project tg04

7/31/2019 Project Tg04

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1.INTRODUCTION TO TESTING OF

TURBOGENERATOR

Testing is an activity, which basically evaluates a

component, and or a product (built up of componentassemblies) as to whether it has the technical capability

that has been built into it by way of design, materials, and

technological processes employed while manufacturing

and workmanship.

As such, testing activities can broadly be classified in to a

number of categories as follows:

- Type tests.

- Routine tests.

- Process tests.


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TESTING OF TURBOGENERATOR

Advantages of testing:

Provides quality assurance.

Meets the requirements of legal & contract requirements.

Reduction in rework cost.

Ensures process capability & develops checklist.

Increases confidence levels in manufacture.

Provides data for optimization of design.

Helps in building of Safety & general O&M manual.Establishes control over raw materials.

Important points for testing

Have an approved procedure.

Tabulate test levels / stages.

Check the testing equipment before use.

Calibrate the test equipment & instruments.

Ensure interlocks of the equipment


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Log the results in proper formats.

Analyse failure & submit a comprehensive report for repair

/ replacement.

PERFORMANCE TESTS ON

TURBOGENERATOR:

With the increasing trend on standardization every country

has its National Standards covering a wide range of

subjects, In India, the Indian Standards are valid andapplicable. The machines produced at Hyderabad fully

conform to Indian and also International Standards, and

many machines are being exported to various countries.

The performance tests on turbo generators include the

following

Measurement of Insulation resistance.


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Measurement of ohmic resistance of windings in cold

state.

Applied H.V. tests.

Measurement of vibrations and mechanical losses.

Measurement of no load characteristics.

Measurement of short circuit characteristics.

Determination of excitation on load and checks of

voltage rise (regulation).

Measurement of leakage and potier reactances.

Measurement of losses and determination of efficiency.

Heat run tests.

Retardation test.


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TEST PROCEDURE

During manufacturing of Turbo-generators the following

stage tests are to be carried out on individual components

to ensure quality of the product and to reduce last minute

delay during acceptances tests. The standards for these

tests will differ from plant to plant.

1.Stator

Checking up of Resistance temperature detectors while

core building.

Ring flux test.

Tan delta measurement on stator winding after

impregnation.

H.V. test on coils during manufacturers and assembly.


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Capacitance measurement.

2.Rotor

H.V. test on excitation connecting leads.

H.V. & inter- turn insulation tests on field coils during

the winding process.

Impedance measurement field coils.

3. Over-speed test.

Over-speed test involves mechanical running of the rotor at

the prescribed % over-speed for the stipulated period of

time. It is later subjected to a very close mechanical

inspection to investigating into the effects of over speed if

any.The rotor isbalancedto the required levels as per

standards. This brings us to measurement of characteristics

and losses of the generator.


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Measurement or determination of efficiency of the

machine is an important step.

For determination of efficiency, losses measurement on the

drive system is to be done and derive machine losses by

subtracting drive motor losses.

4.Determination of efficiency

Having measured the losses, the efficiency can be

estimated from the formula.

Efficiency =(input losses / input = output / (Output +

losses)

Tolerance on guaranteed efficiency is 0.1 (1-efficiency)

when measured by summation of losses method.


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5.Measurement for leakage & potier reactance

Leakage reactance is measured on the stator alone when

winding is completed. The procedure involves supplying

the winding from a 3-phase variable voltage source and

measuring currents voltage and power at the stator

terminals. Depending on the source capacity upto 0.25In

may be passed. Potier reactance as per accepted standard

practices is taken as 0.6 to 0.65 of total leakage reactance.It can alternatively be calculated from the zero power

factor test measurements.

6. Line-to-Line sustained short circuit test

The negative phase sequence reactance is can be

determined from the line-to-line sustained short circuit test.


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Negative phase sequence reactance (X2) = P / 3. (Ik2)2

where P = Power measured and Ik2 is negative phase

sequence current measured during line-to-line sustained

short circuit test.

7.Line to line and to neutral sustained short circuit test

From this test zero phase sequence reactance can be

determined.

Zero phase sequence reactance (Xo) = Vo / Io.

Where Vo = Voltage from measured in open phase voltage

and Io is current measured in line to neutral during line to

line sustained short circuit test.


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8.Retardation test for determination of Moment of

Inertia

The machine speed and time are noted during free coasting

down of the machine.

Moment of inertia =(4 x 365000 x P x T )/ N2 Kg-m2

where: P = Power input in kW to keep machine at rated

speed. N = Rated Speed in rpm.

T time in seconds from curve. (Tangent drawn at ratedrpm)


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2. THEORY OF SYNCHRONOUS

GENERATOR

THEORY:

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.


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The different electromagnetic or active parts of a

generator are as follows:

- Stator core

- Stator coils/ bars

- Stator winding

- Output leads, brushings and conductors

- Rotor excitation leads

- Rotor coils

- Rotor winding

2.1.Stator core

The stator core serves the two fold function of providing

the mechanical support for the stator coils and carrying

effectively the electromagnetic flux generated by the

rotor winding. In order to minimize hysterisis and eddy

current losses the entire core is built of thin laminations.


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Each lamination layer is made up from a number of

individual segments.

2.2.Stator coils/ bars

The stator coils are the individual entities, which are

placed in the slots of the stator core and finally

connected to each other as per a pre-designed scheme to

form a three phase winding. The prime purpose of the

stator bars is to carry the load current at minimal windinglosses.

These coils are provided with high voltage stresses.

Depending upon the size and rated voltage of the

machine different types of stator bars are designed.

2.3.Stator winding

The stator winding is a short pitch; two-layered type

made of individual bars. The bars are located in slots of


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rectangular cross section, which are uniformly

distributed on the circumference of the stator core. In

order to minimize the losses, the bars are composed of

separately insulated stands transposed by 360 degrees.

To minimize the stray losses in the end winding, the

standards of the top and bottom bars are separately

brazed and insulated

from each other.

2.4.Output leads, brushings and phase connectors

Output leads are taken out from the exciter end of stator

from the top and supported on an insulated glass fabric

plate. Six terminals are brought out, three for phase and

three for neutral connections. The phase connections are

connections between the stator winding phase bars /coils

to the output lead brushings.

2.5.Rotor excitation leads


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The excitation leads provide electrical connection

between rotor winding and output from brush less

exciter.

2.6.Rotor winding:

The construction of the rotor winding consists of

placement of pre-formed rotor coils as per the winding

scheme in the slotted rotor body, providing necessary

insulation both in the straight position and overhang,

making connections of the excitation leads, wedging ofthe straight part and mounting of the retaining rings.


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CLASSIFICATION OF SYNCHROUS

GENERATORS

Synchronous generators are classified into two main

categories based on their design as: Smooth cylindrical

rotor machines and salient pole machines. 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.

PRINCIPLE OF OPERATION:

The mechanical power of the prime mover rotates the

shaft of the generator on which the field winding is


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installed. When the field winding is excited using dc

voltage, then a rotating dc flux is produced which

when cut by the stator winding, a 3-phase voltage is

generated owing the principle of Faradays law of

Electromagnetic Induction.

DESIGN CRITERIA:

Any generator design should be in accordance with the

international standards like IEC and National standardslike IS, BS etc. Various inputs required for the designing

purpose of a generator is MVA, MW, PF, Voltage,

frequency, speed, Type of cooling, type of excitation

system etc. The main parameters during design to be

considered are:

Stator core- outer diameter, inner diameter, and no. of

slots, each slots size and size of copper. Rotor- barrel


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diameter, length, no. of slots, slot size and copper size.

The criteria of the design should be in such a way as to

ensure maximum efficiency, short circuit ratio (SCR)

and sub transient reactance as per the standard

stipulations and any other customer commitments.

The generators are classified as gas turbine generators or

steam turbine generators depending on their drive.

Generators driven by gas turbines are usually installedwith a minimum civil foundation on base frame as for

the gas turbine a perfect and proper civil structure is not

very necessary and can be installed outdoors. Gas turbine

generators can be either open circuit air-cooled or closed

circuit air-water cooled. The terminals are usually at the

top of the generator on the exciter side for the on word


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connection to bus ducts through a GAC (Generator

Auxiliary Compartment).

SYNCHRONOUS GENERATORS- LOSSES AND

COOLING:

All electrical machines produce heat owing to various

losses generated inside the machine (like the I2R losses

of stator copper winding). These losses are categorized

as fixed and variable. Friction and windage losses, whichinclude hysterisis and eddy current losses, are all

considered to be fixed losses while the rotor copper

losses, are treated as variable losses. Friction and

windage losses are dependent upon speed and as

synchronous machines run at constant speed, these losses

are constant. As the magnetic flux passes through stator

laminations, hysterisis and eddy current losses result in


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and are dependent on the magnitude of flux. As long as

machine is delivering power at a constant voltage, which

is normal case, these losses in the laminations are fixed.

The stator copper losses and rotor copper losses vary in

square proportion to the stator and rotor currents

respectively. These currents vary in accordance with the

load and thus in turn the losses also vary and hence

termed as variable losses.

As the synchronous machine has to deliver the output

continuously, the heat generated inside the machine has

also to be taken away at the same rate so that the

machine can operate at a stable temperature

continuously; ensuring a longer life for the insulation

system which in turn ensures a longer life of operation of

the generator itself. Thus cooling forms one of the basic


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requirements of any generator and the effective working

of any generator considerably depends on the cooling

system. The insulation used and the cooling employed is

interrelated.

Various methods of cooling employed are:

Air-cooling

Hydrogen cooling and

Water-cooling

Generally Upto 125 MVA air-cooling is employed.

Hydrogen cooling is employed in the machines i.e.,above 125MVA; as it is more efficient compared to air-

cooling.


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For still higher ratings like above 500MVA, Water-

cooling is employed.

Air cooled generators are the simplest in design and

either open air ventilating cooling system or a close air

close water circuit (CACW) cooling can be employed.

Open circuit air-cooling depends on the ambient

temperature unlike the CACW cooling and this open air-

cooling is employed for the Gas turbine generators where

there is scarcity of water.

EXCITATION SYSTEM:

In all industrial countries, the electrical power demand is

ever increasing, doubling itself approximately per

decade. This automatically demands for the design,

development and construction of increasingly large

capacity turbo generators. Such large capacity alternators


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should be highly reliable in operation and this calls for a

reliable and sophisticated mode of excitation system. The

excitation system consists of a small generator coupled

to the main alternator through the excitation leads

running through the shaft.

Conventional D.C Excitation Systems with a D.C.

exciter enjoyed an unchallenged position till recently

was adopted universally for all alternators. With the

growth in unit size of large capacity D.C. exciterscapacity became necessary. Due to problems in

communication it became inevitable to design of large

capacity D.C. exciters at low speeds leading to increase

in the systems. Moreover, the D.C. excitation suffered

from problems like power cabling, problems associated

with commutator and brush gear and maintenance.


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With the advent of high power solid state semiconductor

devices, significant strides were made in the

development of new excitation systems and thus in order

to liquidate the communication and brush gear problems

of the D.C, the A.C exciters were introduced.

A.C excitation:

Systems are classified into two types as:

High Frequency Excitation System was developed. At

present this is the system, which is widely used owing toits reliability, good transient performance and least

maintenance. The system also doesnt suffer from the

problems of communication, brush gear and power

cabling. However, the main disadvantage of the system

is that the rotor is not accessible and thus fast de-

excitation, in case of any fault on rotor winding, is not

possible.


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Static Excitation Systemwas developed contemporarily

as an alternative to brush less excitation system. This

system makes use of generators upto 160 MVA. The

system has got an excellent transient response. But the

system is not free from the power cabling, slip rings,

brush gear and moreover the equipment and thus the

layout of the cubical are not compact.


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3. CONSTRUCTIONAL FEATURES OF

TURBOGENERATOR

The turbo generator is designed for continuous

operation with voltage variations +/- 5% of the rated

voltage and a frequency variation of +/- 1%. In general,

the machine is designed for the altitudes of 1000 meters

and above sea level and below an ambient temperature of

60

0

maximum, with cooling water temperature of 38

0

maximum at the inlet.

The generator consists of the following components:

3.1 Stator:

Stator Frame

End Covers

Stator Core


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3.1. Stator

3.1.1. Stator Frame

The stator frame is of welded construction, supports the

core and the windings. In consists of air duct pipes andradial 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


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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.

3.1.2. 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 fromclamping 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 number of individual segments.

The segments are punched from the silicon steel. In the


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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 pressedfirmly 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


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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.

3.1.3. Stator Winding

The winding is a double layer multi turn lap winding.

The half coils are made up of electrolytic copper stripsinsulated 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


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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 arigid 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.


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Fig 3.1 Wound Stator

3.1..4 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


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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.

3.1.5. 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. Toensure 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


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(13-20deg) is used. On the wide sides of the bars spacers

of insulating material are inserted at regular intervals.

3.1.6. 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 thedimension drawing or in the Technical data. The

ventilating circuit is of the double-ended symmetrical

arrangement.


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3.1.7. 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.

3.1.8. 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


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temperature, with the shrinking tapes contracting so that

a void free insulation is obtained.

3.1.9. 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 arebrought put.


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Photo 3.2. Phase connectors and rings

3.2. 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 through out the active


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length of the rotor body to accommodate the conductors.

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

3.2.1. 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


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cooling gas to be discharged into the air gap after,

intensive cooling of the end windings.

3.2.2. 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 thecooling 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.


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3.2.3. 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.

3.2.4. 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


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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.

3.2.5. 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


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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.

3.2.6. Slip Rings

These are made of forged steel and shrunk on either side

of the rotor between the end cover and the bearing. Themica 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


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surface of the slip rings to have better dissipation of heat,

thus minimizing the brush wear.

3.2.7. 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.


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Photo 3.3 Rotor over hang Portion


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3.2.8. 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.

3.2.9. Field Connections

The field connections provide the electrical connection

between the rotor winding and the exciter.

3.2.10. Terminal Lugs


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Consists of a copper conductor of rectangular cross-

section. One end of the terminal lug is brazed to the rotor

winding, while the other end is screwed to the radial bolt.

3.2.11. 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.

3.3 BEARINGS

The generator rotor is supported at two-journal bearing.

The bearings consist of a bearing pedestal and bearing

shell is split into two halves to facilitate assembly. The

bearing pedestals are iron castings and the bearing shells

are the steel castings. The bearing pedestals are


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providing with a spherical seating surface and bearing

shell rests into with its outer spherical surface. The inner

surface of the bearing shell is provided with spherical

grooves and cast with Babbitt metal.

3.3.1. Bearing Oil Supply

The oil required for the bearing lubrication and cooling

is obtained from the turbine oil supply system supplied

to the lubricating groove in the bottom-bearing sleeve.The upper bearing sleeve consists of a wide overflow

groove through which oil is distributed over the shaft

journal and fed to the lubricating pump.

3.3.2. Bearing Temperatures

One double-element resistance temperature detectors

monitor the temperatures of each bearing. The resistance


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temperature detector is screwed in the position on side of

the low bearing sleeve from outside with the detector

extending to the Babbitt liner.

3.4. VENTILATION AND PROTECTION

EQUIPMENT:

3.4.1. Ventilation Arrangement

The turbo generator is cooled by air circulated by meansof 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.

3.4.2. Space heaters


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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.3.4.3. 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


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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 temperaturedetectors 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


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under different operating conditions of the turbo

generator.

3.4.4. 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 exceeds80deg 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.


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3.5. Insulating systems are of two types:

1.Resin rich system of insulation

2.Resin poor system of insulation

3.5.1. Resin rich system

- Conductor cutting and material used is same as

resin poor system.- Transposition is done same as that of resin poor

system.

- Stacking of coils is done. In this case high resin

glass cloth is used for preventing inter half shorts.

- Putty work.


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- Nomex is used as transposition pieces. Putty

mixture is a composition if mica powder, china clay and

SIB 775 Varnish.

- Straight part baking is done for 1hour at a

temperature of 160OC and a pressure of 150kg/ sq.cm

- Then bending and forming is done.

- Half taping with resin rich tape is done for over

hangs and reshaping is done.

- To ensure no short circuits half testing of coils isdone.

- Initial taping is done and final tapings is done with

resin rich tape to about 13-14 layers.

- Final baling is done for 3hrs at a temperature of

160OC in cone furnace.

- Gauge suiting is done.


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3.6. VACUUM PRESSURE IMPREGNATION

Siemens 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 Siemens patent resin systems. The stringent

quality tests on the resin mixtures and strictly following

the vacuum pressure impregnation and systematiccooling 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, made Siemens pioneers in this field. The

insulating materials used by Siemens for wedges are

resin poor and accelerator treated. For eg. Main

insulation tapes, mica paper tapes, overhang protective


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tapes, shrink tape and glass mates HM693 are treated

with accelerator. After impregnation, they become hard

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 Vaccumpressure impregnation system was brought by Dr.Meyer

with the collaboration of westinghouse in the year 1956.

The resins used were of polyester. Siemens developed

the present Vaccum pressure impregnation system with

epoxy resin and treated accelerator on tapes. The mica

tapes used for Vaccum pressure impregnation systems

are ROGS 275, ROGS 275.1 and ROV 292. ROGS 275


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tapes are with glass cloth baking upto 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 Vaccum pressure impregnation is ET884, 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


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heating in furnace, the 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, 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.

RESIN MIXTURE: The mixing ratio of resin to harden

is 46:54 parts.

The resin mixture required for the siemens Impregnation

tank is 27000lts. A job of 1.9m height and 4.5m dia can

be impregnated.


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Size of the tanks

-Main impregnation tank = 4.5m pie x 3.0m ht.

-There are 3-inch vessels for different sizes jobs

impregnation.

(a) Vessel (1) 3.8m pie x 2.25m ht.

(b) Vessel (2) 3.0m pie x 2.3m ht.

(c) Vessel (3) 2.0m pie x 2.3m ht.

3 Storage tanks of each resin capacity 9000 litres are inthe 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 Vaccum pressure impregnation cycle is as per WIV

114.1 standard.

Job preheating 70oc 12 hrs.


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The job is kept in an oven for a period of 12hrs at a

temperature of 70OC. 6 nos thermocouples are inserted

on the back of the core and measured the temperature.

Job insertion in the impregnation tank at 70oc

The lid of the impregnation tank in open condition. The

vessels are kept clean. Resin is 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 component andobstruct 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 allowed for further operation.

The job is inserted in the tank the temperature

monitoring thermocouples are placed on the back of the


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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.

Vacuum creation 0.35 torr for 2 hrs:

The job temperature is to be maintained always above

65

O

C , 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.


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IMPREGRATION:

The resin mixture is to be heated to 70deg.C. Everyday

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.

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


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is to be created to 3 bar (2 bar over atm. Pressure of 1

bar).

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.

Curing 14 hr 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.


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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.

CHARACTERISTICS OF VPI INSULATION

SYSTEM:

1) Higher mechanical bond

2) Void free insulation

3) High dielectric strength, low dissipation factor,hence longer electrical life.

4) Better heat transfer

5) Higher thermal stability, ensures class-F under

running conditions

6) Less maintenance

7) Cost effective


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8) Low inflammability, hence limited damage

during abnormal operations.

9) High resistance to oil, acid, alkali and moisture.

10) Manufacturing cycle is less

11) Frame size is small, machine cheaper.

12) Elastic response to thermo-mechanical stress,

machine suitable peak load operation

VACUUM PRESSURE IMPREGNATION

PROCESS:

Four stages of Vacuum pressure impregnation cycle

1) vacuum drying:


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temperature : 60oc +/- 3oc

pressure : 0.2 millibar

duration : ~ 16-18 hrs

drying check: 0.06 mbar drop in 10min

2) Imprgnation:

resin temperature : 60oc +/- 2oc

resin filling : ~ 20 min

resin level : ~ 100 mm above

settling time : ~ 10 minresin (epoxy bisophenol a) & hardener ratio 1:1

3) Pressurisation:

N2 pressure : ~ 4 bar

rising : ~ 80 min

holding time : ~ 2 hrs

capacitance measurement to ensure effective


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peneteation and gelling

4) Post curing:

temperature of job : 140oc +/- 5oc

duration : ~ 20 hrs

INSULATING MATERIALS USED IN THE

STATOR WINDING:

USAGE MATERIAL

DESCRIPTION

A foam insulation forslot bottom layer of

stator coil

Semi conductive foamfleece

Slot bottominsulation

Semi conductive fleece

Inter layer insert Glass mat

(compressible)


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Top insulation -do-

Spacers in overhang -do-

Bandage ring spacers -do-Slot wedge Glass mat (Hard)

Fillers for Slot Mergespacer

-do-

Slot Merge spacer -do-

Stiffeners between top& bottom layers

Glass mat (repressed ina hydraulic fixture)

Interlacing for ring andstiffeners

Glass Sleeve

Typing of spacers b/wcollector rings

Glass tape

Insulation of rings Fine mica paper glass

tapeShrink and protectionlayer

Polyester shrink tape

Adhesive varnish fortape ends

Adhesive varnish


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Bandage rings Polyester resin + glassravings

Terminal boards Glass mat (hard)

Table 3.1 List of

insulating materials

Photo 3.4 Wound Stator at VPI Plant


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Photo 3.5 Impregnation Plant


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3.7.EXCITER

3.7.1. Design Features

The exciter consists of

- Rectifier wheels

- Three-phase main exciter

- Three-phase pilot exciter

The three-phase pilot exciter has a revolving field with

permanent-magnet poles. The three-phase ac is fed to the

field of the revolving-armature main exciter via astationary regulator and rectifier unit. The three-phase ac

induced in the rotor of the main exciter is rectified by the

rotating rectifier bridge and fed to the field winding of

the generator rotor through the dc lead in the rotor shaft.

A common shaft carrier the rectifier wheels, the rotor of

the main exciter and the permanent magnet rotor of the

pilot exciter. The generator and exciter rotors are thus


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supported on a total of three bearings. Mechanical

coupling of the two-shaft assemblys results in coupling

of the dc leads in the central shaft bore through the multi

contract electrical contact system.

3.7.1.1. Rectifier wheels:

The main components of the rectifier wheels are the

silicon diodes, which are arranged in the rectifier wheels

in a three-phase bridge circuit. A plate spring assemblyproduces the contact pressure for the silicon water of the

diodes. One diode each is mounted in each light metal

heat sinks and then connected in parallel. Associated

with each diode is a fuse, which serves to switch off the

diode from the circuit if it fails. Each arm of the diode

bridge is provided with one RC block. The three-phase

connection between the armature and diodes is obtained


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with the help of hexagonal bolts. Footings are provided

to support the stator on the skid.


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Photo 3.6 Exciter

4. TESTING OF TURBOGENERATOR

4.1. Objectives of testing


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Testing is the most important process to be conducted

on a machine after it is designed. The testing of

machine is necessary primarily to establish that the

machine performance complies with the customer

specifications. Tests ensure that the piece of

equipment concerned is suitable for and capable for

performing duty for which it is intended.

Testing is done under condition simulating closely aspossible to those, which will apply when the set is

finally installed with a view to demonstrate to

purchasers representative its satisfactory operation.

Test provides the experimental data like efficiency,

losses, characteristics, temperature limits, etc. for the

use of design office, both as confirmation of design


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-Ensures process capability and develops checklist.

- Increases confidence levels in manufacture.

- Establishes control over raw materials.

-Helps in building of safety and general operation

and manual.

4.2. TYPES OF TESTS

Tests on turbo generators are classified under the

following headings, which is also the order in whichthese are performed during the course of manufacture.

1.Tests on the materials and components during the

manufacture so as to control the quality of the materials

in process also known as Process tests.

2. Performance tests on the machine to prove the

performance of the generator in accordance with the

required standard.


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4.3. TESTS DURING MANUFACTURE/

PROCESS TESTS:

Tests on rotor winding

Tests on stator coils.

Balancing and over speeding of rotor.

4.3.1.Rotor winding

The rotor coils and their insulation are subjected to a high

stress when in normal operation. Thus a thorough

inspection of these is necessary before putting them in the

rotor slots as otherwise any replacement of the faultyinsulation or cell would necessitate

removing the coil binding rings and the wedges, which is

a cumber job. A series of graded voltage tests are


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conducted on the rotor cell and coils dusting assembly and

also when finished to test its electrical strength against

likely creep age to ground or inter turn breakdown.

4.3.2.Tests On The Rotor Coils

1. Between turns:

The rotor coils turns are made up of a number of turns

which are formed in halves and then assembled withtheir inter turn insulation and boned with an adhesive in

the steam heat press. Although the normal working

voltage per turn is very small, a turn to test of 240 volts

is done to exercise quality control.

2.Top turn trough:

The insulation the top and bottom of the rotor slot

provides adequate and safe creep age distance between


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copper and rotor steel, in case of slotted copper 500 volts

for one minute to test the top trough.

3. Collecting leads:

A high voltage equivalent to the shipping test plus

1500v is applied to the collector leads when fitted in

bore with studs of seals fitted but before connecting to

the windings.

4.3.3.Tests on stator coils

As per the standards the stator winding has to be

subjected to a shipping pressure test of (2 x line

voltage +1kv). This power frequency voltage applied

for one minute.

In order that machine when found with stands this

final voltage test and any faulty coil is eliminated

during various stages of coil manufacture and


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winding. Because of the continued application of HV

tests overstress the winding insulation, the voltage is

reduced in various stages.

1.Tests between parallel strips

This is a test of strip insulation provided for eddy emf,

on low voltage at the order of 350V for 3 seconds is

applied.

2.Coils in manufacturing and Winding Sections:

When the coils are first tested, a voltage of 8kV in excess

of shipping pressure test is applied, and this voltage tests

are repeated.

3.Tests on Thermocouples:

1000V Megger test is applied to the thermocouples.


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4.3.4. Balancing and over speeding of rotors

1.Balancing:

One of the most important preliminaries to testing is that

of balancing the rotors. Before over speeding, the rotor is

dynamically balanced, in cold as well as hot conditions.

A set of run up and run down is taken sure those critical

speed is well away from the running speed.

2.Over Speeding:

In order to check the soundness of all parts and fitting on

rotor assembly, the rotor is run at an over speed of 14%

for five minutes or 30% for one minute.

4.4. PERFORMANCE TESTS/ TESTS ON

COMPLETED MACHINE:


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The machine is assembled and erected at the heavy

rotating plant test bay for test.

1. Dry out insulation resistance of rotor & stator

windings

- Before starting with running tests, the stator

windings are dried out by circulating current in the

winding from an external dc source Input of power is

so controlled as to limit the temperature of the endwindings to a maximum of 800C by thermometer.

-Progress of dry out is observed by one minute

insulation resistance reading with 1000v Megger.

With the application of heat, the insulation resistance

will initially drop and then will rise again over a

period of time and finally becomes approximately

constant temperature. Ration of ten-minute reading


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i.e. polarization index, when more than 2 gives an

indication of good dry out. Insulation resistance

readings of rotor winding to ground are taken.

2.Resistance of machine windings

Measurement of cold winding resistance, both for stator

and rotor must be very accurate since it forms the

basis of

Calculating copper under cold and hot conditionsFor determining the rise in temperature of rotor winding

by resistance method at the end of temperature test.

All precautions are taken to ascertain correct temperature

of the winding white measuring cold resistance. Since

the winding resistance of turbo generator is quite low: a

modified form of wheat stone bridge i.e. Kelvins double


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bridge does away with the necessity of accounting for

the resistance of loads. Resistance between phases for

stator and between slip rings for is recorded along with

the cold winding temperature at the time of

measurement.

3.Phase sequence test:

The phase sequence test is to check the agreement of the

terminal markings that have been specified using thePhase Sequence Indicator.

4.Zero excitation rated speed run

By wattmeter method when condition is steady. From the

result of above test after deducting drive motor in gear

losses, friction and wind age losses of the machine under

test are computed. These losses are for rated speed.


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Bearing oil quantities with inlet temperatures of oil can

yield calculations for bearings loss. From a previous data

on seal face losses determined from a prototype test, the

total friction loss in the bearings and seals can be

difference. Since bearing loss is computed for design

office use by the difference. Since bearing loss goes to

oil, any heat carried out on the unexcited machine will

give temperature rise due to wind age.

4.4. PERFORMANCE TESTS

The performance tests on the turbo generator are

classified as:

-Type tests

-Routine tests

-Heat run tests


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4.4.1. TYPE TESTS

These are specially requested tests form the customer.

They are not performed on all machines i.e., they are

specific to machine. They include

-Mechanical measurement of leakage reactance of

stator winding

-Measurement of residual voltage of stator winding

at rated speed

- Line to line sustain short test and determination ofnegative sequence reactance [X2]

- Line-to-line and neutral sustain short circuit test and

determination of negative sequence reactance [XO]

- Retardation test for determination of GD2

4.4.1.1 Measurement of leakage reactance of stator

winding


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where Z = U/ 3I,

R = P/ 3 I2

U = voltage measured during the test

I = current measured during the test

P = power measured during the test

As the value of R i.e., stator winding resistance per

phase is negligible compared to Z, measurement of P

is not required.

XL = Z = U/ 3 I ohms% XL = 100(XL / XN)

iii) Potier reactance % XP = a ( % XL)

where a = 1 for salient pole machine and

0.63 for cylindrical pole machine


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parameters are recorded at three values of the short

current limited to 30% at rated current.

- Short circuit current (IK2), through current

transformer

- Voltage between the open line terminal and one of

the short circuit terminals Uk2, through potential

transformer.

-Active power p.

Evaluation of negative sequence reactance (X2)

(i) X2 = P / 3. (I K2)2 ohms

where P = power measured during the test

IK2 = line-to-line short circuit current measured

during the test %X2 = 100(X2/Xn)


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IO = line to neutral current measured during

the test

% Xo = 100 (Xo / Xn)

Note: Minimum time is taken for the test because serious

overhang winding heating may result, if current is

sustained for a longer time or raised to too high a value.


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4.4..1.5.Redardation test for determination of GD2

(Gravitational deterioration)

The machine along with the drive system is run at rated

speed and drive motor input power is noted. Then speed

is increased by 1hz corresponding rpm over the rated

speed and at the stage, the machine is tripped by opening

the in-comer circuit breaker of drive system. Time and

speed are noted with an interval of 5 seconds upto 30

seconds, with an interval of 10 seconds upto 1minute andso on till the machine comes to stand still.

1.Evaluation of GD2

GD2 is calculated as follows:

Time versus speed curve is plotted on a graph paper,

taking X axis as time and Y-axis as speed. A tangent is

drawn at rated speed point on the curve, which meets the


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4.5.1. Static tests

4.5.1.1. Measurement of insulation resistances of stator

and rotor windings before and after high voltage test:

Equipment:

a) Megger (1000V/ 2500V)

b) Earthing rod and earthing wire/ cable.

- Insulation resistances of the stator and rotor

windings are measured separately before and afterhigh voltage test using 2500V Megger for stator and

1000V for rotor winding. These values are taken at

15 seconds and at 60 seconds. Absorption coefficient

of insulation is found out as,

Insulation resistance at 60seconds

Absorption coefficient =

------------------------------------------


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value of 1.8 and 1.7 may be satisfactory, while a

value below 1.5 indicates a damp machine.

-The winding is discharged to earth after each

measurement.

4.5.1.3.Measurement of polarization index of stator

winding

The polarization index of stator winding, all the threephases together is measured using 2500V Megger after

high voltage test. The insulation resistances are noted at

1minute and at 10 minutes from starting of measurement.

The polarization index is evaluated as follows:

Insulation resistance valueat 10 minutes


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The high voltage is applied to winding by increasing

gradually to required value and maintained for one

minute and reduced gradually to minimum. The

transformer is switched off and winding is discharged to

earth by shorting the terminal to earth using earthing rod

connected to earthed wire/ cable. The test is conducted

on all the phases and rotor winding separately.

High voltage test levels:Stator winding: (2Ut + 1) kV = 23 kV for 11 kV

machine.

Rotor winding: (10 Ue) volts.

(with minimum of 1500 V and maximum of 3500V).

where, Ut = Rated voltage of the machine (kv).

Ue = Excitation voltage.

1. Stator winding:


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Testing of stator winding involves the testing of

connecting rings after the assembly and stator bars

during assembly.

Up = (2 Un + 1)

Where, Up is the final test voltage after the test run

and Un is the rated voltage of the generator.

- The connecting rings are tested for 1.2 UP for 1

minute. If there is sparking due to less distance

between the live joints, the same can be done with 1.1UP. If the connecting rings are assembled after laying

bars, they are tested along with the bars.

-The high potential is given to copper and the core is

earthed. The output voltage of the high voltage tester

is continuously increased to test the voltage level,

held for 1 minute and subsequently decreased to

initial level.


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- After the bottom bars are laid they are tested for 1

minute with 1.1 UP. Individual strips are of each bar

are tested with 220V ac for any possible inter half

shorts and inter bundle shorts.

- After the top bars are laid, High voltage testing is

carried out with 1.1 UP for 1 minute and they are

tested for inter half and inter bundle shorts. Inter halfshorts test with 220V ac is carried out after

connecting the top and bottom bars without the

connecting rings.

- High voltage testing of the individual phases with

1.05 UP is carried out for 1 minute after the

completion of the winding . When one phase is under

test the other phases are earthed.


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-Resistances of individual phases are measured .

-During high voltage testing all the instrumentation

cables assembled in the machine are to be earthed.

-Insulation resistance of each phase is to be measured

after each high voltage test.

-Whenever bunch brazing is employed for

connecting top and bottom layers, only inter half

shorts test is to be carried out.

2. Rotor winding

The rotor winding must be tested at various stages of its

manufacture and assembly.

-The output of the high voltage test equipment is

connected to the output lead or to the winding as the

case may be and shaft is earthed. The voltage is

continuously increased to test voltage level,


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maintained for 1 minute and subsequently decreased

to initial value.

-To test for inter turn shorts the required voltage is

applied across the total winding of both the poles and

voltage across the winding corresponding to each

pole is measured and recorded.

- The final test voltage UP is ten times the rated

voltage subjected to a maximum of 3.5 kV and

manimum of 1.5 kV.- Before assembly of rotor bars HV test is carried

with UP + 2000V for one minute. Then both the poles

against earth are tested with UP + 1500 V for one

minute.

- After the assembly of the rotor bars HV test is

carried with UP + 1500 V for one minute initially pole

against pole and then against earth.


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- After over speeding and balancing at standstill HV

testing of the winding against the shaft with UP+200V

ac is carried out for one minute.

- HV testing of the winding is carried out at 3000 rpm

with 500V ac for one minute. Then the winding is

tested against the shaft with UP for one minute.

-The insulation resistance value of the winding is

measured after each high voltage.


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Figure no: 4.3 Single Line Diagram of H.VTesting of Stator Winding

4.5.1.5. Measurement of D.C resistance of Stator

and Rotor windings in cold

condition

Equipment:


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a) Digital micro ohmmeter and its measuring

leads.

b) Thermometer (Hg in glass)

D.C resistances of stator and rotor windings are

measured separately using digital micro ohmmeter.

The instrument terminals are connected to the

machine terminals and proper range in meter is

selected. The stabilized reading is recorded.Ambient temperature from Hg in glass thermometer

is recorded. The stator resistance temperature

detectors values are noted and average value of stator

winding temperature is evaluated.

1.4.1. Evaluation of resistance at 20OC:


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- Evaluation of resistances at 20OC (R20) is done by

using formula:

- R20 = {Rt (235+20)} / (235 + T) milli ohms

- Where, R20 = Resistance at 20OC in milli ohms

- T= The average temperature of the stator winding

in degrees centigrade.

Rt = Measured resistance of the winding in milli

ohms

-Variation in maximum and minimum values of d.cresistance of 3 phases of stator windings up to 5% is

acceptable.


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H.V. application to one of the phases and remaining

phases are connected to body of stator. This gives the

value of Cg+2 Cm, where Cg is capacitance of winding

with respect to ground and Cm is with respect to other

winding (mutual

capacitance).

Arrangement II:

H.V. application to all the phases. This gives the value of

3Cg..

b) Equipment:

a) 50 Hz A.C. high voltage transformer

(T90, 0 - 35kV)

b) Standard capacitor (100 / 1000 pF).

c) Schering bridge

d) Isolation shunt box


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e) Connecting H.T. cables.

f) Earth wire with earthing rod.

g) Voltmeter.

h)Megger (1000V).

i)Null Indicator

(galvanometer).

j) 1- phase supply source for null indicator.

c) Test preparation:i) The stator body is isolated from ground by

placing insulation packing between the body and the

base.

ii) Connections to the Schering Bridge,

standard capacitor, Null indicator and transformer are

done as per figure 4.4 for the selected arrangement.


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iii) Measurements are taken at voltages 0.2Un to

1.0Un in steps of 0.2Un.

iv) The H.V. supply is switched on and raised

to the required value. The bridge is balanced with the

proper selection of variable resistances (R3+S) & the

capacitance C4 and readings are recorded. After all

measurements, voltage is reduced to zero, supply is

switched off and windings are discharged to earth.

e) Formula used:i) Capacitance:

Cn x R4 x (R3+100)Cx = -------------------------- F.

N x (R3+S)

ii) Percentage of tan

% tan = ( x R4 x C4 x 10-4 ) x 100

where, C4 & Cn are in F.


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These tests are run after assembly of machine on test

bed.

Equipment:

a. D.C motor drive system.

b. Bearing lubrication system.

c. Cooling water system.

d. Current transformers 2 nos.

e. Potential transformers 2 nos.

f. D.C current shunts 2 nos.g. AC/DC Power analyzer.

h. Phase sequence indicator.

i. Multimeter for continuity checks.

j. Vibration monitor.

k. Resistance temperature detectors

monitor.

l. 50 Hz A.C High voltage test equipment.


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m. Meggers.

n. Micro ohmmeter.

o. Connecting leads/copper strips and

earthing cables rods etc.

4.5.2.1 . Mechanical run and measurement of

vibrations at rated speed

The turbo-generator under test is assembled separately

without coolers and enclosures (if any), on a testfoundation frame using its own bearings and coupled to

a calibrated d.c drive motor with gearbox of suitable

capacity (1900kW/ 1300kW/ 750kW). The brushless

Exciter and Permanent magnet generator are mounted on

the overhang of the generator rotor. Testing of turbo-

generator, brushless exciter and permanent magnet

generator are done separately. The power to the drive


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motor and the field of the generator are drawn

independently from the thyristor converters suited in

electrical machine controlled rooms and controlled from

test gallery independently.

Before running the machine ensure:

-Lubricating Oil is flowing through bearings and the

gear box.

-All the instruments are working-Roll the machine and check all the parameters.

Slowly raise the speed to one-sixth rated speed.

Observe slow roll vibrations, temperature and oil

flows. Raise the speed to one-third rpm slowly and

record the vibrations, temperature and oil flows.

-The vibrations are measured at rated speed on both

the bearing housings (pedestals) in horizontal,


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vertical and axial directions with the help of vibration

meters, which are internally connected to the monitor

and the vibrations, are noted in the form of graphs.

-The temperature of stator is monitored by

monitoring resistance temperature detectors

embedded in core, tooth and winding. Now raise the

speed to two third the rpm by observing all the

parameters, critical speed and record them. The

machine is rolled and run at rated speed afterensuring the bearing oil and left at rated for

stabilization of bearing temperatures.

4.5.2.2. Measurement of mechanical losses, short

circuit characteristic and losses


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-The machine is prepared for short circuit

characteristic using current transformers and shorting

links as shown in figure 4.5

- The machine is run at rated speed and drive motor

input voltage and current are noted and m/c is excited

gradually in steps, at 20%, 40%, 60%, 80%, 90% and

100% In

(In = Rated current of machine).

At each step the following parameters are noted:

1) Stator current (Ia & Ib)

2) Rotor current (If) corresponding to stator

current.

3) Drive motor voltage (Vd) and current (Id)

corresponding to stator current.


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4) Resistance temperature detectors readings at

rated stator current (100% In).

5) Bearing vibrations at rated stator current (100%

In).

The excitation is reduced and cut off. The speed is

reduced and the machine is cooled at lower speed.

The temperatures are checked from machine

resistance temperature detectors readings. Themachine is stopped when it is sufficiently cooled

down. (The stator winding temperatures to be less

than 60OC).

From the above data, the characteristic curves are

plotted as follows:

a) % In versus If.


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b) % In versus machine looses in kW.


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Figure 4.5 Single line diagram for short circuit

characteristics

4.5.2.3. Measurement of mechanical losses, open

circuit characteristic and losses:

-The machine is prepared for open circuit as shown

in the figure 4.6.

- The machine is run at rated speed and drive motor

input voltage and current are noted and m/c is excited

gradually in steps, at 20%, 40%, 60%, 80%, 100%

and 120% En (En = rated voltage of machine).

At each step the following parameters are noted:


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From the above data, the characteristic curves are

plotted as follows:

c) %En versus If.

d) % En versus machine looses in kW.


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terminals when machine is in open circuit condition at

100%En.

4.5.2.6.. Measurement of rotor impedance (Rotor inside

stator):

Equipment:

a) 50Hz (Power frequency) A.C source.

b)AC/DC Power analyzer.

c) Current transformer (50A/5A or 100A/5A)d)Connecting leads.

Connections are made as per the figure 4.7

A variable 50 Hz A.C. voltage of single phase is

applied across the slip rings /input leads and readings

of voltage and current are noted down from 50V to

200V in steps of 50V. This test is done at 1/3, 2/3 and

at rated speed.


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Evaluation of impedance:

Using formula does evaluation of impedance:

Z = V /I ohms

where Z = impedance in ohms

V = voltage in volts

I = current in amperes

Impedance measurement:

-At rated rpm (Rotor inside stator).-At standstill (Rotor inside stator).

-At standstill (Rotor outside stator).


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Figure 4.7 Single line diagram for measurement of

Rotor impedance

4.6. EVALUATION OF EFFICIENCY

Efficiency of Turbogenerator

Introduction:


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Thus %Efficiency = 100{(output) / (output + losses)}

The Total loss consists of the following component

losses

1.Excitation Circuit Losses:

a. Field I2R loss: The I2R loss in the field winding.

b. Main rheostat loss: The loss in the rheostat in the

main exciting winding.

c. Electrical loss in the brushes: The summation of

I

2

R losses in the brushes and the connectors andbrush contact loss.

d. Exciter loss: All the losses of exciter mechanically

driven from the main shaft which forms part of the

complete unit and is used solely for exciting the

machine, together with the losses in the rheostat in

the field circuit of such an exciter.

2.Losses independent of Current:


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a) Stray load loss determined from the primary

windings determined from the current in the

conductors.

b) Stray load loss in the conductors.

4.6.1. EVALUATION OF EFFICIENCY:

After completion of routine tests, efficiency of the

machine evaluated.

The following sequence of calculation is followed.1.Open circuit characteristics is plotted on a graph paper

from open circuit characteristics results by selecting X

axis as field current and Y- axis % of rated voltage.

Values of field current at 80%,100&,115%,130%En are

taken from the curve.

2.Short circuit characteristic is plotted from S.C.C

results by selecting X axis as field current and Y axis


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as % of rated current. Values of field at 100% In are

taken from the curve.

Turbo generator looses: ref. Fig. 4.8.

Air gap line for open circuit characteristics is drawn and

field current for air gap line at 100%En is obtained.

Copper loss characteristic is plotted from S.C.C results

by selecting X axis, as %of rated current and Y axis

as losses in kW. The value of copper loss (kW cu1) at100%In is taken from the curve.

Iron loss characteristic is plotted from O.C.C results by

selecting X axis, as %of rated current and Y axis as

losses in kW. The value of iron loss (kW fe) at 100%En

is taken from the curve.

Drive motor with gearbox losses:


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i). Average mechanical losses (kW mechanical.) =

Average of mechanical losses before Short circuit

characteristics and open circuit characteristics (kw

average mechanical)

ii) Losses at 100% In i.e. 100%In mech. = kW

average mech. + (kW6 kW3)

iii) Losses at 100% En i.e. 100%En mech. = kW

average mech. + (kW9 kW3)

4. Machine losses:

a. Mechanical losses (Pmech) = kW avg mech.

kW3

b. Stator copper losses at 100% In (Pcu1) = kWcul

kW 100%In mech.


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c. Stator iron losses at 100% En (Pfe) = kWfe kW

100%En mech.

d.Excitation losses: This shall be taken as 5% of

rotor copper losses.

e. Brush drop losses: In case of machine with

conventional excitation system with slip rings on

rotor, the brush drop losses are calculated taking

voltage drop of 1.0 volt each polarity multiplied by

the rated excitation current. For brushless excitationsystem, this loss is non-existent.

To obtain field currents of the turbo generator at

25%, 50%, 75% & 100% loads all the data required

from the test results are fed to the computer program.

The output gives field currents, rotor copper losses

and excitation losses. After obtaining the machine

losses including exciter mechanical losses (if any),


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stator copper losses, stator iron losses, rotor copper

losses, excitation losses, brush drop losses (if any);

all the losses are added to get total loss.

Percentage efficiency (%) is evaluated as follows:

Output%Efficiency = 10 0 X ------------------------

Output + totallosses

4.6.2.Evaluation of short circuit ratio (S.C.R):

From the test data S.C.R is calculated using formula:

Field current at 100% En fromopen circuit testShort circuit ratio =----------------------------------------------------------

Field current at 100% In fromShort circuit test


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4.7. TESTING OF BRUSHLESS EXCITER:


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This test procedure covers the procedure for routine tests

on brushless exciter and permanent magnet generator.

4.7.1.Tests conducted on brushless exciter:

Open circuit characteristic.

Measurement of D.C. resistance of armature

windings and main pole winding.

4.7.2.Tests conducted on Permanent Magnet

Generator

-Measurement of output voltage at rated speed.

-Checking of phase sequence and measurement of

frequency.

-Measurement of load characteristic.

-Measurement of insulation resistance value before

high voltage tests.


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to the terminals in the control gallery where the

measurement is done.

Equipment:

-D.C. motor drive system

-Bearing lubrication system

-D.C. voltmeters

-D.C. current shunts-Phase sequence meter

-Water load resistance bank

-Current Transformers

-A.C Ammeters

-A.C. voltmeters

-Frequency meter

-Vibration probes and Vibration monitor


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4.7.1.2..Load Magnetization curve:

-The machine is prepared for the load magnetization

characteristic. A variable water load resistance is

connected across the slip rings.

- The machine is run at rated speed, load breaker is

closed and the machine is excited gradually in steps.

The load resistance is maintained at R40 (R40: Turbo

generator rotor resistance at calculated for 40

0

C) byadjusting the water load resistance.

-At each step, following parameters are noted:

-Va : Output voltage of the exciter

-Ia: Load current of the exciter

-If: Field current of the exciter

-And bearing vibrations at rated load.

- Test is repeated for load resistances R70 and R100.


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Rm = (kV+1) mega ohms

-where kV = Voltage in kilo volts to be applied for

H.V. test.

High voltage test is done on individual windings using

high voltage test kit by regulating primary voltage to the

transformer. Slowly HV is reached and maintained for 1

minute and is reduced to zero. The earth rod then

discharges the object and the IR values are taken. When

this test is done on one winding, the other windings areearthed.

4.7.1.4. Measurement of DC resistances of Armature

windings and main pole winding:

After dynamic tests the machine is allowed for cooling

and when it is sufficiently cooled, the DC resistances of

all the three armature windings and main pole windings


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are measured separately by the micro-ohmmeter. The

ambient temperature is also recorded and the evaluation

of resistances at 20OC is done by using the formula:

R20 = Rt (235+20)/(235+T)

where, R20 = DC resistance at 20deg

Rt = DC resistance of the winding at t deg

T = Temperature of the winding in deg

4.7.2. Test Procedure of the permanent magnet

generator (PMG)

The permanent magnet generator is assembled along

with the brushless exciter on the generator rotor shaft.

The output is connected to a three-phase resistance load

(variable in steps). As permanent magnet generator has


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permanent magnet generator. The sequence indicated by

the meter is recorded.

At rated speed, a frequency meter is connected across

any two phases of the permanent magnet generator PMG

output terminals and frequency is measured.

4.7.2.3.Measurement Of The Load Characteristic

-Machine is run at rated speed and loaded using

three-phase resistance bank in steps up to rated loadcurrent.

-At each step, load currents and output voltages are

noted.

-Load magnetization curve is drawn as phase-to-

phase voltage versus load current.


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phase windings separately. The ambient temperature is

also recorded and the evaluation of resistances at 20deg

is done as shown in the figure.

5. CONCLUSION

In this project a sincere effort has made for the testing

of turbo generator of 90.59 MVA, 11kv,3000 RPM,

2-Pole Synchrous generator. The various activecomponents of the generator were studied and attempt

was made to acquaint us with the sophisticated design

and technologies involved.

The present project gave us an opportunity to know

above the manufacture of the turbo generator and its

structural components viz., stator, rotor, brushless


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excitation systems etc. and other auxiliary equipment.

A study was also made on most update insulation

technique latest technology of vacuum pressure

project tg04

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