Bhel Training Report

A Technical report on the study of

Manufacture & Assembly of Turbo Generator

Training Incharge: Submitted By:

Mr.Rajendra Kumar Manish Snehi

Proj. Guide: Mr. S K Singh Enroll. No.-11115051

Post-SDGM (BL-1) Btech(EE 4th Yr.)

BHEL, Haridwar IIT ROORKEE

ACKNOWLEDGEMENT

I acknowledge the cordial assistance and guidance provided to

me from several rather unexpected spheres during the course

of this six weeks of study.It would be my pleasure to express

my gratitude to each and every one of them.

I am extremely thankful to Mr. RAJENDRA KUMAR for

providing me with an opportunity to undergo training under

his guidance and imparting me a very deep knowledge of

practice aspect of industrial work culture.

I express my thanks and gratitude to Mr. Satish k Singh and

other authorities of BHEL for instructing me to during whole

training process in this organization and letting me to gain

some work experience.

Table of 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 500 MW Turbo Generator

6. Constructional Features of core

7. Constructional feature of stator body

8. Constructional feature of rotor

9. Constructional features of winding

10. Working Principle

11. Cooling System

12. Excitation system

13. Electrical Generator Protection

14. Conclusion

INTRODUCTION

One of the India’s largest manufacturing and engineering enterprise in energy

specific infrastructure today, a 40 odd years ago,leading the way in indigenously

developes Heavy electrical equipment Plant , that has been well recognized as a

great arena of performance .BHEL manufactures a range of up to 30 general

product,over 180 products and feeds to the major sector of the

indian markets, Transportation, Power transmission and generation

industry, Telecom,energy sector. It’s wide network has four Power

Sector regional centre,14 manufacturing divisions, 18 regional

offices, eight service centre, over 100 projects sites making the

company enable to sincerely cater its customers providing them

appropriate products, enhanced services and system at reasonable

prices. This higher reliability and quality outcomes are because of

greater emphasis on engineering, design, producing at international

levels with best technologies of world and the technologies of it’s

own R&D centre.

Feature of BHEL

• More than 90000 MW of power generation for all the varied sphere

houses of power consumers.

•2,25,000 MVA of transformer capacity and all equipment in

transmission and distribution network of upto 400 KV of AC& DC.

• 25000 motors been supplied with drive control system to Refineries,

power projects, aluminum, Petrochemical, fertilizers, cement plants

Steel, Fertilizer.

•Over 12000 km of railway network been fed in form of Traction electric

and AC&DC locos

•Over one million valves to power plants and other industries has been

supplied.

HEEP

HEEP, (Heavy Electrical Equipment Plant) manufactures electrical

devices for the Turbo Generator’s production.In HEEP there is

production of turbo generator, exciter, turbine, AC/DC motor, etc. HEEP,

started the production from January 1967. Over 40%, electrical energy

generated from the power equipment by BHEL, Haridwar.

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

BAY-1: Bar winding shop, manufactures stator winding of generator.

BAY-2: Manufactures heavy duty generator stator bars with CNC

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

BAY-3: Insulation detail shop, Manufactures hard insulation & then

machines insulation of hard part (Glass textolite) such as packing

washers ,wedges, insulation boxes etc.

Bar Shop: Manufacture turbo generator’s stator winding coil.

Why it is called a bar:-

It is difficult to manufacture, wind in and handle the stator slot for

higher generation capacity generators because of heavy weight and

bigger size.So coil is made in two parts. One part is bottom part of coil

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

TYPES OF GENERATOR:

The generator classified,as based upon the used cooling system in it

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

T= First word denotes type of generator i.e. turbo generator or hydro

generator.

A/H= Second word stands for medium used for the cooling of rotor as

air or hydrogen gas.

R/D/I/F= Third word signifies cooling of rotor as radial, forced,indirect,

direct.

D/I/F= Last word signifies type of cooling if stator as indirect cooling,

forced cooling, direct cooling.

W= Medium being used for cooling of stator coil as water

Resin System

Thermo reactive or Rich resin insulation system :

Bond content of resin is 35-37% in this insulation system. The raw

material required preservation and working on temperature 20-25C and

are ready to use. It’s shelf life is one year when kept at temperature 20C

which is increased from when at a temperature of 5C.

Micalastic or Poor Resin system :

Bond content in this system of resin is 5-7% and accelerator treatment

is used for preparing insulating material. No requirement of temperature

control. The insulating material, applied on job and then is impregnated

in resin.

MANUFACTURING OF BARS:

Some points in manufacturing process are in brief below-

Conductor Cutting:

This is done by an automatic CNC machine. In this process number of

pieces of pre insulated copper conductor is cut in required length (length

given in drawing as per design).And then insulation is removed out from

both side of copper conductor.

Transposition of conductor:

Transposition refers to changing/shifting position of conductors in

active core (slot) part .The required number of conductors after being

cut,is arranged in the comb in staggered manner and then with help of

bending die, bend are given to the conductors at needed distance.The

conductors are then taken out of the comb & die and are placed with

their end with the line for transposition to be carried out.For making

another half of the bar same is repeated. Then the two halves are

overlapped with a spacer placed in between.

Crossover insulation:

Due to mechanical bending in die the pre insulation may be damaged,

hence at crossover position the spacers are provided. A filler material

(insulating putty of moulding mecanite ),to maintain the rectangular

shape and to cover the difference of levels of conductor , is provided

along height of bars is provided.

Stack Consolidation:

The core of bar is pressed in a press(closed box) under high pressure

(varies from product to product) and a temperature of 160C for a given

period. Dimensions are checked after consolidated stack is withdrawn

from press.

Inter Strand Short Test:

The consolidated bar stack is tested for short between conductors, if

found then it is rectified.

Forming:

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

After forming overhang portion is consolidated.

The straight bar stack is bend at the two end portion as per requirement

design.

Brazing of coil Lugs:

The electrical connection contact in water box for inlet or outlet are

brazed in case of water cooled generator bars. 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:

For a given duration nitrogen flow test, pressure test and nitrogen leak

test is tested.

Thermal Shock Test:

To ensure thermal expansion and contraction in joints, thermal shock

test is done by 23 cycle of cold and hot water flow. 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.

Baking and Impregnation :

Micalastic system:

For poor resin system,insulated bars for filling of air gaps are dipped in

heated resin.After draining extra resin it is baked under required

pressure and tempreature

Thermo reactive system:

For reach resin system bar is pressed in closed box and baked under

required temperature and pressure.

VPI Micalastic System :

Bar impregnated in resin and fixture with box is baked under required

temperature.

VIP Micalastic system :

Separate bar heated in vacuum and then dipped in resin. After taking

out is pressed in a closed box and baked at given temperature and

pressure.

Insulation:

Number of layer is provided in insulation to increase the thickness of

insulation.

Finishing:

Baked bars are then smoothened and calibrated for dimensions.

Conducting varnish coating:

End corona Protection:

To minimize end corona and prevent discharge, gray semiconducting

varnish applied on core ends.

OCP (Outer Corona Protection) Coating

Black semiconducting varnish is applied.

Testing:

Tan0 Test: This test ensure quality of dielectric material.

H.V. Test: Bars are tested momentarily for high voltages.

Dispatched for winding:

Bars sent to block-1 for winding with preserved in polythene sleves.

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,HARIDWAR makes turbo generators that have the brushless

excitation mechanism which has been explained in the NTPC report.

BHEL till today has manufactured Turbo-Generators of up to 560 MW

and is working of going up to 660 MW. It also have capability to take up

the manufacture of TG up to 1000 MW suitable for gas based and

combined cycle power generation and thermal power generation, gas

based also for diverse industrial applications like cement, Paper,

Fertilizers, Sugars 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 to increase 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,ventilating machine. 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:-

By separating two contacts in medium such as SF6, having good

arch quenching and dielectric properties current can be

interrupted. After the contact seperates current flows through an

arc and is interrupted when the arc is cooled by gas blast.Gas blast

should be able to cool it swiftly so the temperature is reduced from

20000K to 2000K in order to withstand transient recovery voltage

after interruption.SF6 normally is used in HV circuit breaker(more

than 52 kV).In this process arc energy is used to generate blast by

thermal expansion and to accelerate circuit breaker on other

hand.Over pressure by arc energy is linked with a pistonwhich

accelerates moving part and increasing energy for tripping.

This interrupting principle with increasing the energy delivery for

tripping maintains the opening speed independent of current.This

mechanism is more favorable in high current 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 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 being the largest manufacturing and

engineering 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 interlink

of various units and the way working of whole plant is controlled

made me realize that engineering is not just structural description

but greater part is planning and management.

It has allowed us and an opportunity to get exposure to

implementation of theoretical fundamentals.