A comprehensive report on the study of

Manufacture & Assembly of Turbo Generator

Project Incharge:

Mr. Satish k. Singh

Post-SDGM (BL-1) Submitted By:

BHEL, Haridwar Ajay Jangir

ACKNOWLEDGEMENT

Engineer is a boon for this modern era because of leaps and bound advancement in

modern technology. So it is a very important to impart a practical knowledge and

theoretical knowledge. I am very grateful that I got the opportunity to have training

from BHEL, Haridwar. Which is the no.1 industry in India.

Special thanks to Mr. RAJENDRA VERMA for providing me with an opportunity

to undergo training under his able guidance and offering me a very deep

knowledge of practice aspect of industrial work culture………………

I express my sincere thanks and gratitude to BHEL authorities for allowing me to

undergo the training in this prestigious organization. I will always remain indebted

to them for their constant interest and excellent guidance in my training work,

moreover for providing me with an opportunity to work and gain experience.

CONTENTS

1-Introduction

2-Coil & insulation manufacturing shop (block-4)

3-Electrical machine block (Block-1)

4-Manufacturing process of turbo generator

5-Introduction to 500MW Turbo Generator

6-Constructional features of stator body

7-Constructional features of core

8-Constructional features of Winding

9-Constructional features of Rotor

10-Working principle

11-Cooling system

12-Excitation system

13-Electrical generator protection

14-Conclusion

INTRODUCTION-:

BHEL is the largest engineering and manufacturing enterprise in India in the

energy-related/infrastructure sector, today. BHEL was established more than 40

years ago, ushering in the indigenous Heavy Electrical Equipment industry in India

- a dream that has been more than realized with a well-recognized track record of

performance. The company has been earning profits continuously since 1971-72

and paying dividends since 1976-77.BHEL manufactures over 180 products under

30 major product groups and caters to core sectors of the Indian Economy viz.,

Power Generation & Transmission, Industry, Transportation, Telecommunication,

Renewable Energy, etc. The wide network of BHEL's 14 manufacturing divisions,

four Power Sector regional centre, over 100 project sites, eight service centre and

18 regional offices, enables the Company to promptly serve its customers and

provide them with suitable products, systems and services. Efficiently and at

competitive prices. The high level of quality& reliability of its products is due to

the emphasis on design, engineering and manufacturing to international standards

by acquiring and adapting some of the best technologies from leading companies

in the world, together with technologies developed in its own R&D centre,

BHEL has•Installed equipment for over 90,000 MW of power generation for Utilities,

Captive and Industrial users.

•Supplied over 2,25,000 MVA transformer capacity and other equipment operating

in Transmission & Distribution network up to 400 kV (AC & DC).

•Supplied over 25,000 Motors with Drive Control System to Power projects,

Petrochemicals, Refineries, Steel, Aluminum, Fertilizer, Cement plants, etc.

•Supplied Traction electrics and AC/DC locos to power over 12,000 km Railway

network.

•Supplied over one million Valves to Power Plants and other Industries

HEEP

HEEP is also known as heavy electrical equipment plant. In this plant the electrical

devices is manufacture for the production of the Turbo Generator. In HEEP plant

we produce turbo generator, exciter, turbine, AC/DC motor, etc. HEEP had started

the production from January 1967. More than 40% of the electrical energy is

generated from the power equipment supplied by BHEL, Haridwar.

COIL & INSULATION MANUFACTURING AHOP (BLOCK-4)-:

BAY-1: Bar winding shop manufacturing of stator winding of generator.

BAY-2: manufacturing of heavy duty generator stator bars with new CNC

machine No. 3-464 i.e. Robol bar centre.

BAY-3: Insulation detail shop. Manufacturing of hard insulation & machining of

hard insulation part (Glass textolite) such as packing washer, insulation box,

wedges etc.

Bar Shop: This shop is meant for manufacturing of stator winding coil of turbo

generator.

Why do we call it bar-:

It is quite difficult of manufacture, handle and wind in the stator slot of the

generator of higher generation capacity because, of its bigger size and heavy

weight. That is why we make coil in two parts. One part its bottom part of coil

called bottom or lower bar and other part of coil is called top bar or upper bar.

Turbo – generator: The manufacturing of bars of standard capacity such as:

100MW, 130MW, 150MW, 210/235MW, 210/250MW, 500MW, 600MW

TYPES OF GENERATOR:

The generator may be classified as based upon the cooling system used in the

generators such as: THRI, TARI, THDI, THDD, THDF, THFF, THW.

T= First alphabet significance the type of generator i.e. turbo generator of hydro-

generator.

H/A= Second alphabet stands for the cooling media used for the cooling of rotor

i.e. hydrogen gas or air.

R/D/F/I= Third alphabet significance cooling of rotor e.g. radial, indirect forced,

direct etc.

I/D/F= Last alphabet stands for the type of cooling if stator e.g. indirect cooling,

direct cooling, forced cooling.

W= Cooling media used for cooling of stator coil e.g. water

Resin System

Rich resin or thermo reactive insulation system:

In this type of insulation system the bond content in resin is 35-37%.

The raw material are ready to use and required preservation and working

on temperature 20-25C. Its shelf life is one year when kept on

temperature 20C which could be increased when kept at temperature of

5C.

Poor resin or Micalastic system: In this type of insulation the bond content in the resin is 5-7% and

insulating material is prepared with accelerator treatment. The

temperature control need not required. The insulating material is applied

on job and then the same is impregnated in the resin.

MANUFACTURING PROCESS OF BARS:

Some points of manufacturing process are in brief as below-

Conductor Cutting:

This process is done by automatic CNC machine. In this process the pre insulated

copper conductor is cut into number of pieces of required length (length given in

drawing as per design).Insulation is removed from both side of copper conductor

out.

Transposition of conductor:

Transposition means changing/shifting of position of each conductor in active core

(slot) part .After cutting the required number of conductors the conductors are

arranged in the comb in staggered manner and then bend are given to the

conductors with the help of bending die at required distance. Then the conductor

are taken out from the comb and die and placed with their end with the line and

transposition is carried out. This process is repeated for making another half of the

bar which could be mirror of the first half. The two halves of the bars are

overlapped over each other and a spacer is placed between the two halves.

Crossover insulation:

The pre insulation of the copper conductor may get damaged due to mechanical

bending in die during transposition , hence the insulation spacers are provided at

the crossover position of the conductors . A filler material (insulating putty of

moulding mecanite ) is provided along the height of the bars to maintain the

rectangular shape and to cover the difference of the level of conductors.

Stack Consolidation:

The core part of the bar is pressed in press (closed box) under pressure (varies from

product to product) and temperature of 160`C for a given period. The consolidated

stack is withdrawn from the press and the dimensions are checked.

Inter Strand Short test:

The consolidation bar stack is tested for the short between any two conductor in

the bar, if found then it has to be rectified.

Forming:

The straight bar is stack is formed as per overhang profile (as per design). The

overhang portion is consolidated after forming.

The straight bar stack is bend at the two end portion as per requirement design.Brazing of coil lugs:

For water cooled generator bars, the electrical connection contact water box for

inlet and outlet of water are brazed. The water box is also known as contact slew.

The contact slew is brazed with the help of copper aluminium alloy rod. This rod

is brought to touch to hot contact slew and after melting it fill the spaced, in this

manner the bar is brazed.

Nitrogen leak test:

The bar is tested for nitrogen flow test, nitrogen leak test and pressure test for

given duration.

Thermal Shock Test:

In thermal shock test the 23 cycle of hot and cold water are flew throw the bar to

ensure the thermal expansion and contraction of joints. The temperature of hot

water is about 80`C and the cold water is 30`C. By doing this test if there is any

fracture or voids at the joints are present , then it exposed and easily detected.

Helium leakage test:

This test is performed after the thermal shock test. With the help of this test we can

found very minute leakage if present. In this test the helium gas pipe is connected

at one end and the other end is closed. After this we insert a helium spectrometer to

measure the pressure of the helium gas.

Impregnation and baking:

Thermo reactive system:

In case of reach resin insulation the bar is pressed in closed box in heated

condition and baked under pressure and temperature as per requirement for

a given period.

Micalastic system:

In case of poor resin system the insulated bars are heated under vacuum and

the impregnated (dipped) in heated resin so that all the air gap are filled, layer

by layer, with resin. Then extra resin is drained out and the bar are heated and

baked under pressed condition in closed fixture.

VPI Mecalasti System:

The bar already laid in closed fixture and full fixture is impregnated (dipped)

in resin and then fixture with box is baked under given temperature for given

duration.

VIP Micalastic system:

The individual (separate) bar is heated in vacuum and impregnated in resin.

Then bar is taken out and pressed in closed box fixture and then baked at

given temperature for given duration.

Insulation:

The bar is insulated with the given number of layer to built the wall thickness

of insulation subject to the generating voltage of machine.

Finishing:

The baked and dimensionally correct bars are sanded-off to smoothen the

edges and the surface is calibrated, if required, for the dimension.

Conducting varnish coating:

OCP (Outer Corona Protection) Coating:

The black semiconducting varnish coating is applied on the bar surface on

core length.

ECP (End Corona Protection) Coating:The gray semiconducting varnish is applied on the bend outside corona end of bars

in gradient to prevent from discharge and minimize the end corona.

Testing:

Tan0 Test:

This test is carried out to insure the healthiness of dielectric (Insulation) i.e. dense

or rare and measure the capacitance loss.

H.V. Test:

Each bar is tested momentary at high voltage increased gradually to three times

higher than rated voltage.

Dispatched for winding:

The bars preserved with polythene sleeves to protect from dust, oil, rain etc are

send to block-1 for winding.

ELECTRICAL MACHINE (BLCOK-1)–:

INTRODUCTION-:

1-Block first is design to manufacture Turbo Generators.

2-The block consist of 4 bays-Bay 1(36*482meters), Bay-2(36*360 meters),

and Bay-3 & Bay-4(of size 24*360 meters each).

3-Testing facilities of turbo generator are available in Bay-2

4-There is a special test bed area for testing of T.G. of capacity of 500MW unit

sizes.

MANUFACTURING PROCESS OF TURBO GENERATOR-:

Fabricated components are received in respective machine sections from-

Fabrications blocks (block-2,5, 6, 8), while castings and forgings are received from

sister unit CFFP and other indigenous and foreign sources for turbo generators.

Stampings are received from stampings manufacture block, block-4and coils bars,

insulating details and sheet.

Metal components are received from coils and insulation manufacture and

apparatus and control gear box (Blok-4).

TURBO GENERATOR-:

The turbo-generator is common-shaft excitation AC synchronous generator with

3phases, 2 poles or with 3 phases, 4 poles.

BHEL-Hyderabad makes turbo generators that have the brushless excitation

mechanism which has been explained in the NTPC report. BHEL presently has

manufactured Turbo-Generators of ratings up to 560 MW and is in the process of

going up to 660 MW. It has also the capability to take up the manufacture of

ratings up to 1000 MW suitable for thermal power generation, gas based and

combined cycle power generation as-well-as for diverse industrial applications like

Paper, Sugar, Cement, Petrochemical, Fertilizers, Rayon Industries, etc.

500MW turbo generator at a glance-

2-pole machine with the following features-:

1-Direct cooling of stator winding with water.

2-Direct hydrogen cooling for rotor.

3-Micalastic insulation system.

4-Spring mounted core housing for effective transmission of vibration.

5-Brushless excitation system.

6-Vertical hydrogen coolers.

Salient technical data-

1-Rated output :588MVA, 500MW

2-Terminal voltage :21KV

3-Rated stator current: 16KA

4-Rated frequency :50Hz

5-Rated power factor: 0.85 lag

6-Efficiency : 98.55%

Manufacturing process-:

1- Stator-

The stator is assembled as six parts. It is made up of steel with 4.5% of silica.

Silica decreases hysteresis loss. The sheets are cut at 30 degree angles. The sheets

then are punched with man drill holes, support rod slots and slots for the

conductors. This process is called notching and the cutting part as shearing. The

sheets are then varnished after blanking or smoothening of the surface. This is to

increase the insulation. A bunch of these sheets are stacked together and

compressed onto each other so that air gaps are eliminated. These stacks are then

assembled with a small air gap differentiating each stack. This ventilates the

machine and keeps it cool. After the assembly of the stator shell, the inside of the

slots are varnished. The sheets of the core are varnished with xylor, at a

temperature of 30-400 degrees Celsius. It is heated, coated then cooled. After the

core is assembled , the winding is placed in the stator. The winding type depends

upon the power required and the current required to be produced. The core and the

winding are separated by an insulation called HGL. This prevents the shorting of

the core and winding .The winding in the front and back are also separated by this

material and they are joined as per the winding required (lap or wave) using glass-

o-flex, a pink ribbon like material. The windings are insulated. These windings are

then painted to obtain a the stator, where the power is generated. The windings are

always inserted from the exciter end, one is clockwise and the other anti-

clockwise.

2-The Rotor-

The rotor comprises of following component:

1-Rotor shaft

2-Rotor winding

3-Rotor wedges and other locating parts for winding

4-Retaining ring

5-Fans

6-Field lead connections

The rotor is carved out with the slots into a cylindrical shape from a large block

of metal using Lathe heavy machines. The rotor consists of 2 ends–

•The turbine coupling end

•The exciter end

The turbine end has a coupling shaft which is circular in shape and has slots.

The exciter end has an input lead and an output lead which are used to give the

rotor DC input for the excitation of the rotating field.

The ends of each rotor consist of bearings. These bearings are placed so as to

support the shaft. The bearing consists of oil which is used to support a thin film

over the surface. This lubricates and decreases friction and losses. The bearing has

top end and bottom end and is stationary. The top end is used to supply the oil.

After the construction, the winding is fitted into the slots. The slots and windings

are separated by HGL or hard glass lamination which insulates the core from the

cable. The rotor is constructed so as to obtain brushless excitation. The complete

rotor along with the excitation mechanism is mounted on the shaft and is balanced

for synchronous speed. For better balancing weight removal is done as that is a

better option to adding weight to the system. The rotor ends are provided with

induction motor fans which are used for cooling of the rotor winding. The winding

is made up of 99.99 % copper.

WORKING PRINCIPLE-:

One end of the alternator is coupled to the turbine and other end is coupled through

the exciter. The whole assembly is on the shaft. Turbine act as a prime mover, the

permanent magnet of the exciter creates a permanent magnetic field, which is cut

by the rotor conductors. Making the formation of 3-phase power, this 3-phase

power is fed to the thyristor controlled switches for rectification. The 3-phase

power is fed to main exciter, after that this 3-phase power is given to the diode

wheel so it is produce the dc power. The dc power is given to the main alternator

field without brushes and slip ring. Then alternating field is produce by the cut of

rotor conductors making the production of emf by the FARADAY’S LAW.

Cooling of the Alternator-:

The machine needs to be cooled to avoid damage and for greater life. Heating

causes insulation failure. Hence, cooling is a very important factor that needs to be

taken care of. For cooling, the stator and rotor are provided with a ventilation to

cool it down. Air gaps are provided throughout the machine. But for very high

power machines natural cooling is insufficient so a cooling system is provided. For

collection of hot air, a large chamber is provided. This air is cooled and recycled

into the generator. The rotor of the alternator consists of fans powered by induction

motors. They suck in the air and push it through to the cooling chamber. Another

method is also used which is called hydrogen cooling. Hydrogen acts as ac coolant

and the chamber is shut completely is filled with hydrogen. Hydrogen cools itself.

The chamber is emptied each time the machine is stopped.

TG TEST BED-:

New LSTG [Large Scale Turbo Generator] TEST BED has been put up with

indigenous know –how in record time testing Turbo Generator of rating 500MW

and above up to 1000MW. It caters to the most advanced requirement of testing by

employing on line computer for data analysis.

Circuit –Breakers-:

Current interruption in a high-voltage circuit-breaker is obtained by separating two

contacts in a medium, such as SF6, having excellent dielectric and arc quenching

properties. After contact separation, current is carried through an arc and is

interrupted when this arc is cooled by a gas blast of sufficient intensity. Gas blast

applied on the arc must be able to cool it rapidly so that gas temperature between

the contacts is reduced from 20,000 K to less than 2000 K in a few hundred

microseconds, so that it is able to withstand the transient recovery voltage that is

applied across the contacts after current interruption. Sulphur hexa fluoride is

generally used in present high-voltage circuit-breakers (of rated voltage higher

than52 kV)In arc assisted opening interruption principle arc energy is used, on the

one hand to generate the blast by thermal expansion and, on the other hand, to

accelerate the moving part of the circuit breaker when interrupting high currents.

The over pressure produced by the arc energy downstream of the interruption zone

is applied on an auxiliary piston linked with the moving part. The resulting force

accelerates the moving part, thus increasing the energy available for tripping.

With this interrupting principle it is possible, during high-current interruptions, to

increase by about 30% the tripping energy delivered by the operating mechanism

and to maintain the opening speed independently of the current. It is obviously

better suited to circuit-breakers with high breaking currents such as Generator

circuit-breaker.

COOLING SYSTEM-:

Cooling system is a very important part of the alternator. Mainly two types of

cooling process is occur such as-

1-Radial cooling

2-Axial cooling

Since the cooling system is divided three part such as-

1-Hydrogen cooling

2-Water cooling

3-Air cooling

Cooling system is used because dissipating the heat generated by various losses

and to prolong the life of insulating material. In small generator natural cooling

is adequate. In these machines cooling by natural sources is sufficient, but in

large generators natural cooling is in sufficient, so in these generator air, water

&hydrogen is done. Force air cooling is used for large machine. In this scheme

air is first passed through cleaning filter and then forced through the machine

for cooling purpose. Air cooling system is better and necessary in 500MW &

600MW generator.

EXCITATION SYSTEM-:

Turbo generator is a doubly excited machine. Because it’s field winding is

excited by dc source and it’s armature winding is connected to ac source. For dc

excitation we need use the use of exciter. Hence there are three types of dc

excitation-

1-DC exciter

2-Static excitation

3-Brushless exciter

In our BHEL organization brushless exciter is widely use because slip ring and

brushes is absent and it is provide less losses so that it’s efficiency is high so we

use the brushless exciter. The brushless exciter is used for generating the dc

field which is used to fall on alternator of rotor. When the dc field is fall on the

rotor and the rotor is directly connected to the turbine so that the turbine is

rotate the rotor, the alternating field is generated by the rotor then due to the

induction the alternating emf is generated in the stator core. These emf is

received by the stator terminal those are called ac voltage.

The brushless exciter has mainly two parts such has-

1-Pilot exciter

2-Main exciter

In pilot exciter permanent magnet is used, which produce the permanent

magnetic field. Three phase power from pilot exciter is fed to thyristor

controlled bridge to main exciter. After rectification the controlled dc output is

supplied to stationary field winding of main exciter.

ELECTRICAL GENERATOR PROTECTION-:

Generator may be endangered by short circuit, ground fault, over voltage, under

excitation and excessive thermal stresses. The following protective equipment

is recommended such as–

1-Differential protection

2-Stator ground fault protection

3-Rotor ground fault protection

4-Under excitation protection

5-Over current protection

6-Load unbalance protection

7-Rise in voltage protection

8-Under frequency protection

9-Reverse power protection

10-Over voltage protection

CONCLUSION-:

Bharat heavy electrical limited is the largest engineering and manufacturing

enterprises of kind in the public sector in India. The sector is an important part

in turbo generators. The stator is assembled by the laminated sheets. We use the

UNIVERSAL FORM FICTURE type bar which assemble all the straight part

and the over hang at a time. The universal from facture type bar is more flexible

and its life time more. We use the bar transposition for stator winding which is

more advantages. BHEL has acquired the latest technology in the insulation

system, the VACCUM IMPREGINATION system of insulation, which has

various advantages like cost reduction with improve quality. Thus designed an

manufactured start of turbo generator is used mostly in paper, sugar, cement,

petrochemical, fertilizer, Rayon, industries. The architecture of BHEL, the way

various units are linked and the way working of whole plant is controlled make

the students realize that engineering is not just structural description but greater

part is planning and management.

It has allowed us and an opportunity to get and exposure implementation of

theoretical fundamental.