ELECTRICAL MACHINES MANUFACTURING (TURBO ALTERNATORS) AN IT REPORT SUBMITTED TOWARDS THE PARTIAL FULFILLMENT OF THE REQUIREMENTS OF THE AWARD OF DEGREE OF BACHELOR OF ENGINEERING IN ELECTRICAL ENGINEERING SUBMITTED BY AKSHAY DHAR C.R.NO 377/07 U.R.NO. 725/07 DEPARTMENT OF ELECTRICAL ENGINEERING MAHANT BACHITTAR SINGH COLLEGE OF ENGINEERING & TECHNOLOGY. UNIVERSITY OF JAMMU YEAR 2010
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I hereby declare that the IT report entitled “ ELECTRICAL MACHINES MANUFACTURING(TURBO ALTERNATORS) ” is an authentic record of my own work carried out as the partialfulfillment of the requirements for the award of degree of B.E (electrical engineering) at M.B.S.College of engineering and technology, Jammu during June - July 2010
Akshay Dhar
C.R.NO 377/07
U.R.NO. 725/07
Date:
Certified that the above statement made by the student is correct to the best of my knowledge andbelief.
Ms. Damandeep Kour(Lecturer EE Deptt.)I.T. Coordinator
2.1 Brief Profile 62.2 Establishment & Development Stages 72.3 Climatic & Geographical Conditions 82.4 Power & Water supply system 82.5 Electrical Machines Block (BLOCK-I) 92.6 Basic Training Departments 11
3. Turbo Generators
3.1 Introduction 123.2 Synopsis of the Function of T.G 133.3 Large Sized Turbo Generator 13
4. Stator
4.1 Introduction 174.2 Stator Frame 174.3 Stator Core 184.4 Stator Winding 194.5 Insulation of Bars 204.6 End Cover 214.7 Manufacturing of various parts of stator 22
5. Rotor
5.1 Introduction 265.2 Rotor Shaft 275.3 Various Steps Involved In Rotor Machining 285.4 Rotor Winding 305.5 Construction of field winding 315.6 Conductor Material 335.7 Insulation 335.8 Rotor Slot wedges 355.9 Rotor Retaining Rings 365.10 Rotor Fans 375.11 Bearings 375.12 Field Current lead in shaft base 385.13 Rotor Assembly 385.14 Machine section 38
Fig 1.1 Entrance to the Heavy Electrical Equipments Plant (HEEP)
BHEL was established more than 50 years ago when its first plant was setup in Bhopal ushering in
the indigenous Heavy Electrical Equipment Industry in India. A dream which has been more than
realized with a well-recognized track record of performance it has been earning profits
continuously since 1971-72 and achieved a turnover of Rs 2,658 crore for the year 2007-08,
showing a growth of 17 per cent over the previous year. Bharat Heavy Electricals Limited is
country‟s „Navratna‟ company and has earned its place among very prestigious national and
international companies. It finds place among the top class companies of the world for manufactureof electrical equipments.BHEL caters to core sectors of the Indian Economy viz., Power
Defence, etc. BHEL has already attained ISO 9000 certification for quality management, and ISO
14001 certification for environment management and OHSAS – 18001 certification for
Occupational Health and Safety Management Systems. The Company today enjoys national and
international presence featuring in the “Fortune International -500” and is ranked among the top 10
companies in the world, manufacturing power generation equipment. BHEL is the only PSU amongthe 12 Indian companies to figurein “Forbes Asia Fabulous 50” list.Probably the most significant
aspec t of BHEL‟s growth has been its diversification .The constant re-orientation of the
organization to meet the varied needs in time with a philosophy that has led to total development of
a total capability from concepts to commissioning not only in the field of energy but also in
industry and transportation. In the world power scene BHEL ranks among the top ten
manufacturers of power plant equipments not only in spectrum of products and services offered, it
is right on top. BHEL‟ s technological excellence and turn key capabilities have won it world wide
recognition. Over 40 countries in world over have placed orders with BHEL covering individual
equipment to complete power stations on turn key basis
1.2 BHEL – A BRIEF PROFILE
BHEL is the largest engineering and manufacturing enterprise in India in the energy related
infrastructure sector today. The wide network of BHEL's 14 manufacturing division, four powerSector regional centres, over 150 project sites, eight service centres and 18 regional offices, enables
the Company to promptly serve its customers and provide them with suitable products, systems and
services efficiently and at competitive prices. While the company contributes more than 75% of
the national grid, interestingly a share of 45% comes from its single unit. And this is none other
than BHEL-Haridwar.
BHEL has:-
1) Installed equipment for over 90,000MW of power generation for utilities captive and industrial
users.
2)Supplied over 2, 25,000 MVA transformer capacity and other equipment operating in
transmission and distribution network up to400 kV (AC & DC).
3)Supplied over 25,000 motors with drive control systems to power projects, petrochemicals,
refineries, steel, aluminium, fertilizers, cement plants etc.
4)Supplied Traction electrics and AC/DC locos to power over 12,000 kms railway network.
5)Supplied over one million valves to power plants and other industries.
1.3 BHEL-AN OVERVIEW
The first plant of what is today known as BHEL was established nearly 40 years ago at Bhopal &
was the genesis of the Heavy Electrical Equipment industry in India.BHEL is today the largest
BHEL vision is to world-class engineering enterprise, committed to enhancing stakeholder value.
The greatest strength of BHEL is its highly skilled and committed 44,000 employees.Spread all
over India & abroad to provide prompt and effective service to customers.
BUSINESS SECTOR
BHEL operations are organized around business sectors to provide a strong market orientation.These business sectors are Power Indus and International operations.
POWER SECTOR Power sector comprises of thermal, nuclear, gas and hydro business. Today BHEL supplied
sets account for nearly 65% of the total installed capacity in the country as against nil till
1969-70.
BHEL has proven turnkey capabilities for executing power projects from concept to
commissioning and manufactures boilers, thermal turbine generator set & auxiliaries up to
500MW.
It possesses the technology and capability to procure thermal power generation equipment
Turbo generator or A.C. generators or alternators operates on the fundamental principles of ELECTROMAGNETIC INDUCTION. In them the standard construction consists of armature
winding mounted on stationary element called stator and field windings on rotating element called
rotor. The stator consists of a cast-iron frame, which supports the armature core , having slots on its
inner periphery for housing the armature conductors. The rotor is like a flywheel having alternating
Fig. 3.1Hydrogen-cooled turbogenerator of the 500 MVA class in standardsteam turbine arrangement
north and south poles fixed toits outer rim. The magnetic poles are excited with the help of an
exciter mounted on the shaft of alternator itself. Because the field magnets are rotating the current
is supplied through two slip rings. As magnetic poles are alternately N and S, they induce an e.m.f
and hence current in armature conductors. The frequency of e.m.f depends upon the no. of N and S
poles moving past a conductor in 1 second and whose direction is given by Fleming ‟s right hand
The generator stator is a tight construction supporting and enclosing stator winding, core and
hydrogen cooling medium. Hydrogen is contained within the frame and circulated by fans mountedat either end of rotor. The generator is driven by a direct coupled steam turbine at the speed of 3000
rpm. The generator is designed for continuous rated output. Temperature detector or other devices
installed or connected within the machine, permits the winding core and hydrogen temperature,
pressure and purity in machine.
4.2 STATOR FRAME
Fig 4.1. Stator Frame
The stator frame is used for housing armature conductors. It is made of cylindrical section with two
end shields which are gas tight and pressure resistant. The stator frame accommodates the
electrically active parts of stator i.e. the stator core and stator winding.The fabricated inner cage is
inserted in the outer frame after the stator has been constructed and the winding completed.
To prevent a potential difference and possible corona discharges between the insulation and
slot wall, the slot sections of bars are provided with an outer corona protection. This
protection consists of polyester fleece tape impregnated in epoxy resin with carbon and
graphite as filters.
At the transition from slot to the end winding portion of stator bars a semi-conductive tape
made of polyester fleece is impregnated with silicon carbide as filler is applied for a specific
length. This ensures uniform control of the electric field and prevents the formation of
corona discharge during operation and performance of HV tests.
c) Resistance Temperature Detector
The stator slots are provided with platinum resistant thermometer to record and watch the
temperature of stator core and tooth region and between the coil sides of machine in
operation. All AC machines rated for more than 5 MVA or with armature core longer, the
machine is to be provided with at least 6 resistance thermometers. The thermometer should
be fixed in the slot but outside the coil insulation. When the winding has more than one coil
side per slot, the thermometer is to be placed between the insulated coil sides. The length of
resistance thermometer depends upon the length of armature. The leads from the detectorare brought out and connected to the terminal board for connection onto temperature meter
or relays. Operation of RTD is based on the prime factor that the “electric resistan ce of
metallic conductor varies linearly with temperature”
The moving or rotating part of generator is known as rotor. The axial length of shaft of the rotor isvery large as compared to its diameter in case of turbogenerators. Itis coiled heavily (field coils) as
it has to support large amount of current and voltage.Rotor revolves in most generators at a speed
of 3000 RPM. Field coils are wound over it to make the magnetic poles and to maintain magnetic
strength the winding must carry a very high current. As current flows heat is generated, but the
temperature has to be maintained because as temperature raises problems with insulation becomes
more pronounced. With good design & great care this problem can be solved. Solid rotors are
manufactured from forged alloy steel with suitable alloying elements to achieve very highmechanical and magnetic properties. Rectangular or trapezoidal rotors slots are accurately
machined to close tolerances on slot milling machine. For indirectly cooled generator rotors,
ventilation slots are machined in the teeth. For directly cooled rotors, Sub slots are provided for
cooling Generators rotors of 1500 RPM are of round laminated construction. Punched and
varnished laminations of high tensile steel are mounted over machined shaft are firmly clamped by
Then a free heating of about 1.5 hr is done at low pressure of about 30 kg and 115 ˚C
temperature.
Then for 45 minutes it is heated at temperature of about 130˚C & pressure is increased to
200 kg.
Then keeping the pressure constant the temperature is raised to around 160 ˚C and coils are
heated for around 3 hrs.
Then the coils are removed off the pressure gradually and cooled by spraying water so now
the temperature reaches 60 ˚C then left to cool slowly and the coils are ready to be wedged
in the slots.
Then the coils placed in the slots and tighten up to prevent the loosening by tightening
rings.There are 7 turns per pole per pitch and rotor of 210 MW is ready to test.There is a
slight difference in formation of coils 500 MW turbo-generators.
In those generators the coils are arranged in the following manner.
Firstly they alternate hollow and solid conductors.
There are two solid conductors for every hollow strip and they are marked as
A---- Which has 7 conductors.B---G where they have 9 conductors each coil.
They are transposed by 540* as it removes air gap and improves cross over insulation.
It increases mechanical strength and help in producing equal E.M.F across all the
conductors.
The insulation is moulding mica mite.
Testing involving the coils are thermal shock testing hot and cold.
This testing is done to check the strength of brazing so that there is no water leakage and asa result it can bear thermal stresses easily. Nitrogen test is also performed for cleaning and
leakage purposes and finally impregnating it through vacuum impregnation technique.
The vacuum impregnation technique is the latest technique to insulate the windings of stator and
not used in rotors of any of the generators being used in the power plants now a days. The process
above is discussed is also known as transposition, which involves the bending of the strips used in
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. Ring so
inserted is shrunk on the rotor is an over hang 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
Fig 5.10. Rotor Retaining Rings
end winding without contact on the rotor shaft. This ensures unobstructed shaft deflection at endwindings. 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. To reduce the stray losses and have high strength, the rings are
The cooling air in generator is cold by two axial flow fans located at the rotor shaft one at each end
augment the cooling of the winding. The blades of fan have threaded roots for screwed into the
rotor shaft. Blades are drop forged from aluminium alloy. Threaded root fastenings permit angle to
be changed. Each blade is screwed at its root with a threaded pin.
Fig 5.11.Rotor Blades
5.11 BEARINGS
The turbo generators are provided with pressure lubricated self-aligning type bearing to ensurehigher mechanical stability and reduced vibration in operation. The bearings are provided with
suitable temperature element to monitor bearing metal temperature in operation. The temperature of
each bearing monitored with two RTDs (resistance thermo detector) embedded in the bearing
sleeve such that the measuring point is located directly below Babbitt. Bearing have provision for
vibration pickup to monitor shaft vibration. To prevent damage to the journal due to shaft current,
bearings and coil piping on either side of the non-drive and bearings are insulated from the
Leads are run in axial direction from the radial bolt of the exciter coupling. They consist of low
semi-circular conductors insulated from each other and from the shaft by a tube.The field current
leads are coupled with exciter leads through a multi contact plug in which allows unobstructed
thermal expansion of field current.
5.13 ROTOR ASSEMBLY
Rotor winding assembly and rotor assembly and rotor assembly like rotor retaining ring fitting. All
these four assemblies are carried out in a
ROTOR ASSEMBLY SECTION present in
BAY 1. This section is also in a dust-proof
enclosure with no. of rotators, rotor bars
laying facilities and MI heating and mounting
of retaining rings.
Fig 5.12. A Fully Assembled TG
5.14 MACHINE SECTION
This section is present in BAY-2 (Turbo- Generators and Heavy Motors). This section is equippedwith large size CNC and conventional machine tools such as Lathes and Vertical boring, Horizontal
boring machine, Rotor slot milling and Radial drilling machines for machining stator body, rotor
shaft , End shields, Bearing etc. for Turbogenerators. Same section is present in Bay-3 (Medium
size motors) equipped with medium size machine tools for machining components for medium size
AC and DC machines and smaller components of Turbo-generators and Hydro generators.
The machine is designed with ventilation system having rated pressure. The axial fans mounted on
either side of rotor ensure circulation of hydrogen gas. The rotor is designed for radial ventilation
by stem. The end stator is packets and core clamping and is intensively cooled through special
ventilation system. Design of special ventilation is to ensure almost uniform temperature of rotor
windings and stator core.
6.2 STATOR COOLING SYSTEM
The stator winding is cooled by distillate water which is fed from one end of the machine by Teflon
tube and flows through the upper bar and returns back through the lower bar of a slot. Turbo
generator requires water cooling arrangement over and above the usual hydrogen cooling
arrangement. The stator is cooled in this system by circulating demineralized water trough hollow
conductors. The cooling was used for cooling of stator winding and for the use of very high quality
of cooling water. For this purpose DM water of proper specifying resistance is selected. Generator
is to be loaded within a very short period. If the specific resistance of cooling DM water goes
beyond preset value. The system is designed to maintain a constant rate of cooling water flowthrough the stator winding at a nominal inlet with temperature of 40 degree centigrade, the cooling
water is again cooled by water which is also demineralized to avoid contamination with any impure
water in case of cooler tube leakage, the secondary DM cooling water is in turn cooled by clarified
water taken from clarified water header.
6.3 ROTOR COOLING SYSTEM
The rotor is cooled by means of gap pickup cooling, where the hydrogen gas in the air gap issucked through the scoops on the rotor and is directed to flow along the ventilating canals milled on
the sides of the rotor coil, to the bottom of slot where it takes a turn and comes out on the similar
canal milled on the other side of the rotor coil to the hot zone of the rotor, Due to the rotation of the
rotor, a positive section as well as discharge is created due to which a certain quantity of a gas
flows and cools the rotor. The method of cooling gives uniform distribution of temperature. Also
this method has an inherent of eliminating the deformation of copper due to varying temperature.
The basic use of given exciter system is to produce necessary DC for turbo generator system.
Principal behind this is that PMG is mounted on the common shaft which generates electricity andthat is fed to yoke of main exciter. This exciter generates electricity and this is of AC in nature.
Fig 7.1. Exciter Winding Section
This AC is that converted into DC and is that fed to turbo generator via C/C bolt. For rectifying
purpose we have RC block and diode circuit. The most beautiful feature is of this type of exciter is
that is automatically divides the magnitude of current to be circulated in rotor circuit. This happens
with the help of AVR regulator which means automatic voltage regulator. A feedback path is given
to this system which compares theoretical value to predetermine and then it sends the current to
Automatic Voltage Regulator (AVR) forms a part of the excitation system for a brush-lessgenerator. The AVR is connected in series to the pilot exciter.In addition to regulating the generator
voltage, the AVR circuitry includes under-speed and sensing loss protection features. Excitation
power is derived directly from the generator terminals. Positive voltage build up from residual
levels is ensured by the use of efficient semiconductors in the power circuitry of the AVR. The
AVR is linked with the main stator windings and the exciter field windings to provide closed loop
control of the output voltage with load regulation of +/- 1.0%. In addition to being powered from
the main stator, the AVR also derives a sample voltage from the output windings for voltagecontrol purposes. In response to this sample voltage, the AVR controls the power fed to the exciter
field, and hence the main field, to maintain the machine output voltage within the specified limits,
compensating for load,speed, temperature and power factor of the generator. A frequency
measuring circuit continually monitors the generator output and provides output under-speed
protection of the excitation system, by reducing the output voltage proportionally with speed below
8.2.1 ANNEALING PROCESS This is the process of hardening or softening any metal.
Initially copper rolls are hard & if it undergoes annealing then it may breaks so firstly to
make it soft so that it can easily change to winding.
This process is carried out in the annealing furnace.
8.2.2 WINDING PROCESS
This process undergo following steps:-
Take out the softened copper rolls for pole coil winding.
Winding is done with the help of change plate & winding template so ensure major working
dimensions of change plate & winding template with respect to tool drawing. Adjust & set the winding machine as per the product standards using gear rack,change plate
& winding template. Ensure parallelity of winding template with respect to machine
platform. Maintain height of winding template with platform.Wind the coil in anticlockwise
direction.
NOTE:
The joint in the copper coil shall be located in the straight part of longer side.
If required heating by gas torch of copper profile at corner zone at temperature between
100-150 degree centigrade is allowed. This is to make bending easier.
8.2.3 BRAZING Braze the joint with brazing alloy Ag 40Cd.
Remove the coil with machine with 2 to 3 turns extra than the actual number of turns for
preparation of end-half turns.
Carry out bright annealing of the coil. Take out the coil from the oven after annealing.
8.2.4 PRESSING Pressing of coil is done by hydraulic pressure of 800 tons.
This process is carried out in order to remove wrinkles from the coil.
This process is carried out after every process. In this process, set the coil on the mandrelfor pressing then slide the coil under press and press the coil.
8.2.9 INSULATION Hang the coil on stand and separate out the turn.
Clean each turn with cotton dipped in thinner.
Apply Epoxy varnish on both sides of each turn with brush uniformly all over the leaving
top & bottom turn.
Cut strips of Nomax paper as per contour of coil with technological allowance 3 to 5 mm on
either side.
Stick two layers of Nomax strips between each turn.
Coat varnish layer between two layers of Nomax also.
Let the excess varnish to flow out some time
8.2.10 BAKING AND PRESSING OF COIL Place the coil on mandrel putting technological washer at top & bottom of the coil.
Heat the coil by DC up to 100 +/-50 ˚C, and maintain for 30 to 40 minutes.
Switch off the supply and elongate the coil and tight the pressing blocks from sides.
Start heating coil again and raise temperature gradually in steps up to 130 +/- 50 ˚C, with in
10 +/- 10 minutes.
Apply 110 tones pressure and maintain for 20 to 30 minutes. Then after every half an hour,
increases the pressure and temperature according to product requirement. Stop heating and then allow cooling the coil under pressure below 50 ˚C, and taking out the
coil from the press.
8.2.11 CLEANING AND DRYING Clean outer and inner surface of projected insulation by means of shop made scrubber.
Flow dry compressed air after cleaning.
Check height and window dimensions as per drawing. Check no gap between the turns.
Test the coil from inter turn test at 116 volts AC at a pressure of 480 tonnes in 5 minutes.
Coat the coil with two layers of epoxy red gel.
8.2.12 TURBO ROTOR COIL SECTION
This section is equipped with copper straightening and cutting machines, edge bending machines,
installation for forming and brazing, 10-block hydraulic press and installation for insulation filling.
Rotor coils for water cooled generators (210 /235 MW) are manufactured in this section.
This section is equipped with electric drying ovens, Air drying booths, Bath for armature / rotor
impregnation. Rotors / armatures of AC and DC motors are impregnated in this section.
8.2.14 BABBITING SECTION
This section is equipped with alkaline degreasing baths, hot and cold rinsing baths, pickling baths,
tinning bath, and electric furnaces and centrifugal shot blasting babbiting machines, babbiting of
bearing liners for Turbo generators, Turbines, Hydro generators, AC motors and DC motors is
carried out in this section.
8.4 TEST STANDS
Turbo-generators Test Bed -The Test Bed for Turbo-generators and Heavy motors is equipped withone no. 6 MW drive motor and a test pit for carrying out testing of Turbo-generators and Heavy
motors. Open circuit, short circuit, temperature rise, hydraulic and hydrogen leakage test etc., are
carried out here for Turbo-generators. AC motors up to 11 MVA capacity and DC machines up to
5000 amps and 850 volt can also be tested. Two DC drive motors of 2200 KW and one of 1500
KW are available for type testing of motors. Data logging equipment is also available.
8.5 LARGE SIZE TURBO GENERATOR TEST STAND (LSTG)It is equipped with a 12 MW drive motor and two number test pits. Open circuit ,short circuit ,
sudden short circuit , temperature rise , hydraulic & hydrogen leakage tests are carried out here
Large size Turbo-generators. This test bed can presently test TG s of unit capacity up to 500 MW.
With certain addition in facilities (Higher capacity Drive motor and EOT cranes and modification
in controls and auxiliary systems), Turbo-generators of unit size up to1000 MW can be tested.
8.6 HELIUM LEAK TESTIt is used to check any leakage of gas from stator and rotor as if there is any leakage of gas used for
cooling such as hydrogen then it may cause an explosion. Testing of stator frame involves two
types of testing:-
HYDRAULIC TESTING :- Hydraulic testing involves in empty stator frame with attached end
shields and terminal box is subjected to a hydraulic test at 10 bar to ensure that it will be capable of
withstanding maximum explosion pressure.
PNEUMATIC TESTING:- The pneumatic testing involves filling of hydrogen in the sealed
stator frame and then soap water is used to check the leakage of welding.