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DEPARTMENT OF ELECTRICAL ENGINEERING
RAJASTHAN TECHNICAL UNIVERSITY, KOTA
A VocationalTraining Report
On
Turbo Generator & Excitation System
At
BHARAT HEAVY ELECTRICALS LIMITED,
HARIDWAR
Submitted in partial fulfilment of the requirement for the
award of the degree
OF
Bachelor of Technology
Session: 2013-2017
TENURE OF TRAINING
28 MAY,2016 to 26 JULY,2016
SUBMITTED TO : SUBMITTED BY :
DR. ANNAPURNA BHARGAV YASH KUMAR NATANI
( PROFESSOR ) B.TECH , FINAL YEAR
MR. ASHOK KUMAR SHARMA ELECTRICAL ENGG.
( ASSOCIATE PROFESSOR ) C.R. NO. 13/095
1
CERTIFICATE
2
PREFACE
It is a matter of great pleasure for me to present the following repost on my
INDUSTRIAL TRAINING at BHEL HARIDWAR, otherwise one seldom
gets a chance to go through any industry after on the job training/placement. It
outlines the course of project work during my training in an oriented manner
over a period of 60 days of B. Tech. 7
th
Sem. Electrical Engineering.
I have tried my best to present this training report in a very precise and
profitable manner. Any suggestions in this direction will be gratefully accepted.
Engineering students gain theoretical knowledge only through their books. Only
theoretical knowledge is not sufficient for absolute mastery in any field.
Theoretical knowledge give in our books is not sufficient without knowing its
practical implementation.
It has been experienced that theoretical knowledge is volatile in nature however
makes solid foundation in our mind.
3
The training report consists of construction of Turbo generator and excitation
system & constructional features of main parts of BHARAT HEAVY
ELECTRICAL LIMITED, Haridwar. Adequate diagrams and layouts have
been provided for a more descriptive outlook and clarity of understanding.
ACKNOWLEDGEMENT
“An engineer with only theoretical knowledge is not a complete engineer. Practical
knowledge is very important to develop and to apply engineering skills”. It gives
me a great pleasure to have an opportunity to acknowledge and to express gratitude
to those who were associated with me during my training at BHEL.
Special thanks to DR. DINESH BIRLA ( HOD Department of Electrical
Engineering, Rajasthan Technical University , Kota) for allowing me to undergo 60
days vocational training.
I would like to thank MR. SATISH KUMAR SINGH ( Engineer , Electrical
Machine Planning Block 1,BHEL Haridwar ) under whose dexterous guidance I
learned all I could.
I express my sincere thanks and gratitude to BHEL authorities for allowing me to
undergo the training in this prestigious organization. I will always remain indebted
to them for their constant interest and excellent guidance in my training work,
moreover for providing me with an opportunity to work and gain experience.
Lastly, I would like to thank almighty and my parents for their moral support
and my friends whom with I shared my experience day by day and received lots
of suggestions that improved my quality of work
4
INDEX
1. INTRODUCTION
2. BHEL’S CONTRIBUTION IN DIFFERENT SECTORS
3. BHEL HARIDWAR
4. TURBO GENERATORS
4.4.1 STATOR
5
1.1 BHEL’S UNITS IN INDIA 8
1.2 A BRIEF HISTORY 9
2.1 POWER SECTOR 10
2.2 TRANSMISSION 10
2.3 TRANSPORTATION 11
2.4 INTERNATIONAL OPERATION 11
2.5 RENEWABLE ENERGY 11
2.6 INDUSTRIES 11
3.1 AN OVERVIEW 13-15
3.2 PRODUCTS 16-17
4.1 SYNOPSIS 18
4.2 WORKING 18-19
4.3 LARGE SIZE TURBO GENERATORS 20
4.4 COMPONENTS OF TURBO GENERATOR 21-22
4.4.1.3 STATOR WINDING
4.4.1.3.1 CONSTRUCTION 28
4.4.1.3.2 HOLLOW WINDING 29-30
4.4.1.3.3 METALLIC STRIP WINDING 31
4.4.1.1 STATOR FRAME 23-24
4.4.1.2 STATOR CORE 25-28
4.4.1.2.1 STAMPINGS
4.4.1.6 STATOR COOLING
4.4.2 ROTOR
6
4.4.1.3.4 FLOW CHART OF WINDING MANUFACTURING 32
4.4.1.3.5 WATER SUPPLY 33-34
4.4.1.3.6.1 TYPES OF INSULATION 35
4.4.1.3.6.2 TESTING OF INSULATION 35
4.4.1.4 SPRING AND SPRING BASKET 36-37
4.4.1.3.6 INSULATION OF STATOR WINDING 34
4.4.1.5 MAGNETIC SHUNT 37
4.4.1.6.1 COOLING OF WINDINGS 37-38
4.4.1.6.2 COOLING OF CORE 38-39
4.4.1.7 PRESS RINGS 40
4.4.1.8 END RINGS 40-41
4.4.1.9 TERMINAL BOX AND TERMINAL BUSHING 42-43
4.4.2.1 ROTOR SHAFT 44-47
4.4.2.2 ROTOR WINDING
4.4.2.2.1 CONDUCTOR MATERIAL OF WINDING 47-48
4.4.2.2.2 INSULATION 49
4.4.2.3 ROTOR SLOT WEDGES 49-50
4.4.2.4 ROTOR TERMINALS 51
4.4.2.5 RETAINING RING AND CENATARING ASSEMBLY 52
4.4.2.6 COMPRESSOR HUB 53
4.4.2.7 ROTOR FAN 53-54
5. BEARINGS 55
6. SHAFT SEAL 55
9. LOSSES IN TURBO GENERATOR
7
7. COOLING OF ROTOR 56-57
8. EXCITER 57-58
8.1 MAIN EXCITER 59-60
8.2 PILOT EXCITER 61
8.3 COOLING OF EXCITER 61-62
8.4 RECTIFIER WHEEL 62-64
9.1 COPPER LOSSES 64-65
9.2 MAGNETIC LOSSES 65-66
10. BIBLIOGRAPHY AND REFERENCES 68
9.3 MECHANICAL AND ROTATIONAL LOSSES 66-67
11. CONCLUSION 69
1.INTRODUCTION
In 1956 India took a major step towards the establishment of its heavy engineering
industry when Bharat Heavy Electricals Limited, the first heavy electrical
manufacturing unit of the country was set up at Bhopal. It progressed rapidly and
three more factories went into production in 1956. The aim of establishment BHEL
was to meet the growing power requirement of the country.
BHEL has supplied 97% of the power generating equipment that was
commissioned in India during 1979-80. BHEL has supplied generating equipment
to various utilities capable of generating over 18000MW power. BHEL is one of
the largest power plant equipment manufacturing firms in India and it ranks among
the top ten manufacturers globally. BHEL has covered up many power stations
over 40 countries worldwide.
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 division includes a network of regional offices
throughout India.
1.1 BHEL’S UNITS IN INDIA
S. NO. CITY PLANTS
1. HARIDWAR 2
2. BHOPAL 1
3. JHANSI 1
4. JAGDISHPUR 2
5. HYDERABAD 1
6. GOINDWAL 1
7. TIRUCHIRAPALLI 2
8. THIRUMAYAM 1
9. BANGLORE 3
10. RUDRAPUR 1
11. PANIPET 1
12. VISHAKHAPATNAM 1
8
1.2 A BRIEF HISTORY
The first plant of what is today known as BHEL was established nearly 40 years
ago at BHOPAL and was genesis of Heavy Electrical Equipment industry in India.
BHEL is today the largest engineering enterprise of its kind in India, with a well-
recognized track record of performance making profits continuously since 1971-
72. It achieved a sales turnover of Rs.1022 core in 1997-98. BHEL caters to core
sectors of the Indian Economy via, Power, Industry, Transportation, Defense, etc.
The wide network of BHEL’s 14 manufacturing divisions, 9 service centers & 4
power Sector Regional centers & about 150 project sites enables the service at
competitive prices. Having attained ISO 9000 certification, BHEL is now
embarking upon the Total Quality Management. The company’s inherent potential
coupled with its strong performance over the years, has resulted in it being chosen
as one of the― MAHARATNA PSUs (on 1 February 2013), which are to be
supported by the Government in their endeavor to become future global players. It
is the 7th largest power equipment manufacturer in the world. In the year 2011, it was
ranked ninth most innovative company in the world by US business magazine Forbes.
BHEL is the only Indian Engineering company on the list, which contains online
retail firm Amazon at the second position with Apple and Google at fifth and
seventh positions, respectively. It is also placed at 4th place in Forbes Asia's Fabulous
50 List of 2010
9
2.BHEL’ S CONTRIBUTION IN DIFFERENT
SECTORS
2.1 POWER SECTOR
2.2 TRANSMISSION
Power sector comprises thermal, nuclear, gas & hydro power plant business.
Today, BHEL supplied sets account for nearly 56,318 MW or 65% of the total
installed capacity of 86,636 MW in as against nit till 1969-1970.BHEL has proven
turnkey capabilities for executing power projects from concept to commissioning.
It possesses the technology and capability to produce thermal power plant
equipment upto 1000MW rating and gas turbine generator sets up to a unit rating
of 240 MW. Cogeneration and combined cycle plants have been introduced to
achieve higher plant efficiencies.
To make efficient use of the high ash content coal available in India, BHEL
supplies circulating fluidized bed boilers to thermal and combined cycle power plants.
BHEL manufacturers 235 MW nuclear turbine generator sets and has commenced
production of 500 MW nuclear turbine generator sets. Custom- made hydro
sets of Francis, Pelt on and Kaplan types for different head- discharge
combinations are also engineered and manufactured by BHEL is based upon
contemporary technology comparable to the best in the world & is also
internationally competitive.
BHEL also supplies a wide range of transmission products and systems up to 400
KV Class. These include high voltage power and distribution transformers,
instrument transformers, dry type transformers, SF6 switchgear, capacitors, and
insulators etc. For economic transmission bulk power over long distances, High
Voltage Direct Current (HVDC) systems are supplied. Series and Shunt
Compensation Systems have also been developed and introduced to minimize
transmission losses.
A strong engineering base enables the Company to undertake turnkey delivery of
electric substances up to 400 kV level series compensation systems (for increasing power
transfer capacity of transmission lines and improving system stability and voltage
regulation), shunt compensation systems (for power factor and voltage
7improvement) and HVDC systems (for economic transfer of bulk power). BHEL
has indigenously developed the state-of-the-art controlled shunt reactor (for
reactive power management on long transmission lines). Presently a 400 kV Facts
(Flexible AC Transmission System) project under execution.
10
. 2.3 TRANSPORTATION
2.4 INTERNATIONAL OPERATION
3000MW. The company’s overseas presence includes projects in various countries.
A few notable ones are -150 MW (ISOI) gas turbine to Germany, utility boilers
and open cycle gas turbine plants to Malaysia, Tripoli-west, and power station in
Libya executed on turnkey basis, thermal power plant equipment to Malta and
Cyprus, Hydro generators to New Zealand and hydro power plant equipment to
Thailand. BHEL has recently executed major gas-based power projects in Saudi
Arabia and Oman, a Boiler contract in Egypt and several Transformer contracts in
Malaysia and Greece.
2.5 RENEWABLE ENERGY
Technologies offered by BHEL for non-conventional and renewable sources of
energy include: wind electric generators, solar photovoltaic system, stand alone
and grid-interactive solar power plants, solar heating systems, solar lanterns
and battery-powered road vehicles. The company has taken up R&D efforts for
development of multi-junction amorphous solar cells and fuel cells based systems.
2.6 INDUSTRIES
BHEL is a major contributor of equipment and systems to industries: cement, sugar,
fertilizer, refineries, paper, oil and gas, metallurgical and process industries. The
company is a major producer of large-size thyristor devices.
A high percentage of trains operated by Indian Railways are equipped with
BHEL’s traction and traction control equipment including the metro at
Calcutta. The company supplies broad gauge electrical locomotives to Indian
Railways and diesel shunting locomotives to various industries.5000/6000 hp
AC/DC locomotives developed and manufactured by BHEL have been leased
to Indian Railways. Battery powered road vehicles are also manufactured by the
company.
BHEL’s products, services and projects have been exported to over 50 countries
ranging from United States in the west to New Zealand in Far East. The cumulative
capacity of power generating equipment supplied by BHEL outside India is over
11
It also supplies digital distributed control system for process industries and control &
instrumentation systems for power plant and industrial application. The range of
system & equipment supplied includes: captive power plants,co-generation plants
DG power plants, industrial steam turbines, industrial boilers and auxiliaries.
Water heat recovery boilers, gas turbines, heat exchangers and pressure vessels,
centrifugal compressors, electrical machines, pumps, valves, seamless steel tubes,
electrostatic precipitators, fabric filters, reactors, fluidized bed combustion boilers,
chemical recovery boilers and process controls.
The Company is a major producer of large-size thruster devices. It also supplies
digital distributed control systems for process industries, and control &
instrumentation systems for power plant and industrial applications. BHEL is the only
company in India with the capability to make simulators for power plants, defense
and other applications.
12
3.BHEL HARIDWAR
3.1 AN OVERVIEW
At the foothills of the majestic Himalayas & on the banks of a holy Ganges in Ranipur
near HARIDWAR is located Heavy Electricals Equipment Plant of Bharat Heavy
Electrical Ltd.
BHEL,wholly owned by the government of India is an integrated engineering complex
consisting of several plants in India, where about 70,000 workers are busy in design
&manufacturing of a wide range of heavy electrical equipment. At present 70% of the
Country’s electrical energy is generated by the sets manufacturing by BHEL, Haridwar.
BHEL HARIDWAR is broadly divided in to two parts:
A) CFFP: – Central Foundry Forge Plan
CFFP is divided in to following shops :
13
 Steel Melting Shop (SMS)
 Steel Foundry
 Pattern Shop
 Cast Iron (CI) Foundry
 Machine shop
 Forge shop
B) HEEP: – Heavy Electrical Equipment Plant
HEEP is divided in to following shops:
S. NO. BLOCK MAJOR FACILITIES PRODUCTS
1. Block-I
(Electrical
Machines )
Turbo generators,
exciters, Motors
(AC
& DC).
2. Block-II
(Fabrication
Block)
Marking, cutting,
straightening, gas cutting,
press, welding grinding,
assembly, heat treatment,
cleaning and shot blasting,
machining, fabrication
of pipe coolers, painting
Large size
fabricated
assembles/
components
for power
equipments
3. Block-III
(Turbine and
Auxiliary
block)
Machining,assembly,
preservation and packing, test
stands/ station, painting,
Steam turbines,
hydro turbines,
gas turbines,
turbine
blades,special
Machine shop, winding bar
preparation, assembling,
painting section,packing and
preservation, oven speed
balancing,test bed, test stand,
micalastic impregnation,
babbitting etc.
14
4. Block-IV
(Feeder block)
Bar winding, mechanical
assembly, armature
windings, sheet metal working,
machining, copper profile
drawing, electroplating,
impregnation, machining and
preparation of insulating
components plastic moulding,
press moulding
Windings for
turbo
generators,
hydro
generators,
insulation for
AC and DC
motors,
insulating
components for
TG, HG
and Motors,
control
panels,
contact
relays,
master
control etc.
5. Block-V Fabrication, pneumatic hammer
for forging, gas fired furnaces,
hydraulic manipulators.
Fabricated parts
of steam turbine
water box,
storage tank,
hydro turbines
assemblies
and
components
6. Block-VI
(Fibrication)
Welding, drilling shot blasting,
CNC flame cutting, CNC deep
drilling, shot blasting, sheet
metal work, assembly
Fabricated oil
tanks, hollow
guide blades,
rings,stator
frames, rotor
spiders.7. Block-VI
(Stamping and
Dia
manufacturing)
Machining, turning, grinding, jig
boring, stamping press, de-
varnishing, de-greasing, de-
rusting, varnishing, spot
welding, painting.
All types of
dies, including
stamping dies
and press forms
stamping for
generators
& motors.
15
3.2 PRODUCTS
1. Turbo Generator
2. Excitation System
3. Heat Exchanger
S. NO. PRODUCT IMAGE
16
IMAGE
4. Condenser
5. Steam and Gas
Turbine
17
4.TURBO GENERATOR
4.1 SYNOPSIS OF THE FUNCTION OF TURBO GENERATOR
The generator rotor is driven by prime mover and on driver side gas/ diesel/ steam
hydro depending on the equipment to which it is meant for. The non- drive
side of rotor is equipped with a rotating side of armature which produces AC
voltage. This is rectified to DC by using a DC commutator/rotating diode wheel
depending upon the type of exciter. The rear end of above exciter armature
is mounted with a permanent magnet generator rotor. As the above rotating system
put into operation, the PMC produces AC voltage. The voltage is rectified by
thyristor circuit to DC. This supply is given to exciter field. This field is also
controlled by taking feedback from main generator terminal voltage, to control
exciter field variation by automatic voltage regulator. The rectified DC supply out
of exciter is supplied to turbo generator rotor winding either through brushes or
central which will be directly connected to turbo generator. This depends on the
type of exciter viz. DC commutator machines or brushes exciter. The main AC
voltage of generator is finally available to turbo generator stator.
4.2 PRINCIPLE OF WORKING
The AC generator or alternator is based on the principle of electromagnetic
induction and consist generally of a stationery part called Stator and a rotating
part called Rotor.Stator houses the armature winding. The rotor houses the field
winding. DC voltage is applied to field winding through the slip rings.
18
When the rotor rotates, the lines of magnetic flux cut through the winding..This
induces an electromagnetic EMF in the stator winding. The magnitude of emf is
given by following formula
E = 4.44* ø *ƒ*T volt
Where,
ø= useful magnetic flux per pole in Weber
ƒ= frequency in hertz
T = number of turns in stator winding
ƒ = frequency = P*N / 120
Where,
P = number of poles
N = number of rotations per minute of rotor
19
4.3 LARGE SIZE TURBOGENERATOR (LSTG)
The generators may be classified on the basis of cooling system used in it.
Main types are:
1. THRI
2. TARI
3. THDI
4. THDD
5. THDF
6. THFF
T => first alphabet stands for the type of generator – turbo-generator or hydro
generator.
H/A => second alphabet stands for the cooling media used for the cooling of
rotor i.e. hydrogen gas or air.
R/D/F/I => third alphabet stands for the type of cooling of rotor e.g. radial,
direct, forced, indirect, etc.
I/D/F => last alphabet stands for the type of cooling for stator e.g. indirect,
direct or forced cooling.
20
4.3 COMPONENTS OFTURBOGENERATOR
4.3.1 STATOR
 Stator frame
 Stator core
 Stator winding
 Spring & Spring Basket
 Magnetic Shunt
 Stator Cooling
 Press Rings
21
 End Rings
 Terminal Box & Terminal Bushing
4.3.2 ROTOR
 Rotor winding
 Rotor retaining rings
4.4 BEARINGS
4.5 COOLING SYSTEM
4.6 EXCITATION SYSTEM
4.7 SHAFT SEAL
 ROTOR SHAFT
22
4.4.1 STATOR
CROSS SECTIONAL VIEW OF STATOR FRAME
4.4.1.1 STATOR FRAME
23
PIPE FOR COOLING
GAS
Stator frame is made up of structural steel. The stator frame consist of a cylindrical
center section and two end shields which are gas tight and pressure resistant. The
stator end shields are joined and sealed to the stator frame with an O- ring and
bolted flange connection the stator frame accommodates the electrically active
part of the stator, i.e. the stator core and the stator windings. Both the gas ducts and
a large number of welded circular ribs provides for the rigidity of the stator frame.
Ring shaped support for resilient core suspension are arranged between the circular
ribs. The generator cooler is subdivided into cooler sections arranged vertically in
the turbine side stator End Shield. Stator End Shield also contain the shaft seal and
bearing components. Feet are welded to the stator frame and end shields to
support the stator on the foundation.The Stator is firmly connected to foundation
with anchor bolts through the feet. The generator stator is a tight construction
supporting and enclosing stator winding, core and hydrogen cooling medium.
Hydrogen is contained within frame and circulated by fans mounted at either end
of rotor. The generator is driven by direct coupled steam turbine at the speed of 3000
rpm. The generator is designed for continuous rated output. Temperature detector and
other device installed or connected within machine, permit the windings core and
hydrogen temperature, pressure, and purity in machine.
LONGITUDINAL VIEW OF STATOR FRAME
24
MAN HOLE
4.4.1.2 STATOR CORE :-
CROSS SECTIONAL VIEW OF STATOR CORE
The stator core is made of silicon steel with high permeability and low hysteresis and
eddy current losses. The sheets are suspended in the stator frame from insulated
guide bars. Stator laminations are coated with synthetic varnish; are stacked and held
between sturdy steel clamping plates with non-magnetic pressing fingers which are
fastened or welded to the stator frame.
In order to minimize eddy current losses of rotating magnetic flux which interact
with the core is built of thin laminations. Each lamination layer is made of individual
segments. Core is mainly used for efficiently carrying electrical and mechanical flux
;It is inserted vertically in frame
25
SLOTS FOR WINDING
STAMPINGS FOR 500 MW TURBO GENERATOR
4.4.1.2.1 STAMPING :-
The segments are punched in one operation from electrical sheet steel lamination
having high silicon content and are carefully debarred.
STAMPING FOR 800 MW TURBO GENERATOR
26
HOLES FOR GAS FLOW
HOLES FOR GAS FLOW
The stator laminations are assembled as separate cage core without the stator frame.
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 rectangular bars
which hold them in position. To obtain optimum compression and eliminate
looseness during operation the laminations are hydraulically compressed and heated
during the stacking procedure. To remove the heat, spaced segments are placed at
intervals along the core length which divide the core into sections to provide wide
radial passages for cooling air to flow. Stampings are held in a position by 21 core
bars having dovetail section. Insulating paper pressboards are also put between the
layer of stamping to provide additional insulation and to localize short circuit. Between
two packets one layer of ventilating segments is provided. Steel spacers are spot
welded on stamping (for generators below 500 MW). These spacers form ventilating
ducts where the cold air from gas coolers enter the core radially inwards there by taking
away the heat generated due to eddy current losses. For 600 MW and above spring like
assembly of core stamping is done. Number of stampings used in one round is 10.5,
each stamping is of size 0.5 mm and core length is 6500 mm. So,
136500 stampings are used in a core.
ARRANGEMENT OF STAMPINGS
27
PROCEDURE OF CORE INSERTION
4.4.1.3 STATOR WINDING
4.4.1.3.1 Construction:-
Stator bars, phase connectors and bushings are designed for direct water cooling.
To minimize the stray losses, the bars are composed of separately insulated
strands which are transposed by 540 in the slot portion and bonded together with
epoxy resin in heated mold after bending the end turns are likewise bonded
together with baked synthetic resin filters.
The bar consist of solid and hollow strands distributed over the entire bar cross-
section so that good heat dissipation is ensured at the bar ends, all the solid strand
are jointly brazed into a connection sleeve and the hollow strands into a water box
from which the cooling water enters and exits via Teflon insulating hoses
connected to the annular manifolds.
28
The electrical connection between top and bottom bars is made by a bolted
connection at the connection sleeve. The water manifolds are insulated from stator
frame, permitting the insulation resistance of water-filled winding to be measured.
During operation water manifolds are grounded.
There are two types of stator winding :-
4.4.1.3.2 Hollow Winding
This type of winding is made up of copper.These windings are water cooled.This
type of winding is much superior to strip type winding because cooling is much
better.The end of each winding is connected to header in which water supply is
provided.
29
30
PIPE FOR WATER
ENTRANCE
4.4.1.3.3 Metallic Strip Type Winding
This type of winding is used in small size turbo generators because cooling is less
efficient and entirely depends upon cooling by gas.
31
METALLIC STRIPS
4.4.1.3.4FLOW CHART OF MANUFACTURING OF STATOR
WINDING
32
4.4.1.3.5 WATER SUPPLY
WATER SUPPLY INTO WINDINGS THROUGH HEADER
FROM BLACK PIPES OF TEFLON
The water connection at the stator bar is separate from the electrical connection.
As a result no electrical forces can act on the water connection.
33
TEFLON PIPES
Which the solid strands of the stator bars terminates at the connecting sleeve, the
hollow strands are beared into water boxes, with solid spacers inserted to
compensate for the solid strand. Each water box is consist of two part i.e., the
sleeve shaped lower part enclosing the hollow strands and the cover type upper
part the strand rows are separated from each other by spacers. Each water box is
provided with a pipe connection of non magnetic stainless steel for connection of
the hose. The exciter end water boxes serve for water admission and distribute the
cooling water uniformly to the hollow strand of the bars. The hot water is collected
on leaving the hollow strand in the turbine end water boxes. The cooling water is
then discharged from the generator via the hoses and the ring header.
High-voltage insulation is provided according to the proven Micalastic system.
With this insulation system, several half – over lapped continuous layer of mica tape
are applied to the bars. The mica tape is built 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., the thickness of the insulation depends on the
machine voltage. 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 vacuum, he bars are subjected to pressure,with nitrogen being
used as pressurizing medium (VPI process).
The impregnation bars are formed to the required shape in molds and cured in an
over 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 waterproof and oil resistant.
To minimize corona discharges between the insulation and slot wall, a final coat of
semi conducting varnish is applied to the surfaces of all bars within the slot range.
In addition, all bars are provided with an end corona protection, to control the
electric field at the transition from the slot to the end winding and to prevent the
formation of creep age spark concentrations.
4.4.1.3.6 INSULATION OF STATOR WINDING
34
class Y-upto 90 degree celsius
class A-upto 105 degree celsius
class E-upto 120 degree celsius
class B-upto 130 degree celsius
class F-upto 155 degree celsius
class H-upto 180 degree celsius
class C- > 180 degree celsius
4.4.1.3.6.2 TESTING OF INSULATION
4.4.1.3.6.1 TYPES OF INSULATION
∆ = Angle Of deviation
R4 = Resistance
C4*R4*10-4
=tan∆
Here C4 = Capacitance
This test is carried out to ensure the healthiness of dielectric (Insulation) i.e. dense
or rare and measured the capacitance loss. The capacitance of the bar is found and
the angle of deviation due to the impurity in the insulation is obtained from the formula
a) Tan∆ TEST:
Each bar is tested momentary at high voltage increased gradually to three times
higher than rated voltage.
b) H.V. TEST: (High Voltage Test)
35
The revolving magnetic field exerts a pull on the core, resulting in a revolving and
nearly elliptical deformation of the core which sets up a stator vibration at twice
the system frequency. To reduce the transmission of these dynamic vibrations
to the foundation, the generator core is spring mounted in the stator frame. The
core is supported in several sets of rings. Each ring set consists of two supporting
rings and two core clamping rings.
4.4.1.4 SPRING AND SPRING BASKET
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.
For firm coupling of the ring sets to the core, the supporting ring is solidly pressed
against the core by the clamping ring. The clamping ring consist of two parts which
are held together by two clamps.
Tightening the clamps reduces the gap between the ring segments so that the
supporting ring is pressed firmly against the core.
36
The lower springs prevents a lateral deflection of the core. The flat springs are
resilient to radial movements of the core suspension points and will largely resist
transmission of double frequency vibration to the frame. In the tangential direction
they are, however sufficiently rigid to take up the short circuit torque of the unit.
The entire vibration system is turned so as to avoid resonance with vibrations at
system frequency or twice the system frequency.
4.4.1.5 MAGNETIC SHUNT
Magnetic shunt is a type of ring which is used to confine the magnetic flux within
the stator. One ring is connected on turbine end and one ring is connected at exciter
end. These rings are made up of steel.
4.4.1.6 STATOR COOLING
4.3.1.6.1 COOLING OF WINDINGS
The end windings are enclosed by an annular water manifold to which all stator
bars are connected through hoses. The water manifolds is mounted on the holding
plates of the end winding support ring and connected to the primary water supply
pipe. This permits the insulation resistance of the water filled stator winding to be
measured. The water manifold is grounded during operation. For
measurement of the insulation resistance, eg. during inspection, grounding is
removed by opening the circuit outside the stator frame.
Each ring set is linked to the frame by three flat springs.The core is supported in the
frame via two vertical springs in the vicinity of the generator feet.
37
The hoses, one side of which is connected to ground, consist of a metallic section
to which the measuring potential is applied for measurement of the insulation
resistance of the water-filled stator winding.
The cooling water is admitted to three terminal bushings via a distribution water
manifold flows through the attached phase connectors and is then passed to the
distribution water manifold for water outlet via the terminal bushings on the
opposite side.
The parallel-connected cooling circuits are checked for uniform water flows by a
flow measurement system covering all three phases.
4.3.1.6.2 COOLING OF CORE
A) CO2 Supply:-
As a precaution against explosive mixtures, air must never be directly replaced
with hydrogen during generator filling nor the hydrogen replaced directly with air
during the emptying procedure. In both cases, the generation must be scavenged or
purged with an insert gas, carbon dioxide (CO2) being used for this purpose.
a) CO2 bottle rack:-
The CO2 is supplied in steel bottles in the liquid state. The bottle should be
provided with risers to ensure completely emptying. The arrangement of the CO2
bottle rack corresponds to that of H2 bottle rack. The liquid CO2 which is stored
under pressure, is fed to the gas valve rack via a shutoff valve.
b) CO2 flash Evaporator:-
At the gas valve rack the liquid CO2 is evaporated and expanded in a CO2 flash
evaporator. The heat for vaporization is supplied to the flash evaporator
electrically. A temperature control is provided so that freezing of the flash
evaporator is prevented, and the CO2 is admitted into the generator at the proper
temperature. One safety valve each on the high-pressure and low-pressure sides
protects the pipe system against inadmissibly high pressure.
38
Compressed Air Supply:-
To remove the CO2 from the generator, a compressed air supply with compressed
air filter is connected to the general air system of the power plant.
Under all operating conditions, except for CO2 purging, the compressed air hoses
between the filter and the generator pipe system should be disconnected. This
visible break is to ensure that no air can be admitted into a hydrogen-filled
generator.
B ) Nitrogen (N2) Supply:-
On a water-cooled turbine generator an additional nitrogen supply is required
for
a) Removing the air above the water level in the primary water tank during
initial operation of the primary water system.
b) Removing the oxygen dissolved in the primary water during filling of the
primary water system.
c) Removing the hydrogen gas above the water level in the primary water tank
during shutdown of the primary water system.
d) Removing the hydrogen gas dissolved in the primary water during shutdown
of the primary water system.
The N2 purge during initial operation ensures a compete removal of the oxygen
from the primary water circuit, thus eliminating the risk of corrosion attack.
The N2 purge during shutdown prevents the formation of an explosive
hydrogen-air mixture. During operation hydrogen may enter into the primary water
tank by diffusion at the insulating hoses.
The nitrogen available from a bottle is passed to a pressure reducer for expansion
and admitted into the primary water tank via the N2 supply line.
39
4.4.1.7 PRESS RINGS
The press ring is bolted to the ends of core bars. The pressure of the pressure ring is
transmitted to stator core stamping through press fringes of non-magnetic steel and
duralumin placed adjacent to press ring. To avoid heating of press ring due to end
leakage flow two rings made of copper sheet are used as flux shield. The ring
screens the flux by short-circuiting. To monitor the formation of hot spots resistance
transducer are placed along the bottom of slots. To ensure that core losses are within
limits and there are no hot spots present in the core. The core loss test is done after
completion of core assembly.
4.4.1.8 END RINGS
The end covers are made up of fabricated steel or aluminum castings. They are
employed with guide vans on inner side for ensuring uniform distribution of air or
gas. Cool air flows from sides and hot air flows in centre. Rotor fan sucks the hot air
which then passes through compressor and gets cool and circulates to core.
40
They are used to hold the bearings and shaft seal assembly. It is mounted on both the
ends of the stator.
41
UPPER SHIELD
LOWER SHIELD
4.4.1.9 TERMINAL BOX AND TERMINAL BUSHING
TERMINAL BOX
A) Arrangement of terminal bushing:-
The beginning and ends of the three phases windings are brought out from the
stator frame through terminal bushings, which provides 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. Bushing-type generator current transformers for metering
and relaying are mounted on the bushing outside the generator terminal box. The
customers bus is connected to the air side connection flange of the bushings via
terminal connectors
The generator terminal box located beneath the stator frame at the exciter end
is made from non-magnetic steel to avoid eddy-current losses and resulting
temperature rises.
42
B) Construction of Bushings:-
The cylindrical bushing conductor consist of high conductivity copper with a
central bores for direct primary water cooling.
The insulator is wound directly over the conductor. It consist of impregnated
capacitor paper with conducting fillers for equalization of the electrical direct-axis
and quadrature-axis fields.
The shirunk-on mounting sleeve consist of a gas tight casting of
nonmagnetic steel with a mounting flange and a sleeve type extension extending
over the entire height of the current transformers.
The cylindrical connection ends of the terminal bushing conductors are silver
plated and designed to accommodate bolted two part cast terminal connectors.
Connection to the beginning and each phase inside the terminal box and to the
external bus in by means of flexible connectors. To maintain a uniform and
constant contact pressure, Belleville washers are used for all bolted connections.
TERMINAL BUSHING
43
4.3.2 ROTOR
Rotor rotates in most modern generator at speed of 3000 rotations per minute. It is
also an electromagnet and to give it necessary magnetic strength, the winding must
carry a very high current. The passage of current through windings generates heat.
But the temperature must not be allowed to become too high, otherwise difficulties
will be experienced with insulation. To keep the temperature cross section of the
conductors could not be increased but this would introduce another problems. In
order to make room for large conductor, body and this would cause mechanical
weakness. With good design and great care this problem can be solved.
4.4.2.1 ROTOR SHAFT
ROTOR SHAFT AT INITIAL STAGE
44
SLOTS CUTTING IN ROTOR SHAFT
STEPS INVOLVED IN MACHINING OF ROTOR
45
SLOTS
ROTOR AFTER CUTTING SLOTS
METAL OXIDE PAINT ON ROTOR
46
ROTOR POLES
The high mechanical stresses resulting from the centrifugal forces and short- circuit
torques call for a high quality heat-treated steel. Therefore, the rotor shaft is forged
from a vacuum cast steel ingot. Comprehensive tests ensure adherence to the
specified mechanical and magnetic properties as well as a homogeneous
forging.
The rotor shaft consists of an electrically active portion, the so called rotor body,
and the two shaft journals. Integrally forged flange couplings to connect the rotor
to the turbine and exciter are located out board of the bearings.
Approximately two-thirds of the rotor body circumference is provided with
longitudinal slots which hold the field winding slot pitch is selected so that the two
solid poles are displaced by 180.
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 at twice the system frequency. To reduce these
vibrations the deflections in the direction of the pole axis and neutral axis are
compensated by transverse slotting of the pole.
The solid pole are also provided with additional longitudinal slots to hold the
copper bars of the damper winding. The rotor wedges act as a damper winding in
the area of winding slot.
Details of shaft are given here –
Length = 9 meter (approx.)
Diameter = 1 meter (approx.)
Material – alloy steel
Number of poles = 2
4.4.2.2 ROTOR WINDING
The winding consist of several coils inserted into the slots and the series connected
such that two coils group forms one pole. Each coil consist of several series
connected turns each of which consist of two half turns connected by brazing in end
section.
47
The individual turn of coil are insulated against each other by interlayer
insulation. L-shaped strip of laminated epoxy glass fiber with nomex filter are used
for slot insulation. The slot wedges are made up of high electrical conductivity
material and thus act as damper winding. At their ends, the slots wedges are short
circuited through the rotor body. When rotor is rotating at high speed, the centrifugal
forces tries to lift the winding out of slots, they are contained by wedges. The field
winding consists of several series connected coils into the longitudinal slots of body.
The coil is wound such that two poles are obtained. The solid conductors have a
rectangular cross-section and are provided with axial slots for radial cooling air. All
conductors have identical copper and cooling section.
ROTOR WINDING
4.4.2.2.1 CONDUCTOR MATERIAL OF WINDING
The conductors are made up of copper with silver content of approx. 0.1%. As
compared to electrolytic copper silver alloyed copper features high strength
properties at high temperature so that coil deformations due to thermal stresses are
eliminated. The conductors are made of hard drawn silver bearing copper.
48
The rectangular cross section copper conductors have ventilating ducts on the two
sides thus providing a channel for hydrogen flow. Two individual conductors placed-
one over the other are bent to obtain half turns. Further these half turns are brazed in
series to form coil on the rotor model.
4.4.2.2.2 INSULATION
The insulation between the individual turns is made up of layer of glass fiber
laminate. The coils are insulated from the rotor body with L-shaped strip of glass
fiber laminated to obtain the required leakage path between the coil and rotor body
thick top strips of glass fiber laminate are inserted below wedge. The top strip are
provided with axial slots of same cross-section and spacing and used on the rotor
winding.
4.4.2.3 ROTOR SLOT WEDGES
To protect the winding against the effects of the centrifugal force, the
winding is secured in the slots with wedges. The slot wedges are made from a
copper-nickel-silicon alloy featuring high strength and good electrical
conductivity, and are used as damper winding bars. The slot wedges extend below
the shrink seats of the retaining rings. The rings act as short-circuit rings to induced
currents in the damper windings.
49
ROTOR WEDGES
54
4.4.2.4 ROTOR TERMINALS
These terminals are connected to the excitation system and this side of rotor is
fixed with excitation system.
50
TERMINALS
4.4.2.5 RETAINING RING & CENTERING ASSEMBLY
The centrifugal forces of the end windings are contained by piece rotor retaining
rings. Retaining rings are made up of non-magnetic high strength steel in order to
reduce the stray losses. Each retaining ring with its shrink fitted. Insert ring is
shrunk on the rotor is an overhang position. The retaining ring is secured in the
axial position by snap rings. The rotor retaining rings withstand the centrifugal
forces due to end winding. One end of each ring is shrunk fitted on the rotor body
while the other hand overhangs the end winding without contact on the rotor shaft.
This ensures unobstructed shaft deflection at end windings. The shrunk on hub on
the end of the retaining ring serves to reinforce the retaining ring and serves the end
winding in the axial direction. At the same time, a snap ring is provided against
axial displacement of retaining ring. The shrunk slot of current to reduce the stray
losses and have high strength, the rings are made up of non-magnetic cold worked
material.
51
4.4.2.6 COMPRESSOR HUB
The compressorhub is a type of ring which is made up of structural
steel. The blades of rotor fan are put on compressorhub.
4.4.2.7 ROTOR FAN
The generator cooling gas is circulated by one axial-flow fan located on the
turbine-end shaft journal. To augment the cooling of the rotor winding, the
pressure established by the fan works in conjunction with the gas expelled from the
discharge parts along the rotor.
The moving blades of the fan are inserted into T-shaped grooves in the fan hubs.
The fan hubs are shrink-fitted to the shaft journal spider.
52
ROTOR FAN BLADES
53
The rotor shaft is supported in sleeve bearings having forced-oil lubrication. The
bearings are located in the stator end shields. The oil required for bearing
lubrication and cooling is obtained from the turbine oil system and supplied to the
lubricating gap via pipes permanently installed inside the lower half of the stator end
shield and via grooves in the bearing sleeves.
The lower bearing sleeve rests on the bearing saddle via three brackets with
spherical support sets for self-alignment of the bearing. The bearing saddle is
insulated from the stator end shield and the bearing bracket are insulated from the
bearing sleeve to prevent the flow of shaft currents and to provide for double
insulation of the generator bearing from ground. A radial locator serves to locate
the bearing in the vertical direction and is bolted to the upper half of the stator end
shield. The locator is adjusted to maintain the required clearance between the
bearing sleeve and the insulation of the radial locator.
All generator bearings are provided with a hydraulic shaft lift oil system to reduce
bearing friction during start up. High pressure oil is forced between the bearing
surface and the shaft journal, lifting the rotor shaft to allow the formation of the
lubricating oil film.
The bearing temperature is monitored with one double element
thermocouple located approximately in the plane of maximum oil film pressure.
With this type of shaft seal, the escape of hydrogen between the rotating shaft
and the housing is prevented by maintaining a continuous film of oil between the
shaft and a non-rooting floating seal ring. To accomplish this, seal oil from two
separate circuits i.e., the air side and hydrogen side seal oil circuits, is fed to the
seal ring at a pressure slightly higher than the hydrogen pressure. In addition,
higher pressure air side oil is supplied to the shaft seal for thrust load compensation
of the seal ring.
55
5. BEARINGS
6.SHAFT SEAL
7. COOLING OF ROTOR
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.
The cooler consists of individual sections for vertical mountings. This
arrangement permits the coolers to be mounted without an increase in the overall
generator axial length or cross-sectional area of the stator frame.
The hydrogen flows through the coolers in the horizontal direction. The cold
cooling water flows from the bottom to the top end of the cooler on the cold gas
side and, after reversal in the return water channel, the heated water flows
downward on the hot gas side. This cooling water flow passage is obtained through
a partition in the inlet / outlet water channel.
56
HOLES IN ROTOR WNDING FOR HYROGEN GAS
CIRCULATION
The basic use of given exciter system is to produce necessary DC for turbo
generator system.
57
The Exciter consist of -:
1.Rectifier wheels
2.Three phase main Exciter
3.Three phase pilot Exciter
4.Cooler
8. EXCITER
The three phase pilot exciter has a revolving field with permanent-magnet poles.
The three-phase ac generated by the permanent-magnet pilot exciter is
rectified and controlled by the TVR to provide a variable dc current for exciting
the main exciter. The three phase ac induced in the rotor of the main exciter is
rectified by the rotating rectifier bridge and fed to the field winding of the
generator rotor through the dc leads in the rotor shaft.
A common shaft carrier the rectifier wheels, the rotor of the main exciter and the
permanent-magnet rotor of the pilot exciter. The shaft is rigidly coupled to the
generator rotor. The exciter shaft is supported on a bearing between the main and
pilot exciters. The generator and exciter rotors are thus supported on total of three
bearings.
Mechanical coupling of the two shaft assemblies results in simultaneous coupling
of the dc leads in the central shaft bore through the multi contact electrical contact
system consisting of plug-in bolts and sockets. This contact system is also
designed to compensate for length variations of the leads due to thermal expansion.
58
8.1 MAIN EXCITER
The three-phase main exciter is a six-pole revolving-armature unit. Arranged in the
stator frame are the poles with the field and damper winding. The field
winding is arranged on the laminated magnetic poles. At the pole shoe bars are
provided, their ends being connected so as to form a damper winding. Between
two poles a quadrature-axis coil is fitted for inductive measurement of the
exciter current.
The rotor consist of stacked laminations, which are compressed by through bolts
over compression rings. The three phase winding is inserted in the slots of the
laminated rotor. The winding conductors are transposed within the core length and
the end turns of the rotor winding are secured with steel bonds. The connections
are made on the side facing the rectifier wheels. The winding ends are run to a bus
ring system to which the three phase leads to the rectifier wheels are also
connected. After full impregnation with synthetic resin and curing, the complete
rotor is shrunk on to the shaft.
A general bearing is arranged between main exciter and pilot exciter and has
forced-oil lubrication from the turbine oil supply.
SHAFT OF EXCITER
59
MAIN EXCITER ARMATURE
60
MAIN EXCITER STATOR
8.3 COOLINGOF EXCITER
FAN
61
ROTOR OF PMMG
The three-phase pilot exciter is a 16 pole revolving-field unit. The frame
accommodates the laminated core with the three-phase winding. The rotor consist
of a hub with mounted poles. Each pole consist of 10 separate permanent magnets
which are housed in a non-magnetic metallic enclosure. The magnets are braced
between the hub and the external pole shoe with bolts. The rotor hub is shrunk onto
the free shaft end.
8.2 PILOT EXCITER
The exciter is air cooled. The cooling air is circulated in a closed circuit and
recooled in two cooler sections arranged alongside the exciter.
The complete exciter is housed in an enclosure through which the cooling air
circulates.The rectifier wheels, housed in their own enclosure, draw the cool air in
at both ends and expel the warmed air to the compartment beneath the base plate.
The main exciter enclosure receives cool air from the fan after it passes over the
pilot exciter. The air enters the main exciter from both ends and is passed into
ducts below the rotor body and discharged through radial slots in the rotor core to
the lower compartment. The warm air is then returned to the main enclosure via
the cooler sections.
8.4 RECTIFIER WHEEL
The main components of the rectifier wheels are the silicon diodes which are
arranged in the rectifier wheels in a three phase bridge circuit. The contact pressure
for the silicon wafer is produced by a plate spring assembly. The arrangement of
the diode is such that this contact pressure is increased by the centrifugal force
during rotation.
Additional components are contained in the rectifier wheels. Two diodes each are
mounted in each aluminum alloy heat sink and thus connected in parallel.
Associated with each heat sink is a fuse which serves to switch off the two diodes
if one diode falls (Loss of reverse blocking capacity).
For suppression of the momentary voltage peaks arising from commutation, each
wheel is provided with six RC networks consisting of one capacitor and one
damping resistor each, which are combined in a single resin-encapsulated unit.
62
63
The insulated and shrunken rectifier wheels serves as dc buses for the
negative and positive side of the rectifier bridge. This arrangement ensures good
accessibility to all components and a minimum of circuit connections. The two
wheels are identical in their mechanical design and differ only in the forward
direction of the diodes.
The direct current from the rectifier wheels is fed to the dc leads arranged in the
center bore of the shaft via radial bolt.
The three-phase alternating current is obtained via copper conductors arranged on
the shaft circumference between the rectifier wheels and the three- phase main
exciter. The conductors are attached by means of banding clips and equipped with
screw-on lugs for the internal diode connection. One three phase conductor each is
provided for the four diodes of a heat sink set.
9. LOSSES IN TURBO GENERATOR
The power lost in the form of heat in the armature winding of a generator is known
as Copper loss. Heat is generated any time current flows in a conductor.
loss is the Copper loss, which increases as current increases. The amount of
heat generated is also proportional to the resistance of the conductor. The resistance
of the conductor varies directly with its length and inversely with its cross-
sectional area. Copper loss is minimized in armature windings by using large
diameter wire. Copper loss is again divided as
(i) Armature copper loss
= Armature copper loss. Where Ra =resistance of armature and inter poles
and series field winding etc. This loss is about 30 to 40% of full -load losses.
(ii) Field copper loss : It is the loss in series or shunt field of generator.
is the field copper loss in case of series generators, where Rse is the resistance of
the series field winding.
9.1 COPPER LOSSES
64
is the field copper loss in case of shunt generators.
i) Hysteresis loss (Wh)
Hysteresis loss is a heat loss caused by the magnetic properties of the armature.
When an armature core is in a magnetic field, the magnetic particles of the core
tend to line up with the magnetic field. When the armature core is rotating, its
magnetic field keeps changing direction. The continuous movement of the
magnetic particles, as they try to align themselves with the magnetic field, produces
molecular friction. This, in turn, produces heat. This heat is transmitted to the
armature windings. The heat causes armature resistances to increase. To
compensate for hysteresis losses, heat-treated silicon steel laminations are used in
most dc generator armatures. After the steel has been formed to the proper shape,
the laminations are heated and allowed to cool. This annealing process reduces the
hysteresis loss to a low value.
(ii) Eddy Current Loss (We)
The core of a generator armature is made from soft iron, which is a conducting
material with desirable magnetic characteristics. Any conductor will have currents
induced in it when it is rotated in a magnetic field. These currents that are induced
in the generator armature core are called EDDY CURRENTS. The power
dissipated in the form of heat, as a result of the eddy currents, is considered a loss.
Eddy currents, just like any other electrical currents, are affected by the resistance
of the material in which the currents flow. The resistance of any material is
inversely proportional to its cross-sectional area. Figure, view A, shows the eddy
currents induced in an armature core that is a solid piece of soft iron. Figure, view
B, shows a soft iron core of the same size, but made up of several small pieces
insulated from each other. This process is called lamination.
9.2 MAGNETIC LOSSES (also known as iron or core losses)
65
The currents in each piece of the laminated core are considerably less than in the
solid core because the resistance of the pieces is much higher. (Resistance is
inversely proportional to cross-sectional area.) The currents in the individual pieces
of the laminated core are so small that the sum of the individual currents is much
less than the total of eddy currents in the solid iron core.
As we can see, eddy current losses are kept low when the core material is made up
of many thin sheets of metal. Laminations in a small generator armature may be as
thin as 1/64 inch. The laminations are insulated from each other by a thin coat of
lacquer or, in some instances, simply by the oxidation of the surfaces. Oxidation is
caused by contact with the air while the laminations are being annealed. The
insulation value need not be high because the voltages induced are very small.
Most generators use armatures with laminated cores to reduce eddy current losses.
These consist of
(i) friction loss at bearings
(ii) air-friction or windage loss of rotating armature
These are about 10 to 20% of F.L losses.
9.3 MECHANICAL AND ROTATIONAL LOSSES
66
Careful maintenance can be instrumental in keeping bearing friction to a minimum.
Clean bearings and proper lubrication are essential to the reduction of bearing
friction.Brush friction is reduced by assuring proper brush seating, using proper
brushes, and maintaining proper brush tension. A smooth and clean commutator also
aids in the reduction of brush friction.
Usually, magnetic and mechanical losses are collectively known as Stray Losses.
These are also known as rotational losses for obvious reasons.
67
 Electrical Machine - P.S. Bhimbra
 Electrical Machine - Assfaq Hussain
 BHEL Haridwar Website – www.bhelhwr.co.in
 http://etrical.blogspot.in/2016/04/brushless-excitation-system.html
 http://www.slideshare.net/khemraj298/bhel-haridwar-vocational-training-
report
68
11.BIBLIOGRAPHY AND REFERENCES
The vocational training at Bharat Heavy Electrical, Haridwar is an experience worth
having. I learnt a lot, not only about manufacturing of turbo-generator and its various
components but also the manufacturing of turbine, brushless exciter, stator & rotor
windings, coil & insulation manufacturing, Computer Numerical Control system etc.
69
11.CONCLUSION

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BHEL HARIDWAR TRAINING REPORT

  • 1. DEPARTMENT OF ELECTRICAL ENGINEERING RAJASTHAN TECHNICAL UNIVERSITY, KOTA A VocationalTraining Report On Turbo Generator & Excitation System At BHARAT HEAVY ELECTRICALS LIMITED, HARIDWAR Submitted in partial fulfilment of the requirement for the award of the degree OF Bachelor of Technology Session: 2013-2017 TENURE OF TRAINING 28 MAY,2016 to 26 JULY,2016 SUBMITTED TO : SUBMITTED BY : DR. ANNAPURNA BHARGAV YASH KUMAR NATANI ( PROFESSOR ) B.TECH , FINAL YEAR MR. ASHOK KUMAR SHARMA ELECTRICAL ENGG. ( ASSOCIATE PROFESSOR ) C.R. NO. 13/095 1
  • 3. PREFACE It is a matter of great pleasure for me to present the following repost on my INDUSTRIAL TRAINING at BHEL HARIDWAR, otherwise one seldom gets a chance to go through any industry after on the job training/placement. It outlines the course of project work during my training in an oriented manner over a period of 60 days of B. Tech. 7 th Sem. Electrical Engineering. I have tried my best to present this training report in a very precise and profitable manner. Any suggestions in this direction will be gratefully accepted. Engineering students gain theoretical knowledge only through their books. Only theoretical knowledge is not sufficient for absolute mastery in any field. Theoretical knowledge give in our books is not sufficient without knowing its practical implementation. It has been experienced that theoretical knowledge is volatile in nature however makes solid foundation in our mind. 3 The training report consists of construction of Turbo generator and excitation system & constructional features of main parts of BHARAT HEAVY ELECTRICAL LIMITED, Haridwar. Adequate diagrams and layouts have been provided for a more descriptive outlook and clarity of understanding.
  • 4. ACKNOWLEDGEMENT “An engineer with only theoretical knowledge is not a complete engineer. Practical knowledge is very important to develop and to apply engineering skills”. It gives me a great pleasure to have an opportunity to acknowledge and to express gratitude to those who were associated with me during my training at BHEL. Special thanks to DR. DINESH BIRLA ( HOD Department of Electrical Engineering, Rajasthan Technical University , Kota) for allowing me to undergo 60 days vocational training. I would like to thank MR. SATISH KUMAR SINGH ( Engineer , Electrical Machine Planning Block 1,BHEL Haridwar ) under whose dexterous guidance I learned all I could. I express my sincere thanks and gratitude to BHEL authorities for allowing me to undergo the training in this prestigious organization. I will always remain indebted to them for their constant interest and excellent guidance in my training work, moreover for providing me with an opportunity to work and gain experience. Lastly, I would like to thank almighty and my parents for their moral support and my friends whom with I shared my experience day by day and received lots of suggestions that improved my quality of work 4
  • 5. INDEX 1. INTRODUCTION 2. BHEL’S CONTRIBUTION IN DIFFERENT SECTORS 3. BHEL HARIDWAR 4. TURBO GENERATORS 4.4.1 STATOR 5 1.1 BHEL’S UNITS IN INDIA 8 1.2 A BRIEF HISTORY 9 2.1 POWER SECTOR 10 2.2 TRANSMISSION 10 2.3 TRANSPORTATION 11 2.4 INTERNATIONAL OPERATION 11 2.5 RENEWABLE ENERGY 11 2.6 INDUSTRIES 11 3.1 AN OVERVIEW 13-15 3.2 PRODUCTS 16-17 4.1 SYNOPSIS 18 4.2 WORKING 18-19 4.3 LARGE SIZE TURBO GENERATORS 20 4.4 COMPONENTS OF TURBO GENERATOR 21-22 4.4.1.3 STATOR WINDING 4.4.1.3.1 CONSTRUCTION 28 4.4.1.3.2 HOLLOW WINDING 29-30 4.4.1.3.3 METALLIC STRIP WINDING 31 4.4.1.1 STATOR FRAME 23-24 4.4.1.2 STATOR CORE 25-28 4.4.1.2.1 STAMPINGS
  • 6. 4.4.1.6 STATOR COOLING 4.4.2 ROTOR 6 4.4.1.3.4 FLOW CHART OF WINDING MANUFACTURING 32 4.4.1.3.5 WATER SUPPLY 33-34 4.4.1.3.6.1 TYPES OF INSULATION 35 4.4.1.3.6.2 TESTING OF INSULATION 35 4.4.1.4 SPRING AND SPRING BASKET 36-37 4.4.1.3.6 INSULATION OF STATOR WINDING 34 4.4.1.5 MAGNETIC SHUNT 37 4.4.1.6.1 COOLING OF WINDINGS 37-38 4.4.1.6.2 COOLING OF CORE 38-39 4.4.1.7 PRESS RINGS 40 4.4.1.8 END RINGS 40-41 4.4.1.9 TERMINAL BOX AND TERMINAL BUSHING 42-43 4.4.2.1 ROTOR SHAFT 44-47 4.4.2.2 ROTOR WINDING 4.4.2.2.1 CONDUCTOR MATERIAL OF WINDING 47-48 4.4.2.2.2 INSULATION 49 4.4.2.3 ROTOR SLOT WEDGES 49-50 4.4.2.4 ROTOR TERMINALS 51 4.4.2.5 RETAINING RING AND CENATARING ASSEMBLY 52 4.4.2.6 COMPRESSOR HUB 53 4.4.2.7 ROTOR FAN 53-54 5. BEARINGS 55 6. SHAFT SEAL 55
  • 7. 9. LOSSES IN TURBO GENERATOR 7 7. COOLING OF ROTOR 56-57 8. EXCITER 57-58 8.1 MAIN EXCITER 59-60 8.2 PILOT EXCITER 61 8.3 COOLING OF EXCITER 61-62 8.4 RECTIFIER WHEEL 62-64 9.1 COPPER LOSSES 64-65 9.2 MAGNETIC LOSSES 65-66 10. BIBLIOGRAPHY AND REFERENCES 68 9.3 MECHANICAL AND ROTATIONAL LOSSES 66-67 11. CONCLUSION 69
  • 8. 1.INTRODUCTION In 1956 India took a major step towards the establishment of its heavy engineering industry when Bharat Heavy Electricals Limited, the first heavy electrical manufacturing unit of the country was set up at Bhopal. It progressed rapidly and three more factories went into production in 1956. The aim of establishment BHEL was to meet the growing power requirement of the country. BHEL has supplied 97% of the power generating equipment that was commissioned in India during 1979-80. BHEL has supplied generating equipment to various utilities capable of generating over 18000MW power. BHEL is one of the largest power plant equipment manufacturing firms in India and it ranks among the top ten manufacturers globally. BHEL has covered up many power stations over 40 countries worldwide. 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 division includes a network of regional offices throughout India. 1.1 BHEL’S UNITS IN INDIA S. NO. CITY PLANTS 1. HARIDWAR 2 2. BHOPAL 1 3. JHANSI 1 4. JAGDISHPUR 2 5. HYDERABAD 1 6. GOINDWAL 1 7. TIRUCHIRAPALLI 2 8. THIRUMAYAM 1 9. BANGLORE 3 10. RUDRAPUR 1 11. PANIPET 1 12. VISHAKHAPATNAM 1 8
  • 9. 1.2 A BRIEF HISTORY The first plant of what is today known as BHEL was established nearly 40 years ago at BHOPAL and was genesis of Heavy Electrical Equipment industry in India. BHEL is today the largest engineering enterprise of its kind in India, with a well- recognized track record of performance making profits continuously since 1971- 72. It achieved a sales turnover of Rs.1022 core in 1997-98. BHEL caters to core sectors of the Indian Economy via, Power, Industry, Transportation, Defense, etc. The wide network of BHEL’s 14 manufacturing divisions, 9 service centers & 4 power Sector Regional centers & about 150 project sites enables the service at competitive prices. Having attained ISO 9000 certification, BHEL is now embarking upon the Total Quality Management. The company’s inherent potential coupled with its strong performance over the years, has resulted in it being chosen as one of the― MAHARATNA PSUs (on 1 February 2013), which are to be supported by the Government in their endeavor to become future global players. It is the 7th largest power equipment manufacturer in the world. In the year 2011, it was ranked ninth most innovative company in the world by US business magazine Forbes. BHEL is the only Indian Engineering company on the list, which contains online retail firm Amazon at the second position with Apple and Google at fifth and seventh positions, respectively. It is also placed at 4th place in Forbes Asia's Fabulous 50 List of 2010 9
  • 10. 2.BHEL’ S CONTRIBUTION IN DIFFERENT SECTORS 2.1 POWER SECTOR 2.2 TRANSMISSION Power sector comprises thermal, nuclear, gas & hydro power plant business. Today, BHEL supplied sets account for nearly 56,318 MW or 65% of the total installed capacity of 86,636 MW in as against nit till 1969-1970.BHEL has proven turnkey capabilities for executing power projects from concept to commissioning. It possesses the technology and capability to produce thermal power plant equipment upto 1000MW rating and gas turbine generator sets up to a unit rating of 240 MW. Cogeneration and combined cycle plants have been introduced to achieve higher plant efficiencies. To make efficient use of the high ash content coal available in India, BHEL supplies circulating fluidized bed boilers to thermal and combined cycle power plants. BHEL manufacturers 235 MW nuclear turbine generator sets and has commenced production of 500 MW nuclear turbine generator sets. Custom- made hydro sets of Francis, Pelt on and Kaplan types for different head- discharge combinations are also engineered and manufactured by BHEL is based upon contemporary technology comparable to the best in the world & is also internationally competitive. BHEL also supplies a wide range of transmission products and systems up to 400 KV Class. These include high voltage power and distribution transformers, instrument transformers, dry type transformers, SF6 switchgear, capacitors, and insulators etc. For economic transmission bulk power over long distances, High Voltage Direct Current (HVDC) systems are supplied. Series and Shunt Compensation Systems have also been developed and introduced to minimize transmission losses. A strong engineering base enables the Company to undertake turnkey delivery of electric substances up to 400 kV level series compensation systems (for increasing power transfer capacity of transmission lines and improving system stability and voltage regulation), shunt compensation systems (for power factor and voltage 7improvement) and HVDC systems (for economic transfer of bulk power). BHEL has indigenously developed the state-of-the-art controlled shunt reactor (for reactive power management on long transmission lines). Presently a 400 kV Facts (Flexible AC Transmission System) project under execution. 10
  • 11. . 2.3 TRANSPORTATION 2.4 INTERNATIONAL OPERATION 3000MW. The company’s overseas presence includes projects in various countries. A few notable ones are -150 MW (ISOI) gas turbine to Germany, utility boilers and open cycle gas turbine plants to Malaysia, Tripoli-west, and power station in Libya executed on turnkey basis, thermal power plant equipment to Malta and Cyprus, Hydro generators to New Zealand and hydro power plant equipment to Thailand. BHEL has recently executed major gas-based power projects in Saudi Arabia and Oman, a Boiler contract in Egypt and several Transformer contracts in Malaysia and Greece. 2.5 RENEWABLE ENERGY Technologies offered by BHEL for non-conventional and renewable sources of energy include: wind electric generators, solar photovoltaic system, stand alone and grid-interactive solar power plants, solar heating systems, solar lanterns and battery-powered road vehicles. The company has taken up R&D efforts for development of multi-junction amorphous solar cells and fuel cells based systems. 2.6 INDUSTRIES BHEL is a major contributor of equipment and systems to industries: cement, sugar, fertilizer, refineries, paper, oil and gas, metallurgical and process industries. The company is a major producer of large-size thyristor devices. A high percentage of trains operated by Indian Railways are equipped with BHEL’s traction and traction control equipment including the metro at Calcutta. The company supplies broad gauge electrical locomotives to Indian Railways and diesel shunting locomotives to various industries.5000/6000 hp AC/DC locomotives developed and manufactured by BHEL have been leased to Indian Railways. Battery powered road vehicles are also manufactured by the company. BHEL’s products, services and projects have been exported to over 50 countries ranging from United States in the west to New Zealand in Far East. The cumulative capacity of power generating equipment supplied by BHEL outside India is over 11
  • 12. It also supplies digital distributed control system for process industries and control & instrumentation systems for power plant and industrial application. The range of system & equipment supplied includes: captive power plants,co-generation plants DG power plants, industrial steam turbines, industrial boilers and auxiliaries. Water heat recovery boilers, gas turbines, heat exchangers and pressure vessels, centrifugal compressors, electrical machines, pumps, valves, seamless steel tubes, electrostatic precipitators, fabric filters, reactors, fluidized bed combustion boilers, chemical recovery boilers and process controls. The Company is a major producer of large-size thruster devices. It also supplies digital distributed control systems for process industries, and control & instrumentation systems for power plant and industrial applications. BHEL is the only company in India with the capability to make simulators for power plants, defense and other applications. 12
  • 13. 3.BHEL HARIDWAR 3.1 AN OVERVIEW At the foothills of the majestic Himalayas & on the banks of a holy Ganges in Ranipur near HARIDWAR is located Heavy Electricals Equipment Plant of Bharat Heavy Electrical Ltd. BHEL,wholly owned by the government of India is an integrated engineering complex consisting of several plants in India, where about 70,000 workers are busy in design &manufacturing of a wide range of heavy electrical equipment. At present 70% of the Country’s electrical energy is generated by the sets manufacturing by BHEL, Haridwar. BHEL HARIDWAR is broadly divided in to two parts: A) CFFP: – Central Foundry Forge Plan CFFP is divided in to following shops : 13
  • 14.  Steel Melting Shop (SMS)  Steel Foundry  Pattern Shop  Cast Iron (CI) Foundry  Machine shop  Forge shop B) HEEP: – Heavy Electrical Equipment Plant HEEP is divided in to following shops: S. NO. BLOCK MAJOR FACILITIES PRODUCTS 1. Block-I (Electrical Machines ) Turbo generators, exciters, Motors (AC & DC). 2. Block-II (Fabrication Block) Marking, cutting, straightening, gas cutting, press, welding grinding, assembly, heat treatment, cleaning and shot blasting, machining, fabrication of pipe coolers, painting Large size fabricated assembles/ components for power equipments 3. Block-III (Turbine and Auxiliary block) Machining,assembly, preservation and packing, test stands/ station, painting, Steam turbines, hydro turbines, gas turbines, turbine blades,special Machine shop, winding bar preparation, assembling, painting section,packing and preservation, oven speed balancing,test bed, test stand, micalastic impregnation, babbitting etc. 14
  • 15. 4. Block-IV (Feeder block) Bar winding, mechanical assembly, armature windings, sheet metal working, machining, copper profile drawing, electroplating, impregnation, machining and preparation of insulating components plastic moulding, press moulding Windings for turbo generators, hydro generators, insulation for AC and DC motors, insulating components for TG, HG and Motors, control panels, contact relays, master control etc. 5. Block-V Fabrication, pneumatic hammer for forging, gas fired furnaces, hydraulic manipulators. Fabricated parts of steam turbine water box, storage tank, hydro turbines assemblies and components 6. Block-VI (Fibrication) Welding, drilling shot blasting, CNC flame cutting, CNC deep drilling, shot blasting, sheet metal work, assembly Fabricated oil tanks, hollow guide blades, rings,stator frames, rotor spiders.7. Block-VI (Stamping and Dia manufacturing) Machining, turning, grinding, jig boring, stamping press, de- varnishing, de-greasing, de- rusting, varnishing, spot welding, painting. All types of dies, including stamping dies and press forms stamping for generators & motors. 15
  • 16. 3.2 PRODUCTS 1. Turbo Generator 2. Excitation System 3. Heat Exchanger S. NO. PRODUCT IMAGE 16 IMAGE
  • 17. 4. Condenser 5. Steam and Gas Turbine 17
  • 18. 4.TURBO GENERATOR 4.1 SYNOPSIS OF THE FUNCTION OF TURBO GENERATOR The generator rotor is driven by prime mover and on driver side gas/ diesel/ steam hydro depending on the equipment to which it is meant for. The non- drive side of rotor is equipped with a rotating side of armature which produces AC voltage. This is rectified to DC by using a DC commutator/rotating diode wheel depending upon the type of exciter. The rear end of above exciter armature is mounted with a permanent magnet generator rotor. As the above rotating system put into operation, the PMC produces AC voltage. The voltage is rectified by thyristor circuit to DC. This supply is given to exciter field. This field is also controlled by taking feedback from main generator terminal voltage, to control exciter field variation by automatic voltage regulator. The rectified DC supply out of exciter is supplied to turbo generator rotor winding either through brushes or central which will be directly connected to turbo generator. This depends on the type of exciter viz. DC commutator machines or brushes exciter. The main AC voltage of generator is finally available to turbo generator stator. 4.2 PRINCIPLE OF WORKING The AC generator or alternator is based on the principle of electromagnetic induction and consist generally of a stationery part called Stator and a rotating part called Rotor.Stator houses the armature winding. The rotor houses the field winding. DC voltage is applied to field winding through the slip rings. 18
  • 19. When the rotor rotates, the lines of magnetic flux cut through the winding..This induces an electromagnetic EMF in the stator winding. The magnitude of emf is given by following formula E = 4.44* ø *ƒ*T volt Where, ø= useful magnetic flux per pole in Weber ƒ= frequency in hertz T = number of turns in stator winding ƒ = frequency = P*N / 120 Where, P = number of poles N = number of rotations per minute of rotor 19
  • 20. 4.3 LARGE SIZE TURBOGENERATOR (LSTG) The generators may be classified on the basis of cooling system used in it. Main types are: 1. THRI 2. TARI 3. THDI 4. THDD 5. THDF 6. THFF T => first alphabet stands for the type of generator – turbo-generator or hydro generator. H/A => second alphabet stands for the cooling media used for the cooling of rotor i.e. hydrogen gas or air. R/D/F/I => third alphabet stands for the type of cooling of rotor e.g. radial, direct, forced, indirect, etc. I/D/F => last alphabet stands for the type of cooling for stator e.g. indirect, direct or forced cooling. 20
  • 21. 4.3 COMPONENTS OFTURBOGENERATOR 4.3.1 STATOR  Stator frame  Stator core  Stator winding  Spring & Spring Basket  Magnetic Shunt  Stator Cooling  Press Rings 21
  • 22.  End Rings  Terminal Box & Terminal Bushing 4.3.2 ROTOR  Rotor winding  Rotor retaining rings 4.4 BEARINGS 4.5 COOLING SYSTEM 4.6 EXCITATION SYSTEM 4.7 SHAFT SEAL  ROTOR SHAFT 22
  • 23. 4.4.1 STATOR CROSS SECTIONAL VIEW OF STATOR FRAME 4.4.1.1 STATOR FRAME 23 PIPE FOR COOLING GAS
  • 24. Stator frame is made up of structural steel. The stator frame consist of a cylindrical center section and two end shields which are gas tight and pressure resistant. The stator end shields are joined and sealed to the stator frame with an O- ring and bolted flange connection the stator frame accommodates the electrically active part of the stator, i.e. the stator core and the stator windings. Both the gas ducts and a large number of welded circular ribs provides for the rigidity of the stator frame. Ring shaped support for resilient core suspension are arranged between the circular ribs. The generator cooler is subdivided into cooler sections arranged vertically in the turbine side stator End Shield. Stator End Shield also contain the shaft seal and bearing components. Feet are welded to the stator frame and end shields to support the stator on the foundation.The Stator is firmly connected to foundation with anchor bolts through the feet. The generator stator is a tight construction supporting and enclosing stator winding, core and hydrogen cooling medium. Hydrogen is contained within frame and circulated by fans mounted at either end of rotor. The generator is driven by direct coupled steam turbine at the speed of 3000 rpm. The generator is designed for continuous rated output. Temperature detector and other device installed or connected within machine, permit the windings core and hydrogen temperature, pressure, and purity in machine. LONGITUDINAL VIEW OF STATOR FRAME 24 MAN HOLE
  • 25. 4.4.1.2 STATOR CORE :- CROSS SECTIONAL VIEW OF STATOR CORE The stator core is made of silicon steel with high permeability and low hysteresis and eddy current losses. The sheets are suspended in the stator frame from insulated guide bars. Stator laminations are coated with synthetic varnish; are stacked and held between sturdy steel clamping plates with non-magnetic pressing fingers which are fastened or welded to the stator frame. In order to minimize eddy current losses of rotating magnetic flux which interact with the core is built of thin laminations. Each lamination layer is made of individual segments. Core is mainly used for efficiently carrying electrical and mechanical flux ;It is inserted vertically in frame 25 SLOTS FOR WINDING
  • 26. STAMPINGS FOR 500 MW TURBO GENERATOR 4.4.1.2.1 STAMPING :- The segments are punched in one operation from electrical sheet steel lamination having high silicon content and are carefully debarred. STAMPING FOR 800 MW TURBO GENERATOR 26 HOLES FOR GAS FLOW HOLES FOR GAS FLOW
  • 27. The stator laminations are assembled as separate cage core without the stator frame. 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 rectangular bars which hold them in position. To obtain optimum compression and eliminate looseness during operation the laminations are hydraulically compressed and heated during the stacking procedure. To remove the heat, spaced segments are placed at intervals along the core length which divide the core into sections to provide wide radial passages for cooling air to flow. Stampings are held in a position by 21 core bars having dovetail section. Insulating paper pressboards are also put between the layer of stamping to provide additional insulation and to localize short circuit. Between two packets one layer of ventilating segments is provided. Steel spacers are spot welded on stamping (for generators below 500 MW). These spacers form ventilating ducts where the cold air from gas coolers enter the core radially inwards there by taking away the heat generated due to eddy current losses. For 600 MW and above spring like assembly of core stamping is done. Number of stampings used in one round is 10.5, each stamping is of size 0.5 mm and core length is 6500 mm. So, 136500 stampings are used in a core. ARRANGEMENT OF STAMPINGS 27
  • 28. PROCEDURE OF CORE INSERTION 4.4.1.3 STATOR WINDING 4.4.1.3.1 Construction:- Stator bars, phase connectors and bushings are designed for direct water cooling. To minimize the stray losses, the bars are composed of separately insulated strands which are transposed by 540 in the slot portion and bonded together with epoxy resin in heated mold after bending the end turns are likewise bonded together with baked synthetic resin filters. The bar consist of solid and hollow strands distributed over the entire bar cross- section so that good heat dissipation is ensured at the bar ends, all the solid strand are jointly brazed into a connection sleeve and the hollow strands into a water box from which the cooling water enters and exits via Teflon insulating hoses connected to the annular manifolds. 28
  • 29. The electrical connection between top and bottom bars is made by a bolted connection at the connection sleeve. The water manifolds are insulated from stator frame, permitting the insulation resistance of water-filled winding to be measured. During operation water manifolds are grounded. There are two types of stator winding :- 4.4.1.3.2 Hollow Winding This type of winding is made up of copper.These windings are water cooled.This type of winding is much superior to strip type winding because cooling is much better.The end of each winding is connected to header in which water supply is provided. 29
  • 31. 4.4.1.3.3 Metallic Strip Type Winding This type of winding is used in small size turbo generators because cooling is less efficient and entirely depends upon cooling by gas. 31 METALLIC STRIPS
  • 32. 4.4.1.3.4FLOW CHART OF MANUFACTURING OF STATOR WINDING 32
  • 33. 4.4.1.3.5 WATER SUPPLY WATER SUPPLY INTO WINDINGS THROUGH HEADER FROM BLACK PIPES OF TEFLON The water connection at the stator bar is separate from the electrical connection. As a result no electrical forces can act on the water connection. 33 TEFLON PIPES
  • 34. Which the solid strands of the stator bars terminates at the connecting sleeve, the hollow strands are beared into water boxes, with solid spacers inserted to compensate for the solid strand. Each water box is consist of two part i.e., the sleeve shaped lower part enclosing the hollow strands and the cover type upper part the strand rows are separated from each other by spacers. Each water box is provided with a pipe connection of non magnetic stainless steel for connection of the hose. The exciter end water boxes serve for water admission and distribute the cooling water uniformly to the hollow strand of the bars. The hot water is collected on leaving the hollow strand in the turbine end water boxes. The cooling water is then discharged from the generator via the hoses and the ring header. High-voltage insulation is provided according to the proven Micalastic system. With this insulation system, several half – over lapped continuous layer of mica tape are applied to the bars. The mica tape is built 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., the thickness of the insulation depends on the machine voltage. 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 vacuum, he bars are subjected to pressure,with nitrogen being used as pressurizing medium (VPI process). The impregnation bars are formed to the required shape in molds and cured in an over 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 waterproof and oil resistant. To minimize corona discharges between the insulation and slot wall, a final coat of semi conducting varnish is applied to the surfaces of all bars within the slot range. In addition, all bars are provided with an end corona protection, to control the electric field at the transition from the slot to the end winding and to prevent the formation of creep age spark concentrations. 4.4.1.3.6 INSULATION OF STATOR WINDING 34
  • 35. class Y-upto 90 degree celsius class A-upto 105 degree celsius class E-upto 120 degree celsius class B-upto 130 degree celsius class F-upto 155 degree celsius class H-upto 180 degree celsius class C- > 180 degree celsius 4.4.1.3.6.2 TESTING OF INSULATION 4.4.1.3.6.1 TYPES OF INSULATION ∆ = Angle Of deviation R4 = Resistance C4*R4*10-4 =tan∆ Here C4 = Capacitance This test is carried out to ensure the healthiness of dielectric (Insulation) i.e. dense or rare and measured the capacitance loss. The capacitance of the bar is found and the angle of deviation due to the impurity in the insulation is obtained from the formula a) Tan∆ TEST: Each bar is tested momentary at high voltage increased gradually to three times higher than rated voltage. b) H.V. TEST: (High Voltage Test) 35
  • 36. The revolving magnetic field exerts a pull on the core, resulting in a revolving and nearly elliptical deformation of the core which sets up a stator vibration at twice the system frequency. To reduce the transmission of these dynamic vibrations to the foundation, the generator core is spring mounted in the stator frame. The core is supported in several sets of rings. Each ring set consists of two supporting rings and two core clamping rings. 4.4.1.4 SPRING AND SPRING BASKET 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. For firm coupling of the ring sets to the core, the supporting ring is solidly pressed against the core by the clamping ring. The clamping ring consist of two parts which are held together by two clamps. Tightening the clamps reduces the gap between the ring segments so that the supporting ring is pressed firmly against the core. 36
  • 37. The lower springs prevents a lateral deflection of the core. The flat springs are resilient to radial movements of the core suspension points and will largely resist transmission of double frequency vibration to the frame. In the tangential direction they are, however sufficiently rigid to take up the short circuit torque of the unit. The entire vibration system is turned so as to avoid resonance with vibrations at system frequency or twice the system frequency. 4.4.1.5 MAGNETIC SHUNT Magnetic shunt is a type of ring which is used to confine the magnetic flux within the stator. One ring is connected on turbine end and one ring is connected at exciter end. These rings are made up of steel. 4.4.1.6 STATOR COOLING 4.3.1.6.1 COOLING OF WINDINGS The end windings are enclosed by an annular water manifold to which all stator bars are connected through hoses. The water manifolds is mounted on the holding plates of the end winding support ring and connected to the primary water supply pipe. This permits the insulation resistance of the water filled stator winding to be measured. The water manifold is grounded during operation. For measurement of the insulation resistance, eg. during inspection, grounding is removed by opening the circuit outside the stator frame. Each ring set is linked to the frame by three flat springs.The core is supported in the frame via two vertical springs in the vicinity of the generator feet. 37
  • 38. The hoses, one side of which is connected to ground, consist of a metallic section to which the measuring potential is applied for measurement of the insulation resistance of the water-filled stator winding. The cooling water is admitted to three terminal bushings via a distribution water manifold flows through the attached phase connectors and is then passed to the distribution water manifold for water outlet via the terminal bushings on the opposite side. The parallel-connected cooling circuits are checked for uniform water flows by a flow measurement system covering all three phases. 4.3.1.6.2 COOLING OF CORE A) CO2 Supply:- As a precaution against explosive mixtures, air must never be directly replaced with hydrogen during generator filling nor the hydrogen replaced directly with air during the emptying procedure. In both cases, the generation must be scavenged or purged with an insert gas, carbon dioxide (CO2) being used for this purpose. a) CO2 bottle rack:- The CO2 is supplied in steel bottles in the liquid state. The bottle should be provided with risers to ensure completely emptying. The arrangement of the CO2 bottle rack corresponds to that of H2 bottle rack. The liquid CO2 which is stored under pressure, is fed to the gas valve rack via a shutoff valve. b) CO2 flash Evaporator:- At the gas valve rack the liquid CO2 is evaporated and expanded in a CO2 flash evaporator. The heat for vaporization is supplied to the flash evaporator electrically. A temperature control is provided so that freezing of the flash evaporator is prevented, and the CO2 is admitted into the generator at the proper temperature. One safety valve each on the high-pressure and low-pressure sides protects the pipe system against inadmissibly high pressure. 38
  • 39. Compressed Air Supply:- To remove the CO2 from the generator, a compressed air supply with compressed air filter is connected to the general air system of the power plant. Under all operating conditions, except for CO2 purging, the compressed air hoses between the filter and the generator pipe system should be disconnected. This visible break is to ensure that no air can be admitted into a hydrogen-filled generator. B ) Nitrogen (N2) Supply:- On a water-cooled turbine generator an additional nitrogen supply is required for a) Removing the air above the water level in the primary water tank during initial operation of the primary water system. b) Removing the oxygen dissolved in the primary water during filling of the primary water system. c) Removing the hydrogen gas above the water level in the primary water tank during shutdown of the primary water system. d) Removing the hydrogen gas dissolved in the primary water during shutdown of the primary water system. The N2 purge during initial operation ensures a compete removal of the oxygen from the primary water circuit, thus eliminating the risk of corrosion attack. The N2 purge during shutdown prevents the formation of an explosive hydrogen-air mixture. During operation hydrogen may enter into the primary water tank by diffusion at the insulating hoses. The nitrogen available from a bottle is passed to a pressure reducer for expansion and admitted into the primary water tank via the N2 supply line. 39
  • 40. 4.4.1.7 PRESS RINGS The press ring is bolted to the ends of core bars. The pressure of the pressure ring is transmitted to stator core stamping through press fringes of non-magnetic steel and duralumin placed adjacent to press ring. To avoid heating of press ring due to end leakage flow two rings made of copper sheet are used as flux shield. The ring screens the flux by short-circuiting. To monitor the formation of hot spots resistance transducer are placed along the bottom of slots. To ensure that core losses are within limits and there are no hot spots present in the core. The core loss test is done after completion of core assembly. 4.4.1.8 END RINGS The end covers are made up of fabricated steel or aluminum castings. They are employed with guide vans on inner side for ensuring uniform distribution of air or gas. Cool air flows from sides and hot air flows in centre. Rotor fan sucks the hot air which then passes through compressor and gets cool and circulates to core. 40
  • 41. They are used to hold the bearings and shaft seal assembly. It is mounted on both the ends of the stator. 41 UPPER SHIELD LOWER SHIELD
  • 42. 4.4.1.9 TERMINAL BOX AND TERMINAL BUSHING TERMINAL BOX A) Arrangement of terminal bushing:- The beginning and ends of the three phases windings are brought out from the stator frame through terminal bushings, which provides 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. Bushing-type generator current transformers for metering and relaying are mounted on the bushing outside the generator terminal box. The customers bus is connected to the air side connection flange of the bushings via terminal connectors The generator terminal box located beneath the stator frame at the exciter end is made from non-magnetic steel to avoid eddy-current losses and resulting temperature rises. 42
  • 43. B) Construction of Bushings:- The cylindrical bushing conductor consist of high conductivity copper with a central bores for direct primary water cooling. The insulator is wound directly over the conductor. It consist of impregnated capacitor paper with conducting fillers for equalization of the electrical direct-axis and quadrature-axis fields. The shirunk-on mounting sleeve consist of a gas tight casting of nonmagnetic steel with a mounting flange and a sleeve type extension extending over the entire height of the current transformers. The cylindrical connection ends of the terminal bushing conductors are silver plated and designed to accommodate bolted two part cast terminal connectors. Connection to the beginning and each phase inside the terminal box and to the external bus in by means of flexible connectors. To maintain a uniform and constant contact pressure, Belleville washers are used for all bolted connections. TERMINAL BUSHING 43
  • 44. 4.3.2 ROTOR Rotor rotates in most modern generator at speed of 3000 rotations per minute. It is also an electromagnet and to give it necessary magnetic strength, the winding must carry a very high current. The passage of current through windings generates heat. But the temperature must not be allowed to become too high, otherwise difficulties will be experienced with insulation. To keep the temperature cross section of the conductors could not be increased but this would introduce another problems. In order to make room for large conductor, body and this would cause mechanical weakness. With good design and great care this problem can be solved. 4.4.2.1 ROTOR SHAFT ROTOR SHAFT AT INITIAL STAGE 44
  • 45. SLOTS CUTTING IN ROTOR SHAFT STEPS INVOLVED IN MACHINING OF ROTOR 45 SLOTS
  • 46. ROTOR AFTER CUTTING SLOTS METAL OXIDE PAINT ON ROTOR 46 ROTOR POLES
  • 47. The high mechanical stresses resulting from the centrifugal forces and short- circuit torques call for a high quality heat-treated steel. Therefore, the rotor shaft is forged from a vacuum cast steel ingot. Comprehensive tests ensure adherence to the specified mechanical and magnetic properties as well as a homogeneous forging. The rotor shaft consists of an electrically active portion, the so called rotor body, and the two shaft journals. Integrally forged flange couplings to connect the rotor to the turbine and exciter are located out board of the bearings. Approximately two-thirds of the rotor body circumference is provided with longitudinal slots which hold the field winding slot pitch is selected so that the two solid poles are displaced by 180. 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 at twice the system frequency. To reduce these vibrations the deflections in the direction of the pole axis and neutral axis are compensated by transverse slotting of the pole. The solid pole are also provided with additional longitudinal slots to hold the copper bars of the damper winding. The rotor wedges act as a damper winding in the area of winding slot. Details of shaft are given here – Length = 9 meter (approx.) Diameter = 1 meter (approx.) Material – alloy steel Number of poles = 2 4.4.2.2 ROTOR WINDING The winding consist of several coils inserted into the slots and the series connected such that two coils group forms one pole. Each coil consist of several series connected turns each of which consist of two half turns connected by brazing in end section. 47
  • 48. The individual turn of coil are insulated against each other by interlayer insulation. L-shaped strip of laminated epoxy glass fiber with nomex filter are used for slot insulation. The slot wedges are made up of high electrical conductivity material and thus act as damper winding. At their ends, the slots wedges are short circuited through the rotor body. When rotor is rotating at high speed, the centrifugal forces tries to lift the winding out of slots, they are contained by wedges. The field winding consists of several series connected coils into the longitudinal slots of body. The coil is wound such that two poles are obtained. The solid conductors have a rectangular cross-section and are provided with axial slots for radial cooling air. All conductors have identical copper and cooling section. ROTOR WINDING 4.4.2.2.1 CONDUCTOR MATERIAL OF WINDING The conductors are made up of copper with silver content of approx. 0.1%. As compared to electrolytic copper silver alloyed copper features high strength properties at high temperature so that coil deformations due to thermal stresses are eliminated. The conductors are made of hard drawn silver bearing copper. 48
  • 49. The rectangular cross section copper conductors have ventilating ducts on the two sides thus providing a channel for hydrogen flow. Two individual conductors placed- one over the other are bent to obtain half turns. Further these half turns are brazed in series to form coil on the rotor model. 4.4.2.2.2 INSULATION The insulation between the individual turns is made up of layer of glass fiber laminate. The coils are insulated from the rotor body with L-shaped strip of glass fiber laminated to obtain the required leakage path between the coil and rotor body thick top strips of glass fiber laminate are inserted below wedge. The top strip are provided with axial slots of same cross-section and spacing and used on the rotor winding. 4.4.2.3 ROTOR SLOT WEDGES To protect the winding against the effects of the centrifugal force, the winding is secured in the slots with wedges. The slot wedges are made from a copper-nickel-silicon alloy featuring high strength and good electrical conductivity, and are used as damper winding bars. The slot wedges extend below the shrink seats of the retaining rings. The rings act as short-circuit rings to induced currents in the damper windings. 49 ROTOR WEDGES
  • 50. 54
  • 51. 4.4.2.4 ROTOR TERMINALS These terminals are connected to the excitation system and this side of rotor is fixed with excitation system. 50 TERMINALS
  • 52. 4.4.2.5 RETAINING RING & CENTERING ASSEMBLY The centrifugal forces of the end windings are contained by piece rotor retaining rings. Retaining rings are made up of non-magnetic high strength steel in order to reduce the stray losses. Each retaining ring with its shrink fitted. Insert ring is shrunk on the rotor is an overhang position. The retaining ring is secured in the axial position by snap rings. The rotor retaining rings withstand the centrifugal forces due to end winding. One end of each ring is shrunk fitted on the rotor body while the other hand overhangs the end winding without contact on the rotor shaft. This ensures unobstructed shaft deflection at end windings. The shrunk on hub on the end of the retaining ring serves to reinforce the retaining ring and serves the end winding in the axial direction. At the same time, a snap ring is provided against axial displacement of retaining ring. The shrunk slot of current to reduce the stray losses and have high strength, the rings are made up of non-magnetic cold worked material. 51
  • 53. 4.4.2.6 COMPRESSOR HUB The compressorhub is a type of ring which is made up of structural steel. The blades of rotor fan are put on compressorhub. 4.4.2.7 ROTOR FAN The generator cooling gas is circulated by one axial-flow fan located on the turbine-end shaft journal. To augment the cooling of the rotor winding, the pressure established by the fan works in conjunction with the gas expelled from the discharge parts along the rotor. The moving blades of the fan are inserted into T-shaped grooves in the fan hubs. The fan hubs are shrink-fitted to the shaft journal spider. 52
  • 55. The rotor shaft is supported in sleeve bearings having forced-oil lubrication. The bearings are located in the stator end shields. The oil required for bearing lubrication and cooling is obtained from the turbine oil system and supplied to the lubricating gap via pipes permanently installed inside the lower half of the stator end shield and via grooves in the bearing sleeves. The lower bearing sleeve rests on the bearing saddle via three brackets with spherical support sets for self-alignment of the bearing. The bearing saddle is insulated from the stator end shield and the bearing bracket are insulated from the bearing sleeve to prevent the flow of shaft currents and to provide for double insulation of the generator bearing from ground. A radial locator serves to locate the bearing in the vertical direction and is bolted to the upper half of the stator end shield. The locator is adjusted to maintain the required clearance between the bearing sleeve and the insulation of the radial locator. All generator bearings are provided with a hydraulic shaft lift oil system to reduce bearing friction during start up. High pressure oil is forced between the bearing surface and the shaft journal, lifting the rotor shaft to allow the formation of the lubricating oil film. The bearing temperature is monitored with one double element thermocouple located approximately in the plane of maximum oil film pressure. With this type of shaft seal, the escape of hydrogen between the rotating shaft and the housing is prevented by maintaining a continuous film of oil between the shaft and a non-rooting floating seal ring. To accomplish this, seal oil from two separate circuits i.e., the air side and hydrogen side seal oil circuits, is fed to the seal ring at a pressure slightly higher than the hydrogen pressure. In addition, higher pressure air side oil is supplied to the shaft seal for thrust load compensation of the seal ring. 55 5. BEARINGS 6.SHAFT SEAL
  • 56. 7. COOLING OF ROTOR 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. The cooler consists of individual sections for vertical mountings. This arrangement permits the coolers to be mounted without an increase in the overall generator axial length or cross-sectional area of the stator frame. The hydrogen flows through the coolers in the horizontal direction. The cold cooling water flows from the bottom to the top end of the cooler on the cold gas side and, after reversal in the return water channel, the heated water flows downward on the hot gas side. This cooling water flow passage is obtained through a partition in the inlet / outlet water channel. 56
  • 57. HOLES IN ROTOR WNDING FOR HYROGEN GAS CIRCULATION The basic use of given exciter system is to produce necessary DC for turbo generator system. 57 The Exciter consist of -: 1.Rectifier wheels 2.Three phase main Exciter 3.Three phase pilot Exciter 4.Cooler 8. EXCITER
  • 58. The three phase pilot exciter has a revolving field with permanent-magnet poles. The three-phase ac generated by the permanent-magnet pilot exciter is rectified and controlled by the TVR to provide a variable dc current for exciting the main exciter. The three phase ac induced in the rotor of the main exciter is rectified by the rotating rectifier bridge and fed to the field winding of the generator rotor through the dc leads in the rotor shaft. A common shaft carrier the rectifier wheels, the rotor of the main exciter and the permanent-magnet rotor of the pilot exciter. The shaft is rigidly coupled to the generator rotor. The exciter shaft is supported on a bearing between the main and pilot exciters. The generator and exciter rotors are thus supported on total of three bearings. Mechanical coupling of the two shaft assemblies results in simultaneous coupling of the dc leads in the central shaft bore through the multi contact electrical contact system consisting of plug-in bolts and sockets. This contact system is also designed to compensate for length variations of the leads due to thermal expansion. 58
  • 59. 8.1 MAIN EXCITER The three-phase main exciter is a six-pole revolving-armature unit. Arranged in the stator frame are the poles with the field and damper winding. The field winding is arranged on the laminated magnetic poles. At the pole shoe bars are provided, their ends being connected so as to form a damper winding. Between two poles a quadrature-axis coil is fitted for inductive measurement of the exciter current. The rotor consist of stacked laminations, which are compressed by through bolts over compression rings. The three phase winding is inserted in the slots of the laminated rotor. The winding conductors are transposed within the core length and the end turns of the rotor winding are secured with steel bonds. The connections are made on the side facing the rectifier wheels. The winding ends are run to a bus ring system to which the three phase leads to the rectifier wheels are also connected. After full impregnation with synthetic resin and curing, the complete rotor is shrunk on to the shaft. A general bearing is arranged between main exciter and pilot exciter and has forced-oil lubrication from the turbine oil supply. SHAFT OF EXCITER 59
  • 61. 8.3 COOLINGOF EXCITER FAN 61 ROTOR OF PMMG The three-phase pilot exciter is a 16 pole revolving-field unit. The frame accommodates the laminated core with the three-phase winding. The rotor consist of a hub with mounted poles. Each pole consist of 10 separate permanent magnets which are housed in a non-magnetic metallic enclosure. The magnets are braced between the hub and the external pole shoe with bolts. The rotor hub is shrunk onto the free shaft end. 8.2 PILOT EXCITER
  • 62. The exciter is air cooled. The cooling air is circulated in a closed circuit and recooled in two cooler sections arranged alongside the exciter. The complete exciter is housed in an enclosure through which the cooling air circulates.The rectifier wheels, housed in their own enclosure, draw the cool air in at both ends and expel the warmed air to the compartment beneath the base plate. The main exciter enclosure receives cool air from the fan after it passes over the pilot exciter. The air enters the main exciter from both ends and is passed into ducts below the rotor body and discharged through radial slots in the rotor core to the lower compartment. The warm air is then returned to the main enclosure via the cooler sections. 8.4 RECTIFIER WHEEL The main components of the rectifier wheels are the silicon diodes which are arranged in the rectifier wheels in a three phase bridge circuit. The contact pressure for the silicon wafer is produced by a plate spring assembly. The arrangement of the diode is such that this contact pressure is increased by the centrifugal force during rotation. Additional components are contained in the rectifier wheels. Two diodes each are mounted in each aluminum alloy heat sink and thus connected in parallel. Associated with each heat sink is a fuse which serves to switch off the two diodes if one diode falls (Loss of reverse blocking capacity). For suppression of the momentary voltage peaks arising from commutation, each wheel is provided with six RC networks consisting of one capacitor and one damping resistor each, which are combined in a single resin-encapsulated unit. 62
  • 63. 63
  • 64. The insulated and shrunken rectifier wheels serves as dc buses for the negative and positive side of the rectifier bridge. This arrangement ensures good accessibility to all components and a minimum of circuit connections. The two wheels are identical in their mechanical design and differ only in the forward direction of the diodes. The direct current from the rectifier wheels is fed to the dc leads arranged in the center bore of the shaft via radial bolt. The three-phase alternating current is obtained via copper conductors arranged on the shaft circumference between the rectifier wheels and the three- phase main exciter. The conductors are attached by means of banding clips and equipped with screw-on lugs for the internal diode connection. One three phase conductor each is provided for the four diodes of a heat sink set. 9. LOSSES IN TURBO GENERATOR The power lost in the form of heat in the armature winding of a generator is known as Copper loss. Heat is generated any time current flows in a conductor. loss is the Copper loss, which increases as current increases. The amount of heat generated is also proportional to the resistance of the conductor. The resistance of the conductor varies directly with its length and inversely with its cross- sectional area. Copper loss is minimized in armature windings by using large diameter wire. Copper loss is again divided as (i) Armature copper loss = Armature copper loss. Where Ra =resistance of armature and inter poles and series field winding etc. This loss is about 30 to 40% of full -load losses. (ii) Field copper loss : It is the loss in series or shunt field of generator. is the field copper loss in case of series generators, where Rse is the resistance of the series field winding. 9.1 COPPER LOSSES 64
  • 65. is the field copper loss in case of shunt generators. i) Hysteresis loss (Wh) Hysteresis loss is a heat loss caused by the magnetic properties of the armature. When an armature core is in a magnetic field, the magnetic particles of the core tend to line up with the magnetic field. When the armature core is rotating, its magnetic field keeps changing direction. The continuous movement of the magnetic particles, as they try to align themselves with the magnetic field, produces molecular friction. This, in turn, produces heat. This heat is transmitted to the armature windings. The heat causes armature resistances to increase. To compensate for hysteresis losses, heat-treated silicon steel laminations are used in most dc generator armatures. After the steel has been formed to the proper shape, the laminations are heated and allowed to cool. This annealing process reduces the hysteresis loss to a low value. (ii) Eddy Current Loss (We) The core of a generator armature is made from soft iron, which is a conducting material with desirable magnetic characteristics. Any conductor will have currents induced in it when it is rotated in a magnetic field. These currents that are induced in the generator armature core are called EDDY CURRENTS. The power dissipated in the form of heat, as a result of the eddy currents, is considered a loss. Eddy currents, just like any other electrical currents, are affected by the resistance of the material in which the currents flow. The resistance of any material is inversely proportional to its cross-sectional area. Figure, view A, shows the eddy currents induced in an armature core that is a solid piece of soft iron. Figure, view B, shows a soft iron core of the same size, but made up of several small pieces insulated from each other. This process is called lamination. 9.2 MAGNETIC LOSSES (also known as iron or core losses) 65
  • 66. The currents in each piece of the laminated core are considerably less than in the solid core because the resistance of the pieces is much higher. (Resistance is inversely proportional to cross-sectional area.) The currents in the individual pieces of the laminated core are so small that the sum of the individual currents is much less than the total of eddy currents in the solid iron core. As we can see, eddy current losses are kept low when the core material is made up of many thin sheets of metal. Laminations in a small generator armature may be as thin as 1/64 inch. The laminations are insulated from each other by a thin coat of lacquer or, in some instances, simply by the oxidation of the surfaces. Oxidation is caused by contact with the air while the laminations are being annealed. The insulation value need not be high because the voltages induced are very small. Most generators use armatures with laminated cores to reduce eddy current losses. These consist of (i) friction loss at bearings (ii) air-friction or windage loss of rotating armature These are about 10 to 20% of F.L losses. 9.3 MECHANICAL AND ROTATIONAL LOSSES 66
  • 67. Careful maintenance can be instrumental in keeping bearing friction to a minimum. Clean bearings and proper lubrication are essential to the reduction of bearing friction.Brush friction is reduced by assuring proper brush seating, using proper brushes, and maintaining proper brush tension. A smooth and clean commutator also aids in the reduction of brush friction. Usually, magnetic and mechanical losses are collectively known as Stray Losses. These are also known as rotational losses for obvious reasons. 67
  • 68.  Electrical Machine - P.S. Bhimbra  Electrical Machine - Assfaq Hussain  BHEL Haridwar Website – www.bhelhwr.co.in  http://etrical.blogspot.in/2016/04/brushless-excitation-system.html  http://www.slideshare.net/khemraj298/bhel-haridwar-vocational-training- report 68 11.BIBLIOGRAPHY AND REFERENCES
  • 69. The vocational training at Bharat Heavy Electrical, Haridwar is an experience worth having. I learnt a lot, not only about manufacturing of turbo-generator and its various components but also the manufacturing of turbine, brushless exciter, stator & rotor windings, coil & insulation manufacturing, Computer Numerical Control system etc. 69 11.CONCLUSION