NTPC Summer Training Report.docx

8/10/2019 NTPC Summer Training Report.docx

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SUBMITED TO :- SUBMITED BY:-

Mr. SHOBHIT GARG MOHIT RAWAT

UNIV. ROLL NO. : 2004190

SECTION : B

BATCH : 2011-15

INDUSTRIAL TRAININGREPORT

TRAINING AT

DEPARTMENT OF ELECTRICAL ANDELECTRONICS ENGINEERING


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ACKNOWLEDGEMENT

With profound respect and gratitude, I take the opportunity to convey my thanks to complete

the training here. I do extend my heartfelt thanks to Mr. Shobhit Garg for providing me this

opportunity to be a part of this esteemed organization.

I am extremely grateful to all the technical staff of BTPS / NTPC for their co-operation and

guidance that has helped me a lot during the course of training. I have learnt a lot working under

them and I will always be indebted of them for this value addition in me.


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TABLE OF CONTENT

CHAPTER

NO.

CONTENT PAGE NO.

1. ABOUT TO THE COMPANY 7CORPORATE VISION 7

CORE VALUES 7-8

2. TRAINING ATBTPS 9

3. INTRODUCTION TO THE COMPANY 10

I. About the Company 10-11

II. Strategies 12III. Evolution of NTPC 13IV. About BTPS 14-15

4. BASIC THREE UNITS OF POWER PLANT 16I. STEAM GENERATOR / BOILER 17

II. BOILER FURNACE AND STEAM DRUM 18

III. FUEL PREPARATION SYSTEM 19IV. FUEL FIRING SYSTEM AND IGNITER SYSTEM 20

V. AIR PATH 20

VI. AUXILIARY SYSTEM 21 FLY ASH COLLECTION 21 BOTTOM ASH COLLECTION AND DISPOSAL 21 BOILER MAKE-UP WATER TREATMENT

PLANT AND STORAGE

21

VII. ELECTRIC GENERATOR 21

VIII. CONDENSER 22

IX. FEEDWATER HEATER 23

5. BASIC STEPS OF ELECTRICITY GENERATION 24

I. COAL TO ELECTRICITY BASIC 24

II. COAL TO STEAM 24III. FACTOR AFFECTING THRMAL CYCLE

EFFICIENCY26


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6. ELECTRICAL MAINTAINANCE DEPARTMENT- I 27

I. COAL HANDLING PLANT 27II. OLD COAL HANDLING PLANT 28

III. NEW COAL HANDLING PLANT 29

7. VARIOUS CONSTITUENTS OF NCHP 30

I. WAGON TIPPLER 30II. BREAKER HOUSE 30

III. CRUSHER HOUSE 30IV. WAGON TIPPLER 31

V. CONVEYORS 31

VI. ZERO SPEED SWITCH 32VII. CRUSHER HOUSE 32

VIII. VENTILATION DEVICE 32IX. SAFETY DEVICE FOR BELT CONVEYORS 32

8. MILING SYSTEM 33I. RC BUNKER 33

II. RC FEEDER 33III. BALL MILL 33

IV. CLASSIFIER 33

V. MILL FAN 34VI. CYCLONE SEPARATORS 34

VII. THE TURNIGATE 34

9. VARIOUSINSTRUMENTS AT NCHP 34I. MAGNETIC SEPARATOR 34

II. METAL DETECTOR 34III. WAGON TIPPLER 34

IV. CONVEYOR 35V. ZERO SPED SWITCH 35VI. CRUSHER HOUSE 35

10. SWITCH GEAR 36

I. INTRODUCTION 36II. ISOLATOR 36

III. SWITCHING ISOLATOR 36

IV. CIRCUIT BREAKER 37V. LOAD BREAK SWITCHES 37


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VI. EARTH SWITCHES 37

11. LT SWITCHGEAR 38I. MAIN SWITCH 38

II. FUSES 38

III. CONTRACTORS 38

IV. OVERLOAD RELAY 38V. AIR CIRCUIT BREAKERS 38

12. HT SWITCHGEAR 39I. MINIMUM OIL CIRCUIT BREAKER 39

II. AIR CIRCUIT BREAKER 39

III. SF6 CIRCUIT BREAKER 40IV. VACCUM CIRCUIT BREAKER 40

13. ELECTRIC MOTORS 40I. CATEGORIZATION OF ELECTRIC MOTORS 41II. AC MOTOR 41III. SYNCHRONOUS MOTORS 41

IV. INDUCTION MOTOS 42V. THREE PHEASE INDUCTION MOTORS 42

VI. CONSTRUCTION 43

14. ELECTRICAL MAINTAINANCE DEPARTMENT- II 44I. GENERATORS 44

II. STATOR 45

III. STATOR OF A TURBO GENERATOR 45IV. ROTOR 46

V. BEARING 46VII. AUXILIARY SYSTEMS 47

VIII. LUBRICATING OIL SYSEM 47IX. LUBRICATING OIL SYSTEM LAYOUT 47X. HYDROGEN COOLING SYSTEM 48

XI. SEAL OIL SYSTEM 48

XII. STATOR COOLING WATER SYSTEM 49XIII. EXCITATION SYSTEM 49

XIV. GENERATOR PROTECTION 49-50

15. TRANSFORMER 51I. GENERATOR TRANSFORMER 51


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II. STATION TRANSFORMER 51

III. UNIT AUXILIARY TRANSFORMER 51IV. NEUTRAL GROUNDED TRANSFORMER 51

16. SWITCH YARD 52

I. OUTDOOR EQUIPMENT 52

II. INDOOR EQUIPMENTS 52III. CIRCUIT BREAKER 52

IV. LIGHTING ARRESTER 53V. AIR BREAK EARTHING SWITCH 53

VI. BUS BAR 53

VII. CURRENT TRANSFORMER 54VIII. CAPACITIVE VOLTAGE TRANSFORMER 54

17. CONTROL AND INSTRUMENTATION 55I. MANOMETRY LAB 55II. PROTECTION AND INTERLOCKING LAB 56III. PROTECTION AND INTERLOCKING SYSTEM 57

IV. PYROMETER LAB 57V. FURNANCE SAFETY AND SUPERVISORY

SYSTEM LAB58

VI. ELECTRONICS LAB 58VII. ANNUNCIATING CARDS 59

VIII. TEMPERATURE MEASUREMENT 59IX. EXPANSION THERMOMETER 59-60


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TABLE OF FIGURES

FIGURE NO. TITLE PAGE NO.

1. GROWTH OF NTPC INSTALLEDCAPACITY AND GENERATION

10

2. GRAPHICAL OVERVIEW OFCONTRIBUTION OF NTPC IN POE\WERGENERATION

11

3. TYPICAL DIAGRAM OF COAL BASEDTHERMAL POWER PLANT

17

4. SCHEMATIC DIAGRAM OF A COALFIRED POWER PLANT STEAMGENERATOR

18

5. A TYPICAL WATER COOLEDCONDENSOR

23

6. BASIC STEPS OF COAL TO ELECTRICITY 24

7. A SIMLIFIED DIAGRAM OF A THERMALPOWER PLANT

25

8. RANKIN CYCLE 25

9. COAL HANDLING PLANT LAYOUT 27

10. CURRENT TRANSFORMER DIAGRAM 54


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ABOUT THE COMPANY

CORPORATE VISION

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

presence.

CORE VALUES:

BCOMIT

B- Business ethics

C- Customer focus

O- Organizational & professional pride

M- Mutual respect & trust

I- Innovation & speed

T- Total quality for excellence


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NTPC Limited is the largest thermal power generating company of India, Public Sector Company. Iwas incorporated in the year 1975 to accelerate power development in the country as a wholly ownecompany of the Government of India. At present, Government of India holds 89.5% of the total equitshares of the company and the balance 10.5% is held by FIIs, Domestic Banks, Public and others. Within span of 31 years, NTPC has emerged as a truly national power company, with power generating facilities i

all the major regions of the country.

NTPC's core business is engineering, construction and operation of power generating plants and providing consultancy to power utilities in India and abroad.

The total installed capacity of the company is 31134 MW (including JVs) with 15 coal based and 7 ga based stations, located across the country. In addition under JVs, 3 stations are coal based & another statiouses naphtha/LNG as fuel. By 2017, the power generation portfolio is expected to have a diversified fuemix with coal based capacity of around 53000 MW, 10000 MW through gas, 9000 MW through Hydrogeneration, about 2000 MW from nuclear sources and around 1000 MW from Renewable Energy Source(RES). NTPC has adopted a multi-pronged growth strategy which includes capacity addition through greefield projects, expansion of existing stations, joint ventures, subsidiaries and takeover of stations.

NTPC has been operating its plants at high efficiency levels. Although the company has 18.79% of the totnational capacity it contributes 28.60% of total power generation due to its focus on high efficiency. NTPCs

share at 31 Mar 2001 of the total installed capacity of the country was 24.51% and it generated 29.68% othe power of the country in 2008-09. Every fourth home in India is lit by NTPC. 170.88BU of electricitwas produced by its stations in the financial year 2005-2006. The Net Profit after Tax on March 31, 200was INR 58,202 million. Net Profit after Tax for the quarter ended June 30, 2006 was INR 15528 millionwhich is 18.65% more than for the same quarter in the previous financial year. 2005).

Pursuant to a special resolution passed by the Shareholders at the Companys Annual General Meeting on

September 23, 2005 and the approval of the Central Government under section 21 of the Companies Ac1956, the name of the Company "National Thermal Power Corporation Limited" has been changed t

"NTPC Limited" with effect from October 28, 2005. The primary reason for this is the company's foray inhydro and nuclear based power generation along with backward integration by coal mining.


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TRAINING AT BTPS

I was appointed to do six-week training at this esteemed organization from 24th JUNE to 3rd AUGUST

2012. In these six weeks I was assigned to visit various division of the plant which were :-

1. EMD-I (Electrical Maintenance Department-I) ----- 1 week

2. EMD-II (Electrical Maintenance Department-II) --- 1 week

3. C & I (Control & Instrumentation) ------------------- 4 weeks

This six-week training was avery educational adventure for me. It was really amazing to see tha plant anlearn how electricity, which is one of our daily requirements of life, is produced.

The material in the reort has been gathered from my textbooks, senior student report, and trainer manua provided by training department.the specification & principles are learned by me from the employee of eacdivision of BTPS.


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INTRODUCTION TO COMPANY

NTPC Limited is the largest thermal power generating company of India, Public Sector Company. It waincorporated in the year 1975 to accelerate power development in the country as a wholly owned companof the Government of India. At present, Government of India holds 89.5% of the total equity shares of th

company and the balance 10.5% is held by FIIs, Domestic Banks, Public and others. Within a span of 3years, NTPC has emerged as a truly national power company, with power generating facilities in all thmajor regions of the country.

NTPC's core business is engineering, construction and operation of power generating plants and providinconsultancy to power utilities in India and abroad.

The total installed capacity of the company is 31134 MW (including JVs) with 15 coal based and 7 ga

based stations, located across the country. In addition under JVs, 3 stations are coal based & another statiouses naphtha/LNG as fuel. By 2017, the power generation portfolio is expected to have a diversified fuemix with coal based capacity of around 53000 MW, 10000 MW through gas, 9000 MW through Hydrogeneration, about 2000 MW from nuclear sources and around 1000 MW from Renewable Energy Source(RES). NTPC has adopted a multi-pronged growth strategy which includes capacity addition through greefield project expansion of existing stations, joint ventures, and takeover of stations.

.

Figure No. 1

NTPC has been operating its plants at high efficiency levels. Although the company has 18.79% of the totnational capacity it contributes 28.60% of total power generation due to its focus on high efficiency. NTPCs

share at 31 Mar 2001 of the total installed capacity of the country was 24.51% and it generated 29.68% o

the power of the country in 2008-09. Every fourth home in India is lit by NTPC. 170.88BU of electricitwas produced by its stations in the financial year 2005-2006. The Net Profit after Tax on March 31, 2006


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was INR 58,202 million. Net Profit after Tax for the quarter ended June 30, 2006 was INR 15528 millionwhich is 18.65% more than for the same quarter in the previous financial year. 2005).

NTPC has set new benchmarks for the power industry both in the area of power plant construction anoperations. Its providing power at the cheapest average tariff in the country. NTPC is committed to theenvironment, generating power at minimal environmental cost and preserving the ecology in the vicinity of

the plants. NTPC has undertaken massive a forestation in the vicinity of its plants. Plantations havincreased forest area and reduced barren land. The massive a forestation by NTPC in and around itRamagundam Power station (2600 MW) have contributed reducing the temperature in the areas by abou3c. NTPC has also taken proactive steps for ash utilization. In 1991, it set up Ash Utilization Division.

A GRAPHICAL OVERVIEW

Figure No. 2
http://www.ntpc.co.in/operations/operations.shtmlhttp://www.ntpc.co.in/operations/operations.shtmlhttp://www.ntpc.co.in/infocus/environment.shtmlhttp://www.ntpc.co.in/infocus/ashutilisation.shtmlhttp://www.ntpc.co.in/infocus/ashutilisation.shtmlhttp://www.ntpc.co.in/infocus/environment.shtmlhttp://www.ntpc.co.in/operations/operations.shtml


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STRATEGIES

Technological Initiatives

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

Integrated Gasification Combined Cycle (IGCC) Technology. Launch of Energy Technology Centre -A new initiative for development of technologies with focu

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

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

Partnering government in various initiatives Consultant role to modernize and improvise several plants across the country. Disseminate technologies to other players in the sector. Rural Electrification work under Rajiv Gandhi Garmin Vidyutikaran.

Environment Management All stations of NTPC are ISO 14001 certified. Various groups to care of environmental issues. The Environment Management Group. Ash Utilization Division. Afforestation Group. Centre for Power Efficiency & Environment Protection. Group on Clean Development Mechanism. NTPC is the second largest owner of trees in the country after the Forest department.


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EVOLUTION OF NTPC

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 powerutility.

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

National Thermal Power Corporation is the largest power generation company inIndia. Forbes Global 2000 for 2008 ranked it 317th in the world.

NTPC has also set up a plan to achieve a target of 50,000 MW generationcapacities.

NTPC has embarked on plans to become a 75,000 MW company by 2017.

1975

1997

2005

2004

2008

2009

2017

2012


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ABOUT BTPS

Badarpur thermal power station started working in 1973 with a single 95 mw unit. There were 2 more unit(95 MW each) installed in next 2 consecutive years. Now it has total five units with total capacity of 72MW. Ownership of BTPS was transferred to NTPC with effect from 01.06.2006 through GOIs Gazette

Notification .Given below are the details of unit with the year they are installed.

Address: Badarpur, New Delhi 110 044

Telephone: (STD-011) 26949523

Fax: 26949532

Installed Capacity 720 MW

Derated Capacity 705 MW

Location New DelhiCoal Source Jharia Coal Fields

Water Source Agra Canal

Beneficiary States Delhi

Unit Sizes 3X95 MW2X210 MW

Units Commissioned Unit I- 95 MW - July 1973

Unit II- 95 MW August 1974Unit III- 95 MW March 1975Unit IV - 210 MW December 1978Unit V - 210 MW - December 1981

Transfer of BTPS to NTPC Ownership of BTPS was transferred to NTPC with effect from01.06.2006 through GOIs Gazette Notification


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Operation Room of Power Plant

In Badarpur Thermal Power Station, steam is produced and used to spin a turbine that operates agenerator. Water is heated, turns into steam and spins a steam turbine which drives an electrical generatorAfter it passes through the turbine, the steam is condensed in a condenser; this is known as a Rankine cyclShown here is a diagram of a conventional thermal power plant, which uses coal, oil, or natural gas as fueto 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 o705MW.

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, (BTPS) New Delhi


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Basic 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 otwo (except 2) units is given further.

Coal is conveyed (14) from an external stack and ground to a very fine powder by large metal spheres ithe pulverised fuel mill (16). There it is mixed with preheated air (24) driven by the forced draught fan (20The hot air-fuel mixture is forced at high pressure into the boiler where it rapidly ignites. Water of a hig purity flows vertically up the tube-lined walls of the boiler, where it turns into steam, and is passed to th boiler drum, where steam is separated from any remaining water. The steam passes through a manifold ithe roof of the drum into the pendant super heater (19) where its temperature and pressure increase rapidly around 200 bar and 540C, sufficient to make the tube walls glow a dull red. The steam is piped to the hig pressure turbine (11), the first of a three-stage turbine process. A steam governor valve (10) allows for botmanual control of the turbine and automatic set-point following. The steam is exhausted from the hig

pressure turbine, and reduced in both pressure and temperature, is returned to the boiler reheater (21). Threheated steam is then passed to the intermediate pressure turbine (9), and from there passed directly to thlow pressure turbine set (6). The exiting steam, now a little above its boiling point, is brought into thermcontact with cold water (pumped in from the

Cooling tower) in the condenser (8), where it condenses rapidly back into water, creating near vacuum-likconditions inside the condensor chest. The condensed water is then passed by a feed pump (7) through deaerator (12), and pre-warmed, first in a feed heater (13) powered by steam drawn from the high pressurset, 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 highly visible plume of water vapour, before being pumped back to the condensor (8) in cooling water cyclThe three turbine sets are sometimes coupled on the same shaft as the three-phase electrical generator (5which generates an intermediate level voltage (typically 20-25 kV). This is stepped up by the unitransformer (4) to a voltage more suitable for transmission (typically 250-500 kV) and is sent out onto th

three-phase transmission system (3). Exhaust gas from the boiler is drawn by the induced draft fan (26through an electrostatic precipitator (25) and is then vented through the chimney stack (27).


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Figure No.3 TYPICAL DIAGRAM OF COAL BASED POWER PLANT

Steam Generator/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 oa web of high pressure steel tubes about 2.3 inches (60 mm) in diameter. Pulverized coal is air-blown intthe furnace from fuel nozzles at the four corners and it rapidly burns, forming a large fireball at the centeThe thermal radiation of the fireball heats the water that circulates through the boiler tubes near the boile perimeter. The water circulation rate in the boiler is three to four times the throughput and is typically drive by pumps. As the water in the boiler circulates it absorbs heat and changes into steam at 700 F (370 C) an3,200 psi (22.1MPa). It is separated from the water inside a drum at the top of the furnace. The saturatesteam is introduced into superheat pendant tubes that hang in the hottest part of the combustion gases as theexit the furnace. Here the steam is superheated to 1,000 F (540 C) to prepare it for the turbine. The steam


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generating boiler has to produce steam at the high purity, pressure and temperature required for the steamturbine that drives the electrical generator. The generator includes the economizer, the steam drum, thechemical dosing equipment, and the furnace with its steam generating tubes and the superheated coils Necessary safety valves are located at suitable points to avoid excessive boiler pressure. The air and flue ga path equipment include: forced draft (FD) fan, air preheater (APH), boiler furnace, induced draft (ID) fa

fly ash collectors (electrostatic precipitator or bughouse) and the flue gas stack.

For units over about 210 MW capacity, redundancy of key components is provided by installingduplicates of the FD fan, APH, fly ash collectors and ID fan with isolating dampers. On some units of abo60 MW, two boilers per unit may instead be provided.

Figure No.4- Schematic diagram of a coal-fired power plant steam generator

Boiler Furnace and Steam Drum

Once water inside the boiler or steam generator, the process of adding the latent heat of vaporization oenthalpy is underway. The boiler transfers energy to the water by the chemical reaction of burning somtype of fuel.

The water enters the boiler through a section in the convection pass called the economizer. From theeconomizer it passes to the steam drum. Once the water enters the steam drum it goes down the dowcomers to the lower inlet water wall headers. From the inlet headers the water rises through the water waland is eventually turned into steam due to the heat being generated by the burners located on the front anrear water walls (typically). As the water is turned into steam/vapour in the water walls, the steam/vapou

once again enters the steam drum.


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External View of an Industrial Boiler at BTPS, New Delhi

The steam/vapour is passed through a series of steam and water separators and then dryers inside the steamdrum. The steam separators and dryers remove the water droplets from the steam and the cycle through thwater walls is repeated. This process is known as natural circulation. The boiler furnace auxiliary equipmeincludes coal feed nozzles and igniter guns, soot blowers, water lancing and observation ports (in the furnac

walls) for observation of the furnace interior. Furnace explosions due to any accumulation of combustiblgases after a tripout are avoided by flushing out such gases from the combustion zone before igniting thcoal. The steam drum (as well as the superheater coils and headers) have air vents and drains needed foinitial start-up. The steam drum has an internal device that removes moisture from the wet steam enterinthe drum from the steam generating tubes. The dry steam then flows into the superheater coils. Geotherm plants need no boiler since they use naturally occurring steam sources. Heat exchangers may be used wherthe geothermal steam is very corrosive or contains excessive suspended solids. Nuclear plants also bowater to raise steam, either directly passing the working steam through the reactor or else using anintermediate heat exchanger.

Fuel Preparation System

In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into small pieceand then conveyed to the coal feed hoppers at the boilers. The coal is next pulverized into a very fine powder. The pulverisers may be ball mills, rotating drum grinders, or other types of grinders. Some powestations burn fuel oil rather than coal. The oil must kept warm (above its pour point) in the fuel oil storagtanks to prevent the oil from congealing and becoming unpumpable. The oil is usually heated to abou100C before being pumped through the furnace fuel oil spray nozzles.


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Boiler Side of the Badarpur Thermal Power Station, New Delhi

Boilers in some power stations use processed natural gas as their main fuel. Other power stations may us processed natural gas as auxiliary fuel in the event that their main fuel supply (coal or oil) is interrupted. Isuch cases, separate gas burners are provided on the boiler furnaces.

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 whichimparts a swirling motion to the powdered coal to enhance mixing of the coal powder with the incomin preheated combustion air and thus to enhance the combustion. To provide sufficient combustion temperatuin the furnace before igniting the powdered coal, the furnace temperature is raised by first burning somlight 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 thatmosphere and, first warming it in the air preheater for better combustion, injects it via the air nozzles othe furnace wall. The induced draft fan assists the FD fan by drawing out combustible gases from thefurnace, maintaining a slightly negative pressure in the furnace to avoid backfiring through any opening. Athe furnace outlet and before the furnace gases are handled by the ID fan, fine dust carried by the outlegases is removed to avoid atmospheric pollution. This is an environmental limitation prescribed by law, an

additionally minimizes erosion of the ID fan.


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AUXILIARY SYSTEM

Fly Ash Collection

Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters (osometimes 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 flash 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 thfurnace. 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 du

to blow-down and leakages have to be made up for so as to maintain the desired water level in the boilesteam drum. For this, continuous make-up water is added to the boiler water system. The impurities in thraw water input to the plant generally consist of calcium and magnesium salts which impart hardness to thwater. Hardness in the make-up water to the boiler will form deposits on the tube water surfaces which wilead to overheating and failure of the tubes. Thus, the salts have to be removed from the water and that idone by a seprater.

Electric Generator

The steam turbine-driven generators have auxiliary systems enabling them to work satisfactorily and safelyThe steam turbine generator being rotating equipment generally has a heavy, large diameter shaft. The shaftherefore requires not only supports but also has to be kept in position while running. To minimize thfrictional resistance to the rotation, the shaft has a number of bearings. The bearing shells, in which the sharotates, are lined with a low friction material like Babbitt metal. Oil lubrication is provided to further reducthe friction between shaft and bearing surface and to limit the heat generated.


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Figure No.5 -A typical water cooled condensor

Feedwater Heater

A Rankine cycle with a two-stage steam turbine and a single feedwater heater. In the case of a conventionasteam-electric power plant utilizing a drum boiler, the surface condenser removes the latent heat ovaporization from the steam as it changes states from vapour to liquid. The heat content (btu) in the steam referred to as Enthalpy. The condensate pump then pumps the condensate water through a feedwater heateThe feedwater heating equipment then raises the temperature of the water by utilizing extraction steam frovarious stages of the turbine. Preheating the feedwater reduces the irreversibilitys involved in steam

generation and therefore improves the thermodynamic efficiency of the system.[9] This reduces plan

operating costs and also helps to avoid thermal shock to the boiler metal when the feedwater is introduce back into the steam cycle.


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BASIC STEPS OF ELECTRICITY GENERATION

The basic steps in the generation of electricity from coal involves following steps : Coal to steam

Steam to mechanical power Mechanical power to electrical power

COAL TO ELECTRICITY: BASICS

The basic steps in the generation of coal to electricity are shown below:

Figure No. 6

Coal to Steam

Coal from the coal wagons is unloaded in the coal handling plant. This Coal is transported up to the raw co bunkers with the help of belt conveyors. Coal is transported to Bowl mills by Coal Feeders. The coal i

pulverized in the Bowl Mill, where it is ground to powder form. The mill consists of a round metallic tabon which coal particles fall. This table is rotated with the help of a motor. There are three large steel rollers

which are spaced 120 apart. When there is no coal, these rollers do not rotate but when the coal is fed to thetable it packs up between roller and the table and these forces the rollers to rotate. Coal is crushed by thcrushing action between the rollers and the rotating table. This crushed coal is taken away to the furnacthrough coal pipes with the help of hot and cold air mixture from P.A. Fan. P.A. Fan takes atmospheric air, part of which is sent to Air-Preheaters for heating while a part goes directly to the mill for temperatur

control. Atmospheric air from F.D. Fan is heated in the air heaters and sent to the furnace as combustion air


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Water from the boiler feed pump passes through economizer and reaches the boiler drum. Water from thedrum passes through down comers and goes to the bottom ring header. Water from the bottom ring header idivided to all the four sides of the furnace. Due to heat and density difference, the water rises up in the watwall tubes. Water is partly converted to steam as it rises up in the furnace. This steam and water mixture iagain taken to the boiler drum where the steam is separated from water.

BASIC POWER PLANT CYCLE

Figure No.7 -A simplified diagram of a thermal power plant

The thermal (steam) power plant uses a dual (vapour+ liquid) phase cycle. It is a close cycle to enable thworking fluid (water) to be used again and again. The cycle used is Rankin Cycle modified to includsuperheating of steam, regenerative feed water heating and reheating of steam.

Figure No. 8- RANKIN CYCLE


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On large turbines, it becomes economical to increase the cycle efficiency by using reheat, which is a way o partially overcoming temperature limitations. By returning partially expanded steam, to a reheat, the averagtemperature at which the heat is added, is increased and, by expanding this reheated steam to the remaininstages of the turbine, the exhaust wetness is considerably less than it would otherwise be conversely, if thmaximum tolerable wetness is allowed, the initial pressure of the steam can be appreciably increased.

Bleed Steam Extraction: For regenerative system, nos. of non-regulated extractions is taken from HP, IPturbine.Regenerative heating of the boiler feed water is widely used in modern power plants; the effect being tincrease the average temperature at which heat is added to the cycle, thus improving the cycle efficiency.

FACTORS AFFECTING THERMAL CYCLE EFFICIENCY

Thermal cycle efficiency is affected by following :

Initial Steam Pressure. Initial Steam Temperature. Whether reheat is used or not, and if used reheat pressure and temperature. Condenser pressure. Regenerative feed water heating.


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ELECTRICAL MAINTAINANCE DEPARTMENT- I(EMD I)

COAL HANDLING PLANT

SWITCHGEAR

ELECTRIC MOTORS

1. Coal Handling Plant

Coal is delivered by highway truck, rail, and barge or collier ship. Some plants are even built nearCoal mines and coal is delivered by conveyors. A large coal train called a "unit train" may be a kilometre

(over a mile) long, containing 60 cars with 100 tons of coal in each one, for a total load of 6,000 tons. Alarge plant under full load requires at least one coal delivery this size every day. Plants may get as many athree to five trains a day, especially in "peak season", during the summer months when power consumptiois high. A large thermal power plant such as the Badarpur Thermal Power Station, New Delhi stores severamillion tons of coal for use when there is no wagon supply.

Figure No. 9- COAL HANDLING PLANT


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Coal Handling Plant Layout

Modern unloaders use rotary dump devices, which eliminate problems with coal freezing in Bottom dumpcars. The unloaded includes a train positioner arm that pulls the entire train to position each car over a coahopper. The dumper clamps an individual car against a platform That swivels the car upside down to dumthe coal. Swivelling couplers enable the entire 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", whicrelies on air pressure from the engine plus a "hot shoe" on each car. This "hot shoe" when it comes intocontact with a "hot rail" at the unloading trestle, shoots an electric charge through the air dump apparatuand causes the doors on the bottom of the car to open, dumping the coal through the opening in the trestlUnloading one of these trains takes anywhere from an hour to an hour and a half. Older unloaders may stiuse manually operated bottom-dump rail cars and a "shaker" attached to dump the coal. Generating stationadjacent to a mine may receive coal by conveyor belt or massive diesel electric- drive trucks.

Coal is prepared for use by crushing the rough coal to pieces less than 2 inches (50 mm) in size. The coal ithen transported from the storage yard to in-plant storage silos by rubberized Conveyor belts at rates up t4,000 tons/hour. In plants that burn pulverized coal, silos feed coal pulverisers (coal mill) that take the

larger 2 inch pieces grind them into the consistency of face powder, classify them, and mixes them wit primary combustion air which transports the coal to the furnace and preheats the coal to drive off excesmoisture content. In plants that do not burn pulverized coal, the larger 2 inch pieces may be directly fed intthe silos which then feed the cyclone burners, a specific kind of combustor that can efficiently burn large

pieces of fuel.

OLD COAL HANDLING PLANT

It feeds units 1, 2, 3 (95 MW each). OCHP has two streams from wagon tippler to tippler conveyors in thmain power house building via crusher house; each stream contains one wagon tippler, two vibrating feede below wagon tippler, one vibrating screen, one building conveyors and necessary conveyors. A singltelescopic chute reclaim hopper and series conveyors achieve the stacking and reclaiming.

Coal unloaded by the wagon tippler is fed to the main conveyor by the vibrating feeders. The mainconveyors 1A/1B each of 600 m tones per hour, which is running partly underground and partly oveground, conveys coal to the crusher house. Coal is fed to the crusher through vibrating screen.

The coal after being crushed in the crushers is transported to the bunker conveyor and from the undeconveyor coal is fed into the bunker with the help of travelling tipplers with the help of bunker conveyoAlternatively when the bunkers are full, uncrushed coal is by passed in the crusher house and transported i

the stock yard for stacking through the telescopic chutes. However, the provisions also make to stack thcoal into the yard after crushing in the crusher house.


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The motor of 75 HP used in the wagon tippler is fed by three feeders. One main feeder which remain alwayhold and two other feeders which are operated alternatively, one during one side rotation of the motor anthe other during the other side rotation of the motor. There is a limiting switch associated with motor. Fromwagon tippler the coal falls in the hopper, from hopper it falls on the screen from where the coal of the largsize is separated .When the vibrator vibrates, the coal falls on the conveyor from the screen.

NEW COLD HANDLING PLANT

N.C.H.P feeds units 4 and 5(210 MW each). It consists double stream (one working at a time) of conveyoof capacity 600 mph, which is single. One wagon tippler, four vibrating feeders of 300mtph each below thwagon tippler, two rotator breakers of 600mtph each in breaker house (primary crusher house) reject binhouse. Two crushers (ring granular), two vibrating feeders and two belt feeders of 600mtph each insecondary crusher house. One telescopic chute for stacking, two sets of reclaim hoppers, necessary transfe

points and new rail tracks for wagon tippler are provided.The wagon tippler is provided with internal weighbridge for recording the gross and true weight of thwagon and located beyond the old marshalling yard. Due to space limitation only one wagon tippler i provided. Car pullers are used for placing loaded wagon on the wagon tippler and removing the emptwagon. The locomotive does marshalling of the load wagon rake for placing it to the inhaul side and fotaking the away the empty wagon rake. The marshalling yard is used for placing the loaded rake; the coafrom the wagon tippler house (6 in numbers) is fed to the reclaim conveyor by the vibrating feeders, th

reclaim conveyors are partly under the ground and partly over the ground. From reclaim conveyors coal itransported to the bunker house (primary crusher house) and fed into the rotatory breakers.

In the rotatory breakers the coal side is reduced to 100mm and the foreign materials like stone shale etc. arseparated. The coal is sent to secondary crusher house for secondary crushing or to the old stockyard fostacking through cantilever conveyor with telescopic chute. The reject conveyors convey the foreignmaterial to the reject bin. Dump trucks are used to carry the reject from the reject bin to reject disposal areIn the secondary crusher house coal is fed to the secondary rusher of ring granulator type (2 in numberthrough vibrating feeders. The coal after being crushed in the secondary crusher to 20mm in size istransports to the coalbunker conveyor for unit 4 and 5 finally. Finally coal is fed into the through travellintipplers. Stacking of the coal in the coal stockyard is done by the cantilever conveyors with telescopic chutwhich is conical stockpile of 15mm height. The stockpile is spread by means of bulldozers for making common stockpile for the plant. Normally coal is fed to the bunkers of unit 4 and 5 from N.C.H.P Necessary dust systems are provided. There is a separate control room with necessary control panel anMCCS for N.C.H.P.


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VARIOUS CONSTITUENTS OF NCHP

WAGON TIPPLER

There are 3 wagon tipplers in the BTPS-two for OCHP and one for NCHP.In this unit coal comes from

Jawar Mines in Bihar through wagons, so transportation is done by Indian Railways for BTPS. Each wagocarries about 50-60 tonnes of coal, wt. of wagon are about 10-15m tonnes, so wagon tippler is handlinabout 70-75m tons of coal. During unloading of wagon, wagon is brought to the base of the wagon tipplerThis base is operated with the help of the gear system. This gear system is then operated by motor of 75hcoupled to the gear box, the torque from the motor is then transported to the wagon tippling base, which then rotated with the help of the rake and pinion arrangement, the complete rotation of the wheel is 15degree angle. To prevent the full rotation counter weight are provided. Heat resistant belting is alwayrecommended for handling material at temperature over 60 degrees centigrade.

BREAKER HOUSE

Size of the coal at wagon tippler is about 300mm, which is supposed to be very large. To prevent muchload on the crushers, breakers are provided in between which reduces the size of coal to 100mm. Coal icarried to breaker house through conveyor 12A/12B, which is then dropped inside the hopper, from hoppethe coal goes to chute. Now the direction of coal is selected. It can either be sent to rotatory breakers odirectly to the reversible bulk feeders (RBF 1, 2). There are two rotatory breakers (RB). Each breaker hatwo rotatory drums. The coal comes in between these drums and broken to smaller pieces. The ston particles which are not crushed by the rotatory drums are thrown out of the breaker system due to rotation the drum to conveyor belts 18A/18B which takes them out to reject bin house.

CRUSHER HOUSE

Coal of 100mm size from transfer point (TP 7) is carried to the crusher house main hopper in the conveyo belts 14A/14B. Before dropping into the main hopper, a magnetic separator (MS) is provided to remove aferrous impurities. A conveyor belt is continuously used, moving around the MS on which magnetiimpurities are attached and carry to the iron chute. From main hopper coal goes to vibrating feeders (VF 78). From this place it goes to the crusher. There are two crushers in the crusher house; using electric motooperates crusher (CR 1, 2). In crusher house there are four rows and each has two shafts there are two typeof hammers used

1. Plane hammer

2. Teethed hammer


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These are arranged alternatively in each row. The number of hammers in each row follows the sequence13,14,13,14. Thus total no. of hammers is 54, breaking plates are provided inside the crusher. The coal i being crushed between the hammers and breaking plates. The crushed coal is passed through a screen or wire mesh which determines the size of crushed coal. Bigger pieces wont pass through the screen. Capacity

of the crusher is 600mtones/hr.The size of the coal after crushing is 20mm, which is then fed to the be

feeder (BF 1, 2) through flap gates (FG 12, 13) to conveyor belts 15A/15B. Crushed coal from this conveyo passes through the metal detector. After detection the metal pieces are removed manually. The coal is thetransferred to the TP 8and then to the bunkers. NCHP crushed coal is sent to the boiler unit 4 and 5. The coto the units 1, 2, 3 can be fed from this plant. The coal is further pulverised in bowl mill. Belt wares ar provided to conveyors 15A/15B.

WAGON TIPPLER

Power : 75W

Rated Voltage : 415V

Rated Current : 102A

Phase : 3 phase

RPM : 1480 rpm

Frequency : 50HZ

CONVEYORS

There are 14 conveyors in the plant. They are numbered so that their function can be easily demarcated

Conveyors are made of rubber and more with a speed of 250-300m/min. Motors employed for conveyorhas a capacity of 150 HP. Conveyors have a capacity of carrying coal at the rate of 400 tons per hour. Fewconveyors are double belt, this is done for imp. Conveyors so that if a belt develops any problem the proceis not stalled. The conveyor belt has a switch after every 25-30 m on both sides so stop the belt in case oemergency


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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 protethis switch checks the speed of the belt and switches off the motor when speed is zero.

CRUSHER HOUSE

Power 400HP

Rated Voltage 415V , 3 phase

RPM 1480 rpm

Frequency 50 HZ

VENTILLATION DEVICES

Dust extraction or dust separation pipes come under this category. Fan is used to blow the dust out pipefrom which it goes to cyclone separator and where water is spread over it to form slurry and get separated.

SAFETY DEVICES FOR BELT CONVEYORS

Sometimes the belt is wet due to any reason, so it may not run due to reduced friction. A switch senses th

and prevents the belt from choking. Sometime any accident may occur which requires the belt to stop, th pull cords are pulled to stop the conveyor. This system starts again only when the pull cords are rest.

There is a push button in the control room from where the belt can be stopped in case of emergencystoppage. Other equipments are pulley. Pulleys are made of mild steel, rubber logging is provided toincrease the friction factor between the pulley and belt.


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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. thdepth 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 becontrolled by speed control of aviator drive controlling damper and aviator change.

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 baon coal and attraction as per the particles move over each other as well as over the Armour lines, the coagets crushed. Large particles are broken by impact and full grinding is done by attraction. The Drying angrinding option takes place simultaneously inside the mill. In ball mill coal is converted to powdered formand due to pneumatic action the powdered form of coal is transferred upwards.

Motor specification : squirrel cage induction motor

Rating : 340 KW

Voltage : 6600KV

Current : 41.7A

Speed : 980 rpm

Frequency : 50 Hz

No-load current : 15-16 A

4. Classifier :

It is equipment which serves separation of fine pulverized coal particles medium from coarse medium. Th

pulverized coal along with the carrying medium strikes the impact plate through the lower part. Larg particles are then transferred to the ball mill.


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5. MILL FAN

From ball mill the powdered coal is sucked through mill fan.

6. Cyclone Separators

It separates the pulverized coal from carrying medium. The mixture of pulverized coal vapour caters thcyclone separators.

7. The Turnigate

It serves to transport pulverized coal from cyclone separators to pulverized coal bunker or to wormconveyors. There are 4 turnigates per boiler.

VARIOUS INSTRUMENTS/EQUIPMENTS AT

NCHP

MAGNETIC SEPERATOR

They are two in numbers and attached to conveyors 14A/14B.There might be possibility that coal has somiron particles in it.It is a box containing impuritys coil wounded over the magnetic material. Electr ic currentis passed after operating it from control unit. A very heavy high magnetic flux density of 700wb/sqm i produced. This flux can attract the iron pieces of 30-40kg.

METAL DETECTOR

They are provided near the conveyor 15A/15B to detect metal pieces. It has two plates having constan

reluctance between them. Coal and belt are non metallic type, so doesnt affect the reluctance. But as soonas any metal part comes, reluctance is affected so a change in voltage is sensed and motor is tripped. Thmotor tripping gives current to the solenoid which attracts the metal rod inside it and sand bag marke provided just after MD falls when metal detected.

WAGON TIPPLER

Power : 75HP


Rated Current : 102A


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Phase : 3 phase

RPM : 1480 rpm

Frequency : 50HZ

CONVEYORS

There are 14 conveyors in the plant. They are numbered so that their function can be easily demarcatedConveyors are made of rubber and more with a speed of 250-300m/min. Motors employed for conveyorhas a capacity of 150 HP. Conveyors have a capacity of carrying coal at the rate of 400 tons per hour. Fewconveyors are double belt, this is done for imp. Conveyors so that if a belt develops any problem the procesis not stalled. The conveyor belt has a switch after every 25-30 m on both sides so stop the belt in case oemergency. The conveyors are 1m wide, 3 cm thick and made of chemically treated vulcanized rubber. Th

max angular elevation of conveyor is designed such as never to exceed half of the angle of response andcomes out to be around 20 degrees.

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 protethis switch checks the speed of the belt and switches off the motor when speed is zero.

CRUSHER HOUSE

Power : 400HP


Phase : 3 phase

RPM : 1480 rpm

Frequency : 50 HZ


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SWITCH GEAR

INTRODUCTION

Switchgear is one that makes or breaks the electrical circuit.

The equipments that normally fall in this category are:-

1. ISOLATOR

An isolator is one that can break the electrical circuit when the circuit is to be switched on no load. These aused in various circuits for isolating the certain portion when required for maintenance etc. An operatin

mechanism box normally installed at ground level drives the isolator. The box has an operating mechanismin addition to its contactor circuit and auxiliary contacts may be solenoid operated pneumatic three phasmotor or DC motor transmitting through a spur gear to the torsion shaft of the isolator. Certain interlocks aalso provided with the isolator.

These are

1. Isolator cannot operate unless breaker is open.

2. Bus 1 and bus 2 isolators cannot be closed simultaneously.

3. The interlock can be bypass in the event of closing of bus coupler breaker.

4. No isolator can operate when the corresponding earth switch is on

2. SWITCHING ISOLATOR

Switching isolator is capable of:

1. Interrupting charging current.

2. Interrupting transformer magnetising current.

3. Load transformer switching.

Its main application is in connection with the transformer feeder as the unit makes it possible to switchgeaone transformer while the other is still on load


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3. CIRCUIT BREAKER

One which can make or break the circuit on load and even on faults is referred to as circuit breakers.

This equipment is the most important and is heavy duty equipment mainly utilized for protection of

various circuits and operations on load. Normally circuit breakers installed are accompanied by

isolators.

4. LOAD BREAK SWITCHES

These are those interrupting devices which can make or break circuits. These are normally on same

circuit, which are backed by circuit breakers.

5. EARTH SWITCHES

Devices which are used normally to earth a particular system, to avoid any accident happening due to

induction on account of live adjoining circuits. This equipments do not handle any appreciable

current at all. Apart from this equipment there are a number of relays etc. which are used in

switchgear


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LT SWITCHGEAR

In LT switchgear there is no interlocking. It is classified in following ways:-

1. Main Switch

Main switch is control equipment which controls or disconnects the main supply. The main switch for phase supply is available for that range 32A, 63A, 100A, 200Q, 300A at 500V grade.

2. Fuses

With Avery high generating capacity of the modern power stations extremely heavy carnets would flow inthe fault and the fuse clearing the fault would be required to withstand extremely heavy stress in process.It used for supplying power to auxiliaries with backup fuse protection. Rotary switch up to 25A. With fuses,quick break, quick make and double break switch fuses for 63A and 100A, switch fuses for 200A, 400A,600A, 800A and 1000A are used.

3. Contractors

AC Contractors are 3 poles suitable for D.O.L Starting of motors and protecting the connected motors

4. Overload Relay

For overload protection, thermal over relay are best suited for this purpose. They operate due to the actionof heat generated by passage of current through relay element.

5. Air Circuit Breakers

It is seen that use of oil in circuit breaker may cause a fire. So in all circuits breakers at large capacity air ahigh pressure is used which is maximum at the time of quick tripping of contacts. This reduces the possibility of sparking. The pressure may vary from 50-60 kg/cm^2 for high and medium capacity circu breakers.


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HT SWITCHGEAR

1. Minimum oil Circuit Breaker

These use oil as quenching medium. It comprises of simple dead tank row pursuing projection from it. The

moving contracts are carried on an iron arm lifted by a long insulating tension rod and are closedsimultaneously pneumatic operating mechanism by means of tensions but throw off spring to be provided amouth of the control the main current within the controlled device.

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

2. Air Circuit Breaker

In this the compressed air pressure around 15 kg per cm^2 is used for extinction of arc caused by flow of aaround the moving circuit . The breaker is closed by applying pressure at lower opening and opened byapplying pressure at upper opening. When contacts operate, the cold air rushes around the movable contactsand blown the arc.

It has the following advantages over OCB:-

i. Fire hazard due to oil are eliminated.ii. Operation takes place quickly.iii. There is less burning of contacts since the duration is short and consistent.iv. Facility for frequent operation since the cooling medium is replaced constantly.Rated Voltage-6.6 KVCurrent-630 AAuxiliary current-220 V/DC


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3. SF6 Circuit Breaker

This type of circuit breaker is of construction to dead tank bulk oil to circuit breaker but the principle ofcurrent interruption is similar to that of air blast circuit breaker. It simply employs the arc extinguishingmedium namely SF6. The performance of gas. When it is broken down under an electrical stress. It willquickly reconstitute itself

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

4. Vacuum Circuit Breaker

It works on the principle that vacuum is used to save the purpose of insulation and it implies that pr. of gasat which breakdown voltage independent of pressure. It regards of insulation and strength, vacuum issuperior dielectric medium and is better that all other medium except air and sulphur which are generallyused at high pressure. Rated frequency-50 Hz Rated making Current-10 Peak KA

Rated Voltage-12 KV

ELECTRIC MOTORS

An electric motor uses electrical energy to produce mechanical energy. The reverse process that ofusing mechanical energy to produce electrical energy is accomplished by a generator or dynamo. Tractiomotors used on locomotives and some electric and hybrid automobiles often performs both tasks if thevehicle is equipped with dynamic brakes. A High Power Electric Motor


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Categorization of Electric Motors

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

(AC) types. The on-going trend toward electronic control further muddles the distinction, as modern drive

have moved the commutator out of the motor shell. For this new breed of motor, driver circuits are relieupon to generate sinusoidal AC drive currents, or some approximation of. The two best examples are: th brushless DC motor and the stepping motor, both being poly phase AC motors requiring external electroncontrol.There is a clearer distinction between a synchronous motor and asynchronous types. In theSynchronous types, the rotor rotates in synchrony with the oscillating field or current (eg. Permanent magnmotors). In contrast, an asynchronous motor is designed to slip; the most ubiquitous example being thcommon AC induction motor which must slip in order to generate torque.

At Badarpur Thermal Power Station, New Delhi, mostly AC motors are employed for various purposeWe had to study the two types of AC Motors viz. Synchronous Motors and Induction Motor. The motorhave been explained further.

AC Motor

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

outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and ainside rotor attached to the output shaft that is given a torque by the rotating field.There are two types of AC motors, depending on the type of rotor used. The first is theSynchronous motor, which rotates exactly at the supply frequency or a sub multiple of the supply frequencThe 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 supplfrequency. 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 magneat the same rate as the alternating current and resulting magnetic field which drives it. Another way osaying 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 locagrid it's connected to. It does this by providing reactive power to or consuming reactive power from the griIn this case the synchronous motor is called a Synchronous condenser. Electrical power plants almost alway


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use synchronous generators because it's very important to keep the frequency constant at which thegenerator 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 th eir position when a DC current is applied to both the stator and the rotorWindings.

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 currenslightly, which can help achieve a better power factor Correction for the whole installation.

Their construction allows for increased electrical efficiency when a low speed is required (As in ball miland 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 devi 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 severways to supply power to the rotor. In a DC motor this power is supplied to the armature directly from a DCsource, while in an AC motor this power is induced in the rotating device. An induction motor is sometimecalled a rotating transformer because the stator (stationary part) is essentially the primary side of thtransformer and the rotor (rotating part) is he secondary side. Induction motors are widely used, especiall

poly phase induction motors, which are frequently used in industrial drives.Induction motors are now the preferred choice for industrial motors due to their rugged


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Construction, lack of brushes (which are needed in most DC Motors) and thanks to modern Powerelectronics the ability to control the speed of the motor.

Construction

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

conductor. The number of 'poles' can vary between motor types but the poles are always in pairs (i.e. 2, 4, 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 aluminium that span the length of the rotor, and are connected through a ring at each en

The rotor bars in squirrel-cage induction motors are not straight, but have some skew to reduce noise anharmonics.

The motor's phase type is one of two types:1. Single-phase induction motor2. 3-phase induction motor

Types: Based on type of phase supply1. three phase induction motor (self starting in nature)2. Single phase induction motor (not self-starting)

Other

1. Squirrel cage induction motor2. Slip ring induction motor


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ELECTRICAL MAINTAINANCE DEPARTMENT- II

(EMD II) GENERATOR

PROTECTION

TRANSFORMER

SWITCHYARD

GENERATORS

The basic function of the generator is to convert mechanical power, delivered from the shaft of the turbineinto 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 direccurrent in the copper winding of the rotor or field, which generates three-phase alternating currents anvoltages in the copper winding of the stator (armature). The stator winding is connected to terminals, whicare in turn connected to the power system for delivery of the output power to the system the class ogenerator under consideration is steam turbine-driven generators, commonly called turbo generators. Thesmachines are generally used in nuclear and fossil fuelled power plants, co-generation plants, and combustioturbine units. They range from relatively small machines of a few Megawatts (MW) to very large generato

with ratings up to 1900 MW. The generator particular to this category are of the two- and four-pole desigemploying round-rotors, with rotational operating speeds of 3600 and 1800 rpm in North America, parts oJapan, and Asia(3000 and 1500 rpm in Europe, Africa, Australia, Asia, and South America). At BadarpuThermal 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 combustionturbine) needs to be admitted to the turbine to increase power output. Hence more energy is transmitted tthe generator from the turbine, in the form of a torque. This torque is mechanical in nature, bu

electromagnetically coupled to the power system through the generator. The higher the power output, thhigher the torque between turbine and generator.The power output of the generator generally follows the load demand from the system.


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Therefore the voltages and currents in the generator are continually changing based on the load demand. Thgenerator design must be able to cope with large and fast load changes, which show up inside the machine achanges in mechanical forces and temperatures. The design must therefore incorporate electrical currentcarrying materials (i.e., copper), magnetic flux-carrying materials (i.e., highly permeable steels), insulatinmaterials (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.

STATOR

The stator winding is made up of insulated copper conductor bars that are distributed around then siddiameter of the stator core, commonly called the stator bore, in equally spaced slots in the core to ensursymmetrical flux linkage with the field produced by the rotor. Each slot contains two conductor bars, one otop of the other. These are generally referred to as top and bottom bars. Top bars are the ones nearest the slo

opening (just under the wedge) and the bottom bars are the ones at the slot bottom. The core area betweeslots 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. Wyeconnection is done to allow a neural grounding point and for relay protection of the winding. The thre

phases are connected to create symmetry between them in the 360 degree arc of the stator bore. Thdistribution of the winding is done in such a way as to produce a 120degree difference in voltage peaks fromone phase to the other, hencethe term three- phase voltage. Each of the three phases may have one or more parallel circuits within the phase. The parallels can be connected in series or parallel, or a combination o both if it is a four-pole generator. This will be discussed in the next section. The parallels in all of the phaseare 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 overla between top and bottom bars. The overlap is staggered between top and bottom bars. The top bars on onside of the stator bore are connected to the bottom bars on the other side of the bore in one direction whilthe bottom bars are connected in the other direction on the opposite side of the stator. This connection witthe bars on the other side of the stator creates a reach or pitch of a certain number of slots. The pitch istherefore the number slots that the stator bars have to reach in the stator bore arc, separating the two bars t be connected. This is always less than 180 degrees.


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Once connected, the stator bars form a single coil or turn. The total width of the overlapping parallels called the breadth. The combination of the pitch and breadth create a winding or distribution factor. The

distribution factor is used to minimize the harmonic content of the generated voltage. In the case of a tw parallel path winding, these may be connected in series or parallel outside the stator bore, at the terminatioend of the generator. The connection type will depend on a number of other design issues regarding curren

carrying ability of the copper in the winding.

ROTOR

The rotor winding is installed in the slots machined in the forging main body and is distributedsymmetrically around the rotor between the poles. The winding itself is made up of many turns of copper tform the entire series connected winding. All of the turns associated with a single slot are generally called coil. The coils are wound into the winding slots in the forging, concentrically in corresponding positions o

opposite sides of a pole. The series connection essentially creates a single multi-turn coil overall, thadevelops the total ampere-turns of the rotor (which is the total current flowing in the rotor winding times thtotal number of turns).There are numerous copper-winding designs employed in generator rotors, but all rotor windings functio basically in the same way. They are configured differently for different methods of heat removal durinoperation. In addition almost all large turbo generators have directly cooled copper windings by air ohydrogen cooling gas.

BEARINGS

All turbo generators require bearings to rotate freely with minimal friction and vibration. The main roto body must be supported by a bearing at each end of the generator for this purpose. In some cases where throtor shaft is very long at the excitation end of the machine to accommodate the slip/collector rings, steady bearing is installed outboard of the slip collector rings. 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 thoverall generator rotor or the turbo generator line. There are generally two common types of bearingemployed in large generators, journal and tilting pad bearings. Journal bearings are the most common.

Both require lubricating and jacking oil systems, which will be discussed later in the book, under auxiliarsystems. When installing the bearings, they must be aligned in terms of height and angle to ensure that throtor sits in the bearing correctly. Such things as shaft catinery must be considered and pre -loading orshimming of the bearings to account for the difference when the rotor is at standstill and at speed. Getting

any of these things wrong in the assembly can cause the rotor to vibrate excessively and damage either throtor shaft or the bearing itself. Generally, a wipe of the bearing running surface or babbitt results.


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AUXILIARY SYSTEMS

All large generators require auxiliary systems to handle such things as lubricating oil for the rotor bearinghydrogen cooling apparatus, hydrogen sealing oil, de-mineralized water for stator winding cooling, anexcitation systems for field-current application. Not all generators require all these systems and the

requirement depends on the size and nature of the machine. For instance, air cooled turbo generators do norequire hydrogen for cooling and therefore no sealing oil as well. On the other hand, large generators withigh outputs, generally above 400MVA, have water-cooled stator windings, hydrogen for cooling the statocore and rotor, seal oil to contain the hydrogen cooling gas under high pressure, lubricating oil for th bearings, and of course, an excitation system for field current.There are five major auxiliary systems that may be used in a generator. They are given asfollows:

1. Lubricating Oil System2. Hydrogen Cooling System3. Seal Oil System4. Stator Cooling Water System5. Excitation System

Each system has numerous variations to accommodate the hundreds of different generator configurationthat may be found in operation. But regardless of the generator design and which variation of a system is i

use, they all individually have the same basic function as described before.

Lubricating Oil System

The lube-oil system provides oil for all of the turbine and generator bearings as well as being the source oseal oil for the seal-oil system. The lube-oil system is generally grouped in with the turbine components anis not usually looked after by the generator side during maintenance. It is mentioned primarily focompleteness.

1.Lubricating Oil System Layout

The main components of the lube-oil system consists generally of the main lube-oil tank, pumps, heaexchangers, filters and strainers, centrifuge or purifier, vapour extractor, and various check valves andinstrumentation. The main oil tank serves both the turbine and generator bearing and is often also the sourcof the sealing oil for the hydrogen seals. It is usually located under the turbines and holds thousands ogallons of oil.Heat exchangers are provided for heat removal from the lube oil. Raw water from the local lake or river icirculated on one side of the cooler to remove the heat from the lube oil circulating on the other side of thheat exchanger.


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Full flow filters and/or strainers, or a combination of both, are employed for removal of debris from the luboil. Strainers are generally sized to remove larger debris and filters for debris in the range of a few micronand larger. They can be mechanical or organic type filters and strainers. Debris removal is important toreduce the possibility of scoring the bearing Babbitt or plugging of the oil lines.A centrifuge or purifier is used to remove moisture from the oil. Moisture is also a contaminant to oil an

can cause it to lose its lubricating properties.

2. Hydrogen Cooling System

As the hydrogen cooling gas picks up heat from the various generator components within the machine, ittemperature rises significantly. This can be as much as 46oC, and therefore the hydrogen must be cooledown prior to being re-circulated through the machine for continuous cooling. Hydrogen coolers or heaexchangers are employed for this purpose.

Hydrogen coolers are basically heat exchangers mounted inside the generator in the enclosed atmosphereCooling tubes with fins are used to enlarge the surface area for cooling, as the hydrogen gas passes over

the outside of the finned tubes. Raw water (filtered and treated) from the local river or lake is pumped

through the tubes to take the heat away from the hydrogen gas and outside the generator. The tubes must bextremely leak-tight to ensure that hydrogen gas does not enter into the tubes, since the gas is at a highe pressure than the raw water.

3. Seal Oil System

As most large generators use hydrogen under high pressure for cooling the various internal components. Tkeep the hydrogen inside the generator, various places in the generator are required to seal against hydrogeleakage to atmosphere. One of the most difficult seals made is the juncture between the stator and throtating shaft of the rotor. This is done by a set of hydrogen seals at both ends of the machine. The seals ma be of the journal (ring) type or the thrust-collar type. But one thing both arrangements have in common the requirement of high pressure oil into the seal to make the actual seal. The system, which provides the

oil to do this, is called the seal-oil system. In general, the most common type of seal is the journal type. Tharrangement functions by pressurized oil fed between two floating segmented rings, usually made of bronzor Babbitt steel. At the ring outlet, against the shaft, oil flows in both directions from the seals along throtating shaft. For the thrust-collar type, the oil is fed into a Babbitt running face via oil delivery ports, anmakes the seal against the rotating thrust collar. Again, the oil flows in two directions, to the air side and thehydrogen side of the seals.The seal oil itself is actually a portion of the lube oil, diverted from the lubricating oil system. It is then feto a separate system of its own with pumps, motors, hydrogen detraining or vacuum degassing equipmenand controls to regulate the pressure and flow.


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4. Stator Cooling Water System

The stator cooling water system (SCW) is used to provide a source of de-mineralized water to the generatostator winding for direct cooling of the stator winding and associated components. SCW is generally used machines rated at or above 300 MVA. Most SCW systems are provided as package units, mounted on

singular platform, which includes all of the SCW system components. All components of the system argenerally made from stainless steel or copper materials.

Excitation System

STATIC EXCITATION SYSTEM

The generators in stage -1(u-1&u-2) have this excitation system. Static excitation system has slip ring ancarbon brush arrangement. It consists of step down transformer, converter and AVR (automatic voltageregulator).

BRUSHLESS EXCITATION SYSTEM

The generators in stage -2(U-3, U-4&&U- 5) have this excitation system. It has two exciters, one is maiexciter and other is pilot exciter.

GENERATOR PROTECTION

STATOR PROTECTION

The neutral of star connected winding is connected to primary of neutral grounding transformer, so thaearth fault current is limited by over voltage relay.

DIFFERENTIAL PROTECTION

In case of phase-to-phase fault generator is protected by longitudinal differential relay.


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TRANSFORMER

TYPE OF TRANSFORMERS

GENRATOR TRANSFORMER:

This is a step up transformer. This supply gets its primary supply from generator and its secondary suppliethe switchyard from where it is transmitted to grid. This transformer is oil cooled. The primary of thitransformer is connected in star. The secondary is connected in delta. These are four in number.

STATION TRANSFORMER:

This transformer has almost the same rating as the generator transformer. Its primary is connected in deltand secondary in star. It is a step down transformer. These are 4 in number.

UNIT AUXILIARY TRANSFORMER :

This is a step down transformer. The primary receives from generator and secondary supplies a 6.6 KV bus. This is oil cooled. These are 8 in number.

NEUTRAL GROUNDED TRANSFORMER:

This transformer is connected with supply coming out of UAT in stage-2. This is used to ground theexcess voltage if occurs in the secondary of UAT in spite of rated voltage.


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SWITCH YARD

As we know that electrical energy cant be stored like cells, so what we generate should be consumed

instantaneously. But as the load is not constants therefore we generate electricity according to need i.e. thgeneration depends upon load. The yard is the places from where the electricity is send outside. It has bot

outdoor and indoorequipments .

OUTDOOR EQUIPMENTS

BUS BAR

LIGHTENING ARRESTER

WAVE TRAP

BREAKER

CAPACITOR VOLTAGE TRANSFORMER

CORONA RING

EARTHING ROD

CURRENT TRANSFORMER

POTENTIAL TRANSFORMER

LIGHTENING MASK

LIGHTENING MOOSE

INDOOR EQUIPMENTS

RELAYS

CONTROL PANELS

CIRCUIT BREAKER:

The code for circuit breaker is 52. An electric power system needs some form of switchgear in order t

operate it safely & efficiently under both normal and abnormal conditions. Circuit breaker is an arrangeme by which we can break the circuit or flow of current. A circuit breaker in station serves the same purpose a


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switch but it has many added and complex features. The basic construction of any circuit breaker requirethe separation of contact in an insulating fluid that servers two functions:

It extinguishes the arc drawn between the contacts when circuit breaker opens.

It provides adequate insulation between the contacts and from each contact to earth.

The insulating fluids commonly used in circuit breakers are:

Compressed air

Oil which produces hydrogen for arc excitation.

Ultra high vacuum

Sulphur hexa fluorides

LIGHTING ARRESTER:

It saves the transformer and reactor from over voltage and over currents. We have to use the lightningarrester both in primary and secondary of transformer and in reactors. A meter is provided which indicatethe surface leakage and internal grading current of arrester.

Green arrester is healthy Red arrester is defective.

In case of red we first de-energize the arrester and then do the operation.

AIR BREAK EARTHING SWITCH:

The code of earthling switch is 5, 6, 7.The work of this equipment comes into picture when we want to shudown the supply for maintenance purpose. This help to neutralize the system from induced voltage fromextra high voltage. This induced power is up to 2KV in case of 400 KV lines.

BUS BAR:

Bus bars generally are of high conductive aluminum conforming to IS-5082 or copper of adequate crossection .Bus bar located in air insulated enclosures & segregated from all other components .Bus bar is preferably cover with polyurethane


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Current Transformer (CT):

A current transformer is a type of instrument transformer designed to provide a current in its secondarwinding proportional to the alternating current flowing in its primary

.

Figure No. 9 -Current Transformer Diagram

Application:

They are commonly used in metering and protective relaying in the electrical power industry where thefacilitate the safe measurement of large currents, often in the presence of high voltages.

The current transformer safely isolates measurement and control circuitry from the high voltagestypically present on the circuit being measured.

Current transformers are used extensively for measuring current and monitoring the operation of th power grid. The CT is typically described by its current ratio from primary to secondary. Often, multipCTs are installed as a "stack" for various uses (for example, protection devices and revenue metering mause separate CTs).

Capacitive Voltage Transformer (CVT):

A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down extra higvoltage signals and provide lowvoltage signals either for measurement or to operate a protective relay. Iits most basic form the device consists of three parts: two capacitors across which the voltage signal isplit, an inductive element used to tune the device to the supply frequency and a transformer used toisolate and further step-down the voltage for the instrumentation or protective relay


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CONTROL & INSTRUMENTATION

MANOMETRY LAB

PROTECTION AND INTERLOCK LAB AUTOMATION LAB FURNACE SAFETY SUPERVISORY SYSTEM(FSSS) ELECTRONICS TEST LAB

MANOMETRY LAB

TRANSMITTERS

It is used for pressure measurements of gases and liquids, its working principle is that the input pressure iconverted into electrostatic capacitance and from there it is conditioned and amplified. It gives an output o4-20 ma DC. It can be mounted on a pipe or a wall. For liquid or steam measurement transmitters imounted below main process piping and for gas measurement transmitter is placed above pipe.

MANOMETER

Its a tube which is bent, in U shape. It is filled with a liquid. This device corresponds to a difference in

pressure across the two limbs.

PRESSURE GAUGE

Its an oval section tube. Its one end is fixed. It is provided with a pointer to indicate the press ure on acalibrated scale. It is of 2 types:

(a) Spiral type: for Low pressure measurement.(b) Helical Type: for High pressure measurement.


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PROTECTION AND INTERLOCK LAB

INTERLOCKING

It is basically interconnecting two or more equipment so that if one equipment fails other one can performthe tasks. This type of interdependence is also created so that equipment connected together are started andshut down in the specific sequence to avoid damage.For protection of equipment tripping are provided for all the equipment. Tripping can be considered as theseries of instructions connected through OR GATE. When a fault occurs and any one of the tripping issatisfied a signal is sent to the relay, which trips the circuit. The main equipment of this lab are relay andcircuit breakers. Some of the instrument uses for protection are:

1. RELAY

It is a protective device. It can detect wrong condition in electrical circuits by constantly measuring theelectrical quantities flowing under normal and faulty conditions. Some of the electrical quantities arevoltage, current, phase angle and velocity.

2. FUSES

It is a short piece of metal inserted in the circuit, which melts when heavy current flows through it and thus breaks the circuit. Usually silver is used as a fuse material because:a) The coefficient of expansion of silver is very small. As a result no critical fatigue occurs and thus thecontinuous full capacity normal current ratings are assured for the long time. b) The conductivity of the silver is unimpaired by the surges of the current that produces temperatures justnear the melting point.c) Silver fusible elements can be raised from normal operating temperature to vaporization quicker than anyother material because of its comparatively low specific heat.

MINIATURE CIRCUIT BREAKER

They are used with combination of the control circuits to.a) Enable the staring of plant and distributors. b) Protect the circuit in case of a fault.In consists of current carrying contacts, one movable and other fixed. When a fault occurs the contactsseparate and are is stuck between them. There are three types of- MANUAL TRIP- THERMAL TRIP- SHORT CIRCUIT TRIP


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PROTECTION AND INTERLOCK SYSTEM

1. HIGH TENSION CONTROL CIRCUIT

For high tension system the control system are excited by separat

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