hydrogen temperature control

system.

16

ROTOR:

ROTOR SHAFT: The cylindrical rotor with non-salient pole forms one of the most important parts of the

turbo generator, which is loaded to the maximum limit of mechanical strength of the material as well as heat

transfer capability. Due to the high speed of rotation high mechanical centrifugal stresses are encountered in

the rotor teeth as well as in the rotor retaining ring. The rotor shaft is forged from a vacuum cast steel ingot.

Due to the non-uniform slot distribution on the circumference, different moments of inertia are obtained in

the main axis of the rotor. This in turn causes oscillating shaft deflections al twice the system frequency. To

reduce these vibrations, the deflections in the direction of pole axis and the neutral axis are compensated by

transverse slotting of the pole.

The rotor forging is heat-treated and stress relieved at the forging plants and is tested for the absence of

various defects by conducting the following test:

1. Ultra-sonic test

2. Sulpher prints

3. Check for residual stress

4. Test for mechanical strength

Rotor Shaft

ROTOR WINDING:

17

Construction of Rotor bar

In the 500MW turbo generator, there are two poles in the rotor and there are seven coils in each pole.

The seven coils named as A, B, C, D, E, and F & G. A coil has six conductor and remaining six coils have

nine conductors. The conductors are made of copper with a silver content of approximately 0.12%. as

compare to electrolyte copper, silver alloyed copper features high strength properties at high temperatures

so that coil deformations due to thermal stresses are eliminated. For manufacturing the rotor bars, the

number of operations are as follows:

1. Number punching : Pole number, coil number and conductor number are punched on the coil.

2. Marking: Center line of coil and centers of gas inlets are marked.

3. Drilling of gas inlets & outlets : For the passage of gas ducts are formed having diameter of 21mm

&25mm.

4. Chamfering on gas outlets and inlets : Cooling ducts edges are chamfered.

5. Deburring: After drilling and chamfering, extra chips on the bar are removed by using rubbing paper.

6. Cleaning of canal by brush passing: A brush is passed through the canal to remove the chips.

7. Rinsing in trichloroethylene : to remove oil, grease bars are rinsed in trichloroethylene.

8. Filling and caucking of fillers : Fillers are filled in the ducts for providing appropriate path to the gas.

9. Annealing of ends : ends are heated up to 500-5400C and then quenched in water.

10.Edge wise bending : Bars are bended at the end portion according to the proper marking.

11.Pressing of bends : bends are presses to adjust the increased thickness at the bend portion up to normal

thickness.

12.Annealing of overhang portion :

13.Radius bending : Cylindrical forming is done and length of bar is maintained.

14.End cutting milling of overhang portion :

15.Filler brazing : To cover the empty space an extra conductor

16.Deburring:

17.Cleaning of canal by brush &compressed air :

WINDING

Construction: The field winding consists of several coils inserted in to the longitudinal slots of the rotor

body. The coils are wound around the poles so that one north and one south magnetic pole is obtained.

Insulation: The insulation between the individual turns is made of layers of glass fiber laminate.

Rotor slot wedges: To protect the winding against the effects of the centrifugal force, the winding is

secured in the slots with wedges.

18

FIELD CONNECTIONS

The field current is supplied to rotor winding through radial terminal bolts and two semicircular

conductors located in the hollow bores of the exciter and rotor shafts. The field current leads are connected

to the exciter leads at the exciter coupling with Multicontact plug in contact which allows for unobstructed

thermal expansion of the field current leads

FANS

The generator cooling gas is circulated by an axial-flow fan located on the turbine end shaft journal. To

augment the cooling of the rotor

The generator cooling gas is circulated by two single stage axial flow propeller type fans. The fans are

shrinking fitted on either side of rotor body.

ROTOR COOLING SYSTEM

For direct cooling of the rotor winding, cold gas is directed to the rotor end windings at the turbine and

exciter ends. The rotor is symmetrical relative to the generator centre line and pole axis

ACTIVITIES ON THE ROTOR SHAFT

Deburring and cleaning of rotor shaft.

Painting of rotor shaft.

Assembly of field lead bar.

Lying of coil.

Inter coil connection.

First pressing (heating & curing).

Dismantling the fixture, liner measurement.

19

Slot liner preparation & fitting of overhang portion.

Drilling of centre wedges.

Slot wedging, preparation of FLCB.

FLCB & CC bolt assembly.

Brazing connection piece & second pressing.

Preparation for retaining ring mounting.

Dry out & H.V. test.

Intermediate ring & compressor hub mounting.

Drilling and locking of compressor hub.

Silver plating of axial hole.

Balancing

Polishing & Run out check.

Final H.V. test & He test.

IR test & Impedance test

BEARINGS

The generator rotor is supported on the end-shield mounted on the journal bearings on both ends

SHAFT SEALS

Shaft seals are provided at the points where the rotor shaft passes through the stator casing. These radial

seal rings are guided in the seal carrier rings which in turn are bolted to the end shields

EXCITATION:20

BRUSHLESS EXCITATION SYSTEM FOR

TURBOGENERATORS:

An important characteristic of large turbo-generator is that the excitation requirements increased sharply

with the rating of the m/c. since excitation voltage is limited from insulation considerations, excitation

current levels increase sharply.

Brush-less excitation system connected through driven revolving armature a.c. exciter connected through

shaft mounted rectifiers to the rotating field of the turbo generator with no coupling of excitation power

between the source of generation and point of supply to the generator field. Today, leading manufacturers

offer brush-less excitation with rotating diodes as the preferred excitation system.

MERITS:

The merits of brush-less excitation system are:-

(a)Completely eliminates brush gear, slip rings, field breaker and excited bus or cable.

(b)Eliminates the hazard of changing brushes and leads.

(c)Carbon dust is no longer produced and hence the operation is fully dust free.

(d)Brush losses are eliminated.

(e)Operating costs are reduced.

(f) The system is best suited for atmospheres contaminated with oil, salt, chemical etc.and where sparking

may be a fire hazard

(g)The system is simple and requires practically no maintenance except for an occasional inspection.

Maintenance costs are thus reduced.

(h)Ideally suited for locations where maintenance is likely to be rare due to continuous demand on the

m/c.

(i) Brush-less system with shaft mounted pilot exciter is of self generating type and the excitation is

unaffected by system faults and disturbances.

(j) Reliability is better.

(k)Ideally suited for large sets.

(l) Increasingly popular system the world over

CONTRUCTIONAL FEATURES OF BRUSHLESS EXCITER :

The excitation system has permanent magnet with a revolving field. 3 phase ac output of thisexciter is fed to the field of the main exciter via a stationary regulator & rectifier unit. 3-phaseac induced in the rotor of the main exciter is rectified by the rotary Rectifier Bridge .The fieldwinding of the generator rotor is supplied with 3 phase ac through the dc lead in the rotor

21

shaft.The various components of the brushless exciter are:

Permanent magnet pilot exciter

Automatic voltage regulator

Three phase main exciter

Rectifier wheels

Cooling system

PERMANENT MAGNETIC PILOT EXCITER:

It is a 6-pole revolving field unit. laminated core with the three-phase winding is accommodated within

the frame. Each pole comprises of separate permanent magnets that are housed in a non-magnetic metallic

enclosure.

PMG

AUTOMATIC VOLTAGE REGULATOR:

The voltage regulator is intended for the excitation and control of generators equipped with alternator

exciters employing rotating uncontrolled rectifiers. The main parts of the regulator equipment are two

closed-loop control systems including a separate gate control set and thyristor set each, field discharge

circuit, an open loop control system for exchanging signal between the regulator equipment and the

control room, and the power supply circuits.

THREE PHASE MAIN EXCITER:

The main exciter is a three phase 6 pole armature revolving unit. Magnetic poles are made laminated to

settle the field winding on them. On the pole shoe, bars are made available which constitute a damper

winding by their connection. In between the two poles, a quadrature-axis coil is provided. After

completing winding & insulation etc., the complete rotor is shrunk on the shaft.

RECTIFIER WHEELS:

The silicon diode is the main component of the rectifier wheels, which are arranged in a threephase bridge

circuit. With each diode, a fuse is provided which serves to cut off the diode from the circuit if it fails. For

subdual of the transitory voltage peaks rising occurring because of commutation, R-C blocks are provided

22

in each bridge in parallel with each set of diodes. The rings, which form the positive & negative side of the

bridge, are insulated from the rectifier wheel which in turn is shrunk on the shaft. The three phase

connections between armature & diodes are acquired via copper conductors organized on the

circumference of the shaft between the rectifier wheels and the main exciter armature.

RECTIFIERWHEELS

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 turbo generators main shaft. The pilot Exciter,

which is a small D.C. shunt generator, feeds the field winding of main exciter is connected to the field

winding of the main alternator, through slip rings and brushes. The function of the regulator is to keep the

alternator terminal voltage constant at a particular value.

In this second scheme it consists of main A.C. exciter and stationary solid-state rectifier. The A.C.

main exciter, which is coupled to shaft of generator, has rotating field and stationary armature. The

armature output from the A.C. exciter has a frequency of about 400 Hz. This output is given to the

stationary solid-state controlled rectifier. After rectification, the power is fed to the main generator field,

through slip rings and brushes.

In third scheme,the A.C. exciter coupled to the shaft that drives the main 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 same shaft. The output from these rectifiers is also

given, along the main shaft, to the man generator field, without any slip rings and brushes. In the other

words, the power flows along the wires mounted on the main shaft, from the A.C. exciter to the silicon

diode rectifiers and then to the main generator field. Since the scheme does not require any sliding

23

contacts and brushes, this arrangement of exciting the turbo generators has come to be called as Brush less

Excitation system.

For large turbo generators of 500 MW excitation systems, the direct cooling required by the rotating field

winding increases considerably (up to 10 kA or so). In such cases, the brush gear design becomes more

complicated and reliability of turbo generator operation decreases. The only promising solution of feeding

the field winding of large turbo generator is the brush less excitation system. In view of its many

advantages, the brush less excitation system is employed in almost all large turbo generators being

designed and manufactured now days.

BRUSHLESS EXCITER.

24

CONCLUSION

This industrial training at BHEL Haridwar provided a chance to come across such bulky machines like 500MW, 600MW, 800MW and 1000 MW turbo-generator hydro generator etc. The architecture of BHEL, manner in which the 8 large blocks are working so systematically and in order make the students understand that engineering not only involves technological knowledge and application but also involves managerial aspects to a great extent. The position and prestige of BHEL in global technological and manufacturing market inspire students to be a part of this organization. The training has proved to be satisfactory. It has provided us with an opportunity to see the practical implementation of our theoretical knowledge which we have gained during our BTech course.

25

BIBLIOGRAPHY

1) B.H.E.L SITES

2) B.H.E.L. MANUALS

3) P.S BHIMBRA

4) TURBO GENERATOR (500MW) MANUAL

26