QUATER-1-PE-HEALTH-LC2- this is just a sample of unpacked lesson
Training report
1. TRAINING REPORT
ON
INSULATION AND MANUFACTURING PROCESS OF
500MW TURBO GENERATOR BARS
SubmittedBy:
RAGHVENDRA PRARAP SINGH
ElectricalEngineering(3rd
Year)
1006321077
GLA Institute technology&Management
Mathura(U.P.)
Under the Guidance Of
Mr. A.K. Dhiman (DGM)
BHEL, HARIDWAR
2. ACKNOWLEDGEMENT
An engineer with only theoretical knowledge is not a complete engineer. Practical
knowledge is very important to develop and apply engineering skills‖. It gives me
a great pleasure to have an opportunity to acknowledge and to express gratitude to
thosewho were associated with me during my training at BHEL, Haridwar.
Special thanks to Mr. A.K Dhiman for providing me with an opportunity to
undergotraining under his able guidance and offering me a very deep knowledge of
practicalaspects of industrial work culture...I
express my sincere thanks and gratitude to BHEL authorities for allowing me
toundergo the training in this prestigious organization. I will always remain
indebted tothem for their constant interest and excellent guidance in my training
work, moreoverfor providing me with an opportunity to work and gain experience.
Raghvendra pratap singh
GLA ITM MATHURA
Electrical &Electronics Engineering
4. BHEL: AN OVERVIEW
BHEL is the largest engineering and manufacturing enterprise on India in the energy
related/infrastructure sector. BHEL was established more than 40 years ago, ushering in the
indigenous Heavy Electrical Equipment industry in India, a dream which has been more than
released with a well-recognized track record of performance. It has been earning profit
continuously since 1971-72.
BHEL caters to core sectors of India economy viz. Power Generation and Transmission,
Renewable Energy , Defense etc. The wide network of BHEL’s 14 manufacturing divisions, 4
power sector regional centers, 8 service centers, 15 regional offices and a large number of
projects sites spread all over India and abroad enables the company to promptly serve as
customer and provide them with suitable products, systems and services- efficiently and at
competitive prices.
BHEL has attained ISO 9001:2000 certifications for quality management and all the
manufacturing units divisions of BHEL have been upgraded to the latest ISO 9001:2000version.
All the major units divisions of BHEL have been awarded ISO 14001 certification for
Environmental Management System and OHSAS-18001 certification for Occupational Health
and Safety management System. BHEL become the first public sector Company in the country to
win the coveted prize for in Haridwar unit under the CII Exim Award for the business excellence
as per the globally recognized model of European Foundation for quality management. BHEL is
the only PSU among the 12 Indian Companies to figure in ―Forbes Asia Fabulous 50‖ list. It
has also won the ―Business standard star Public Sector Company Award 2006‖. The company
received MoU Excellence award for 2004-2005 and Merit Certificate for MoU Excellence for
2005-2006.
Power Generation
Power generation Sector comprises Thermal Gas, Hydrogen, Nuclear power plant
business. As of 31.3.2007. BHEL supplied sets accounts for 80,781 MW or nearly 65% of the
total install capacity of 1, 25,414 MW in the country.
Significantly these sets contribute 73% of the total power generated in the country. BHEL
has proven turnkey capabilities for executing power projects from concepts to commissioning. It
possesses the technology and capability to produce Thermal sets with super critical parameters
up to 1000 MW unit rating and gas turbine generator sets of up to300 MW units rating. Co-
generating 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 also supplies
circulating Fluidized Bed Combustion (CFBC) boilers for thermal plants.
5. The company has proven expertise in Plant Performance Improvement through
renovation, modernization and upgrading of a variety of Power plant equipment, besides
specialized know-how of residual life assessment health diagnostics and life extension of plants.
Overall, BHEL built Thermal sets achieved the highest ever PLH of 78.3% in 2006-2007 which
is 2.5% higher than the National average. The combined operating availability of these sets was
84.7%.
Heavy Electrical Equipment Plant
BHEL's Heavy Electrical Equipment Plant (HEEP) was set up in technical collaboration
with USSR, for the manufacturing of power plant equipment, AC/DC motors of various rating
with associated control equipment and started production in January 1967. In 1976, BHEL
entered into a collaboration agreement with M/s Kraft werk Union, AG of Germany for design,
manufacturing, erection and commissioning of large size steam turbines. More than40 percent of
the country's electrical energy is generated from the power equipment supplied by BHEL,
Haridwar.
BHEL offer wide ranging products and systems for T & D applications. Product
manufactured include power transformers, instrument transformers, dry type transformers ,series
and stunt reactor, capacitor tanks, vacuum and SF circuit breakers gas insulated switch gears and
insulators.
The products, which are manufactured in HEEP, are: - Steam Turbines, Turbo Generators,
hydro turbines, Gas turbines, etc
6.
7. COIL & INSULATION MANUFACTURING
SHOP(BLOCK-IV)
Introduction
As the complete one peace coil is not practicable so the coils are manufactured in two parts,
upper and lower bars. Out of the various BLOCKS as mentioned before the coil and insulation
manufacturing block is BLOCK-4. This block is known as the COIL ANDINSULATION
MANUFACTURING block. Block-4 is a feeder block for insulating items ,winding with class-B
Bituminous insulation and sheet metal components for all the products of Block-1 i.e. Turbo-
generators, Hydro-generators, A.C. and D.C. machines. There are three BAYS in this block each
bay manufactures stator bars and coils for different machines as mentioned below:
BAY-I: Bar winding shop: manufacturing of stator winding bars of generator.
BAY-II: Manufacturing of heavy duty generator stator bars with New CNC M/c No. 3-464
i.e. Roebel bar centre.
BAY-III: Insulation detail shop: Manufacturing of hard insulation & machining of hares
insulation part (Glass Textolite) such as packing, washer, insulation box, wedges
etc. & CNC taping machine.
Bar Shop: This shop is meant for manufacturing of stator winding coils of turbo-generator and
hydro generator.
Why do we call it bar?
It is quite difficult (rather impossible) to manufacture, handle and wind in the stator slot
of generator of higher generation capacity because of its bigger size and heavy weight. That
iswhy we make coil in two parts. One part its bottom part of coil called bottom or lower barand
other part of coil is called top bar or upper bar..
Turbo-Generators:
The manufacturing of bars of standard capacity such as 100MW,130MW, 150MW, 210/235MW,
210/250MW, 500MW. The plant has capacity andtechnology to manufacture 800MW and
1000MW generators.
Types of generators:
The generator may be classified based upon the cooling system used inthe generators such as:
THRI, TARI, THDI, THDD, THDF, THFF, and THW.
T => First alphabet signifies the type of generator i.e. 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 signifies the type of cooling of rotor e.g. radial,
indirect,forced, direct etc.
8. I/D/F => Last alphabet stands for the type of cooling of stator e.g. indirect cooling,
directcooling, and forced cooling
W => Cooling media used for cooling of stator coil e.g. water.
Sections in Block IV
(a)Assembly Section
MechanicalAssemblySection: - It is equipped with small size drilling machines,welding
sets and hydraulic testing equipment for manufacturing turbo-generatormechanical
assemblies.
Close Cubical Assembly Section
(b) Stator Bar Winding Section
Conductor cutting, insulation and transposition section having facilities fortransposing
the bars.
Stack consolidation section, forming and lug brazing sections have block typehydraulic
press, steel former and induction brazing installations respectively.
Insulation taping sections with automatic taping facilities in air-conditionedtemperature
covering maximum slot portion each overhung ay both ends.
Baking and pressing section having baking moulds for simultaneous curving of straight
and overhead portion with electrical heating.
(c) Armature Winding, Rotor coil and Stator bar Section :-
Coils are diamond pulled type with Class-B (bitumen) and Class-F (conventional or resinrich
discontinuous epoxy insulation) and Class-H Silicon insulation for machines rangingfrom 5 to
460 KW capacity.
This section has the following work centers:-
Conductors cutting, U- bending and terminal conductor cutting machines, U-
bendingmachines and terminal baths
Forming and Insulation of DC coils.
Main and Interpole Winding: - It is having semi-automatic winding machine.
Planking, boat pulling and diamond pulling machine.
Insulation and pressing of AC coils: - it is equipped with hydraulic presses of 608
Tcapacities.
(d) Impregnation Section :-
It is equipped with impregnation tank, ovens for impregnation of DC pole coils.
(e) Insulation Section :-
Insulating details, machining is equipped with small size lathes, milling and
radialdrilling machines and jet cutting saw.
Press Molding Section: - It has electrical ovens, hydraulic presses, shearing andcircular
saw cutting machines for manufacturing press molded components of all theelectrical
machines.
Plastic Molding Section: - Is equipped with various presses for plastic molded parts.
Bitumen Mica Tape Manufacture: - Is equipped with mica tape manufacturingmachine
and lathe for slitting mica tape to the required size.
9. MFG. Process flow chart of 500MW TG stator bar
1. Conductor draws from store.
2. Conductor cutting and end cleaning.
3. Transposition of conductor.
4. Assembly of all conductors to be used in stator bars.
5. Cross over insulation.
6. Consolidation if slot portion of bar.
7. I.S Test (i.e. inter strand test).
8. Forming of bar (to shape overhang portion).
9. Pickling of bar ends (1).
10. Mounting of contact sleeve & bottom part of water box.
11. Brazing of contact sleeve & bottom part of water box.
12. Pickling of bar ends (2).
13. Mounting of water box leak test.
14. Re-Pickling.
15. Water flow and Nitrogen test.
16. Thermal Shock Application.
17. Helium leak test.
18. Reforming of bar (i.e. overhang portion).
19. Insulation of bar on CNC machine.
20. Impregnation & curing of bar insulation
21. Surface finishing of stator bar.
22. OCP on stator bar.
23. Preparation of bar for HV and Tan δ test.
24. If O.K. Dispatch to Block-1 for lying in the generator.
10.
11. Chapter 2
MANUFACTURING PROCESS OF BARS
BAY-1
Some points of manufacturing process is in brief as below
–
1. Insulation Check
Fo r the manufacturing of stator bars insulated copper conductors are brought from
Bangalore, it’s of two type’s i.e. solid copper conductor & hollow copper conductors
which are used in water cooled stator layer glass insulation.
Insulating materials and the conductors are ensured to be certified.
If required the insulation is checked by the respective agencies
2. Conductor cutting
This process is done by automatic CNC machine. In this process the pre-insulated
copperconductor is cut into number of pieces of required length (length given in drawing as
perdesign) insulation is removed from both ends of the copper conductor out
Lower Bar:
Conductor Size Length Number of conductors
8*4.6*1.5mm(Hollow) 10200mm Hollow – 20
8*2.8mm(Solid) 10200mm Solid - 20
Upper Bar:
Conductor Size Length Number of conductors
8*4.6*1.5mm(Hollow) 10500mm Hollow – 20
8*1.3mm(Solid) 10500mm Solid - 40
3.Transposition:
Transposition means changing/shifting of position of each conductor in active core (slot)part.
After cutting the required number of conductors, the conductors are arranged on the 12comb in
staggered manner and then bends are given to the conductors with the help of bending die at
required distance. Then the conductors are taken out from the comb anddie and placed with their
ends in a line and transposition is carried out. This process isrepeated for making another half the
12. bar which would be mirror image of the first half. The two halves of the bar are overlapped over
each other and a spacer is placed between the two halves.
Transposition is done in two ways:
Half Pitch Transposition: - In this transposition, the first conductor at one end of the
barbecomes the last conductor at the other end of the bar.
Full Pitch Transposition: - In this method of transposition, the first conductor at one
endof the bar becomes the last conductor in the mid of the bar and then again becomes
thefirst conductor at the other end of the bar.
1.To reduce eddy current losses.
2. Equalize the voltage generator.
3. To minimize skin effect of ac current, small cross section of conductor is used andalso hollow
conductors are used to effect cooling by D.M water.
4. Crossover insulation :
The pre insulation of the copper conductor may get damaged due to mechanical bendingin
die during transposition, hence the insulating spacers are provided at the crossoverportion of the
conductors. A filler material (insulating putty of molding micanite) isprovided along the height
of the bar to maintain the rectangular shape and to cover thedifference of level of conductors. To
eliminate inter turn short at bends during edge wisebending and leveling of bars in slots portion
for proper stacking.
5. Stack Pressing:-
This process is basically done to consolidate the solid as well as the hollow conductorsinto a
single bar, the insulating material provide at crossover positions which has gluingproperties
melts and helps in the proper consolidation of the bar. In this process the bar ispressed both
vertically and horizontally in the Pressing Machine. The pressing machines are also provided
with the heaters
Each bar is on each tier of heating plate and it is then provided with an initial pressureof35
±5kgpercm2 and an initial temperature of 100-110° C. then the temperature is allowed to raise to
the maximum of 160°C, this temperature is kept for at least one hour with a final pressure of
80±10 kg per cm2 vertically and 70±10 kg per cm2horizontally.
After pressing the bar at specified pressure and maximum temperature for one hour, the
bars are then cooled placing them on cooling plates through which water is allowed to 13follow
13. below 50°C. The cooled bars are checked for their heights and widths at pressed portion of the
bar.
This complete process performed above is for one half of the bar. The same process is
then repeated for the other half of the bar similarly and then checked for bar’s height and
width at pressed portions as done before. Then the ends of both the bars are cleaned with
rectified spirit and sand paper for the inter strand test.
6. Inter Strand Short test : -
The consolidation bar stack is tested for the short between any two conductors in the bar ,if
found then it has to be rectified. This is done to ensure that no local current is flowing due to
short circuit between conductors. (300V A/C supply).
For this test all the bare conductors at both the ends are separated from each other so that they do
not short circuit. Then a live wire is connected to a conductor and received from it consecutive
conductor to light a lamp. Hence if the lamp lights up it shows short circuit between the two
conductors due to improper insulation between them. It shows insulation failure between the
conductors, these conductors are then replaced and bar is followed through all the previous
processes. Similarly all the conductors are checked for any short circuit. After passing both the
half bars from I.S.T. the bars are combined together and pressed into a single bar. A sheet of
mica glass insulation is provided between the two halves as the insulation also has some gluing
property to consolidate th two halves into a single bar. All the steps of pressing are again
followed for the complete bar and then it is allowed to cool.
7. Forming : -
In heavy generators each stator coil is very large in size and hence its manufacturing is difficult
as it will be very difficult to handle and process the complete coil. So each coil is manufactured
in two halves i.e. Upper half and Lower half. The bars which are processed till this process are
straight and hence they are required to be formed into the upper half or the lower half. Hence this
process of forming is very important as in this process the bars are bending from both the ends of
the bar i.e. at exciter side and turbine side at specific angles and shape as per design. This
process is done manually. First the former is set according to the design making different angles
at different positions. Each bar of a variant is bent or formed at sameangle. Once the former is
set, the bar is mounted on it and formed manually by melleting it from both the ends. After
forming the formed portion of the bars are assumed to get loose creating airgaps between the
conductors due to such a heavy melleting. Thus the formed portion of the bar are clamped at
different places and provided with heaters to reconsolidate the formed portion. After few hours
the bar is then allowed to cool at room temperature.
14. 8.
End Conductor Cutting:
Due to heavy malting of the bar for forming it from both the side i.e. exciter side andturbine
side, the conductors of the bar are produced at the ends of the bar. Therefore tobring all the
conductors of the bar in a plane End Conductor Cutting is required to bedone. Both the solid and
hollow conductors are cut and from both the sides of the bar.Also this process of cutting of the
hollow conductors helps in opening of vents of hollowconductors from both the ends of the bar.
9.
Pickling Process:
After the forming and cutting process of the bar and due to the transportation of the bar,there
accumulate very minute particles of dust on the ends of the bar. These particles maycause
hindrances at the time of brazing and may create some air gaps.So, in order to remove these
unwanted particles, basically the oil particles picklingprocess is performed. The basic solution
used for this process is called pickling solution.The constituents of the pickling solution are:
Sulphuric acid (H
2
SO
4
)-10%
Phosphoric acid (H
3
PO
4
15. )-5%
Hydrogen peroxide (H
2
O
2
)-5%
Water (H
2
O)
There are many other solutions used in this process, these are:
Ammonia
Thinner
Water
Rectified spirit
NitrogenIn this process the following steps are involved:
The end of the bar is dipped in thinner to remove the dust or oil particles.
The end is then dried with the help of N
2
gas.
Then the bar end is dipped in pickling solution for 5 to 10 minutes.
This is then followed with dipping in water.
16.
As there is acid in the pickling solution, so accordingly to neutralize the acidic effectof the acid it
has to be treated with some base, so the bar is then dipped in Ammonia(10%).
It is then followed with dipping in water.
As water takes a lot of time to evaporate, it may let the tiny chemical particles on thebar to react
with it and leave spots on the bar, this may weaken the insulation at thoseparticular points and
thus damage it, further it may lead to poor brazing. So in order toavoid such a damage the bar is
dipped in rectified spirit to make the water contentsevaporate as soon as possible.
The bar is then dried with N
2
gas.
15
Finally it is wrapped with cotton cloth to avoid any manual touch which may depositany dust
particle on it until it is ready for brazing. The same process of pickling isthen preformed on the
other end of the bar.
10.
Contact Sleeve Mounting:
After the pickling process is complete, contact sleeve and water box bottom parts aremounted on
both the ends of the bar. Contact sleeve, as clear from the name itself, it is arectangular sleeve
which is used to make contact between upper and lower bars when laidout in the generator to
form a complete coil. All the solid conductors are cut from theends of the bar after the contact
sleeve except the outer solid conductors. None of theconductor is cut before the contact sleeve so
that to make proper contact between theupper and the lower bars.The water box is mounted in
two halves; first the water box bottom part is mountedafter the contact sleeve keeping some
distance between them.Both the ends of the bar are then again pickled along with contact sleeve
and waterbox bottom part following the same procedure of pickling.
11.
Brazing of coil lugs
: -
For water cooled generator bars, the electrical connection contact and water box for inletand
outlet of water are brazed. The contact sleeves, which are used to make contactbetween the upper
bar and the lower bar to form a complete coil and the water boxbottom part, both together are
17. called Coil Lug, so the brazing of these two parts at the endof a bar is called Coil Lug Brazing.
Brazing is basically the process of fixation of both thecontact sleeve and water box bottom part
or we can say both are properly consolidatedusing brazing material at high
temperatures.Consolidation is properly done so that no air gap is left which would adversely
affectthe conducting properties of the contact sleeve and the bar.The two types of brazing
processes are:
Thermal brazing (using LPG)
Induction brazingAs induction brazing is more beneficial than thermal brazing as it does not
requires anyinflammable gas for heating. So now a
day’s
Induction brazing process is used. For brazingas we use very high temperature so that is possible
due to carbon strips fixed on the brazer.Carbon has very high resistance and when the current is
allowed to pass through it due toinduction the material to be brazed i.e. Contact Sleeve gets super
heated. Induction heating ishence faster and even more efficient than thermal heating.
16When the contact sleeve becomes red hot at 750ºC, the brazing material is thenpushed to fill
the air gaps and to consolidate the contact sleeve on the bar. It is then allowedto cool.The types
of brazing materials used are:
LAG 15P ( Alloy Silver 15 Phosphorous)
LAG 40Cd ( Alloy Silver 40 Cadmium)Same process of brazing is then repeated for the water
box bottom part. After the brazing of water box bottom part the bar is then allowed to cool at
room temperature.
12.
18. EndConductorCutting
As is clear from the name itself this is the process of cutting of extra conductors i.e. thehollow
conductors left after the water box bottom part are cut from both the ends of thebar. These
conductors are required to be cut so that water box top part with a nozzle is tobe mounted on the
water box bottom part. The vents of the hollow conductors are visiblefrom the ends of the water
box bottom part. The openings of the vents of the hollowconductors are then checked to be
uniform.After cutting of extra conductors from both the ends of the bar, pickling process isdone.
Samepicklingprocessasmentionedbeforeisthendoneatboththeendsofthebarfor removing the dust
particles, oil particles and other unwanted impurities which weassume to be there after the
brazing process of the contact sleeve and water box bottompart. After pickling the bar ends are
then wrapped in cotton cloth until the water test isperformed.
13.
WaterTest:
Water test is performed so that there not any blockage in the vents and also to check theflow of
water. Flow should be uniform i.e. all the vents should have same water flow.In this test water is
supplied from one side of the bar and is collected from the otherside of the bar in a tank and is
supplied back to the first end. Flow of the water ischecked by measuring the distance of the flow
of water.If there is any kind of blockage inside the hollow conductors of the bar then it
isindicated by flow of water i.e. flow of water will be not uniform and the bar is assumedto be
chocked. Then cocked conductors are changed or repaired and the bar is reformedand water test
is again performed to check the flow of water.
14.
BrazingOfWaterBoxTopPart:
Brazing of water box top part is done with water box bottom part in brazing section of Block-
4.For this it should be kept in mind that water box bottom part should have samematerial as that
of water box top part.The difference in previous brazing and this brazing is that, now flux is also
introducedwith brazing material and also flux is mixed with copper chips. Copper chips are
addedto make the electrical contact between the top and bottom part without the copper chipsthis
will be not possible.In this brazing material is formed in the shape as that of water box side
where it has tobe brazed. Brazing material is formed in square shape for top and bottom part and
in ringshape for the brazing of nozzle for water flow. Then both the parts are heated
withinduction brazer as done earlier. It is heated until they become red hot then the
brazingmaterial melts due to its low melting temperature then the melting temperature of
thewater box top and bottom part. Brazing material is also introduced at the boundaries untilit is
completely consolidated that is the entire air gap is completely filled.After the brazing of water
box top part the bar is then allowed to cool at roomtemperature.
19. 15.
CheckingOfThreadsandPicklingProcess:
As mentioned earlier that water box top part has got nozzle for flow of water, it also hasgot
threads which is provided for the proper fixation of water supply through water pipeto the bar.
These threads are checked for its uniformity by fixing water pipe to thenozzle. If threads are not
found satisfactory than the nozzle is replaced with new oneand again its threads are
checked.Also the pickling process is again done for the removal of any dust particles
andlubricants etc. the detail of this process is same as mentioned earlier in pickling process.
16.
Nitrogenleaktest:-
As the name suggests Nitrogen gas is the main constituent of the test. This test is similarto
puncture test that is inflated tube is dipped in water for any leakage, the air bubblesgives us the
exact position of the puncture.
Similarly on the same steps this test is performed. Basically this test is performed tocheck any
leakage in bar i.e. to check the brazing. In this test nitrogen at a pressure of 10Kg/Cm
2
is forced from one end of the bar and other end of the bar is blocked then thepressure of
10Kg/Cm
2
is maintained and both the ends of the bar are dipped in water.The bubbles if there any tells us
that brazing is weak or not done properly. So if bubblesappear then brazing is done again and
same test is performed for the proper brazing of water box top and bottom part.Then both the
ends of the bar wrapped in cotton cloth so that it is not disturbed i.e. to
17
14.
avoid any manual touch which may deposit any dust particle on it until it is ready forbrazing.
17.
InternalPickling
After various test performed on the bar the pickling process i.e. removal of any dustparticles
lubricants etc is done only on outer surface of the bar (ends). But from inside itis assumed that
there must be some impurities, foreign material must be present. For thispurpose inside pickling
20. is done.As mentioned earlier same process is repeated but from inside of the hollowconductors
this time.In this process the following steps are involved:
The thinner is passed through the bar to remove the dust or oil particles.
The dried with the help of N
2
gas.
Then the pickling solution is passed for 5 to 10 minutes.
Then water is flowed in the bar.
As there is acid in the pickling solution, so accordingly to neutralize the acidic effectof the acid it
has to be treated with some base, so the bar is filled with Ammonia(10%).
It is then followed flowing of water again.
As water takes a lot of time to evaporate, it may let the tiny chemical particles in thebar to react
with it and leave spots in the bar, this may weaken the insulation at thoseparticular points and
thus damage it, further it may lead to poor brazing. So in order toavoid such a damage the
rectified spirit is flowed in the bar to make the watercontents evaporate as soon as possible.
The bar is then dried with N
2
gas.
Finally it is wrapped with cotton cloth to avoid any manual touch which may depositany dust
particle on it until it is ready for brazing.
18.
BaroscopicTesting
This test is performed to check the impurities or foreign material inside the bar. To look inside
with naked eye is not possible so we use baroscopic for this purpose.So after internal pickling we
use a baroscopic to look inside the bar. Baroscopic ishaving a probe having a LED (light
emitting diode). LED is used to provide light insidethe bar. The probe of the baroscopic is
inserted from one end of the bar and seen from amagnifying lens. The probe gives a light which
21. is reflected by the sides of the bar(inside) and with the help of magnifying lens we get a clear
image that what is there inthe bar.If impurities are present then these are removed then only after
the bar is send to nextoperation.
19
19.
WaterTest:
Here again water test is performed. In earlier water test water flow was checked withoutthe water
box top part
.
But now the top part is brazed to the bottom part and to check itsflow this test is performed.Also
to check the proper flow from the nozzle this test is performed. In this test wateris forced or
pushed from one end of the bar and flow of water is checked from other endof the bar. This test
tells us the presence of any choke vents of water box top part. If anychoke vent is present then it
is repaired or whole of the water box top part is changedwith new one.
20.
ThermalShockTest:
Thermal shock test is performed to check whether the bar can withstand extremeconditions i.e.
when the generator is working or running at about 3000 Rpm. This isachieved by thermal shock
test.Thermal shock test consist of series of hot water & cold water cycles alternatively. Sofirstly
hot water at temperature of about 90ºC is passed through the bar and then coldwater at about
room temperature 27ºC approx. is flowed inside the bar alternatively. Thisprocessisrepeatedagain
andagain.This process is repeated for about 26 times i.e. it has 26 cycles of hot and cold water.So
this test tells us the strength of the bar so that it can withstand the working conditionsof the
generator. Temperature of the bar is taken in account according to the workingtemperature of the
generator. The cycles of hot (8
00
C) and cold (3
00
C) water are flownthrough the bar to ensure the thermal expansion and contraction of the joints.
21.
HeliumLeakageTest:
Helium test is the most important test of all, because helium test is performed to check any
minute leakage within the bar and at the brazed portion. Any minute leakage which
couldn’t be checked by water test can easily be observed by helium test because helium
is one of the lightest gases. So this is also the customers check point, before performingthis test
customer is by called and they see themselves the test being performed and if They find the test
all right then only the bar is send to next process.In helium test, whole of the bar is wrapped in
the polythene excluding the end points.The helium gas at pressure of 11Kg/Cm
2
is passed through the bar and a probe connectedto the gauge is inserted inside the polythene at
different places. The gauge will showdeflection if there is any helium atom present. Gauge will
22. show reading even if 1 heliumatom in 100000 atoms is present. This test checks the strength of
brazing and insulation.
20
22.
Reforming:
After all the previous processes which had undergone on the bar it is
assumedthattheshape of the bar is deformed from its original shape due to handling of the bar
from oneplace to another for different processes. So to keep the shape of the bar as per design,
thebar is checked if it is found distorted then it is reformed in the previous former machineby
placing the bar on the former and malleting.
23.
Insulation:-
The bar is insulated with the given number of layers to build the wallthickness of insulation
subjected to the generating voltage of the machine. Insulation isbasically done to prevent any
kind of short circuit between the bar and the stator corewhen the bar is assembled in the stator of
the machine. The stator bars are insulated with
Micalastic
(trade name) insulation. High quality mica, selected epoxy resins and amatching vacuum
impregnation process are the characteristic features of the micalasticinsulation for large turbo
generators.The bar is provided with 14 layers of insulation. Out of these fourteen layers, 12layers
are provided by using a machine called CNC TAPPING MACHINE manufacturedby a company
named MICAMATION. The rest of the two layers are provided manually.The insulating material
varies as according to the rating of the machines as follows:
For 500 MW : Mica Splitting Tape
For THRI : Mica GlassDuring machine taping in the slot portion the transition from machine to
hand taping isadjusted at the start of the bend for a tape width for every layer from bar center.
Afterabout half the number of layers, the taping is to be started further at the bend.The mica tape
consists of a thin high strength baking material to which the mica isbounded by synthetic resin.
The number of layers i.e. the thickness of insulation isdetermined by the voltage of the machine.
24.
Impregnationandbaking:
a)
23. Thermo reactive System:
In case of rich resin insulation the bar is pressed in closed boxin heated condition and baked
under pressure and temperature as per requirement for agiven period.
b)
Micalastic System
: In case of poor resin system the insulated bars are heated undervacuum and the impregnated
(dipped) in heated resin so that all the air gaps are filled,layer by layer, with resin. Then extra
resin is drained out and bars are heated and bakedunder pressed condition in closed box fixture.
c)
VPI Micalastic System: -
The bars already lay in closed fixture and full fixture isimpregnated (dipped) in resin and then
fixture with box is baked under giventemperature for given duration.
25.
MicalasticInsulationandImpregnation
For insulation with micalastic, the conductor strands are arranged together to form acompact
assembly and set to the required shape. This assembly is then baked with epoxyresin to give it
mechanical strength required for further processing. The bars are thendried under vacuum and
impregnated with synthetic resin, which by reason of its lowviscosity penetrates the insulation
thoroughly and eliminates all voids. After impregnationunder vacuum, the bars are subjected to
pressure, with nitrogen being used as pressurizingmedium. The impregnated bars with direct
conductor cooling are then brought to therequired dimensions in moulds and cured in an oven at
a high temperature.This complete process involves pressing of the bars, drying by heating,
impregnationin resin and finally curing. These processes are discussed briefly below:
Pressing:
The bars are pressed to bring them back to the original dimensions.
Drying:
The stator windings are to be dried under vacuum 0.1 m bar at (60±5) °C for15 hours, minimum.
The drying temperature is to be increased to (65±2) °C if theinitial viscosity of the impregnating
resin mixture is high.
The temperature distribution should be as uniform as possible. The drying undervacuum can be
stopped if the pressure rises, 10 minutes after closing of vacuum valveis less than 0.06 m bar.
24. Impregnation:
The impregnation resin mixture is to be heated in the working tank, to(60±3) °C or in case of
higher initial viscosity. At a temperature of 50ºC, theimpregnating resin mixture is to be
degassed with 1-5 m bar vacuum. Subsequentlythe stator windings are to be dipped continuously
in resin hardener mix such that thehighest locations of the windings are at least 100 mm below
the resin level. After 10minutes of resin stabilization,
pressure is increased
by application of nitrogen.Pressure is to be gradually increased in uniform stages within 80
minutes to 4 barsand to be maintained for 120 minutes in the impregnation tank.The
impregnation of the stator winding is to be monitored continuously.Further it is to be decided
whether to increase the pressure or to stop the impregnationprocess, however the total period of
nitrogen pressure cycle shall in any case notexceed 4 hours. The impregnation tank during shut
down is to be closed and kepteither filled with nitrogen (1.1bar) or low vacuum.
Curing:
To prevent heating in the overhang portion, the curing of the impregnatedstator winding is to be
done with a maximum 160°C hot air. The curing period isextended for such a long time till the
measurement positions in the core indicate(140±5) ºC for minimum 8 hours.
22
26.
Finishing:-
The baked and dimensionally correct bars are sanded - off to smoothen theedges and the surface
is calibrated, if required, for the dimension.
27.
Conductingvarnishcoating:
(i)
OCP (Outer Corona Protection) Coating: -
The black semi-conducting varnish coatingis applied on the bar surface on the core length.
(ii)
ECP (End Corona Protection) Coating:
The grey semi-conducting varnish is applied atthe bend outside core end of bars in gradient to
prevent from discharge and minimizethe end corona.
25. Resin System
a)
Rich resin or Thermo reactive insulation system:
In this type of insulation system thebond content in resin is 35-37%. The raw materials are ready
to use and requirepreservation and working on temperature 20-25
0
C. Its shelf life is one year when kept attemperature 20
0
C which could be increased when kept at temperature of 5
0
C.
b)
Poor resin or Micalastic insulation system:
In this type of insulation the bond content inthe resin is 5-7% and insulating material is prepared
with accelerator treatment. Thetemperature control need not required. The insulating material is
applied on job and thenthe same is impregnated (fully dipped) in the resin.
Testing
When the bar is dried it is wrapped with aluminum sheet to make outer surface of the bar
conducting so that tan δ and H.V. (High voltage test) can be performed. After these tests the
coating of red gel is applied at both the ends of the bar.
Tan
∆
Test
Test is performed to find the capacitance of the bar because bar will act as capacitor when itis
laid in the stator of the generator. In this test Schearing Bridge which works on theprinciple of
wheat-stone bridge is used to find the unknown capacitance of the bar. For goodefficiency,
capacitance of the bar should be high but we never approach pure capacitance.In this test also
same bar which is wrapped with aluminum is used to make the barconductive throughout the
outer surface of the bar. The two conducting material i.e. thealuminum sheet and the conductors
of the bar act as two plates of the capacitor and theinsulation on the bar act as dielectric medium
for the capacitor. The capacitance of the bar isfound and of angle of deviation due to impurity in
the insulation is obtained from theformula:C
4
* R
4
* 10
-4
26. = tan δFor different ratings of the bar the acceptable value of tan δ is fixed according to their
insulation requirement as per design considerations.
23
H.V. (High Voltage) Testing
This test is also known as insulation test because this test is performed to check the insulationof
the bar. In this test the bar which is already wrapped with aluminum is used. High voltageis
applied to the bar using auto-transformer and it is increased in steps according to theworking
voltage of the generator. If the insulation is weak the bar will puncture at the placeof weaker
insulation. For 500 MW the working voltage of the bar is 64.5 KV & for 210 MWthe working
voltage of the bar is 63 KV. If any of the bar fails this test i.e. bar is punctured atany point then
the bar is sent back for re-insulation and all the processes are repeated again.
27.
28. 24
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hapter
3
BAY-2
Introduction:Bay 2 is the manufacturer of stator bars of hydro generators, stator coils of AC motors
andstator coils of DC Exciter. The stator coils of AC motors of up to 11 KV, stator bars of
Hydrogenerators of 200 MW and DC Exciters of all the 500 MW THRI generators
aremanufactured in this bay.The processes involved in the manufacturing of AC motors are as
follows:
Insulation Check
For the manufacturing of stator coils of AC motors, insulated copper conductors of
specificdimensions rolled on the drums are brought from Bangalore. Before performing any
processon that conductor, the insulation of the conductor is checked.
Insulating materials and the conductors are ensured to be certified.
If required the insulation is checked by the respective agencies.
29. Conductor Tapping
The copper conductor is first provided with two layers of insulation, this is also known asdouble
layer tapping. The insulation tape used in this is Micafabriglass Tape. In this processthe copper
drums are loaded on the stand and tapping rolls on taping heads of the Tappingmachine. The
copper conductor is insulated with two layer of tape in butt as per design andhence the insulated
copper conductor is again rolled on the drum from other side of themachine. The insulation on
the copper is checked, which is provided by the automaticallymoving tapping rolls with some
tension.
Winding Boat Coil
The next process is forming a boat shape coil with the insulated copper conductor. In thisprocess
the former of the boat shape coil, which is adjustable in length, is first set as perlength of the coil
required according to the design. The number of conductors per turn and thetotal number of turns
in a coil are all set according to the design. The insulated copperconductor drums are loaded on
stand on one side of the former, the former is then rotated andhence a boat shaped coil of
specified length and specific number of turns is formed.The boat coil is then checked for its
length and number of turns.
25
Boat Insulation
The boat coil is then sending to the insulation block for its insulation. Here the complete boatcoil
is insulated with single layer of polythene and then the stack consolidation length of thecoil is
marked and the coil is send for the next process.
Stack Pressing
In this process the press plank is first cleaned then the boat coil is loaded in the press. Theboat
coil is cured for 35 minutes at 155 ± 5 °C under high pressure (to ensure closing of box)after
attaining the temperature. 0.1 mm filler gauge should not go inside the box. The stack length and
width of the boat coil is checked at slot portions. The pressing of the boat coil isdone for the
consolidation of the coil. The length of heating plates should be approximatelyequal to the stack
consolidation length of coil.
Forming
The forming of the boat coil is done in an automatic machine i.e. Schumann Pulling
Machine.The machine is first set, and then the forming plates are mounted for overhang on
30. themachine. The forming plates mounted are according to the overhang design of the coil.
Therequired variant of boat coil is pulled into the diamond shape. The loading of boat coil
shouldbe as per the variant of boat coil given in the design. The coil dimensions and geometry of
thecoil is then checked on the Universal Model. The terminals of the coil are set according to
thedesign and also the first bends and the overhang portions are marked.
Insulation
In this process the slot portion and the first bends of the coil are insulated with acceleratortreated
Mica Tape as per design. For the stator coil of 11 KV AC motor, total 8 layers of insulation
tapping are provided i.e. three layers at the slot portion and the rest five layers allover the coil.
Generally for the stator coils of low rating motors total five layers of insulationtapping is
provided. The insulation tape used is Epoxy Mica Paper tape. Red tape is thefinishing tape
provided at the overhang portions of the coil. The black colored insulation tapein conducting in
nature and it is provided at the slot portion of the coil. The insulation tape atthe bend portions of
the coil is grey in color and is semi conducting in nature.Then the perimeters and width of the
insulated coil is checked at the slot portion of the coil.A release film is to be provided on the
entire coil including coil terminals. On slot portiontwo layers of release film is provided. The
coil is now sending for the next process.
Impregnation
For impregnation pressing strips are mounted on the coil. The pressing strips are checked tobe
closed properly
.
The coils are then impregnated in micalastic resin as per design.
26The impregnation resin mixture is to be heated in the working tank, to (60±3) °C or in caseof
higher initial viscosity. At a temperature of 50ºC, the impregnating resin mixture is to
bedegassed with 1-5 m bar vacuum. Subsequently the stator windings are to be
dippedcontinuously in resin hardener mix such that the highest locations of the windings are at
least100 mm below the resin level. After 10 minutes of resin stabilization,
pressure is increased
byapplication of nitrogen. Pressure is to be gradually increased in uniform stages within
80minutes to 4 bars and to be maintained for 120 minutes in the impregnation tank.The
impregnation of the stator winding is to be monitored continuously. Further it is to bedecided
whether to increase the pressure or to stop the impregnation process, however thetotal period of
nitrogen pressure cycle shall in any case not exceed 4 hours. The impregnationtank during shut
down is to be closed and kept either filled with nitrogen (1.1bar) or lowvacuum.
Curing
After the impregnation of the coil
31. ,
it is then cured at 140
± 10 ºC for 18 hours after attainingthe required temperature. Curing of the coil is done for the
proper consolidation of the coil.The regime is then required to be checked. The pressing strips
are disassembled after thecuring of the coil. The dimensions of the coil are then checked.
Finishing
In this process the release film is removed and the coil is finished with sand paper. Thestraight
length of the coil is marked. The coil is then coated with corona protection varnish asper design
and then the coil is allowed to dry properly for 6 hours. The slot portiondimensions and the
quality coating varnish are then checked.
The coil is checked for its insulation using tan δ
and H.V. (High Voltage) Test.
27
BAY -3
Introduction:
Bay 3 is the manufacturer of insulating material of different shapes and sizes as
requiredaccording to the design. This bay is also called as I.D. Section (Insulation Design
Section).For the manufacturing of insulations, different raw materials having insulating
properties arebrought by this section. The raw materials having different insulating properties are
thenprocessed in this section and molded to different shapes as per design.The raw materials
used in this bay are:
Glass based Textolite Sheet
Cotton based Textolite Sheet
PaperbasedTextoliteSheet
32. MicaGlasssheet
Teflon Sheet
MicaSheet
NylonSheet
Ebonite
PerpexGlassSheet
Nomex Paper
Asbestos Sheet
Asbestos PaperAll the insulating raw materials mentioned above are in the decreasing order of
theirinsulating property. The insulating materials used in the manufacturing of insulation
mouldsare categorized according to their laying requirement in the machine i.e. if an
insulationmould is to be fixed in the place where the risk of fire is more then at those places
moulds of Glass based Textolite sheet are preferred because cotton based or paper based textolite
sheetcould catch fire at those places.Teflon Sheet has an important property and i.e. Teflon is
non heat transferring material. Soan insulating mould of Teflon is placed above the bearings of
the rotor so that is any fault inthe bearings of the rotor produces any heat then it is prevented by
this material to gettransferred to the rotor, and hence prevents the rotor of the machine.For the
manufacturing of insulation moulds, the glass insulation raw material in fibers isfirst pressed into
blocks in a pressing machine with the help of heaters and hydraulicpressure. Fibers are made into
blocks because if fiber is used as it is then volume of thematerial will be very large. So blocks
are placed on weighing machine and then weighedequal to the product required according to
design. So then these blocks are placed in themould and heated and molded in the shape as that
of the mould by applying sufficientpressure and temperature.
28
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hapter
4
33. ELECTRICAL MACHINES BLOCK (BLOCK
—
I)
Introduction
1.
Block-I is designed to manufacture Turbo Generators.2.
The block consists of 4 bays- Bay-I (36*482 meters), Bay-II (36*360 meters) and Bay-IIIand
Bay-IV (Of size 24*360 meters each).3.
For handling and transporting the various components over-head crane facilities areavailable,
depending upon the products manufactured in each Bay. There are also anumber of self-
propelled electrically driven transfer trolleys for the inter-bay movementof components /
assemblies.4.
Testing facilities for Turbo generator are available in Bay-II.5.
There is a special test bed area for testing of T.G. of capacity of 500 MW Unit sizes.
Manufacturing Process
Fabricated components are received in respective machine sections from Fabrication
blocks(Block
—
II, V, VI, VIII), while castings and forgings are received from sister unit CFFP andother
indigenous and foreign sources for Turbo Generators. Stampings are received fromstampings
manufacture block, block
—
VI and coils, bars, insulating details and sheet metalcomponents are received from coils and
insulation manufacture and apparatus and controlgear box (block
—
IV).
1.
Turbo Generators
–
a)
Making of blanks is done for checking the availability of machining allowances.b)
Machining of the major components is carried out in Bay - I & Bay - II and othersmall
components in Bay - III and Bay - IV. The boring and facing of stators are doneon CNC
horizontal boring machine using a rotary table. The shaft is turned on lathehaving swift 2500 mm
and the rotor slots are milled on a special rotor slot millingmachines.c)
In case of large size Turbo Generators core bars are welded to stator frame with the
34. 29help of telescopic centering device. The centering of core bar is done very precisely.Punching
is assembled manually and cores are heated and pressed in number of stagesdepending on the
core length.d)
Stator winding is done by placing stator on rotating installation. After lying of lowerand upper
bars, these are connected at the ends, with the help of ferrule and thensoldered by resistance
soldering.e)
Rotor winding assembly is carried out on special installation where coils areassembled in rotor
slots. The pressing of overhang portion is carried out on specialring type hydraulic press,
whereas slot portion is pressed manually with the help of rotor wedges. Coils are wedged with
special press after laying and curing. Thedynamic balancing of rotors is carried out on the over
speed balancing installation.500 MW Turbo Generators are balanced in vacuum balancing
tunnel.f)
General assembly of Turbo Generators is done in the test bed. Rotor is inserted in thestator and
assembly of end shields; bearings etc. are carried out to make generatorsready for testing. Prior
to test run the complete generator is hydraulically tested forleakages.
g)
Turbo Generators are tested as per standard practices and customer requirements.
Turbo Generator
500MWTurbogeneratorsataglance-
2-Pole machine with the following features:-
Direct cooling of stator winding with water.
Direct hydrogen cooling for rotor.
Micalastic insulation system
Spring mounted core housing for effective transmission of vibrations.
Brushless Excitation system.
Vertical hydrogen coolers
Salient technical data-
35. Rated output : 588 MVA , 500 MW
Terminal voltage : 21 KV
Rated stator current : 16 KA
Rated frequency : 50 Hz
Rated power factor : 0.85 Lag
Efficiency : 98.55%
27
BAY -3
Introduction:
30
Important dimensions & weights -
Heaviest lift of generator stator : 255 Tons
36. Rotor weight : 68 Tons
Overall stator dimensions [L*B*H] : 8.83m*4.lm*4.02m
Rotor dimensions(Dia. and length) : 1.15m and 12.11m
Total weight of turbo generator : 428 Tons
Unique installations-
Heavy Electrical Equipment Plant, Haridwar is one of the best equipped and most modernplants
of its kind in the world today. Some of the unique manufacturing and testing facilitiesin the plant
are:
TG Test Bed-
New LSTG [Large Scale Turbo Generator] Test Bed has been put up with indigenous know-how
in record time for testing Turbo generators of ratings 500 MW and above up to 1000MW. It
caters to the most advanced requirement of testing by employing on-line computerfor data-
analysis.
Other major facilities are as follows
–
Major facilities like stator core pit equipped with telescopic hydraulic lift, micalastic plantfor the
manufacture of stator bars, thermal shocks test equipment, rotor slot millingmachine etc. have
been specially developed by BHEL.
12 MW/10.8 MW, 6.6 KV, 3000 RPM AC non salient pole, synchronous motor havebeen used
for driving the 500 MW Turbo-generator at the TEST Bed. The motor hasspecial features to suit
the requirement of TG testing (500 MW and above). This is thelargest 2-pole (3000 rpm).
Over speed balancing vacuum tunnel -
For balancing and over speeding large flexible Turbo generators rotors in vacuum for ratingsup
to 1,000 MW, an over speed and balancing tunnel has been constructed indigenously.
Thisfacility is suitable for all types of rigid and flexible rotors and also high speed rotors for
lowand high speed balancing, testing at operational speed and for over speeding.
Generator transportation -
Transport through300 Tons 24-Axle carrier beam railway wagon specially designedindigenously
and manufactured at Haridwar.
The wagon has been used successfully for transporting one generator -from Calcutta Portto
Singrauli STPP.
37. 31
CONSTRUCTIONAL FEATURES OF STATOR WINDING
1)
General
–
The stator has a three phase, double layer, short pitched and bar type of windingshaving two
parallel paths. Each slots accommodated two bars. The slot lower bars and slotupper are
displaced from each other by one winding pitch and connected together by bus barsinside the
stator frame in conformity with the connection diagram.
2)
Conductor Construction
–
Each bar consists of solid as well as hollow conductor with cooling water passingthrough the
latter. Alternate arrangement hollow and solid conductors ensure an optimumsolution for
increasing current and to reduce losses. The conductors of small rectangular crosssection are
provided with glass lapped strand insulation.A separator insulates the individual layers from each
other. The transposition providesfor mutual neutralization of voltage induced in the individual
strands due to the slots crossfield and end winding field. The current flowing through the
conductor is uniformlydistributed over the entire bar cross section reduced.To ensure that strands
are firmly bonded together and give dimensionally stability inslot portion, a layer of glass tape is
wrapped over the complete stack. Bar insulation is donewith epoxy mica thermosetting
insulation. This insulation is void free and posses bettermechanical properties. This type of
insulation is more reliable for high voltage. Thisinsulation shows only small increases in
dielectric dissipation factor with increasing testvoltage. The bar insulation is cured in an
electrically heated process and thus epoxy resin fillall voids and eliminate air inclusions.
3)
Method Of Insulation
–
Bar is tapped with several layers of thermosetting epoxy tape. This is appliedcontinuously and
half overlapped to the slot portion. The voltage of machine determines thethickness of insulation.
The tapped bar is then pressed and cured in electrical heated pressmould for certain fixed
temperature and time.
38. 4)
Corona Prevention
–
To prevent corona discharges between insulation and wall of slots, the insulation inslot portion is
coated with semiconductor varnish. The various test for manufacturing the barare performed
which are as follows-(a)
Inter turn insulation test on stuck after consolidation to ensure absence of inter short.(b)
Each bar is subjected to hydraulic test to ensure the strength of all joints.
32(c)
Flow test is performed on each bar to ensure that there is no reduction in cross sectionarea of the
ducts of the hollow conductor.(d)
Leakage test by means of air pressure is performed to ensure gas tightness of all joints.(e)
High voltage to prove soundness of insulation.(f)
Dielectric loss factor measurement to establish void free insulation.
5)
Laying Of Stator Winding
–
The stator winding is placed in open rectangular slots of the stator core, which areuniformly
distributed on the circumference. A semi conducting spacer is placed in bottom of slots to avoid
any damage to bar due to any projection. Driving in semi conducting fillerstrips compensates any
manufacturing tolerances.After laying top bar, slot wedges are inserted. Below slots wedges,
high strength glasstexolite spacers are put to have proper tightness. In between top and bottom
bars, spacers arealso put.
6)
Ending Winding
–
In the end winding, the bars are arranged close to each other. Any gaps due to designor
manufacturing considerations are fitted with curable prepag with spacer in between. Theprepag
material is also placed between the brackets and binding rings. Lower and upperlayers are fixed
with epoxy glass ring made in segment and flexible spacer put in betweentwo layers.Bus bars are
connected to bring out the three phases and six neutrals. Bus bars arealso hollow from inside.
39. These bus bars are connected with terminal bushing. Both are water-cooled. Brazing the two lugs
properly makes connection.
CONSTRUCTIONAL FEATURES OF ROTOR
The rotor comprises of following component:1) Rotor shaft2) Rotor winding3) Rotor wedges and
other locating parts for winding4) Retaining ring5)Fans6) Field lead connections
331)
Rotor Shaft
–
The rotor shaft is a single piece solid forging manufactured from a vacuum
casting.Approximately 60 % of the rotor body circumference is with longitudinal slots, which
holdthe field winding. The rotor shaft is a long forging measuring more than 9m in length
andslightly more than one meter in diameter. The main constituents of the steel are
chromium,molybdenum, nickel and vanadium. The shaft and body are forged integral to each
other bydrop forging process.Following tests are done: -(a)
Mechanical test(b)
Chemical analysis(c)
Magnetic permeability test(d)
Micro structure analysis(e)
Ultrasonic examination(f)
Baroscopic examinationOn 2/3 of its circumference approximately the rotor body is provided
with longitudinal slot toaccommodate field winding. The slot pitch is selected in such a way that
two solid polesdisplacedby180
o
C are obtained. For high accuracy the rotor is subjected to 20% overspeeding for two minutes.
The solid poles are provided with additional slots in short lengthsof two different configurations.
One type of slots served as an outlet for hydrogen which hascooled the overhang winding and
other type used to accommodate finger of damper segmentsacting as damper winding.
2)
Rotor Winding
–
After preliminary turning, longitudinal slots are milled on sophisticated horizontal slotmilling
machine. The slot house the field winding consists of several coils inserted into thelongitudinal
slots of rotor body
–
40. 2.1.
Copper Conductor
–
The conductors are made of hard drawn silver bearing copper. The rectangular crosssection
copper conductors have ventilating ducts on the two sides thus providing achannel for hydrogen
flow. Two individual conductors placed-one over the other arebent to obtain half turns. Further
these half turns are brazed in series to form coil onthe rotor model.
41.
42. 352.2.
Insulation
–
The individual turns are insulated from each other by layer of glassprepag strips on turn of
copper and baked under pressure and temperature to give amonolithic inter turn insulation. The
coils are insulated from rotor body by U-shapedglass laminate module slot through made from
glass cloth impregnated with epoxyvarnish.At the bottom of slot D-shaped liners are put to
provide a plane seating surfaces forconductors and to facilitate easy flow of gas from one side to
another. These linersare made from molding material. The overhang winding is separated by
glasslaminated blocks called liners. The overhang winding are insulated from retainingrings
segments having L-shape and made of glass cloth impregnated by epoxy resin.
2.3.
Cooling Of Winding
–
The rotor winding are cooled by means of direct cooling method of gap pick-upmethod. In this
type of cooling the hydrogen in the gap is sucked through theelliptical holes serving as scoop on
the rotor wedges and is directed to flow alonglateral vent ducts on rotor cooper coils to bottom of
the coils. The gas then passesinto the corresponding ducts on the other side and flows outwards
and thrown intothe gap in outlet zones.In this cooling method the temperature rise becomes
independent of length of rotor. The overhang portion of the winding is cooled by axial two
systems andsectionalized into small parallel paths to minimize temperature rise. Cold gas
entersthe overhang from under the retaining rings through special chamber in the endshields and
ducts under the fan hub and gets released into the air gap at rotor barrelends.
3)
RotorWedges
–
For protection against the effect of centrifugal force the winding is secured in the slotsby slot
wedge. The wedges are made from duralumin, an alloy of copper, magnesium andaluminum
having high good electrical conductivity and high mechanical strength.Thewedgesattheendsofslot
aremadefromanalloyofchromiumandcopper.These are connected with damper segments under the
retaining ring for short circuit inducedshaft current. Ventilation slot wedges are used to cover the
ventilation canals in the rotor sothat hydrogen for overhang portion flows in a closed channel.
4)
Retaining Ring
–
The overhang portion of field winding is held by non-magnetic steel forging of retaining ring
against centrifugal forces. They are shrink fitted to end of the rotor body barrelat one end; while
at the other side of the retaining ring does not make contact with the shaft.
43. 36The centering rings are shrinking fitted at the free end of retaining ring that serves toreinforce
the retaining ring, securing, end winding in axial direction at the same time. Toreduce stray
losses, the retaining rings are made of non-magnetic, austenitic steel and coldworked, resulting in
high mechanical strength.
5)
Fans
–
Two single stage axial flow propeller type fans circulate the generator cooling gas.The fans are
shrinking fitted on either sides of rotor body. Fans hubs are made of alloy steelforging with three
peripheral grooves milled on it. Fan blades, which are precision castingwith special alloy, are
machined in the tail portion so that they fit into the groove of the fanhub.
6)
Field Lead Connections
–
6.1
Slip Rings
–
The slip ring consists of helical grooved alloy steel rings shrunk on thebody shaft and insulated
from it. The slip rings are provided with inclined holes forself-ventilation. The helical grooves
cut on the outer surfaces of the slip rings improvebrush performance by breaking the pressurized
air pockets that would otherwise getformed between the brush and slip rings.
6.2
Field Lead
–
The slip rings are connected to the field winding through semi flexiblecopper leads and current-
carrying bolts placed in the shaft. The radial holes withcurrent carrying bolts in the rotor shafts
are effectively sealed to prevent the escape of hydrogen.A field lead bar, which has similar
construction as, does the connection betweencurrent carrying bolt and field winding that of semi
flexible copper leads (they areinsulated by glass cloth impregnated with epoxy resin for low
resistance and ease of assembly).
CONCLUSION
The second phase of training has proved to be quite faithful. It proved an opportunity
forencounter with such huge machines like turbo-generator hydro generator etc.The architecture
44. of B.H.E.L., the way various units are linked and the way working of whole plant is controlled
make the students realize that Engineering is not just structuraldescriptionbutgreaterpartisplanning
andmanagement.Itprovidesanopportunitytolearntech.Used at proper place and time can save a lot of
labor.However,traininghasprovedtobesatisfactory.Ithasallowedusanopportunitytogetanexposureofthe
practicalimplementationoftheoreticalfundamentals.
37
BIBLIOGRAPHY
BHarat Heavy Electrical Ltd. BHEL Turbo Generators Manual. In BHEL,
BHEL product technical Manual.
Bharat Heavy Electricals Limited. (2005).
Bharat Heavy Electricals Ltd. Product Information
. Retrieved May 2010, from http://www.bhel.com
Bharat Heavy Electricals Ltd. (1993).
BHEL Pro/E Manuals.
Haridwar: BHEL.
meena, A. (n.d.).
electrical report at BHEL haridwar
. Retrieved May 2010, fromScribd: http://www.scribd.com/doc/31295276/electrical-report-at-
BHEL-haridwar
Verma, A. (2010, May). Daily Diary.
BHEL visiting notes
. Haridwar, Uttrakhand,India
