project report ee vt

7/31/2019 Project Report Ee Vt

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TURBOGENERATOR

INTRODUCTION

A turbo generator is a turbine directly connected to an electric generator for

the generation of electric power. Large steam powered turbo generators

(steam turbine generators) provide the majority of the world's electricity andare 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

much better fuel efficiency and are also more reliable, but on the other hand

they are much heavier and need 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.

The Turbo generator was invented by a Hungarian engineer OttBlthy.[citation needed]

Turbo generators were also used on steam locomotives as a power source for

coach lighting and heating systems.

since the 1901 invention of the cylindrical rotor of

Charles Brown for a high-speed generator, the turbo generator 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 withimpressive power generation plants, having generator units in the 100

MVA range (see Fig.1). 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-voltagegenerator 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

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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 155C, and which

has been lasting into these days. By end of the 1960, with the power

semiconductors becoming mature, the dc machine excitation (Fig.2) 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-gapwindings 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 up rating

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

1996.

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TURBOGENERATOR

A 500 MW TURBO GENRATOR

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, immediatelybeing used for the key competences, such as magnetic field calculations,

nonlinear coolant flow networks and mechanical turbine generator

shaft calculations. Some programs of that area are even in use in the todays

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.

The two poles and four poles differ considerably in construction.

At 50c\s. the former run at 3000r.p.m and the latter at 1500.The useful rangeof two pole machines has been extended to 300 MVA. , and in consequence

the four-pole Construction is obsolete.

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STATOR OF TURBO GENRATOR

Generally, the stator of a turbo generator comprises: a cylindrical core,

which extends along a first longitudinal axis and comprises a plurality of

axial cavities and two opposite headers; connection terminals of the turbo

generator; a plurality of electrical windings, which are split into groups and

which extend along paths defined in part in the axial cavities and in part at

the headers; the electrical windings of each group being isopotential and

connected in parallel between a pair of terminals.

A known stator of a three-phase turbo generator comprises six terminals

(three of which are connected to earth and three of which are connected tothe electrical energy distribution main), nine electrical windings which are

split into three groups each comprising three isopotential electrical windings

connected in parallel between a pair of terminals; seventy-two cavities, each

of which is occupied at the same time by two different portions of electrical

windings. The electrical windings have straight segments accommodated in

the cavities and connection segments, which are arranged at the headers and

which have the function of connecting together the straight segments

arranged in different axial cavities and some straight segments to the

terminals.

Considering that, according to the wiring diagram of the stator describedabove, each axial cavity is occupied at the same time by two different

electrical windings and that each electrical winding presents a path

essentially identical to the other electrical windings, each electrical winding

presents sixteen straight segments, which are arranged at corresponding

axial cavities, and a plurality of connection segments, which are adapted to

connect the straight segments to each other and to the terminals, and are

arranged at the headers.

The connection segments determine a considerable axial dimension at the

header of the stator, above all considering that the electrical windings aregenerally defined by bars which must be maintained spaced apart one from

the other. Furthermore, the axial dimension of the stator is increased by the

wiring configuration followed by the electrical windings: indeed, in an

electrical winding it is often necessary to connect together two straight

segments arranged in diametrically opposite axial cavities.

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The technical solution of forming isopotential electrical windings between a

pair of terminals, rather than a single electrical winding between a pair of

terminals, allows to decrease the current value in the single isopotential

electrical windings; to increase the cooling surface; and to reach higher

unitary powers with respect to traditional electrical windings and for a given

ventilating gas. The currently known solutions envisage the formation of two

or three isopotential electrical windings connected in parallel between each

pair of terminals.

The stators which adopt this type of solution, i.e. of fractioning the electrical

windings of the stator, in addition to the aforementioned drawback of the

axial dimensions due to the high number of connection segments at theheaders, present the drawback of overloading with electrical current the

connection zones of the electrical windings to the terminal pair to which

they lead.

GENERATOR STATOR

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STATOR CORE

The active part of the stator consists of segmental lamination of low loss

alloy steel the slots, ventilation holes and dovetail keyholes, are punched out

in one operation the stampings are rather complicated on account of the

number of holes and slots that have to be produced .

The use of cold-rolled grain-oriented steel sheet has possibilities in machines

as well as in transformers, most particularly in two pole machines where the

major loss occurs in the annular part of the core external to the slotting. Hear

the flux direction is manlyCircumferential, and by cutting the core-plate sectors in such a way that the

preferred flux direction is at right angles to their central radial axis,

substantial reduction in core-loss can be secured

It is of great important that the assembled stator laminations are uniformly

compressed during and after building, and that slot are accurately located.

The core plates are assembled between end plates with fingers projecting

between the slots to support the flanks of the teeth. The end plates are almost

invariably of non-magnetic material, for this stepped reduces stray load loss.

The end packets of core plates may be stepped to a larger bore for the same

reason.

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STATOR WINDING

The windings of two pole machines are comparatively straightforward. The

number of slots must be a multiple of 3(or 6 if two parallel circuits are

required ).single layer concentric or two-layer short-pitched windings maybe used.

The single layer concentric winding is readily clamped in the

overhang, but causes a higher load loss because the end connections run

parallel to the stator end plates. chording is not possible so that flux

harmonics have full effect.

The two layer winding is more common ,chorded to about 5/6 pitch

which practically eliminates 5th and 7th harmonics from the open circuit e.m.f

wave . The end windings are packed ,and clamped or tied with glass cord.

It is invariable practice with two layer windings to make the coils as halfturns and to joint the ends. The conductors must always be transposed to

reduce eddy-current losses. The conductors are insulated in many cases with

bitumen-bonded micanite, wrapped on as tape ,vaccume dried,then

impregnated with bitumen under pressure and compressed size. The process

is illustrated in picture.each copper bar A forming part of a conductor is

insulated with mica tape ,B and C . A set of bars forming one conductor is

assembled and pressed,D.the conductor is insulated with layers of mica

tape,E;then the conductors are assembled to form a slot bar,F,and pressed to

the required dimensions.synthetic resinsbhave now replaced bitumen.

Within the slots,the outer surface of the conductor insulation is atearth potential: in the overhang it will approach more nearly to the potential

of the enclosed copper. Surface discharge will take place if the potential

gradient at the transition from slot to overhang is excessive, and it is usually

necessary to introduce voltage grading by means of a semi conducting

(e.g.graphitic) surface layer, extending a short distance outward from the slot

ends.

The slot inductance is increased by setting the winding more deeply in to

the slots. This has the incidental advantage of spacing the overhang farther

away from the rotor end-rings.

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Stator winding

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VENTILATIONS

Forced ventilation and total enclosure are necessary to deal with the large-

scale losses and rating per unit volume . the primary cooling medium is air

or hydrogen , which is in turn passed through a water-cooled heat-

exchanger.

AIR COOLING

The water coolers are normally in two section, so that one can be cleared

while the machine is operating. Fans on the rotor,or separate fans,may beemployed ,the latter in large machines where bearing-spacing or limitation

of the diameter makes integral fans inadequate.

With integral fans mounted on the rotor ,the air is fed to the space

surrounding the stator overhang,and pipes and channels convey a proportion

towards the centre of the stator core.thereform it flowes readily inward to the

airgap,then axiallynto the end outlet compartments. With separate fans

,however,air can be fed directly to the middle as well as to the ends.An

improvement of the efficiency by reduction of the airflow losses is in

continuous progress using as support CFD programs. In the last decades the

improvement of the cooling, such as axial ventilation of the rotor andindirect cooling of the stator winding, allowed huge capability enhancement,

a better utilisation of the materials as well as a better efficiency.

This trend continues especially for the hydrogen and the aircooled

generators.

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HYDROGEN COOLING

A hydrogen-cooled turbo generator is a turbo generator with gaseous

hydrogen as a coolant. Hydrogen-cooled turbo generators are designed to

provide a low-drag atmosphere and cooling for single-shaft and combined-cycle applications in combination with steam turbines. Because of the high

thermal conductivity and other favorable properties of hydrogen gas this is

the most common type in its field today. Based on the air-cooled turbo

generator, gaseous hydrogen went into service as a coolant in the rotor and

the stator in 1937 at Dayton, Ohio, in October by the Dayton Power & Light

Co[2] allowing an increase in specific utilization and a 99.0 % efficiency

The use of gaseous hydrogen as a coolant is based on its properties, namely

low density, high specific heat, and highest thermal conductivity at 0.168 W/(mK) of all gases; it is 7-10 times better coolant than air. Other advantage

of hydrogen is its easy detection by hydrogen sensors. A hydrogen-cooled

generator can be significantly smaller, and therefore less expensive, than an

air-cooled one. For stator cooling, water can be used.

Helium with a thermal-conductivity of 0.142 W/(mK) was considered as

coolant as well, however its high cost hinders its adoption despite its non-

flammability.[3]

Generally, three cooling approaches are used. For generators up to 300 MW,

air cooling can be used. Between 250-450 MW hydrogen cooling is

employed. For the highest power generators, up to 1800 MW, hydrogen andwater cooling is used; the rotor is hydrogen-cooled, the stator windings are

made of hollow copper tubes cooled with water circulating through them.

The generators produce high voltage; the choice of voltage depends on the

tradeoff between demands to electrical insulation and demands to handling

high electric current. For generators up to 40 MVA, the voltage is 6.3 kV;

large generators with power above 1000 MW generate voltages up to 27 kV;

voltages between 2.3-30 kV are used depending on the size of the generator.

The generated power is left to a nearby station transformer, where it is

converted to the electric power transmission line voltage (typically between115 and 1200 kV).

To control the centrifugal forces at high rotational speeds, the rotor is

mounted horizontally and its diameter typically does not exceed 1.25 meter;

the required large size of the coils is achieved by their length. The generators

operate typically at 3000 rpm for 50 Hz and 3600 rpm for 60 Hz systems for

two-pole machines, half of that for four-pole machines.

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The turbogenerator contains also a smaller generator producing direct

current excitation power for the rotor coil. Older generators used dynamos

and slip rings for DC injection to the rotor, but the moving mechanical

contacts were subject to wear. Modern generators have the excitation

generator on the same shaft as the turbine and main generator; the diodes

needed are located directly on the rotor. The excitation current on larger

generators can reach 10 kA. The amount of excitation power ranges between

0.5-3% of the generator output power.

The rotor usually contains caps or cage made of nonmagnetic material; its

role is to provide a low-resistance path for eddy currents which occur when

the three phases of the generator are unevenly loaded. In such cases, eddy

currents are generated in the rotor, and the resulting Joule heating could in

extreme cases destroy the generator.[4]

Hydrogen gas is circulated in a closed loop to remove heat from the active

parts then it is cooled by gas-to-water heat exchangers on the stator frame.The working pressure is up to 6 bar.

An on-line thermal conductivity detector (TCD) analyzer is used with three

measuring ranges. The first range (80-100% H2) to monitor the hydrogen

purity during normal operation. The second (0-100% H2) and third (0-100%

CO2) measuring ranges allow safe opening of the turbines for

maintenance[5].

Hydrogen has very low viscosity, a favorable property for reducing drag

losses in the rotor; these losses can be significant, as the rotors have large

diameter and high rotational speed. Every reduction in the purity of the

hydrogen coolant increases windage losses in the turbine; as air is 14 times

more dense than hydrogen, each 1% of air corresponds to about 14%

increase of density of the coolant and the associated increase of viscosity

and drag. A purity drop from 97 to 95% in a large generator can increase

windage losses by 32%; this equals to 685 kW for a 907 MW generator.[6]

The windage losses also increase heat losses of the generator and the

associated cooling problems.[7]

The absence of oxygen in the atmosphere within significantly reduces the

damage of the windings insulation by eventual corona discharges; these can

be problematic as the generators typically operate at high voltage, often 20kV.[8]

The bearings have to be leak-tight. A hermetic seal, usually a liquid seal, is

employed; a turbine oil at pressure higher than the hydrogen inside is

typically used. A metal, e.g. brass, ring is pressed by springs onto the

generator shaft, the oil is forced under pressure between the ring and the

shaft; part of the oil flows into the hydrogen side of the generator, another

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part to the air side. The oil entrains a small amount of air; as the oil is

recirculated, some of the air is carried over into the generator. This causes a

gradual air contamination buildup and requires maintaining hydrogen purity.

Scavenging systems are used for this purpose; gas (mixture of entrained air

and hydrogen, released from the oil) is collected in the holding tank for the

sealing oil, and released into the atmosphere; the hydrogen losses have to be

replenished, either from gas cylinders or from on-site hydrogen generators.

Degradation of bearings leads to higher oil leaks, which increases the

amount of air transferred into the generator; increased oil consumption can

be detected by a flow meter associated to each bearing.[9]

Presence of water in hydrogen has to be avoided, as it causes deterioration to

hydrogen cooling properties, corrosion of the generator parts, arcing in the

high voltage windings, and reduces the lifetime of the generator. A

desiccant-based dryer is usually included in the gas circulation loop,

typically with a moisture probe in the dryer's outlet, sometimes also in itsinlet. Presence of moisture is also an indirect evidence for air leaking into

the generator compartment.[10] Another option is optimizing the hydrogen

scavenging, so the dew point is kept within the generator manufacturer

specifications. The water is usually introduced into the generator atmosphere

as an impurity in the turbine oil; another route is via leaks in water cooling

systems.[11]

The flammability limits (4-75% of hydrogen in air at normal temperature,

wider at high temperatures[12]), its autoignition temperature at 571C, its

very low minimum ignition energy, and its tendency to form explosive

mixtures with air, require provisions to be made for maintaining the

hydrogen content within the generator above the upper or below the

flammability limit at all times, and other hydrogen safety measures. When

filled with hydrogen, overpressure has to be maintained as inlet of air into

the generator could cause a dangerous explosion in confined space. The

generator enclosure is purged before opening it for maintenance, and before

refilling the generator with hydrogen. During shutdown, hydrogen is purged

by an inert gas, then the inert gas is replaced by air; the opposite sequence is

used before startup. Carbon dioxide or nitrogen can be used for this purpose,

as they do not form combustible mixtures with hydrogen and areinexpensive. Gas purity sensors are used to indicate the end of the purging

cycle, which shortens the startup and shutdown times and reduces

consumption of the purging gas. Carbon dioxide is favored as due to very

high density difference it is easily displaced by hydrogen.

Hydrogen is often produced on-site in electrolyzers, as this reduces the need

for stored amount of compressed hydrogen and allows storage in lower

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pressure tanks, with associated safety benefits and lower costs. Some

gaseous hydrogen has to be kept for refilling the generator but it can be also

generated on-site.

As technology evolves no materials susceptible to hydrogen embrittlement

are used in the generator design. Not adhering to this can lead to equipment

failure.

STATOR OF A HYDROGEN COOLED TURBOGENERATOR

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DIRECT COOLING

Direct cooling of stator winding is applied at ratings rather higher than that

which makes the method necessary for rotors .tubular conductors can be

used or thin walled metal ducts lightly insulated from normal statorconductors. A similar design serves for water cooling a stator. Here

arrangements are required in the overhang for the parallel flow of coolant as

well as for the series connection of successive coil-sides. Insulating tubes

convey the liquid to and from the water headers, and the water itself must

have adequate resistivity to limit conduction loss. Water cooling has obvious

disadvantages for rotors.

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ROTOR OF TURBOGENERATOR

The rotor accommodates the field winding whose poles are made of steel

laminations. A squirrel cage winding for absorbing purposes compensates

for parallel services and abnormal load operation. The rotor is dynamicallybalanced and designed to withstand to the electrical and mechanical effects

of overspeed as required by the applicable standard and of the triggering

according to the design. Manufactured with non-salient poles, the rotor has a

constant air gap along the whole iron core periphery. The rotor has a

cylindrical shape in whose periphery slots is inserted the excitation winding.

The field coils are made of bars, wires or copper laminations insulated with

a class-H insulating material. The non-salient pole rotor of the

turbogenerator is practically a monobloc with no overhangs or recesses. As

a result, it becomes sturdier and more resistant to overspeed and coiltriggering.

Generator rotor, including an inner and an outer concentric rotor part having

a non-drive side and enclosing a high vacuum space, a first and a second

bearing disposed on the non-drive side, a hollow shaft end of the outer rotor

part being supported in the first bearing, a journal of the inner rotor part

being extended through the hollow shaft end and separately supported in the

second bearing, a high-vacuum contact less liquid seal disposed between the

hollow shaft end and the journal and having a sealing gap formed there

between, a co-rotating sealing-liquid reservoir connected to the liquid seal,

and magnetic field means for holding magnetic sealing liquid in the sealinggap.

Rotors are most generally made from solid forgings must be homogeneous

and flawless. Test pieces are cut from the circumference and the ends to

provide information about the mechanical qualities and the micro structure

of the material. A chemical analysis of the test pieces is subsequently made.

One of the most important examinations is the ultrasonic test, which will

discover internal faults such as crackes and fissures. This will usually render

the older practice of trepanning along the axis necessary.

The rotor forging is planed and milled to form the teeth. About two-thirds of

the rotor pole-pitch is slotted, leaving one-third unslotted for the pole centre.

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ROTOR OF A TURBOGENERATOR

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ROTOR WINDING

The normal rotor winding is of silver-bearing copper. The heat developed in

the conductors causes them to expands, while the centrifugal force presses

them heavily against the slot wedges, imposing a strong frictional resistanceto expension. Ordinary copper soften when hot, and may be subject to

plastic deformation. As a result, when the machine is stopped and the copper

cools,it contracts to a shorter length than originally. The phenomenan of

copper-shortening can be overcome by preheating the rotor before starting

up with new machines the use of silver-bearing copper, having a much

higher yield point,mitigates the trouble.

Concentric multi-turn coils accommodated in a slot number that is a multiple

of four are used,the slot-pitch being chosen to avoid undesirable harmonics

in the waveform of the gap density. The slots are radial and the coils formedof flat strip with seprators between turns.the coils may be performed. The

insulation is usually micanite,but bonded asbestos and glass fabric have both

been used.As much copper as possible is accommodated in the rotor slots,the

depth and width of the slots being limited by the stresses at the roots of the

teeth,and by the hoop stresses in the end in retaining rings. The allowable

current depends on cooling and expension. Comparatively high temperature-

rises are allowed:the hot spot temperature may reach 140 degree centigrade.

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EXCITER

Installed at the non-drive end side of the generator, the exciter is formed by

fixed poles that accommodate the excitation field coils, the armature and therotating rectifier bridge. Its purpose is to supply direct voltage to exciter

rotor. It supplies direct current controlled by the voltage regulator according

to the load requirements, thus maintaining constant voltage for the main

generator.

Exciter Stator The poles accommodate the field coils which are seriesconnected, their ends being connected to the terminal block (I(+) and K(-)).

Its purpose is to supply the flux to the exciter rotor. It is supplied with a

direct current controlled by the voltage regulator according to the load

requirements, thus keeping the main generator voltage constant.

Exciter Rotor The exciter rotor is mounted on the main shaft of themachine. The rotor is formed by laminations with slots that accommodate a

star-connected three-phase winding. The phases are connected to the rotating

rectifying diode set.

exciter

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SLIP RINGS

Slip rings are required for conveying the exciting current to and from the

rotor winding. Rings of steel ,shrunk over micanite, may be placed one at

each end of the rotor,or both at one end, inside or outside the bearing.

INSULATION

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Since its introduction at the end of the 1950ies the synthetic resin mica tape

insulation technology has been in use. Over the past years a worldwide re-

evaluation of insulation technologies has been observed. On the far horizon

polymer insulations might become an option. However when benchmarking

with mica tape insulation, the required tight quality control for the

application in manufacturing and the non-existent inherent fault tolerance for

inner discharges become obstacles. Therefore it looks that small steps in

todays proven insulation technology will be realized earlier. Such novelties

close to introduction are: - Improved tape, now commercially available: high

thermal conductivity using fillers (HTC), higher mica content by denser

roving carrier. Both technologies are in verification tests. The maximum

achievable thermal conductivity is at 0.5 W/mK. - Improving the insulation

system to a higher thermal class (class 180). Such a technology is in final

verification and will soon be available. - Increasing the electrical field stressto a higher value, a 15% gain seems achievable. This allows a better heat

transfer and more copper in the slot. As specified by standards, insulation

verification tests are commonly based on comparative tests in specific

characteristics. Any modified insulation system must be at least as good in

these characteristics as the established technology. Other criteria are

sensitivity to manufacturing variances, throughput time, environmental

compliance and second source availability for the components. All these

improvements for the stator winding insulation look likely to shift the

bottleneck into the rotor. Fortunately, the rotor material technology brings

along all prerequisites to be upgraded into class 180 technology. This is due

to the fact that many components are inherently class 180 and simply need a

tighter specification to become qualified. In the case of class 180, allowing

class 155 operation, and probably in a later stage class 180 peaking, it is of

utmost importance that both stator and rotor winding designs can

accommodate their elongation due to thermal expansion. A set of design

measures has been worked out to provide this safety. The materials used in

laminates can be the same or different. An example of the type of laminate

using different materials would be the application of a layer of plastic film

the "laminate" on either side of a sheet of glass the laminatedsubject. Vehicle windshields are commonly made by laminating a tough

plastic film between two layers of glass. Plywood is a common example of a

laminate using the same material in each layer. Glued and laminated

dimensioned timber is used in the construction industry to make wooden

beams, Glulam, with sizes larger and stronger than can be obtained from

single pieces of wood. Another reason to laminate wooden strips into beams

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is quality control, as with this method each and every strip can be inspected

before it becomes part of a highly stressed component such as an aircraft

undercarriage.

Examples of laminate materials include Formica and plywood. Formica and

similar plastic laminates (such as Pionite, Wilsonart, Lamin-Art or

Centuryply Mica) are often referred to as High Pressure Decorative

Laminate (HPDL) as they are created with heat and pressure of more than 5

psi (34 kPa). A new type of HPDL is produced using real wood veneer or

multilaminar veneer as top surface. Alpikord produced by Alpi spa and

Veneer-Art, produced by Lamin-Art are examples of these types of laminate.

Laminating paper, such as photographs, can prevent it from becoming

creased, sun damaged, wrinkled, stained, smudged, abraded and/or marked

by grease, fingerprints and environmental concerns. Photo identification

cards and credit cards are almost always laminated with plastic film. Boxes

and other containers are also laminated using a UV coating. Lamination isalso used in sculpture using wood or resin. An example of an artist who used

lamination in his work is the American, Floyd Shaman.

Further, laminates can be used to add properties to a surface, usually printed

paper, that would not have them otherwise. Sheets of vinyl impregnated with

ferro-magnetic material can allow portable printed images to bond to

magnets, such as for a custom bulletin board or a visual presentation.

Specially surfaced plastic sheets can be laminated over a printed image to

allow them to be safely written upon, such as with dry erase markers or

chalk. Multiple translucent printed images may be laminated in layers to

achieve certain visual effects or to hold holographic images. Many printing

businesses that do commercial lamination keep a variety of laminates on

hand, as the process for bonding many types is generally similar when

working with arbitrarily thin material..

INSULATION RESISTANCE

When the generator is commissioned immediately after receipt, it should be

protected against moisture, high temperature and dirt, thus preventing

damages on the insulation resistance. The winding insulation resistance mustbe measured before the generator operation. If the ambient is very wet, the

winding resistance must be measured from time to time during the storage

period. It is difficult to prescribe fixed rules for the machine insulation

resistance values, since they change according to the environment conditions

(temperature, moisture), machinecleaning conditions (dust, oil, grease, and

dirt), quality and conditions of the used insulating material. A considerable

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dose of common sense, resulted from experience, must be applied to

conclude when a machine is or is not suitable for service. Periodic records

are useful for this conclusion.

BEARINGS

The bearings are mounted at the frame ends and their purpose is to support

the rotor mass and allow it to turn. Sleeve bearings are lubricated with oil

and the rolling bearings can be lubricated with grease or oil. Correct storage,

operation and maintenance procedures are determinant for their performance

and useful life.

Oil-lubricated bearing

Depending on its mounting position, the generator can be transported

with or without oil in the bearings.

The generator must be stored in its mounting position with oil in the

bearings;

The oil level must be respected, remaining in the sight glass half.

During the storage period, at every two months, the shaft-locking device

must be removed and the shaft turned manually to keep the bearing in good

lubrication condition.

After 6 months of storage and before starting the operation, the bearings

should be relubricated. If the generator is stored for more than 2 years, the

bearings must be washed, inspected and relubricated.

Grease-lubricated bearing

The bearings are factory lubricated for the performance of the generator

tests.


must be removed and the shaft turned manually to keep the bearing in good

lubrication conditions.After 6 months of storage and before starting the operation, the bearings

should be relubricated.

If the generator is stored for more than 2 years, the bearings must be

washed, inspected and lubricated again.Sleeve Bearing

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TURBOGENERATOR

Depending on the mounting position, the generator can be transported

with our without oil in the bearings and must be stored in its mounting with

oil in the bearings;

The oil level must be respected, remaining in the sight glass half.


must be removed and the shaft rotated at 30 rpm to circulate the oil and keep

the sleeve bearing in good lubrication condition.

Sealing

After bearing maintenance, both halves of seal labyrinth should be fixed

together by a circlip ring. They must be inserted into the ring seat, so the

locking pin is fitted into the undercut of the upper half part of housing. Poorinstallation damages the sealing. Before seal assembling, clean carefully the

contact surfaces of the ring and seating and coat the contact area with soft

sealing compound. Drain holes at bottom half of the ring should be cleaned

and cleared. When installing this halve of the sealing ring, press it slightly

against bottom shaft side.

CONCLUSION

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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 foradaptations 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 .

REFERENCES

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[1] R. Joho, C. Picech, K. Mayor, Large air-cooled turbogenerators

-extending the boundaries, CIGRE Session 2006, paper A1-106.

[2] C. Ginet, B. Zimmerli, A. Ziegler, W. Shugui, "Ten years of operational

experience with ALSTOMs air-cooled TOPAIR turbogenerator in the

300 MVA class and above", Power-Gen Asia 2006, Hong Kong, China.

[3] J. Haldemann, Transpositions in stator bars of large turbogenerators,

IEEE Trans. on EC, vol. 19, no. 3, Sept. 2004.

[4] Turbo generator by M.G SAY

project report ee vt

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