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Industrial Training on TurboGenerators and

@ BHEL,Hyderabad

C R SUDE

REDDY

105111013

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BHEL - AN OVER VIEW

BHEL is the largest engineering and manufacturenterprise in India in the energy related manufra

sector today.

The wide network of BHEL comprises 14 manufa

divisions, four Power Sector regional centers, eig

centers and 18 regional offices and a large numb

project sites.

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TURBO GENERATOR Here we have a detail study of the design and manufacturing of TGENERATOR.

Maximum percentage of total power generation is obtained by co

power plant where always alternators are used.

An AC generator is basically a device for converting mechanical electrical energy.

It works on the principle of Faradays Law of Electromagnetism.

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MAIN COMPONENTS

In AC generator the statorholds the armature winding anrotorholds the field winding .

In generator, the armature is stationary, the field is rotatin

For the rotating magnetic field, the DC excitation to theRotor is necessary.

The excitation is supplied using a DC machine called

Exciterwhich is generally driven with the same shaft.

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EXCITATION SYSTEM

Types of d.c exciters are:

(1) High frequency excitation

(2) Brush less excitation(3) Static excitation

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EXCITERS

Exciters are those components, which are used for giving high vo

generator during the start up conditions. The main parts that are i

the exciter assembly are:

(1) Rectifier wheels

(2) Three phase main exciter

(3) Three phase pilot exciter

(4) Metering and supervisory equipment

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PERMANENT MAGNETGENERATOR

This system is highly reliable with least maintenance, flexibility ooperation, fast response and is ideally suitable for gas driven ge

This system was successfully adapted to medium and large cap

Turbo generators.

Though the system offers very good transient performance, theassociated with slip rings and brush gear system are still presen

This system consists of rectifier transformer, thyristor convertors

breaker and AVR.

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AUTOMATIC VOLTAGEREGULATOR

The main features of AVR are:

(1) It has an automatic circuit to control outputs of auto channel achannel and reduces disturbances at the generator terminals d

transfer from auto regulation to manual regulation.

(2) It is also having limiters for the stator current for the optimum u

of lagging and leading reactive capabilities of turbo generator.

(3) There will be automatic transfer from auto regulation to manua

regulation in case of measuring PT fuse failure or some internal fa

the auto channel.

(4) The generator voltage in both channels that is in the auto chan

the manual channel can be controlled automatically.

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Press shop

Stator Core Assembly

Light Machine Shop

Heavy Machine Shop

Copper Shop

Coil shop

Stator Winding

Rotor Winding

Insulation Shop

Machine Assembly

Testing Of Machines

MANUFACTURING UNITS

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THE STATOR

1. Stator frame

2. Stator core

3. Stator windings

4. Stator end covers

5. Output leads / bushings

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LAMINATIONS

The sheets are 4% Silicon Alloyed COLD ROLLED NON-

GRAIN ORIENTED SHEETS (CRNGO).

To reduce the Eddy Current Losses, the core is build up of

0.5mm thickness laminations, which are insulated from each

other.

The core is built up of 6 sectors, each of 60 cut accordingly tothe specifications.

The lamination sheets are passed through a conveyor, which

has an arrangement to sprinkle the varnish.

Following which a thorough QC is done by a variety of tests

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Stator Lamination

CUTTING OF STATOR CORE LAMINATION SEGMENT

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STATOR FRAME

The stator frame is horizontally split type,welded construction ansupports the lamination core and the winding.

Both the air duct pieces and welded radial ribs provide rigidity to

the stator frame.

The stator is firmly fixed to the foundation plates.

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STATOR CORE

The main purposes of the stator core are : Supporting the

winding and Carrying the flux.So, the selection of material for

building up of core plays a vital role.

The losses i.e.; magnetic losses are mainly two types.

1. Hysteresis Losses: Due to the residual magnetism in the mater

2. Eddy Current Losses: Due to the EMF produced in the core of t

stator. In order to minimize the Hysteresis losses silicon alloyedsteel sheets are used for building up of core.

The sheets has the following composition,

Steel - 95.5%

Silicon - 4%

Impurities - 0.2%

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STATOR CORE

The stator core is made up of stacked steel laminations with a loindex and suspended in the stator frame from insulated rectan

guide bars.

Axial compression of the stator core is obtained by clamping fin

pressure plates and non magnetic clamping bolts, which are reg

from the core.

The clamping finger ensures a uniform clamping pressure, espe

within the range of the teeth and provided for uniform intensiv

of stator core ends

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STATOR WINDING

The stator winding is a diamond shape wound, two layered ,consists of individual bars.

The bars are located in slots of rectangular cross section whic

uniformly distributed on the circumference of the stator core.

In order to minimize losses, the bars are composed of separinsulated strands which are exposed to 540 degrees transpos

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CORE ASSEMBLY

Trial core assembly:

Three packets are assembled on the clamping plate and all

relevant checks are carried out.

After fulfilling the entire above requirement the packets are

disassembled.

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REGULAR CORE ASSEMB

The packets assembly is carried out as per drawing requireme

segments are staggered from layer to layer so that a core of hmechanical strength and uniform permeability to magnetic flux

obtained.

Stacking mandrels and bolts are inserted into the winding slot

during stacking.

The length of each packet of laminations should be as per the

Between each packet ventilation lamination sheets is assemb

whose thickness is 0.65 mm and on which I beams are spot

This provides the ventilation in radial directions

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Assembled Stator Core

St t

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StatorConnecting

Rings

Stator

Terminals

InsulatedCopper Bars

are placed in

the slots to

form 3 Ph

winding

Clamping P

& Ring

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VPIVACUUM PRESSURE IMPREGN

The stator is impregnated in a tank under vacuum and pressure wi

viscosity epoxy resin that penetrates the winding thoroughly. After

impregnation, the stator is cured at appropriate temperature in an

The high voltage insulation thus obtained is characterized by its ex

electrical, mechanical and thermal properties

Its moisture absorption is extremely low and it is oil resistant.

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CURING OF IMPREGNATED STATOR: TEMP. OF JOB :140DEG. C +/- 5 DEG. C DURATION : ~20 HRS

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CURED STATOR

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ROTOR1. Rotor body

2. Rotor winding

3. Rotor shaft

4. Rotor retaining rings

5. Fans

6. Field connection

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ROTOR SHAFT

Rotor shaft is a single piece solid forging.

Slots for insertion of field winding are milled into the rotor body

The longitudinal slots are distributed over the circumference.

To ensure that only high quality forgings are used, strength tesanalysis and ultrasonic tests are performed during manufactur

rotor.

After completion, the rotor is based in various planes at differe

and then subjected to an over speed test at 120% of rated spe

minutes.

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ROTOR WINDING The rotor winding consists of several coils, which are inserted i

the slots and series connected such that two coil groups form o

pole.

Each coil consists of several connected turns, each of which co

of two half turns which are connected by brazing by dove tail j

the end section.

The individual turns of the coils are insulated against each otheinsulation L-shaped strips of laminated epoxy glass fibre with n

are used.

The slot wedges are made of high electrical conductivity mate

and thus act as damper winding.

Rotor

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Finished Rotor with Retaining Ring

Rotor

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RETAINING RINGS

The centrifugal forces of the rotor windings are compensby single piece of non magnetic high strengthened stee

slot.

In order to reduce stray losses, each retaining ring with

grooves is inserted onto the rotor body in an overhang p

The retaining rings are secured in the axial position by

ring.

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Retaining Ring

BEARINGS AND CONTAC

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BEARINGS AND CONTAC

The field current is supplied to the rotor through multi contact sy

arranged at the exciter side shaft end.

The generator rotor is supported by two sleeve bearings. To elim

shaft current the exciter and bearing is insulated from foundatio

oil piping.

The temperature of each bearing is maintained with 2 RTDs (R

Temperature Detector) embedded in the slots.

All bearings have provisions for fitting vibration pick up to monit

vibrations.

The oil supply of bearings is obtained from the turbine oil system

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Bearings

Stator Frame Location

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Stator Frame

Top Frame

Base Frame

Ventilation

Chambers

Hot/Cold

output lea

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Assembled Generator

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TESTINGOF

TURBOGENERATORS

TESTING OF TURBO GENERATOR ROTORWINDING

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WINDING HIGH VOLTAGE TEST: Conducted at U2=Ut+1 KV , where U2 is

voltage and Ut is 10*rated rotor voltage but the resulting test volt

should be neither lower than 2.5KV nor above 4.5KV.

Once the insulating condition with a 1000V Megger is lower than

for each KV of the tested voltage, the ohmic resistance of the win

measured.

After baking and forming of the winding and removing of the clam

perform High Voltage test for one minute with a value of 1.15Ut.

The rotor insulation is also tested at 3000 rpm in a centrifugal tun

Finally, just before the dispatch of the finished rotor measure the

insulation resistance and perform High Voltage test with a value o

for one minute

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MEASUREMENT OF D.C RESISTA

The D.C resistance value of rotor winding is measured by using a Mi

Ohmmeter. First connect the micro ohmmeter to 230V AC supply. And measure

resistance and the temperature using RTD.

This resistance at T temperature has to be converted to resistance a

by using the formula:

R20= Rt * (235+20)/(235+T) mi ll i ohm s

Where R20= Resistance at 20 C in m

T= temp in degree Celsius

Rt= measured resistance of winding in m.

A deviation of 10 % from design values is acceptable.

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MEASUREMENT OF IMPEDA By applying 50-200 V in steps of 50 V, Impedance value is measu

standstill and at the rated speed.

Impedance is measured by using the formula: Z=V/I

In the measurement of Impedance there will be a graph plotted be

voltage v/s current

In this, there is no perfect value for the impedance but the only co

that the impedance should increase with the increase in voltage.

TESTING OF TURBO GENERATOR STBARS

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BARS After bars manufacturing bars are tested at four times the rated voltage :

Ut=4*Urated

Individual bars will be tested for tan

.Is the angle between actual curreline current. When the insulation is perfect and dielectric strength is optim

zero. But due to the presence of impurities in the insulation there will be a

angle difference between the two currents.

This tanmeasurement is known as loss angle measurement or dielectr

measurement. tanvalues should be within 2%.

Outer corona protection resistance is measured and this value should be

the range of 75-300 ohms/Sq.cm

Interstrip and Interhalf shorts are checked. Interstrip means between the

conductor strips and interhalf means between the halves. This shorts are

checked by a series bulb test.

TESTING OF TURBO GENERATOR STATOR W

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TESTING OF TURBO GENERATOR STATOR W

1). After lying bottom bars, bars are subjected to (2Un+7) KV, where

rated voltage

2). After lying top bars, bars are subjected to (2Un+5) KV, where Un

rated voltage

3). After lying bottom, top and eyes joining, High Voltage test is cond

(2Un+3) KV, where Un is the rated voltage

4). After final assembling and connections, customer witness test is c

(2Un+1) KV, where Un is the rated voltage

5). Interhalf shorts are also checked.

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INTER TURN INSULATION TEST:

The insulation between the windings of the rotor is tested by

applying a high frequency current of about 500HZ. The insulation sh

be able to withstand this test.

RING FLUX TEST ON STATOR CORE:

Ring flux test is carried out on the stator core before winding

in the slots. The rated flux density is generated in the stator core by

passing current in it. This results in the temperature rise and genera

heat. The stator core is observed for the temperature rise through itssurface by using RTDs. If there is any hot spot found in the core, it

detected. Then it is rectified by carrying out electrolysis using phosp

acid as electrolyte.

ROUTINE TESTS ON TURB

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ROUTINE TESTS ON TURBGENERATOR

MECHANICAL RUN AND MEASUREMENT OF VIBRATIONS AT RATED SPEED:

The machine is rolled and run at rated speed after ensuring the

oil and kept at rated speed for stabilization of bearing temperatu

The vibrations are measured at rated speed on both the bearing

housings in Horizontal, Vertical and Axial directions.

The temperature of stator is monitored by monitoring RTDs emb

in core, tooth and winding.

The vibrations should be less than 5 microns and noise level sh

in between 75-90 db.

SHORT CIRCUIT TEST

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SHORT CIRCUIT TEST The machine is prepared for short circuit characteristic using curren

transformers and shorting the terminals

The machine is run at rated speed and drive motor input voltage andnoted and machine is excited gradually in steps, at 20%, 40%, 60%

rated current of machine (In).

The excitation is reduced and cut off. The speed is reduced and the

cooled at lower speed. The temperature are checked from machine

machine is stopped when it is sufficiently cooled down. The stator wtemperature should be less than 60 degree Celsius)

From the Short Circuit test, we will get copper losses.

The short circuit characteristics is plotted from SCC results by selec

as field current and Y-axis as % rated current

OPEN CIRCUIT TEST

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O C CU S The machine is run at rated speed and the motor input voltage and

noted and machine is excited gradually in steps, at 20%, 40%, 60%

95%, 100%, 105%, 110% and 120% of rated voltage of machine (En

At 100% rated voltage the following parameters are noted: Shaft vo

of phase sequence, Bearing vibration and RTDs readings.

The excitation is reduced, cut off, the speed is reduced, and the mac

at lower speed. The temperatures are checked from machine RTDs

is stopped when it is sufficiently cooled down. The stator core tempeless than 60C.

From the Open Circuit test, we will get Iron losses.

The Open Circuit Characteristics are plotted on a graph from OCC r

selecting X-axis as field current and Y-axis as % rated voltage

MEASUREMENT OF SHAFT VOLTA

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MEASUREMENT OF SHAFT VOLTA

When the rotor shaft rotates inside the stator there will be some in

EMF developed inside the rotor

This voltage has to be reduced otherwise, the rotor will get heated

bearing pedestal is placed on insulation called HGL.

When the machine is under Open Circuit Characteristic testing sh

voltage is measured with multimeter and high input impedance ACvoltmeter across the two ends of the rotor at 100% rated voltage.

voltage should be as minimum as possible.

MEASUREMENT OF INSULATION RESISTANCE OF STATOR AND

WINDNGS BEFORE AND AFTER HIGH VOLTAGE TEST (machine

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WINDNGS BEFORE AND AFTER HIGH VOLTAGE TEST (machine

Insulation Resistance of the stator and rotor windings is measured separat

and after high voltage test using Megger of 2500 V for stator & 1000 V for

windings.

The Insulation Resistance values are taken at 15 sec and at 60 sec

The ratio of insulation resistance at 15 sec and 60 sec is known as Absorp

Coefficient. Absorption Coefficient = IR at 60s/ IR at 15s. This Absorption C

High Voltage test should be less than1.3

When the machine is under OCC condition at 100% rated voltage, phase sgenerator is checked using a phase sequence indicator

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HIGH VOLTAGE TEST LEVE

High Voltage test levels are

Stator winding = (2 Ut + 1) kV

Rotor winding = (10* Up) V

Where Ut = Rated voltage of the machine unde

Up = Excitation voltage

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CONCLUSION

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CONCLUSION During the training period, I was amazed at the employees wo

and work culture

The training period also proved to be an eye-opener in regard

work atmosphere in a manufacturing unit.

I got to see gigantic machines go at their work with marvelous

accuracy and precision.

I also witnessed how on-the-ground problems could occur and

how they were overcome.

These experiences certainly helped in building my own impres

what an engineer is expected to do in and for the society.

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