VPI for turbo generator

Automation of Vacuum Pressure Impregnation process of Insulation for an Air cooled Turbo generator

DEPT. OF EEE 1 AITS-HYD

1. INTRODUCTION

Electrical insulating materials are defined as materials that offer alarge resistance to

the flow of current and for that reason they are used to keepthe current in its proper path i.e.

along the conductor. Insulation is the heart ofthe generator.

Since generator principle is based on the induction of e.m.f in aconductor when

placed in a varying magnetic field. There should be properinsulation between the magnetic

field and the conductors.

For smaller capacitiesof few KW, the insulation may not affect more on the

performance of thegenerator but for larger capacities of few MW (>100MW) the

optimization ofinsulation is an inevitable task.

Moreover the thickness of insulation should beon par with the level of the voltage,

also non homogenic insulation provisionsmay lead to deterioration where it is thin and

prone to hazardous short circuits.

Also the insulating materials applied to the conductors are required to be flexibleand

have high specific (dielectric) strength and ability to withstand unlimitedcycles of heating

and cooling.

Keeping this in view among other insulating materials like solidsgases etc liquid

dielectrics are playing a major role in heavy electrical equipmentwhere the can embedded

deep into the micro pores and provide betterinsulating properties.

Whereas solid di-electrics provide better insulation withlower thickness and with

greater mechanical strength.

So the process ofinsulation design which has the added advantage of both solid and

liquiddielectrics would be a superior process of insulation design.

One such processwhich has all the above qualities is the VPI (vacuum pressurised

impregnation)process and has proven to be the best process till date.

Vacuum impregnation as an industrial process has been in commercial use for more

than 60 years.

For the world’s largest manufacturers, it continues to be the preferred process through

which to guarantee the pressure-proof, leak-proof, and corrosion-proof requirements of

parts and components in critical operations.



1.1NECESSITY

During normal operation,Electrical machines like Generators, Transformers etc are

subjectedto the failure of the insulation system. How long an insulation system will be

serviceable depends on the materials chosen and the service environment.Thermal,

mechanical, voltage and environmental stresses all combine to reduce the service life of the

Electrical machines.

a) To reduce this losses, We have to manufacture all Electrical machines like

Generators, Transformers using the Vacuum Pressure Impregnation (VPI) process.

b) This system strengthens the insulation system and extends the service life of the

transformer. The VPI process is the most advanced system in use today.

c) VPI includes pressure in addition to vacuum, thus assuring goodpenetration of the

varnish in the coil.

d) The result is improved mechanical strengthand electrical properties.

e) With the improved penetration, a void free coil isachieved as well as giving greater

mechanical strength.

1. 2OBJECTIVE

The ultimate goal of vacuum impregnation is to seal leak / migration paths without

impacting the functional,assembly or appearance characteristics of a part. Functional

characteristics include the ability for fluids or gasses to flow only where needed in order to

enhance in-service performance of the components’ design. Assembly characteristics, which

must be maintained, include performance of tapped holes; the integrity of mating and

sealing surfaces; the elimination of residual internal contamination in water jackets; sockets;

surfaces; and dimensional areas. Appearance characteristics include oxidation and

discoloration.

The processing methods may be used to variety of impregnate parts. The method

selected depends on the sealant and the requirements of the parts. Fundamentally, vacuum

impregnation sealing of porosity addresses a pair of fluid mechanics problems. The laws of

fluid mechanics govern the flow problem of removing the air from the pores and the flow

problem of filling the pores with liquid sealant.



1.3 THEME

To insulate winding elements in rotating high voltage electrical machines the

impregnation technique based on vacuum pressure impregnation has become very popular in

recent years, In doing so, the winding elements for construction engineering reasons are made

either as preformed coils or conduct and scolds preferably performed bars. The winding

elements are provided with mica-containing mail solution and are further tired in a vacuum

pressure impregnation process.

The main theme/characteristics of this insulation system are:

a. Better heat transfer resulting from penetration into minute air

gaps in between laminations and bar insulation.

b. Low dielectric loss resulting in increased life of insulation and so

the machine.

c. High resistance against the effect of moisture.

d. Reduction of time cycle of insulation.

1.4 ORGANISATION

In this project documentation we have initially put the definition and objective of the

project as well as the design of the project which is followed by theimplementation and

testing phases

Chapter 1: It explains about the introduction to the project, necessity of the project.

Chapter 2: This chapter explains the Literature survey about VPI.

Chapter 3: This chapter explains about development of the VPI.

Chapter 4: This chapter explains the analysis of the VPI process for the stator of Turbo-

generator

Finally the project has been concludedsuccessfully and also the future enhancements

of the project were given in this documentation.



2. LITERATURE SURVEY

2.1 INTRODUCTION

The VPI process is the most effective way known to eliminate the dead air spaces that

cause hot spots within the Electric Machines like large generators and transformer coils.

These hot spots can be 20* higher than the average coil temperature. The VPI process, along

with a good resin, provides a low thermal resistance path that lowers the average operating

temperature of the Machine.

During the VPI process, the resin seals the machine against environmental conditions

and bonds all components of the insulation system together for good mechanical strength.

This is very effective in reducing mechanical vibrations. This greatly reduces the audible

noise level of the generator. The VPI process and resin also enhances the dielectric capability

between windings and between the windings and ground. This allows the transformer to

survive higher voltage stress levels without failure.

2.2 EXISTING SYSTEM

Electrical machines quality is highly dependent on the vacuum pressure impregnation

insulation system. All the high voltage machines, pole coils irrespective of size and shape are

being impregnated under vacuum and pressure of self-developed resin systems. The stringent

quality tests on the resin mixtures and strictly following the vacuum pressure impregnation

and systematic cooling and heating cycle of resin mixture and sophisticated automatic control

systems made the insulation systems for better and better quality for more than 30 years. The

insulating materials used for wedges are resin poor and accelerator treated. For example Main

insulation tapes, mica paper tapes, overhang protective tapes, shrink tape and glass mates

HM693 are treated with accelerator.

After impregnation, they become hard and experiments were conducted for voltage

endurance at room temperature and at evaluated temperature continuously for more than 3

years. Though the mica tape can withstand 20kv per mm, the extrapolation has been done at

4kv/mm and life expectancy is around 100yrs. With an operation stress level of less than

4kv/mm, factor of safety is considerable. The Vacuum pressure impregnation system was

brought by Dr.Meyer with the collaboration of wasting house in the year 1956. The resins

used were of polyester. The mica tapes used for Vacuum pressure impregnation systems are

ROGS 275, ROGS 275.1 and ROV 292. ROGS 275 tapes are with glass cloth baking up to



13.8 kV voltage levels ROV 292 mica paper tapes are with polyester fleece above and more

penetration of resin. ROGS 275.1 tape is special glue varnish for tropical countries like India

and Brazil to resist higher humidity. The glue being used for main insulation tape is X2026

and for conductor insulation is X2027.

The resin used for Vacuum pressure impregnation is ET 884, a mixture of epoxy resin

E1023 (lekuther m x 18) and hardener H1006 in 1:1.2 ratio by weight. In kwu, the

components are mixed in 1:1 ratio.

E1023: The resin is in drums of 220 kgs weight. It is in crystal form at temperature of 14 or

20deg.C the container is resin is available in drum the reason is faster heating in furnacethe

resin in liquid state shall not come out of the container. The drums are kept in oven and

heated up to 1000

C for about 18hrs. If the resin is not fully in liquid condition, it can be

heated up to 1250C. The storage tank is filled with resin first depending on the volume and

ratio of mixture at a temperature of 600 C through hose pipes. Resin filling is being done by

creating 0.2 bar vacuum in the tank.

2.2.1 RESIN MIXTURE

The mixing ratio of resin to harden is 46:54 parts. The resin mixture required for the

Impregnation tank is 27000lts. A job of 1.9m height and 4.5m diameter can be impregnated.

a )Size of the tanks:

Main impregnation tank = 4.5m (pie) x 3.0m ht.

There are 3-inch vessels for different sizes jobs impregnation.

I. Vessel (1) – 3.8m pie x 2.25m ht.

II. Vessel (2) – 3.0m pie x 2.3m ht.

III. Vessel (3) – 2.0m pie x 2.3m ht.

Three Storage tanks of each resin capacity9000 litres are in the operation for storing.

The resin mixture cooling and heating cycle is by circulating the resin through the heat

exchangers. Oil heated by water is being used for heat exchangers.

The Vacuum pressure impregnation cycle is as per WIV 114.1 standard. The job is

kept in an oven for a period of 12hrs at a temperature of 70OC. Six no. of thermocouples are

inserted on the back of the core and measured the temperature. Job insertion in the

impregnation tank is at 70oc. The lid of the impregnation tank will be in open condition. The

vessels are kept clean. Resin available is wiped out by Methylene. Traces of resin shall not be



allowed on the inner side of the tank. It reacts with humidity and scale formation will takes

place. These components obstruct the filters also. The resin at the time of cleaning is

carefully removed by wiping with rubber sheets. Keeping the vessel in slant position on the

ground also cleans the inner vessels. After ensuring the perfect cleaning, the tank should be

allowed for further operation. The job is inserted in the tank the temperature monitoring

thermocouples are placed on the back of the core. The lid is allowed to come down by

hydraulic motor. Silicon grease is applied on the surface of tank where the lid is touching.

A rubber gasket is also provided on the rim not to allow any leakage. Air pipes are closed and

vacuum pumps will be started.

b)Vacuum creation – 0.35 torr for 2 hrs:

The job temperature is to be maintained always above 65OC, if found less, tank can be

heated up. In practice, the vacuum can be created in 2 hrs. Siemens adept before starts of 2nd

shift (3.0 pm), they create 0.35 torr vacuum and it will be continued till next day morning 1st

shift (6.00 am) min. requirement is 2hrs.During this time the resin cooling is being carried

out to reach 10deg.C and heated up automatically to 70deg.C.

2.2.2 IMPREGNATION

The resin mixture is to be heated to 70deg.C. Every day morning a 20ml sample will

be taken to laboratory tests. Viscosity will be measured at 70deg.C. It should not be more

than 45 CD +10%. Anew resin will beat 15 CP. New resin and hardener mixture is to be

added if the viscosity is more. The resin filling is being completed in 25 minute. At this time,

the vacuum reduces to 0.5 Torr – 1 Torr level. The resin is to be allowed to settle for 15 min.

The level of resin is above 100mm over the job.

a) Pressuring – 3 bar:

With the hydrostatic pressure of the resin, only surface of the insulation can be filled with

resin. To have an effective penetration up to the end of a barrier, pressure is to be created to 3

bar (2 bar over atm. Pressure of 1 bar).

b)Gelling time:

The polymerization of resin and accelerator take place at this time. At 65OC, the time

required is 170 min. The insulation gets hardened.

c) Curing – 14 hour at 140 O

C:

The resin is to be pumped back to the storage tank. The job is to be removed from the tank

and allowed for dripping. It is kept in oven at 140deg.C for min of 14 hrs. The accelerator



B1057.1 is to be placed at 4 corners of the oven. In curing process the accelerator vapors will

react with surface resin and cures.

2.3 DISADVANTAGES OF EXISTING SYSTEM

a. If any short circuit is noticed, the repairing process is difficult and need of excess

resin from outside.

b. Dependability for basic insulating material on foreign supply

2.4 CONCLUSION

Hence Vacuum-Pressure Impregnation technology can be used in a wide range of

applications from insulating electrical coil windings to sealing porous metal castings. It

normally produces better work in less time and at a lower cost than other available

procedures.

These systems can be large or small, simple or highly sophisticated and equipped with

manual, semi-automatic or automatic controls. Vacuum Pressure Impregnation (VPI) yields

superior results with better insulating properties, combined with “flexible” rigidity, resulting

in greater overall reliability and longer life. VPI reduces coil vibration by serving as an

adhesive between coil wires, coil insulation, and by bonding coils to their slots.



3. SYSTEM DEVELOPMENT

3.1. INTRODUCTION (Vacuum Pressure Impregnation)

VPI produces a better insulation system than can be obtained by conventional

methods, better environmental protection and superior chemical and moisture resistance

(salt water immersion tests).The removal of air voids from the windings assures longer

electrical life and less opportunity for corona. In addition, more solid fill means heat will be

conducted to the outside more efficiently, better thermal endurance, lower hot-spot

temperatures, and lower temperature rise. Further, VPI with a solvent less product provides

greater mechanical and structural strength and may eliminate the need for a surge ring.

Blocking or tying may be replaced with Dacron felt pads that will form the necessary

blocking when impregnated with resin.

Global vacuum pressure impregnation insulation system exhibits various merits in

insulation performance and reliability for operation including maintenance. Therefore, the

system is suitable for ordinary turbine generators, especially, the generators for geothermal

power plant. Developed a global vacuum pressure impregnation insulation system (F-resin/G

insulation system) for large size turbine generators and had put into practical use in 1993.

In the process of evaluation of insulation system, evaluated impregnating ability,

electrical, and mechanical characteristics. From evaluation able to achieve the improvement

of heat cycle, heat resistance and V-t characteristics against usual insulation system, because

of the utilization of internal electrical field relaxation layer, thermal stress relaxation layer,

insulation tapes with excellent impregnation ability and epoxy resin with high heat resistance.

As the insulation characteristics are affected not only utilized materials and their composition

but also manufacturing process, it is reasonable to suppose that we can obtain the

improvement of insulation performances and stabilization of quality by using the taping

simulation technique.

In the global vacuum impregnation insulation system, stator winding inserted into

stator is immersed in epoxy resin, and is impregnated under vacuum and pressure. Through

this VPI process not only the coil insulation is formed but also the resin penetrates into stator

slot clearance, wedges and coils. Additionally, all stator parts are coated by the resin.

Furthermore, the stator coil insulation is impregnated by the resin continuously andrigidly

from slot portion to coil end conductor connecting portion. Therefore, there are a lot of merits



such as high reliability of winding, no looseness of stator core, corrosion proof, and

prevention of coil vibration as well as excellent heat conductivity from the conductor to the

core owing to filling up of stator slot clearance by the resin. Furthermore, replacement of

wedges is not required because no wedge looseness is induced. These features are suitable for

ordinary turbine generators, especially, the generators for geothermal power plant,

surrounded by atmosphere containing hydrogen sulphide Though this insulation system is

mainly applied to air cooled turbine generators with output range of from 20 to 260MVA, it

is also possible to manufacture hydrogen cooled turbine generators with output range of from

50 to340MVA, utilizing the merits of global vacuum pressure impregnation insulation

system.

3.1.1. FEATURES OF F-RESIN/G INSULATUION SYSTEM

Fig. 3.1 Appearance of 126MVA air cooled turbine generator stator.

Global vacuum pressure impregnation insulation system retains many merits such as

improvement of insulation performances, stabilization of quality, shortening of

manufacturing period and mitigation of maintenance load. In particular, since a thermal stress



relaxation layer is provided in the F-resin/G insulation system, a stable heat cycle resistance

characteristic is realized and enables to serve for the DSS (daily start and stop) operation

mode which corresponds to current power demand.

The main features of the F-resin/G insulation system are listed below, and Figure 2 shows

cross section of winding.

a) Utilization of epoxy impregnation resin with long enduring life and high heat

resistance.

b) Utilization of main insulation tapes with excellent impregnation ability.

c) Utilization of internal electrical field relaxation layer

d) Utilization of thermal stress relaxation layer

3.2. Glossary of VPI terms:

1)Bond Strength:The measure of force required to break the bond of varnished helical coils

of enamelled magnet wire.

2)Bump: Briefly revert from vacuum to atmospheric pressure and again draw the vacuum.

Applied in the wet vacuum cycle to help dislodge trapped air and improve penetration.

3)Centipoise:Unit of viscosity. Usually measured by the drag on a turning spindle immersed

in the liquid, Brookfield viscosity. A force of 0.01 dyne per centimetre.

4)Film Build: Average build-up of cured resin on one side of a metal panel.

5)Copolymer: A polymer formed by the of the resin.

6)Deaerate:Remove air and other gasses by vacuum. Note that initial deaeration after a tank

fill can take from several hours to as much as 3 or 4 days depending on the amount, type and

condition of the resin.

7)Dielectric Constant:The property of a material that determines how much charge is stored

per unit volume when unit voltage is applied. The capacitance of a material compared with

the capacitance of an equal volume of air or vacuum.

8)Dielectric Strength: The voltage a material can withstand before breakdown occurs.

Usually expressed in “Volts Per Mil”. Interestingly, a thicker section of material has a higher



total breakdown but a lower dielectric strength, i.e. dielectric strength for one mil Mylar tape

may be 3000 VPM but for 2 mils, breakdown would be only 5000 Volts (2500 VPM).

9)Dissipation Factor:An indication of energy loss in the circuit, as in the production of

unused heat. A multiplier used to obtain useful energy compared to supplied energy.

10Electrical Varnish:A resinous material used to protect and insulate electrical apparatus,

which is applied as a liquid and converted by chemical action, with heat or without, to form a

solid film or mass.

11) Flash Point: The temperature at which enough vapour is generated to flash if a spark or

flame is introduced.

12) Foaming: An accumulation of frothy bubbles caused under vacuum by the expansion of

air and other gasses trapped within the resin.

13) Form Wound: Describes a coil that is formed or shaped over a fixture. Often made with

rectangular conductors laid precisely together, interleaved with flexible insulation. Also

usually covered with one or several wraps of half lapped tape. Also a motor incorporating

such coils.

14)Green: Describes coils or devices that have not been treated, coated or sealed.

15)Half Lap: Spiral tape wrap in which each turn overlaps the previous one by a half tape

width. Provides a double thickness of tape.

16)Hertz: A term indicating the frequency of one cycle per second.

Hg: Chemical symbol for the element, mercury.

18)Holding Tank: A reservoir for keeping the varnish when it is not in use. Should be

equipped with heavy duty mixer and vacuum capability. Refrigeration may be needed in

warmer climates and/or where hot dipping or continuous use is anticipated. Also consider

cooling when infrequent use (low tank turnover) is anticipated. Storage @ <75°F is

suggested. Vacuum cycles can be short- ended by storing the resin under vacuum to prevent

build up of air and other gasses in the resin.

19)Millibar: A unit of atmospheric pressure: 0.75 mm Hg (75 microns). One mm equals 1.33

mbar.

Penetration and Fill: The process by which

the varnish is drawn or forced into and retained



20)Preheat:To bake the device before processing.

21)Preheated Oven:Oven heated until the skins(inside walls) are at temperature and

temperaturehas stabilized. May take several hours.

22)psi :Abbreviation for “Pounds per Square Inch”.Random Wound: Describes a coil in

which thewires do not lie in an even pattern. Not shapedbefore insertion in the devise. Also a

motor containing such coils. Sometimes called “Mush Wound”.

23)Resins:A class of organic, liquid, fusible materials of synthetic or natural origin that are

polymeric in structure. Storage Life: The time during which a liquid resin can be stored @

70°F and remain suitable for use. Also called “Shelf Life”. See Tank Life.

24)Stress Crack: A fissure in the cured resin caused by unequal expansion and contraction

of the core, flexible insulation, resin, etc.

25)Tank Life:The time the product remains usable in service. Tank life is affected by the

frequency of use, processing temperature, turnover of material, storage temperature, and

occasionally by contaminants. Also called “Pot Life”. Thermal Conductivity: The ability of a

material to conduct heat. Usually expressed as: Calories/sec/cm2/°F/cm thickness.

26)Thixotropic (Thixotropy):Describes materials that liquefy or flow when agitated

(mixed) and return to a thick consistency when allowed to rest, e.g. ketchup. A thixotropic

material can therefore, be used at both high and low viscosities.

27)Torr: Unit of pressure (vacuum): 1 mm Hg

28) Vacuum Chamber:Vessel where devices are processed. May be equipped for both

vacuum and pressure. Usually also includes 2 portholes, the sight port and the light port, one

for illumination, the other for viewing the process .

29)VapourPressure: An indication of the evaporation rate. The pressure in an enclosed

container when the vapour and liquid are in equilibrium.

30)Viscosity:The resistance of a material to flow. Higher viscosity liquid flows more slowly,

lower more quickly. May be measured in centipoise, or in minutes and seconds.

31)Volume Resistivity: The ability of a material to resist the passage of electricity through

its bulk. The value is expressed in “Ohm-Cm”.

Resins: A class of organic, liquid, fusible materials of



3.3. Typical VPI cycle...

This process should be varied according to the VPI equipment, resin and apparatus to

be treated. Equipment to be processed must be green (untreated), and tapes untreated, open,

or permeable so as not to block the resin. Resin filled or B-Staged tapes that cure with heat

should not be used.

A)Preheat:

The part is placed in an oven and heated to 250°-325°F. The preheat serves to

evaporate moisture and any volatile oils, which may be present. It also improves penetration

and fill by lowering resin viscosity surrounding the part, and creates suction when the part is

cooled by immersion in the resin. Before proceeding to the next step, cool to 150°F or cooler.

B)Dry Vacuum:

After placing the part in the vacuum chamber, apply vacuum, typically 1 - 4 mm Hg,

for 30 minutes. During this phase, air and any remaining moisture, oil, etc. is removed.

NOTE: During the dry vacuum, the resin in the holding tank should be deaerated and

thixotropic products should be agitated (mixed) in the holding tank for at least 15 minutes.

Agitation will reduce viscosity for effective penetration and fill.

C)Wet Vacuum:

Immediately after mixing, introduce the resin into the vacuum chamber allowing it to

flow up from the bottom so as not to block further penetration. The resin should cover the

part by a depth of at least 1 inch. If excessive foaming occurs during the vacuum process,

slow down the introduction of resin to allow time for air and gasses to escape. Maintain

recommended vacuum for 20-60 minutes. Larger units and those with more layers of tape

will require a longer time under vacuum. For fine wire coils and constricted parts, bumping

the vacuum may increase penetration.

3.4. Pressure Cycle:

When the wet vacuum portion of the cycle is complete and the parts are still totally

immersed, pressurize to 90 – 100 psi with air for an hour or longer. Note: Depending on resin

characteristics, an inert gas may be required to bring vacuum up to atmospheric pressure.

Form wound devices will require about 15 minutes per half lap of tape. Release pressure.



Thixotropic products will have a higher build if allowed an atmospheric soak for 30-60

minutes.

a)Removal and Drain:

Vent pressure and remove the part or drain the resin. A removal rate of 4 inches per

minute or slower should be used so that the resin forms a uniform coating.

Drain may take place over the tank so that runoff can be captured and returned to the

reservoir. While draining, the part should hang at an angle so that flat surfaces can drain

readily.

This will tend to eliminate thick sections, which might promote stress cracks. Drain

until major runoff stops. Follow specific recommendations on the product data sheet.

If using a thixotropic product, allow a period of 1-2 hours or more after drain to

promote resin retention during cure. Thixotropic products should show minimal drain in the

oven.

b) Bake: Place the treated part in a fully preheated oven. Cure using DOLPH’

recommendations for time and temperature according to the product data sheet.

Applications for VPI...

1) High Voltage Machines

2) High Temperature Apparatus

3) Transformers

4) HID Ballasts

5) Random Wound Stators

6) Chemical Duty Motors

7) Rugged Duty Motors

8) Inverters

9) Form Wound Coils

10) Armatures With Coils Installed

11) Precision Wound Transformers

12) Ferro-Resonant Units

Bake:

ake:



3.5 EPOXY RESINS:

Epoxy resins are poly ethers derived from epi-chlorohydrin and Bis-phenol monomers

through condensation polymerization process. These resins are product of alkaline condensed

of epi-chlorohydrin and product of alkaline condensed of epi-chlorohydrin and poly-hydric

compounds.

In epoxy resins cross-linking is produced by cure reactions. The liquid polymer has

reactive functional group like oil etc, otherwise vacuum as pre polymer. The pre polymer of

epoxy resins allowed to react curing agents of low inductor weights such as poly-amines,

poly-amides, poly-sulphides, phenol, urea, formaldehyde, acids anhydrides etc, to produce

the three dimensional cross linked structures.Hence epoxy resins exhibit outstanding

toughness, chemical inertness and excellent mechanical and thermal shock resistance. They

also possess good adhesion property. Epoxy resins can be used continuously up to 300F, but

with special additions, the capability can be increased up to a temperature of 500F.

Epoxy resins are made use as an efficient coating material. This includes coating of

tanks containing chemicals, coating for corrosion and abrasion resistant containers. Epoxy

resins are made up of as attractive corrosion and wear resistant floor ware finishes.

These are also used as industrial flooring material. They are also used as highways

Surfacing and patching material. Moulding compounds of epoxy resins such as pipe fitting

electrical components bobbins for coil winding and components of tooling industrial finds

greater application in industries.The epoxy resins similar to polyester resins can be laminated

and Fibre Reinforced (FPR) and used in glass fibre boats, lightweight helicopters and

aeroplanes parts.

In the modern electronic industry, the application of epoxy resins is great. Potting and

encapsulation (coating with plastic resin) is used for electronic parts. Most of the printed

circuits bodies are made of laminated epoxy resin which is light but strong and tough.

3.5.1 PROPERTIES:

1. Epoxy resins have good mechanical strength less shrinkage and excellent

dimensional stable after casting.

2. Chemical resistance is high.

3. Good adhesion to metals.

4. To impact hardness certain organic acid anhydrides and alphabetic amines are mixed.



3.5.2 APPLICATIONS:

1. They are used in the manufacture of laminated insulating boards.

2. Dimensional stability prevents crack formation in castings. They are also used as

insulating varnishes.

Epoxy resins are polyether resins containing more than one epoxy group capable of

being converted into thethermoset form. These resins, on curing, do not create volatile

products in spite of the presence of a volatile solvent. The epoxies may be named as oxides,

such as ethylene oxides (epoxy ethane), or epoxide. The epoxy group also known as oxirane

contains an oxygen atom bonded with two carbon atoms, which in their turn are bound by

separate bonds as in Scheme I:

Fig.3.2 Seheme I

The simplest epoxy resin is prepared by the reaction of bisphenol A (BPA) (80-05-7)

with epichlorohydrine(ECH) (106-89-8) (Scheme II). The value of n varies from 0 to 25.

This determines the end-use applications of the resin.

Fig.3.3 Scheme II



Applications for epoxy resins are extensive: adhesives, bonding, construction

materials (flooring, paving, and aggregates), composites, laminates, coatings, molding, and

textile finishing. They have recently found uses in the air- and spacecraft industries.

A)EPOXIDATION :

There are three important methods of producing epoxides. First is catalytic

epoxidation. Here the oxidation of olefins is carried out by directly oxidizing them in the

vapor phase in the presence of a catalyst such as silver Second is epoxidation by organic

peroxides and their esters. Unsaturated compounds such as hydrocarbon fatty acids and their

esters are epoxidized by peroxyacetic acid.Third is epoxidation by inorganic peroxides and

inorganic peroxy-acids. Sodium peroxide or tungstic acid deposited on a inert surface is used

for the epoxidation of olefins by hydrogen peroxide.

B)CHEMISTRY:

Epoxy resins are prepared by the reaction of active hydrogen-containing compounds

with epichlorohydrinfollowed by dehydro-halogenation. BisphenolA (BPA) (80-05-7), on

reaction with epichlorohydrin (ECH) (106-89-8) in the presence of caustic soda, produces

diglycidyl ether of bisphenol A (DGEBPA) (1675-54-3). Here nis nearly zero (0.2). The resin

is liquid when n < 1 and solid when n > 2.

C)Curing:

The curing of the epoxy group takes place either between the epoxide molecules

themselves or by the reaction between the epoxy group and other reactive molecules with or

without the help of the catalyst.The former is known as homopolymerization, or corrective

curing; and the latter is an addition or catalytic curing reaction. Both reactions result in

coupling as well as crosslinking (Scheme III).



Fig.3.4 Scheme III

Curing of DGEBPA with a diamine occurs in three stages: propagation of the linear chain,

formation of a branched structure, and crosslinking. Primary and secondary amines are

widely used to cure epoxy resins. The reaction between the oxiranegroup of the epoxy resin

with primary amines is shown in Scheme IV.

Fig.3.5 Scheme IV

Tertiary amines also are used to bring about catalytic polymerization of epoxy resin

and the mechanism given inScheme V. To suit the requirements of the end products, other

nitrogen compounds used for curing are triamines (DETA, TETA), polyamides (two)

obtained from vegetable oils, polyureas (two), polyisocyanates, dicyanamide, polyurethane,

and imidazole. Polymercaptans, polyhydric alcohols, polyphenols, novalacs, and silanes also

are usedfor epoxidations. Magnetic fields and photoinitiation also are used for

polymerization. Hydantoin-based epoxyresin (15336-81-9) is used to form DGEBPA.

Glycidyl esters of dimerfatty acids can also be produced fromvegetable oils. Curing agents

such as cyclic acid anhydrides are used. The reaction is shown in Scheme VI.



Fig.3.6 Scheme V

Fig.3.7 Scheme VI

DGEBPA also is produced from aliphatic diols such as butane-1,4-diol (2425-79-8),

propylene glycol(16096-30-3), hydrogenated BPA (13410-58-7), triglycidyl adduct of p-

aminophenol, hetrocyclicglycidyl amidesand imides, and triglycidylisocyanurate (2451-62-

9). Lewis acids such as boron trifluoride complexes are also usedas curing agents. Cationic



catalysts such as metal halides, coordination catalysts such as metal chelates

andphotoinitiation are used to bring about polymerization.

3.6. THE MANUFACTURING PROCESS

The epoxy resins can be obtained in either liquid or solid states.

a)Liquid Epoxy Resins :

In this process ECH and BPA are charged into a reactor in the ratio of 10:1. A

solution of 20-40% caustic sodais added slowly to the reaction vessel as the solution is

brought to the boiling point. The solution is kept boilinguntil 2 mol of caustic soda per mole

of BPA have been added. The solution breaks up into two layers. UnreactedECH is removed

by vacuum distillation. An inert solvent is then added to the resin and the reaction is

completedwith excess of caustic soda solution. The resin separates into brine solution, which

is thoroughly washed with waterto obtain a clear resin. The solvent is removed by vacuum

distillation.

b)Solid Epoxy Resin :

Here ECH and BPA are added to the reactor in theoretical molar ratio with a little

excess of ECH. Aqueouscaustic soda is well mixed into the system. After one hour the

reaction is complete and a taffylike mass is obtained.Phase separation is brought about by

adding an inert solvent. Brine is withdrawn and the resin solution isthoroughly washed with

water to remove traces of salts. The solid resin is obtained by removing the solvent byvacuum

distillation.

c)Modified Epoxy Resins :

Epoxy resins form adducts with vinyl, acrylic, polyester resins, phenol novolac (9003-

35-7), cresol novolac(37382-79-9), bis-[4(2,3-epoxy propyoxy) phenyl] methane (2467-02-

9), and phenol hydrocarbon novalac(13446-85-0).

3.7. STRUCTURE

Ethylene oxide is a cyclic ether.The carbon atoms in oxirane are trigonallysp2

hybridized. One orbital fromeach carbon atom overlaps with the atomic orbitals of the

oxygen atom to form molecular orbital in the center ofthe ring. Atomic p orbitals, in the plane

of the ring, overlap sideways.

This explains the conjugative ability of epoxyring, and results in a bent bond structure. Since

the H-C-H bond is 116° 15à, the carbon will be sp2 hybridized. But italso shares the



triangular ring, so it is possible to give the correct hybridization structure.Very often the

epoxy groups deform to keep the area of the ring constant. The ring atoms do not lie along

thelines of greatest electron density of the atomic orbitals from the neighboring atoms. The

smaller amount ofoverlapping is more than offset by a decrease in the strain energy.

3.8. CHARACTERIZATION AND PROPERTIES

The end groupsÌepoxy, hydroxide, glycol, chlorine, and bisphenolAÌare estimated by

the usual chemical methods.Researchers have found aqueous concentrated hydrochloric acid

with dioxane to be a suitablereagent for estimating epoxide content. Curing agents such as

amines are characterized by refractive index andspecific gravity. Thin-layer chromatography

has been used for identification.

The reactive dye labeling techniquehas also been used for studying the curing

reaction.The epoxy resins do not soften at a specific temperature but appear to undergo a

gradual and imperceptiblechange. The softening of epoxy resins can be empirically graded by

the ring and ball method.

The curing of epoxy resins is an exothermic process, resulting in the production of

limited-size molecules,having molecular weights of a few thousands. Their weight is

determined by the usual physical methods.

Thenumber average molecular weight (Mn) is determined by gas density, and

cryoscopic, ebulioscopic, and osmoticpressure methods. The weight average molecular

weight (Mw) is estimated by viscosity and light scattering methods.Solubility parameters and

critical surface tension (surface tension below which a liquid drop makes zero contactangle)

have been used to find the molecular weights between the cross-links (Mc).

Epoxy resins have a very wide molecular weight distribution. This can be estimated

by comparing the Mw and Mnvalues. The greater the difference, the wider the distribution.

Gel permeation chromatography has been used forfinding this distribution.Liquid epoxy

resins or their solids in 40% diethylene glycol solution do not behave as Newtonian liquids.

Thekinematic or intrinsic viscosities of epoxy resins are measured by viscometers, which can

measure the dependenceof viscosity on shear rate.

Viscosity studies also provide information regarding the formation of networks and

theiraging. The linear viscoelastic response of epoxies displays the internal characteristics of

tensile relaxation andfracture response.

Chemorheology studies display the changes in deformation and flow properties of the

resin.Continuous and intermittent stress relaxation measures the appearance of network

formation.



Researchers haveused a variety of techniques to study the thermal and environmental

stability of epoxy polymers.The effect of moisture on epoxy resins has been studied from the

point of view of both absorption that bringsabout degradation and of sorption behavior itself.

Water absorption has been found to decrease the Tg because ofstrong hydrogen bonds.

It has been shown that in amine-cured resins, water is homogeneously distributed as

aplasticizer and that water clusters are present at microcracks.The strength and toughness of

epoxy resins below the glass transition temperature Tg depend on the mechanismof the

movement of short segments in the solid state, and above Tg mechanical properties are

influenced bycross-linking density and Mc.

Epoxy resins shrink on curing. Thus both the density and refractive index increase. It

is necessary to distinguishbetween shrinkage in the liquid stage and shrinkage in the gel or

solid state. Shrinkage in the gel or solid stateintroduces stress.

Thus gelation temperature has a direct effect on the degree of shrinkage. Refractometry

ordilatometric measurements are used to measure shrinkage, which determines the cure rate.

Epoxy resins are noncrystalline, and cured resin finds its structural applications below

the heat distortion orglass transition temperature (Tg). Continuous and intermittent stress

relaxation measures the appearance of networkformation.

A variety of techniques have been used to study the thermal and environmental

stability of epoxypolymers. Several mechanical properties of epoxy resins are closely related

with chemical composition and internalcohesive energy of the resin. This has been found to

be true well below the transition temperature, whererotational motion related to

configurational entropy and stress relaxation processes do not occur.

Epoxy resins undergo alpha, beta, and gamma thermal transition through proper

selection of epoxy monomersand curing agents. The temperature, location, and magnitude of

these transitions directly influence thethermo-mechanical properties of the resin.

These transitions also are influenced by the mechanism of crosslinkingproduced by

amines, BF3-amine complex, and anhydride curing agents. These transitions can be studied

bydynamic mechanical analysis (DMA) and nuclear magnetic resonance (NMR).

Epoxy resins have good electrical insulation properties. They have a 3-6 dielectric constant, a

low dissipationand loss factor, and good arc, surface, and volume resistance.

These properties are affected by moisture andincrease in temperature. The resins can

be made conductive and semiconductive by use of suitable fillers andcuring agents.

3.9. APPLICATIONS



1)Foams :

Epoxy resins are used to form rigid, lightweight, foamy structures with good

insulation properties. They areparticularly used for foam-in-place applications in the

“potting” process, as well as in casting. They are producedeither by chemical reaction or by

incorporating aprefoamed filler in the liquid system.

2)Adhesives :

The versatile properties of epoxy resins make them valuable as adhesives in civilian

and military applications.About five percent of total epoxy resin production is consumed as

adhesive in a wide range of structuralapplications. Epoxy resin adhesives form strong bonds

with almost all surfaces, with the exception of somenonpolar substrates. Very often special

modifiers and curing agents must be used to produce specific properties.

The formulation of epoxy adhesives into a serviceable adhesive binding system is a

highly specialized technology.Adhesives based on epoxide resins are available as room-

temperature-curing two-component liquids, heat-curingliquids, powders, hot-melt adhesives,

films, and tapes.Adhesive formulation based on epoxy resins requires a wide variety of

curing and modifying agents. GenerallyDGEBA and oligomers are used, but to produce some

specific effects alicyclic or heterocyclic epoxides are alsoincluded.

Polyvinyl modified resins are used to increase flexibility and as toughening agents. Epoxy

polyurethane resinsmake high-strength structural adhesives. Acrylates are also used to

modify epoxy adhesives. Rubber- andelastomer-modified resins have been used to produce

adhesive that cures under water.

3)Construction :

Epoxy resins are now used as binders in materials for construction. Generally a two-

component systemcontaining liquid epoxy resin, diluents, fillers, thickening agents, and

curing agents is used. They are used to bondconcrete, and to produce industrial seamless thin-

set tarrazzo floors. This use has been extended to the laying ofroads, construction of

buildings, and filling cracks in concrete structures.

3.10. COATINGS:

The coatings industry is the biggest consumer of epoxy resins. These resins are used

mostly as chemical andspecial purpose coatings. Epoxy resins provide thin-layer durable

coatings having mechanical strength and goodadhesion to a variety of substrates. They are

resistant to chemicals, corrosion, and solutions. They find applicationsin washing machines

and appliances, ships and bridges, pipelines and chemical plants, automobiles,

farmimplements, containers, and floor coatings. Epoxy coating formulations are available as



liquid resins, solid resins,high molecular weight thermoplastic resins, multifunctional resins,

radiation curable resins, and special purpose resins.

Aliphatic amines, aromatic amines, and ketamines are used as curing agents for

package epoxy systems.Epoxy baking finishes are obtained by high molecular weight epoxy

resins crosslinked by phenolic or aminoresins. These resins are used as lining for tanks, cars,

drums, pails, pipes, downhole oilfield tubing, and food cans.Epoxy acrylic systems provide

excellent coatings for appliances, kitchen cabinets, outdoor furniture, aluminumsiding, and

other metal products.

High-solid coating solution formulations attain maximum film properties (adhesion,

appearance, and freedomfrom defects). These are based on liquid epoxy resin acrylic adducts

with epoxy resins. These adducts have proveduseful in automotive primers. Epoxy resins

cured with aliphatic amines, polyamides, or aliphatic liquid amineadducts are used in

seamless floors. Industrial floors require extra epoxy resin.Waterborne coatings are made by

dispersing or emulsifying the resins with surfactants. Such coatings also havebeen based on

emulsified liquid epoxy resins cured with emulsified polyamide resins. These formulations

are usedin anionic electrodeposited coatings. They provide exterior and interior coatings for

underground pipes, andelectrical equipment appliances reinforcement. High-solid coatings

have an additional advantage, as they are usefulon steel, brass, metal furniture, buildings, and

miscellaneous products. Application of powders is accomplished byelectrostatic spray

fluidized-bed coating and electrostatic fluidized-bed coating. For marine use, epoxy resins

thatcure under water or are resistant to seawater have been developed.

3.11. OTHER APPLICATIONS

Epoxy resins improve the crease resistance or breaking of fibers. They are also used

as intermediates for stabilizers and plasticizers.

This is the over view of Resins. This gives information about the development and

usage of Resins in manufacturing process of Turbo generators.

3.12. DEVELOPMENT OF TURBO GENERATOR TECHNOLOGIES:

Since the 1901 invention of the cylindrical rotor of Charles Brown for a high-speed

generator, the turbogenerator has been the unique solution for converting steam turbine

power into electrical power. The continuously transposed stator bar, invented by Ludwig

Roebel in 1912, opened the door for large scale winding application. Up to the 1930ies the

generators were designed in 2-, 4- and even 6- pole, in accordance with the speed optimums



of the steam turbines in those days. The 1920ies ended with impressive power generation

plants, having generator units in the 100 MVA range. The stator winding insulation consisted

in the beginning of plied-on mica-paper, compounded by Shellac varnish, later substituted by

asphalt. Voltages were up to 12 kV.

In the early 1930ies two European manufacturers were introducing 36 kV stator

windings, thus eliminating the machine transformer. All such designs were suffering of

continuous heavy electrical discharges, and were soon discontinued. After a 60-year time-out,

a manufacturer surprised the world in 1998 with a cable-based high-voltage generator up to

400 kV. However again, the cable technology was not ready for turbo generator

requirements, and a breakthrough for commercial application was not achieved. In the 1930

US manufacturers were introducing hydrogen as coolant. When combined with direct

conductor hydrogen cooling in the rotor, and later in the stator, this allowed a considerable

increase in specific utilization and efficiency.

By early 1960 the unit ratings were achieving 500 MVA. At that time deionized water

cooling in the stator winding was introduced. Around 1960 all major manufacturers changed

their insulation system to mica tape with synthetic resin impregnation, a technology for

thermal qualification at 155°C, and which has been lasting into these days. By end of the

1960, with the power semiconductors becoming mature, the dc machine excitation was

superseded by the static excitation, and by an ac exciter machine with rotating diodes.

The 1970ies brought again a tremendous growth in unit ratings, going along with the

introduction of nuclear power. Units of 1200 MVA at 3000 rpm and 1600 MVA at 1500 rpm

at up to 27 kV were designed and put in operation. The rotor diameters were arriving at their-

physical limits. Water-cooling of the rotor winding was introduced. Along with plans for

2000 MVA and beyond, superconducting rotor windings and stator air-gap windings were

studied. However, in early 1980 the market focus was shifting to gas turbine technology, with

some 100 MW beginning to grow into the area of large power plants, and initiating a new

round of uprating the simple and robust air-cooling technology in the 300 MVA range by

1996. The generator has for a long time been developed by repeating the cycle: design – test

– adjust design tools – extrapolate design. A tremendous breakthrough came with the large

computers in the 1960ies, immediately being used for the key competences, such as magnetic

field calculations, nonlinear coolant flow networks and mechanical turbinegenerator shaft

calculations. Some programs of that area are even in use in the today’s PC environment. As

an example, magnetic equivalent circuits were established to determine excitation currents.



Once these programs were calibrated on measured data, they have been proven very accurate

and still today, for most applications make obsolete any FEM method.

TODAY’S TURBOGENERATOR TECHNOLOGIES

1.Small units up 150 MVA :

The size of these small air cooled units has evolved quite quickly. These machines are

mainly devoted for gas turbines and steam turbines accepting cycling expansion. The gas

turbines market has led to a very standardized range of machine based on the evolution of the

turbine technologies and on the market requests. The models developed in 1980 for 40 MW

50 Hz/60 Hz; same generator for 50 Hz and 60 Hz with a gear box wheel and pinion

adaptation; are nowadays joined by models in the 130-150 MW range. These generators are

always designed using the simplest solution in order to reach low costs using modular

solutions. For example the stator is cooled using one chamber and the excitation system does

not need a third bearing and no pilot exciter. By this way, the models used for gas turbines

are easily adapted for steam turbine or double drive solutions.

All these machines are easy to transport and to mount on site and are very often

mounted and coupled to the turbine by the turbine manufacturer. They are delivered in a short

time and a lot of engineering is done to improve the through put time of these models. The

maintenance of these groups is quite simple requiring a small storage of spare parts.

A recent trend is the increase of the power of the electrical drives used in the oil and

gas industry, mainly for liquid natural gas pumps. Such drive motors require options similar

to those developed for the generators, however having a variable speed drives controlled by

static frequency converters. The performance is evolving quite strongly: a world record for

this kind of motor at 21 MW 5900 rpm in 1985, seems modest in view of today’s 100 MW.

The speed values are close to generation with values between 3600 and 4200 rpm.

2.Medium range up to 500 MVA :

Since the introduction of the 300 MVA class ten years ago, subsequent development

has extended the rating up to the 400 MVA range. One of the main technology drivers has

been the improvement of the rotor axial cooling and winding indirect cooling using a modular

stator multi-chamber airflow. These generators are characterized by their simplicity and ease

of operation and maintenance. They have also proven their maturity in GT24/GT26 gas

turbine applications as well as on numerous steam turbines and turbines of other

manufacturers. The new ratings of the air-cooled generator series allow for the application of



air-cooled technology in power ranges where hydrogen cooled generators were used

previously. As a result of electrical and cooling optimization the present air-cooled

turbogenerators achieve efficiency up to 98.8 % and are used with a maximum voltage of 21

kV. Aircooled turbogenerators technology with highest ratings has now accumulated more

than 1.8 million of successful operating hours with more than 100 units in operation. In two

decades the power output of air-cooled generators has been increased from 200 MVA to 400

MVA. Fig.4 shows this exceptional increase in generator power as a function of the time. It is

clear that this strong increase in power that has occurred in the last decade was a direct

response to the market demands.

Recently, the increase of air-pressure inside the generator was realized. This measure

allows a better cooling and consequently enhances the capability of the air-cooled turbo

generators. The hydrogen-cooled types have hydrogen filling up to 5.5 bar. They are

designed for single-shaft and combined-cycle applications and are increasingly used with

steam turbines. The main features of the gas-cooled design are the same as the air-cooled.

The cooling principle, end winding support system, the retightening system and the

aluminum press plate are excellent examples of the design similarities. The hydrogen-cooled

types are setting the benchmark for efficiency, large units commonly achieving 99.0 %. Since

1996, ALSTOM has supplied more than 50 units hydrogen-cooled turbogenerators of the 500

MVA range. However, the achievable power is much higher and will be soon at 600 MVA.

Fig.3.8Evolution of the air-cooled turbogenerators in the last decades.

3.Large units up to 2000 MVA :



These generators are driven by steam turbines in large coalfired power plants and

nuclear power plants. They are all equipped with hydrogen-cooling with up to 6 bar

overpressure, and with direct water cooling in the stator winding bars. The two-pole

generator series begins at 500 MVA, and units up to 1300 MVA are in commercial operation.

They are of highest specific utilization and therefore need complete direct cooling.

Depending on the size the rotor, cooling is performed by axial flow of hydrogen through all

conductors of a slot, either in one path over half-length of the rotor, or in two paths,

supported by a sub slot. The stator core is axially flown by hydrogen, symmetrically fed from

both ends driven by a radial fan, arranged on the non-driving end of the rotor shaft. The stator

winding is cooled by water-flown stainless steel tubes embedded in the Roebel bars. Thanks

to the watercooling the stator winding has ever been open factor for upratings. The rotor

winding has revealed to be the limiting part for upratings. At 1.25 m for 50 Hz, the rotor

diameter is at the limits of mechanical stress. Any extension in active length beyond 8m

needs careful consideration of the shaftline dynamics. Potential lies in multi-zone cooling

concepts for the rotor winding, in an increase of hydrogen absolute pressure and fan pressure.

All the described measures will lead to a consolidation at 1400 MVA unit rating.

Any higher unit rating must go along with a break in rotor winding cooling, and the

parasitic effects due to stray flux will remain a challenge as such. The four poles machines

are running at 1500 rpm up to 1700 MVA. This is a key advantage for nuclear units, where

the temperature of the steam is relatively low and its flow in the low pressure parts of the

turbines huge. This allows the turbine to have very large diameter by using very long blades.

The hydrogen/water-cooled generators coupled to these turbines are the largest electric turbo

machines both in term of size and performance. This type of machine is ensuring 80% of the

electrical production in France, which is a country with a very high electrical nuclear

production. Some 50 machines in operation of this type have shown a very good reliability in

operation and have a potential of improvement in performance.

Based on this situation, the solution preferred in the nuclear market are not based on

new technologies, but, more safely, the tend to still improve the existing validated well-

running units. The 2000 MVA limit for turbogenerators for the 3rd

generation of reactors is

now close to be reached with improved life time and reliability. In order to reach this level of

power, following choices have been done:

I. Use the basic solutions validated by years of operation on running nuclear

units.



II. Analyze those parts which have led to the faults on existing machines.

III. Implement improvements validated on full-speed hydrogen and water-cooled

machines in the last decades.

IV. Adapt the cantilever type of excitation technology and adapt it to be even less

sensitive to diode aging.

V. Implement an improved type of cooling in the rotor copper ducts.

The maintenance of such a machine has to be done very carefully in order to reach the

guaranteed lifetime. The periodic stops to refuel the reactor are to be used for optimum

maintenance. The trend on the modern reactors is also to reduce the time between refueling

and the maintenance has to be adapted accordingly. A wide experience has been accumulated

on the existing machines.

1. Market trends :

As a part of the energy chain, the turbogenerator requires present and future

developments that have to comply with the market requirements as following:

i. Higher efficiency

ii. Higher reliability

iii. Low cost energy production

iv. Grid stability enhancement

To fulfill continuously these requirements huge developments are in progress as presented in

the following sections.

Substitution of hydrogen-cooled units by air-cooled units for higher reliability and

low cost energy productionThe substitution of hydrogen-cooled units by air-cooled andof

hydrogen/water-cooled by hydrogen-cooled will becontinuing to shift the ratings upwards.

The limits are given by transport dimensions, by the established temperatureclasses, and by

the degree of complexity of design. The engineering will further exploit these limits

involving mainlycooling and insulation materials developments. Air-cooled turbogenerators

offer many benefits to the operator. Some of which are listed below:

i. Excellent reliability

ii. Less civil work, simpler foundation

iii. No hydrogen treatment system

iv. No seal oil system and less sealing

v. Less piping

vi. Simple engineering work due to its advanced technology



These advantages are the consequences of not using hydrogen gas as a cooling

medium. This results in much simpler and shorter maintenance periods as well as a shorter

delivery time and an increased reliability. The good experience with large air-cooled

turbogenerators demonstrates the high potential of these generators. The largest air-cooled

generator was designed for 500 MVA. This design has been proven by tests and represents

the maximum achievable capability of air-cooled generators.

2. Efficiency enhancement :

The improvement of the efficiency is of first importance for the turbogenerator of all

kind in particular in air-cooled 60 Hz units for closing the gap to the benchmark values of

hydrogen-cooled units. Actually, it is one of the first issues considered in any new

turbogenerator development. In this section, some examples of new design solutions and new

technologies implementation to increase the efficiency will be described.

D. Stability improvement: Excitation booster :

Generally speaking, the excitation current of large generators is managed thanks to an

avr-controlled thyristorrectifier, directly supplied by the three phase voltages generated by the

generator itself. In the case this voltage drops down, the avr will counteract. This can become

impossible when the thyristor rectifier reaches limits given by its AC feeding. A possible

solution is to oversize the transformer connected between the output of the generator and the

thyristor rectifier, to keep the control of the excitation current for obtaining the over-

excitation of the generator, even if its output voltages are at a low level.

A solution is to add an additional energy source in the form of a pre-charged

supercapacitor bank that allows the control of the excitation current, even in case of heavy

drop of the main supply. Supercapacitors seem to be well adapted in view power density. A

study in collaboration with EPFL and Technical University of St-Petersburg is in progress to

demonstrate the positive impact of such a system on the stability of an electrical grid. To

assess the real benefit, the system is incorporated to every turbogenerator of the modeled

electrical grid. The simulation is going to be performed with SIMSEN and Matlab Simulink

E. Engineering calculation tools :

Concerning the future of engineering tools we expect the further linking of the design

geometry with the modeling tools, and this in both ways. Furthermore we expect more use of

CFD, eventually replacing large test arrangements. FEM will be interactively combined with

machine parameter tools, a precursor is the virtual short circuit testing program of EPFL.

FEM integrated in machine models which themselves are part of simulation tools could be

used for investigations of harmonics of currents or voltages on the generator components.



Two main categories of programs are used at the present. The first is employed to simulate

events in the electrical grid and to demonstrate the consequences on grid stability. These

programs integrate transient and subs transient models of generators. For the turbogenerator,

a complete result including stator and rotor current, stator voltage, powers, torques in

function of time can be obtained. Some of the more used are:

1) SIMSEN

2) Matlab Simulink

The second category of programs is based on FEM calculation and gives detailed

information of what happens in the generator. The magnetic field, eddy currents, losses and

forces are calculated. Ventilation models are introduced in order to know the resulting

temperature distribution in the generator. For this kind of calculation the detailed design of

the generator is required. Some of the most used programsare :

1. Magnet (Infolytica)

2. Electra (Vector Fields)

3. Maxwell (AusSoft)

4. ANSYS/ Emag

5. UNIFELD (in-house development)

An approach, which mixes both categories of programs and gives combined results

for the grid as well as the generator, is the most interesting for turbogenerator applications.

The application of such a program provides a better understanding of the turbogenerator

coupled with the electrical grid.

3.13 CONCLUSION

Since more than 100 years turbogenerators have been in use for steam turbine and gas

turbine applications of any size. The technical evolution has not stopped; new market

requirements and new material technologies ask for adaptations in design. The future market

will be characterized by a revitalized need for very large turbogenerators, both two-pole and

4-pole. The future will also be characterized by an exciting competition between well-

established conventional solutions and new “high tech” solutions. In any case highly skilled

engineers paired with the best available design tools will be required.



4. ANALYSIS

4.1 INTRODUCTION

Vacuum Pressure Impregnation has been used for many years as a basic process for

thorough filling of all interstices in insulated components, especially high voltage stator coils

and bars. Prior to development of Thermosetting resins, a widely used insulation system for

6.6kv and higher voltages was a Vacuum Pressure Impregnation system based on Bitumen

Bonded Mica Flake Tape is used as main ground insulation. After applying the insulation

coils or bars were placed in an autoclave, vacuum dried and then impregnated with a high

melting point bitumen compound. To allow thorough impregnation, a low viscosity was

essential. This was achieved by heating the bitumen to about 180C at which temperature it

was sufficiently liquid to pass through the layers of tape and fill the interstices around the

conductor stack. To assist penetration, the pressure in the autoclave was raised to 5 or 6

atmospheres. After appropriate curing and calibration, the coils or bars were wound and

connected up in the normal manner. These systems performed satisfactorily in service

provided they were used in their thermal limitations. In the late 1930’s and early 1940’s,

however, many large units, principally turbine generators, failed due to inherently weak

thermoplastic nature of bitumen compound.

4.2 CONTENT OF PROJECT

This Vacuum Pressure Impregnation (VPI) system is mainly used for insulation

of Electrical machines like Turbo generators, Large motors and transformers etc . So as I

want to explain about VPI, I have to explain about Turbo Generator, Insulation systems of

Turbo Generator. This is the basic and required introduction about Turbo Generator and

others.

4.2.1 Introduction to Turbo Generator:

Machine acts as a generator converts the mechanical energy into electrical energy.

The machine, which acts as a motor, converts electrical energy into mechanical energy

The basic principle of rotating machine remains the same i.e.



“FARADAY’S LAWS OF ELECTRO MAGNETIC INDUCTION”.

Faraday’s first law states that whenever conductor cuts magnetic flux, dynamically

induced EMF is produced. This EMF causes a current flow if the circuit is closed.

Faraday’s second law states that EMF induced in it, is proportional to rate of change

of flux.

𝑒 =−𝑁d

dt Eq.4.1

EMF induced will oppose both the flux and the rate of change of flux.

In the case of AC generators the armature winding is acts as stator and the field

winding acts as rotor.

Efficiency of a machine is equal to the ratio of output to input

= Output

input =

Output

output +losses Eq. 4.2

To increase the efficiency of any machine we must decrease the losses, but losses are

inevitable. There are different types of losses that occur in a generator.

They are broadly divided into 2 types

(1) Constant losses

(a) Iron losses

(b) Friction and windage losses (air friction losses).

(2) Variable losses

(a) Copper losses

3 Phase all machines are of two types AC machines & DC machines. AC machines

are divided into single-phase AC machines and poly phase AC machines. poly phase AC

machines divided into

1 Synchronous Machines:

Synchronous Generators (or) Alternators are those in which the speed of the

rotor and flux are in synchronism (or) The machine which rotates with its

Synchronous speed.

Synchronous speed (Ns) = 120𝑓

𝑝rpm. Eq. 4.3



2 Asynchronous Machines:

These are the machines in which the flux speed and rotor speed will not be the

same. (or) The machine which rotates less than its Synchronous speed.

Ex: Induction motors.

a) Inherently all the machines are AC machines. AC or DC depends upon the flow

of current in the external circuit.

b) Synchronous generators can be classified into various types based on the medium

used for generation.

1. Turbo-Alternators Steam (or) Gas

2. Hydro generators

3. Engine driven generators

In every machine they are two parts

(1) Flux carrying parts

(2) Load carrying parts

In large synchronous machines the stator have the load carrying parts, i.e. armature

and the rotor has the flux carrying parts i.e.; field winding.

Iron losses are also called as magnetic losses and core losses. They are broadly divided

into

(1) Hystersis losses

(2) Eddy current losses

These losses occur in the stator core.

Copper losses occur in both stator and rotor winding.

The general efficiency of a synchronous generator is 95-98.

A synchronous generator is the core of any generating power plant. A synchronous

generator is a rotating electromagnetic device that converts mechanical energy into electrical

energy by taking the mechanical input from a prime mover (Gas turbine or Steam turbine)

and magnetic energy from excitation.

Generators driven by steam or gas turbines have cylindrical/ round rotors with slots

into which distributed field windings are placed. These round rotor generators are usually



referred to as turbo generators and they usually have 2 or 4 poles. Generators driven by

hydraulic turbines have laminated salient pole rotors with concentrated field winding and a

large number of poles.

Turbo Generator:

Fig.4.1Turbo Generator.

A turbo generator is the combination of a turbine directly connected to an electric

generator for the generation of electric power. Large steam powered turbo generators provide



the majority of the world's electricity and are also used by steam powered turbo-electric

ships.

Smaller turbo-generators with gas turbines are often used as auxiliary power units.

For base loads diesel generators are usually preferred, since they offer better fuel efficiency,

but on the other hand diesel generators have a lower power density and hence, require more

space. The efficiency of larger gas turbine plants can be enhanced by using a combined cycle,

where the hot exhaust gases are used to generate steam which drives another turbo generator

4.2.2 History of turbo generator :

The Turbo generator was invented by a Hungarian engineer OttóBláthy.A turbo

generator is a turbine directly connected to electrical generator for the generation of electric

power. An electrical generator is a machine which converts mechanical energy to electrical

energy.

Generators are based on the theory of electromagnetic induction, which was

discovered by Michael Faraday in 1831, a British Scientist. Faraday discovered that if an

electric conductor, like a copper wire, is moved through a magnetic field, electrical current

will flow(be induced) in the conductor. So the mechanical energy of the moving wire is

converted into the electric energy of the current that flows in the wire.

4.2.3 Components of turbo generator:

1) The generator consists of the following components

2) Stator

3) Rotor

4) Ventilation and Protection System

5) Cooling System

6) Insulation

7) Vacuum pressure impregnation system

8) Exciter

9) Base frame

4.2.4 STATOR

a)Stator Frame:

The stator frame is of welded construction, supports the core and the windings. In

consists of air duct pipes and radial ribs, which provide rigidly to the frame. Footings are

provided to support the stator on the skid. The stator frame should be rigid due to the various



forces and torque during operation. The welded stator frame consists of the two end plates,

axial and radial ribs. The arrangement and dimensioning of the ribs are determined by the

cooling air passages, the required mechanical strength and stiffness.

The end covers are Aluminum alloy castings. The stator frame is fixed to the skid

with the help of hexagonal bolts. The skid is temporarily fixed to the concrete foundation

through bolts.

b) Stator Core:

Stator core is stacked from the insulated electrical sheet laminations and in the stator

frame from insulated dovetailed guide bars. Axial compression is from clamping fingers,

clamping plates and non-magnetic clamping bolts which are insulated from the core. In order

to minimize the hysteresis and eddy current losses of the rotating magnetic flux, which

interacts with the core, the entire core is built up of lamination, each layer of which is made

from a no. of individual segments. The segments are punched from the silicon steel. In the

outer circumference the segments are stacked in insulated trapezoidal guide bars, which hold

them in position. The guide bar is not insulated to provide for grounding the core. The

laminations are hydraulically compressed and heated during the stacking procedure. The

complete stack is kept under pressure and fixed in the frame by means of cells.

The core packed into the stacking frame is pressed firmly together between the end

plates of the machine frame and fixed in this position by welding the axial ribs of the core

and end of the plates of frame. End fingers on the inside diameter of the end plates transmit

the pressure to the teeth of the core. The compressive force produced prevents the

laminations and teeth from vibrating. An eye is welded to each end plate for attaching

suitable lifting gear with adequate lifting capacity for transporting the complete machine. All

the forces that occur during normal operation or on short circuits are transmitted from the

stator yoke to the frame via the seating plates and into the foundation.

c) Stator Winding:

The winding is a double layer multi turn lap winding. The half coils are made up of

electrolytic copper strips insulated with mica based epoxy insulation of suitable thickness to

give a long and uninterrupted service. Each strip is staggered to 360degrees and it passes

through all the sides of the coil. This process is called transposition. The purpose of

transposition is to avoid the circulation currents due to eddy current and also to avoid corona



losses. The straight parts of the half bar are coated with conductive varnish to prevent corona

discharges in the slot. The end winding is specially shaped to form a basket with an inviolate

shaped over hang of the bars. The straight portion of the winding is secured by means of

wedges driven into the slot position. The resistance thermometer elements are placed in the

core teeth at carefully selected points to measure the temperature rise of the machine. Epoxy

glass laminated brackets support the end winding. Epoxy glass laminated spacers to give a

rigid structure to withstand the short circuit forces of the three-phase winding are connected

to the connecting strips, which are also insulated and secured in position. Six output terminals

are brought out from the rings of the insulated covers.



Fig.4.2 Wound Stator



Fig.4.3Stator Winding



d) End Covers:

The end covers are the castings of the aluminum alloy and are bolted to the side plates

of the stator frame. The inlet passage is specially designed with built in guide vanes, which

ensure uniform distribution of the air to the fan. Air ceiling is provided around the shaft and

at the parting plane of the top and bottom parts of the end covers so that suction of oil vapor

from the bearings does not take place.

e) Location of Bars:

A semi-conducting wrapper of graphite paper in the slot protects the bar. The stator

winding is protected against the effects of current forces in the slot section. To ensure tight

seating of the bar at the slot bottom, a slot bottom-equalizing strip of stress path is inserted. A

top ripple spring is arranged between two compression strips to exert a continuous pressure

on the bars. The bars are shaped so that, cone shaped end windings are obtained. In order to

reduce the stray losses a small cone taper of (13-20deg) is used. On the wide sides of the bars

spacers of insulating material are inserted at regular intervals.

f)Enclosure:

The enclosure consists of the inner and outer components. The inner components

comprises of the winding covers, which from an angular enclosure of top and bottom parts

and is designed as required for particular degree of protection, as indicated in the dimension

drawing or in the “Technical data”. The ventilating circuit is of the double-ended

symmetrical arrangement.

g) Electrical Connections of Bars and Phase Connection:

Brazing makes electrical connection of Bars: Electrical connection between the top

and bottom bars, one top bar being brazed to the associated bottom bar. The coil connections

are wrapper depends on the machine voltage. After tapping, an insulating varnish is applied.

h) Phase Connectors:

The phase connectors consist of flat copper sections, the cross section of which results

in a low specific current loading. The connections to the stator winding are of riveted and

soldered type. The phase connectors are wrapped with resin rich mica type, which contain

synthetic resin having very good penetration properties. The phase connectors are then cured

at a certain temperature, with the shrinking tapes contracting so that a void free insulation is

obtained.



i) Output leads:

The beginning and ends of three phase windings are solidly bolted to the output leads

with flexible. The output leads consist of flat copper sections with mica insulation. To

prevent eddy-current losses and inadmissible temperature rises: the output leads are brought

out.

Fig.4.4 Phase connectors and rings



Table 4.1: Insulating materials used in the stator winding:

Usage Material description Specifications

A foam insulation for slot bottom

layer of stator coil

Semi conductive foam fleece HL657

Slot bottom insulation Semi conductive fleece HL656

Inter layer insert Glass mat (compressible) HM693

Top insulation Glass mat (compressible) HM693

Spacers in overhang Glass mat (compressible) HM693

Bandage ring spacers Glass mat (compressible) HM693

Slot wedge Glass mat (Hard) HM694.52

Fillers for Slot Merge spacer Glass mat (Hard) HM693

Slot Merge spacer Glass mat (Hard) HM694.5

Stiffeners between top & bottom

layers

Glass mat (repressed in a

hydraulic fixture)

SN763353

Interlacing for ring and stiffeners Glass Sleeve SCHL559

Typing of spacers b/w collector rings Glass tape GSBD552

Insulation of rings Fine mica paper glass tape GSBD552

Shrink and protection layer Polyester shrink tape L611

Adhesive varnish for tape ends Adhesive varnish KIL 875.2

Bandage rings Polyester resin + glass

ravings

PG822 + GSSTR588

Terminal boards Glass mat (hard) HM 694.5



4.2.5 ROTOR :

The rotor is forged from a homogeneous steel ingot of specially alloy steel properly

heat treated to meet the required mechanical, metallurgical and magnetic properties. Axial

slots are milled throughout the active length of the rotor body to accommodate the

conductors. The slots are dovetailed at the top of housing the wedges.

1. Rotor shaft:

The rotor shaft is forged from a vacuum cast steel ingot. The high mechanical stresses

resulting from the centrifugal forces and short circuit torque call for high quality heat-treated

steel. The rotor consists of an electrically active portion and two shafts end. Approximately

60% of the rotor body circumference has longitudinal slots, which hold the field winding.

Slot pitch is selected so that 1800 displace the two solid poles. The rotor wedges act as

damper winding within the range of winding slots. The rotor teeth at the ends are provided

with the axial and radial holes, enabling the cooling gas to be discharged into the air gap

after, intensive cooling of the end windings.

2. Rotor Winding:

The field winding consists of several series connected coils inserted into the

longitudinal slots of the rotor body. The coils are wound so those two poles are obtained. The

solid conductors have a rectangular cross-section and are provided with axial slots for radial

discharge of the cooling gas. The individual conductors are bent to obtain half turns. After

insertion into the rotor slots, these turns are combined to form full turns of the series

connected turns of one slot constituting one coil. The individual coils of the rotor winding are

electrically series connected so that one north and one south magnetic pole are obtained.

Fig.4.5 Rotor shaft



Fig.4.6Laminated Rotor before winding

3. Rotor Slot Wedges:

To protect the winding against the effects of the centrifugal force, the winding is

secured with wedges. The slot wedges are made from an alloy high strength and good

electrical conductivity, and are also used as damper wedged bars. The retaining rings act as

short circuit rings to induced current in the damper windings.

4. Cooling of Rotor Windings:

Each turn is subdivided into four parallel cooling zones. One cooling zone includes

the slot from the center to the end of the rotor body, while another covers half the end

winding to the center of the rotor body. The cooling air for the slot portion is a limited into

the slot bottom ducts below the rotor winding.

The hot gas at the end of the rotor body is then discharged into the air gap between the

rotor body and stator core through the radial openings in the conductors and in the rotor slot

wedges. The cooling air for the end windings is drawn from below the rotor-retaining ring. It

rises radically along the individual coils and is then discharged into the air gap.



5. Rotor Retaining Rings:

The rotor retaining rings with stand the centrifugal forces due to the end windings one

end of each ring is shrunk on the rotor body, while the other end of the ring overhangs the

end winding without contact on the shaft. The shrunk on the hub at the free end of the

retaining serves to reinforce the retaining ring and secures the end winding in the axial

director at the same time. The shrink seat of the retaining ring is silver plated, ensuring a low

contact resistance for the induced current. To reduce the stray losses and have high strength,

the rings are made of non-magnetic core worked materials.

6. Slip Rings:

These are made of forged steel and shrunk on either side of the rotor between the end

cover and the bearing. The mica splitting is used to insulate the slip rings from the rotor

body. The excitation to the rotor winding is taken from these slip rings. The connection leads

are suitably insulated and taken through slots milled on the surface of the rotor. Wedges are

provided to keep the leads in position. A helical groove is machined on the outer surface of

the slip rings to have better dissipation of heat, thus minimizing the brush wear.

7. Rotor Fan:

The generator cooling air circulated by the two axial flow fans located on the rotor

shaft at either end. To augment the cooling of the rotor winding the pressure established by

the fan works in conjunction with the air expelled from the discharge ports along the rotor

shaft. The blades are screwed into the rotor shaft. The blades are forged from an aluminum

alloy. Threaded root fastening permits the blade permits the blade angle to be changed.

8. Rotor Balancing:

The rotor is balanced with the help of sophisticated balancing machine. The balancing

weights are provided in the hubs under retaining rings and in the fans. The rotor is

dynamically balanced and subjected to an over speed of 20% for 2min.

9. Radial Bolt:

The field current lead located in the shaft bore is connected to the terminal lug

through a radial bolt. The radial bolt is made from steel and screwed into the field current

lead into the shaft bore.



Fig.4.7 Rotor over hang Portion

4.2.6 Ventilation and protection equipment:

A) Ventilation Arrangement:

The turbo generator is cooled by air circulated by means of two axial fans. Air coolers

cool the air after circulation. The air is drawn through suction ducts by axial fans mounted on

either side of the rotor. The warm air flows out through the exhaust at the bottom of the stator

frame.

B) Space heaters:

These heaters are used to circulate warm air inside the turbo generator and during

outages to prevent condensation of the moisture inside the machine. They are of strip type

and robust design. The heating elements are enclosed in a steel sheet with specific rating of

15W per sq. inch of the surface. They are so designed that they may be fixed in the suction

ducts of the turbo generator. The heaters are completely covered in order to prevent the

accidental contact with the heat units.

C) Resistance Temperature Detectors:

The resistance temperature detectors are made up of Platinum resistance elements.

The detectors are placed in a groove cut in a rectangular glass laminate and embedded in

different positions like stator teeth, stator core, and slots. There are 12 active and three spare

elements distributed in different locations in 3 different planes, 5active plus 3 spare elements

are placed in stator slots, 4 active are placed in stator core, 3 are placed in teeth to measure

the hot and the cold air temperatures.



The resistance thermometers are fixed in the exhaust hood of the stator frame and the

end covers. The leads from these resistance thermometers are brought out and connected to

the terminal board. The leads coming from the spare elements are brought up to the terminal

board and left inside the machine. These resistance temperature detectors operate on the

principle that the resistance of the elements will change depending on the temperature

coefficient of the element. The change in resistance can be accurately measured in a bridge

circuit. A graph is drawn showing the variation of resistance with temperature, which is used

to know the temperature rise under different operating conditions of the turbo generator.

d) Fire Detectors:

For the protection of turbo generator against any possible fire hazards 12 fire

detectors relays are provided on either side of the stator winding. These relays have a set of

normally open contacts. The set of contacts will close when the temperature surrounding the

first relay exceeds 80deg Celsius. The other relay set of contacts close when the temperature

exceeds 1000. These contacts are wired up to the terminal board provide on the stator frame

for the resistance temperature detectors. Both the sets of contacts are used for automatic fire

alarm shutting down of the turbo generator system and for the release of CO2 gas from the

Carbon dioxide system.

4.2.7 COOLING SYSTEM

Cooling is one of the basic requirements of any generator. The effective working of

generator considerably depends on the cooling system. The insulation used and cooling

employed is inter-related.

The losses in the generator dissipates as the heat, it raises the temperature of the

generator. Due to high temperature, the insulation will be affected greatly. So the heat

developed should be cooled to avoid excessive temperature raise. So the class of insulation

used depends mainly on cooling system installed.

There are various methods of cooling, they are:

a. Air cooling- 60MW

b. Hydrogen cooling-100MW

c. Water cooling –500MW

d. H2& Water cooling – 1000MW

Hydrogen cooling has the following advantages over Air-cooling:



1. Hydrogen has 7 times more heat dissipating capacity.

2. Higher specific heat

3. Since Hydrogen is 1/14th of air weight. It has higher compressibility

4. It does not support combustion.

A. DISADVANTAGES:

1. It is an explosive when mixes with oxygen.

2. Cost of running is higher.

Higher capacity generators need better cooling system.

The two-pole generator uses direct cooling for the rotor winding and indirect air-

cooling for the stator winding. The losses in the remaining generator components, such as

iron losses, wind age losses, and stray losses are also dissipated through air.

The heat losses arising in the generator interior are dissipated through air. Direct

cooling of the rotor essential eliminates hot spots and differential temperatures between

adjacent components, which could result in mechanical stresses, particularly to the copper

conductors, insulation and rotor body. Indirect air-cooling is used for stator winding.

Axial-flow fans arranged on the rotor via draw the cooling air for axial-flow

ventilated generator via. Lateral openings in the stator housing. Hot air is discharged via.

Three flow paths after each fan.

FLOW PATH 1:

It is directed into the rotor end windings space and cools the rotor windings, part of

the cooling air flows past the individual coils for cooling the rotor end windings space via

bores in the rotor teeth at the end of the rotor body.

The other portion of the cooling airflow is directed from the rotor end winding space

into the slot-bottom ducts from where it is discharged into the air gap via.

A large number of radial ventilating slots in the coils and bores in the rotor wedges

along these paths the heat of rotor winding is directly transferred to the cooling air.



FLOW PATH 2:

It is directed over the stator end windings to the cold air ducts and into the cold air

compartments in the stator frame between the generator housing and rotor core. The air then

flows into the air gap through slot in the stator core where it absorbs the heat from the stator

core and stator winding.

FLOW PATH 3:

It is directed into the air gap via, the rotor retaining-ring. The air then flows past the

clamping fingers via. Ventilating slot in the stator core into the hot air compartments in the

stator frame being discharged to the air cooler. The flow path mainly cools the rotor retaining

rings, the ends of the rotor body and the ends of the stator core.

Flow 2&3 mix in the air gap with 1 leaving the rotor. The cooling air then flows

radially outward through ventilating slots in the core within the range of the hot air

compartments for cooling of the core and winding. The hot air is discharged to air cooler.

B. AIR AND HYDROGEN COOLING

Many of the internal generator components do not have the capability in their design

to have direct liquid cooling and yet they incur substantial losses during operation. In

addition there is the problem of rotation of the rotor and the windage and friction that goes

with it. Therefore large generator designs need a cooling medium that has good heat transfer

properties and low windage and friction characteristics.

Turbo generators employ either air or hydrogen as the internal cooling medium of the

generator. Air is used in the smaller machines (now a days up to about 300 MVA and

growing), but hydrogen is the most effective gas for ventilating a rotating machine and is

used in the larger machines to achieve higher ratings. Generally, hydrogen is used in all large

turbine generators and most of the medium-size machines, but it has been also used in some

smaller generators.

When hydrogen is for used as a coolant in generators, it is supplied at a purity of

approximately 98% or better. It is usually maintained from a continuous supply of

commercial grade hydrogen of high purity. It is necessary to maintain a large supply for

filling the generator after overhauls and to replace gas lost during operation. Hydrogen



consumption occurs in the generator by absorption into the seal oil and through small leaks in

the hydrogen coolers, stator winding, rotor terminal stud seals, or out of the casing. A

pressure regulator holds the hydrogen pressure at the rated level specified by the generator

design. Hydrogen’s density at 98% purity is of the order of one-tenth that of air at a

comparable pressure. This reduces the fan and windage losses to an extremely low value.

Because of this, it is possible to increase hydrogen pressure in machines to as high as 75 psi

relative to atmospheric pressure. Because of low windage and friction, the higher pressure

does not compromise efficiency.

The main benefit of increasing the hydrogen pressure is that it greatly increases the

heat removal capability of the hydrogen. Hydrogen’s properties are such that its heat transfer

coefficient is 50% more effective than that of air at the same pressure. Therefore hydrogen is

much more effective in removing heat from a surface.

The heat capacity per unit volume (the product of specific heat at constant pressure

and density) of hydrogen is approximately equal to that of air at the same pressure. Therefore

the temperature rise of hydrogen would be approximately the same as that of air if the same

volume flow rate of the two gasses were used to remove the same amount of heat. The

temperature rise is substantially reduced because the fan and windage loss is reduced in

hydrogen. The hydrogen is circulated throughout the generator by shaft mounted fans or

blowers. The hot rotor gas is discharged to the air gap, after having absorbed the heat from

the field winding losses. The hydrogen is also circulated through the core and stator terminals

and then back to the coolers for cooling and re-circulation. To remove or introduce hydrogen

in the generator, an external system is connected that employs CO2 for hydrogen purging on

removal and air purging when admitting hydrogen into the machine. This ensures that an

explosive mixture of hydrogen and oxygen cannot happen, as would be the case if purging

were done with air.Instrumentation is also generally provided for monitoring of hydrogen

gaspurity, dewpoint and temperatures. Air-cooled turbine generators are commonlyopen

ventilated taking air from outside the machine and discharging the warmair back to the

outside in another location.

C. HYDROGEN COOLERS

As the hydrogen cooling gas picks up heat from the various generator components

within the machine, its temperature rises significantly. This can be as much as 46◦C, and

therefore the hydrogen must be cooled down prior to being recirculatedthrough the machine

for continuous cooling. Hydrogen coolers or heat exchangers are employed for this purpose.



Hydrogen coolers are basically heat exchangers mounted inside the generator in the

enclosed atmosphere. Cooling tubes with “fins” are used to enlarge the surface area for

cooling, as the hydrogen gas passes over the outside of the finned tubes. “Raw water”

(filtered and treated) from the local river or lake is pumped through the tubes to take the heat

away from the hydrogen gas and outside the generator. The tubes must be extremely leak-

tight to ensure that hydrogen gas does not enter into the tubes, since the gas is at a higher

pressure than the raw water.

Fig.4.8Relative Cooling Properties of theVarious Cooling Mediums Used in Turbogenerators

4.2.8. INSULATING SYSTEMS

1.Resin rich system of insulation:

1) Conductor cutting and material used is same as in resin poor system.

2) Transposition is done same as that of resin poor system.

3) Stacking of coils is done. In this case high resin glass cloth is used for

preventing inter half shorts.

4) Putty work.

5) Nomex is used as transposition pieces. Putty mixture is a composition if mica

powder, china clay and SIB 775 Varnish.

6) Straight part baking is done for 1hour at a temperature of 160OC and a

pressure of 150kg/ sq.cm

7) Then bending and forming is done.

8) Half taping with resin rich tape is done for over hangs and reshaping is done

9) To ensure no short circuits half testing of coils is done.

10) Initial taping and final tapings is done with resin rich tape to about 13-14

layers.



11) Final baling is done for 3hrs at a temperature of 160OC in cone furnace.

12) Gauge suiting is done.

13) Conductive/ graphic coating (643) and semi-conductive coating 642 are done.

14) High voltage testing is done at four times that of rated voltage and tanδ

testing, inter strip, inter half testing are done. Finally glass taping and epoxy

gel coating are carried out.

Advantages of resin rich system of insulation:

1) Better quality and reliability is obtained.

2) In case of any fault (phase-ground/phase-phase), the repair process is very easy.

3) Addition of excess resin will be avoided because of using resin rich mica tape.

2. Resin poor system of insulation:

Advantages of resin poor system of insulation:

a) It has got better dielectric strength

b) Heat transfer coefficient is much better

c) Maintenance free

d) It gives better capacitance resulting in losses due to which the insulation life will be

more

e) The cost is less and it is the latest technology

f) Reduction in time cycle and consumption MW is also less and it gives high quality.

Disadvantages of resin poor system of insulation:

a) Dependability for basic insulation materials on foreign countries

b) If any short circuit is noticed, the repairing process is difficult

This is the introduction about Turbo Generator, Construction Details, main parts, insulation

systems used in Turbo Generator. Now we have to know about what is Vacuum Pressure

Impregnation (VPI).

4.2.9 Vacuum Pressure Impregnation (VPI)

Vacuum Pressure Impregnation is a very popular insulating technique today not

only for motors but also for turbo generators. This technique has been used since the middle

of the last century, mainly for small and medium size motors. More recently VPI has been

extended successfully to large size turbo generators too. Such a long period of application

makes it possible to try surveying this topic and summarizing important conclusions from this

experience. This questionnaire is mainly devoted and limited to investigating field-experience

on VPI treatment of large motors. As a consequence motors with power ratings of 800 kW



and above and voltage ratings of 1kV and higher for power generation and industrial

applications are within the scope of the questionnaire.

VACCUM PRESSURE IMPREGNATION INSULATION PROCESS:-

1. Vacuum Drying Of Job:

a. Placement of stator winding bar in the impregnation tub kept on the trolley of

Impregnation Tank

b. Drive in the trolley inside the Impregnation Tank

c. Closing of the front cover of Impregnation Tank, Commencement of heating the job

d. Commencement of evacuation of the job

e. Drying of job under vacuum ≤0.1 mbar at temperature 75 ±5 Degree Centigrade for

minimum 10 hour

f. Drying of job under vacuum will be stopped if the pressure rise in impregnation tank

in 10 minutes after closing of vacuum valve is less than 0.05 mbar

2. Impregnation Cycle:

1. While job is under vacuum drying, resin mixture is heated in storage tank at

temperature 70 ±3 Degree Centigrade and the vapor’s are sucked under vacuum ≤ 5

mbar at temperature ≥60 Degree Centigrade

2. Transferring resin mixture from storage tank to impregnation tub, on certification

proper drying under vacuum as per point. no.( 6.0) in Sl. no. 3.3.1 of Vacuum Drying

cycle of job

3. Maintaining resin mixture level 100.00 mm above than the highest part of the job

4. Pressurization of resin mixture with Nitrogen gas after 10 minutes of resin

stabilization

5. Increase in Nitrogen pressure to 5 bar within 80 minutes in uniform stages 6.0)

Holding the 5 bar pressure for 120 minutes

3. Back Transferring Of Resin Mixture:

1. On completion of Impregnation Cycle as per point no. (6.0) of Sl. No. 3.3.2 above,

Quick Back Transferring of resin mixture from impregnation tub to storage tank

through filter, by pressure difference in 2



2. Quick cooling of resin mixture in storage tank at temperature at 10 ±2 Degree

Centigrade but not less than 8 Degree Centigrade, in 2 hours

3. Opening of front cover after dripping of resin mixture from job for 10 minutes in

impregnation tub

4. Extraction of fumes of resin mixture at the mouth of impregnation tank for 10 minutes

5. Driving out the trolley from impregnation tank

6. Removal of impregnated job from impregnation tub for next operation

Viscosity at 70 Degree Centigrade = 40 cP

Specific heat = 0.35 kcal

degreeKkg Eq.4.4

Weight of charge / job: Maximum 1500.00 kg

4. Technical Specification of Automatic Vacuum Pressure Impregnation

Plant:

Automatic Vacuum Pressure Impregnation Plant shall consist of following major

items explained below in addition to other essential auxiliaries, equipment’s and optional

items required for trouble free and effective operation of the Automatic Vacuum

Impregnation Plant.

5. Impregnation Tank:

a. Internal Diameter : 2200.00 mm;

b. Cylindrical Length : 14000.00 mm;

c. Operating Vacuum : < 0.1 mbar;

d. Operating Pressure : 7 bar;

e. Operating Temperature : 90 Degree Centigrade



Fig.4.9Horizontal Impregnation chamber

Impregnation Tank shall be welded structure complete with Rear Dished End with suitable

electrical / brine solution heating arrangement; Internal Rails for trolley movement; Electrical

/ Brine Solution Heating arrangement for heating the cylindrical portion of Impregnation

Tank;

Front Cover with bayonet locking arrangement with automatic closing and opening

system, highly effective sealing system and electrical heating arrangement; all sealing parts;

all mountings on the Impregnation Tank for the measurement of temperature and vacuum;

Effective Ventilator unit for the fume extraction at the mouth of Impregnation Tank;

resin mixture inlet / outlet connection; Vacuum pipe connection; Nitrogen gas inlet

connection, viewing glass with provision of illumination etc.



Fig.4.10Before putting the job into furnace

Fig.4.11After Completing Assembly of Stator Bars



6. Impregnation Tub:

Impregnation tub suitable for impregnation of stator winding bar of 1000 MW TG set,

shall be supplied by the vendor. Impregnation tub will be fabricated structure for static

operating load of total 13500.00 KG (1500.0 KG of the job + 12000.0 KG of resin mixture).

Small inclination is to be provided at the bottom base of the impregnation tub so that resin

mixture is completely drained out during back transferring of resin mixture from

impregnation tub to storage tanks. Height of impregnation tub is to be designed so that the

job kept inside the impregnation tub, is visible through the viewing glass provided along the

length of cylindrical portion of impregnation tank.

7. Flexible Hose Pipe

Suitable length flexible steel hose pipe for the resin mixture inlet / outlet to / from

impregnation tub should have flange connection at one end for fixing on the flange of the

impregnation tub and one Quick Coupling Arrangement at the other end for fixing with resin

inlet / outlet connection of impregnation tank.

Fig.4.12View of VPI wound stator



8. Resin Mixture Storage Tanks

For usable resin mixture 13.0 Cubic Meter1 no. vertical storage tank for inner

cylindrical volume 10.0 Cubic Meter.

Resin mixture storage tanks shall be complete with motorized agitator; heating

arrangement either by electrical heating or brine solution to heat up the resin mixture; cooling

by forced water cooling in two stages : First Stage - by water cooling and Second Stage - by

chilled water through refrigeration unit -; connection for evacuation in the storage tanks;

connection of pressurization of resin mixture with Nitrogen gas, mounting for the

measurement of the temperature of resin mixture and vacuum, viewing glass with

illumination arrangement at the top of the storage tanks, reliable and effective level switch for

the indication of resin mixture level etc.

Temperature for heating the resin mixture in Resin Storage Tanks: 75 Degree Centigrade;

Temperature for storing the resin mixture = 10 ± 2 Degree Centigrade;

Regulation of Temperature during heating and cooling mode = ±2 Degree Centigrade;

Heating up time for resin mixture from 10 ± 2 Degree Centigrade to 75 Degree

Centigrade in approx. 2 hours; Total cooling down time of resin mixture for each storage

tank to 10 ± 2 Degree Centigrade from 75 Degree Centigrade should be in approx. 2 hours.

Very fast heating and cooling system should be provided.

Resin Pipe lines for connecting Storage Tank to Impregnation Plant : Resin pipe lines

shall be supplementary heated either by electrical band heaters wrapped on the resin pipe

lines / by hot brine solution so that temperature of heated resin does not fall while transferring

the resin mixture from both the storage tanks to impregnation tub. Similarly resin mixture

pipe lines connecting 10 cubic Mtr. and 3 cubic Mtr, is also to be heated up as above.

Suitable filter is to be provided on the return path (impregnation tub to storage tank after

completion of impregnation of job) of resin mixture.

Valves of Resin Mixture, Brine Solution and Nitrogen Pipe Lines: All valves must be

FLANGE ENDS. NO WELDED JOINT VALVES WILL BE ACCEPTABLE. This is

essential for dis-assembly, re-assembly and replacement of the valves for the maintenance

purpose. All the valves shall be pneumatically controlled. Interlocks for opening and closing

of valves, shall be provided in the control.



Heat Exchanger for the Brine Solution (if impregnation tank and storage tanks are

heated up with brine solution): Suitable capacity and effective electrical heat exchanger shall

be supplied for heating brine solution to heat up impregnation tank and the resin mixture

stored in both the storage tanks. All necessary safety measures such as lack / starvation of

brine solution in heat exchanger, maximum temperature limit, lack of pressure in brine

solution and fire detection etc. shall be provided and integrated to the automatic control of the

impregnation plant.

9. THERMAL INSULATION

Best quality and long lasting Thermal Insulation shall be provided for Impregnation

Tank, Storage Tanks, Resin Mixture & Brine Solution Pipe Lines and Heat Exchanger etc.

Rock wool / Mineral wool must be provided for the thermal insulation of the valves

for the resin mixture pipe lines and brine solution pipe lines and adjacent portion of the

valves so that old- thermal insulation can be applied again after attending the problem if any

pertaining to repair / replacement of any valve

10. Vacuum Systems for the Impregnation Plant

Vacuum System for the Impregnation Tank: To achieve ultimate vacuum less than 0.1

mbar, reliable and highly effective vacuum pumps and its system shall be supplied. At the

start, rough vacuum pump shall be SWITCH ON and the fine vacuum pump shall be

SWITCH ON on attaining the vacuum 0.5 mbar in impregnation tank. The fine vacuum pump

will be under operation till transferring of resin mixture in impregnation tub.

a) 1 no. additional rough vacuum pump shall also be supplied and connected in the system,

ready for use as and when required.

b) One no. fine vacuum pump shall be included in the list of Spares.

Vacuum System for the Resin Storage Tanks: Reliable and effective vacuum pump

shall be offered for both the resin storage tanks to achieve vacuum level 5 mbar while storing

the resin mixture

Vacuum systems shall be supplied with condensate separator, drainage valve, aeration

valve, accessories for cooling circuit, vacuum measuring device, other essential instruments



etc, and automatic SWITCH ON of the stand by rough vacuum pump in case any problem

and SWITCH ON the fine vacuum pump at set value.

11. Refrigerating Equipment

Suitable capacity, effective , operation & maintenance friendly Refrigeration

Equipment shall be offered to cool down the resin mixture at 10 +/- 2 Degree Centigrade

from 75 Degree Centigrade in approx. 2 hours, maintain the temperature 10 + /- 2 Degree

Centigrade of resin mixture while storing in the resin mixture in storage tanks.

Mounting Arrangement of the bobbin of the insulating strip:-

12. Brine Solution Tank

Suitable capacity of brine solution tank to heat up simultaneously impregnation tank

and storage tanks if not heated electrically, complete with necessary valves, level switch

indicator, provision for makeup water etc. are to be provided

13. Circulating Pumps:

Suitable capacity and effective circulating pumps are to be provided for circulating

the brine solution, are to be provided

14. Automatic control of Vacuum Pressure Impregnation Plant:

Provision is to be incorporated in the Automatic Control of the Resin Mixture

Heating in resin storage tanks and Evacuation of job in Impregnation tank as detailed out

below.

I) Selection of Required number of resin storage tanks for heating the resin mixture

II) Setting of vacuum drying cycle of the Impregnation Tank

III) Timer to pre-select starting time of heating of resin mixture in storage tanks

IV) Timer to pre-select the completion of vacuum drying cycle with reference to job

temperature

V) Time to pre-select FEED - IN of heated resin mixture

VI) Time to pre-select resin return

VII) Time to pre-select resin dripping, opening of front cover and evacuation resin fumes

etc.



Impregnation Plant must be provided with suitable indication on MIMIC Diagram on

operator panel / monitor for following features.

Direct indication of actual readings of temperature, pressure, vacuum, resin levels

shall be displayed

The ON / OFF state of pumps, valves and other motors, shall be in different colors for

ON, OFF and Intermediate Stages

Separate screens / menus shall be provided for Resin Flow, Brine Flow, Vacuum /

Pressure Alarms, Events, Parameter setting,

Provision for manual ON / OFF of all devices as Pumps / Motors / Heaters / Valves

etc. shall be provided

Provision shall be made for Checking / Trouble Shootings of non-functioning of any

device (i.e. output from the control) with the help of logic / flow diagram and diagnosis

screen

Diagnosis screen shall provide the information for alarm and messages giving cause

and remedial action

Separate screen shall be provided to see the status of all inputs and outputs

independently and by ladder / logic diagram

Overvoltage protection for Input / Output cards

3 level electronic lock is to be provided in the system for security reasons

Provision to be made for the measurement of vibration, winding temperature of the motor of

vacuum pumps as and when necessary to check the health of vacuum pumps. This provision

is to be offered as an OPTIONAL ITEM.

15. Air Compressor

Dedicated suitable capacity and effective Air Compressor shall be included in the

offer, for pneumatic function and control of the impregnation plant. Air Compressor must be

complete with matching filters and dryers.



Portable He- Leak Detector complete with sniffer probe etc. shall be offered as an optional

item for the checking of any leakage in the system.

General arrangement drawing of complete Automatic Vacuum

Impregnation Plant:

General Layout Drawing indicating the position of Impregnation tank, Resin Storage

Tanks, Vacuum Pumps, Heat Exchanger, Brine Solution Tank, Refrigerator UNIT,

Accumulator, Air Compressor, Control Panel, Diagram for the flow path of Resin Mixture,

Brine solution, Nitrogen gas lines, Vacuum, Cold Water, Chilled Water and Exhaust etc.

Overall area, Maximum Height and Maximum weight of any single item / single sub-

assembly / single assembly to be handled during erection of the plant, is to be indicated in the

offer. Requirement of Total Electrical Power, Brine solution, Water, Nitrogen Gas, Hydraulic

Oil and other consumables etc. are to be clearly indicated in the offer

Operational & Maintenance Manual of Complete Automatic Vacuum Impregnation Plant:

In addition to other information, operational & maintenance Manual should contain the

following also:

1) Erection Manual

2) Detail Operation Manual

3) Detail Maintenance Manual, instruction for assembly and dis-assembly of the main

items of the Impregnation Plant.

4) Electrical wiring diagram indicating layout of the cables, plugs, junction box,

terminal strips etc

5) Ladder Diagram / Flow Diagram

6) Cross reference list of Inputs and Outputs

7) Inputs and Output lists

8) Alarm list and fault diagnostic manual

9) Programming manual of PLC / System

10) In case PC is used for control, a recovery CD having all software along with written

instruction using it to restore the hard disk ( Old / New), shall be provided

11) Complete detail of the control system (operation and interfacing) shall be provided

with the offer

12) Operation & maintenance manual of all auxiliary systems / equipment



13) Electrical wiring circuit of all auxiliary system / equipment along with the part list /

bill of material of all the components used

14) Safety instruction for the operation of the Impregnation Plant and its auxiliaries

16.Power supply and Environment Condition

BHEL will provide input power supply 3 phase, 3 wire, 415 ±15% volt, 50 ± 3% Hz

to Isolator Switch (BHEL scope) nearby main control panel of Impregnation Plant. Cable

connection from isolator switch to control panel and remaining cabling / wiring for the

Impregnation Plant and other auxiliaries / equipment, will be in the scope of vendor. There

will be no neutral wire and earthing will be provided through shop structure column.

Uninterrupted Power Supply (UPS) device of at least 15 minutes duration is required

under the event of power failure, if the Control system is not equipped with in built UPS.

Reputed make UPS shall be supplied by the Indian agent in case of foreign vendor, in Indian

Rupees.

When switching off the machine or when sudden power interruption, UPS device will

give message to operating system. All open files then are closed automatically. During this

period, the UPS will be supplying power to the control only. UPS will also protect the control

against power spikes and power fluctuation

17. Environment Condition

Impregnation Plant should be suitable for tropical condition with ambient temperature

from 0 to 50 Degree Centigrade and relative humidity maximum 97 %

18. Noise Level

Maximum noise level of any item of Impregnation Plant should be below 85 dB (A)

one meter away from the machine with correction factor for background noise.

Vendors will demonstrate the noise level as per international standard like DIN 45635-16, if

asked for.

I.Spares:

(Optional) Set of spares indicating essential and optional items on following

categories, required for 2 years trouble free operation of the Impregnation Plant, system and

its accessories.



II.Mechanical

Flexible hose, Fine vacuum pump, Resin inlet valve for impregnation tank, Level

sensor, Pirani Gauge and McLeod gauge for vacuum measurement etc. shall also be included

in the list of mechanical spares.

III.Electrical

Offer is to be submitted for Contactors, Relays, Automats, Overload, and Power

Supplies (1 of each type) along with the other items

IV.Electronics

Offer is to be submitted for Drives (if used), I (input) / O (output) cards, Limit

Switches, Level Sensors along with the other electronic components

V.Control system

Offer is to be submitted for Control Cards, ad ON Cards, Display and Key Board,

Hard Disc loaded with all software’s in case a PC is provided

19.FOUNDATION FOR IMPREGNATION PLANT

Vendor shall indicate preliminary foundation scheme for the Impregnation Tank,

Storage Tanks and for any other item which require foundation and the same are to be

indicated in General Layout Drawing along with the offer.

Vendor shall submit the layout and foundation drawing for getting BHEL's approval

within one month from the date of Letter of Intent (LOI) or Purchase Order, whichever is

earlier. Complete Foundation Design and Final Layout drawings should consist of all

requirements pertaining to complete Impregnation Plant indicating all major items, line

diagram for resin pipe lines - vacuum pipe lines - brine solution pipe line, exhaust pipe lines,

hot and cold water pipe lines, Nitrogen gas pipe lines.

Total Plan Area, Highest point of any component of Impregnation Plant from shop

floor level, requirement of total power, cable trenches, quantity of water, quantity and quality

of Nitrogen gas for the control of any equipment and during pressurization cycle, Vacuum oil

for the vacuum pump, other lubricating oil and grease etc.



BHEL shall construct complete foundation for the Impregnation Plant as per vendor's

drawing under the supervision of vendor and vendor's representative. Vendor should arrange

the equipment’s required for the testing of foundation, if required by the vendor. The vendor

shall also indicate detailed specification of grouting compound and grouting procedure etc.

for foundation bolts of the Impregnation Plant.

Foundation bolts, leveling elements, cable trays and other items required for the

erection of the Impregnation Plant, shall be supplied along with the main installation.

20.Erection & Commissioning Of the Complete Impregnation Plant

Vendor shall take full responsibility for carrying out the erection and commissioning

of each item of Impregnation Plant, Automatic Control of complete Impregnation Plant & all

other supplied equipment’s / accessories etc. Service requirement like power, air and water

shall be provided by BHEL. The same are to be indicated by the vendor in their layout

drawings. Details of these requirements should be informed / discussed by the vendor and

agreed with BHEL in advance. EOT crane 10 Ton capacity available in the shop. In case

higher capacity crane is required, representative of vendor shall hire mobile crane from local

sources. Compressed air pressure available in BHEL shop is in the order 3.0 kg / square

centimeter.

Applications:

Vacuum impregnation is used in a variety of industries including automotive, heavy

truck, agriculture, aviation, defense and industrial.

1) Type of parts impregnated are

2) Automotive / Heavy Truck / Agriculture

Engine blocks & heads, transmissions, intakes, hydraulics

Connectors, cabling assemblies, fuel cells

1) Aviation / Defense

Fuel delivery systems, landing gear, aircraft braking systems

Missile propulsion, flight control, oil systems, compression systems

2) Industrial

Pumps, hydraulics, control valve, natural gas, graphite plates.



5.CONCLUSION

5.1Conclusion

Hence Vacuum-Pressure Impregnation technology can be used in a wide range of

applications from insulating electrical coil windings to sealing porous metal castings. It

normally produces better work in less time and at a lower cost than other available

procedures.

Our VPI systems can be configured in a variety of ways, depending on the size and

form of the product to be impregnated, the type of impregnant used and other production

factors. System packages include all necessary valves, gauges, instruments and piping. These

systems can be large or small, simple or highly sophisticated and equipped with manual,

semi-automatic or automatic controls.

Vacuum Pressure Impregnation (VPI) yields superior results with better insulating

properties, combined with “flexible” rigidity, resulting in greater overall reliability and longer

life. VPI reduces coil vibration by serving as an adhesive between coil wires, coil insulation,

and by bonding coils to their slots.

Considering the manifold advantages of VPI System of insulation the leading

manufacturers of World are going to adopt this system for generators up to 400 MW with

hydrogen gas cooling. It has better thermal, electrical, mechanical and chemical properties

and its life time is about 540 years.

In view of the above, in the coming decades the Indian grids will use more of such

generators. In the scenario of World market which demands generators with less cost at the

best possible time with better reliability VPI system of insulation will provide most viable

solution.



REFERENCES

Hiwasa H. et al. Present Developmental Status of Fuji’s Turbine Generator. Fuji

Electric Journal. Vol. 78, No. 2, 2005, p. 126-130.

Lee, H.; Neville, K. HandBook of Epoxy Resins, McGraw Hill: New York, NY,

1982.

May, C. A.; Tanaka, Y. Epoxy ResinsÌChemistry and Technology; Marcel Dekker:

New York, NY, 1987.

Adhesion Polymers, Japan Welding Society: Tokyo, 1993.

Bhatnagar, M. S. Epoxy Resins; Universal Book: Bombay, India, 1996.

Encyclopedia of Polymer Science and Technology, John Wiley & Sons: New York,

NY, 1986, Vol. 6; pp 208-271; 322-382.

Encyclopedia of Polymer Science and Engineering, John Wiley & Sons: New

York, NY, 1986, Volume 6; pp,208-271; 322-382.

M. Tari, K. Yoshida, and S. Sekito, “HTC Insulation Technology Drives Rapid

Progress of Indirect-Cooled Turbo Generator Unit Capacity,” /Toshiba Corp., and

R. Brutsch,

J. Allison, and A. Lutz, IEEE PES 2001 Summer Power Meeting, Vancouver, BC.

Von RolttsolaIncorp.



WEBSITES:

http://en.wikipedia.org/wiki/Porosity_sealing

http://www.impregnation.co.uk/process.htm

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=

0CDoQFjAA&url=http%3A%2F%2Fwww.geothermal-

energy.org%2Fpdf%2FIGAstandard%2FWGC%2F2000%2FR0785.PDF&ei=-R-

xUv_1KsHRrQe4roCwCg&usg=AFQjCNFVOrZ4M5kn0Km4tpXmUeC8cHfjLg&bvm=

bv.58187178,d.bmk

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&ved=

0CFcQFjAE&url=http%3A%2F%2Fwww.fujielectric.com%2Fcompany%2Ftech%2Fpdf

%2F55-03%2FFER-55-3-093-2009.pdf&ei=-R-

xUv_1KsHRrQe4roCwCg&usg=AFQjCNGTmWQsTrj0QujbvZ0mpX5tDM5ITQ&bvm

=bv.58187178,d.bmk

https://sites.google.com/site/finalyearmajorproject/insulation-system-for-air-cooled-turbo-

generator-by-v-p-i-process

BIBLIOGRAPHY:

1. Electrical Design, Operation and Maintenance Manuals :BHELHyderabad

2. Engineering Chemistry : Daniel Yesudian

3.Electrical insulating Materials : R.K.Rajput

4.Alternating Current Machines : M.G.Say

5. Electrical Machines : S.K.BattaCharya

http://en.wikipedia.org/wiki/Porosity_sealing

http://www.impregnation.co.uk/process.htm

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CDoQFjAA&url=http%3A%2F%2Fwww.geothermal-energy.org%2Fpdf%2FIGAstandard%2FWGC%2F2000%2FR0785.PDF&ei=-R-xUv_1KsHRrQe4roCwCg&usg=AFQjCNFVOrZ4M5kn0Km4tpXmUeC8cHfjLg&bvm=bv.58187178,d.bmk





http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&ved=0CFcQFjAE&url=http%3A%2F%2Fwww.fujielectric.com%2Fcompany%2Ftech%2Fpdf%2F55-03%2FFER-55-3-093-2009.pdf&ei=-R-xUv_1KsHRrQe4roCwCg&usg=AFQjCNGTmWQsTrj0QujbvZ0mpX5tDM5ITQ&bvm=bv.58187178,d.bmk





https://sites.google.com/site/finalyearmajorproject/insulation-system-for-air-cooled-turbo-generator-by-v-p-i-process

https://sites.google.com/site/finalyearmajorproject/insulation-system-for-air-cooled-turbo-generator-by-v-p-i-process

VPI for turbo generator

Technology

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