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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
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
i
CERTIFICATE
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.
iii
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
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
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
vi
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
vii
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
viii
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
1
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
2
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
3
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)
4
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)
5
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.
6
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.
7
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
8
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.
9
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.
10
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.
11
Fig No.3.2 (BOILER)
12
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
13
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.
14
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.
15
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
16
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)
17
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
18
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
19
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
20
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
21
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
22
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
23
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)
24
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
25
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
26
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
27
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
28
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.
29
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
30
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 –
31
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.
32
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.
33
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
34
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
35
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.
36
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
37
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'
38
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)
39
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.
40
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
41
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
42
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
43
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.
44
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.
45
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.
46
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.
47
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.
48
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
49
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.
50
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
51
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.
52
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.
53
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
54
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.
55
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
56
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