Ntpc Deposit

8/3/2019 Ntpc Deposit

1/64

AN ORIENTATION

REPORT ON

INDUSTRIAL TRAINING AT

Badarpur Thermal Power Station(BTPS)

NTPC Badarpur Division

New Delhi

Submitted by

Arjit Agarwal

B.Tech III Year

Department of Electrical Engineering

Malaviya National Institute Of Technology

Jaipur


2/64

CERTIFICATE

TO WHOMSOEVER IT MAY CONCERN

I hereby certify that Arjit Agarwal Roll No 2008UEE107 of Malaviya National

Institute Of Technology,Jaipur has undergone 2 months industrial training from 16May 2010 to 14 July 2011 at our organization to fulfill the requirements for the

award of degree of B.tech Electrical Engineering. She worked on Power Plant

Overview project during the training. During his tenure with us we found himsincere and hard working.

We wish him a great success in the future.

Training Incharge

NTPC Badarpur

NEW DELHI


3/64

ACKNOWLEDGEMENTI am extremely thankful to my college for giving me an opportunity to undergo

industrial training in such a wonderful enterprise. I am grateful to Mr. Rohit

Goyal(Head of Dept. of training & placement,MNIT Jaipur) for his help and support.

I am very much indebted to NTPC Badarpur for providing me such a wonderful 60

days orientation programme to give us an insight and practical knowledge about our

subject.

They gave a new horizon to the industrial training in such a wonderful environment.

The help rendered by Ms Rachana Singh Bhal, Supervisor, National ThermalPower Corporation for experimentation is greatly acknowledged.

The author would like to express a deep sense of gratitude and thanks profusely to Mr.

G.D. Sharma,Training Coordinator, without the wise counsel and able guidance, itwould have been impossible to complete the training successfully.

My special thanks to Mr. M.K. Chopra, Mr. Rajat Garg,Mr. Saurabh Garg,Mr. RajeshGarg,Mr. Maha Singh,Mr. Rajarshi Sharma,Mr. B.P. Sinha and Ms. Usha Kumari of

EMD-1 and EMD-2 for enlightening us with their knowledge and assigning

technicians for plant visit.

In the last I would like to express my gratitude to all the engineers and technicians,

who gave me the possibility to complete my training successfully.


4/64

Training at BTPS

I was appointed to do nine-weeks training at this esteemed organization from 16th

May to 14th July 2011. In these nine weeks I was assigned to visit various division of

the plant which were:-

1. Electrical maintenance division I (EMD-I)2. Electrical maintenance division II (EMD-II)

This nine-weeks training was a very educational adventure for me. It was really

amazing to see the plant by your self and learn how electricity, which is one of our

daily requirements of life, is produced.

This report has been made by self-experience at BTPS. The material in this report has

been gathered from my textbooks, senior student report, and trainer manual provided

by training department. The specification & principles are at learned by me from the

employee of each division of BTPS.


5/64

TABLE OF CONTENTS

1. Introduction to the Company

a. About the Company

b. Vision

c. Strategiesd. Evolution

2. Introduction to the Project

3. Project Report

a. Operationi. Introduction

ii. Steam Boiler

iii. Steam Turbineiv. Turbine Generator

b. EMD Ii. Coal Handling Plant

ii. Motorsiii. Switchgear

iv. High Tension Switchgearv. Direct On Line Starterc. EMD II

i. Generatorii. Protection

iii. Transformer

4.Last word

5.References


6/64

INTRODUCTION TO

THE COMPANY

About the CompanyVision

StrategiesEvolution

National Thermal Power Corporation Limited

Badarpur Thermal Power Station

Badarpur, New Delhi


7/64

ABOUT THE COMPANY

NTPC, the largest power Company in India, was setup in 1975 to accelerate power developmentin the country. It is among the worlds largest and most efficient power generation companies. In

Forbes list of Worlds 2000 Largest Companies for the year 2007, NTPC occupies 411th place.It

is a MAHARATNAcompany

A View of Badarpur Thermal Power Station,New Delhi

Wagons bringing coal

NTPC has installed capacity of 29,394 MW. It has 15 coal based power stations (23,395 MW), 7gas based power stations (3,955 MW) and 4 power stations in Joint Ventures (1,794 MW). The

company has power generating facilities in all major regions of the country. It plans to be a75,000 MW company by 2017.

NTPC has gone beyond the thermal power generation. It has diversified into hydro power, coalmining, power equipment manufacturing, oil & gas exploration, power trading & distribution.

NTPC is now in the entire power value chain and is poised to become an Integrated PowerMajor.


8/64

NTPC's share on 31 Mar 2008 in the total installed capacity of the country was 19.1% and it

contributed 28.50% of the total power generation of the country during 2007-08. NTPC has set

new benchmarks for the power industry both in the area of power plant construction andoperations.

With its experience and expertise in the power sector, NTPC is extending consultancy servicesto various organizations in the power business. It provides consultancy in the area of power

plant constructions and power generation to companies in India and abroad.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 of India. NTPC thus became a listedcompany with Government holding 89.5% of the equity share capital and rest held by

Institutional Investors and Public.

The issue was a resounding success. NTPC is among the largest five companies in India in terms

of market capitalization.

Recognizing its excellent performance and vast potential, Government of the India has identifiedNTPC as one of the jewels of Public Sector 'Navratnas'- a potential global giant. Inspired by itsglorious past and vibrant present, NTPC is well on its way to realize its vision of being

"A world class integrated power major, powering India's growth, with increasing global

presence".

Coal Based Power Stations

With 15 coal based power stations, NTPC is the largest thermal power generating company in the

country. The company has a coal based installed capacity of 27,535 MW.

COAL BASED(Owned

by NTPC)STATE

COMMISSIONED

CAPACITY(MW)

1. Singrauli Uttar Pradesh 2,000


9/64

2. Korba Chhattisgarh 2,600

3. Ramagundam Andhra Pradesh 2,600

4. Farakka West Bengal 2,100

5. Vindhyachal Madhya Pradesh 3,260

6. Rihand Uttar Pradesh 2,000

7. Kahalgaon Bihar 2,340

8. NCTPP, Dadri Uttar Pradesh 1,820

9. Talcher Kaniha Orissa 3,000

10. Feroze Gandhi, Unchahar Uttar Pradesh 1,050

11. Talcher Thermal Orissa 460

12. Simhadri Andhra Pradesh 1,500

13. Tanda Uttar Pradesh 440

14. Badarpur Delhi 705

15. Sipat Chhattisgarh 1,660

Total 27,535

Operations

In terms of operations, NTPC has always been considerably above the national average. The

availability factor for coal based power stations has increased from 89.32% in 1998-99 to 91.62% in

2010-11, which compares favourably with international standards. The PLF has increased from

76.6% in 1998-99 to 88.29% during the year 2010-11.


10/64

The table below shows that while the installed capacity has increased by 73.33% in the last twelve

years the generation has increased by 101.39%

VISION

A world class integrated power major, powering India's growth with increasing global presence.

To be the worlds largest and best power producer, powering Indias growth.

MISSION

Develop and provide reliable power related products and services at competitive prices,

integrating multiple energy resources with innovative & Eco-friendly technologies andcontribution to the society.

Core Values - BCOMITBusiness ethicsCustomer Focus

Organizational & Professional PrideMutual Respect & Trust

Innovation & Speed

Total Quality for Excellence

STRATEGIES-

Technological Initiatives

Introduction of steam generators (boilers) of the size of 800 MW

Integrated Gasification Combined Cycle (IGCC) Technology

Launch of Energy Technology Center -A new initiative for development of technologies

with focus on fundamental R&D

The company sets aside up to 0.5% of the profits for R&D


11/64

Roadmap developed for adopting Clean DevelopmentMechanism to help get / earn Certified Emission Reduction

Corporate Social Responsibility

As a responsible corporate citizen NTPC has taken up number of CSR initiatives

NTPC Foundation formed to address Social issues at national levelNTPC has framed Corporate Social Responsibility Guidelines committing up to 0.5% of net

profit annually for Community Welfare Measures on perennial basis

The welfare of project affected persons and the local population around NTPC projects

are taken care of through well drawn Rehabilitation and Resettlement policies

The company has also taken up distributed generation for remote rural areas

Environment Management

All stations of NTPC are ISO 14001 certified

Various groups to care of environmental issuesThe Environment Management Group

Ash Utilization DivisionAfforestation Group

Centre for Power Efficiency & Environment ProtectionGroup on Clean Development Mechanism

NTPC is the second largest owner of trees in the country after the Forest department.

Partnering government in various initiatives

Consultant role to modernize and improvise several plants across the country

Disseminate technologies to other players in the sector

Consultant role Partnership in Excellence Programme for improvement of PLF of 15

Power Stations of SEBs.

Rural Electrification work under Rajiv Gandhi Grameen Vidyutikaran Yojana

NTPC BADARPUR

Installed capacity720 MW

Derated Capacity705 MW LocationNew DelhiCoal SourceJharia Coal Fields Water SourceAgra Canal Beneficiary StatesDelhi

Unit Sizes3X95 MW

2X210 MW

UnitsCommissionedUnit I- 95 MW - July 1973

Unit II- 95 MW August 1974

Unit III- 95 MW March 1975

Unit IV - 210 MW December 1978

Unit V - 210 MW - December 1981

International Assistance Ownership of BTPS was transferred to NTPC with effect from

01.06.2006 through GOIs Gazette Notification.


12/64

EVOLUTION

1975-NTPC was set up in 1975 with 100% ownership by the Government ofIndia. In the last30 years, NTPC has grown into the largest power utility in India.

1997-In 1997, Government of India granted NTPC status of Navratna being one of the ninejewels of India, enhancing the powers to the Board of Directors.

2004-NTPC became a listed company with majority Government ownership of 89.5%.NTPCbecomes third largest by Market Capitalization of listed companies

2005-The company rechristened as NTPC Limited in line with its changing business portfolioand transforms itself from a thermal power utility to an integrated power utility.

2008-National Thermal Power Corporation is the largest power generation company in India.Forbes Global 2000 for 2008 ranked it 411th in the world.

2009- 3000MW installed capacity mark crossed

2010-Joint Venture Agreement executed between NTPC and NPCIL


13/64

INTRODUCTION TOTHEMAL POWER

PLANT

Introduction

Classification

Functioning


14/64

INTRODUCTION

Power Station (also referred to as generating station or power plant) is an industrial facility for

the generation of electric power. Some prefer to use the term energy center because it more

accurately describes what the plants do, which is the conversion of other forms of energy, like

chemical energy, gravitational potential energy or heat energy into electrical energy.

A coal-fired Thermal Power Plant

At the center of nearly all power stations is a generator, a rotating machine that converts

mechanical energy into electrical energy by creating relative motion between a magnetic field

and a conductor. The energy source harnessed to turn the generator varies widely. It depends

chiefly on what fuels are easily available and the types of technology that the power company has

access to.

In thermal power stations, mechanical power is produced by a heat engine, which transforms

thermal energy, often from combustion of a fuel, into rotational energy. Most thermal power

stations produce steam, and these are sometimes called steam power stations. About 80% of allelectric power is generated by use of steam turbines. Not all thermal energy can be transformed

to mechanical power, according to the second law of thermodynamics. Therefore, there is always

heat lost to the environment. If this loss is employed as useful heat, for industrial processes ordistrict heating, the power plant is referred to as a cogeneration power plant or CHP (combined

heat-and-power) plant. In countries where district heating is common, there are dedicated heatplants called heat-only boiler stations. An important class of power stations in the Middle East

uses byproduct heat for desalination of water.


15/64

CLASSIFICATIONBy fuel

Nuclear power plants use a nuclear reactor's heat to operate a steam turbine generator.

Fossil fuelled power plants may also use a steam turbine generator or in the case of

natural gas fired plants may use a combustion turbine.

Geothermal power plants use steam extracted from hot underground rocks.

Renewable energy plants may be fuelled by waste from sugar cane, municipal solidwaste, landfill methane, or other forms of biomass.

In integrated steel mills, blast furnace exhaust gas is a low-cost, although low-energydensity,fuel.

Waste heat from industrial processes is occasionally concentrated enough to use forpower generation, usually in a steam boiler and turbine.

By prime mover

Steam turbine plants use the dynamic pressure generated by expanding steam to turn the

blades of a turbine. Almost all large non-hydro plants use this system.

Gas turbine plants use the dynamic pressure from flowing gases to directly operate the

turbine. Natural-gas fuelled turbine plants can start rapidly and so are used to supply

"peak" energy during periods of high demand, though at higher cost than base-loaded

plants. These may be comparatively small units, and sometimes completely unmanned,

being remotely operated. This type was pioneered by the UK, Prince town being the

world's first, commissioned in 1959.

Combined cycle plants have both a gas turbine fired by natural gas, and a steam boiler

and steam turbine which use the exhaust gas from the gas turbine to produce electricity.

This greatly increases the overall efficiency of the plant, and many new base load powerplants are combined cycle plants fired by natural gas.

Internal combustion Reciprocating engines are used to provide power for isolated communitiesand are frequently used for small cogeneration plants. Hospitals, office

buildings, industrial plants, and other critical facilities also use them to provide backuppower in case of a power outage. These are usually fuelled by diesel oil, heavy oil,

natural gas and landfill gas.

Micro turbines, Sterling engine and internal combustion reciprocating engines are low

cost solutions for using opportunity fuels, such as landfill gas, digester gas from water

treatment plants and waste gas from oil production.


16/64

FUNCTIONINGFunctioning of thermal power plant:

In a thermal power plant, one of coal, oil or natural gas is used to heat the boiler to convert the

water into steam. The steam is used to turn a turbine, which is connected to a generator. When

the turbine turns, electricity is generated and given as output by the generator, which is then

supplied to the consumers through high-voltage power lines.

Detailed process of power generation in a thermal power plant:

1) Water intake: Firstly, water is taken into the boiler through a water source. If water isavailable in a plenty in the region, then the source is an open pond or river. If water is scarce,then

it is recycled and the same water is used over and over again.2) Boiler heating: The boiler is heated with the help of oil, coal or natural gas. A furnace is used

to heat the fuel and supply the heat produced to the boiler. The increase in temperature helps inthe transformation of water into steam.

3) Steam Turbine: The steam generated in the boiler is sent through a steam turbine. Theturbine has blades that rotate when high velocity steam flows across them. This rotation of

turbine blades is used to generate electricity.4) Generator: A generator is connected to the steam turbine. When the turbine rotates, the

generator produces electricity which is then passed on to the power distribution systems.

5) Special mountings: There is some other equipment like the economizer and air pre-heater.

An economizer uses the heat from the exhaust gases to heat the feed water. An air pre-heater

heats the air sent into the combustion chamber to improve the efficiency of the combustion

process.

6) Ash collection system: There is a separate residue and ash collection system in place to collect

all the waste materials from the combustion process and to prevent them from

escaping into the atmosphere.

There are various other monitoring systems and instruments in place to keep track of the

functioning of all the devices.


17/64

PROJECT

REPORT

OPERATION

EMD I

EMD II


18/64

Module I

OPERATION

Introduction

Steam Generator or Boiler

Steam Turbine

Electric Generator


19/64

IntroductionThe operating performance of NTPC has been considerably above the national average. The

availability factor for coal stations has increased from 85.03 % in 1997-98 to 90.09 % in 2006-

07, which compares favourably with international standards. The PLF has increased from 75.2%

in 1997-98 to 89.4% during the year 2006-07 which is the highest since the inception of NTPC.

Operation Room of Power Plant

In a Badarpur Thermal Power Station, steam is produced and used to spin a turbine that operates

a generator. Water is heated, turns into steam and spins a steam turbine which drives an electrical

generator. After it passes through the turbine, the steam is condensed in a condenser; this is

known as a Rankine cycle. The electricity generated at the plant is sent to consumers through

high-voltage power lines.

The Badarpur Thermal Power Plant has Steam Turbine-Driven Generators which has a collective

capacity of 705MW. The fuel being used is Coal which is supplied from the Jharia Coal Field inJharkhand. Water supply is given from the Agra Canal.Table: Capacity of Badarpur Thermal Power Station, New Delhi

Sr.No. Capacity No. No.of Generators Total Capacity

1. 210MW 2 420MW

2. 95MW 3 285MW

Total 705MW

There are basically three main units of a thermal power plant:

1. Steam Generator or Boiler

2. Steam Turbine

3. Electric GeneratorWe have discussed about the processes of electrical generation further.A complete detailed description of the three units is given further.


20/64

Typical Diagram of a Coal based Thermal

Power Plant

1. Cooling tower 2. Cooling water

pump

3. Transmission line (3-

phase)

4. Unit transformer (3-

phase)

5. Electric generator

(3-phase)

6. Low pressure turbine

7. Condensate

extraction pump

8. Condensor 9. Intermediate

pressure turbine

10. Steam governor

valve

11. High pressure

turbine

12. Deaerator

13. Feed heater 14. Coal conveyor 15. Coal hopper

16. Pulverised fuel

mill

17. Boiler drum 18. Ash hopper


21/64

19. Superheater 20. Forced draught

fan

21. Reheater

22. Air intake 23. Economiser 24. Air preheater

25. Precipitator 26. Induced draught 27. Chimney Stack

Coal is conveyed (14) from an external stack and ground to a very fine powder by large metal

spheres in the pulverised fuel mill (16). There it is mixed with preheated air (24) driven by the

forced draught fan (20). The hot air-fuel mixture is forced at high pressure into the boiler whereit rapidly ignites. Water of a high purity flows vertically up the tube-lined walls of the

boiler,where it turns into steam, and is passed to the boiler drum, where steam is separated fromany

remaining water. The steam passes through a manifold in the roof of the drum into the pendantsuperheater (19) where its temperature and pressure increase rapidly to around 200 bar and

540C, sufficient to make the tube walls glow a dull red. The steam is piped to the high pressureturbine (11), the first of a three-stage turbine process. A steam governor valve (10) allows for

both manual control of the turbine and automatic set-point following. The steam is exhausted

from the high pressure turbine, and reduced in both pressure and temperature, is returned to the

boiler reheater (21). The reheated steam is then passed to the intermediate pressure turbine

(9),and from there passed directly to the low pressure turbine set (6). The exiting steam, now a

little above its boiling point, is brought into thermal contact with cold water (pumped in from the

cooling tower) in the condensor (8), where it condenses rapidly back into water, creating near

vacuum-like conditions inside the condensor chest. The condensed water is then passed by a feed

pump (7) through a deaerator (12), and pre-warmed, first in a feed heater (13) powered by steamdrawn from the high pressure set, and then in the economiser (23), before being returned to the

boiler drum. The cooling water from the condensor is sprayed inside a cooling tower (1),creating

a highly visible plume of water vapor, before being pumped back to the condensor (8)in cooling

water cycle.The three turbine sets are sometimes coupled on the same shaft as the three-phase

electrical generator (5) which generates an intermediate level voltage (typically 20-25 kV). Thisis stepped up by the unit transformer (4) to a voltage more suitable for transmission (typically

250-500 kV)and is sent out onto the three-phase transmission system (3).Exhaust gas from theboiler is drawn by the induced draft fan (26) through an electrostatic precipitator (25) and is then

vented through the chimney stack (27).

Steam Generator or Boiler

The boiler is a rectangular furnace about 50 ft (15 m) on a side and 130 ft (40 m) tall. Its wallsare made of a web of high pressure steel tubes about 2.3 inches (60 mm) in diameter.

Pulverized coal is air-blown into the furnace from fuel nozzles at the four corners and it rapidly

burns, forming a large fireball at the center. The thermal radiation of the fireball heats the water

that circulates through the boiler tubes near the boiler perimeter. The water circulation rate in theboiler is three to four times the throughput and is typically driven by pumps. As the water in the

boiler circulates it absorbs heat and changes into steam at 700 F (370 C) and 3,200 psi(22.1MPa). It is separated from the water inside a drum at the top of the furnace. The saturated

steam is introduced into superheat pendant tubes that hang in the hottest part of the combustion


22/64

gases as they exit the furnace. Here the steam is superheated to 1,000 F (540 C) to prepare it forthe turbine.The steam generating boiler has to produce steam at the high purity, pressure and

temperaturerequired for the steam turbine that drives the electrical generator. The generator includes the

economizer, the steam drum, the chemical dosing equipment, and the furnace with its steam

generating tubes and the superheater coils. Necessary safety valves are located at suitable points

to avoid excessive boiler pressure. The air and flue gas path equipment include: forced draft(FD)fan, air preheater (APH), boiler furnace, induced draft (ID) fan, fly ash collectors(electrostatic

precipitator)and the flue gas stack.

Schematic diagram of a coal-fired power plant steam generator

For units over about 210 MW capacity, redundancy of key components is provided by installing

duplicates of the FD fan, APH, fly ash collectors and ID fan with isolating dampers.

Boiler Furnace and Steam Drum

Once water inside the boiler or steam generator, the process of adding the latent heat ofvaporization or enthalpy is underway. The boiler transfers energy to the water by the chemicalreaction of burning some type of fuel.The water enters the boiler through a section in the

convection pass called the economizer. From the economizer it passes to the steam drum. Oncethe water enters the steam drum it goes down,the down comers to the lower inlet water wall

headers. From the inlet headers the water rises through the water walls and is eventually turnedinto steam due to the heat being generated by the burners located on the front and rear water

walls (typically). As the water is turned into steam/vapor in the water walls, the steam/vapor onceagain enters the steam drum.


23/64

External View of an Industrial Boiler at Badarpur Thermal Power Station, New Delhi

The steam/vapour is passed through a series of steam and water separators and then dryers inside

the steam drum. The steam separators and dryers remove the water droplets from the steam andthe cycle through the water walls is repeated. This process is known as natural circulation.The

boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot blowers,water lancing and observation ports (in the furnace walls) for observation of the furnace interior.

Furnace explosions due to any accumulation of combustible gases after a trip-out

are avoided by flushing out such gases from the combustion zone before igniting the coal.The

steam drum (as well as the superheater coils and headers) have air vents and drains needed

for initial startup. The steam drum has an internal device that removes moisture from the wet

steam entering the drum from the steam generating tubes. The dry steam then flows into the

superheater coils.

Fuel Preparation System

In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into

small pieces and then conveyed to the coal feed hoppers at the boilers. The coal is next

pulverized into a very fine powder. The pulverizers may be ball mills, rotating drum grinders, orother types of grinders.


24/64

Boiler Side of the Badarpur Thermal Power Station, New Delhi

Fuel Firing System and Igniter System

From the pulverized coal bin, coal is blown by hot air through the furnace coal burners at an

angle which imparts a swirling motion to the powdered coal to enhance mixing of the coal

powder with the incoming preheated combustion air and thus to enhance the combustion.To

provide sufficient combustion temperature in the furnace before igniting the powdered coal,the

furnace temperature is raised by first burning some light fuel oil or processed natural gas (by

using auxiliary burners and igniters provide for that purpose).

A

ir PathExternal fans are provided to give sufficient air for combustion. The forced draft fan takes air

from the atmosphere and, first warming it in the air preheater for better combustion, injects it viathe air nozzles on the furnace wall.The induced draft fan assists the FD fan by drawing out

combustible gases from the furnace,maintaining a slightly negative pressure in the furnace.At thefurnace outlet, and before the furnace gases are handled by the ID fan, fine dust carried by the

outlet gases is removed to avoid atmospheric pollution. This is an environmental limitationprescribed by law, and additionally minimizes erosion of the ID fan.

Auxiliary Systems-

Fly Ash Collection

Fly ash is captured and removed from the flue gas by electrostatic precipitators located at the

outlet of the furnace and before the induced draft fan.The fly ash is periodically removed from

the collection hoppers below the precipitators . Generally, the fly ash is pneumatically

transported to storage silos for subsequent

transport by trucks or railroad cars.


25/64

Bottom Ash Collection and DisposalAt the bottom of every boiler, a hopper has been provided for collection of the bottom ash from

the bottom of the furnace. This hopper is always filled with water to quench the ash and clinkersfalling down from the furnace.Some arrangement is included to crush the clinkers and for

conveying the crushed clinkers and bottom ash to a storage site.

Boiler Make-up Water Treatment Plant and StorageSince there is continuous withdrawal of steam and continuous return of condensate to the

boiler,losses due to blow-down and leakages have to be made up for so as to maintain the desired

water level in the boiler steam drum. For this, continuous make-up water is added to the boiler

water system. The impurities in the raw water input to the plant generally consist of calcium and

magnesium salts which impart hardness to the water. Hardness in the make-up water to the boiler

will form deposits on the tube water surfaces which will lead to overheating and failure of the

tubes. Thus, the salts have to be removed from the water and that is done by a water

demineralising treatment plant (DM). A DM plant generally consists of cation, anion and mixed

bed exchangers. The final water from this process consists essentially of hydrogen ions and

hydroxide ions which is the chemical composition of pure water. The DM water, being very pure, becomes highly corrosive once it absorbs oxygen from the atmosphere because of its very high

affinity for oxygen absorption. The capacity of the DM plant is dictated by the type and quantityof salts in the raw water input.

Ash Handling System at Badarpur Thermal Power Station, New Delhi

However, some storage is essential as the DM plant may be down for maintenance. For this

purpose, a storage tank is installed from which DM water is continuously withdrawn for boilermake-up.The storage tank for DM water is made from materials not affected by corrosive

water,such as PVC.DM water make-up is generally added at the steam space of the surface

condenser (i.e., the vacuum side). This arrangement not only sprays the water but also DM water

gets deaerated, with the dissolved gases being removed by the ejector

of the condenser itself.


26/64

Steam Turbine

Steam turbines are used in all of our major coal fired power stations to drive the generators oralternators, which produce electricity. The turbines themselves are driven by steam generated in

'Boilers' or 'Steam Generators' as they are sometimes called.

Energy in the steam after it leaves the boiler is converted into rotational energy as it passes

through the turbine. The turbine normally consists of several stages with each stage consisting ofa stationary blade (or nozzle) and a rotating blade. Stationary blades convert the potential energy

of the steam (temperature and pressure) into kinetic energy (velocity) and direct the flow onto

the rotating blades. The rotating blades convert the kinetic energy into forces, caused by pressure

drop, which results in the rotation of the turbine shaft. The turbine shaft is connected to a

generator, which produces the electrical energy. The rotational speed is 3000 rpm for Indian

System (50 Hz) systems and 3600 for American (60 Hz) systems.

In a typical larger power stations, the steam turbines are split into three separate stages, the first

being the High Pressure (HP), the second the Intermediate Pressure (IP) and the third the Low

Pressure (LP) stage, where high, intermediate and low describe the pressure of the steam. After

the steam has passed through the HP stage, it is returned to the boiler to be re-heated to itsoriginal temperature although the pressure remains greatly reduced. The reheated steam then

passes through the IP stage and finally to the LP stage of the turbine.Steam turbines can be configured in many different ways. Several IP or LP stages can be

incorporated into the one steam turbine. A single shaft or several shafts coupled together may beused. Either way, the principles are the same for all steam turbines. The configuration is decided

by the use to which the steam turbine is put, co-generation or pure electricity production.

Nozzles and Blades


27/64

Steam enthalpy is converted into rotational energy as it passes through a turbine stage. A turbinestage consists of a stationary blade and a rotating blade. Stationary blades convert the potential

energy of the steam (temperature and pressure) into kinetic energy and direct the flow onto therotating blades. The rotating blades convert the kinetic energy into impulse and reaction forces

caused by pressure drop, which results in the rotation of the turbine shaft or rotor.Steam turbines

are machines which must be designed, manufactured and maintained to high tolerances so that

the design power output and availability is obtained. They are subject to a number of damagemechanisms, with two of the most important being:

Erosion due to Moisture: - The presence of water droplets in the last stages of a turbine causes

erosion to the blades.

Solid Particle Erosion: - The entrainment of erosive materials from the boiler in the steam causes

wear to the turbine blades.

Cogeneration Cycles

In cogeneration cycles, steam is typically generated at a higher temperature and pressure than

required for a particular industrial process. The steam is expanded through a turbine to produce

electricity and the resulting extractions at the discharge are at the temperature and pressurerequired by the process.

Bearings and Lubrication

Two types of bearings are used to support and locate the rotors of steam turbines:Journal bearings are used to support the weight of the turbine rotors. A journal bearing consists

of two half-cylinders that enclose the shaft and are internally lined with Babbitt, ametal alloy usually consisting of tin, copper and antimony; and

Thrust bearings axially locate the turbine rotors.

High-pressure oil is injected into the bearings to provide lubrication. The oil is carefully filtered

to remove solid particles.

Shaft Seals

The shaft seal on a turbine rotor consist of a series of ridges and groves around the rotor and its

housing which present a long, tortuous path for any steam leaking through the seal. The seal

therefore does not prevent the steam from leaking, merely reduces the leakage to a minimum.

Turning Gear

Large steam turbines are equipped with "turning gear" to slowly rotate the turbines after they

have been shut down and while they are cooling. This evens out the temperature distribution

around the turbines and prevents bowing of the rotors.

VibrationThe balancing of the large rotating steam turbines is a critical component in ensuring the reliable

operation of the plant. Most large steam turbines have sensors installed to measure the movement

of the shafts in their bearings. This condition monitoring can identify many potential problemsand allows the repair of the turbine to be planned before the problems become serious.


28/64

Electric GeneratorThe steam turbine-driven generators have auxiliary systems enabling them to work satisfactorily

and safely. The steam turbine generator being rotating equipment generally has a heavy, large

diameter shaft. The shaft therefore requires not only supports but also has to be kept in position

while running. To minimize the frictional resistance to the rotation, the shaft has a number of

bearings. The bearing shells, in which the shaft rotates, are lined with a low friction material like

Babbitt metal. Oil lubrication is provided to further reduce the friction between shaft and bearingsurface and to limit the heat generated.

A 95 MW Generator at Badarpur Thermal Power Station, New Delhi

Turning Gear

Turning gear is the term used for the mechanism provided for rotation of the turbine generator

shaft at a very low speed (about one revolution per minute) after unit stoppages for any reason.

Once the unit is "tripped" (i.e., the turbine steam inlet valve is closed), the turbine starts slowingor "coasting down". When it stops completely, there is a tendency for the turbine shaft to deflect

or bend if allowed to remain in one position too long. This deflection is because the heat insidethe turbine casing tends to concentrate in the top half of the casing, thus making the top half

portion of the shaft hotter than the bottom half. The shaft therefore warps or bends by millionthsof inches, only detectable by monitoring eccentricity meters.But this small amount of shaft

deflection would be enough to cause vibrations and damage the entire steam turbine generatorunit when it is restarted. Therefore, the shaft is not permitted to come to a complete stop by a

mechanism known as "turning gear" that automatically takes over to rotate the unit at a preset

low speed.If the unit is shut down for major maintenance, then the turning gear must be kept in

service until the temperatures of the casings and bearings are sufficiently low.

Condenser

The surface condenser is a shell and tube heat exchanger in which cooling water is circulated

through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is


29/64

cooled and converted to condensate (water) by flowing over the tubes as shown in the adjacentdiagram.

A Typical Water Cooled Condenser

For best efficiency, the temperature in the condenser must be kept as low as practical in order toachieve the lowest possible pressure in the condensing steam. Since the condenser temperature

can almost always be kept significantly below 100oC where the vapor pressure of water is much

less than atmospheric pressure, the condenser generally works under vacuum. Plants operating inhot climates may have to reduce output if their source of condenser cooling water becomes

warmer; unfortunately this usually coincides with periods of high electrical demand for airconditioning. The condenser generally uses either circulating cooling water from a cooling tower

to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.

Feedwater HeaterA Rankine cycle with a two-stage steam turbine and a single feedwater heater.In the case of a

conventional steam-electric power plant utilizing a drum boiler, the surface condenser removes

the latent heat of vaporization from the steam as it changes states from vapour to liquid. The heatcontent in the steam is referred to as Enthalpy. The condensate pump then pumps the condensate

water through a feedwater heater. The feedwater heating

equipment then raises the temperature of the water by utilizing extraction steam from various

stages of the turbine.


30/64

A Rankine cycle with a two-stage steam turbine and a single feedwater heater

Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore

improves the thermodynamic efficiency of the system.[9] This reduces plant operating costs and

also helps to avoid thermal shock to the boiler metal when the feedwater is introduced back into

the steam cycle.

Superheater

As the steam is conditioned by the drying equipment inside the drum, it is piped from the upper

drum area into an elaborate set up of tubing in different areas of the boiler. The areas known as

superheater and reheater. The steam vapor picks up energy and its temperature is nowsuperheated above the saturation temperature. The superheated steam is then piped through the

main steam lines to the valves of the high pressure turbine.

Deaerator

A steam generating boiler requires that the boiler feed water should be devoid of air and otherdissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal. Generally, power stations use a deaerator to provide for the removal of air and other dissolved gases from

the boiler feedwater.


31/64

Auxiliary Systems

Oil System

An auxiliary oil system pump is used to supply oil at the start-up of the steam turbine generator.It

supplies the hydraulic oil system required for steam turbine's main inlet steam stop valve, the

governing control valves, the bearing and seal oil systems, the relevant hydraulic relays and othermechanisms.

Generator Heat Dissipation

The electricity generator requires cooling to dissipate the heat that it generates. While small units

may be cooled by air drawn through filters at the inlet, larger units generally require special

cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, is used because it has the

highest known heat transfer coefficient of any gas and for its low viscosity which

reduces windage losses. This system requires special handling during start-up, with air in thechamber first displaced by carbon dioxide before filling with hydrogen. This ensures that the

highly flammable hydrogen does not mix with oxygen in the air.The hydrogen pressure inside thecasing is maintained slightly higher than atmospheric pressure to avoid outside air ingress. The

hydrogen must be sealed against outward leakage where the shaft emerges from the casing.Mechanical seals around the shaft are installed with a very small annular gap to avoid rubbing

between the shaft and the seals. Seal oil is used to prevent the hydrogen gas leakage toatmosphere. The generator also uses water cooling. Demineralized water of low conductivity is

used.

Generator High Voltage System

The generator voltage ranges from 10.5 kV in smaller units to 15.75 kV in larger units. The

generator high voltage leads are normally large aluminum channels because of their high current

as compared to the cables used in smaller machines. They are enclosed in well-grounded

aluminum bus ducts and are supported on suitable insulators. The generator high voltage

channels are connected to step-up transformers for connecting to a high voltage electrical

substation (of the order of 220 kV) for further transmission by the local power grid. Thenecessary protection and metering devices are included for the high voltage leads. Thus, the

steam turbine generator and the transformer form one unit

Other Systems-

Monitoring and Alarm systemMost of the power plants operational controls are automatic. However, at times, manual

intervention may be required. Thus, the plant is provided with monitors and alarm systems thatalert the plant operators when certain operating parameters are seriously deviating from their

normal range.

MAIN GENERATOR

Maximum continuous KVA rating 24700KVA

Maximum continuous KW 210000KW

Rated terminal voltage 15750V

Rated Stator current 9050 A


32/64

Rated Power Factor 0.85 lag

Excitation current at MCR Condition 2600 A

Slip-ring Voltage at MCR Condition 310 V

Rated Speed 3000 rpm

Rated Frequency 50 Hz

Short circuit ratio 0.49

Efficiency at MCR Condition 98.4%

Direction of rotation viewed Anti Clockwise

Phase Connection Double Star

MAIN TURBINE DATA

Rated output of Turbine

210 MW

Rated speed of turbine 3000 rpm

Rated pressure of steam before emergency 130 kg/cm^2

Stop valve rated live steam temperature 535 degree Celsius

Rated steam temperature after reheat at inlet to receptor

valve535 degree Celsius

Steam flow at valve wide open condition 670 tons/hour

Rated quantity of circulating water through condenser 27000 cm/hour

1. For cooling water temperature (degree Celsius) 24,27,30,33

1.Reheated steam pressure at inlet of interceptor valve in

kg/cm^2 ABS23,99,24,21,24,49,24.82

2.Steam flow required for 210 MW in ton/hour 68,645,652,662

3.Rated pressure at exhaust of LP turbine in mm of Hg 19.9,55.5,65.4,67.7


33/64

An Engineer monitoring the various parameters at NTPC, New Delhi

Battery Supplied Emergency Lighting & Communication

A central battery system consisting of lead acid cell units is provided to supply emergency

electric power, when needed, to essential items such as the power plant's control systems,

communication systems, turbine lube oil pumps, and emergency lighting. This is essential for a

safe, damage-free shutdown of the units in an emergency situation.


34/64

Module II

EMD I

Coal Handling Plant

Motors

Switchgear

High Tension Switchgear

Direct On Line Starter


35/64

It is responsible for maintenance of:

1. Boiler side motors

2. Turbine side motors

3. Outside motors

4. Switchgear

1. Boiler side motors:

For 1, units 1, 2, 3

1.1D Fans 2 in no.

2.F.D Fans 2 in no.

3.P.A.Fans 2 in no.

4.Mill Fans 3 in no.

5.Ball mill fans 3 in no.

6.RC feeders 3 in no.

7.Slag Crushers 5 in no.

8.DM Make up Pump 2 in no.

9.PC Feeders 4 in no.

10.Worm Conveyor 1 in no.

11.Furnikets 4 in no.

For stage units 1, 2, 3

1.I.D Fans 2 in no.

2.F.D Fans 2 in no.

3.P.A Fans 2 in no.

4.Bowl Mills 6 in no.

5.R.C Feeders 6 in no.

6.Clinker Grinder 2 in no.

7.Scrapper 2 in no.

8.Seal Air Fans 2 in no.

9.Hydrazine and Phosphorous Dozing 2 in no.

2/3 in no.


36/64

Coal Handling PlantCoal is delivered by highway truck, rail, barge or collier ship. Some plants are even built near

coal mines and coal is delivered by conveyors. A large coal train called a "unit train" may be a

kilometers (over a mile) long, containing 60 cars with 100 tons of coal in each one, for a total

load of 6,000 tons. A large plant under full load requires at least one coal delivery this size every

day. Plants may get as many as three to five trains a day, especially in "peak season", during the

summer months when power consumption is high. A large thermal power plant such as the

Badarpur Thermal Power Station, New Delhi stores several million tons of coal for use whenthere is no wagon supply.

Coal Handling Plant Layout

The unloader includes a train positioner arm that pulls the entire train to position each car over a

coal hopper. The dumper clamps an individual car against a platform that swivels the car upsidedown to dump the coal.


37/64

Layout of Coal Handling Plant at Badarpur Thermal Power Station, New Delhi

Coal is prepared for use by crushing the rough coal to pieces less than 2 inches (50 mm) in

size.The coal is then transported from the storage yard to in-plant storage silos by rubberized

conveyor belts at rates up to 4,000 tons/hour.In plants that burn pulverized coal, silos feed coal

pulverizers (coal mill) that take the larger 2 inch pieces grind them into the consistency of face

powder, classify them, and mixes them with primary combustion air which transports the coal to

the furnace and preheats the coal to drive off excess moisture content.

Run-Of-Mine (ROM) CoalThe coal delivered from the mine that reports to the Coal Handling Plant is called Run-of-

mine,coal. This is the raw material for the CHP, and consists of coal, rocks,minerals and

contamination. Contamination is usually introduced by the mining process.ROM coalcan have a large variability of moisture and maximum particle size.

Coal HandlingCoal needs to be stored at various stages of the preparation process, and conveyed around the

CHP facilities. Coal handling is part of the larger field of bulk material handling, and is a

complex and vital part of the CHP.

Stockpiles

Stockpiles provide surge capacity to various parts of the CHP. ROM coal is delivered with large

variations in production rate of tonnes per hour (tph). A ROM stockpile is used to allow the

washplant to be fed coal at lower, constant rate.


38/64

Coal Handling Division of Badarpur Thermal Power Station, New Delhi

A simple stockpile is formed by machinery dumping coal into a pile, either from dump

trucks,pushed into heaps with bulldozers or from conveyor booms.Taller and wider stockpiles

reduce the land area required to store a set tonnage of coal.

Coal Sampling

Sampling of coal is an important part of the process control in the CHP. A grab sample is a

oneoff sample of the coal at a point in the process stream, and tends not to be very representative.

Aroutine sample is taken at a set frequency, either over a period of time or per shipment.

ScreeningScreens are used to group process particles into ranges by size. These size ranges are also called

grades. Screens can be static, or mechanically vibrated.

Magnetic Separation

Magnetic separators shall be used in coal conveying systems to separate tramp iron from the coal.

Basically, two types are available. One type incorporates permanent or electromagnets into thehead pulley of a belt conveyor. The tramp iron clings to the belt as it goes around the pulley drum

and falls off into a collection hopper or trough after the point at which coal is charged from thebelt. The other type consists of permanent or electromagnets incorporated into a belt conveyor

that is suspended above a belt conveyor carrying coal. The tramp iron is pulled from the movingcoal to the face of the separating conveyor, which in turn holds and carries the tramp iron to a

collection hopper or trough. Magnetic separators shall be used just ahead of the coal crusher.Coal Crusher

Before the coal is sent to the plant it has to be ensured that the coal is of uniform size, and so it is

passed through coal crushers. Also power plants using pulverized coal specify a maximum coal

size that can be fed into the pulverizer and so the coal has to be crushed to the specified size

using the coal crusher. Rotary crushers are very commonly used for this purpose as they can

provide a continuous flow of coal to the pulverizer.


39/64

PulverizerMost commonly used pulverizer is the Boul Mill. The arrangement consists of 2 stationary rollers

and a power driven baul in which pulverization takes place as the coal passes through the sides ofthe rollers and the baul. A primary air induced draught fan draws a stream of heated air through

the mill carrying the pulverized coal into a stationary classifier at the top of the pulverizer.

An external view of a Coal Pulverizer

Advantages of Pulverized Coal

Pulverized coal is used for large capacity plants.It is easier to adapt to fluctuating load as there are no limitations on the combustion capacity.

Coal with higher ash percentage cannot be used without pulverizing because of the problem oflarge amount ash deposition after combustion.

Increased thermal efficiency is obtained through pulverization.The use of secondary air in the combustion chamber along with the powered coal helps in

creating turbulence and therefore uniform mixing of the coal and the air during combustion.

Greater surface area of coal per unit mass of coal allows faster combustion as more coal isexposed to heat and combustion.The boiler can be easily started from cold condition in case of emergency.

The furnace volume required is less as the turbulence caused aids in complete combustion of

the coal with minimum travel of the particles.

The pulverized coal is passed from the pulverizer to the boiler by means of the primary air that is

used not only to dry the coal but also to heat is as it goes into the boiler. The secondary air is

used to provide the necessary air required for complete combustion.The coal is sent into the

boiler through burners. A very important and widely used type of burner arrangement is the

Tangential Firing arrangement.

Tangential Burners:The tangential burners are arranged such that they discharge the fuel air mixture tangentially toan imaginary circle in the center of the furnace. The swirling action produces sufficient

turbulence in the furnace to complete the combustion in a short period of time and avoid thenecessity of producing high turbulence at the burner itself. High heat release rates are possible

with this method of firing.The burners are placed at the four corners of the furnace. At theBadarpur ThermalPower Station five sets of such burners are placed one above the other to form

six firing zones.


40/64

Ash HandlingThe ever increasing capacities of boiler units together with their ability to use low grade high ash

content coal have been responsible for the development of modern day ash handling systems.TheHydraulic Ash handling system is used at the Badarpur Thermal Power Station.

Hydraulic Ash Handling System

The hydraulic system carried the ash with the flow of water with high velocity through a channeland finally dumps into a sump. The ash is carried along with the water and they are separated at

the sump.NEW COAL HANDLING PLANT (N.C.H.P)

The old coal handling plant caters to the need of units 2,3,4,5 and 1 whereas the latter supplies

coal to units 4 and V.O.C.H.P. supplies coal to second and third stages in the advent coal to

usable form to (crushed) form its raw form and send it to bunkers, from where it is send to

furnace.

Major Components

1. Wagon Tippler: - Wagons from the coal yard come to the tippler and are emptied here. The process is

performed by a slip ring motor of rating: 55 KW, 415V, 1480 RPM. This motor turns the wagon by 135degrees and coal falls directly on the conveyor through vibrators. Tippler has raised lower system which

enables is to switch off motor when required till is wagon back to its original position. It is titled byweight balancing principle. The motor lowers the hanging balancing weights, which in turn tilts the

conveyor. Estimate of the weight of the conveyor is made through hydraulic weighing machine.2. Conveyor: - There are 14 conveyors in the plant. They are numbered so that their function can beeasily demarcated. Conveyors are made of rubber and more with a speed of 250-300m/min. Motors

employed for conveyors has a capacity of 150 HP. Conveyors have a capacity of carrying coal at the rate

of 400 tons per hour. Few conveyors are double belt, this is done for imp. Conveyors so that if a beltdevelops any problem the process is not stalled. The conveyor belt has a switch after every 25-30 m on

both sides so stop the belt in case of emergency. The conveyors are 1m wide, 3 cm thick and made of

chemically treated vulcanized rubber. The max angular elevation of conveyor is designed such as never toexceed half of the angle of response and comes out to be around 20 degrees.

3. Zero Speed Switch:-It is safety device for motors, i.e., if belt is not moving and the motor is on the

motor may burn. So to protect this switch checks the speed of the belt and switches off the motor whenspeed is zero.

4. Metal Separators: - As the belt takes coal to the crusher, No metal pieces should go alongwith coal. To achieve this objective, we use metal separators. When coal is dropped to the

crusher hoots, the separator drops metal pieces ahead of coal. It has a magnet and a belt and the

belt is moving, the pieces are thrown away. The capacity of this device is around 50 kg. .The

CHP is supposed to transfer 600 tons of coal/hr, but practically only 300-400 tons coal is transfer

5. Crusher: - Both the plants use TATA crushers powered by BHEL. Motors. The crusher is of

ring type and motor ratings are 400 HP, 606 KV. Crusher is designed to crush the pieces to 20

mm size i.e. practically considered as the optimum size of transfer via conveyor.

6. Rotatory Breaker: - OCHP employs mesh type of filters and allows particles of 20mm size to

go directly to RC bunker, larger particles are sent to crushes. This leads to frequent clogging.

NCHP uses a technique that crushes the larger of harder substance like metal impurities easing

the load on the magnetic separators.


41/64

MILLING SYSTEM

1. RC Bunker: - Raw coal is fed directly to these bunkers. These are 3 in no. per boiler. 4 & tons of coal are fed in 1 hr. the depth of bunkers is 10m.

2. RC Feeder: - It transports pre crust coal from raw coal bunker to mill. The quantity of raw

coal fed in mill can be controlled by speed control of aviator drive controlling damper and aviatorchange.

3. Ball Mill: - The ball mill crushes the raw coal to a certain height and then allows it to fall

down. Due to impact of ball on coal and attraction as per the particles move over each other as

well as over the Armor lines, the coal gets crushed. Large particles are broken by impact and full

grinding is done by attraction. The Drying and grinding option takes place simultaneously inside

the mill.

4. Classifier:- It is an equipment which serves separation of fine pulverized coal particles

medium from coarse medium. The pulverized coal along with the carrying medium strikes theimpact plate through the lower part. Large particles are then transferred to the ball mill.

5. Cyclone Separators: - It separates the pulverized coal from carrying medium. The mixture of

pulverized coal vapour caters the cyclone separators.

6. The Tturniket: - It serves to transport pulverized coal from cyclone separators to pulverizedcoal bunker or to worm conveyors. There are 4 turnikets per boiler.

7. Worm Conveyor: - It is equipment used to distribute the pulverized coal from bunker of one

system to bunker of other system. It can be operated in both directions.

8. Mills Fans: - It is of 3 types:

Six in all and are running condition all the time.

(a) ID Fans: - Located between electrostatic precipitator and chimney.

Type-radical

Speed-1490 rpm

Rating-300 KW

Voltage-6.6 KV

Lubrication-by oil

(b) FD Fans: - Designed to handle secondary air for boiler. 2 in number and provide ignition of

coal.

Type-axial

Speed-990 rpmRating-440 KWVoltage-6.6 KV

(c)Primary Air Fans: - Designed for handling the atmospheric air up to 50 degrees Celsius, 2 in

number

And they transfer the powered coal to burners to firing.


42/64

Type-Double suction radialRating-300 KW

Voltage-6.6 KVLubrication-by oil

Type of operation-continuous

9. Bowl Mill: - One of the most advanced designs of coal pulverizes presently manufactured.

Motor specification squirrel cage induction motor

Rating-340 KW

Voltage-6600KV

Curreen-41.7A

Speed-980 rpm

Frequency-50 Hz

No-load current-15-16 A

NCHP

1. Wagon Tippler:-

Motor Specification(i) H.P 75 HP

(ii) Voltage 415, 3 phase(iii) Speed 1480 rpm

(iv) Frequency 50 Hz

(v) Current rating 102 A

2. Coal feed to plant:-

Feeder motor specification

(i) Horse power 15 HP

(ii) Voltage 415V,3 phase

(iii) Speed 1480 rpm

(iv) Frequency 50 Hz

3. Conveyors:-10A, 10B

11A, 11B

12A, 12B13A, 13B14A, 14B

15A, 15B

16A, 16B

17A, 17B

18A, 18B

4. Transfer Point 6


43/64

5. Breaker House

6. Rejection House

7. Reclaim House

8. Transfer Point 7

9. Crusher House

10. Exit

The coal arrives in wagons via railways and is tippled by the wagon tipplers into the hoppers. If

coal is oversized (>400 mm sq) then it is broken manually so that it passes the hopper mesh.

From the hopper mesh it is taken to the transfer point TP6 by conveyor 12A ,12B which takes the

coal to the breaker house , which renders the coal size to be 100mm sq. the stones which are not

able to pass through the 100mm sq of hammer are rejected via conveyors 18A,18B to therejection house . Extra coal is to sent to the reclaim hopper via conveyor 16. From breaker house

coal is taken to the TP7 via Conveyor 13A, 13B. Conveyor 17A, 17B also supplies coal fromreclaim hopper, From TP7 coal is taken by conveyors 14A, 14B to crusher house whose function

is to render the size of coal to 20mm sq. now the conveyor labors are present whose function is torecognize and remove any stones moving in the conveyors . In crusher before it enters the

crusher. After being crushed, if any metal is still present it is taken care of by metal detectorsemployed in conveyor 10.


44/64

ELECTRIC MOTORSAn electric motor uses electrical energy to produce mechanical energy. The reverse process that

of using mechanical energy to produce electrical energy is accomplished by a generator or

dynamo.

A High Power Electric Motor

Categorization of Electric Motors

The classic division of electric motors has been that of Direct Current (DC) types vs AlternatingCurrent (AC) types.There is a clearer distinction between a synchronous motor and asynchronous

types. In the synchronous types, the rotor rotates in synchrony with the oscillating field or current

(eg.permanent magnet motors). In contrast, an asynchronous motor is designed to slip; the most

ubiquitous example being the common AC induction motor which must slip in order to generate

torque.

AC Motor

Internal View of AC Motors


45/64

An AC motor is an electric motor that is driven by an alternating current. It consists of two basicparts, an outside stationary stator having coils supplied with AC current to produce a rotating

magnetic field, and an inside rotor attached to the output shaft that is given a torque by therotating field.There are two types of AC motors, depending on the type of rotor used. The first is

the synchronous motor, which rotates exactly at the supply frequency. The magnetic field on the

rotor is either generated by current delivered through sliprings or a by a permanent magnet.

The second type is the induction motor, which turns slightly slower than the supplyfrequency.The magnetic field on the rotor of this motor is created by an induced current.

Synchronous Motor

A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing

magnets at the same rate as the alternating current and resulting magnetic field which drives it.

Another way of saying this is that it has zero slip under usual operating conditions.Contrast this

with an induction motor, which must slip in order to produce torque.Sometimes a synchronous

motor is used, not to drive a load, but to improve the power factor on

the local grid it's connected to. It does this by providing reactive power to or consuming reactive

power from the grid. Electrical power plants almost always use synchronous generators because

it's very important to keep the frequency constant at which the generator is connected.Advantages

Synchronous motors have the following advantages over non-synchronous motors:Speed is independent of the load, provided an adequate field current is applied.

Their power factor can be adjusted to unity by using a proper field current relative to the load.Also, a "capacitive" power factor, (current phase leads voltage phase), can be obtained by

increasing this current slightly, which can help achieve a better power factor correction for thewhole installation.

Their construction allows for increased electrical efficiency when a low speed is required

Induction Motor

An induction motor (IM) is a type of asynchronous AC motor where power is supplied to the

rotating device by means of electromagnetic induction.An electric motor converts electrical

power to mechanical power in its rotor (rotating part).An induction motor is sometimes called a

rotating transformer because the stator(stationary part) is essentially the primary side of the

transformer and the rotor (rotating part) is the secondary side.

Induction motors are now the preferred choice for industrial motors due to their rugged

construction and lack of brushes (which are needed in most DC Motors)

Construction

The stator consists of wound 'poles' that carry the supply current that induces a magnetic field in

the conductor. The number of 'poles' can vary between motor types but the poles are always inpairs (i.e. 2, 4, 6 etc). There are two types of rotor:

1. Squirrel-cage rotor2. Slip ring rotor

The most common rotor is a squirrel-cage rotor. It is made up of bars of either solid copper (most

common) or aluminum that span the length of the rotor, and are connected through a ring at eachend. The rotor bars in squirrel-cage induction motors are not straight, but have some skew toreduce noise and harmonics.

Principle of Operation

The basic difference between an induction motor and a synchronous AC motor is that in the latter

a current is supplied onto the rotor. This then creates a magnetic field which, through magnetic

interaction, links to the rotating magnetic field in the stator which in turn causes the rotor to turn.

It is called synchronous because at steady state the speed of the rotor is the same as the speed of

the rotating magnetic field in the stator.


46/64

By way of contrast, the induction motor does not have any direct supply onto the rotor; instead,asecondary current is induced in the rotor. To achieve this, stator windings are arranged around

the rotor so that when energised with a polyphase supply they create a rotating magnetic fieldpattern which sweeps past the rotor. This changing magnetic field pattern can induce currents in

the rotor conductors. These currents interact with the rotating magnetic field created by the stator

and the rotor will turn. However, for these currents to be induced, the speed of the physical rotor

and the speed of the rotating magnetic field in the stator must be different, or else the magneticfield will not be

moving relative to the rotor conductors and no currents will be induced. If by some chance this

happens, the rotor typically slows slightly until a current is re-induced and then the rotor

continues as before. This difference between the speed of the rotor and speed of the rotating

magnetic field in the stator is called slip. It has no unit and the ratio between the relative speed of

the magnetic field as seen by the rotor to the speed of the rotating field. Due to this an induction

motor is sometimes referred to as an asynchronous machine.

Types:

1. Squirrel cage induction motor

2. Slip ring induction motor


47/64

SWITCHGEARThe term switchgear, used in association with the electric power system, or grid, refers to the

combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical

equipment. Switchgear is used both to de-energize equipment to allow work to be done and to

clear faults downstream.

Today, oil-filled equipment has largely been replaced by air-blast, vacuum, or SF6 equipment,allowing large currents and power levels to be safely controlled by automatic equipment

incorporating digital controls,mrotection, metering and communications.

A View of Switchgear at a Power Plant

TypesA piece of switchgear may be a simple open air isolator switch or it may be insulated by some

other substance. An effective although more costly form of switchgear is "gas insulated

switchgear" (GIS), where the conductors and contacts are insulated by pressurized (SF6) sulfurhexafluoride gas. Other common types are oil [or vacuum] insulated switchgear.

Circuit breakers are a special type of switchgear that are able to interrupt fault currents. Their

construction allows them to interrupt fault currents of many hundreds or thousands of amps. The

quenching of the arc when the contacts open requires careful design, and falls into four types:Oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil through the arc.

At badarpur

Type-HKH 12/1000c Rated Voltage-66 KV

Normal Current-1250A Frequency-5Hz

Breaking Capacity-3.4+KA Symmetrical 3.4+KA Asymmetrical

360 MVA Symmetrical

Operating Coils-CC 220 V/DC

FC 220V/DC

Motor Voltage-220 V/DC

Gas (SF6) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon

the dielectric strength of the SF6 to quench the stretched arc.


48/64

At badarpur Circuit Breakers-HPA

Standard-1 EC 56 Rated Voltage-12 KV

Insulation Level-28/75 KV

Rated Frequency-50 Hz

Breaking Current-40 KA Rated Current-1600 A

Making Capacity-110 KA

Rated Short Time Current 1/3s -40 A

Mass Approximation-185 KG

Auxiliary Voltage

Closing Coil-220 V/DC

Opening Coil-220 V/DC

Motor-220 V/DC

SF6 Pressure at 20 Degree Celsius-0.25 KG

SF6 Gas Per pole-0.25 KG

Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the

contact material).At badarpur

Rated frequency-50 Hz

Rated making Current-10 Peak KA

Rated Voltage-12 KV

Supply Voltage Closing-220 V/DC

Rated Current-1250 A

Supply Voltage Tripping-220 V/DC

Insulation Level-IMP 75 KVP

Rated Short Time Current-40 KA (3 SEC)

Weight of Breaker-8 KG

Air circuit breakers may use compressed air to blow out the arc.

Circuit breakers are usually able to terminate all current flow very quickly: typically between30ms and 150 ms depending upon the age and construction of the device.

FunctionsOne of the basic functions of switchgear is protection, which is interruption of short-circuit and

overload fault currents while maintaining service to unaffected circuits. Switchgear also provides

isolation of circuits from power supplies. Switchgear also is used to enhance system availabilityby allowing more than one source to feed a load.Safety

To help ensure safe operation sequences of switchgear, trapped key interlocking provides

predefined scenarios of operation.


49/64

HIGH TENSION SWITCHGEARHigh voltage switchgear is any switchgear and switchgear assembly of rated voltage higher than

1000 volts. High voltage switchgear is any switchgear used to connect or to disconnect a part of a

high voltage power system. These switchgears are essential elements for the protection and for a

safety operating mode without interruption of a high voltage power system.The high voltage is avoltage above 1000 V for alternating current and above 1500 V for direct current.

High Tension Switchgear of a Thermal Power Plant

Functional Classification

Disconnectors and Earthing Switches

They are above all safety devices used to open or to close a circuit when there is no current

through them. They are used to isolate a part of a circuit, a machine, a part of an overhead-line

or an underground line for the operating staff to access it without any danger.The opening of the

line isolator or busbar section isolator is necessary for the safety but it is not enough. Grounding

must be done at the upstream sector and the downstream sector on the device which they want to

intervene.

Fuses

The fuses can interrupt automatically a circuit with an overcurrent flowing in it for a fixedtime.The current interrupting is got by the fusion of an electrical conductor which is graded.They

are mainly used to protect against the short-circuits. They limit the peak value of the faultcurrent.

In three-phase electric power, they only eliminate the phases where the fault current is

flowing,which is a risk for the devices and the people.

Circuit Breaker

A high voltage circuit breaker is capable of making, carrying and breaking currents under the

rated voltage (the maximal voltage of the power system which it is protecting) :Under normal


50/64

circuit conditions, for example to connect or disconnect a line in a power system; Under specifiedabnormal circuit conditions especially to eliminate a short circuit. From its characteristics, a

circuit breaker is the protection device essential for a high voltage power system, because it is theonly one able to interrupt a short circuit current and so to avoid the others devices to be damaged

by this short circuit.

To operate on long lines, the circuit breakers are equipped with a closing resistor to limit the

overvoltages.

DIRECT ON LINE STARTERA direct on line starter, often abbreviated DOL starter, is a widely-used starting method of

electric motors.There are many types of motor starters, the simplest of which is the DOL starter.A motor starter is an electrical/electronic circuit composed of electro-mechanical and electronic

devices which are employed to start and stop an electric motor. Regardless of the motor type(AC or DC), the types of starters differ depending on the method of starting the motor. A DOL

starter connects the motor terminals directly to the power supply. Hence, the motor is subjectedto the full voltage of the power supply. Consequently, high starting current flows through the

motor. This type of starting is suitable for small motors below 5 hp (3.75 kW). Reduced-voltagestarters are employed with motors above 5 hp.

Internal View of a Direct On Line Starter

Major ComponentsThere are four major components of a Direct On Line Starter. They are given as follows:

1. Switch2. Fuse

3. Conductor (Electromagnetic)4. Thermal Overload Relay (Heat & Temperature)

According to our desire and use of work, we can use auxiliary components in a DOL Starter.

Motor Direction ReversalChanging the direction of a 3-Phase Squirrel-Cage Motor requires swapping any two phases.


51/64

Module II

EMD II

Generator

Protection

Transformer


52/64

GENERATORSThe basic function of the generator is to convert mechanical power, delivered from the shaft of

the turbine, into electrical power. Therefore a generator is actually a rotating mechanical energy

converter. The mechanical energy from the turbine is converted by means of a rotating magnetic

field produced by direct current in the copper winding of the rotor or field, which generates

three-phase alternating currents and voltages in the copper winding of the stator (armature). The

stator winding is connected to terminals, which are in turn connected to the power system for

delivery of the output power to the system.

The class of generator under consideration is steam turbine-driven generators, commonly calledturbo generators.The generators particular to this category are of the two- and four-pole design

employing round-rotors.At Badarpur Thermal Power Station 3000 rpm, 50 Hz generators areused of capacities 210 MW and 95 MW.

As the system load demands more active power from the generator, more steam (or fuel in acombustion turbine) needs to be admitted to the turbine to increase power output. Hence more

energy is transmitted to the generator from the turbine, in the form of a torque.The higher the power output, the higher the torque between turbine and generator.The power output of the

generator generally follows the load demand from the system.Therefore the voltages and currentsin the generator are continually changing based on the load demand. The generator design must

be able to cope with large and fast load changes, which show up inside the machine as changes in

mechanical forces and temperatures. The design must therefore incorporate electrical current-

carrying materials (i.e., copper), magnetic flux-carrying materials (i.e., highly permeable steels),

insulating materials (i.e., organic), structural members (i.e., steel and organic), and cooling media

(i.e., gases and liquids), all working together under the operating conditions of a turbo generator.

Since the turbo generator is a synchronous machine, it operates at one very specific speed to

produce a constant system frequency of 50 Hz, depending on the frequency of the grid to which it

is connected. As a synchronous machine, a turbine generator employs a steady magnetic flux

passing radially across an air gap that exists between the rotor and the stator.This flux pattern

rotates

with the rotor, as it spins at its synchronous speed. The rotating magnetic field moves past athree-phase symmetrically distributed winding installed in the stator core, generating an

alternating voltage in the stator winding. The voltage waveform created in each of the threephases of the stator winding is very nearly sinusoidal. The output of the stator winding is the

three-phase power, delivered to the power system at the voltage generated in the statorwinding.In addition to the normal flux distribution in the main body of the generator, there are

stray fluxes at the extreme ends of the generator that create fringing flux patterns and induce

stray losses in the generator. The stray fluxes must be accounted for in the overall design.

Generators are made up of two basic members, the stator and the rotor, but the stator and rotor

are each constructed from numerous parts themselves. Rotors are the high-speed rotating member

of the two, and they undergo severe dynamic mechanical loading as well as the electromagnetic

and thermal loads.

These components are very carefully designed for high-stress operation. The stator isstationary,as the term suggests, but it also sees significant dynamic forces in terms of vibrationand torsional loads, as well as the electromagnetic, thermal, and high-voltage loading. The most

critical component of the stator is arguably the stator winding because it is a very high cost itemand it must be designed to handle all of the harsh effects described above. Most stator problems

occur with the winding.STATOR

The stator winding is made up of insulated copper conductor bars that are distributed around the

inside diameter of the stator core, in equally spaced slots in the core to ensure symmetrical flux


53/64

linkage with the field produced by the rotor. Each slot contains two conductor bars, one on top ofthe other. These are generally referred to as top and bottom bars. Top bars are the ones nearest

the slot opening (just under the wedge) and the bottom bars are the ones at the slot bottom. Thecore area between slots is generally called a core tooth.

The stator winding is then divided into three phases, which are almost always wye

connected.Wye connection is done to allow a neural grounding point and for relay protection of

the winding. The three phases are connected to create symmetry between them in the 360 degreearc of the stator. The distribution of the winding is done in such a way as to produce a 120

0

difference in voltage peaks from one phase to the other, hence the term three-phase

voltage. The parallels in all of the phases are essentially equal on average, in their performance

in the machine. Therefore, they each seeequal voltage and current, magnitudes and phase

angles, when averaged over one alternating cycle.

The stator bars in any particular phase group are arranged such that there are parallel paths,which

overlap between top and bottom bars.

Stator

The pitch is the number slots that the stator bars have to reach in the stator bore arc, separatingthe two bars to be connected. This is always less than 180 degrees.

The distribution factor is used to minimize the harmonic content of the generated voltage.The currents normally flowing in large turbo generators can be in the order of thousands of

amperes. Due to the very high currents, the conductor bars in a turbo generator have a large

cross-sectional area. In addition they are usually one single turn per bar. These stator orconductor bars are also very rigid and do not bend unless significant force is exerted on them.

ROTOR

The rotor winding is installed in the slots machined in the forging main body and is distributed

symmetrically around the rotor between the poles. The winding itself is made up of many turnsof copper to form the entire series connected winding. All of the turns associated with a single

slot are generally called a coil. The coils are wound into the winding slots in the forging,


54/64

Rotor

concentrically in corresponding positions on opposite sides of a pole. In addition almost all large

turbo generators have directly cooled copper windings by air or hydrogen cooling gas.Cooling

passages are provided within the conductors themselves to eliminate the temperature drop acrossthe ground insulation and preserve the life of the insulation material.In an axially cooled

winding, the gas passes through axial passages in the conductors, being fed from both ends, andexhausted to the air gap at the axial center of the rotor. The winding is held in place in the slots

by wedges, in a similar manner as the stator windings.

The difference is that the rotor winding loading on the wedges is far greater due to centrifugalforces at speed. The wedges therefore are subjected to a tremendous static load from these forcesand bending stresses because of the rotation effects.

As in the rotor slots, the copper turns in the end-winding must be isolated from one another so

that they do not touch and create shorts between turns. Therefore packing and blocking are used

to keep the coils separated, and in their relative position as the rotor winding expands from

thermal effects during operation.

The A.C. Generator or alternator is based upon the principle of electromagnetic induction and

consists generally of a stationary part called stator and a rotating part called rotor. The stator housed

the armature windings. The rotor houses the field windings. D.C. voltage is applied to the field

windings through slip rings. When the rotor is rotated, the lines of magnetic flux (viz magnetic field)

cut through the stator windings. This induces an electromagnetic force (e.m.f.) in the stator windings.The magnitude of this e.m.f. is given by the following expression.

E = 4.44 /O FN volts

0 = Strength of magnetic field in Webers.

F = Frequency in cycles per second or Hertz.

N = Number of turns in a coil of stator winding

F = Frequency = Pn/120


55/64

Where P = Number of poles

n = revolutions per second of rotor.

From the expression it is clear that for the same frequency, number of poles increases with decrease

in speed and vice versa. Therefore, low speed hydro turbine drives generators have 14 to 20 poles

where as high speed steam turbine driven generators have generally 2 poles. Pole rotors are used inlow speed generators, because the cost advantage as well as easier construction.

BEARINGS

All turbo generators require bearings to rotate freely with minimal friction and vibration. The

main rotor body must be supported by a bearing at each end of the generator for this purpose.

This ensures that the excitation end of the rotor shaft does not create a wobble that transmits

through the shaft and stimulates excessive vibration in the overall generator rotor

or the turbo generator line.

AUXILIARY SYSTEMS

All large generators require auxiliary systems to handle such things as lubricating oil for the rotor

bearings, hydrogen cooling apparatus, hydrogen sealing oil, de-mineralized water for stator

winding cooling, and excitation systems for field-current application. Not all generators require

all these systems and the requirement depends on the size and nature of the machine.

There are five major auxiliary systems that may be used in a generator. They are given asfollows:

1. Lubricating Oil System2. Hydrogen Cooling System

3. Seal Oil System

4. Stator Cooling Water System5. Excitation SystemEach system has numerous variations to accommodate the hundreds of different generator

configurations that may be found in operation. But regardless of the generator design and which

variation of a system is in use, they all individually have the same basic function .

1. Lubricating Oil System

The lube-oil system provides oil for all of the turbine and generator bearings as well as being the

source of seal oil for the seal-oil system.


56/64

Lubricating Oil System Layout

The main oil t

Date post:	06-Apr-2018
Category:	Documents
Upload:	juhi-bhatnagar
View:	228 times
Download:	0 times

Ntpc Deposit

Documents