practical training panipat thermal plant

79
PRACTICAL TRAINING REPORT ON PANIPAT THERMAL POWER PLANT Submitted By Name: Rahul Poriya Roll No: 0703064 Under The Guidance Of Er. Santosh Kumar Gupta, XEN/TRG C&I Unit-3 (Panipat Thermal Power Station) Submitted To Department Of Electronics And Communication. Deenbandhu Chhotu Ram University Of Science And Technology. JULY 2011

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Page 1: Practical Training panipat thermal plant

PRACTICAL TRAINING REPORT

ON

PANIPAT THERMAL POWER PLANT

Submitted By

Name: Rahul Poriya

Roll No: 0703064

Under The Guidance Of

Er. Santosh Kumar Gupta, XEN/TRG

C&I Unit-3 (Panipat Thermal Power Station)

Submitted To

Department Of Electronics And Communication.

Deenbandhu Chhotu Ram University Of Science And Technology.

JULY 2011

Page 2: Practical Training panipat thermal plant

PRACTICAL TRAINING REPORT

ON

PANIPAT THERMAL POWER PLANT

Under The Guidance Of

Er. Santosh Kumar Gupta, XEN/TRG

C&I Unit-3 (Panipat Thermal Power Station)

Submitted By:

Rahul Poriya

0703064

Department Of Electronics And Communication.

Deenbandhu Chhotu Ram University Of Science And Technology.

Submitted To:

Rajeshwar Dass

Assistant Proff.

(ECE Deptt.)

D.C.R.U.S.T., Murthal

Page 3: Practical Training panipat thermal plant

i

CERTIFICATE

Page 4: Practical Training panipat thermal plant

ii

PREFACE

Training work is a major part of our course. It is a period in which we are introduced to the

industrial environment or in other words we can say that industrial training is provided for the

familiarization with the industrial environment, with the increased automation in the industries to

increase their production.

The object of this training work is to raise the level of performance in one or more of its aspects

and this may be achieved by teaching new trends, by imbuing an individual with new attitudes,

motives & other personality characteristics.

Practical training is an important part of theoretical studies. It covers all that remains in the

classroom i.e. without it our studies remains ineffective & Incomplete. Also it explores a student

to an invaluable treasure of experience.

Also it is a well known fact that practical training plays a very important role in future building

of an individual. Only gaining theoretical knowledge is just not sufficient for sure success in life,

practical training is must & I have been given an opportunity to gain practical experience at

PANIPAT THERMAL POWER PLANT . I avail this instance in a very satisfactory manner &

think it will be very beneficial for me in building my future.

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DECLARATION

I hereby certify that this Training report entitled ‗ Practical Training Report On Panipat Thermal

Power Plant is honestly my own work under the guidance of Er. Santosh Kumar Gupta. I am

fully aware that I have quoted some statements and ideas from various sources, and they are

properly acknowledged in the text.

The work presented here in this training report has not been submitted by me for the award of

any other degree of this or any other Institute/University.

Rahul Poriya

0703064

7th

Semester

ECE Department

Page 6: Practical Training panipat thermal plant

iv

ACKNOWLEDGEMENT

Inspiration and guidance are invaluable in all aspect of life, especially when it is academic. I

acknowledge my gratitude to all those who has given me timely help me in completing my

training report.

I am highly obliged to Mr. S.C. Vasishtha (Chief Engineer/PTPS-2, HPGCL) for allowing us to

join PTPS, Panipat as a trainee. I also want to express deep sense and gratitude to Er. AMOD

JINDAL, XEN (C & I -III) & Er. SHISH PAL SINGH, AEE (C & I -III) for his personal efforts

in taking me to sites, explaining the working of power plant Turbine, Generator & its aux. his

valuable guidance during my training at Panipat Thermal Power Station. At last but not the least

my special thanks to Er. Santosh Gupta, XEN (Training Division) for providing necessary

documents information and help in writing the report.

Rahul Poriya

0703064

7th

Semester

ECE Department

Page 7: Practical Training panipat thermal plant

v

LIST OF FIGURES

Figure Description

Page No.

1 1.1 Capacity Of P.T.P.S. 2

2 1.2 Power Generated By P.T.P.S.1 3

3 1.3 Performance Of P.T.P.S.1 4

4 1.4 Power Generated By P.T.P.S.2 4

5 1.5 Performance Of P.T.P.S.2 5

6 3.1 General Working Of Thermal Power Station 8

7 3.2 Boiler 13

8 3.3 A View of Turbine 17

9 3.4 Steam To Mechanical Power 18

10 3.5 A View Of Deaerator 23

11 3.6 Cooling Tower 25

12 3.7 Base of cooling tower with falling water 25

13 3.8 Cooling Tower system 25

14 4.1 Visual Display Unit 40

15 5.1 Unit Control 42

16 5.2 Proportional Control 44

7 5.3 Concept of C&I In Thermal Power Station 50

18 5.4 Typical Bourdon Tube Pressure Gages 52

19 5.5 Venturimeters 55

20 5.6 Control Valves 55

21 6.1 U Shaped Manometer 58

22 6.2 Relays 60

23 6.3 Fuse 61

24 6.4 Liquid In Glass Thermometer 63

25 6.5 Ultra Violet Sensor 64

26 6.6 Thermocouple 64

27 7.1 Summary of thermal power plant 68

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CONTENTS

CERTIFICATE i

PREFACE ii

DECLARATION iii

ACKNOWLEDGEMENT iv

LIST OF FIGURES v

1. INTRODUCTION

1.1 Introduction To P.T.P.S. 1

1.2 Salient Aspects of P.T.P.S.1 2

1.3 Salient Aspects of P.T.P.S.2 4

2. Inputs Of Thermal Power Plant

2.1 Water 6

2.2 Fuel Oil 6

2.3 Coal 7

3. General Working Of Thermal Power Station

3.1 Description For Boiler

3.1.1 Coal Cycle 10

3.1.2 Oil Cycle 11

3.1.3 Air & Flue Gas Cycle 11

3.2 Boiler Furnace and Steam Drum 14

3.3 Electric Generator 14

3.4 Cooling Tower as a flue gas stack 24

3.5 Electric Motor 26

3.5.1 AC Motor 26

3.5.2 Synchronous Motor 27

3.5.3 Induction Motor 27

3.6 Transformer 29

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4 Instrumentation In Thermal Plants

4.1 Introduction 31

4.2 Power Station instrumentation 31

4.3 Types Of Instruments

4.3.1 Indicator 32

4.3.2 Recorders 32

4.4 Presentation of information 33

4.5 Coding of instruments 33

4.6 Selection Criteria of instruments 34

4.7 Concept of instrument in Thermal Power Station 34

4.8 Power Station instrumentation

4.8.1 Temperature Measuring instruments 35

4.8.2 Pressure Measuring instruments 36

4.8.3 Level Measurement 37

4.8.4 Flow Measurement 38

4.8.5 Analytical instruments 38

4.8.6 Data Acquisition and Data Logging 39

4.8.7 Visual Display Unit (V.D.U.) 39

5 AUTOMATIC CONTROL

5.1 Introduction 41

5.2 AUTOMATION: the benefits 42

5.3 Control System Scheme

5.3.1 Proportional Control 43

5.3.2 Integral Control 45

5.3.3 Derivative Control 45

5.3.4 Combination Of Proportional, Integral and Derivative Control 46

5.4 Requirement of Control System 46

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6 Various Labs For Control And Instrumentation

6.1 Manometry Lab 56

6.2 Protection and Interlocking Lab 58

6.2.1 Relay 58

6.2.2 Fuses 60

6.3 Turbine Supervisory Instrumentation Lab (TSI) 61

6.4 Pyrometry Lab 61

6.5 Furnace Safeguard Supervisory System (FSSS) 64

7 Summary 67

8 Reference 70

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CHAPTER NO-1

ORGANISATION: AN INTRODUCTION

Thermal Power Stations require a number of equipments performing a number of complex

processes with the ultimate aim to convert chemical energy of coal or oil to electrical energy.

This involves the generation of steam in the boiler by burning coal and/or oil. The steam in turn

drives the turbine. The generator coupled with the turbine produces electricity which is stepped

up with the help of transformers and is fed into grid station through transmission lines.

1.1 INTRODUCTION OF P.T.P.S.:

Haryana Power Sector comprises four wholly State-owned Corporations viz. HPGCL, HVPNL,

UHBVNL and DHBVNL which after unbundling of the HSEB in 1998 are responsible for power

generation, transmission, distribution and trading in the State. The State power sector was

restructured on August 14, 1998. The Haryana State Electricity Board (HSEB) was recognized

initially into two State-owned Corporations namely Haryana Vidyut Prasaran Nigam Ltd.

(HVPN) and Haryana Power Generation Corporation Ltd. (HPGCL). HPGCL was made

responsible for operation and maintenance of State‘s own power generating stations. HVPNL

was entrusted the power transmission and distribution functions. The demand of Haryana is

increasing exponentially @ more than 14 % per year on account of industrialization and more

consumption on agriculture sector and also because of being part of National Capital Region.

Panipat Thermal Power Station (PTPS) has a total installed generation capacity of 1367.8 MW

comprising of four Units of 110 MW each( unit1 unrated to 117.8 MW during R&M) , two Units

of 210 MW each and two Units of 250 MW each. As all the balance of plant facilities viz. Coal

Handling Plant, Ash Handling Plant, Cooling towers, C.W. System are separate for 4x110 MW

Unit 1 to 4 and are completely independent from Units 5 to 8. Keeping this in view and in order

to improve the performance of the Plant and to have a better control, a need was felt to bifurcate

PTPS into two Thermal Power Station i.e. PTPS-1, comprising of 4x110MW Units 1 to 4 and

PTPS-2 comprising of 210MW /250MW Units 5 to 8.In this regard the Board of Directors in its

54th meeting held on 29.03.07, approved the proposal of bifurcation of Panipat Thermal Power

Station, Panipat into two Thermal Power Stations i.e. PTPS-1, comprising of 4x110MW Units I

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to IV and PTPS-2 comprising of 210MW / 250MW Units V to VIII. The matter was

subsequently taken up with Central Electricity Authority (CEA), New Delhi for according

approval of Government of India (Ministry of Power) regarding bifurcation of PTPS. CEA, New

Delhi vide letter dated 16.10.07 have conveyed their acceptance to HPGCL proposal of

bifurcation of Panipat Thermal Power Station into two Thermal Power Stations namely PTPS-1

and PTPS-2.

Panipat Thermal Power Station:-

Name and Address Stage Units Capacity Date of

commissioning

Panipat Thermal Power Station,

Village Assan, Jind road,

Panipat.

Phone: 0180-2561573

Fax: 0180-2566806

Stage-I Unit-I 117.8 MW 01.11.1979

Unit-II 110 MW 27.03.1980

Stage-II Unit-III 110 MW 01.11.1985

Unit-IV 110 MW 11.01.1987

Stage-III Unit-V 210 MW 28.03.1989

Stage-IV Unit-VI 210 MW 31.03.2001

Stage-V Unit-VII 250 MW 28.09.2004

Stage-VI Unit-VIII 250 MW 28.01.2005

Fig.No.1.1 (Capacity Of P.T.P.S.)

1.2 Salient Aspects Of P.T.P.S.1

In order to improve the performance of all the 4X110 MW Units of PTPS-1which are quite old

and of obsolete technology, the Renovation & Modernization of these units has been started with

the following objectives:

To extend the life of the Units by 15 to 20 years

To restore original rated capacity of the units.

To improve Plant availability/load factor.

To enhance operational efficiency and safety

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To remove ash pollution and to meet up environmental standards.

The R&M of Unit-1 & 2 has already been done by M/s BHEL which are now running at full

capacity. The process of R&M of the Units 3 &4 is under consideration and shall be carried out

shortly. With the completion of R&M, these old Units are expected to generate maximum cost

effective electricity for the State of Haryana.

Year Generation

(MU)

Plant Load Factor (%)

PTPS-1 All India (110 MW

Group)

2003-04 2800.2 72.45 53.6

2004-05 2377.6 61.69 42.9

2005-06 2226.8 57.77 52.8

2006-07 2566.6 66.59 55.8

2007-08 2296.3 59.41 55.4

Fig. No.1.2 (Power Generated By P.T.P.S.1)

Performance Of P.T.P.S.1

Fig.No.1.3 (Performance Of P.T.P.S.1)

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1.3 Salient Aspects Of P.T.P.S.2:

Panipat Thermal Power Station-2 (PTPS-2) has a total installed generation capacity of 920 MW

comprising of two Units of 210 MW each and two Units of 250 MW each.

Year

PTPS-2

Generation

(MU)

Plant Load Factor (%)

PTPS-2

(Unit 5&6)

All India

(210 MW

Group)

PTPS-2

(Unit 7&8)

All India

(250 MW

Group)

2003-04 3149.1

85.59 79.4 - 86.5

2004-05 3379.0 80.14 79.8 - 90.2

2005-06 5908.9 85.75 79.2 63.57 87.7

2006-07 7341.5

91.48 82.4

90.78 93.7

2007-08 7564.9

94.71 83.0

92.70 88.8

Fig. No .1.4 (Power Generated By P.T.P.S.2)

Fig. No. 1.6 (Performance Of P.T.P.S.2)

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CHAPTER NO-2

INPUTS OF THERMAL POWER PLANT:

There are three major inputs or raw materials required for the type of thermal power station.

These are:

1. WATER.

2. FUEL OIL.

3. COAL.

1. WATER:

The raw water required for the thermal power station has been taken from WESTERN

YAMUNA CANAL through a channel. This water is lifted by RAW WATER PUMPS and is fed

into CLARIFIERS to remove the turbidity of the water. The clean water is stored in CLEAR

WELLS, from there it is sent to WATER TREATMENT PLANTS, COOLING WATER

SYSTEMS and SERVICE WATER SYSTEMS.

The water in the WATER TREATMENT PLANT is FILTERED and DEMINERALISED. The

filtered water is sent to PLANT and COLONY through plant and colony potable pumps. The

DEMINERALISED WATER (D.M water) is stored in bulk storage tanks for use in boiler and

turbine. The cooling water for condensation of steam is circulated with the help of

CONDENSATE WATER (C.W) PUMPS through COOLING TOWERS. The hot water from the

outlet of the condenser is sprayed in the cooling towers to reduce its temperature. Some part of it

is used in cooling various auxiliaries in plant through BEARING COOLING WATER PUMPS.

2. FUEL OIL

In this power house, three types of fuel oil are used, for preheating and at low load of the boiler

due to less problems faced in ignition of oil rather than coal. These three types are:

1. HIGH SPEED DIESEL OIL.

2. HEAVY FURNANCE OIL.

3. LOW SULPHER HEAVY STOCK.

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The high speed diesel oil reaches Power Station by LORRY TANKERS. The oil is decanted

through pumps and is stored in BULK STORAGE TANKS. The H.F.O & L.S.H.S comes to site

through rail tankers. As this oil is viscous, it is heated with steam and decanted with pumps. The

oil is stored in bulk storage tanks with steam heating coils. H.F.O & L.S.H.S is burnt in the

furnace of Boiler after atomizing with steam.

3. COAL:

The coal reaches the Power Station in RAILWAY WAGONS. The daily consumption of coal in

STAGE-I&II is about 3000 M Tonnes & for Stage-III, it is about 2500 M Tonnes. The

unloading of coal from railway wagons is done mechanically by tilting the wagon by WAGGON

TIPPLER. The coal is then sent to COAL CRUSHER by conveyor belts. The crushed coal

(about 20 mm) is sent either to coal mill bunkers or storage yard. The coal is also transported to

coal bunkers from storage yard through conveyor belts when the coal wagons are not

available. The crushed coal stock for 15 days to 1 month is kept in coal stock yard. The coal

from the mill bunkers goes to coal mills through RAW COAL FEEDERS where it is further

pulverized to powder form & is then transported to the furnace of the boiler with the help of

PRESURED AIR from PRIMARY AIR (P.A.) FANS. In PTPS direct pressurized pulverized

fuel firing system has been used.

On an average, the daily consumption of coal at PTPS, Panipat and FTPS, Faridabad is around

21,500 MT and 2800 MT respectively, with all the Units running at rated capacity.

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CHAPTER NO-3

GENERAL WORKING OF THERAM POWEER STATION:

Fig no. 3.1 (General Working Of Thermal Power Station)

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

1. Steam Generator or Boiler

2. Steam Turbine

3. Electric Generator

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

in the pulverized fuel mill. There it is mixed with preheated air driven by the forced draught fan.

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 remaining water. The steam

passes through a manifold in the roof of the drum into the pendant super heater where its

temperature and pressure increase rapidly to around 200 bar and 540°C, sufficient to make the

tube walls glow a dull red. The steam is piped to the high pressure turbine, the first of a three-

stage turbine process. A steam governor valve allows for both manual control of the turbine and

automatic set-point following. The steam is exhausted from the high pressure turbine, and

reduced in both pressure and temperature, is returned to the boiler re heater. The reheated steam

is then passed to the intermediate pressure turbine, and from there passed directly to the low

pressure turbine set. 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 condenser, where it

condenses rapidly back into water, creating near vacuum-like conditions inside the condenser

chest. The condensed water is then passed by a feed pump through a deaerator, and prewar med,

first in a feed heater powered by steam drawn from the high pressure set, and then in the

economizer, before being returned to the boiler drum. The cooling water from the condenser is

sprayed inside a cooling tower, creating a highly visible plume of water vapor, before being

pumped back to the condenser in cooling water cycle. The three turbine sets are sometimes

coupled on the same shaft as the three-phase electrical generator which generates an intermediate

level voltage (typically 20-25 kV). This is stepped up by the unit transformed to a voltage more

suitable for transmission (typically 250-500 kV) and is sent out onto the three-phase transmission

system. Exhaust gas from the boiler is drawn by the induced draft fan through an electrostatic

precipitator and is then vented through the chimney stack.

3.1 Description For 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.

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3.1.1.Coal Cycle

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 pulverizes may be ball mills, rotating drum grinders, or

other types of grinders.

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. The

thermal radiation of the fireball heats the water that circulates through the boiler tubes near the

boiler perimeter. 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 pre heater 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.

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.

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3.1.2. OIL CYCLE

In the oil cycle the oil is pumped and enters the boiler from four corners at three elevations. Oil

guns are used which sprays the oil in atomized form along with steam so that it catches fire

instantly. At each elevation and each corner there are separate igniters which ignite the fuel oil.

There are flame sensors which sense the flame and send the information to the control room.

3.1.3. AIR & FLUE GAS CYCLE:

For the proper combustion to take place in the boiler right amount of Oxygen or air is needed in

the boiler. The air is provided to the furnace in two ways- PRIMARY AIR & SECONDARY

AIR. Primary air is provided by P.A. fans and enters the boiler along with powdered coal from

the mills. While the secondary air is pumped through FORCED DRAFT FANS better known as

F.D Fans which are also two in numbers A&B. The outlet of F.D fans combine and are again

divided into two which goes to Steam coiled Air pre heaters (S.C.A.P.H) A&B where its

temperature is raised by utilizing the heat of waste steam. Then it goes to Air Pre heater-A&B

where secondary air is heated further utilizing the heat of flue gases. The temperature of air is

raised to improve the efficiency of the unit & for proper combustion in the furnace. Then this air

is fed to the furnace. From the combustion chamber the flue gases travel to the upper portion of

the boiler and give a portion of heat to the PLATIUM SUPER HEATER. Further up it comes in

contact with the REHEATER and heats the steam which is inside the tubes of reheated. Then it

travels horizontally and comes in contact with FINAL SUPER HEATER. After imparting the

heat to the steam in super heater flue gases go downward to the ECONOMIZER to heat the cold

water pumped by the BOILER FEED PUMPS (B.F.P.). These all are enclosed in the furnace.

After leaving the furnace the flue gases go to the Air Heaters where more heat of the flue gases is

extracted to heat primary and secondary air. Then it goes to the ELECTROSTATIC

PRECIPITATORS (E.S.P.) Stage A&B where the suspended ash from the flue gases is removed

by passing the flue gas between charged plates. Then, it comes the INDUCED DRAFT FAN

(I.D. Fan) which sucks air from E.S.P. and releases it to the atmosphere through chimney. The

pressure inside the boiler is kept suitably below the atmospheric pressure with the help of I.D.

Fans so that the flame does not spread out of the openings of boiler and cause explosion. Further

very low pressure in the boiler is also not desirable because it will lead to the Quenching of

flame.

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Fig No.3.2 (BOILER)

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3.2 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. From the 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. 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 super heater 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 super heater coils.

STEAM WATER CYCLE

The most complex of all the cycles is the steam & water cycle. Steam is the working substance in

the turbines in all the thermal and nuclear power plants. As there is very high temperature and

pressure inside the boiler, initially water has to be pumped to a very high pressure. Water has

also to be heated to a suitably high temperature before putting it inside the boiler so that cold

water does not cause any problem. Initially cold water is slightly heated in low pressure heaters.

Then it is pumped to a very high pressure of about 200 Kg/Cm2 by BOILER FEED PUMPS- A

& B. After this it is further heated in high pressure heaters by taking the heat from the high

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pressure steam coming from various auxiliaries and/or turbines. Then this water goes to the

economizer where its temperature is further raised by the flue gases. This hot water then goes to

the BOILER DRUM. In the boiler drum there is very high temperature and pressure. It contains a

saturated mixture of boiling water and steam which are in equilibrium. The water level in the

boiler is maintained between certain limit. From here relatively cold water goes down to the

water header situated at the bottom, due to difference in density. Then this cold water rises

gradually in the tubes of the boiler on being heated. The tubes are in the form of water walls.

These tubes combine at the top in the hot water header. From here the hot water and steam

mixture comes back to the boiler drum completing the small loop. From the boiler drum hot

steam goes to PLATIUM SUPER HEATER situated in the upper portion of the boiler. Here the

temperature of the steam is increased. Then it goes to the FINAL SUPER HEATER.

3.3 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.

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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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. 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˚C where the vapor pressure of water is much less than

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

condensable 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.

Feed water Heater

A Ranking cycle with a two-stage steam turbine and a single feed water 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 vapor to liquid. The heat

content (btu) in the steam is referred to as Enthalpy. The condensate pump then pumps the

condensate water through a feed water heater. The feed water heating equipment then raises the

temperature of the water by utilizing extraction steam from various stages of the turbine.

Super heater

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

super heater 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.

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3.3.1Steam Turbine:

THE turbine is a three cylinder machine with HIGH PRESSURE (H.P), INTERMEDIATE

PRESSURE (I.P) & LOW PRESSURE (L.P) casings taking efficiency into the account .The

turbine speed is controlled by HYDRO DYNAMIC GOVERNING SYSTEM.

Fig No. 3.3 (A view of Turbine)

The three turbines are on the same shaft which is coupled with GENERATOR

3.3.2 GENERATORS

.

The generator is equipped with D.C EXCITATION SYSTEM. The steam from the final super

heater comes by MAIN STEAM LINE to the H.P turbine. After doing work in the H.P Turbine

its Temperature is reduced. It is sent back to the boiler by COLD REHEAT LINE to the

REHEATER. Here its temperature is increased and is sent to the I.P turbine through HOT

REHEAT LINE. After doing work in the I.P turbine steam directly enters L.P turbine. The

pressure of L.P turbine is maintained very low in order to reduce the condensation point of

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steam. The outlet of L.P turbine is connected with condenser. In the condenser, arrangement is

made to cool the steam to water. This is done by using cold water which is made to flow in tubes.

This secondary water which is not very pure gains heat from steam & becomes hot. This

secondary water is sent to the cooling towers to cool it down so that it may be reused for cooling.

The water thus formed in the condenser is sucked by CONDENSATE WATER PUMPS (C.W.

PUMPS) and is sent to deaerator.

Fig. No. 3.4 (Steam to Mechanical Power)

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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.

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 Panipat 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 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. 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

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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)

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. The

stator winding is then divided into three phases, which are almost always wyes connected. Wyes

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 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.

ROTOR

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

symmetrically around the rotor between the poles. The winding itself is made up of many turns

of copper to form the entire series connected winding. All of the turns associated with a single

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

concentrically in corresponding positions on opposite sides of a pole. The series connection

essentially creates a single multi-turn coil overall, that develops the total ampere-turns of the

rotor (which is the total current flowing in the rotor winding times the total number of turns).

There are numerous copper-winding designs employed in generator rotors, but all rotor windings

function basically in the same way. They are configured differently for different methods of heat

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removal during operation. In addition almost all large turbo generators have directly cooled

copper windings by air or hydrogen cooling gas. Cooling passages are provided within the

conductors themselves to eliminate the temperature drop across the ground insulation and

preserve the life of the insulation material. In an ―axially‖ cooled winding, the gas passes

through axial passages in the conductors, being fed from both ends, and exhausted to the air gap

at the axial center of the rotor. In other designs, ―radial‖ passages in the stack of conductors are

fed from sub slots machined along the length of the rotor at the bottom of each slot. In the ―air

gap pickup‖ method, the cooling gas is picked up from the air gap, and cooling is accomplished

over a relatively short length of the rotor, and then discharged back to the air gap. The cooling of

the end-regions of the winding varies from design to design, as much as that of the slot section.

In smaller turbine generators the indirect cooling method is used (similar to indirectly cooled

stator windings), where the heat is removed by conduction through the ground insulation to the

rotor body. The winding is held in place in the slots by wedges, in a similar manner as the stator

windings. The difference is that the rotor winding loading on the wedges is far greater due to

centrifugal forces at speed. The wedges therefore are subjected to a tremendous static load from

these forces and bending stresses because of the rotation effects. The wedges in the rotor are not

generally a tight fit in order to accommodate the axial thermal expansion of the rotor winding

during operation.

BEARINGS

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

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

some cases where the rotor shaft is very long at the excitation end of the machine to

accommodate the slip/collector rings, a ―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 the overall generator rotor or the

turbo generator line.

AUXILIARY SYSTEMS

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

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

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

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

instance, air cooled turbo generators do not require hydrogen for cooling and therefore no sealing

oil as well. On the other hand, large generators with high outputs, generally above 400 MVA,

have water-cooled stator windings, hydrogen for cooling the stator core and rotor, seal oil to

contain the hydrogen cooling gas under high pressure, lubricating oil for the 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 as

follows:

1. Lubricating Oil System

2. Hydrogen Cooling System

3. Seal Oil System

4. Stator Cooling Water System

5. Excitation System

PROTECTION

The protection system of any modern electric power grid is the most crucial function in the

system. Protection is a system because it comprises discrete devices (relays, communication

means, etc.) and an algorithm that establishes a coordinated method of operation among the

protective devices. This is termed coordination. Thus, for a protective system to operate

correctly, both the settings of the individual relays and the coordination among them must be

right. Wrong settings might result in no protection to the protected equipment and systems, and

improper coordination might result in unwarranted loss of production. The key function of any

protective system is to minimize the possibility of physical damage to equipment due to a fault

anywhere in the system or from abnormal operation of the equipment (over speed, under voltage,

etc.). However, the most critical function of any protective scheme is to safeguard those persons

who operate the equipment that produces, transmits, and utilizes electricity. Protective systems

are inherently different from other systems in a power plant (or for that matter any other place

where electric power is present). They are called to operate seldom, and when they are, it is

crucial they do so flawlessly. One problem that arises from protective systems being activated

not often is that they are sometimes overlooked. This is a recipe for disaster. The most common

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reason for catastrophic failure of equipment in power systems is failure to operate or miss-

operation of protective systems.

Deaerator

Fig No. 3.5 (A view of Deaerator)

A suitable water level is maintained in the hot well of condenser. Water or steam leakages from

the system are compensated by the makeup water, line from storage tanks which are connected to

the condenser. The pressure inside condenser is automatically maintained less then atmospheric

pressure and large volume of steam condense here to form small volume of water. In the

Deaerator the water is sprayed to small droplets & the air dissolved in it is removed so that it

may not cause trouble at high temperatures in the Boiler. Moreover, the water level which is

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maintained constant in the Deaerator also acts as a constant water head for the BOILER FEED

PUMPS. Water from Deaerator goes to the Boiler feed pumps after the heated by L.P. Heaters.

Thus the water cycle in the boiler is completed and water is ready for another new cycle. This is

a continuous and repetitive process.

The major steam parameters for boilers under 4*110MW and 1*210 MW are as under:

110 MW 210 MW

----- ------

MAIN STEAM TEMPERATURE 540 540

(Degree centigrade)

MAIN STEAM PRESSURE 138 155

(Kg/Cm2)

STEAM FLOW 375 680

(MT/hr)

The major parameters for turbine and generator (TG) are:

SPEED 3000

(RPM)

GENERATING VOLTAGE 11 for 4x110 MW

(KV) 15.75 for 1x210 MW

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3.4 Cooling tower as a flue gas stack:

Fig No. 3.6 (Cooling Tower)

At some modern power stations, equipped with flue gas purification like the Power Station,

Panipat cooling tower is also used as a flue gas stack (industrial chimney). At plants without flue

gas purification, problems with corrosion may occur.

Wet cooling tower material balance:

Fig. No. 3.8 (Cooling Tower System)

Fig No.3.7 (Base of a cooling tower with falling

water)

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Quantitatively, the material balance around a wet, evaporative cooling tower system is governed

by the operational variables of makeup flue rate, evaporation windage losses, draw-off rate, and

the concentration cycles.

C = Circulating water in m³/h

D = Draw-off water in m³/h

E = Evaporated water in m³/h

W = Windage loss of water in m³/h

X = Concentration in ppmw(of any completely soluble salts … usually chlorides)

XM = Concentration of chlorides in make-up water (M), in ppmw

XC = Concentration of chlorides in circulating water (C), in ppmw

Cycles = Cycles of concentration = XC / XM (dimensionless)

ppmw

= parts per million by weight

In the above sketch, water pumped from the tower basin is the cooling water routed through the

process coolers and condensers in an industrial facility. The cool water absorbs heat from the hot

process streams which need to be cooled or condensed, and the absorbed heat warms the

circulating water (C). The warm water returns to the top of the cooling tower and trickles

downward over the fill material inside the tower. As it trickles down, it contacts ambient air

rising up through the tower either by natural draft or by forced draft using large fans in the tower.

That contact causes a small amount of the water to be lost as windage (W) and some of the water

(E) to evaporate. The heat required to evaporate the water is derived from the water itself, which

cools the water back to the original basin water temperature and the water is then ready to

recalculate. The evaporated water leaves its dissolved salts behind in the bulk of the water which

has not been evaporated, thus raising the salt concentration in the circulating cooling water. To

prevent the salt concentration of the water from becoming too high, a portion of the water is

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drawn off (D) for disposal. Fresh water makeup (M) is supplied to the tower basin to compensate

for the loss of evaporated water, the windage loss water and the draw-off water.

3.5 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.

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 (e.g. 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. At Panipat Thermal

Power Station, Haryana, 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.

3.5.1 AC Motor:

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. 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

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turns slightly slower than the supply frequency. The magnetic field on the rotor of this motor is

created by an induced current.

3.5.2 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.

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, e.g. 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.

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

(as in ball mills and similar apparatus).

3.5.3 Induction Motor:

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

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

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

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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) and — thanks to modern

power electronics — 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

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 energized with

a polyphase supply they create a rotating magnetic field pattern which sweeps past the rotor. This

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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.

3.6 TRANSFORMERS

Transformer is a static electronic device which is used for the transmission of electrical energy at

constant frequency through magnetic coupling.

Principle

When voltage is applied to primary of the transformer, a magnetic flux sets up, the voltage is

induced in primary winding by self induction. This flux also links with the secondary of the

transformer & a voltage is induced in the secondary winding by mutual inductance.

Construction

Two types of constructions are mainly employed in the transformer construction. The

transformer core is made of laminated silicon steel lamination to avoid eddy current & hysteresis

losses.

a. Core type construction:- In this type the core is made of two vertical limbs & two

horizontal yokes. The primary winding is wounded over the yoke & the secondary

winding is wounded over it. Two windings form a concentrated winding.

b. Shell type construction: - In shell type construction the core consists of three limbs &

two horizontal yokes. The LV & HV windings are placed alternately on the central limb

& form sandwiched winding. It is not easy to dismantle shell type winding for repair and

core type winding offers more natural cooling.

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Insulation

The winding is dipped into varnish to provide insulation. The transformer oil used for cooling

also provides insulation for the winding.

Two type of insulation are mainly employed:-

a. Major insulation

b. Minor insulation

Transformer Accessories-

The following accessories are associated with the transformer

a. OIL RESERVER

b. BREATHER

c. BUCHHOLTZ RELAY

d. MARSHALLING BOX

e. RADIATOR AND FAN

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CHAPTER-4

INSTRUMENTATION IN THERMAL PLANTS

4.1 INTRODUCTION

Thermal Power Stations employ a great number of equipments performing number of complex

processes the ultimate aim being the conversion of chemical energy into Electricity. In order to

have stable generating conditions, always a balance is maintained between the Heat in-put and

Electricity output plus losses. But the balance is frequently disturbed due to (i) grid disturbance

external to the process and machines, (ii) the troubles in the process itself or (iii) the trouble in

the equipments. When the balance is disturbed, all the process variables deviate from their

normal valves thus creating the necessity for the following:-

I. Instruments : To measure and indicate the amount of deviations.

II. Automatic Control: To correct the deviation and bring back the system to normal.

III. Annunciation : To warn about the excessive deviations, if any.

IV. Protection : To isolate the equipments process from dangerous operating

conditions caused due to such excessive deviations.

4.2. POWER STATION INSTRUMENTATION:

The proportionate cost of instrumentation during seventies was about 2.3 to 2.5% of the total

cost of boiler, turbine and their Auxiliaries. When the unit size were 60/100MW turbine But this

has become about 7% when the unit size has become 210MW and is expected to reach about 10-

12% of even higher in the near future for the same capacity units. This increase in

instrumentation cost is due to –

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Increase in installed capacity making the units to operate at higher parameter for economic

reasons.

New innovations, improvements, modernization of instruments and equipments.

Expected change in the duty cycles of the boiler and turbine facilitating two shift operation,

quick run up etc.

Improved awareness among the personnel about the utility of the instruments.

4.3 TYPE OF INSTRUMENTS:

The emphasis is only on the process instrumentation measuring the physical quantities such as

temperature, pressure, level flow etc. The other type of instruments is the electrical instruments,

measuring electrical quantities such as current, voltage etc. The different type of instruments

normally in use is given below:

4.3..1 INDICATORS

Indicators are of two categories local indicators are self contained, self operative and are

mounted at site. The remote indicators are used for telemeter purposes and mounted in the

centralized control room or control panel. The indicators both local and remote are sometimes

provided with signaling contacts where ever required. The remote indicators depend upon

electricity, electronics, pneumatic or hydraulic system for their operation and accordingly they

are named. The indicators can be classified as analogue or digital on the basis of final display of

the reading. Indicators are available for single point measurement or can be connected to a

number of points through a selectors switch or automatic scanner system. This multipoint system

considerably reduces the number of instruments without affecting the measurements much.

4.3..2 RECORDERS

Recorders are necessary where ever the operating history is required for analyzing the trends and

for any future case studies or efficiency purposes. Recorders can be of single point measuring a

single parameter or multipoint measuring a number of parameters by a single instrument.

Multipoint recorders are again categorized as multipoint continuous recorders/multipoint dot

recorders. The multipoint dot recorders select the point one after the other in sequence where as

the continuous recorders measure simultaneously all the points.

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4.4 PRESENTATION OF INFORMATION

Enormous amount of information measured and received from the various parts of the

plants/process are to be presented to the operators giving appropriate importance to each one. In

order to have an easy and effective presentation, the information‘s are generally grouped into the

following three groups.

4.4.1 Vital information which are required by operators at all times for the safe operation of the

plant. These information‘s are presented through single point indicator recorder, placed on the

front panels. Main stream pressure, temperature condenser level, vacuum, drum, furnace pressure

etc. are some such parameter.

4.4.2 The second group of information‘s are generally not vital under the normal operation of the

plant. But they become vital whenever some sections of the plant start malfunctioning. Such

needs are met through multipoint indicators/recorders placed in the front panels. Temperature

and draft across the flue gas path bearing temperatures of the motors of fans etc. are some such

examples.

4.4.3 The last group of information‘s are not required by the operators but for the occasional

need of the efficiency engineers. These informations are given by recorders mounted on back

panels or local panels. D.M. makes up quantity, fuel oil flow quantities etc. are some examples.

4.5. CODING OF INSTRUMENTS

In order to distinguish the parameters required from the other instantly, coding for shape of

instrument face is being adopted. This is a useful practice and invariably finds place in power

stations. However coding may vary as per the practices of the organization. A general approach

could be as below:

Level instruments - Horizontal edgewise

Temperature instruments - Horizontal edgewise

Pressure instruments - Circular.

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4.6. SELECTION CRITERIA OF INSTRUMENTS

Instrument engineers are required to work in close association with the system design

requirement as well as the equipment design requirement in selecting instruments and sensing

systems. After deciding the capacity of the Thermal Power station the designs of boiler turbine

and auxiliary equipments such as mills, pumps, fans deaerator, feed heaters etc. are taken up.

Based on the design of the main and auxiliary equipments, the parameters values for efficient

and economic operation at determined load are specified. The instruments and system design

engineers decide the location for the measurement of various parameters such as level, pressure,

flow differential pressure, temperature and other parameters based on the system design and

layout conditions.

Then the instruments engineers select the appropriate instruments influenced by the following

factors:

i) Required accuracy of measurement

ii) Range of measurement

iii) The form of final data display required

iv) Process media

v) Cost

vi) Calibration and repair facilities required/available

vii) Layout restrictions

viii) Maintenance requirements/availability

4.7. CONCEPT OF INSTRUMENT IN THERMAL POWER STATION

The concepts of instrumentation are that:

Instruments should be independent for their working.

The total instrumentation should be inter-dependent to each other in assessing the process

condition.

Instrumentations should be sufficient to provide adequate information‘s to the operators for :

a) Cold start of the unit

b) Warm/hot start of the unit

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c) Shut down both planned and emergency shutdown.

4.8 POWER STATION INSTRUMENTATION

The process conditions and the equipment conditions are to be assessed by the operators from the

information‘s received from the various instruments. The instruments and range vary widely as

per the process media. The following section deals with these instruments. The inter dependence

and inter relations of these instrument play very significant role in the stability and the efficiency

of the heat balance.

4.8.1 TEMPERATURE MEASURING INSTRUMENTS

Accurate measurement of temperature is required to assess the material fatigue, heat balance,

heat transfer etc. The measurement ranges varies from ambient temperatures where as air inlet to

F.D fan is measured, to 2300 to 1400 degree centigrade inside the furnace zone. Temperature

measurement is to be made in many medias such as, water/steam, oil (Fuel oil and lubricating

oil), air, flue gases, hydrogen gas, metal temperatures of bearing, turbine top and bottom,

generator winding and cores, SD.H. tube metal etc.

Filled system thermometry such as mercury in glass, mercury in steel, vapor filled or gas filled

are used for local indication of temperature, bimetallic thermometers can also be used for local

indication. The selection of thermometer depends upon the range of the temperatures to be

measured. These instruments are available with electrical contacts for setting up annunciation

and protection system wherever required.

Resistance thermometers or thermocouples are used as primary sensors in remote measurement

of temperature depending upon the range. Resistance thermometers are of platinum and copper

resistance type. Platinum resistance thermometers are calibrated to have resistance value of

either 46 ohms or 100 ohms at 0 degree centigrade. While copper resistance thermometers have a

value 53 ohms at 0 degree centigrade. The secondary instruments used in conjunction are cross

coil indicators or electronic bridges. These instruments indicate temperature by measuring the

value of resistance which changes with the change in temperature. Resistance thermometers are

used generally up to 300 degree centigrade. Above 300 degree centigrade, thermocouples are

used as primary sensors. The common type of thermocouples used in thermal power plant is

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Chromel-Alumel or Chromel-copel type depending upon the temperature. Iron-Constantan is

another thermocouple in use. The secondary instruments used in thermocouple sensors are

pyrometric mill volt meters or electronic potentiometers. Null balance method is used for the

very accurate measurement of mill volts generated by thermocouples sensing the process

temperature. The electronic bridges and potentiometers can be either indicators or indicator cum

recorders with alarm protection contacts and with remote transmission facilities.

4.8.2 PRESSURE MEASURING INSTRUMENTS

The pressure measurement in Thermal Power Station ranges from 1 Kg/Cm2 (nearly) at

condenser to hydraulic test pressure of the boiler. Here again many medias exist such as

steam/water, lubricating oil, fuel oil, air, flue gases, hydrogen etc. For local indication of

pressure, mainly two types of pressure gauges are employed in the plant.

1. Bourdon Type

2. Diaphragm Type

1. BOURDEN TYPE GAUGES:

These gauges are employed for the measurement of higher pressure. These gauges are employed

for the measurement of higher pressure Burdon gauges measure the difference between the

system pressure inside the tube and atmospheric pressure. It relies on the deformation of a bent

hollow tube of suitable material which, when subjected to the pressure to be measured on the

inside (and atmospheric pressure on the outside), tends to unbend. His moves a pointer through a

suitable gear-and- lever mechanism against a calibrated scale.

2. DIAPHRAM TYPE GUAGES:-

In such gauges, there is a diaphragm which expends or contracts as pressure increase or

decreases which in turn is converted to angular movement of the pointer and is shown on the

scale. Diaphragm gauges are more sensitive than the former type of gauges and so these are used

to measure low pressure. In addition to these gauges there are U types.

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If Z is the difference in heights of fluid columns in the two limbs of the U tube (fig b-1 and b-2)

and d the density of the fluid and g the acceleration due to gravity, then from the elementary

principle of hydrostatics, the gauge pressure Pg is given by

Pg = Z.d.g. N/m2

The pressure measured by any type of pressure gauge is known as gauge pressure and the

pressure relative to a perfect vacuum is called absolute pressure.

Absolute Pressure= Gauge Pressure + Atmospheric pressure.

Remote measurements of pressure are done by transmitters either electronic or pneumatic

coupled with a secondary instrument indicator/ recorder. Many varieties of transmitters are in

use. In these transmitters the mechanical movement of sensing elements such as bourdon,

bellows, diaphragm etc. due to the pressure, causes an electrical property to change such as

current. Voltage, resistance capacitance, reluctance inductance etc. which is utilized as a measure

of pressure in the secondary instruments. The secondary instruments are either indicators or

recorders which may incorporate signally contacts.

4.8.3. LEVEL MEASUREMENT

Level measurement is generally carried out as differential pressure measurement. In power

stations, level measurement in open tanks such as D.M. storage tank and fuel oil and lub oil tanks

and is closed tanks such as deaerator, condenser hot well, boiler drum and L.P. & H.P. heaters

are to make. Gauge glasses and floats are used for local indication of levels and the transmitters

used for measuring the differential pressures are used along with the secondary instruments for

remote level measurements. The measurement of boiler drum level poses many problems

because of varying pressure and temperatures and many computations and corrections are to be

made in order to get correct levels. A recent development in this area is the `HYDRA STEP'.

Though it is very costly but it improves the accuracy and reliability of this measurement. Other

problem area is the solid level measurement where the coal bunker levels and dust collector

hopper level are required. In both these cases continuous level measurement is not possible.

However fairly reliable and accurate provisions are available to indicate the extreme levels on

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either directions (low or high). The nucleonic level gauges or the capacitance and resistance type

sensors serve in this area very well.

4.8.4. FLOW MEASUREMENT

Flow measurement of solids, liquids, liquids and gases are required in Thermal Power Stations.

Though the liquid flow measurements are made very accurately, the gas flow measurement

cannot be done accurately whereas steam flow measurement requires density correction under

varying pressures. The air and flue gas flow measurement suffer accuracy and reliability due to

variation in pressure, temperature, duct leakage, dust accumulation etc. The solid flow

measurement is very difficult and only a rough idea is arrived at about the P.F. flow through

differential means. In power stations flow measurements are based on differential Principles.

Differential Pressure is created by placing suitable throttling devices in the flow path of the

fluids in the pipes/ducts. The throttling devices are suitably selected depending upon the media,

flow quantity etc. from among orifice, venture, flow nozzle ball tube etc. The differential

pressure developed across such sensing devices in proportional to the square of the flow

quantity. The differential pressure is measured by the devices discussed in 8 with additional

square root extraction facilities.

4.8.5 ANALYTICAL INSTRTUMENTS

Apart from the above there are few quantity measurements necessary in thermal power

generating plants of high capacities. These include feed water quality measuring instruments

such as conductivity PH dissolved oxygen, and sodium instruments, steam quality measuring

instruments such as conductivity, silica and HP analyzers. The combustion quality is assessed

by the measurement of the percentage of oxygen, carbon monoxide or carbon dioxide in the flue

gases. The purity of hydrogen inside in the generator housing is measured by utilizing the

thermal conducting capacity of the hydrogen gas. The water and steam purity is measured as the

electrolytic conductivity by electronic bridge method in which one arm from the electrodes of

conductivity cell dipped into the medium. The volume percentages of oxygen in combustion

gases are made utilizing the paramagnetic properties of oxygen. The carbon mono oxide

percentage is measured by the `ABSORPTION OF ELECTROMAGNETIC RADIATION'

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Principle. Both these gas analyzers require elaborate sampling and sample conditioning system

resulting in poor reliability and availability of these measurements. Recent developments in these

fields have brought out on line `in situ' instruments for these two parameters where the problem

of sampling is dispensed with. The `ANALYTICAL INSTRUMENTS' as the above instruments

are called had been the neglected lot so far in the power stations. But now the authorities seem to

think their importance for the process.

4.8.6. DATA ACQUISITION AND DATA LOGGING

The conventional central control room is rather a cumbersome system. Large number of

instrument must be observed to know what is happening inside the plant. The Data Acquisition

simplifies this job by collecting all the measurements transmitted from the process, converting

them into digital term and storing in the memory bank. The periodic loggings of parameter by

the operators are dispensed with after the introduction of data acquisition system which prints out

the periodic conditions on predetermined time intervals. All the important measurements at one

time are printed along a row. Data loggers thus reduce the use of graphical recorders. Since data

logging gives too many measurements at a time, it cannot be easily digested by the control staff.

Now data reduction systems are finding their use where only the process quantity deviated from

normal value is shown.

4.8.7 VISUAL DISPLAY UNIT (V.D.U.)

Visual display units go along with the data acquisition system. In V.D.U. pre-selected schemes,

flow paths with parameters, running alarm conditions etc. can be brought on color television

tubes on demands. This gives the life picture of the happening inside the plant making the

operation easy and effective.

Fig no. 4.1 (VISUAL DISPLAY UNIT)

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TESTING AND CALIBRATION OF PRESSURE GUAGES:

1) Comparison method

2) Dead weight method

1. COMPARISION METHOD

In this method inside the tubes there is oil. There are two outlets on the tube, on one outlet,

master gauge (accurate) is applied and on the other end the gauge to be checked or calibrated is

applied. Valve No.1 and 2 are opened. Oil from chamber connected to valve 1(Chamber 1 say)

goes to chamber connected to valve 2 (say chamber 2). Now tighten the valve 1 so that on

tightening valve the oil should not reenter chamber 1 rather goes to the two gauges. Now valve 2

is steadily tightened so that the pressure shown by both the gauges should be exactly equal. In

this way the gauge can be checked or calibrated.

2. DEAD WEIGHT METHOD

This method is more accurate than the former one. The basic principle of its working is almost

same as that of former one. Here instead of employing a master gauge, we use weights placed on

a pan. The master gauge may be wrong but weights are always correct so this is more accurate

method.

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CHAPTER-5

AUTOMATIC CONTROL

Fig No. 5.1 (UNIT CONTROL)

5.1 Introduction The word automation is widely used today in relation to various types of applications, such as

office automation, plant or process automation. This subsection presents the application of a

control system for the automation of a process / plant, such as a power station. In this last

application, the automation actively controls the plant during the three main phases of operation:

plant start-up, power generation in stable or put During plant start-up and shut-down, sequence

controllers as well as long range modulating controllers in or out of operation every piece of the

plant, at the correct time and in coordinated modes, taking into account safety as well as

overstressing limits.

During stable generation of power, the modulating portion of the automation system keeps the

actual generated power value within the limits of the desired load demand. During major load

changes, the automation system automatically redefines new set points and switches ON or OFF

process pieces, to automatically bring the individual processes in an optimally coordinated way

POWER PLANT CONTROL

UNIT CONTROL

TURBINE GENERATOR BOILER

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to the new desired load demand. This load transfer is executed according to pre- programmed

adaptively controlled load gradients and in a safe way.

5.2 AUTOMATION: THE BENEFITS

The main benefits of plant automation are to increase overall plant availability and

efficiency. The increase of these two factors is achieved through a series of features

summarized as follows:

Optimization of house load consumption during plant start- up, shut-down and

operation, via:

Faster plant start-up through elimination of control errors creating delays.

Faster sequence of control actions compared to manual ones. Even a well- trained

operator crew would probably not be able to bring the plant to full load in the same time

without considerable risks.

Co-ordination of house load to the generated power output.

Ensure and maintain plant operation, even in case of disturbances in the control system, via:

Coordinated ON / OFF and modulating control switchover capability from a sub process

to a redundant one.

Prevent sub-process and process tripping chain reaction following a process component

trip.

Reduce plant / process shutdown time for repair and maintenance as well as repair costs, via:

Protection of individual process components against overstress (in a stable or unstable

plant operation).

Bringing processes in a safe stage of operation, where process components are protected

against overstress

5.3 Control System Scheme

An automatic control scheme compares a control condition value with a desired value and

automatically corrects any deviation. There are three basic types of controls and they are as

follows:

1. PROPORTIONAL

2. INTEGERAL

3. DERIVATIVE

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Fig no. 5.2 (Proportional Control)

5.3.1 PROPORTIONAL CONTROL

This type of control is used where the deviation is not very large or the deviation is not sudden.

The control gives a change in regulator position which is directly proportional to a change in

conditions. The regulator position is directly related to the deviation and for every controlled

condition value there is a regulator position which is dependent upon the control sensitivity. The

regulator takes up a position tending to reduce the deviation, the amount of excursion from its

initial setting being dependent upon the sensitivity setting. If the deviation is increasing rapidly

the regulator will apply the correction rapidly. The regulator position resulting from a deviation

of the variable from a desired value depends upon the position it occupies when there is no

deviation. The range of values of the variable.

Scale of the instrument to move the regulator through its full travel. The desired value indicator

is normally set between 50% & 75% scaled range position, with the proportional band balanced

MEASUREMENT

CLOSE-LOOP

CONTROL

OPEN-LOOP

CONTROL

PROTECTION

MONITORING

INSTRUMENTATION

AND

CONTROL

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equally on the either side. The regulator movement is tied rigidly in proportion to the deviations

of the measuring index from the desired value. If the load changes, the measuring index will

move away from the desired value and the regulator will move proportionally in an attempt to

correct for this deviation. If the deviation is within the range of the regulator, the regulator will

assume a new position and the measured value will again be under control but at a different

value. The amount by which the controlled condition deviates from the desired value is the

offset, and it depends on the amount of load change and the proportional band setting.

To correct the offset condition the relative positions of the desired value and the proportional

band must be altered, without changing the value of the proportional band. This is affected by

resetting the desired value indicator by an amount equal and opposite to the offset. The measured

variable will then return to, and be controlled at the desired value. The desired value indicator

will no longer be displaying the true desired value. As a high proportional sensitivity (narrow

proportional band) enables the regulator to move a large amount for a very small deviation, it is

possible to reduce the offset to negligible amount if a sufficiently small proportional band is

permissible. Normally, the proportional band must be made wide to avoid hunting or instability,

so as alternative method of deviating offset must sometimes be used (proportional plus integral

control).

Another effect of increasing the proportional band is to increase the period of cycling, so that the

initial deviation becomes larger. The offset also becomes larger and it is, therefore, important

that the proportional band of a controller be set to the very minimum that is consistent with

stable recovery. Proportional control is used where

Load changes are small

Offset can be tolerated

The process reaction rate is such as to permit a narrow P.O. since this reduces the amount of

offset.

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5.3.2 INTEGERAL CONTROL

With Integral Control the controller is only at rest when the controlled condition is at the desired

value. The regulator moves, when there is a deviation, in a direction which applies correction and

continues to move until either the extreme regulator position is reached or the variable returns to

the desired value. The speed of movement of the regulator is directly proportional to the amount

of deviation, and can be adjusted to give any required speed per unit deviation. This adjustment

is known as Integral Action Time adjustment. The speed of regulator movement is related to the

amount of deviation and not, as in proportional control, to the rate of deviation. For certain

integral action time sensitivity the speed of travel of the regulator for a one unit deviation is half

the speed of travel for a two unit deviator.

The term "integral" is derived from the mathematical consideration of this type of control.

Integral calculus considers the sum of an infinite number of small increments; the actual

regulator position at any instant is dependent on the amount of deviation and the time for which

the deviation has been maintained. Integral control can be used in a system but dead-time results

in a sustained hunting unless the sensitivity is drastically reduced. The system's main attribute is

that the regulator position is not rigidly tied to the set point. Therefore, if used with proportional

control, integral control provides automatic elimination of offset.

Integral action is used where

Offset must be eliminated

Integral saturation due to sustained deviation is not objectionable

5.3.3 DERIVATIVE CONTROL

Using this control the regulator is not influenced by the desired value but moves in accordance

with the direction and with rate of change of the deviation. If the change in the variable is a

sudden step movement, its rate of change is infinitely fast and the regulator travels (moves)

gradually at a constant rate, the regulator will move by an amount proportional to that rate and

then stop until the rate of change of deviation alters. Derivative control is not used alone but

normally in conjunction with proportional or proportional plus integral control.

Derivative action is used where

Large transfer of distance velocity logs is present.

It is necessary to minimize the amount of deviation caused by plant load changes.

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5.3.4 COMBINATION OF PROPORTIONAL, INTEGERAL AND DERIVATIVE

CONTROL

The combination of proportional and integral control provides automatic elimination of the

offset. When a deviation occurs, the regulator moves under proportional control by an amount

proportional to the deviation. The regulator then continues to move under integral control at a

constant rate towards its extreme position. The combined integral and proportional wave lags

behind the proportional wave by a value of less than 90 degrees and is dependent upon the

relative sensitivities. Therefore, a more stable form of control is provided.

The integral function is derived from the proportional function. The time required for the integral

action to increase the control output to the regulator, by an amount equal to the output change

caused by the proportional action, is termed the Integral Action Time. This assumes that the

deviation remains constant. The integral sensitivity can be adjusted to give either a fast or a slow

return to the desired value after a change in load has resulted in an offset. The period of

oscillation will become progressively longer as the integral sensitivity is increased; the integral

action time is decreased. The integral derivative action gives the regulator a slight offset

movement because the rate of change is low. As the change progresses at a constant rate the

derivative action remains constant. The remaining regulator movement will now be controlled by

the combined proportional and integral action. The proportional action is linear and is a mirror

image of the deviation response; the integral action continually increases the speed of the

regulator towards its extreme travel as the amount of deviation increases.

5.4 REQUIREMENT OF CONTROL SYSTEM

A control system, to be effective, must satisfy the following requirements. It must be possible o

measures the condition to be controlled, preferably by the standard application of a proven

instrument. The regulator must be capable of handling the plant under all load conditions and at

all probable desired value settings, preferably with a little range to spare; if the system is

continually out ranging the regulator, satisfactory control will be impossible. The measuring

point must be as close as possible to the regulator in order to minimize lags.

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SENSITIVITY ADJUSTMENT

Two major requirement of an automatically controlled plant are:

The variable must be returned to the desired value as quickly as possible after a disturbance.

The control system must be stable and show no tendency to hunt. These two conditions are

incompatible since an increase in sensitivity improves one at the expense of the other. Sensitivity

is normally adjusted to give as fat a return to stable control as possible without causing

overshoot and a tendency to `hunt' about the set point. In the combination of proportional and

derivative control, the derivative function is derived from the proportional function and not

directly from the deviation. The effect is the same since the speed of the proportional action is in

turn related to the rate of change of deviation. The derivative function is not only dependent on

its own sensitivity adjustment but also on the proportional sensitivity. The derivative wave leads

the proportional wave by 90 degree and for a combination of proportional plus derivative control

the load is less than 90 degrees, dependent upon the relative sensitivities.

For controller having both proportional and derivative functions, the regulator output by an

amount equal to the output change caused by the derivative action is termed, the Derivative

Action Time (fig. 2.9). This assumes that the deviation is changing at a constant rate. The

proportional plus integral plus derivative control is used when close control is required on a plant

that is liable to sudden or large fluctuations, or to serve plant or instrument legs.

Then a step change occurs in the variable, the regulator moves rapidly to its extreme position due

to derivative action because the variable is changing at its maximum speed. When the change in

the variable stabilizes at this new position but extreme position again, in an attempt to return the

measured variable to its set point. Following gradual deviation of the measured variable the each

method of control previously described has its particular advantages regarding sensitivity

requirements, and these may be summarized as follows:

Proportional control is a stable system but does not necessarily ensure that the measured variable

is always at the desired value under various load conditions.

Integral control always returns the measured variable to the desired value, but tends to make the

control loop less stable and the inherent frequency of plant oscillation lower.

Derivative control tends to make some control loops more stable (this depends upon the plant

characteristics) and increases the inherent frequency of plant oscillation. It is not concerned,

however, with the absolute value of the controlled variable.

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Thus, the overall sensitivity of particular method or combination or methods becomes a

compromise between stability and the requirement of returning to the desired value quickly. The

relative sensitivities of the methods employed in a combined system are derived by compromises

to achieve the best results.

Guidelines for the settings of P I and D actions cannot be given to any accuracy, because prop,

band depends upon the range of controller as well as plant characteristics.

The following however, gives a rough (very) guideline for the required setting for controller

modes.

Control Prop. Band Int. action Derivation

------- ---- ---- ------------- ------------

Flow High (250%) Past (Sec.) Never

Level Low Cap. dependent rarely

Temp. Low Cap. dependent usually

Analytical High Usually slow (min) sometimes

Pressure Low Usually slow (min) sometimes.

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Concept Of C&I In Thermal Power Station

Fig no. 5.3 (Concept of C & I in Thermal Power Station)

The control and automation system used here is a micro based intelligent multiplexing

system. This system, designed on a modular basis, allows to tighten the scope of control

hardware to the particular control strategy and operating requirements of the process regardless

of the type and extent of process to control provides system uniformity and integrity for:

Signal conditioning and transmission

Modulating controls

CONTROL AND MONITORING MECHANISMS: There are basically two types of Problems faced in a Power Plant

Metallurgical

Mechanical

Mechanical Problem can be related to Turbines that is the max speed permissible for a

turbine is 3000 rpm, so speed should be monitored and maintained at that level

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Metallurgical Problem can be view as the max Inlet Temperature for Turbine is 1060 C so

temperature should be below the limit.

Monitoring of all the parameters is necessary for the safety of both:

Employees

Machines

So the Parameters to be monitored are:

Speed

Temperature

Current

Voltage

Pressure

Eccentricity

Flow of Gases

Vacuum Pressure

Valves

Level

Vibration

PRESSURE MONITORING:

Pressure can be monitored by three types of basic mechanisms

Switches

Gauges

Transmitter type

For gauges we use Bourdon tubes: The Bourdon Tube is a non liquid pressure

measurement device. It is widely used in applications where inexpensive static pressure

measurements are needed.

A typical Bourdon tube contains a curved tube that is open to external pressure input on

one end and is coupled mechanically to an indicating needle on the other end, as shown

schematically below.

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Fig No. 5.4 (Typical Bourdon Tube Pressure Gages)

Bourdon tubes measure gauge pressure, relative to ambient atmospheric pressure, as opposed

to absolute pressure; vacuum is sensed as a reverse motion. Some aneroid barometers use

Bourdon tubes closed at both ends (but most use diaphragms or capsules). When the measured

pressure is rapidly pulsing, such as when the gauge is near a reprocating pump,

an orfice restriction in the connecting pipe is frequently used to avoid unnecessary wear on the

gears and provide an average reading; when the whole gauge is subject to mechanical vibration,

the entire case including the pointer and indicator card can be filled with an oil or glycerin.

Typical high-quality modern gauges provide an accuracy of ±2% of span, and a special high-

precision gauge can be as accurate as 0.1% of full scale. For Switches pressure switches are used

and they can be used for digital means of monitoring as switch being ON is referred as high and

being OFF is as low. All the monitored data is converted to either Current or Voltage parameter.

Bourdon pressure gauge- is an oval section tube . it‘s one end is fixed. It is provided with the

pointer to indicate the pressure on a calibrated scale.

It is of 2 types: Spiral type - it is used for low pressure measurement.

Helical type - it is used for high pressure measurement.

The Plant standard for current and voltage are as under

Voltage : 0 – 10 Volts range

Current : 4 – 20 milliAmperes

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We use 4mA as the lower value so as to check for disturbances and wire breaks.

Accuracy of such systems is very high.

ACCURACY: + - 0.1 %

The whole system used is SCADA based.

Programmable Logic Circuits (PLCs) are used in the process as they are the heard of

instrumentation.

ROTAMETERS:

A Rotameter is a device that measures the flow rate of liquid or gas in a closed tube. A rotameter

consists of a tapered tube, typically made of glass with a 'float', actually a shaped weight, inside

that is pushed up by the drag force of the flow and pulled down by gravity. Drag force for a

given fluid and float cross section is a function of flow speed squared only.

A higher volumetric flow rate through a given area results in increase in flow speed and drag

force, so the float will be pushed upwards. However, as the inside of the rotameter is cone

shaped (widens), the area around the float through which the medium flows increases, the flow

speed and drag force decrease until there is mechanical equilibrium with the float's weight.

Floats are made in many different shapes, with spheres and ellipsoids being the most common.

The float may be diagonally grooved and partially colored so that it rotates axially as the fluid

passes. This shows if the float is stuck since it will only rotate if it is free. Readings are usually

taken at the top of the widest part of the float; the center for an ellipsoid, or the top for a cylinder.

Some manufacturers use a different standard.

Note that the "float" does not actually float in the fluid: it has to have a higher density than the

fluid, otherwise it will float to the top even if there is no flow.

Advantages

A rotameter requires no external power or fuel, it uses only the inherent properties of the

fluid, along with gravity, to measure flow rate.

A rotameter is also a relatively simple device that can be mass manufactured out of cheap

materials, allowing for its widespread use.

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It is occasionally misspelled as 'rotameter'. It belongs to a class of meters called variable area

meters, which measure flow rate by allowing the cross sectional area the fluid travels through to

vary, causing some measurable effect.

A rotameter consists of a tapered tube, typically made of glass, with a float inside that is pushed

up by flow and pulled down by gravity. At a higher flow rate more area (between the float and

the tube) is needed to accommodate the flow, so the float rises. Floats are made in many different

shapes, with spheres and spherical ellipses being the most common. The float is shaped so that it

rotates axially as the fluid passes. This allows you to tell if the float is stuck since it will only

rotate if it is not.

For Digital measurements Flap system is used.

For Analog measurements we can use the following methods:

Flow meters

Venurimeters / Orifice meters

Turbines

Mass flow meters ( oil level )

Ultrasonic Flow meters

Magnetic Flow meter ( water level )

Selection of flow meter depends upon the purpose, accuracy and liquid to be measured

so different types of meters used.

Turbines are the simplest of all.

They work on the principle that on each rotation of the turbine a pulse is generated and

that pulse is counted to get the flow rate.

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VENTURIMETERS:

Fig No.5.5 (VENTURIMETERS)

Referring to the diagram, using Bernoulli's equation in the special case of incompressible fluids

(such as the approximation of a water jet), the theoretical pressure drop at the constriction would

be given by (ρ/2)(v2 2 - v1 2).

And we know that rate of flow is given by:

Flow = k √ (D.P)

Where DP is Differential Pressure or the Pressure Drop.

CONTROL VALVES

Fig no. 5.6 (CONTROL VALVES)

A valve is a device that regulates the flow of substances

(either gases, fluidized solids, slurries, or liquids) by

opening, closing, or partially obstructing various

passageways. Valves are technically pipe fittings, but

usually are discussed separately.

Valves are used in a variety of applications including

industrial, military, commercial, residential, transportation.

Plumbing valves are the most obvious in everyday life, but

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many more are used. Some valves are driven by pressure only, they are mainly used for safety

purposes in steam engines and domestic heating or cooking appliances. Others are used in a

controlled way, like in Otto cycle engines driven by a camshaft, where they play a major role in

engine cycle control. Many valves are controlled manually with a handle attached to the valve

stem. If the handle is turned a quarter of a full turn (90°) between operating positions, the valve

is called a quarter-turn valve. Butterfly valves, ball valves, and plug valves are often quarter-turn

valves. Valves can also be controlled by devices called actuators attached to the stem. They can

be electromechanical actuators such as an electric motor or solenoid, pneumatic actuators which

are controlled by air pressure, or hydraulic actuators which are controlled by the pressure of a

liquid such as oil or water. So there are basically three types of valves that are used in power

industries besides the handle valves.

They are:

Pneumatic Valves – Pneumatically controlling valves are valves that control the flow of

pressurized air. Another medium such as water (hydraulics) or electricity, for example,

may be used to control the valves. they are air or gas controlled which is compressed to

turn or move them.

In some cases, the valves are operated manually rather than automatically.

Hydraulic valves – they utilize oil in place of Air as oil has better compression.

Hydraulic topics range through most science and engineering disciplines, and cover

concepts such as pipe flow, dam design, fluidics and fluid control

circuitry, pumps, turbines, hydropower, computational fluid dynamics, flow

measurement, river channel behavior and erosion.

Motorized valves – these valves are controlled by electric motors. Electric motors are

found in applications as diverse as industrial fans, blowers and pumps, machine tools,

household appliances, power tools, and disk drives. They may be powered by direct

current (e.g., a battery powered portable device or motor vehicle), or by alternating

current from a central electrical distribution grid or inverter. The smallest motors may be

found in electric wristwatches. Medium-size motors of highly standardized dimensions

and characteristics provide convenient mechanical power for industrial uses. The very

largest electric motors are used for propulsion of ships, pipeline compressors, and water

pumps with ratings in the millions of watts.

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CHAPTER-6

VARIOUS LABS FOR CONTROL AND INSTRUMENTATION

This division basically calibrates various instruments and table care of any faults that occur in

any of the auxiliaries

in the plant. It has the following labs.

· Manometry lab

· Protection and interlocking lab

· Pyrometry lab

· Turbo supervisory instrument (TSI) lab

· Furnace safety supervisory instrument (FSSS) lab

· Electronics lab

This department is the brain of the plant because from relay to transmitter followed by the

electronics computation chipsets and recorders and lastly the controlling circuitry, all fall under

their responsibility.

6.1 MANOMETRY LAB

Various instruments used in this lab are-

Transmitter- it is used for pressure measurement of gas liquid. Its working principle is that the

input pressure is converted into electrostatic capacitance and from there it is conditioned and

amplified. It gives an output of 4 to 20mA DC.

Manometer- it is to be which is best in the U-shaped it is filled with liquid. This device

corresponds to a difference in the pressure across the 2 limits. A manometer could also be

referring to a pressure measuring instrument, usually limited to measuring pressures near to

atmospheric. The term manometer is often used to refer specifically to liquid column hydrostatic

instruments.

A single-limb liquid-column manometer has a larger reservoir instead of one side of the U-tube

and has a scale beside the narrower column. The column may be inclined to further amplify the

liquid movement. Based on the use and structure following type of manometers are used

1. Simple Manometer

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2. Micromanometer

3. Differential manometer

4. Inverted differential manometer

Fig no. 6.1 (U SHAPED MANOMETER)

A very simple version is a U-shaped tube half-full of liquid, one side of

which is connected to the region of interest while the reference pressure

(which might be the atmospheric pressure or a vacuum) is applied to

the other. The difference in liquid level represents the applied pressure.

The pressure exerted by a column of fluid of height h and density ρ is

given by the hydrostatic pressure equation, P = hgρ. Therefore the

pressure difference between the applied pressure Pa and the reference

pressure P0 in a U-tube manometer can be found by solving Pa − P0 = hgρ. In other words, the

pressure on either end of the liquid (shown in blue in the figure to the right) must be balanced

(since the liquid is static) and so Pa = P0 + hgρ. If the fluid being measured is significantly dense,

hydrostatic corrections may have to be made for the height between the moving surface of the

manometer working fluid and the location where the pressure measurement is desired except

when measuring differential pressure of a fluid (for example across an orifice plate or venturi), in

which case the density ρ should be corrected by subtracting the density of the fluid being

measured.

Although any fluid can be used, mercury is preferred for its high density (13.534 g/cm3) and low

vapour pressure. For low pressure differences well above the vapour pressure of water, water is

commonly used (and "inches of water" is a common pressure unit). Liquid-column pressure

gauges are independent of the type of gas being measured and have a highly linear calibration.

They have poor dynamic response. When measuring vacuum, the working liquid may evaporate

and contaminate the vacuum if its vapor pressure is too high. When measuring liquid pressure, a

loop filled with gas or a light fluid can isolate the liquids to prevent them from mixing but this

can be unnecessary, for example when mercury is used as the manometer fluid to measure

differential pressure of a fluid such as water. Simple hydrostatic gauges can measure pressures

ranging from a few Torr (a few 100 Pa) to a few atmospheres. (Approximately 1,000,000 Pa)

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6.2 PROTECTION AND INTERLOCKING LAB:

PROTECTION AND INTERLOCKING SYSTEMS

1. High tension control circuit - for high tension systems, the control system are excited by

separate DC supply. For the starting, the circuit condition should be in series with the starting of

equipment to energize it because if even a single condition is not true, then the system will not

start.

2. Low tension control circuit - For this type of circuits, the control circuit are directly excited by

0.415 kV AC supply. The same circuit achieves both excitation and tripping. Here the tripping

coil is provided for emergency tripping if the interconnection is failed.

INTERLOCKING

It is basically interconnecting two or more equipments so that if equipment fails, other can

performs the task. This type of inter dependence is also created, so that the equipments

connected together are started and shut down in a specific sequence to avoid damage for

protection of equipment tripping are provided for all the equipments. Tripping can be considered

as the series of instructions connected through OR gate. When a fault occurs and one of the

tripping is satisfied a signal is send to the relay, which trips the circuit.

The main equipments of this lab are relay and circuit breakers. Some of the instruments used for

the protection are:-

6.2.1. RELAY - It is protective device. It can detect wrong condition in electrical circuits. By

constant measuring the electrical quantities flowing under normal and faulty conditions. Some of

the electrical quantities are voltage, current, phase angle and velocity. A simple electromagnetic

relay consists of a coil of wire surrounding a soft iron core, an iron yoke which provides a

low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts

(there are two in the relay pictured). The armature is hinged to the yoke and mechanically linked

to one or more sets of moving contacts. It is held in place by a spring so that when the relay is

de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of

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contacts in the relay pictured is closed, and the other set is open. Other relays may have more or

fewer sets of contacts depending on their function. The relay in the picture also has a wire

connecting the armature to the yoke. This ensures continuity of the circuit between the moving

contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke,

which is soldered to the PCB.

When an electric current is passed through the coil it generates a magnetic field that attracts the

armature, and the consequent movement of the movable contact(s) either makes or breaks

(depending upon construction) a connection with a fixed contact. If the set of contacts was closed

when the relay was de-energized, then the movement opens the contacts and breaks the

connection, and vice versa if the contacts were open. When the current to the coil is switched off,

the armature is returned by a force, approximately half as strong as the magnetic force, to its

relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in

industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage

application this reduces noise; in a high voltage or current application it reduces arcing.

It is of two types:-

a. Current type relay

b. Potential relay

Fig No.6.2 (RELAYS)

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6.2.2 FUSES - A fuse consists of a metal strip or wire fuse element, of small cross-section

compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually)

enclosed by a non-conducting and non-combustible housing. The fuse is arranged in series to

carry all the current passing through the protected circuit. The resistance of the element generates

heat due to the current flow. The size and construction of the element is (empirically) determined

so that the heat produced for a normal current does not cause the element to attain a high

temperature. If too high a current flows, the element rises to a higher temperature and either

directly melts, or else melts a soldered joint within the fuse, opening the circuit.

The fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and

predictable characteristics. The fuse ideally would carry its rated current indefinitely, and melt

quickly on a small excess. The element must not be damaged by minor harmless surges of

current, and must not oxidize or change its behavior after possibly years of service. The fuse

element may be surrounded by air, or by materials intended to speed the quenching of the

arc. Silica sand or non-conducting liquids may be used.

It is short piece of metal inserted in the circuit which melt when a heavy current flow through it.

Usually silver is used as fuse material.

A. The coefficient of expansion of silver is very small

B. The conductivity of silver is unimpaired by surge of the current that produces temperature

near the map.

C. It has low specific heat.

Fig No.6.3 (FUSE)

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6.3 TURBINE SUPERVISORY INSTRUMENTATION LAB (TSI)

1. TURBINE SPEED:-

The speed of the turbine is to be kept constant so that frequency of the generator

electricity is close to 50 Hz. The indicator of the speed gives us a remote indication of the

speed when barring gear rotates the rotor.

2. AXIAL SHIFT-

During the rotation of the turbine at high speeds where there is the wearing down of

bearing there is an axial shift. Depending on the bearings which have become worn the

thrust collar is either on working pad or surge pad. The position of the thrust collar is

given respect to working pads.

3. SHAFT ECCENTRICITY-

Eccentricity is the deviation of the mass centre from the geometrical centre of the

bearing case. It usually occurs in the rotor where there is shut down. If it becomes large

then there will be lot of vibration which can be dangerous. To measure the eccentricity a

passive and the active magnetic reluctance type transducer in combination with bridge

ckt.

4. BEARING VIBRATION-

This is one of the most vital parameters of the turbine and it has to be monitored vibration

is the to and fro motion of the machine under the influence of oscillatory forces caused by

unbalanced masses in the rotating system.

6.4 PYROMETRY LAB:

This lab consists of various temperature measuring instruments. Various devices used are:-

1. LIQUID IN GLASS THERMOMETER- Mercury in glass thermometer boils at 340˚C

which limits the range of temperature that can be measured. It is an L shaped

thermometer, which is designed to reach all inaccessible places. Calibrated marks on the

tube allow the temperature to be read by the length of the mercury within the tube, which

varies according to the heat given to it. To increase the sensitivity, there is usually a bulb

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of mercury at the end of the thermometer which contains most of the mercury; expansion

and contraction of this volume of mercury is then amplified in the much narrower bore of

the tube. The space above the mercury may be filled with nitrogen or it may be less than

atmospheric pressure, which is normally known as a vacuum.

Fig No. 6.4 (Liquid In Glass Thermometer)

2.ULTRA VIOLET SENSOR- this device is used in furnace and it measures the intensity

of ultra violet rays there and according to the wave generated a signal of the order ‗mV‘ is

generated which directly indicates the temperature in the furnace. UV Sensor is a precision

instrument that detects ultraviolet (UV) radiation at wavelengths of 290 to 390 nanometers.

The UV Sensor is comprised of the following components:

Shield—The outer shell shields the sensor body from thermal radiation and provides a

path for convection cooling of the body, minimizing heating of the sensor interior. It

provides a cutoff ring for cosine response, a level indicator, and fins to aid in aligning

the sensor with the sun‘s rays.

Sensor Body—Houses the following components:

• Diffuser—Provides, with gasket, a weather-tight seal and excellent cosine response.

• Filter—Provides the Erythema Action spectral response. Encased in multiple hardoxide

coatings, the filter is stable in the presence of heat and humidity.

• Detector—Contains a semiconductor diode that, with the filter, responds to radiation

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only in the specified wavelengths.

• Amplifier—Converts the detector current into a 0 to +2.5V signal.

Fig No. 6.5 (Ultra Violet Sensor)

3 THERMOCOUPLE-

Fig. No.6.6 (THERMOCOUPLE MEASURING CIRCUIT)

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Thermocouples are a widely used type of temperature sensor for measurement and

control and can also be used to convert a heat gradient into electricity. They are inexpensive,

interchangeable, are supplied with standard connectors, and can measure a wide range of

temperatures. In contrast to most other methods of temperature measurement, thermocouples

are self powered and require no external form of excitation. The main limitation with

thermocouples is accuracy and system errors of less than one degree Celcius(c) can be

difficult to achieve. It works on principle of seeback effect. Two different metals are joined

to form a junction and then change in temperature causes potential difference which can be

measure through voltmeter and converted into corresponding temperature scale using

transducers. BTPS uses nickel chrome thermocouple. It has a maximum range of 1600˚C. To

measure the temperature inside boiler, these thermocouples are inserted into boiler, while on

other end temperature is measured. For typical metals used in thermocouples, the output

voltage increases almost linearly with the temperature difference (ΔT) over a bounded range

of temperatures. For precise measurements or measurements outside of the linear temperature

range, non-linearity must be corrected. The nonlinear relationship between the temperature

difference (ΔT) and the output voltage (mV) of a thermocouple can be approximated by a

6.5 FURNACE SAFEGUARD SUPERVISORY SYSTEM (FSSS)

FSSS as a contrast to combustion control. It is an independent and discrete digital logic system

specially meant for safety and protection during starting shut down, low load and emergency

conditions. It does not take part in regular station, operation a sin the case with combustion,

control which, sends out continuous analogous signal to maintain combustion rate at optimum

value to match the demand of the boilers.

FSSS is also called as Burner Management System (BMS). It is a microprocessor based

programmable logic controller of proven design incorporating all protection facilities

required for such system. Main objective of FSSS is to ensure safety of the boiler.

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The 95 MW boilers are indirect type boilers. Fire takes place in front and in rear side.

That‘s why its called front and rear type boiler.

The 210 MW boilers are direct type boilers (which means that HSD is in direct contact

with coal) firing takes place from the corner. Thus it is also known as corner type boiler.

6.5.1 IGNITER SYSTEM

Igniter system is an automatic system, it takes the charge from 110kv and this spark is

brought in front of the oil guns, which spray aerated HSD on the coal for coal

combustion. There is a 5 minute delay cycle before igniting, this is to evacuate or burn

the HSD. This method is known as PURGING.

6.5.2 PRESSURE SWITCH

Pressure switches are the devices that make or break a circuit. When pressure is applied,

the switch under the switch gets pressed which is attached to a relay that makes or break

the circuit.

Time delay can also be included in sensing the pressure with the help of pressure valves.

Examples of pressure valves:

1. Manual valves (tap)

2. Motorized valves (actuator) – works on motor action

3. Pneumatic valve (actuator) _ works due to pressure of compressed air

4. Hydraulic valve

6.5.3 FUNCTIONS OF FSSS

The furnace safeguard supervisory system has been designed to provide increased safety ,

reliability , flexibility and overall performances of the boiler. It consist the following:-

a. Furnace purge supervision:-To interlock for scanner purge airflow drum level and all fuel.

b. Secondary air damper control: - To automatically maintain wind box furnace differential,

regulate air to the fuel compartment and control the secondary air dampers.

c. Igniter control supervision: - To interlock for igniter flame, furnace purge , ignition fuel

pressure and igniter tip value position.

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d. Heavy oil control and supervision: - To remote and manual start/stop. It includes interlocks for

heavy oil pressure and temperature, oil gun value positions igniter, energy atomizing differential

and local maintenance switches.

e. Mill and feed control and supervision:- which has automatic operation from a single operator

start/stop switch for each mill. Individual switches are also provided for the operator to control

each mill.

f. Flame scanner intelligence and checking: - it includes automatic checking of each scanner,

scanner counting network and scanner cabinet.

g. Overall boiler flame failure protection: - which during light up and low load operations.

h. Boiler trip protection: - which shut down all fuel in the following events

1. Both emergency trip buttons pushed

2. Loss of all fuel

3. Turbine trip

4. Air flow less than minimum preset value (during start-up only)

5. Tripping of FD or ID fans.

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CHAPTER-7

SUMMARY:

Fig No. 7.1 (Summary of thermal power plant)

1. Cooling tower

2. Cooling water pump

3. Transmission line (3-phase)

4. Unit transformer (3-phase)

5. Electric generator (3-phase)

6. Low pressure turbine

7. Boiler feed pump

8. Condenser

9. Intermediate pressure turbine

10. Steam governor valve

11. High pressure turbine

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12. Deaerator

13. Feed heater

14. Coal conveyor

15. Coal hopper

16. Pulverized fuel mill

17. Boiler drum

18. Ash hopper

19. Super heater

20. Forced draught fan

21. Reheater

22. Air intake

23. Economizer

24. Air preheater

25. Precipitator

26. Induced draught fan

27. Chimney Stack

Description:

In a typical coal-fired thermal power plant Coal is conveyed (14) from an external stack and

ground to a very fine powder by large metal spheres in the pulverized 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 remaining water.

The steam passes through a manifold in the roof of the drum into the pendant super heater (19)

where its temperature and pressure increase rapidly to around 200 bar and 570°C, 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.

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A steam governor valve (10) allows for both manual control of the turbine and automatic set

point following.

The steam is exhausted from the high-pressure turbine, and reduced in both pressure and

temperature, is returned to the boiler re heater (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 condenser (8), where it condenses rapidly back

into water, creating near vacuum-like conditions inside the condenser chest.

The condensed water is then passed by a feed pump (7) through a deaerator (12), and prewar

med first in a feed heater (13) powered by steam drawn from the high pressure set, and then in

the economizer (23), before being returned to the boiler drum.

The cooling water from the condenser is sprayed inside a cooling tower (1), creating a highly

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

cycle.

The three turbine sets are 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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REFERENCES

WWW.WIKIPEDIA.ORG

WWW.HPGCL.GOV.IN

Thermal Power Plant Simulation And Control by Damian Flynn

Thermal Power Station by Fredric P Miller, Agnes F Vandome

Power-plant control and instrumentation: the control of boilers and HRSG systems By David

Lindsley, Institution of Electrical Engineers