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NTPC LimitedKahalgaon

Training ReportJune 20, 2011 to July 20, 2011

APPROVED BY

Submitted By:

Name: SAILESH KUMAR

University Roll No. 0801021083

Branch: Electrical & Electronics Engineering

College: United Col lege of Engineering & Research,Naini, Allahabad

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ACKNOWLEDGEMENT

In this era of global meltdown we need a great balance betweentheoretical and practical knowledge. In this respect the vocational trainingis a great boon for the engineering students. It gives us a great chance tocome in line with the actual problems going on in the industries andgetting a chance to work with the engineers and learn how to tackle everysituation.

I am thankful to the staff of the NTPC Limited for their time and effort

and their willingness in sharing their valuable experiences. This Training

is the result of initiative of Sri S.K. Rohilla, DGM (C & I) for which I am

thankful. I am very grateful for the help of Sri T.K Jha, DGM (EMD-I/C)

and the maintainers in useful discussions.

Sri U. K. Das. Supdt. (EMD) and Sri D. Bhattacharya. Sr. Supdt. (C&I)

showed me different ways to approach a research problem and the need to

be persistent to accomplish any goal.

The great ambience of NTPC Limited has kept me in good spirits.

I would like to thank Mr V. Laxman (EMD), Mr P. Singh (EMD), Mr.

Ashutosh Gautam (EMD) and Mr. Sujeet Kumar Singh (EMD) without

their encouragement and constant guidance I could not have finished this

file. They provided me with all the necessary documents at the

documentation centre. The documents helped in exploring the ideas,

organization, requirements and development of this training program.

SAILESH KUMAR

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PREFACE

The summer training programs are designed to give the practicalknowledge of industrial world. Training is usually meant for suchvocations where advance theoretical knowledge is to be backed up bypractical experience on the job and it is because of this reason thatsummer training programs are designed. So, that the future manger mustbe ready to take the future responsibilities.

It was exactly in this context that I wasprivileged enough to join NTPC limited one of the biggest powerproducing power plant in the world.

I achieved lots of experience and confidence over the past four weekswhich will help me to take the future responsibility on my shoulder.

During this period, I was given to find out the “PROCESS OFPRODUCTION OF ELECTRICITY & ITS TRANSMISSION”. In thetraining program I had tried my level best to arrange the work insystematic and chronological way.

This endeavor work or industrial vocation had provided me a great knowledgeabout the process of production of power. Therefore, I hope with allsincerity that this work shall be of definite use to the organization.

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ABSTRACTVocational education or vocational education and training prepare traineesfor jobs that are based on manual or practical activities, traditionally non-academic, and totally related to a specific trade, occupation, or vocation. It issometimes referred to as technical education as the trainee directly developsexpertise in a particular group of techniques or technology. In 2006, thelanguage vocational education was updated to career technical education.

Vocational education may be classified as teaching procedural knowledge. Thiscan be contrasted with declarative knowledge, as used in education in a usuallybroader scientific field, which might concentrate on theory and abstractconceptual knowledge, characteristic of tertiary education. Vocationaleducation can be at the secondary or post-secondary level and can interact withthe apprenticeship system. Increasingly, vocational education can berecognised in terms of recognition of prior learning and partial academic credittowards tertiary education (e.g., at a university) as credit; however, it is rarelyconsidered in its own form to fall under the traditional definition of highereducation.

As the labour market becomes more specialized and economies demand higherlevels of skill, governments and businesses are increasingly investing in thefuture of vocational education through publicly funded training organizationsand subsidized apprenticeship or traineeship initiatives for businesses. At thepost-secondary level vocational education is typically provided by an instituteof technology, or by a local community college.

Vocational education has diversified over the 20th century and now exists inindustries such as retail, tourism, information technology, funeral services andcosmetics, as well as in the traditional crafts and cottage industries.

Vocational training in India is provided on a full time as well as part time basis.Full time programs are generally offered through I.T.I.s industrial traininginstitutes. The nodal agency for grant the recognition to the I.T.I.s is NCVTwhich is under the Ministry of labour, Government of India. Part time programsare offered through state technical education boards or universities who alsooffer full-time courses. Vocational training has been successful in India only inindustrial training institutes and that too in engineering trades. There are manyprivate institutes in India which offer courses in vocational training andfinishing, but most of them have not been recognized by the Government. Indiais a pioneer in vocational training in Film & Television and InformationTechnology. Maharashtra State Government also offered vocational Diplomasin various trades.

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DECLARATION

I SAILESH KUMAR, a bonafide student of from United College ofEngineering & Research , Naini Allahabad, hereby declare that theInstitutional Training Report submitted in partial United College ofEngineering & Research fulfilment of the requirement of the degree ofBACLER OF TECHNOLGY University is my original work. This workis not being submitted under any other institution.

DATE:

PLACE: NAINI ALLAHABADSAILESH KUMAR

University Roll No.:0801021083

Branch: Electrical &Electronics Engineering

College: United College ofEngineering & Research,Naini, Allahabad.

Contents

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1. Acknowledgement2. Preface3. Abstract4. Declaration5. Contents6. List of tables7. List of figures8. INRODUCTION8.1 National Thermal Power Corporation8.2 Installed Capacity8.3 NTPC Kahalgaon ( Overview )

9. NTPC Limited

9.1 Introduction

9.2 National Thermal Power Corporation Layout

10. Major Areas in NTPC Kahalgaon

10.1 Coal Handling Plant

10.2 Boiler and its Auxiliaries

10.3 Turbine Auxiliaries

10.4 Generator and its auxiliaries

10.5 Switchyard and Transmission Equipments

11. Transformers

12. Turbine

13. Governor

14. Bibliography

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LIST OF TABLES

1. An Overview

2. Regional Spread Of Generating Facilities

3. Coal Based Power Stations

4. Gas/Liquid Fuel Based Power Stations

5. Power Plants With Joint Ventures

6. Data Of KhSTPP

7. Electrical Machines Used In CHP

8. Datasheet Of ID Fan

9. Datasheet Of FD Fan

10.Datasheet Of PA Fan

11.Fly Ash Composition(By Weight)

12.Generator Parameters

13.Excitation System Parameters

14.Generator Rating

15.Generator Transformer, GT-(1, 2, 3, 4,) Ratings

16.Generator Transformer, GT-(5) Ratings

17.UST-3A

18.UTA-2A

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LIST OF FIGURES

1. Growth Of NTPC Installed Capacity &Generation

2. NTPC’s Share In Total Generation In India

3. Some Of The Major Project In The Northern Region

4. NTPC Ltd., Kahalgaon

5. National Thermal Power Corporation Layout

6. Boiler Auxiliaries (Stage-I & Ii)

7. FD Fan & ID Fan

8. Turbine Auxiliaries

9. Stator Frame Interior

10.Rotor Shaft

11.Generator Hydrogen Cooling Circuit

12.Seal Oil System

13.Static Excitation System

14.Air Blast Circuit Breaker

15.SF6 Circuit Breakers

16.Circuit Isolator

17.Current Transformer

18.Capacitor Voltage Transformer

19.Governor Characteristics

20.Turbine Speed Governing System

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INRODUCTION

2.1. NTPC LIMITED:

NTPC, the largest power Company in India, was setup in 1975 to acceleratepower development in the country. It is among the world’s largest and mostefficient power generation companies. In Forbes list of World’s2000 LargestCompanies for the year 2007, NTPC occupies 411th place.

Once the NTPC stands for NATIONAL THERMAL POWER CORPORATIONbut due to the involvement of this company in other resources i.e. production ofpower with the help of natural gases , water etc. So after this the company isknown as “NTPC Limited”.

NTPC has installed capacities of 29,394 MW. It has 15 coal based powerstations (23,395 MW), 7 gas based power stations (3,955 MW) and 4 powerstations in Joint Ventures (1,794 MW). The company has power generatingfacilities in all major regions of the country. It plans to be a 75,000 MWcompany by 2017.

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NTPC has gone beyond the thermal power generation. It has diversified intohydro power, coal mining, power equipment manufacturing, oil & gasexploration, power trading & distribution. NTPC is now in the entire powervalue chain and is poised to become an Integrated Power Major.

NTPC's share on 31 Mar 2008 in the total installed capacity of the country was19.1% and it contributed28.50% of the total powergeneration of the countryduring 2007-08. NTPC has setnew benchmarks for the powerindustry both in the area ofpower plant construction andoperations with its experienceand expertise in the powersector, NTPC is extendingconsultancy services to variousorganisations in the power business. It provides consultancy in the area ofpower plant constructions and power generation to companies in India andabroad.

In November 2004, NTPC came out with its Initial Public Offering (IPO)consisting of 5.25% as fresh issue and 5.25% as offer for sale by Government ofIndia. NTPC thus became a listed company with Government holding 89.5% ofthe equity share capital and rest held by Institutional Investors and Public. Theissue was a resounding success. NTPC is among the largest five companies inIndia in terms of market capitalization.

Recognising its excellent performance and vast potential, Government of theIndia has identified NTPC as one of the jewels of Public Sector 'Maharatnas'- apotential global giant. Inspired by its glorious past and vibrant present, NTPCis well on its way to realise its vision of being "A world class integrated powermajor, powering India's growth, with increasing global presence".

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2.2. INSTALLED CAPACITY:

Ø AN OVERVIEW:

  Number Of Plants Capacity MWNTPC OwnedCoal 15 23395Gas/Liquid Fuel 7 3955Total 22 27350

Owned By JVsCoal & Gas 4 2044Total 26 29394

Ø REGIONAL SPREAD OF GENERATING FACILITIES:

Region Coal Gas TotalNorthern 7035 2312 9347Western 5860 1293 7153Southern 3600 350 3950Eastern 6900 - 6900JVs 564 1480 2044Total 23959 5435 29394

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Ø PROJECT PROFILE:

ü COAL BASED POWER STATIONS:

  Coal based State CommissionedCapacity

(MW)1. Singrauli Uttar Pradesh 2,0002. Korba Chhattisgarh 2,1003. Ramagundam Andhra Pradesh 2,6004. Farakka West Bengal 1,6005. Vindhyachal Madhya Pradesh 3,2606. Rihand Uttar Pradesh 2,0007. Kahalgaon Bihar 2,3408. NTCPP Uttar Pradesh 8409. Talcher Kaniha Orissa 3,00010. Unchahar Uttar Pradesh 1,05011. Talcher Thermal Orissa 46012. Simhadri Andhra Pradesh 1,00013. Tanda Uttar Pradesh 44014. Badarpur Delhi 70515. Sipat Chhattisgarh 500

Total (Coal) 23,395

ü GAS/LIQUID FUEL BASED POWER STATIONS:

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  Gas based State CommissionedCapacity

(MW)16. Anta Rajasthan 41317. Auraiya Uttar Pradesh 65218. Kawas Gujarat 64519. Dadri Uttar Pradesh 81720. Jhanor-Gandhar Gujarat 64821. Rajiv Gandhi CCPP

KayamkulamKerala 350

22. Faridabad Haryana 430Total (Gas) 3,955

ü POWER PLANTS WITH JOINT VENTURES:

  CoalBased

State Fuel CommissionedCapacity

(MW)23. Durgapur West Bengal Coal 12024. Rourkela Orissa Coal 12025. Bhilai Chhattisgarh Coal 32426. RGPPL Maharastra Naptha/LNG 1480

Total(JV) 2044Grand Total (Coal + Gas + JV) 29,394

2.3. NTPC Limited KAHALGAON ( AN OVERVIEW ):

The area is in Kahalgaon on the bank of River Ganga in the state of Bihar.Kahalgaon is one of the major energy sources of India. The place once was a

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waste land which was unavailable for agriculture. The land was of no use to thelocal people. In the late fifties, a large scale dam was built in West Bengal onthe River Ganges which provided sufficient water for people. Later, rich coaldeposits spread over an area of 2200 km² in the state of Jharkhand werediscovered that could be used to generate electricity.

The population of Kahalgaon mainly consists of professionals and workers ofthese large industrial units and businessmen and employees of otherorganizations dealing with the power or coal industry, in addition to staffmembers of various government agencies.

Photo1. National Thermal Power Corporation Ltd., Kahalgaon

3. NTPC Limited:

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3.1. INTRODUCTION:

NTPC full form is National Thermal Power Corporation. The Place is nowknown as NTPC Kahalgaon. There is brief detail:-

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Address National Thermal Power Corporation , KahalgaonApproved Capacity 2840 MWInstalled Capacity 2340 MWLocation Kahalgaon, BiharWater Source River GangaMain Fuel CoalBeneficiary States State & Union territories of NR, WR, ER,SR, Uttar Pradesh, Bihar

4.1 million tonnes per year for Stage IFuel Requirement 6.62 million tonnes per year for 2nd Unit of Stage II

3.67 million tonnes per year for 3rd Unit of Stage IISource of fuel Rajmahal, Murra, Chuperbita Coal field of Eastern Coal Field LimitedTotal Area 3300 AcresApproved Investment Rs. 1715 Crore (Stage I)

Rs.6330 Crore ( Stage II)Unit Sizes Stage-I: 4*210 MW

Stage-II: 3*500 MWUnits Commissioned Unit-I : 200 Mw March 1992

Unit-II : 200 MW March 1994Unit-III : 200 MW March 1995Unit-IV 200 mW November 1996

3.2. NTPC LAYOUT:

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The general layout of thermal power plant consists of mainly four circuits asshown.

1. Coal and Ash circuit2. Air and Gas circuit3. Feed Water and Steam circuit4. Cooling Water circuit

Coal and Ash Circuit:

In this circuit, the coal from the storage is fed to the boiler through coalhandling equipment for the generation of steam. Ash produced due tocombustion of coal is removed to ash storage through ash-handling system.

Air and Gas Circuit:

Air is supplied to the combustion chamber of the boiler either through forceddraught or induced draught fan or by using both. The dust from the air isremoved before supplying to the combustion chamber. The exhaust gasescarrying sufficient quantity of heat and ash are passed through the air-heaterwhere the exhaust heat of the gases is given to the air and then it is passedthrough the dust collectors where most of the dust is removed before exhaustingthe gases to the atmosphere.

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Feed Water and Steam Circuit:

The steam generated in the boiler is fed to the steam prime mover to develop thepower. The steam coming out of the prime mover is condensed in the condenserand then fed to the boiler with the help of pump. The condensate is heated in thefeed-heaters using the steam tapped from different points of the turbine. Thefeed heaters may be of mixed type or indirect heating type. Some of the steamand water are lost passing through different components of the system;therefore, feed water is supplied from external source to compensate this loss.The feed water supplied from external source to compensate the loss. The feedwater supplied from external source is passed through the purifying plant toreduce to reduce dissolve salts to an acceptable level. This purification isnecessary to avoid the scaling of the boiler tubes. Purification is done by DMplants.

Cooling Water Circuit:

The quantity of cooling water required to condense the steam is considerablyhigh and it is taken from a lake, river or sea. At the Kahalgaon thermal powerplant it is taken from an artificial lake created near the plant. The water ispumped in by means of pumps and the hot water after condensing the steam iscooled before sending back into the pond. This is a closed system where thewater goes to the pond and is re circulated back into the power plant. Generallyopen systems like rivers are more economical than closed systems.

2. MAJOR AREAS IN NTPC:

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2.1. COAL HANDLING PLANT (CHP):

Coal source of plant are Rajmahal, Murra, Chuperbita Coal field of EasternCoal field Ltd. 14.3 million tonnes of coal are consumed by plant per year. Thecoal reaches to the CHP through MGR where the size of coal is approx. lessthan 200 mm. The coal is thrown into Track Hopper (These self-cleaning,double rack and pinion style valves receive material from railroad cars ormaterial reclaimed from outdoor storage piles by bulldozers. Their purpose is toshut off the material flow from the hoppers to material handling conveyorsbelow.) From Track Hopper threw conveyer belts coal reaches to the CrusherHouse (it is a 6 store building where the coal is cursed into a size of less than20mm) in between track hopper and crusher house “Suspended Magnets””Magnetic Detector” and “Magnetic Separators” are placed so that only coalpieces reach to the crusher house because if heavy metal pieces reach to thecrusher house they will damage it. Then if plant unit need coal threw conveyerbelts coal reaches to the coal bunkers of Unit. Coal Bunkers (they store the coalfor a single unit and supply coal to furnace threw coal mills when it needs) butwhen coal bunkers are full then the coal is stacked in the coal yard using thecoal stacker and reclaimer machine (it is a huge machine used to stack/reclaimthe coal used in the plant they are always placed in coal yard where coal isstacked. In NTPC KhSTPP there are 3 such type of machines are available twofor stage-I and one for stage-II. ).

In NTPC KhSTPP Different types of Electrical machines are used in CHPwhich are:

S.No.

Name Type Ratings

1. Conveyermotor

Squirrel cage induction motor 6.6 KV / 0.4 KV

2. Ploughmotor

Squirrel cage induction motor 6.6 KV

3. Traversedrive motor

Squirrel cage induction motor 6.6 KV

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2.1. BOILER & ITS AUXILIARIES:

2.1.1. BOILER:

“BOILER IS A CLOSED VESSEL IN WHICH STEAM IS GENERATED BYMEANS OF HEAT ENERGY; BOILER HAVING CAPACITY OF 22.75 LITERSCOMES UNDER BOILER ACT.”

Type of boiler used in NTPC KhSTPP in Stage-I and II are Water-Walled TubeBoilers. A water-walled tube boiler is a type of boiler in which water circulatesin tubes heated externally by the fire. Water-walled tube boilers are used forhigh pressure boilers. Fuel is burned inside the furnace, creating hot gas whichheats up water in the steam generating tubes. In smaller boilers, additionalgenerating tubes are separate in the furnace, while larger utility boilers rely onthe water-filled tubes that make up the walls of the furnace to generate steam.

The heated water then rises into the boiler drum. Here, saturated steam isdrawn off the top of the drum. In some services, the steam returns the furnacein, through a super heater in order to become superheated. Superheated steamis used in driving turbines. Since water droplets can severely damage turbineblades, steam is superheated to 730°F (390°C) or higher in order to ensure thatthere is no water entrained in the steam.

Cool water at the bottom of the boiler drum returns to the feed water drum vialarge-bore 'down comer tubes', where it helps pre-heat the feed water supply.(In 'large utility boilers', the feed water is supplied to the steam drum and thedown comers supply water to the bottom of the water walls). To increase theeconomy of the boiler, the exhaust gasses are also used to pre-heat the airblown into the furnace and warm the feed water supply. Such water-tube boilersin thermal power station are also called steam generating units.

Properties of fuel:

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n Flash point- it is a minimum TEMPERATURE AT which the fuel is heated togive off inflammable vapour in sufficient quantity to ignite when broughtin contact of flame.

n Pour point- it is a minimum Temperature at which oil can handle or canflow easily in pipe line.

n Fire point- it is a minimum Temperature of fuel at which it starts burningwithout external support.

n Calorific value- it is a heat energy liberated by complete combustion ofunit mass of fuel.

· COAL BURNERS :

EFFECTIVE UTILISATION OF PULVERISED COAL DEPENDS ON THE ABILITY OFBURNERS TO PRODUCE UNIFORM MIXING OF COAL AND AIR.

In NTPC KhSTPP (Stage-I and Stage-II) TANGENTIAL FIRINGMETHOD is used in which from corners tangentially the air and fuel arepassed inside furnace region where burning takes place as shown in figure.

Ø Role of Air Heaters

· To recycle the heat of exit flue gas back in the combustion process· Efficient coal combustion and pulverization depends on air heater

performance· For every 20 deg drop in flue gas exit temperature the boiler

efficiency increased by about 1%.

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2.1.2. BOILER AUXILIARIES (Stage-I & II):

Figure: Arrangement of Boiler Auxiliary and various parts.

Ø Coal Mill

A ball mill is a pulveriser that consists of a horizontal rotating cylinder, upto three diameters in length, containing a charge of tumbling or cascadingsteel balls, pebbles, or rods.

A tube mill is a revolving cylinder of up to five diameters in length used forfine pulverization of ore, rock, and other such materials; the material, mixedwith water, is fed into the chamber from one end, and passes out the otherend as slime.

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n ESP (ELECTROSTATIC PRECIPITATOR):

An electrostatic precipitator (ESP) is a particulate collection device thatremoves particles from a flowing gas (such as air) using the force of aninduced electrostatic charge. ESP are highly efficient filtration devices thatminimally impede the flow of gases through the device and can easilyremove fine particulate matter such as dust and smoke from the air stream.

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· INDUCED DRAUGHT FAN

Made by BHELType of motor used 3 phase Squirrel cage induction

motorStator connection Y (star)

Operated at Frequency 50 HzVoltage 6600 VCurrent 138.5 APower 1300 KWPower factor 0.85

Efficiency 95.5

Rotor speed 744 rpmWeight 13700 KgLubricant Greave servogem-2

Maximum Winding Temperature 48°C

· FORCED DARUGHT FAN

Made by BHELType of motor used 3 phase Squirrel cage induction

motorStator connection Y (star)

Operated at Frequency 50 HzVoltage 6600 V

Current 84.5 APower 800 KWPower factor 0.875

Efficiency 94.8

Rotor speed 1490rpmLubricant Greave servogem-2

Maximum Winding Temperature 48°CØ PRIMARY AIR FAN

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Made by BHEL

Type of motor used 3 phase Squirrel cage induction motor

Stator connection Y (star)

Operated at Frequency 50 Hz

Voltage 6600 V

Current 84.5 A

Power 1400 KW

Power factor 0.87

Efficiency 96.3

Rotor speed 1493 rpm

Lubricant Greave servogem-2

Maximum Winding Temperature 48°C

Ø FLY ASH COMPOSITION(BY WEIGHT):

AL2O3 20-25%

CAO 01.0%

FE2O3+FE3O4 05-8%

K2O 02.0%

MGO 00.7%

MNO 00.02%

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NA2O 00.24%

TIO2 0.7-1.5%

SILICA 64.78%

Ø Ash Utilization

Ash utilization is one of the key concerns at NTPC. The Ash UtilizationDivision, set up in 1991, strives to derive maximum usage from the vastquantities of ash produced at its coal-based stations. The division proactivelyformulates policy, plans and programme for ash utilization. It further monitorsthe progress in these areas and works at developing new fields of ashutilization.As the emphasis on gainful utilization of ash grew, the usage over the years alsoincreased. From 0.3 million tonnes in 1991-1992, the level of utilization during2006-07 stood at over 20.76 million tonnes.

NTPC has adopted user friendly policy guidelines on ash utilisation. Theseinclude actions identified for:

i. Ash Collection & Storage Systemii. Facilities & Incentives to usersiii. Direct Department Activitiesiv. Administrative & Financial aspects.

2.2. TURBINE AUXILIARIES

Figure shown below gives the perfect representation of the arrangement ofturbine auxiliaries. For proper function of turbine the auxiliaries are arrangedat different location peeping the view of easy installation, proper operation andmaintenance and technical requirement.

Ø CONDENSATE SYSTEM

This comprise of

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§ Condensate pumps – 3 per Unit of 50% capacity each located nearthe condenser Hot well.

§ L.P. Heater – Normally 4 in number with no. 1 located at the upperpart of the condenser and No. 2,3,and 4 around 4m level.

Deaerator – one per unit located around 18’M’ level in CD bay.

Ø Feed Water system

The main equipment coming under this system are§ Boiler feed pump - 3 per Unit of 50% capacity each located 0 ‘M’

levels in the T.G. bay.§ High Pressure Heater – Normally three in number and located

near TG bay.§ Drip Pumps – Generally two in number of 100% capacity each

situated beneath the LP heater.

Ø Turbine Lubrication Oil System :

It consist of main oil pump (M.O.P) ,Starting Oil Pump (S.O.P.) AC standby oil pumps and emergency DC oil pump and jacking oil pump (JOP)

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(one at each Unit).

Ø Auxiliary Steam System :

The main 16 ata header runs parallel to BC bay at the level of around 18‘M’.

2.3. GENERATOR AND ITS AUXILIARIES

Ø Constructional Features

STATORCOMPONENTS1. Stator frame2. Stator Core3. Stator windings4. Bushings

1. Stator Frame

Totally enclosed gas tight fabricatedstructure made of high quality mild steel.It houses the stator core and Hydrogencoolers.

2. Stator Core

Ø The entire core is laminated to minimize magnetic and eddy current

Stator Frame Interior:

1. Frame Housing

2. Clamp

3. Supporting Ring

4. Dovetail Bar

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lossesØ Each laminations is made up of cold rolled high quality silicon steel

3. Stator Winding

Ø The stator has a three phase, double layer, short pitched and bar typewindings having two parallel paths.

Ø Each slot accommodates two bars.Ø Each bar consists of solid as well as hollow conductors with cooling

water passing through the hallow space.Ø In the straight slot portion the strands are transposed by 360 0 to reduce

the eddy losses.Ø Bar is taped with several layers of thermosetting epoxy mica tape.Ø To prevent corona discharges between insulation and the wall of the

slot, the slot portion is coated with semi conducting varnish.

4. BushingsThree phases and six neutral terminals are brought out from the statorframe through bushings which are capable of withstanding high voltageand provided with gas tight joint.The conductor of the bushing is made of high conductivity copper tube onwhich silver plated terminal plates are brazed at both ends.

ROTOR

It comprises of the fallowing componentsØ Rotor shaftØ Rotor windingsØ Retaining ringØ FansØ Slip rings

§ Rotor Shaft

The main constituents are chromium, molybdenum, nickel and vanadiumon 2/3 of its circumference approximately, the rotor body is provided with

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longitudinal slots to accommodate field windings.

§ Rotor windings

The conductors are made of hard drawn silver bearing copper whichexhibits high creep resistance so that coil deformations due to thermalcycling. The individual turns are insulated from each other by layer ofglass laminates.

§ Retaining Ring

The overhang portion of field windingis held by non magnetic steel forging ofretaining ring against centrifugalforces.To reduce stray losses, the retainingrings are made of nonmagnetic, steeland cold worked, resulting highmechanical strength.

§ Rotor Fan

The generator cooling gas is circulated by two single stage axial flowpropeller type fans. These Fan hubs are made of alloy steel.

§ Slip rings

The slip rings consist of helically grooved alloy steel rings shrunk onrotor body shaft and insulated from it. The slip rings are provided withinclined holes for self ventilation.

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Ø GENERATOR PARAMETERS:

Generator Volume 56 cu m

CO2 required for expelling H2 atstandstill

120 cu m

CO2 required for expelling H2under rolling

160 cu m

H2 filling quantity at standstill 300 cu m

H2 filling quantity underStandstill

336 cu m

Nominal pressure of hydrogen 3.0 ksc

Permissible variations +/-0.2 ksc

Hydrogen purity 99 %

Purity of H2 (minimum) 97%

Maximum temperature of Coldgas

44 deg c

Maximum moisture content ingenerator casing

15 mg/m3 of H2

Gas flow per Cooler 7.5 m3/sec

Heat Load 528 KW

Cooling water flow per cooler 87.5m3/sec

Number of H2 coolers 4

Pressure Drop through cooler 17.5mmwcl

Minimum Temperature of coolingwater to maintain minimum 20

13deg C

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degree C cold gas

Ø Cooling of Generator

§ IT COOLS1. ROTOR.2. STATOR CORE.

§ COMPOMENTS:1. ROTOR FAN.2. H2 COOLERS.3. H2 DRIER.

Ø Generator Hydrogen Cooling Circuit Cold Gas

Hot Gas

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§ SEAL OIL SYSTEMThe locations where the rotor shaft passes through the stator casing areprovided with radial seal rings.The gap between the seal ring and the shaft is sealed with seal oil.Toensure effective sealing seal oil pressure in the annular gap is maintainedat a higher level than the gas pressure within the generator casing.

ØSEAL

OIL

OPERATION:

Seal oil supplied to the shaft seals is drained from both air & H2 sides.The air side seal oil is directly returned to SOT via a float valve. The oildrained from H2 side of the shaft seal is discharged into generatorprechambers. The prechambers permit the escape of entrained gasbubbles and deforming of the oil. Oil from prechambers flow to IOT & afloat valve maintains the oil level in IOT excess oil is returned back toSOST.IOT act as a gas barrier preventing the ingress of H2 to SOT.

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§ EXCITATION SYSTEM:

Static excitation system is used in mainly 200MW Generator set. The ACpower is trapped off from generator terminal. Stepped down and rectifiedby fully controlled thyristor bridge and then feed to generator field asexcitation power. To control the generator output voltage. A high controlspeed is achieved by using an inertia free control and power electronicssystem. Any deviation in generator terminal voltage is sensed by errordetector and causes the voltage regulator to advance or retard the firingangle of thyristor there by controlling the field excitation.

The Static Excitation System Consists of:

§ Rectifier Transformer§ Thyristor Converter§ Automatic voltage Regulator§ Field Flashing Circuit§ Field Breaker and Field Discharge Equipment

§

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2 Pole 3000 RPM Hydrogen / Hydrogen and Watercooled Turbo-generators:

The Hydrogen and water cooled machines (THDF type) are offered withthe stator winding directly water-cooled and the rotor winding directlycooled with Hydrogen. The stator core has a leaf spring suspension. Themachines are with Micalastic system of impregnation and the bearings aremounted on end shields. The stator overhang is with a support ring. Amagnetic shunt traps the end leakage flux. These machines are providedwith multistage compressors and vertical coolers on turbine end. These canbe offered with either brushless /static type of excitation systems

The (THW) type machines have the stator winding directly cooled by waterwhereas the rotor winding is directly cooled by Hydrogen by gap pick upmethod. The stator core is mounted resiliently on flexible core bars. Resinrich thermo-reactive insulation is used for the stator winding and topripple springs are placed in the stator slots. These machines are alsocharacterized by enclosed type slip rings with forced ventilation. Two axialfans are provided on rotor and four Hydrogen coolers are provided forsystematic ventilation. These are offered with static excitation system.

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GENERATOR RATING:

KW Rating 500,000 KW

Power Factor 0.85 lagging

KVA Rating 588,000 KVA

Stator Voltage 21,000 V

Stator Ampere 16,200 A

Rotor Voltage 340 VRotor Ampere 4040 ARotor Speed 3000 rpmFrequency 50 HzPhase 3Connection Type Y Y ( Star, Star)Coolant Used Water & HydrogenGas Pressure 4 BarInsulation Class BType TG-HH-0500-2Make BHEL- Haridwar

2.4. SWITCHYARD & TRANSMISSION EQUIPMENTS

An electric power system is composed of high –voltage transmission linesthat feed power to a medium voltage (MV) network by means of substations.In NTPC Kahalgaon these MV networks generally operated at voltagesbetween 15.7 KV to 22.0 KV. In turn they supply thousands of independentlow voltage system that function between 220V to 600V.

Switchyard and transmission equipments are:

Substations are used throughout an electrical system. Starting with thegenerating station, a substation raises the medium-voltage generated by theSynchronous generator to the high-voltage needed to transmit the energyeconomically.

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The high transmission-line voltage is then reduced in those substationslocated close to the power consuming center. The electrical equipment insuch distribution substation is similar to that found in substation associatedwith generating plant.

Substations Equipments:

§ Transformers§ Circuit breakers§ Surge arresters§ Current Limiting Reactor§ Isolators§ Instrument transformers§ Relay and protection devices

Ø TRANSFORMERSGenerator Transformer - (1, 2, 3, 4,) Ratings:

Maker BHEL Bhopal

Vector group YNd11

Cooling method OFWF

KVA rating 250

KV (no load), HV 400 KV

KV (no load), LV 15.75 KV

Line Ampere, HV 360.9 A

Line Ampere, LV 9164.6 A

Number of phases 3

Frequency 50 Hz

Independent volt 14.41 KV

Top oil temperature rise 35 Degree C

Mean Windings Temperature Rise 40 Degree C

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Generator Transformer-(5) Ratings:

Maker ABB

Vector group YNd11

Cooling method OFAF

KVA rating 250

KV (no load), HV 250 KV

KV (no load), LV 250 KV

Line Ampere, HV 343.66 A

Line Ampere, LV 9164.28 A

Number of phases 3

Frequency 50 Hz

Independent volt 14.41 KV

Top oil temperature rise 35 Degree C

Mean Windings Temperature Rise 40 Degree C

UST-3A

Maker BBL Bombay

KVA Rating 1600

Voltage at No Load, HV 6600 V

Voltage at No Load, LV 433 V

Ampere, HV 140 A

Ampere, LV 2133 A

Number of phases/ Frequency 3/50 Hz

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UTA-2A

Maker: Hackbridge Hewittic and Easun Ltd.

KVA Rating 1600

Voltage at No Load, HV 6600 V

Voltage at No Load, LV 433 V

Ampere, HV 140 A

Ampere, LV 2133 A

Number of phases 3

Frequency 50 Hz

Ø CIRCUIT BREAKERS:A circuit breaker is an automatically-operated electrical switch designed toprotect an electrical circuit from damage caused by overload or shortcircuit. Unlike a fuse, which operates once and then has to be replaced, acircuit breaker can be reset (either manually or automatically) to resumenormal operation. Circuit breakers are made in varying sizes, from smalldevices that protect an individual household appliance up to largeswitchgear designed to protect high voltage circuits feeding an entire city.

CIRCUIT BREAKER OPERATION:All circuit breakers have common features in their operation, althoughdetails vary substantially depending on the voltage class, current rating andtype of the circuit breaker.

The circuit breaker must detect a fault condition; in low-voltage circuitbreakers this is usually done within the breaker enclosure. Circuit breakersfor large currents or high voltages are usually arranged with pilot devices tosense a fault current and to operate the trip opening mechanism. The tripsolenoid that releases the latch is usually energized by a separate battery,

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although some high-voltage circuit breakers are self-contained with currenttransformers, protection relays, and an internal control power source.

Once a fault is detected, contacts within the circuit breaker must open tointerrupt the circuit; some mechanically stored energy within the breaker isused to separate the contacts, although some of the energy required may beobtained from the fault current itself. The stored energy may be in the formof springs or compressed air. Small circuit breakers may be manuallyoperated; larger units have solenoids to trip the mechanism, and electricmotors to restore energy to the springs.

The circuit breaker contacts must carry the load current without excessiveheating, and must also withstand the heat of the arc produced wheninterrupting the circuit. Contacts are made of copper or copper alloys, silveralloys, and other materials. Service life of the contacts is limited by theerosion due to interrupting the arc. Miniature circuit breakers are usuallydiscarded when the contacts are worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts.

When a current is interrupted, an arc is generated - this arc must becontained, cooled, and extinguished in a controlled way, so that the gapbetween the contacts can again withstand the voltage in the circuit. Differentcircuit breakers use vacuum, air, insulating gas, or oil as the medium inwhich the arc forms. Different techniques are used to extinguish the arcincluding:

§ Lengthening of the arc

§ Intensive cooling (in jet chambers)

§ Division into partial arcs

§ Zero point quenching

§ Connecting capacitors in parallel with contacts in DC circuits

Finally, once the fault condition has been cleared, the contacts must againbe closed to restore power to the interrupted circuit.

In NTPC KhSTPP type of High-voltage circuit breakers used are given below:

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· Air blast Circuit Breaker

· SF6 Circuit Breaker

AIR BLAST CIRCUIT BREAKER:

These circuit breakers interrupt the circuit by blowing compressed air atsupersonic speed across the opening contact. Compressed air is stored inreservoirs at a pressure of about 27-31 Kg/cm2 and is replenished bycompressor located in the substation. The most powerful circuit breakerscan typically open short-circuits current of 40KA at a line Voltage of 765KVin a matter of 3 to 6 cycles on a 60Hz line.

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SF6 CIRCUIT BREAKERS:

· Simplicity of the interrupting chamber which does not need an auxiliarybreaking chamber

· Autonomy provided by the puffer technique

· The possibility to obtain the highest performance, up to 63 kA, with areduced number of interrupting chambers

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· Short break time of 2 to 2.5 cycles

· High electrical endurance, allowing at least 25 years of operationwithout reconditioning

· Possible compact solutions when used for GIS or hybrid switchgear

· Integrated closing resistors or synchronized operations to reduceswitching over-voltages

· Reliability and availability

· Low noise levels.

The reduction in the number of interrupting chambers per pole has led to aconsiderable simplification of circuit breakers as well as the number of partsand seals required. As a direct consequence, the reliability of circuitbreakers improved, as verified later on by CIGRE surveys.

Ø Lightning Arrester:

The purpose of lightning arrester is to limit the over voltage that mayoccur across transformers and other electrical apparatus due either to

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lightning or switching surges. The upper end of the arrester is connectedto the line or terminal that has to be protected, while the lower end issolidly connected to ground.

Ideally a lightning arrester clips any voltage in excess of a specifiedmaximum, by permitting a large current, if needed be, to be diverted toground. In this way the arrestor absorbs energy from the incoming surge.So the E-I characteristics of an ideal surge arrester is therefore, ahorizontal line whose level corresponds to the maximum permissiblesurge voltage. In practice, the E-I characteristics slopes upward but isstill considered to be reasonably Flat.

Ø Current-Limiting Reactor:

The MV bus in the NTPC KhSTPP usually energized several feeders,which carry power to regional load centers surrounding the substation. Ifso happens that the output impedance of the MV bus is usually very low.Consequently, If the short circuit should occur on one of the feeders, theresulting short-Circuit current could be disastrous.

Ø CIRCUIT-ISOLATOR:

Circuit-Isolator provides three-pole, group-operated, visible-air-gapisolation in distribution substations. The Circuit-Isolator II can be used tointerrupt low-level charging currents associated with substation bus workand circuit-breaker bushings, as well as other low-voltage currentscommonly present in substations.

Benefits:

§ Ideal for isolating transformers, circuit breakers, and other substationequipment for repair and maintenance.§ Each disconnect is factory-assembled and adjusted for easy installation.§ Can be custom engineered for mounting on almost any customer-suppliedstructure.

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Fig: Circuit Isolator Fig. Current Transformer

Ø INSTRUMENT TRANSFORMERS:

1. CURRENT TRANSFORMER:

A current transformer (CT) is a type of instrument transformer designed toprovide a current in its secondary winding proportional to the alternatingcurrent flowing in its primary. They are commonly used in metering andprotective relaying in the electrical power industry where they facilitate the safemeasurement of large currents, often in the presence of high voltages. Thecurrent transformer safely isolates measurement and control circuitry from thehigh voltages typically present on the circuit being measured.

2. CAPACITOR VOLTAGE TRANSFORMER:

A capacitor voltage transformer (CVT) is a transformer used in power systemsto step-down extra high voltage signals and provide low voltage signals eitherfor measurement or to operate a protective relay. In its most basic form thedevice consists of three parts: two capacitors across which the voltage signal is

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split, an inductive element used to tune the device to the supply frequency and atransformer used to isolate and further step-down the voltage for theinstrumentation or protective relay. The device has at least four terminals, ahigh-voltage terminal for connection to the high voltage signal, a groundterminal and at least one set of secondary terminals for connection to theinstrumentation or protective relay. CVTs are typically single-phase devicesused for measuring voltages in excess of one hundred kilovolts where the use ofvoltage transformers would be uneconomical. In practice the first capacitor, C1,is often replaced by a stack of capacitors connected in series. This results in alarge voltage drop across the stack of capacitors that replaced the firstcapacitor and a comparatively small voltage drop across the second capacitor,C2, and hence the secondary terminals.

Fig. Circuit diagram of Capacitor Voltage Transformer

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TURBINEThere are three turbines for each generator. These are meant to extractmaximum heat energy from the steam so as to achieve maximum efficiency.These turbines are named as:

a) High pressure turbine (HP Turbine)b) Intermediate pressure turbine (IP Turbine)c) Low pressure turbine (LP Turbine)

· Steam comes into the HP turbine from boiler through the main streamline (MSL).the initial temperature and pressure of this steam is 540⁰Cand 170 atm respectively. Each turbine consists of several stages and onestage is made up of one rotor blade and one stator blade.

· For 500 MW, HP turbine consists of 6 stages. Final temperature andpressure after passing through all the stages of HP turbine becomes345⁰C and 45 atm respectively.

· Steam comes out of HP turbine and goes back to reheater in boilerthrough cold reheating line. Steam is then reheated in reheater and is fedto intermediate pressure turbine through hot reheating line (HRH). Initialtemperature and pressure of steam in IP turbine is 540⁰C and 40 atmrespectively.

· Steam then passes through various stages and then the used steam isagain fed back to boiler at reduced temperature and pressure.

· Finally steam is fed to the LP turbine and steam is then passed to thecondenser where it is converted back to water.

· At the bottom of the condenser there is a hot well where water collects.

· There are three condensate extract pumps (CEP) out of which two workat a time and extract the water from the hot well.

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· Steam coming out of the various outlets combines at one place in draincooler where the temperature and pressure of various steams comes to acommon level.

· Now water need to be fed into the boiler but before that it needs somepreheating.

· There are three low pressure heaters (LP Heaters) and two high pressureheaters (HP Heaters)

· The heating elements in these heaters are steam coming out of variousstages of the IP Turbine and LP Turbine.

· From HP Heater, the water goes to economizer.

· From economizer heated water goes to the boiler drum. Boiler drumcontains water and steam both.

· Boiler drum is at a height of 90 meter. Steam being lighter collects at thetop of the boiler drum and water flows to the bottom ring header.

· Because of high potential energy, water from boiler drum goes down inthe boiler, gets heated, its temperature rises and attains enough kineticenergy to reach back to the boiler drum.

· Steam from the boiler drum passes through superheater and attains ahigh temperature of 540⁰C at 170 atm pressure and goes to the HPturbine.

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GOVERNORThe widespread use of electric clocks, the need for satisfactory operation ofpower stations running in parallel and the relation between systemfrequency and the speed of the motors has led to the requirement of closeregulation of power system frequency. Control of system frequency and loaddepends upon the governors of the prime-movers. Fig.1 shows the basiccharacteristics of a governor. It is seen that with a given setting there is adefinite relationship between turbine speed and the load being carried by theturbine. If the load carried by the turbine increases the speed decreases. Inorder to keep the speed same the governor setting by changing the springtension in the fly-ball type of governor will be resorted to and thecharacteristics of the governor will be indicated by the dotted line. Inpractice the change in characteristics is obtained by remotely operating thegovernor control motor from the control room. A turbine can be adjusted tocarry any given load at a desired speed. If constant frequency is required theoperator can adjust the speed of the turbine by changing the governorcharacteristics as and when desired.

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SPEED GOVERNING SYSTEM:

Fig. 2 shows the schematic diagram of a speed governing system which controlsthe real power flow in the power system. The speed governing system consists ofthe following parts:

1. Speed governor: this is a fly-ball type of speed governor and constitutesthe heart of the system as it senses the change in speed or frequency. Withthe increase in speed the fly-balls move outwards and the point B onlinkage mechanism moves downwards and vice-versa.

2. Linkage mechanism: ABC and CDE are the rigid links pivoted at B andD respectively. The mechanism provides a movement to the control valvein the proportion to change in speed. Link 4(l4) provides a feedback fromthe steam valve movement.

Fig.2 Turbine Speed governing system

3. Hydraulic Amplifier: This consists of the main piston and the pilot valve.

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Low power level pilot valve movement is converted into high power levelpiston valve movement which is necessary to open or close the steamvalve against high pressure steam.

4. Speed changer: The speed changer provides a steady state power outputsetting for the turbine. The downward movement of the speed changeropens the upper pilot valve so that more steam is admitted to the turbineunder steady condition. The reverse happens when the speed changermoves upward.

BOILER· Boiler is a long column where coal is fired to produce heat and to convert

water into superheated steam.· In NTPC – Kahalgaon, the height of the boiler is 90 meter.· In the boiler section there are ten elevations which are meant for coal

input. Coal is pulverized in the form of fine powders and fed into theboiler at different elevations.

· Oil is sprayed in between these elevations to ignite the coal powders andto allow the heat to sustain for the maximum time in the boiler.

· There are numerous fine tubes inside the boiler through which waterflows. This water while flowing through the tubes extracts heat from theboiler and gets converted to steam at suitable temperature and pressure.

· Maximum temperature is available at the topmost part of the flame. Dueto this reason the boiler drum is located at the top (90 meter height).

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BIBLOGRAPHY

BOOKS:

1. S. S. Rao, “Switchgear and Protection”, Khanna Publishers.

2. C.L. Wadhwa, “Electrical Power System”, New Age International.

3. P.S.Bimbhra, “Electrical Machinery”, Khanna Publisher.

4. Husain Ashfaq ,” Electrical Machines”, Dhanpat Rai & Sons.

INTERNET:

1. Google.co.in

2. Wikipedia.com

3. NTPC.com