18679234 NTPC 6 Weeks Project ReportAnkush

8/3/2019 18679234 NTPC 6 Weeks Project ReportAnkush

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LINAGAY'S INSTITUTE OF MGT. & TECHNOLOGY

FARIDABAD

TO WHOM IT MAY CO CER

I hereby certify that AnkushArya Roll No 06-EE-013 of Lingaya'sInstt.ofMgt&Tech.

Faridabad has undergone six weeks industrial training from 1st July, 2009 to 8th August

2009 at our organization to fulfill the requirements for the award of degree of B.E Electrical

& Elecctronics Engineering. He works on Power Plant Overview project during the training

under the supervision of Mr. G. D. Sharma. During his tenure with us we found him sincere

and hard working.

We wish him a great success in the future.

Signature of the Student

Ankush Arya


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ACK OWLEDGEME T

The authors are highly grateful to the Mr Y.S Goyal, Principal, Lingayas Instt. Of Mgt. &Tech. (LIMAT), faridabad, for providing this opportunity to carry out the six weeks industrial

training at National Thermal Power Corporation, New Delhi.

The authors would like to express a deep sense of gratitude and thanks profusely to Mr. R. S.

Sharma, CMD of the Company, without the wise counsel and able guidance, it would have been

impossible to complete the report in this manner.

The help rendered by Ms Rachana Singh Bhal, Supervisor, National Thermal Power Corporation

for experimentation is greatly acknowledged.

The author expresses gratitude to the HOD and other faculty members of Department of

Electrical & Electronics Engineering of LIMAT for their intellectual support throughout the

course of this work.

Finally, the authors are indebted to all whosoever have contributed in this report work

and friendly stay at Badarpur Thermal Power Station, New Delhi.

Ankush [email protected]


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CONTENT

1. Introduction to the Company

a. About the Company

b. Vision

c. Strategies

d. Evolution

2. Introduction to the Project

3. Project Report

a. Operation

i. Introduction

ii. Steam Boiler

iii. Steam Turbine

iv. Turbine Generator

b. EMD - I

i. Coal Handling Plant

ii. Motors

iii. Switchgear

iv. High Tension Switchgear

v. Direct On Line Starter

c. EMD - II

i. Generatorii. Protection

iii. Transformer

4. Reference


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I TRODUCTIO TO

THE COMPA Y

About the Company

VisionStrategies

Evolution

ational Thermal Power Corporation LimitedBadarpur Thermal Power Station

Badarpur, ew Delhi


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ABOUT THE COMPANY

NTPC, the largest power Company in India, was setup in 1975 to accelerate power development

in 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.

A View of Badarpur Thermal Power Station, ew Delhi

NTPC has installed capacity of 29,394 MW. It has 15 coal based power stations (23,395 MW), 7

gas 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 a

75,000 MW company by 2017.

NTPC has gone

beyond the thermal

power generation. It

has diversified into

hydro power, coal

mining, power

equipmentmanufacturing, oil &

gas exploration, power

trading & distribution.

NTPC is now in the

entire power value

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 was 19.1% and it

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


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

operations.

With its experience and expertise in the power sector, NTPC is extending consultancy services

to 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 listed

company 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 identified

NTPC as one of the jewels of Public Sector 'Navratnas'- a potential global giant. Inspired by its

glorious 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".


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VISION

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

Mission

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

integrating multiple energy resources with innovative & Eco-friendly technologies and

contribution to the society

View of a well flourished power plant

Core Values - BCOMIT

Business ethics

Customer Focus

Organizational & Professional Pride

Mutual Respect & Trust

Innovation & Speed

Total Quality for Excellence


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EVOLUTION

1975

1997

2004

2005

2008

NTPC was set up in 1975 with 100% ownership by the Government of

India. In the last 30 years, NTPC has grown into the largest power

utility in India.

In 1997, Government of India granted NTPC status of Navratna being

one of the nine jewels of India, enhancing the powers to the Board of

Directors.

NTPC became a listed company with majority Government ownership

of 89.5%.

NTPC becomes third largest by Market Capitalization of listed

companies

The company rechristened as NTPC Limited in line with its changing

business portfolio and transforms itself from a thermal power utility to

an integrated power utility.

National Thermal Power Corporation is the largest power generation

company in India. Forbes Global 2000 for 2008 ranked it 411th in the

world.

TPC is the largest power utility in India, accounting for about 20% of Indias installed

capacity.


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I TRODUCTIO TO

THEMAL POWERPLA T

Introduction

Classification

Functioning


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INTRODUCTION

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

the generation of electric power. Power plant is also used to refer to the engine in ships, aircraft

and other large vehicles. 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. However, power

plant is the most common term in the U.S., while elsewhere power station and power plant are

both widely used, power station prevailing in many Commonwealth countries and especially in

the United Kingdom.

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 powerstations produce steam, and these are sometimes called steam power stations. About 80% of all

electric 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 or district 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 heat plants called heat-only boiler stations. An important class of power stations in the

Middle East uses byproduct heat for desalination of water.


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CLASSIFICATION

By 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 solid

waste, landfill methane, or other forms of biomass.

In integrated steel mills, blast furnace exhaust gas is a low-cost, although low-energy-

density, fuel.

Waste heat from industrial processes is occasionally concentrated enough to use for

power 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 power

plants are combined cycle plants fired by natural gas.

Internal combustion Reciprocating engines are used to provide power for isolated

communities and are frequently used for small cogeneration plants. Hospitals, office

buildings, industrial plants, and other critical facilities also use them to provide backup

power 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.


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FUNCTIONING

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

supplied to the consumers through high-voltage power lines.

Process of a Thermal Power Plant

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 is

available 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 in the transformation of water into steam.


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3) Steam Turbine: The steam generated in the boiler is sent through a steam turbine. The

turbine 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.

Apart from this, there are various other monitoring systems and instruments in place to keep

track of the functioning of all the devices. This prevents any hazards from taking place in the

plant.


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PROJECT

REPORTOPERATIO

EMD - I

EMD - II


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Module - I

OPERATIO

IntroductionSteam Generator or Boiler

Steam Turbine

Electric Generator


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Introduction

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

this is known as a Rankine cycle. Shown here is a diagram of a conventional thermal power

plant, which uses coal, oil, or natural gas as fuel to boil water to produce the steam. 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 in Jharkhand. Water supply is given from the Agra Canal.

Table: Capacity of Badarpur Thermal Power Station, New Delhi

Sr. o. Capacity o. of Generators Total Capacity

1. 210 MW 2 420 MW

2. 95 MW 3 285 MW

Total 705 MW


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

1. Steam Generator or Boiler

2. Steam Turbine

3. Electric Generator

We have discussed about the processes of electrical generation further. A complete detailed

description of the three units is given further.

Typical Diagram of a Coal based Thermal Power Plant

1. Cooling tower 10. Steam governor valve 19. Superheater

2. Cooling water pump 11. High pressure turbine 20. Forced draught fan

3. Transmission line (3-phase) 12. Deaerator 21. Reheater

4. Unit transformer (3-phase) 13. Feed heater 22. Air intake

5. Electric generator (3-phase) 14. Coal conveyor 23. Economiser

6. Low pressure turbine 15. Coal hopper 24. Air preheater

7. Condensate extraction pump 16. Pulverised fuel mill 25. Precipitator8. Condensor 17. Boiler drum 26. Induced draught fan

9. Intermediate pressure turbine 18. Ash hopper 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 where

it 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 from any


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remaining water. The steam passes through a manifold in the roof of the drum into the pendant

superheater (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 pressure

turbine (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 theboiler 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

steam drawn 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). This is 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 the boiler is drawn by the induced draft fan (26) through an electrostatic

precipitator (25) and is then vented through the chimney stack (27).


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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 walls

are 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 the

boiler 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 (22.1

MPa). 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 gases

as they exit the furnace. Here the steam is superheated to 1,000 F (540 C) to prepare it for the

turbine.

The steam generating boiler has to produce steam at the high purity, pressure and temperature

required 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 or baghouse) 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. On some

units of about 60 MW, two boilers per unit may instead be provided.


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Boiler Furnace and Steam Drum

Once water inside the boiler or steam generator, the process of adding the latent heat of

vaporization or enthalpy is underway. The boiler transfers energy to the water by the chemical

reaction of burning some type of fuel.

The water enters the boiler through a section in the convection pass called the economizer. Fromthe economizer it passes to the steam drum. Once the 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 turned into 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 once again enters the steam drum.

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

The steam/vapor 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 and

the 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.


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Geothermal plants need no boiler since they use naturally occurring steam sources. Heat

exchangers may be used where the geothermal steam is very corrosive or contains excessive

suspended solids. Nuclear plants also boil water to raise steam, either directly passing the

working steam through the reactor or else using an intermediate heat exchanger.

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, or

other types of grinders.

Some power stations burn fuel oil rather than coal. The oil must kept warm (above its pour

point) in the fuel oil storage tanks to prevent the oil from congealing and becoming unpumpable.

The oil is usually heated to about 100C before being pumped through the furnace fuel oil spray

nozzles.

Boiler Side of the Badarpur Thermal Power Station, ew Delhi

Boilers in some power stations use processed natural gas as their main fuel. Other power stations

may use processed natural gas as auxiliary fuel in the event that their main fuel supply (coal or

oil) is interrupted. In such cases, separate gas burners are provided on the boiler furnaces.


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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).

Air Path

External 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 via

the 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 to avoid backfiring through any opening.

At the furnace 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 limitation

prescribed 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 or fabric bag

filters (or sometimes both) 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 or bag

filters. Generally, the fly ash is pneumatically transported to storage silos for subsequent

transport by trucks or railroad cars.

Bottom Ash Collection and Disposal

At 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 clinkers

falling 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 Storage

Since 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


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

demineralising treatment plant (DM).

Ash Handling System at Badarpur Thermal Power Station, ew Delhi

A DM plant generally consists of cation, anion and mixed bed exchangers. The final water fromthis 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 quantity of salts in the raw water input.

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 boiler

make-up. The storage tank for DM water is made from materials not affected by corrosive water,

such as PVC. The piping and valves are generally of stainless steel. Sometimes, a steam

blanketing arrangement or stainless steel doughnut float is provided on top of the water in the

tank to avoid contact with atmospheric air. 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.


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Steam Turbine

Steam turbines are used in all of our major coal fired power stations to drive the generators or

alternators, 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 of

a 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 its

original 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.


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A distinction is made between "impulse" and "reaction" turbine designs based on the relative

pressure drop across the stage. There are two measures for pressure drop, the pressure ratio and

the percent reaction. Pressure ratio is the pressure at the stage exit divided by the pressure at the

stage entrance. Reaction is the percentage isentropic enthalpy drop across the rotating blade or

bucket compared to the total stage enthalpy drop. Some manufacturers utilise percent pressure

drop across stage to define reaction.

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 be

used. 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. For co-

generation, the steam pressure is highest when used as process steam and at a lower pressure

when used for the secondary function of electricity production.

Nozzles and Blades

Steam enthalpy is converted into rotational energy as it passes through a turbine stage. A turbine

stage consists of a stationary blade (or nozzle) and a rotating blade (or bucket). 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 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 damage mechanisms, 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. This has led to the imposition of an allowable limit of about 12%

wetness in the exhaust steam;


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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.The leaking steam is collected and returned to a low-pressure part of the steam circuit.

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.

Vibration

The 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

problems and allows the repair of the turbine to be planned before the problems become serious.


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Electric Generator

The 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 bearing

surface and to limit the heat generated.

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

Barring Gear (or Turning Gear)

Barring 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 slowing

or "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 inside

the 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 millionths

of inches, only detectable by monitoring eccentricity meters.


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But this small amount of shaft deflection would be enough to cause vibrations and damage the

entire steam turbine generator unit when it is restarted. Therefore, the shaft is not permitted to

come to a complete stop by a mechanism known as "turning gear" or "barring 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 barring 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

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

diagram. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous

removal of air and gases from the steam side to maintain vacuum.

A Typical Water Cooled Condenser

For best efficiency, the temperature in the condenser must be kept as low as practical in order to

achieve the lowest possible pressure in the condensing steam. Since the condenser temperature

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

less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-

condensible air into the closed loop must be prevented. Plants operating in hot 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 air conditioning.

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.


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Feedwater Heater

A 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 heat content (btu) 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.

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.


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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 now

superheated 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 other

dissolved 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. A deaerator typically includes a vertical, domed deaeration

section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler

feedwater storage tank.

Boiler Feed Water Deaerator (with vertical, domed aeration section and horizontal water storage section)

There are many different designs for a deaerator and the designs will vary from one

manufacturer to another. The adjacent diagram depicts a typical conventional trayed deaerator. If

operated properly, most deaerator manufacturers will guarantee that oxygen in the deaerated

water will not exceed 7 ppb by weight (0.005 cm/L).


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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

other mechanisms.

At a preset speed of the turbine during start-ups, a pump driven by the turbine main shaft takes

over the functions of the auxiliary system.

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 the

chamber 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 the casing 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 to atmosphere.

The generator also uses water cooling. Since the generator coils are at a potential of about 15.75

kV and water is conductive, an insulating barrier such as Teflon is used to interconnect the water

line and the generator high voltage windings. 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.

The necessary protection and metering devices are included for the high voltage leads. Thus, the

steam turbine generator and the transformer form one unit. In smaller units, generating at 10.5

kV, a breaker is provided to connect it to a common 10.5 kV bus system.


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Other Systems

Monitoring and Alarm system

Most 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.

An Engineer monitoring the various parameters at TPC, ew 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.


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Module - II

EMD - ICoal Handling Plant

Motors

Switchgear

High Tension Switchgear

Direct On Line Starter


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Coal Handling Plant

Coal 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 when

there is no wagon supply.

Coal Handling Plant Layout

Modern unloaders use rotary dump devices, which eliminate problems with coal freezing in

bottom dump cars. 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 upside down to dump the coal. Swiveling couplers enable the entire


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operation to occur while the cars are still coupled together. Unloading a unit train takes about

three hours.

Shorter trains may use railcars with an "air-dump", which relies on air pressure from the engine

plus a "hot shoe" on each car. This "hot shoe" when it comes into contact with a "hot rail" at the

unloading trestle, shoots an electric charge through the air dump apparatus and causes the doors

on the bottom of the car to open, dumping the coal through the opening in the trestle. Unloading

one of these trains takes anywhere from an hour to an hour and a half. Older unloaders may still

use manually operated bottom-dump rail cars and a "shaker" attached to dump the coal.

Generating stations adjacent to a mine may receive coal by conveyor belt or massive diesel-

electric-drive trucks.

Layout of Coal Handling Plant at Badarpur Thermal Power Station, ew 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. In plants that do not burn pulverized coal, the larger 2 inch pieces may

be directly fed into the silos which then feed the cyclone burners, a specific kind of combustor

that can efficiently burn larger pieces of fuel.


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Run-Of-Mine (ROM) Coal

The coal delivered from the mine that reports to the Coal Handling Plant is called Run-of-mine,

or ROM, coal. This is the raw material for the CHP, and consists of coal, rocks, middlings,

minerals and contamination. Contamination is usually introduced by the mining process and

may include machine parts, used consumables and parts of ground engaging tools. ROM coal

can have a large variability of moisture and maximum particle size.

Coal Handling

Coal 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.

Coal Handling Division of Badarpur Thermal Power Station, ew 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. More controlled stockpiles are


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formed using stackers to form piles along the length of a conveyor, and reclaimers to retrieve the

coal when required for product loading, etc.

Taller and wider stockpiles reduce the land area required to store a set tonnage of coal. Larger

coal stockpiles have a reduced rate of heat lost, leading to a higher risk of spontaneous

combustion.

Stacking

Travelling, lugging boom stackers that straddle a feed conveyor are commonly used to create

coal stockpiles. Stackers are nominally rated in tph (tonnes per hour) for capacity and normally

travel on a rail between stockpiles in the stockyard. A stacker can usually move in at least two

directions typically: horizontally along the rail and vertically by luffing its boom. Luffing of the

boom minimises dust by reducing the height that the coal needs to fall to the top of the stockpile.

The boom is luffed upwards as the stockpile height grows.

Wagon Tripler at Badarpur Thermal Power Station, ew Delhi

Some stackers are able to rotate by slewing the boom. This allows a single stacker to form two

stockpiles, one on either side of the conveyor.

Stackers are used to stack into different patterns, such as cone stacking and chevron stacking.

Stacking in a single cone tends to cause size segregation, with coarser material moving out

towards the base. Raw cone ply stacking is when additional cones are added next to the first

cone. Chevron stacking is when the stacker travels along the length of the stockpile adding layer

upon layer of material.


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Stackers and Reclaimers were originally manually controlled manned machines with no remote

control. Modern machines are typically semi-automatic or fully automated, with parameters

remotely set.

ReclaimingTunnel conveyors can be fed by a continuous slot hopper or bunker beneath the stockpile to

reclaim material. Front-end loaders and bulldozers can be used to push the coal into feeders.

Sometimes front-end loaders are the only means of reclaiming coal from the stockpile. This has

a low up-front capital cost, but much higher operating costs, measured in dollars per tonne

handled.

Coal Storage Area of the Badarpur Thermal Power Station, ew Delhi

High-capacity stockpiles are commonly reclaimed using bucket-wheel reclaimers. These can

achieve very high rates.

Coal Sampling

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

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

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

Screening


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

grades. Dewatering screens are used to remove water from the product. Screens can be static, or

mechanically vibrated. Screen decks can be made from different materials such as high tensile

steel, stainless steel, or polyethelene.

Screening and Separation Unit of Coal Handling Division of a Thermal Power Plant

Magnetic Separation

Magnetic separators shall be used in coal conveying systems to separate tramp iron (including

steel) from the coal. Basically, two types are available. One type incorporates permanent or

electromagnets into the head 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 the belt. 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 moving coal 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, if any, and/or just prior to coal discharge to the in-plant

bunker or silo fill system.

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


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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.

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 of the 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. The classifier separates the pulverized coal from the unpulverized coal.

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 of large 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

is exposed to heat and combustion.


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The combustion process is almost free from clinker and slag formation.

The boiler can be easily started from cold condition in case of emergency.

Practically no ash handling problem.

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

primary air may vary anywhere from 10% to the entire air depending on the design of the

boiler. 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 mixturetangentially to an 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 the necessity 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 the Badarpur Thermal

Power Station five sets of such burners are placed one above the other to form six firing zones.

These burners are constructed with tips that can be angled through a small vertical arc. By

adjusting the angle of the burners the position of the fire ball can be adjusted so as to raise or

lower the position of the turbulent combustion region. When the burners are tilted downward thefurnace gets filled completely with the flame and the furnace exit gas temperature gets reduced.

When the burners are tiled upward the furnace exit gas temperature increases. A difference of

100 degrees can be achieved by tilting the burners.

Ash Handling

The 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. The widely used ash handling systems are1. Mechanical Handling System

2. Hydraulic System

3. Pneumatic System

4. Steam Jet System

The Hydraulic Ash handling system is used at the Badarpur Thermal Power Station.


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Ash Handling System of a Thermal Power Plant

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 hydraulic system is divided into a low velocity and high

velocity system. In the low velocity system the ash from the boilers falls into a stream of water

flowing into the sump. The ash is carried along with the water and they are separated at the

sump. In the high velocity system a jet of water is sprayed to quench the hot ash. Two other jets

force the ash into a trough in which they are washed away by the water into the sump, where

they are separated. The molten slag formed in the pulverized fuel system can also be quenched

and washed by using the high velocity system. The advantages of this system are that its clean,

large ash handling capacity, considerable distance can be traversed, absence of working parts in

contact with ash.


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ELECTRIC MOTORS

An 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. Traction motors used on locomotives and some electric and hybrid automobiles often

performs both tasks if the vehicle is equipped with dynamic brakes.

A High Power Electric Motor

Categorization of Electric Motors

The classic division of electric motors has been that of Direct Current (DC) types vs Alternating

Current (AC) types. The ongoing trend toward electronic control further muddles the distinction,

as modern drivers have moved the commutator out of the motor shell. For this new breed of

motor, driver circuits are relied upon to generate sinusoidal AC drive currents, or some

approximation of. The two best examples are: the brushless DC motor and the stepping motor,

both being polyphase AC motors requiring external electronic control.

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.


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Comparison of Motor Types

Type

AC Induction

(Shaded Pole)

AC Induction

(split-phase

capacitor)

AC

Synchronous

Stepper DC

Brushless DC

Brushed (PM)

DC

Advantages

Least expensive

Long life

high power

High power

high starting

torque

Rotation in-sync

with freq

long-life

(alternator)

Precision

positioning

High holding

torqueLong lifespan

low maintenance

High efficiency

Low initial cost

Simple speed

control (Dynamo)

Disadvantages

Rotation slips from

frequency

Low startingtorque

Rotation slips from

frequency

More expensive

Slow speed

Requires a

controllerHigh initial cost

Requires a

controller

High maintenance

(brushes)Low lifespan

Typical

Application

Fans

Appliances

Clocks

Audio turntables

tape drives

Positioning in

printers and floppy

drivesHard drives

CD/DVD players

electric vehicles

Treadmill exercisers

automotive starters

Typical

Drive

Uni/Poly-

phase AC

Uni/Poly-

phase AC

Uni/Poly-

phase AC

Multiphase

DC

Multiphase

DC

Direct

(PWM)

At Badarpur Thermal Power Station, New Delhi, mostly AC motors are employed for various

purposes. We had to study the two types of AC Motors viz. Synchronous Motors and Induction

Motor. The motors have been explained further.

AC Motor

Internal View of AC Motors

An AC motor is an electric motor that is driven by an alternating current. It consists of two basic

parts, 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 the

rotating field.


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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 or a sub multiple of the supply

frequency. The magnetic field on the rotor is either generated by current delivered through slip

rings or a by a permanent magnet.

The second type is the induction motor, which turns slightly slower than the supply frequency.

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. In this case the synchronous motor is called a Synchronous condenser.

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.

Accurate control in speed and position using open loop controls, eg. Stepper motors.

They will hold their position when a DC current is applied to both the stator and the rotor

windings.

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 the whole installation.


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

(as in ball mills and similar apparatus).

Examples

Brushless permanent magnet DC motor.

Stepper motor. Slow speed AC synchronous motor.

Switched reluctance motor.

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.

Three Phase Induction Motors

An electric motor converts electrical power to mechanical power in its rotor (rotating part).

There are several ways to supply power to the rotor. In a DC motor this power is supplied to the

armature directly from a DC source, while in an AC motor this power is induced in the rotatingdevice. 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 widely used, especially polyphase induction motors,

which are frequently used in industrial drives.

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

construction, lack of brushes (which are needed in most DC Motors) andthanks to modern

power electronicsthe ability to control the speed of the motor.


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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 in

pairs (i.e. 2, 4, 6 etc). There are two types of rotor:

1. Squirrel-cage rotor

2. 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 each end. The rotor bars in squirrel-cage induction motors are not straight, but have some

skew to reduce noise and harmonics.

The motor's phase type is one of two types:

1. Single-phase induction motor

2.3-phase induction motor

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.

By way of contrast, the induction motor does not have any direct supply onto the rotor; instead,

a secondary 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 field

pattern 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 magnetic field 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:

Based on type of phase supply

1. three phase induction motor (self starting in nature)

2. single phase induction motor (not self starting)

Other

1. Squirrel cage induction motor

2. Slip ring induction motor


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SWITCHGEAR

The 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.

The very earliest central power stations used simple open knife switches, mounted on insulating

panels of marble or asbestos. Power levels and voltages rapidly escalated, making open

manually-operated switches too dangerous to use for anything other than isolation of a de-

energized circuit. Oil-filled equipment allowed arc energy to be contained and safely controlled.

By the early 20th century, a switchgear line-up would be a metal-enclosed structure with

electrically-operated switching elements, using oil circuit breakers. 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,

protection, metering and communications.

A View of Switchgear at a Power Plant

Types

A 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.

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.


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HIGH TENSION SWITCHGEAR

High 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. This type of equipment is really important

because it is directly linked to the quality of the electricity supply.

The high voltage is a voltage above 1000 V for alternating current and above 1500 V for direct

current.

High Tension Switchgear of a Thermal Power Plant

The high voltage switchgear was invented at the end of the 19th century for operating the motors

and others electric machines. It has been improved and it can be used in the whole range of high

voltage until 1100 kV.

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.


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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 thanks to the earthing switches.

In principle, disconnecting switches do not have to interrupt currents, but some of them can

interrupt currents (up to 1600 A under 10 to 300V) and some earthing switches must interrupt

induced currents which are generated in a non-current-carrying line by inductive and capacitive

coupling with nearby lines (up to 160 A under 20 kV) ).

A Vacuum Circuit Breaker (High Tension Switchgear)

High-Current Switching Mechanism

They can open or close a circuit in normal load. Some of them can be used as a disconnecting

switch. But if they can create a short-circuit current, they can not interrupt it.

Contactor

Their functions are similar to the high-current switching mechanism, but they can be used athigher rates. They have a high electrical endurance and a high mechanical endurance.

Contactors are used to frequently operate device like electric furnaces, high voltage motors.

They cannot be used as a disconnecting switch.

They are used only in the band 30 kV to 100 kV.

Fuses

The fuses can interrupt automatically a circuit with an overcurrent flowing in it for a fixed time.

The current interrupting is got by the fusion of an electrical conductor which is graded.


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They are mainly used ot protect against the short-circuits. They limit the peak value of the fault

current.

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. Against this trouble, the fuses can be associated

with high-current switches or contactors.

They are used only in the band 30 kV to 100 kV.

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

circuit conditions, for example to connect or disconnect a line in a power system; Under

specified abnormal 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 the only one able to interrupt a short circuit current and so to avoid the

others devices to be damaged by this short circuit. The international standard IEC 62271-100

defines the demands linked to the characteristics of a high voltage circuit breaker.The circuit breaker can be equipped with electronic devices in order to know at any moment

their states (wear, gaz pressure) and possibly to detect faults from characteristics derivatives

and it can permit to plan maintenance operations and to avoid failures.

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

overvoltages.

They can be equipped with devices to synchronize the closing and/or the opening to limit the

overvoltages and the inrush currents from the lines, the unloaded transformers, the shunt

reactances and the capacitor banks.

Some devices are designed to have the characteristics of the circuit breaker and the disconnector.

But their use is limited.


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DIRECT ON LINE STARTER

A direct on line starter, often abbreviated DOL starter, is a widely-used starting method of

electric motors. The term is used in electrical engineering and associated with 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 electronicdevices 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 subjected

to 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-voltage

starters are employed with motors above 5 hp. Although DOL motor starters are available for

motors less than 150 kW on 400 V and for motors less than 1 MW on 6.6 kV. Supply reliability

and reserve power generation dictates the use of reduced voltage or not.

Internal View of a Direct On Line Starter

Major Components

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

1. Switch

2. Fuse

3. Conductor (Electromagnetic)

4. Thermal Overload Relay (Heat & Temperature)

Auxiliary Components

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

are basically two types of Auxiliary Components given as follows:

1. Auxiliary Conductor

2. Timer (Range - 0.5s to 60s)


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DOL Reversing Starter

Most motors are reversible or, in other words, they can be run clockwise and anti-clockwise. A

reversing starter is an electrical or electronic circuit that reverses the direction of a motor

automatically. Logically, the circuit is composed of two DOL circuits; one for clockwise

operation and the other for anti-clockwise operation.

External View of a Direct On Line Starter

Example of Motor Starters

A very well-known motor starter is the DOL Starter of a 3-Phase Squirrel-Cage Motor. This

starter is sometimes used to start water pumps, compressors, fans and conveyor belts. With a

400V, 50 Hz, 3-phase supply, the power circuit connects the motor to 400V. Consequently, the

starting current may reach 3-8 times the normal current. The control circuit is typically run at

24V with the aid of a 400V/24V transformer.

Motor Direction Reversal

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

This could be achieved by a contactor KM1 swapping phase L2 and L3 between the supply and

the motor.


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Module - II

EMD - IIGenerator

Protection

Transformer


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GENERATORS

The 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.

A 210 MW Turbine Generator at Badarpur Thermal Power Station, ew Delhi

The class of generator under consideration is steam turbine-driven generators, commonly called

turbo generators. These machines are generally used in nuclear and fossil fueled power plants,

co-generation plants, and combustion turbine units. They range from relatively small machines

of a few Megawatts (MW) to very large generators with ratings up to 1900 MW. The generators

particular to this category are of the two- and four-pole design employing round-rotors, with

rotational operating speeds of 3600 and 1800 rpm in North America, parts of Japan, and Asia

(3000 and 1500 rpm in Europe, Africa, Australia, Asia, and South America). At Badarpur

Thermal Power Station 3000 rpm, 50 Hz generators are used of capacities 210 MW and 95 MW.

As the system load demands more active power from the generator, more steam (or fuel in a

combustion 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. This torque is


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mechanical in nature, but electromagnetically coupled to the power system through the

generator. 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 currents in 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.

An open Electric Generator at Power Plant

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. (The term air gap

is commonly used for air- and gas-cooled machines). For the machines in this discussion, this

means a magnetic flux distribution of two or four poles on the rotor. This flux pattern rotates

with the rotor, as it spins at its synchronous speed. The rotating magnetic field moves past a

three-phase symmetrically distributed winding installed in the stator core, generating analternating voltage in the stator winding. The voltage waveform created in each of the three

phases 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 stator winding.

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.


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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. The most critical component in the generator are the

retaining rings, mounted on the rotor.

These components are very carefully designed for high-stress operation. The stator is stationary,

as the term suggests, but it also sees significant dynamic forces in terms of vibration and

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 item

and 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, commonly called the stator bore, in equally spaced slots in the

core to ensure symmetrical flux linkage with the field produced by the rotor. Each slot contains

two conductor bars, one on top of the 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. The core area between slots is generally called a core tooth.

Stator of a Turbo Generator

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 degree arc

of the stator bore. The distribution of the winding is done in such a way as to produce a 120

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

voltage. Each of the three phases may have one or more parallel circuits within the phase. The


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parallels can be connected in series or parallel, or a combination of both if it is a four-pole

generator. This will be discussed in the next section. The parallels in all of the phases are

essentially equal on average, in their performance in the machine. Therefore, they each see

equal 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. The overlap is staggered between top and bottom

bars. The top bars on one side of the stator bore are connected to the bottom bars on the other

side of the bore in one direction while the bottom bars

18679234 NTPC 6 Weeks Project ReportAnkush

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