STUDY OF MANUFACTURING OF

TURBO GENERATORS

PROJECT REPORT
By
DIVYAREDDY DHAMMA
KAVYA NATTE
MONITHA SAI CHINNALA
PRAVALLIKA PUNUMALLI
NAGASRI BURA

Under the guidance of

A UMA SREENIVASA CHARY

Manager,

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 Electrical Machines Production

CONTENTS

1. ABOUT BHEL HYDERABAD.

2. DESCRIPTION OF ELCTRCAL MACHINES FEATURES.

3. VARIOUS SHOP FLOOR ACTIVITIES IN EM (02), BHEL HYD.

4. TG STATOR MANUFACTURING PROCESS.

5. CONCLUSION.

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 BHEL AT RAMACHANDRAPURAM

A vital link of chain of BHEL manufacturing units is a unit at Ramachandrapuram; Hyderabad.

BHEL Hyderabad manufactures Turbo Generators of 1.5MW to 270MW capacities. They will be
manufactured according to the customer requirement.

These turbo-generators are supplied together with turbines and matching excitation systems and
are used mostly in paper, sugar, cement, petrochemicals, fertilizers etc., and thermal power
stations. The turbo generators are based on the proven design know how backed by over 5
decades of experience gained by BHEL. It is the largest engineering and manufacturing
enterprise in India in the energy related infrastructure sector today which manufactures turbo
generators (2-pole and 4-pole) ranging up to 270 MW.

The manufacturing process of turbo generator is mainly divided into stator section and rotor
section where stator frame, stator core, stator windings, end covers are received from the stator
building section and rotor with rotor windings and rotor retaining rings is received from rotor
section and assembled at the assembly section. Each and every process is carried out in a
sequential process. Turbo generators are designed with the Closed-circuit air cooling with water
or air coolers mounted in the pit.

The layout of the manufacturing plant is such that it is well streamlined to enable smooth
material flow from the raw material stages to finished goods. The raw material that are produced
for manufacture are used only after thorough material testing in the testing lab and with strict
quality checks at various stages of productions. Latest technologies like vacuum press
impregnated micalastic high voltage insulation, polyester fleece tape impregnation for outer
corona protection is implemented to produce high quality insulation for turbines, outstanding
performance and long-lasting lifetime.

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 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 Tiruchirappalli with
Russian and Czechoslovak assistance.
 These plants have been at the core of BHEL’s efforts to grow and
Diversify and become India’s leading engineering company.
 The company now has 14 manufacturing divisions, 8 service centers and 4 power sectors
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’ 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 400kV – AC & DC, Supplied over 25,000
Motors with Drive Control System Power 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.
 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

4
 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 a
record time is a testimony of BHEL’s 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, nonconventional
energy sources and telecommunication.

 A wide-spread network of 14 manufacturing divisions, 8 service centers and 4 regionals

offices besides a large number of project sites spread all over India and abroad, enables
BHEL to be close to its customers and 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 India’s industrial
ambassador to the world.

There are nine important products are manufactured at Ramachandrapuram.

1. Gas turbines
2. Steam Turbines
3. Compressors
4. Generators and Exciters
5. Heat exchangers
6. Pumps
7. Pulverizes
8. Oil Field Equipment’s
9. Switch gear/circuit breakers

BHEL has borrowed technology for manufacturing generators from SKODA Exports
Czechoslovakia in 1960's they borrowed from M/s. Siemens, Germany and its sister company
KWU (Kraftwerk Union) in Germany. They borrowed less than 12 modules, from semen's
Germany. Till now the BHEL has developed more than 70 modules on their own.

The turbo generators are based on proven designs and know how backed by over 3 decades of
experiences gained by BHEL engineers in this field keeping pace with the latest development in
insulation systems to optimize the design. BHEL Hyderabad is the only one in Asia that has the
latest type of insulation system called the Vacuum Pressure Impregnation System.

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 SPECIAL FEATURES OF THE TURBO GENERATORS DESIGNED
BY BHEL
1. High output to weight ratio
2. Thermo setting class F epoxy insulation both resin rich and micalastic vacuum impregnation.
3. Low loss high-grade silicon steel for laminations.
4. Optimally designed fans on the rotors.
5. Better voltage waveform with less harmonic content.
6. Low wind age loosed and low noise.
7. Static/blushless excitation.
8. Split casing design for low manufacturing cycle for VPI design.

ELECTRICAL MACHINES
Machine acts as a generator converts the mechanical energy into electrical energy. The machine, which
acts as a motor, converts electrical energy into mechanical energy. The basic principle of rotating
machine remains the same i.e.
“FARADAY’S LAWS OF ELECTRO MAGNETIC INDUCTION”.
Faraday’s first law states that whenever conductor cuts magnetic flux, dynamically
induced EMF is produced. This EMF causes a current flow if the circuit is closed.
Faraday’s second law states that EMF induced in it, is proportional to rate of change of
flux.
e = -N df/dt
EMF induced will oppose both the flux and the rate of change of flux.
In the case of AC generators, the armature winding is acts as stator and the field winding acts as
rotor.
Efficiency of a machine is equal to the ratio of output to input
h = Output / input = Output / output + losses
To increase the efficiency of any machine we must decrease the losses, but losses are
inevitable. There are different types of losses that occur in a generator.
They are broadly divided into 2 types
(1) Constant losses
(a) Iron losses
(b) Friction and windage losses (air friction losses).
(2) Variable losses
(a) Copper losses
Electrical machines are of two types. AC machines & DC machines. AC machines are
divided into single-phase AC machines and polyphase AC machines
3 Phase AC machines are divided into

6
 1. SYNCHRONOUS MACHINES:
Synchronous Generators (or) Alternators are those in which
the speed of the rotor and flux are in synchronism

2. ASYNCHRONOUS MACHINES:
These are the machines in which the flux speed and rotor
speed will not be the same.

Ex: Induction motors.

Inherently all the machines are AC machines. AC or DC depends upon the flow of current in the
external circuit.
Synchronous generators can be classified into various types based on the medium used for
generation.
1. Turbo-Alternators Steam (or) Gas
2. Hydro generators
3. Engine driven generators
In every machine they are two parts
 Flux carrying parts
 Load carrying parts
In large synchronous machines the stator has the load carrying parts, i.e., armature and the
rotor has the flux carrying parts i.e.; field winding.
Iron losses are also called as magnetic losses and core losses. They are broadly divided into
1) Hysteresis losses
2) Eddy current losses
These losses occur in the stator core.
Copper losses occur in both stator and rotor winding.
The general efficiency of a synchronous generator is 95-98%
The main parts in a synchronous-generator are:
STATOR, ROTOR, EXCITATION SYSTEM, COOLING SYSTEM, INSULATION
SYSTEM, BEARINGS.

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ELECTRICAL MACHINES:
GENERATORS (1 MW to 270 MW)
EXCITERS (Matching to Generators up to 270 MW)

Generators:
H2 COOLED 3000 RPM STG (up to 270 MW)
AIR COOLED GENERATORS (1 MW to 150 MW)

2- Pole Generators
STG (18 MW to 270MW)
GTG (FR 5 to FR9FA)

4- Pole Generators
STG (1- 30 MW)
GTG (FR1,3 & 5)

Classification of Synchronous Generators:

• TYPE OF PRIME MOVER GT/ST
• TYPE OF CONSTRUCTION 2-POLE/ 4-POLE
• FREQUENCY 50 / 60 Hz
• COOLING MEDIUM AIR/ HYDROGEN
• TYPE OF COOLING OPEN AIR/ CACW
Type of Prime Mover:

 Gas Turbine
 Steam Turbine
 Closed Circuit Air Cooled
 Coolers on Top
 Coolers on Side
 Open Air Cooled
 Terminals on Side/Top
 Outdoor/Indoor Installation

Steam Turbine:
1. Coolers Below/Side of the M/C
2. Terminals from Bottom/Side
3. Indoor Installation

Type of Construction:
1. Synchronous Generator
2. Round Rotor
3. Salient Pole Rotor

Round Rotor
1. Solid Rotor
2. Laminated Rotor

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 Salient Pole Rotor
1. Solid Pole
2. Laminated Pole

Type of Cooling:

1. Air Cooled
2. Hydrogen Cooled

Air Cooled
1. Open air cooled
2. Closed circuit air cooled

Closed Circuit Air Cooled

1. Coolers on Top
2. Coolers on Side
3. Coolers below the M/C

Generators Manufactured At BHEL, Hyderabad

 Continuous improvement and up gradation of design features
 Overhang type brushless exciters
 Terminal box option up to 40 MW
 µ-processor based numerical protection system
 Digital AVR
 High degree of standardization of components based on modular concept.

Characteristics of VPI Insulation

 Higher mechanical bond
 Void-free insulation
 High dielectric strength, low dissipation factor and hence longer electrical life
 Better heat transfer
 Higher thermal stability, ensures Class-F in running condition
 Less maintenance
 Cost effective

Advantages of Global Impregnation

 Heat transfer coefficient is better
 Void free insulation
 Non-hygroscopic
 Less volume for given output
 Lower life time cost

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Salient Features of 2 Pole Generators
 Collaborator: Siemens, Germany
 Range: 18 MW To 270 MW; 6.6, 11.0,13.8 & 15.0 KV
 Insulation type: Micalastic with Global Vacuum Pressure Impregnation
 No. of machines manufactured: approx. 300
 Compact size, cost effective
 Less manufacturing cycles
 Terminals at top or side for GTG and at bottom for STG
 Bar windings with 3600 transpositions to reduce eddy current losses
 Solid rotor forging of Cr Ni Mo V alloy steel
 Silver bearing semi hard electrolytic copper conductor for rotor winding
 Half coil technology for rotor winding to achieve better forming and consolidation of end
winding
 Slot wedges of good electrical conductivity shorted at the end by retaining rings
 18 Mn 18 Cr retaining rings of forged non-magnetic steel shrunk fitted on the rotor barrel
 2 Nos. of axial fans mounted on each side of rotor for ventilation of Generator with screwing
type individual fan blades
 2 nos. of journal bearings with one insulated to eliminate bearing currents
 RTDs for temperature measurement of stator winding and core.
 Central cooling technology for uniform cooling of the stator core and windings
 Advanced four flute cooling for rotor giving improved cooling effect

4 POLE GENERATORS AT BHEL, HYDERABAD

 Collaborator: Siemens, Germany
 Range: 3 MW To 30 MW; 3.3, 6.6, 11 kV
 Insulation Type: Micalastic with Global Vacuum Pressure Impregnation
 No. of machines manufactured: approx. 60
 Multi-turn windings with pulled coil technology for minimum cycle time to manufacture
 Laminated round rotor construction
 Compact size, modular designs which are cost effective
 Less manufacturing cycles
 Terminals at top or side for GTG and at bottom for STG
 2 Nos. of radial fans mounted on each side of rotor for ventilation of Generator
 2 nos. of journal bearings with one insulated to eliminate bearing currents
 Total generator can be dispatched as a single package

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 Main Parameters Influencing Design:
 Apparent Power (MVA) / pf
 Active Power (MW)
 Voltage (3.3/6.6/11/13.8 Kv)
 Speed (1500/1800/3000/3600 RPM)
 Drive (ST / GT / Others)
 Cooling Medium (Air/Hydrogen/Water)
 Type Of Load (Step loads, motor starting etc.)
 System fault levels (Machine reactance’s)
 Harmonic currents (Thyristor loads)
 V/F variations
 Open/ closed cooling water circuit

TECHNICAL DESCRIPTION OF AIR COOLED 2-POLE GENERATORS

1.0 INTRODUCTION:
The synchronous generator is of two poles, 3-phase air cooled type and is designed for
continuous operation at its rated output. The constructional features ensure reliability, easy
maintenance and economical operation.

2.0 STATOR:

2.1 STATOR FRAME:

The stator frame is of welded steel construction and supports the laminated core and the winding.
The welded circular ribs as well as the axial stiffeners provide the required rigidity for the stator
frame.

2.2 STATOR CORE:

The stator core is stacked from thin cold rolled non-oriented electromagnetic sheet steel
punching’s having low loss factor and high permeability and is suspended in the stator frame
from the insulated guide bars. The laminations are slotted, deburred and varnished with high
quality synthetic varnish. The core is divided into packets of required dimensions and these
packets are separated by radial ducts to provide adequate passage for the flow of coolant. These
ducts are formed by insulated thick stamping steel laminations on which ventilating spacers are
spot welded. Glass laminate sheets are placed adjacent to each thick lamination sheet of every
packet to provide additional insulation. For reducing the stray load losses, the air gap is enlarged
at both ends of the core by means of stepped end packets which are glued together to prevent
vibration during operation. During the assembly of the core, the laminations are pressed together
under heat using a hydraulic press to ensure a rigid and consolidated core and is firmly held
together by means of clamping fingers, end plates and non-magnetic through type insulated

11
clamping bolts which are so arranged as to ensure a uniform clamping pressure especially within
the teeth area and at the same time providing for uniform intensive cooling of the stator core
ends.

2.3 STATOR WINDING:

The stator winding is of short chorded pitch, double layer lap-bar type construction. The stator
bars are composed of varnished and glass covered copper strips. The strips are stacked to form a
Roebel bar with 360 deg. transposition in order to reduce eddy current losses. The stator after
placement of coils in the slots is impregnated in VPI system and hot cured thereafter to form a
consolidated mass. This ensures excellent electrical and mechanical properties of stator
winding. To prevent corona discharges, the bars are wrapped with conductive polyester fleece
during insulation of bar stage. The overhang of the winding is supported with resin absorbent
glass mats and tying which ensure a very rigid support after resin absorption and hot curing. Six
terminals are brought out of the stator end cover at exciter end.

3.0 ROTOR

3.1 ROTOR SHAFT:

The rotor shaft is a single piece, solid forging of special Alloy steel manufactured by vacuum
casting by reputed shops under strict inspection and control. To ensure that only high-quality
forgings are used, strength tests, material analysis, and ultrasonic tests are carried out during
manufacture. Radial slots are milled axially on the rotor body to accommodate the field
windings. The slots are distributed over the circumference so that two solid poles are
obtained. After completion, the rotor is balanced thoroughly and subjected to an over-speed test
at 120% of the rated speed for 2 minutes.

3.2 ROTOR WINDINGS:

The rotor winding consists of several coils made of high conductivity silver bearing
electrolytic copper conductors ensuring high thermal stability. Each coil consists of several
series connected turns comprising two half turns each of which is connected by brazing in the
end winding portions. Slots are punched in the coils to provide ventilation paths. The
individual turns of the coil are insulated against each other by epoxy glass laminates. L-shaped
slot troughs of epoxy glass cloth with Nomex filler are used as slot insulation. The wedges
are made of well conducting material and short-circuited at their ends through the retaining
rings which are silver plated at the contact surfaces to act as an effective damper
winding.

3.3 RETAINING RINGS:

The centrifugal forces of the rotor end windings are taken up by single-piece retaining rings.
The retaining rings are forged out of non-magnetic steel in order to reduce stray losses and are
cold worked to have high mechanical strength. The forgings are subjected to mechanical tests
and non-destructive tests to ensure soundness and high quality. The retaining rings are shrink

12
fitted on the rotor barrel on one side, and on the hubs on the other side. Each retaining ring is
secured axially by a snap ring. They are insulated from the rotor winding by high quality
insulation of sufficient thickness.

3.4 FANS:

The cooling air is circulated by two axial flow fans located on either side of the rotor barrel.
The fan blades have threaded roots for being screwed into the rotor shaft. The blades are die
forged from aluminium alloy. Each blade is secured at its root by grub screws against
loosening.

4.0 BEARINGS:

The generator rotor is supported on two journal bearings. The bearings are lined with babbitt
material to reduce the wear and damages to the journal. To eliminate shaft currents, one bearing
is insulated. The bearing temperature is supervised by a thermo-element arranged in the lower
half of the bearings, so that the measuring point is located directly below and nearer the
babbitt. Each bearing is provided with facilities for fitting vibration pick-ups for vibration
supervision. The oil supply for the bearings is provided from the turbine oil system.

5.0 VENTILATION:

The turbogenerator is designed with closed circuit forced air cooling system. Radial type of
ventilation system is employed in the stator and rotor. The cooling air is passed through the
various ventilation paths and the hot air flows out of the stator frame and is cooled in water-air
heat exchangers. The air is circulated by the axial fans in the machine.

6.0 TEMPERATURE_MEASUREMENTS:

The temperature at different points in the stator winding, cold air region, hot air region and the
generator and exciter bearing metal are measured by means of resistance temperature
detectors (R.T.D.s) of Platinum Pt 100 type, placed at a number of suitable places. These
R.T.D.s would be connected to a temperature scanner provided in the generator control panel.

TECHNICAL DESCRIPTION OF AIR COOLED 4-POLE GENERATORS

1.0 INTRODUCTION
The synchronous generator is of 4-pole, 3-phase air cooled type and is designed for continuous
operation at its rated output. The constructional features ensure reliability, easy maintenance
and economical operation. The generator is suitable for operation with any of the modern
excitation systems.

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 2.1 STATOR:

2.1 STATOR FRAME:

The stator frame consists of two end clamping plates with welded-on pressing fingers
designed to hold the laminations in position by means of axial ribs welded under pressure at the
back of the core and to the clamping plates.

2.2 STATOR CORE:

The stator core made of cold rolled non-grain-oriented silicon sheet steel punching having low
loss factor and high permeability is stacked between the two end clamping plates. The
laminations are slotted, deburred and varnished with high quality synthetic varnish. The core is
divided into packets of required dimensions and these packets are separated by radial ducts to
provide adequate passage for the flow of cooling air. These ducts are formed by insulated 1mm.
thick stamping steel laminations on which ventilating spacers are spot welded.

2.3 STATOR WINDING:

Stator coils are of diamond pulled type with fine mica paper tape insulated copper strips and with
ground insulation of resin poor mica paper tapes. This cured insulation has excellent electrical
characteristics and provides highly reliable protection against mechanical and atmospheric
effects. These coils are inserted into the slots punched in the stator core and the individual coils
are joined by brazing. In order to withstand short circuit forces, the winding overhangs are
stiffened by spacers between the coil ends and with bandage rings. The whole stator, including
the winding will be kept in a tank and immersed in synthetic resin and impregnated under
vacuum and pressure. After impregnation it will be cured at a specified temperature in an oven.
This process results in extremely good mechanical and electrical strength. The insulation of the
winding corresponds to Class 'F'. Three neutral terminals, three phase terminals are brought out
on the non-drive end of generator.

3.0 ROTOR:

3.1 ROTOR SHAFT:

The rotor shaft is forged out of chrome-nickel-molybdenum or equivalent material with the
required mechanical and metallurgical properties. The shaft has axial ventilation grooves milled
on the barrel surface for supplying the cooling air to the rotor core. An axial bore is made in the
exciter side of the shaft for taking the input leads to the field winding through two inclined holes
opening into the ventilation grooves at the rotor overhang portion

3.2 ROTOR CORE:

The rotor core is made of low-loss silicon sheet steel laminations of circular shape coated with
synthetic varnish. Slots are punched in the stampings for accommodating the windings and
damper bars.
The rotor core is divided into small packets by radial ventilation spacers for adequate cooling air
passage. Steel clamping plates are used at both ends of the core and the fixing nuts of the tension
bolts are welded to these plates after tightening.

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 3.3 ROTOR WINDINGS:
The rotor winding consists of single-layer former-wound coils. The coils are of bare silver
bearing copper and are inserted into the slots and wedged with Class 'F' insulation. The rotor
winding is impregnated with epoxy resin. The damper bars are driven into the slots in the outer
periphery of the laminated core and welded to the clamping plate on both sides to form a damper
cage. The overhang winding will be protected against the centrifugal forces by glass-fibre
banding tapes and held in position by non-magnetic Austenitic steel retaining ring forgings.

3.4 FANS:
Two radial-flow fans are mounted on both sides of the rotor to circulate the required cooling
air into the machine.

4.0 BEARINGS:
Two radial sleeve bearings are provided to support the rotor. Each bearing essentially consists of
the bearing pedestal, sealing rings, split bearing shell, a sight glass for checking the oil level and
oil ring. The bearings are provided with ring lubrication in addition to the pressure lubrication.
The bearing pedestal is secured to the base frame by means of hexagonal bolts and is located in
position after alignment by dowels. The bearing at the non-drive end is insulated from the
machine base frame to prevent the flow of shaft currents.

5.0 BASE FRAME:

The base frame is fabricated out of structural steel plates. This is designed to support the
generator along with bearings and exciter (in case of brushless exciter) and to withstand short-
circuit conditions.

6.0 ENCLOSURE:
The enclosure is fabricated out of structural steel material with adequate stiffening and is
designed in two parts viz. top part of the enclosure and bottom part of the enclosure. The
enclosure rests on the rubber beading on the base frame. The construction of the enclosure is
such that it reduces the structure-borne noise to the minimum and provides the required
protection to the machine. The design of the enclosure shall suit the ventilation system required
for the machine.

The main parts in a turbo generator are:

1. Stator.
2. Rotor.
3. Excitation system.
4. Cooling system.
5. Insulation system.
6. Bearings.
7. Protective devices.

Stator part includes:

1. Stator frame and Enclosers.
15
2. Stator core.
3. Stator bars.
4. Stator windings.
5. Output leads/bushings.

Rotor parts include:

1. Rotor Shaft.
2. Field connection.
3. Rotor winding.
4. Rotor retaining rings.
5. Fans Blade Assembly.
6. Journal bearings.

Excitation system is of 3 types.

1. DC excitation system.
2. Static excitation system.
3. Brushless excitation system.

ROTOR

The rotor consists of the shaft, the rotor core, the field winding, the damper winding, the fans, the
slip rings or the rotor of the brushless exciter.

The shaft transmits the torque to the machine. The rotor is carried by two bearings. The field
winding is inserted in the slot groups of the rotor core, connected and linked to the terminals of
the direct coupled exciter by leads run through the hollow shaft. The bars of the damper winding
are driven into the slots at the periphery of the core and are connected to an end disc at either
end.

In a turbo generator there are two types of rotor designs.

Forged solid rotor
Laminated rotor
The main function of the rotor is that the rotor acts like an electromagnet by taking currents from
the excitation system. It is coupled to the turbine rotor to take the driving torque and thus produce
a flux, which leads for the generation of current. The change in the flux produced by the rotor
windings induces voltage in the stator winding. It also has to withstand high power torque
produced by the turbine and the backward torque produced due to the generator current.
For large capacity machines solid forged rotor is preferred. It is made from vacuum cast steel
ingot. About 60% of the rotor body circumference has longitudinal slots which hold the winding.
There are two types of rotors are used in generators.
a. Salient pole type
b. Cylindrical pole type

16
SALIENT (PROJECTING) POLE TYPE:

It is used in low and medium speed (engine driven) generators. It has a large number of
projecting poles, having their cores bolted or dovetailed onto a heavy magnetic wheel of cast
iron, or steel of good magnetic quality. Such generators are characterized by their large diameters
and short axial lengths. The poles and pole shoes are laminated to minimize the heat due to eddy
currents. The salient pole synchronous machines have non-uniform air gap between the rotor and
the stator. The air gap is minimum under the pole centers and maximum between the poles.

SMOOTH CYLINDRICAL TYPE:

It is used for steam turbine driven i.e., turbo generators, which run at high speeds. The rotor of a
two-pole machine is forged taking into account the strength considerations and the speed. In case
of the four-pole machine the centrifugal force developed is 1/4 of that of a two-pole machine and
hence the core of such a turbo generator is laminated. The lamination of the rotor core reduces
the losses due to eddy currents. This also provides for a reduction in the cost when compared to
the rotor of the two-pole machine. In this type of rotor, the air gap is the same throughout
neglecting the slot openings. Generally synchronous machines consist of the high-power
armature winding on the stator and the low power field winding on the rotor.

ROTOR SHAFT: The shaft of the rotor is forged from vacuum degassed alloy steel to impart
required mechanical properties. The rotor is designed to withstand the stress due to centrifugal
forces in operation and fatigue due to start and stop operations throughout its life. The rotor
consists of an electrically active portion called barrel and two shaft ends integrally forged. The
rotor of two-pole machine is forged, whereas the rotor of the four-pole machine is a laminated
core. Along the core of the rotor, longitudinal slots of rectangular shape are milled to form a
cylindrical rotor. At the bottom of the rotor slot is a vent canal to conduct the cooling gas towards
the center. The central position of the slot accommodates the winding with insulation and in the
top of the slots the wedges are driven to keep the winding against the centrifugal forces. The
tapped holes to screw the balancing weights and the moon slots which minimize the double
frequency vibrations of the core are machined along the length of the two pole faces. On the

17
turbine side a coupling is shrunk along with a key to give connection to the LP turbine rotor. The
central bore in the non-driving end of the shaft houses the field lead, which connects the winding
and the slip rings.
The rotating components are attached to the shaft by means of keys or are shrink fit. The
shaft is made of alloy steel forging. Shaft is dimensioned as required for the torque to be
transmitted, taking into account the stresses occurring during shorting, to ensure that the static
deflection is kept to a minimum and that the natural frequency of the critical flexural vibration of
the shaft differs sufficiently from the rated speed.
The rotor shaft is a single-piece solid forging manufactured from a vacuum casting. Slots
for insertion of the field winding are milled into the rotor body. The longitudinal slots are
distributed over the circumference so that two solid poles are obtained.
To ensure that only high quality forgings are used, strength tests, material analysis, and
ultrasonic tests are performed during manufactured of the rotor. After completion, the rotor is
balanced in various planes at different speeds and then subjected to an over-speed test at 120% of
rated speed for two minutes.

FIELD WINDING:
The field winding consists of several series connections of coils inserted into the
longitudinal slots of the rotor body. The coils are wound in such a way that the required number
of poles is obtained. The individual conductors are made from 0.1% Silver alloyed copper in case
of a two-pole machine and Douglas copper in the case of a four pole machine. This silver alloyed
copper is bent to form full turns and the continuous turns of slots constitute one coil. The silver
alloyed copper as compared to electrolytic copper features very high mechanical strength at
elevated temperatures and has more of fatigue and creep resistance and thus eliminates coil
deformations due to thermal stresses .The individual conductors are provided with axial slots for
radial discharge of cooling gas and all conductors have identical cooling ducts cross sections.

INSULATION:
The individual turns of every coil are insulated by glass fiber laminates with matching
ventilating holes. The L shaped strips of glass fiber laminated with Nomex interleaving is used as
insulation between the coil and the rotor body. The space between the individual coils and the
end winding is filled with insulating members in order to prevent the coil movement under
stresses.

RETAINING RINGS:
The concentric shaped overhand of the rotor winding is retained in the place against
centrifugal forces by non magnetic cold expanded steel rings called retaining rings. The material
of the retaining rings is stress and corrosion resistant. It is cold worked to reduce stray losses.
The high quality of the rings is ensuring by the mechanical and nondestructive tests. These rings
are shrunk fitted on the steps, machined at the ends of the rotor barrel and are locked against
axial movement by a ring nut and four parted arrestment ring. The ring nut is threaded internally
and is shrunk fitted on the threads machined on the retaining rings At the other end of the rings ,
a floating type of the centering ring called hub is fitted. The hub shields the end of the rotor
winding and the coolant enters through the annular gap between the shaft and the hub. Thus one
ring holds the rotor body while the other holds the overhang. This ensures and unobstructed shaft

18
 deflection at the end winding. A snap ring is provided for additional protection against the axial
displacement of the retaining rings. The wedges and the retaining constitute the damper circuit of
the rotor.

Alloy Steel forging has the following properties.

1. A very high mechanical strength.
2. Nonmagnetic in nature.

FIELDS CONNECTIONS:

The field’s connections, comprising of connectors, radial bolt and field lead complete the
electrical connection between the rotor winding and the slip rings. The field lead consists of two
semicircular steel conductors insulated from each other by an intermediate plate and from the
shaft by a tube and is located at the central bore of the rotor shaft. The insulated radial steel bolts
connect one end of the field lead to the winding and the other end to the slip rings through
connectors. Flexible copper connectors are employed at the coil during operation. One end of the
connector is brazed to the coil and the other end is fastened to the radial bolt. A t the slip ring end
rigid copper connectors, one end bolted to slip rings and the other end to the radial bolts, provide
the necessary connection. Rubber gaskets at the radial bolts ensure gas tight sealing and prevent
leakage of hydrogen through bolts.

DAMPER WINDINGS:
Most of the generators have their pole shoes slotted for receiving copper bars of a grid or
damper winding. The coppers bars are short circuited at both ends by heavy copper rings. These
dampers are useful in preventing the hunting (momentary

DETAILED MANUFACTURING PROCESS IN VARIOUS SHP

FLOORS IN EM
PRESS SHOP:
1. RECEPTION OF SILICON STEEL ROLLS: - Silicon steel rolls are checked for chemical,
mechanical, electrical and magnetic properties as per the specifications. If they are all
satisfactory then they are cleared for further operation.

2. BLANKING: -Silicon steel rolls are fed into the cutting machine. it is processed to required
shape as per the design requirement.

19
3. NOTCHING: -Notching is defined as a process of getting the required dimension and required
shape. It is of two types COMPOUND and INDIVIDUAL notching.
Compound notching is a means of getting the required dimension of required shape by
processing at one stroke. It is carried out in two machines 315 and 500 tones M/cs.Individual
notching processes sheets individually for individual operations.

4. DEBURRING: -All the laminations are deburred up to 5microns.

5. VARNISHING: -After completion and processing of lamination, the sheets are varnished with
4000 CPV DR-BECK. The thickness of the varnish should be 7-12microns per side.
In order to achieve 7-12microns per side following checks are carried out.
 VISCOSITY: -Viscosity of varnish should be maximum for 44secs with a din-4-cup.
 ADHESIVENESS: -Pour some xylol on the lamination sheet and wait for 1 min and see that
varnish doesn’t dissolve in xylol. This indicates that the varnish is adhesive.
 CHECKING OF HARDNESS: -The varnished laminations are hit and the varnish should not
flake.
 Insulation resistance measurement: -Stack 20 laminations on hydraulic press with copper
conductor at top and bottom. Press 26 kg/cm^2 and check with megger by connecting with
copper strips. I.R value should be greater than 1 M ohm.
 MEASUREMENT OF COATING THICKNESS: -Varnish thickness measured by mini tester
should be 7-12microns.
 TEMPERATURE OF THE FURNACE: -Temperature should be maintained at 300-400
degrees.

6. CORE ASSEMBLY: -Check the horizontal plate in test pit with spirit level (0)
Place the hydraulic blocks over the horizontal plate as per design requirement. Then place
stumbling blocks over the horizontal plate. Place finger plate over stumbling block. Carry out for
trial packet assembly. Assembly one trial packet assembly by placing laminations sheets by using
mandrills and assembly drifts. After completion of 1 packet check for inside dia with inspection
drift. There should be no lamination projections inside or outside slots. Dismantle the trial packet
if all the points are met.
Assemble stepped packets over the clamping plates. Place one layer of ventilation lamination.
Carry out normal packet assemblies. Assemble 0.5mm lamination segments by forming the
required diameter. After completion of 1 packet, assemble 1 layer of ventilation lamination. Over
it place 1 layer of HGL. Again place 0.5mm silicon steel laminations up to a thickness of
1packet.By inserting assembly drifts into the slots and mandrills into the holes and check for
inside dia and slot freeness with inspection drift. There should be no lamination projections
inside or outside slots. Assemble 1more layer of ventilation lamination for normal packet. Over it
place 1layer of HGL. Again place 0.5mm silicon steel laminations up to a thickness of 1packet.
By inserting assembly drifts into the slots and mandrills into the holes and check for inside dia
and slot freeness with inspection drift. There should be no lamination projections inside or
outside slots.

7. The above procedure is continued until we obtain 800mm core height. 1 st pressing is carried
out by giving pressure of 20kg/cm2.Check for core height, inside dia and slot freeness with

20
 inspection drift. There should be no lamination projections inside or outside slots. Similarly
following the above procedure core height is assembled up to pre final core length by pressing
intermittently for every 800mm, until we achieve the final core height. Then pre final pressing is
carried out. Check for core height, inside dia and slot freeness with inspection drift. There should
be no lamination projections inside or outside slots. If the final height isn’t obtained replenish the
laminations in the subsequent final packets.
Assemble the final core assembly. After its completion do final pressing. Assemble top
clamping plate and final pressing fixtures. Carry out final pressing by giving the calculated load
20 kg/cm2 for the specified design. Under the load check for core height. If core height is as per
the design specification, then assemble tension bolts into respective mandrills’ holes and tighten
it by using torque wrenched spanners. Dismantle the assembly fixture and check for inside dia
and slot freeness with inspection drift. There should be no lamination projections inside or
outside slot. On the top clamping plate assemble winding brackets as per design requirement and
welding is carried out. Check for 90 degrees. Carry out full welding of each and every bracket
and check for die penetration test. Assemble guide bars into respective grooves of laminations.
Clamp the bars by bottom half, middle half and top half rings. Half rings are pressed with
hydraulic system. All the three rings are compressed with hydraulic press until guide bars are
fitted into the dovetail grooves. The welding is carried out from bottom to top clamping plate.
After completion carry out D.P test on all the welds. The total core is shifted horizontally by
using assembly’s fixtures. Then onto the bottom clamping plate winding brackets are assembled
as per design requirement and welding is carried out. Check for 90 degree and D.P test is also
conducted. Total core is checked for sharp corners, lamination projections and interruption of
foreign matter.
If detected they are rectified. Core is cleaned thoroughly and subjected for core flux test. It is
carried out in order to detect hot spots of the core. If no hot spots noticed the Stator core cleared
for stator winding.

COIL SHOP:

STATOR WINDINGS IN RESIN-POOR PROCESS:

1. RECEPTION OF CONDUCTOR ROLLS: - Conductor rolls are checked for chemical,

mechanical, electrical and chemical properties as per the specifications. If they are all satisfactory
then they are cleared for further operation.

2. CONDUCTORS CUTTING: -Copper roll is fed into cutting machine. First conductor is
checked for drawing specification. Then conductor length is fixed. Stopper is also fixed for
specified length. If the length is satisfactory then mass cutting operation is allowed.

3. TRANSPOSITION: -All the required number of conductors is arranged in the given template
and the fixtures center to center length is checked as per the specifications and the dies are
matched properly and then transposition is carried out for first bundle. Similarly, it is carried out
for second bundle. Now after obtaining 2nd bundle both the bundles are joined together by
inserting half insulation (Nomex) and tied with cotton tape. The total bundle is the total stator
bar.

21
4. PUTTY OPERATION: -All the uneven surfaces on the width face are filled up with Nomex
pieces in order to make the bar even and eliminate inter-strip shorts. Mica folium is assembled on
the straight (width face) of the bar and tied with PTFE tape.

5. STACK CONSOLIDATION: -After completion of putty operation stator bars are subjected for
straight part consolidation by heating up to 140-150 degrees for a duration of 2-3hrs under
pressure of 150kg/cm^2 horizontally as well as vertically.

6. DIMENSIONAL CHECK, INTER-STRIP AND INTER-HALF SHORTS DETECTION: -

All the bars are checked for dimensions (width and height of the bar) by go and no-go gauges.
Inter-strip and Inter-half shorts are detected by 230V lamp test.

7. 1ST AND 2ND BENDING: -1st and 2nd bends are carried out on the bending fixture as per the
drawing requirement.
8. OVERHANG AND 3RD BEND FORMATION: -Overhang and 3rd bend formation is carried
out in the cone as well as universal former. After completion of the operation Nomex insertion is
carried out from the end of the straight portion to the 3 rd bend. We have to apply rut pox and
hardener (5:1) and apply to Nomex sheets. Consolidate the bar at 60degrees for 30 min.

9. CLEANING AND FINISHING OF STATOR COILS: - All the bars before taking for final
operation are cleaned with sand paper and then the bar is prepared for final taping by checking
the bar for inter-half and inter-strip shorts.

10. FINAL TAPING: -Each individual bar is subjected for final taping. First Fine mica tape is
wrapped in the straight portion by spreading the copper foil

11. Width wise ICP tape is wrapped and then Wrapping in resin-poor tape i.e., 8*1/2 overlap of fine
mica either manually or by machine around the periphery is carried out. Split mica tape is
wrapped alternately with OCP tape to ovoid overlapping. Over that we tape it again with OCP
tape. Then ECP tape is wrapped around the 1 st bend and hyper seal tape is taped from the end of
ECP tape to the 3rd bend. After that we send it to stator winding shop.

22
 LIGHT MACHINE SHOP:

1. Name : Vertical Lathe

Type : SK12
Specification : 1200 mm dia. Chuck with 3 tool post
Machine components : Bearings rings, retaining rings, Snap rings,
Intermediate rings, Hubs, Yokes,
Rectifier rings, RR wheels, sealing rings,
Clamping Plates

2. Name : Vertical Milling Machine

Type : FA5V
Specification : Sleave Borse tapper 50
Machine components : Bearings , Profiles, Grooves,
Step cutting, Depth Cut
Cutting Tools : End mill, T-max, Slot Drill bit

3. Name – : Centre Lathe

Type – : SU 80
Specification - : 1M diameter chuck
Machine Components : Facing, Planning , Turning,
Step Cutting, Ball forming Grooving,
Thread Cutting

4. Name : Radial Drilling Machine

Type : VR8
Specification
Machine Components : Drilling, Tapping, Reaming

5. Name : Horizontal Milling machine

Type : FGS 50
Specification : Spherical diameter for bearing outside
Machine Components : Surfacing, Milling

23
COPPER SHOP
1. RECEPTION OF COPPER CONDUCTORS: - Copper Conductor are received in rectangular
strips and checked for chemical, mechanical, electrical and chemical properties as per the
specifications. If they are all satisfactory then they are cleared for further operation.

2. VENTILATION PUNCHING: -Rectangular conductors are fed through a template into a

ventilation punching machine to get the desired ventilation holes as per the drawing requirement.
Further checking is carried out and random checking is done during processing.

3. CHAMFERING: -All the ventilation holes are punched or chamfered to remove the extra
material projected out of the ventilation slot.

4. EDGE-WISE BENDING: -Bending is carried out on the bending machine on both the sides.
Dimensions are checked with respect to centre of the conductor and the desired specifications are
achieved.

5. ANNEALING: -Annealing is carried out by heating on bend zones on both sides of the
conductor at 600 degrees and it is then quenched in water for getting it cooled.

6. CORNER PRESSING: -The conductors are pressed at the corners to normal size by hydraulic
press and it is checked for dimensions with gauges.

7. 90 DEGREES RECTIFICATION: -All the conductors are rectified for 90 degrees on bending
table and checked for 90 degrees from centre of conductor on both the sides.

8. DOVE-TAIL PUNCHING: -Conductors are processed for male and female joints by punching
in a dove tail machine. After processing all the conductors for 1 set of coils,1 set of coils is
arranged to know the window dimension.

24
 9. RELIEF FILING: -This process is carried out on both ends of the straight portion as per the
drawing requirement and it is checked with gauges.

10. CLEANING: -All the conductors are cleaned for bright surface with emery paper by removing
sharp corners, burrs. If the conductors are bright and free from above defects then it is varnished
with air drying.

11. RADIUS FORMATION AND BRAZING: -All the conductors are bent for half radius on the
bending table as per the desired dimensions. If it is found satisfactory then it is brazed with silver
coil to complete one coil and then all the processed coils are sent for rotor winding.

ROTOR WINDING

1. RECEPTION OF ROTOR: -The rotor is received and it is checked for sharp corners, burrs and
foreign matter interruption in all the respective slots. It is even checked for completion of prior
operations.

2. INPUT D-LEAD ASSEMBLY: -The input d-lead assembly is divided into two d’s to make one
circle. Each individual d is insulated with HGL and they are assembled in two halves. The total
circle is inserted into a HGL tube. D-lead is assembled into rotor bore and two output studs are
assembled to two d-leads. It is subjected to high voltage and impedance test.

FOOTINGS ASSEMBLY: -Footings are temporary supports to overhangs till the 1 st curing.
They are assembled on both sides i.e., the turbine and exciter side to facilitate the assembly of
rotor windings. The diameter of the footings is checked and then they are wrapped with
insulation tape as per the drawing requirement.

3. LAYING OF COILS: -Start laying A1 coils in pole1 after laying one conductor or completing 1
loop before laying 2nd conductor, assembly glasoflex insulation in straight portion matching to
the ventilation holes. Lay 2nd conductor. Before laying 3rd conductor once again assemble
glasoflex insulation in each slot. This process is continued until designed number of conductors
are laid into respective slots. Pole1 is completed and similarly Pole2 is completed.

4. CENTRING OF COILS WITH RESPECT TO THE ROTOR: -Arrange all the pressing
fixtures on both the overhangs and in slots drive metal wedges. After completion of fixture
arrangement, the rotor is heated by giving DC supply to the input leads. After attaining a
temperature of 90 degrees gel formation starts. Then start tightening overhang fixtures and metal
wedges on the straight portion up to 110 degrees. Then raise the temperature to 140+- 10 degrees
for duration of 14hr.Cool down and dismantle all the fixtures. Subject the rotor for high voltage
and impedance test. Check for the depth measurement to calibrate the under-wedge insulation
length and overhang length and even the overhang diameter. Then assemble resin treated mica
sheets on the overhang portion to specified thickness. Once again assemble the fixtures
overhangs and metal clamps on straight portion. Subject the rotor to DC current and follow the
same cycle of baking as in the 1 st baking. Cool down the rotor. Subject for high voltage and
25
 impedance test. If all these are satisfactory then assemble the under-wedge insulation and drive
permanent wedges. Check for ventilation blockages and rectify if any.

5. ASSEMBLY OF RETAINING RINGS: - Retaining rings are non-magnetic and they are
assembled on both sides by shrink fitting. Subject the rotor for balancing.

BRUSHLESS EXCITATION SYSTEM:

BASIC ARRANGEMENT OF BRUSHLESS EXCITATION SYSTEM WITH ROTAITNG

DIODES:
The Excitation system consists of:
i. Rectifier wheels
ii. 3 phase main exciter
iii. 3 phase pilot exciters
iv. Cooler
v. Meter and supervising equipment

The 3-phase pilot exciter has a revolving field with permanent magnet poles. The 3-phase ac is
fed to the field of revolving armature main exciter via a stationary regulator and rectifier unit.
The 3-phase ac induced in the rotor of main exciter is rectified by the rotating rectifier bridge and
fed to the field winding of generator rotor through dc lead in the rotor shaft. A common shaft
carried the rectifier wheels, the rotor of main exciter and permanent rotor of the pilot exciter. The
shaft is rigidly coupled to the generator rotor and supported on bearings between main and pilot
exciters. The generator and exciter rotors are thus supported on a total of 3 bearings. Mechanical
coupling of the 2 shaft assemblies results in simultaneous coupling of dc leads in the central shaft
bore. This also compensates the length variations of leads due to thermal expansion.

26
RECTIFIER WHEELS:
The main components are silicon diodes, which are arranged in rectifier wheels in a 3-phase
bridge circuit. A plate spring assembly produces the contact pressure for silicon wafer. The
arrangement is such that the pressure is increased by centrifugal force during rotation. For
suppression of the momentary volt peaks arising form commutation, each wheel is provided with
6 RC networks consisting of 1 capacitor and 1 damping resistor each. The wheels are identical in
their mechanical design and differ only in the forward direction of the diodes. The dc from
rectifier wheels id fed to the dc leads via radial bolts. The 3-phase ac is obtained via copper
conductors arranged on the shaft circumference between the rectifier wheels and 3-phase main
exciter. One 3 phase conductor is provided for each diode. The conductors originate at a bus ring
system of the main exciter.

1. PILOT EXCITER:
The 3-phase pilot exciter is a 6-pole revolving field unit. The frame accommodates the laminated
core with 3 phase winding. The rotor consists of a hub with mounted poles. Each pole consists of
a separate permanent magnet, which is housed in non-magnetic metallic enclosure. The magnets
are braced between the hub and external pole shoe with bolts. The rotor hub is shrunk onto free
shaft end.

2. MAIN EXCITER:
3-phase main exciter is a 6-pole revolving armature unit. Arranged in the frame are poles with
field and damper windings. The field winding is arranged on laminated magnetic poles. At pole
shoe, bars are provided which are connected to form a damper winding. The rotor consists of
stacked laminations, which are compressed by through bolts over compression rings. The 3 phase
winding is inserted into the slots of the laminated rotor. The winding conductors are transposed
within the core length and end turns of the rotor winding are secured with steel bands. The
connections are made on the side, facing rectifier wheels. The winding ends are run to a bus ring
system to which the 3 phase leads leading to the rectifier wheels are also connected. After full
impregnation with synthetic resin and cooling, the complete rotor is shrunk onto the shaft.

CONSTRUCTION of BRUSHLESS EXCITER:

The exciter is brush-less and takes the form of a stationary field generator. Its rotor is mounted on
the overhang of main machine shaft end. The stator may be fixed either to be base frame of the
main machine or to a separate steel or concrete foundation. A permanent magnet three phase pilot
exciter driven directly by the common shafting or a static auxiliary excitation unit is used for
exciting the field of the stationery field generator via a voltage regulator. The auxiliary excitation
equipment is described elsewhere. The three-phase current flowing in the rotor winding is
rectified by Silicon diodes in the rotating rectifier and fed into the field winding of main machine
via the excitation leads which pass through the hallow shaft of the main machine.

27
ROTOR:
The rotor is fitted on the shaft extension of the main machine and locked to it in the
circumferential direction by parallel keys which are capable of accepting shock loads caused by
short circuit in the main machine without being over stressed.

The rotor hub is of welded construction and called the laminated core which is compressed
axially by means of a clamping ring welded to the hub. Specially shaped supporting elements for
the rotating rectifier modules are welded between the arms of the rotor spider within the ring
formed by laminated core.

ROTOR WINDING:
The 3-phase rotor winding inserted in the slots of the laminated core is connected in star. It is a
two-layer winding to insulation of class F. The end leads of the individual windings are on the A
end and connected to the u, v,w and neutral bus rings arranged at the same end. Both winding
overhangs are bound with heat setting glass fiber tapes to afford protection against centrifugal
forces. The rotor winding is impregnated with epoxy resin.
RECTIFIER:
The rectifier accommodated inside the rotor core and rotor winding comprises six diode
assemblies and the protection circuit. The diode assemblies each consist of a light metal heat sink
with integrally formed cooling fans containing one disc type diode secured by means of a
clamping plate. As the heat sinks are electrically live, they are insulated from the rotor hub to
which they are fixed. A contact face provided on the inside of each heat sink is connected by
meanks of links to the appropriate bus ring on the 3-phase side. The connections to the dc bus
rings are established by longitudinally arranged bus connector, which is connected to the contact
bolts protruding from the clamping plates.

Diode assemblies situated on opposite sides of the rotor spider have opposite polarities. The sign
of polarity, which appears on the front face of the heat sink, should be observed. The dc bus rings
carry the protective varistors are screwed to the B end of the rotor spider by means of insulating
mounts. The two bus rings, each have a terminal lug for the copper bars which are connected to
the excitation cable of the main machine.
The excitation cables are led through the insulated hollow shaft of the main machine and are
provided with special cable lugs at the shaft openings.

VARISTOR:
To protect the rectifier bridge against over voltages occurring during starting or during fault
conditions, a non-linear resistor is provided. This protective varistor consists of 12 varistor discs
in parallel, connected between the positive and negative bus rings.

The varistor discs are clamped between the bus rings by means of insulated screws. Electrical
contact between the varistor discs and the bus rings is ensured by discs of annealed copper
inserted between them.

28
MAIN EXCITER:
The 3-phase pilot exciter is a 6 pole revolving armature unit. Arranged in the frame are the poles
with the field and damper windings. The field winding is arranged on the laminated magnetic
poles. Each coil is made from individually insulated tube. To reduce eddy current in the coil,
copper strips in each coil is transposed. At the pole shoe, hair is provided which are connected to
form a damper winding. Between the 2 poles of quadrature axis, a coil is fixed for inductive
measurement of field current.
The rotor consists of stacked silicon steel laminations forming the rotor core. The 3 phase
winding is inserted in the slots of laminated rotor. The winding conductors are transposed within
the core length and the end turns of rotor winding are secured with steel bands.

The stator slots form indentations in the air gap boundary. Therefore as the rotor flux moves
across the stator teeth the change in performance due to the slot opening introduces median
frequency pulsations. These pulsations induce harmonic voltages in the surface of the stator
teeth. But due to the laminated construction, the resultant leaves are kept to minimum. The
winding ends are connected to a burring system to which the 3 phase leads loading to the rectifier
wheel are also connected. A journal bearing is arranged between main and the pilot exciters and
has forced oil lubrication from the turbine oil supply; rotor windings and core are air-cooled.

ROTATING RECTIFIER WHEEL:

Ac power from the main exciter is fed to RR wheel where it is converted to dc. The main
components of the rectifier wheel are the silicon diodes, which are arranged inside the retaining
ring in a 3-phase bridge circuit. The internal arrangement of the diode is shown in fig. The
arrangement of the diode is such that the contact pressure produced by plate spring assembly is
increased by the centrifugal force during rotation. The rotating rectifier includes 20% standby
capacity ensuring continued and restricted operation in the unlikely event of the diode failure.
Anode based diodes are used in positive arms and cathode based diodes in negative arm of the
bridge. Additional components contained in rectifier wheel are heat sinks, RC networks, fuses,
Each diode is mounted in each light metal heat sink and thus connected in parallel associated
with each diode with HRC fuse, which serves to switch off the diode if it fails.

Rotating rectifier wheel is provided with 6 RC networks each consisting of one capacitor and one
damping resistor, which are connected, in single resin encapsulated unit.

When high voltage surges occur, the capacitor gets charged until normal conditions occur. When
a low voltage surge occurs, the charge through the capacitor is dissipated through the damping
resistor.

Three-phase alternating current is obtained via copper conductors arranged on the shaft
circumference between rectifier wheel and 3 phase main exciter. One 3 phase conductor
originating as a bus ring system of the main exciter is provided for each diode.

The dc current from the rectifier wheels is fed to the DC leads arranged in the central bore of the
shaft via radial bolts.

29
 PILOT EXCITER:
Some of different types of pilot exciters are salient pole, inductor type, and homopolar and
heteropolar designs. Salient pole PMG is a 3-phase medium frequency machine providing a
constant voltage supply to the thyristor converter and AVR circuits.

PMG poles are manufactured from high-energy material such as Alcomax. The permanent
magnet pieces are bolted to a steel hub and held in place by pole shoe. The bolts are made from
non-magnetic steel to prevent formation of magnetic shunt. To improve the waveform of the
output voltage and reduce electrical noise, the pole shoes are skewed one pole pitch over the
stator length. Stator core is constructed from a stack of low loss sheet steel laminations
assembled within the fabricated steel frame. Radial and axial cooling ducts are provided at
intervals along the core length to allow cooling of core and windings. The stator windings is a
two layered, each conductor consisting of a number of small diameter copper wires insulated
with polyster enamel. The coils are connected to give rated 3 phase voltage output and insulated
with class F epoxy glass material.
A steel frame is fitted over PMG stator provides mechanical protections and reduces medium
frequency noise emitted from the PMG to an acceptable level. Cooling of PMG is achieved by
drawing air through mesh-covered apertures in the frame.

BALANCING OF TG ROTOR & EXCITER ARMATURE:

1.0 Scope:
This standard cover the balancing of turbo generator rotors (utility of industrial), all types of
exciter armatures of repair rotor.

2.0 Balancing stages :

The assembled rotor shall be subjected to the following stages of balancing
1. Low speed balancing
2. High speed balancing
3. Performance of over speed test
4. Performance of heat cycles.
5. Final balancing
3.0 Balancing Method:
Balancing shall be carried out as per ISO 11342
4.0 Low speed Balancing:
Low speed balancing shall be carried out at a speed below one third of the rotor first critical
speed (Generally at 400 RPM)
1.0 High speed balancing :
High speed balancing shall be carried out from 70% of first critical speed up to rated speed.
2.0 Over Speed Test :
The over speed test is performed after high speed balancing is carried out. The test lasts after a
duration of two minutes at 120% of operating speed.
3.0 Performance of Heat cycles :
If mentioned on the Balancing test advice, heat cycles are to be performed on the rotor as per
TG45233. This is only an internal test.
30
4.0 Final Balancing
The final balancing shall be carried out to achieve the limits specified
in 9.0
5.0 Acceptance Criteria:
Vibration displacement measured on bearing pedestals forms the basis for acceptance criteria of
balance quality. The acceptance limits.
At Operating speed - 10 Microns (p-p)
At all other Speeds - 16 Microns (p-p)
6.0 Recording

Test protocol for a balanced rotor contains the following information.

1. Type of rotor mentioning work order No. forge No. weight of the rotor
2. Over speed test details
3. Balancing weights disposition plan.
4. Vibration amplitude in displacement units at the various speed.

ASSEMBLY SHOP
 In assembly shop the rotor is placed on bearings, in which their clearances are made to the
standard given by the drawing.

1. Mechanical run test.

2. Bearing vibration measurement.
3. Mechanical heat run test.
4. Measuring of mechanical loses three phase short circuit characteristic.
5. Bearing vibration measurement at 100% In.
6. Short circuit heat run test at 119.1 % In.
7. Measurement of mechanical losses, Open circuit characteristic.
8. Phase sequence check.
9. Shaft voltage measurement at 100% En
10. Vibration measurement at 100% En.
11. Measurement of residual voltage of stator winding at rated speed.
12. Open Circuit heat run test at 110% En.
13. Voltage wave form analysis and determination of THF
14. Line to Line sustained short circuit test and determination of Negative sequence reactance (X2).
15. Line to Line and to Neutral sustained short circuit test and determination of Zero sequence
reactance (Xo)
16. Retardation test for determination of Gd2.
17. Impedance measurement on rotor winding at 0, 1/3, 2/3 and 3/3 of rated speed. (Rotor inside the
stator).
18. 3-Phase sudden short circuit test at 20%, 35% & 50% En.
19. I.R. value measurement, High voltage test on stator and rotor winding
20. Checking of RTDs and Polarizations Index of stator winding.
21. D.C. resistance measurement on stator and rotor winding.
22. Capacitance and tan delta measurement on stator winding

31
 Major components to be assembled in Assembly shop

 Stator Frame Fabrication & machining

 Stator dummies or HGL gap seal
 Air guide rings
 Labyrinth ring or Sealing rings
 Enclosures or rubbers
 Clamping device
 Laminations & Ventilations
 Core Bolts & guide bars
 Core bolt rings & Winding holders
 Bearing brass
 Labyrinth Rings
 Plugs/Side stoppers
 Bearing pedestals
 Sealing rings
 Exciter frame & yoke
 Base frames
 Partitions & End Winding Covers
 Balancing plugs & weights
 Fan blades
 Rotor wedges
 Exciter poles & coils
 Exciter pedestal
 AS cover / BS cover
 Ducting & yoke supports
 Armature Shaft
 Armature core
 PMG hub & Shoes

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Major operation in Assembly shop:

Rotor wedges assembly &

Stator top & dummies Drilling & Tapping& Ends Bearing Brass spherical
disassembly jackup matching
Stator frame deburring & Fan-Locking holes Jack oil holes driling&
Rust preventive application drilling&tapping Deburring & Tapping
Stator frame painting
(carrier section tack Fan blades suiting& 'O' Bearing Brass bedding with
welding) angle setting Journals
Dummies rubber pasting & Preparation for rotor
bottom dummies assembly Cover plates assembly insertion
Gapseal holes retapping & Rotor wedges&Fan OD
gapseal rubber assembly turning Rotor insertion
Stator core-marking of Wedges&fans numbering Bearings & Bearing
suspension plates diassembly pedestals assembly
Core suspension plates
welding Rotor deburring for painting Air gap & MA setting
Stator core centering & Finish maching of Stator top assembly &
welding rotor&angle hole drilling Gapseal HGL assembly
Stator top assembly & Air R.R wheel hub
guides Labyrinth rings assembly&Locking (HGL
centering rings,keys) Air guide rings assembly
Armature shrink Labyrinth rings & S.R.
Welds grinding & Painting fitting&Locking assembly
HGL cap
Gapseal HGL plates assembly&Magnets
assembly assembly - Ø 216 M&C placing on Bed
Brg pedestals blue Balancing weights&Plugs
matching on stator frame assembly D.M alignment

33
 Major activities in Assembly shop:
 Stator top & dummies disassembly
 Stator frame deburring & Rust preventive application
 Stator frame painting (carrier section tack welding)
 Dummies rubber pasting / bottom dummies assembly
 Gap seal holes retapping & gap seal rubber assembly Stator core-making of suspension plates
 Core suspension plates welding
 Stator core centering & welding
 Stator top assembly & Air guides Labyrinth rings centering
 Welds grinding & Painting
 Gap seal HGL plates assembly
 Bearing pedestals blue matching on stator frame
 Space heaters assembly & RTD board assembly

Operations on Rotor:
 Rotor deburring for wedges
 Rotor wedges assembly & Drilling & Tapping & Ends jack up
 Fan-Locking holes drilling/tappling
 Fan blades suiting & ‘O’ angle setting
 Rotor wedges & Fan OD turning
 Wedges/fans numbering disassembly
 Rotor deburring for painting
 R.R. wheel hub assembly & locking
 HGL cap assembly & Magnets assembly  216
 Balancing weights & Plugs assembly
 Fan blades assembly & Angle setting & Final Locking
 Core plates assembly & Locking
 Rotor balancing
 Rotor HV test & Painting
 Preparation for rotor insertion
 Rotor insertion

Operation on Bearings:
 Bearing pedestal blue matching
 Bearing Brass spherical matching
 Jack oil holes drilling & Deburring & Tapping
 Bearing Brass bedding with Journals

34
 Operations on Test bed:
 Test bed preparation and machine placing on bed.
 Bearings & Bearing pedestals assembly
 Air gap & MA setting
 Stator to assembly & Gap seal HGL assembly
 Air guide rings assembly
 Labyrinth rings & S.R. assembly
 Drive Motor alignment.

STATOR WINDING:

W.C.3216 STATOR

E.M. PLANNNG & RECEIPT OF RECEIPT OF STATOR FROM ASSLY.

RECEIPT OF STATOR COILS FROM

QUALITY
LAYING OF STATOR
BARS

WEDGIN
TOOLS & GUAGES FROM SHOP

EYE

TESTING EYE

DESPATCH TO W.C.3215 FOR IMPREGNATION OF

TESTIN

DESPATCH TO ASSLY.

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 Stator bar design incorporates the use of thermosetting (resin rich/VPI) epoxy mica
insulation conforming to class “F”. The bars/coils during manufacture are provided with
conductive tape/wrapping for minimization of corona discharge.
Double layer lap winding with half roebel / multiturn type / diamond shaped coils are employed
in stator winding.

The main activities of 2/4 pole TG Stator winding process are:

 Stator core ,slot checking(slot cleaning and gauge checking)
 Assembly of winding Holders, Ring Holders and welding of Fasteners.
 Assembly of Bandage rings.
 Slot bottom insert(Case specific)
 Assembly of bottom bars(Coil laying)
a. Bar pressing in Hydraulic fixture, Determination of pressure
b. Bar centering, lowering of the bar by pressing fixtures (Stums) by screw jacks.
c. Overhang Fastening, specification of sleeves and tapes used, Soft Glass mat as comfortable
packing.
 Interstage HV, IH, IT tests (case specific)
 Assembly of stiffeners, overhang spacers.
 Assembly of Interlayer inserts, RTDs in the winding.
 Assembly of top layer winding
 Wedging process.
 Interstage testing, HV test levels.
 Brazing process specification of brazing material, Temperature, duration for each brazing.
 Eye insulation details.
 Assembly of connecting rings, Full rings (4 pole) and ring segments (2 pole).
 Study of winding scheme: star connection (Y Y Y), Distributed winding, short pitch, Lap/ Wave
winding, Double layer, Multi/Single turn, Progressive/ Retrogressive.
 Testing of TG stator in post Impregnation stage: Insulation Resistance (IR), Absorption
coefficient (AC), Polarization Index (PI),
 HV, Tan delta, DLA, Partial discharge.
 Assembly of Output lead bushings and connectors- Study of different types of bushing design.

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STATOR WINDING PROCESS:
1. RECEPTION OF STATOR CORE: - The stator core is received and checked for all prior
operations and it is cleared by Quality Control. It is even checked for lamination projection in
slots, sharp corners and foreign matter interruptions.

2. CLEANING AND ROTATION: - Rotate the core continuously on the rollers until no
foreign matter dropping from the slots.

3. WINDING HOLDERS ASSEMBLY: - Assemble the windings holders on both the sides by
placing 5mm glass matt under the holder and tightening with nuts and bolts. After aligning all the
winding holders with respect to core. nuts are locked on the turbine side by tack-welding.

4. HGL RINGS ASSEMBLY: - Assemble HGL Bandage rings on the exciter side, and then
assemble HGL ring centering with respect to core on both the sides.

5. BOTTOM BAR LAYING: - Prior to laying bottom bar, each bottom bar is to be pressed in
pressing fixture for a duration of 75kgs/cm^2 (for 2 pole TG bars) for a duration of 30 min in
order to obtain slot-width dimension. Also, inter-half shorts are checked for each bar and bars are
laid into the respective slots. First lay 1 bar into respective slot by centering the bar with respect
to the core and insert the bar into slot by pressing fixture. Then lock the bar by temporary
wedges. Lay all the bars in a similar way. Glass mat is inserted on both the overhangs and tied
with neoprene glass sleeve. It is also checked for 3 rd bend matching. After laying of all the
bottom bars, subject the total bottom bar for DCHV (Direct Current High Voltage) test. If all the
bars have passed testing, then further operation is carried out.

6. STIFFENERS ADOPTATION: - Assemble stiffeners on both the sides by placing 5mm

glass mat on each stiffener bottom and tying all the stiffeners with neoprene glass sleeve.RTD
slots are identified and marked as per the drawing requirement. Before laying the bars the RTD’s
are inserted between the bottom and top bar as per the drawing requirement with inter layer
inserts. These are used in each and every slot between bottom and top.

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7. TOP BAR LAYING:- Insert one top bar into the pressing fixtures apply 75kg/cm^2 for 30
min in order to obtain slot width thickness and also check for inter-half shorts by lamp test and
remove bar from fixtures and insert in the respective slots by centering the stator bar w.r.t. the
stator core and checking for the bend matching on both the sides and press the bar into the slot by
inserting the inter layer slot inserts and applying the pressure over the top bar by using the
fixtures such that the top bars are inserted into the slot. Lay one more bar by following the above
procedure and insert glass material on both the sides and tie with neoprene glass sleeve. Similarly
lay all the top bars into the respective slots by following the same procedure. After completion of
top bar laying subject DCHV, if bars are passed then carry out further processing.

8. EYES JOINING AND BRAZING: conductor to conductor jointing and resistance brazing is
carried out overlapping by 10mm by using fillers (silver foil is inserted between the conductor by
carrying out resistance brazing. Similarly, all the conductors are done in the same fashion. After
completion of brazing check the eye length from the core as per the drawing requirement.
Similarly, all the eyes are brazed by using the above procedure on both the sides. After
completion of eye operation each eye is opened into two halves bottom and top on both the sides.
Cleaning is carried out and silver lumps are cleaned halve insulation is inserted between two
halves, taped with mica folium tape. Similarly for all the eyes the same process is repeated .

9.CONNECTING RINGS ASSEMBLY: -Connecting Rings are assembled as per the drawing
requirement on exciter side for jointing the phase groups through the conductors and terminating
3 phases and 3 neutrals. Total winding is subjected to DCHV test. If it passes, then allow for VPI
cycle.

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STATOR WINDING TECHNICAL DETAILS:
The three-phase stator winding is a fractional pitch two-layer type consisting of individual
bars; each stator slot accommodates two bars. It is a double layer lap winding with 60 o phase
spread fractional Windings are used to reduce higher order harmonics and pitch of the winding is
so Selected that 5th and 7th harmonics are greater reduced.
The slot bottom bars and top bars are displaced form each other by one winding pitch and
connected at their ends to form coil groups. The coil groups are connected together with phase
connectors inside the stator frame. This arrangement and shape of the bars at the results in a cone
shaped winding having particularly favourable characteristics both in respect of its electrical
properties and resistance of only one turn insulation and main insulation identical.

Stator core received after the core assembly is checked for the availability of foreign
matter, so coil projections are checked in each slot.HGL drift is passed in each and every slot to
detect bottom core projections. Winding holders are adopted and binding rings are assembled on
both sides. The HGL binding rings are cantered to the core and then bottom bars are laid. Each
bar is pressed with a pressing fixture to obtain specified dimensions. By adopting this above
procedure, the entire bottom bars are laid in respective slots. After completing of bottom bar
layer reinforcing the overhang portion by tying with nipping glass sleeve.

Temporary wedging is carried out, HV testing is done and then stiffeners are assembled.
Top bars are laid by pressing each bar with a pressing fixture and all the bars are laid in
respective slots. In between top and bottom bars HGL spacers are kept. And then top bars are
tested.

Individual eye jointing and bracing is carried out. Then after eyes jointing individual eyes
are insulated with fine mica tape. After completion of eyes jointing connector rings are
assembled & connected as per drawing and three neutral and three phases terminal are terminated
out. Once again HV test is carried out before sending the stator to impregnation.

CONNECTION OF BARS:
Brazing makes the electrical connection between the top and bottom bars. One top bars
strand each is brazed to one strand of the associated bottom bar so that beginning of each strands
is connected without having any electrical contact with the Remaining strands. This connection
offers the advantage that circulating current losses in the stator bars are kept small. The strands
are insulated from each other at the brazed joints. The coils connected are wrapped with dry
mica/glass fabric tapes half overlapped. The thickness of the wrapper depends on the machine
voltage. The gaps between the individual coil commendations being sufficiently large, no
additional insulation is required.

PHASE CONNECTORS:
The phase connectors consist of flat copper sections, the cross section of which results
in a low specific current loading. The connections to the stator winding are of riveted and
soldered tape and are like-wise wrapped with dry mica/glass fabric tapes. The phase connectors
are firmly mounted on the winding support using clamping pieces and glass fabric tapes.

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TERMINAL BUSHINGS:

1. ARRANGEMENT OF TERMINAL BUSHINGS

The beginning and ends of the three phase windings are brought out from the stator frame
through bushings, which provides for high voltage insulation. The bushings are bolted to the
stator frame at the exciter end by their mounting flanges. Bushing type current transformers for
metering and relating may be counted on the Bushings courtside the stator frame. The generator
main leads are connected to the terminal connectors outside the stator frame.

2. CONSTRUCTION OF TERMINAL BUSHINGS:

The bushing conductor consists of high conductivity copper buses. All connection flanges are
silver-plated to minimize the contact resistances of the bolted connections. The supporting
insulator of glass silk cloth is impregnated with epoxy resin. The copper buses are attached to the
insulator only at one end and are thus free to expand. Flexible connectors allow for thermal
expansion between the terminal bushing and the phase connectors. To prevent eddy current
losses and inadmissible overheating, the mounting flange is made of glass silk cloth as well.

3. COOLING OF TERMINAL BUSHINGS:

To dissipate the heat the terminal bushings are directly cooled with cold air. Cold air forms the
discharge end of the fan is pressed in to the insulator. The hot air is returned to the suction intake
of the fan via the passage between the two copper buses.

SUBMITTED BY
1.DIVYAREDDY DHAMMA
2.KAVYA NATTE
3.MONITHA SAI CHINNALA
4.PRAVALLIKA PANUMALLI
5..NAGASRI BURA

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