1. 1
Chapter 1
INTRODUCTION
NSPCL (NTPC-SAIL Power Company Limited) is a joint venture company of NTPC limited and SAIL to
generate power for various steel plants throughout India.NTPC and SAIL joined forces in March 2001 and
took over a captive power plant (consisting of 2*60 MW generators) located at the Durgapur Steel Plant and
another (also 2*60 MW ) at the Rourkela Steel Plant.
NTPC formed another joint venture company with SAIL on in March 2002 in the name of Bhilai Electric
Supply Company Ltd.(BESCL).BESCL took over a captive power plant (comprising 2*30 MW generators)
located at the Bhilai Steel Plant from SAIL.Effective 11 September 2006,BESCL became part of
NSPCL.Since 2006,NSPCL has provided all power required by the Bhilai,Durgapur and Rourkela steel
plants.To meet growing demands,NSPCL commissioned an expansion project at Bhilai comprising two
250MW generators during 2008-2009,and brought the units online in 2009-2010.Additional growth to
generate an additional 1750MW is anticipated at other SAIL facilities.
1.1 Durgapur Captive PowerPlant
NTPC Durgapur is located near Waria railway station,5 km from Durgapur city in West Bengal.The power
plant is one of the coal based power plants of Durgapur.
Fig. 1.1 Durgapur Captive Power Plant
Its objective is to supply power to Durgapur Steel Plant of Steel Authority of India Limited (SAIL) from its
coal based captive power plant-II at Durgapur (West Bengal) 2*60 MW on captive basis.

2. 2
Chapter 2
LAYOUT OF THE PLANT
Fig.2.1 Layout of the Plant
2.1 Descriptionof layout of the plant
A thermal power plant is based on the Rankine Cycle.A plant layout study is an engineering study used to
analyze different physical configurations for an manufacturing plant.It is also known as Facilities Planning
and layout. A thermal power station is one that takes chemical energy and forms heat (thermal) and
then converts that heat into electrical energy. Here, the prime mover is mainly steam driven. Water is heated,
turns into steam and spins a steam turbine which drives an electrical generator. After the steam passes through
the turbine, the steam is condensed in a condenser. This principle is known as Rankine Cycle.
Chapter 3

3. 3
SITE SELECTION OF THE PLANT
For steam stations,the choice of plant location is governed by the following considerations:
3.1.1 Transmissionofenergy:
A power plant should be located as near the load centre as possible.This reduces the transmission costs and
losses in transmission.
3.1.2 Costofreal estate and taxes:
Steam stations need lot of space for installation of equipment and storage of fuel.The cost of land near a load
centre may be very high as compared to that at a remote place.In addition to the fixed cost on the capital
invested in real estate,the taxes on land should be taken into account.
3.1.3 Transportationoffuel:
Steam stations need lot of coal every day.The site should be such that coal can be transported easily from
mines to the plant.It has been seen often that the railways are used to deliver coal from coal mines to the coal
yards of the plant.
3.1.4 Availability of water:
An ample supply of water must be available for condenser cooling water.Thus,sites adjacent to large bodies
of water are preferable.Alternatively tube wells and cooling towers have to be installed and their cost must be
taken into account.
3.1.5 Disposalofash:
A steam station produces huge quantity of ash.A site where ash can be disposed off easily will naturally be
advantageous.
3.1.6 Reliability of supply:
The generating stations should be located in different areas of the state so that reliability of supply is good at
all points.
3.1.7 Pollutionand Noise:
A site near a load centre may be objectionable from the point of view of noise and pollution.(Ref. 1)
Chapter 4

4. 4
SELECTION OF FUEL
Coal,the most abundant fossil fuel,was formed by the decomposition of vegetation which was buried under
the earth million of years ago.The conversion of vegetation into coal requires ages of time.Coal contains
moisture,carbon,hydrogen,sulphur,nitrogen,oxygen and ash.Semi-bituminuous coal has properties in between
those of bituminous and anthracite coal and is widely used in power plants.Its calorific value is about
27000kJ/Kg.
4.1 Selectionofcoalfor powerplants:
The selection of coal for a power plant depends on a number of factors.Some of them are:
4.1.1 Calorific value:
It represents the amount of energy in a given mass.Coal with a higher calorific value is,obviously,preferable.
4.1.2 Weatherability:
It is a measure of the ability of coal to withstand exposure to environment without excessive crumbling.Every
power plant has considerable storage of coal.If coal crumbles severly during storage,the small particles will
be washed away in rainstorms causing financial and energy loss and pollution of the surroundings.
4.1.3 Sulphur content:
Sulphur is one of the combustible elements in the coal and produces energy.However its primary combustion
product,sulphur dioxide,is a health hazard.It is difficult and expensive to remove sulphur from the coal or to
remove sulphur dioxide from the combustion products.
4.1.4 Grindability Index:
The grindability index is inversely proportional to the power required to grind the coal to a certain
fineness.Coal with a high grindability index is preferable.
4.1.5 Ash content:
Ash is an impurity,produces no heat and must be removed from the furnace and disposed off.
4.1.6 Particle size:
Coal must be reduced to small size (approx 20 mm) to promote rapid and complete combustion.(Ref. 1)
Chapter 5
COAL HANDLING PLANT

5. 5
NTPC Durgapur has a coal yard of capacity one lakh tonnes in its coal handling plant.Coals are available there
from various coal mines through railways via Waria railway station and unloaded by the wagon tippler and
then transferred to the crusher through conveyor belts.
Fig. 5.1 Layout of Coal handling plant
5.1 COAL HOPPER:
Coals, from colliery, come to the loco wagon by rail and road. From rail wagon, coal is tripped by using wagon
tippler to the coal hopper. The hopper is equipped with the vibrator which places the coal on the conveyer in
a controlled manner. The hopper does not allow the larger sized coals to pass through and they are needed to
be broken manually using a hammer. The conveyer, carrying the coal from hopper, allows it to fall through a
chute (generally telescopic) when dozing operation is done. Then it falls through another hopper & the 2nd
conveyor belt carries the coal to the crusher. The capacity of the belt is 250 tons/hr.

6. 6
Fig.5.2 Coal handling plant control panel
5.2 CRUSHER:
In the crusher the coal is broken into pieces of dimension of about 25mm when the ring hammers suspended
from the suspension bars of the rotors heat the coal on the breaker plate mounted on cage frame in the crusher
body. Ring hammers may be teethed or plain. The teethed ones guide the coal & plain ones break them.The
crusher rotor has 84 no. of ring hammers with equal no of each type. Crushed coal is supplied by the conveyor
belt to 6 bunkers. From bunkers coal is supplied to the coal feeder which controls the amount of coal supplied
to the mill. There are suspension magnets to the separate magnetic material from coal before feed into mills.

7. 7
Fig.5.3 Crushed coal
5.3 COAL MILLS:
The coal is put in the boiler after pulverization.For this pulverizer is used.A pulverizer is a device for grinding
coal for combustion in a furnace in a power plant.
5.3.1 Types of Pulverizers:
5.3.1.1 Ball and Tube Mill
Ball mill is a pulverizer that consists of a horizontal rotating cylinder, up to three diameters in length,
containing a charge of tumbling or cascading steel balls, pebbles, or rods.Tube mill is a revolving cylinder of
up to five diameters in length used for fine pulverization of ore, rock, and other such materials; the material,
mixed with water, is fed into the chamber from one end, and passes out the other end as slime.
5.3.1.2 Ring and Ball
This type consists of two rings separated by a series of large balls. The lower ring rotates, while the upper ring
presses down on the balls via a set of spring and adjuster assemblies. Coal is introduced into the center or side
of the pulverizer (depending on the design) and is ground as the lower ring rotates causing the balls to orbit
between the upper and lower rings. The coal is carried out of the mill by the flow of air moving through it.
The size of the coal particals released from the grinding section of the mill is determined by a classifer
separator. These mills are typically produced by B&W (Babcock and Wilcox).

8. 8
In unit-4, 5 out of 8 mills are always in service. The purpose of coal mill is to pulverize the coal employing in
3- heavy rollers in each mill. The pulverized coal is flown away by the primary air & injected in the furnace.
For better combustion pulverized coal is preheated by primary air. Cold primary air is used to prevent over
heating & burning of coal in the mill. In the furnace, first oil is burnt by using a spark plug for initiation &
then coal firing is started & when coal starts burning, oil firing is withdrawn.NTPC Durgapur has ball ring
type pulverizer.
5.4 COAL FEEDER:
From bunker, the coal comes to the coal feeders to protect the mill (Pulverizer) from large size stones or
metallic impurities.
5.5 CONVEYOR BELT:
Conveyor belts are used to carry the coal, first, from wagon tippler to the raw coal yard, then from raw coal
yard to crusher house, and from crash coal yard to the coal bunker. The belts rest over rollers. The rollers are
placed in a “V” shape in forward direction, and flat rollers are used in reverse direction. A Dead weight is
hanged from two pulleys to allow the extension and contraction of the belt.
Fig.5.4 Conveyor belt

9. 9
Chapter 6
WATER TREATMENT PLANT
This is the place, where, the water of the river Damodar, is prepared through a number of steps for using in
the plant and for the colony adjacent to it. The water of the river, known as the Raw water, contains many
impurities, like gases causing erosion and corrosion of metal,hard salts leading to overheating by forming hard
scales,soft salts forming scales and dissolved solids,organic matters, silt, clay, silica and other impurities in
colloidal form.Various steps are taken to eliminate these impurities and prepare usable water.
The water coming from the station service pump is first passed through a multi stage surface spreader. As a
result of this, the water gets more surface contact with the air and atmosphere and so more air is dissolved into
it.The water is then mixed with Chlorine to kill the harmful bacteria. This mixing process is done with great
care as excess amount of chlorine is harmful for both machines and humans.While water from S.S pump flows
to clarifier bed,chlorine gas is added to water with continuous stream of water which flows through a pipeline.
In the pipeline,there is a nozzle and when water flows through the nozzle, pressure falls at the outlet of the
nozzle.This pressure (or lack of it) is the driving force to carry chlorine from its storage. After this, Alum is
fed into this water. The alum mixes with low density particles to form slag which floats on the surface of
water. First, Alum is mixed with water to prepare a solution in a tank with motor driven stirrers. Then, this
solution is mixed with water flowing through S.S Pump to clarifier. Then the filter is sent to respective pumps
for distribution.After this, the water is taken to clarifier bed where coagulation and precipitation of suspended
particles occur. The water is then sent to Sand filled gravity filters, where it gets filtrated with the help of filter
beds made of sand, gravels etc. The filtrated water is then supplied to different fields by various pumps for
demineralisation.
Fig.6.1 Water treatment plant

10. 10
CHAPTER 7
DEMINERALISATION PLANT
This Plant is used to remove all the minerals in the form of silicates chlorides and sulphates from the water.
These salts are responsible for the hardness of the water. If they are not removed, then they form scales on the
surface. Maintaining the PH level is also one of the important reasons of demineralization. It is the last step,
through which water passes before reaching the demineralized water tank. The steps are as follows:
7.1 Activated Carbon Filter:
It is a closed tank, that has activated carbon within, that absorb residual chlorine and other non volatile gases
present in the water. It has three steps, backwash, rinse and Service.

11. 11
Fig.7.1 Activated carbon filter
7.2 Cationic Exchanger:
As the name suggests, it exchanges cation (Ca++ and Mg++ ion) present in the water in the form of their
salts with H+ ions.The exchanger is fed with Resin (R-SO3-H). As Water comes in contact with it,
the hydrogen ion of resin gets replaced with calcium or magnesium ions resulting in free hydrogen
ion, that causes the water to be slightly acidic.
2R-SO3-H + X2+ (R-SO3)2X + H3O+

12. 12
After some period, the resin gets deactivated due to replacement of all the hydrogen atoms. At that time
Sulphuric Acid or Hydrochloric Acid is needed to be added to activate the resin back.
(R-SO3)2X + H2SO4 XSO4 + 2R-SO3H
After this, water is sent for service. So Cationic exchanger has four steps, Backwash, Regeneration,
Rinse, and Service.
Fig.7.2 Cation exchanger
7.3 Anionic Exchanger:

13. 13
This exchanger works similarly like a cationic exchanger except that it removes anions like chlorides,
sulphates, silicates etc. The functional group of resin here is OH. Like cationic exchanger, it also has 4
steps, i.e. Backwash, Regeneration, Rinse and Service.
R-SO3-OH + HCl R-SO3-Cl + H2O
In anionic exchanger, resin is re generated by using NaOH.
R-SO3-Cl + NaOH R-SO3-OH + NaCl
Fig.7.3 Anion exchanger
7.4 Mixed BedType:
In actual practice, both the cationic and anionic exchangers are not able to completely remove the
cationic and anionic parts, therefore a further processing is needed in the form of a mixed bed which removes
both the cationic and anionic part. This bed contains both type of resins.
In reality, completely 100% pure water is not achievable but however a certain industrial level of purity
and quality is maintained that is Ph of 6.8,zero hardness,silica level 0.01 ppm.

14. 14
Now the water is stored in a storage tank called Degassed tank,from here it is feed to the boiler for the further
processes.

15. 15
Fig.7.4 Degassed tank
Chapter 8
COMPONENTS USED IN THE PLANT
8.1 Boiler:
Now that pulverized coal is put in boiler furnance.Boiler is an enclosed vessel in which water is heated and
circulated until the water is turned in to steam at the required pressure.
Coal is burned inside the combustion chamber of boiler.The products of combustion are nothing but
gases.These gases which are at high temperature vaporize the water inside the boiler to steam.Some times this
steam is further heated in a superheater as higher the steam pressure and temperature the greater efficiency the
engine will have in converting the heat in steam in to mechanical work. This steam at high pressure and
tempeture is used directly as a heating medium, or as the working fluid in a prime mover to convert thermal
energy to mechanical work, which in turn may be converted to electrical energy. Although other fluids are
sometimes used for these purposes, water is by far the most common because of its economy and suitable
thermodynamic characteristics.
8.1.1 Classificationofboilers:
8.1.1.1 Fire tube boilers :
In fire tube boilers hot gases are passed through the tubes and water surrounds these tubes. These are
simple,compact and rugged in construction.Depending on whether the tubes are vertical or horizontal these
are further classified as vertical and horizontal tube boilers.In this since the water volume is more,circulation
will be poor.So they can't meet quickly the changes in steam demand.High pressures of steam are not
possible,maximum pressure that can be attained is about 17.5kg/sq cm.Due to large quantity of water in the
drain it requires more time for steam raising.The steam attained is generally wet,economical for low
pressures.The outut of the boiler is also limited.

16. 16
Fig. 8.1 Fire tube boiler
8.1.1.2 Water tube boilers:
In these boilers water is inside the tubes and hot gases are outside the tubes.They consists of drums and
tubes.They may contain any number of drums. Feed water enters the boiler to one drum (here it is drum below
the boiler).This water circulates through the tubes connected external to drums.Hot gases which surrounds
these tubes wil convert the water in tubes in to steam.This steam is passed through tubes and collected at the
top of the drum since it is of light weight.So the drums store steam and water (upper drum).The entire stea m
is collected in one drum and it is taken out from there.As the movement of water in the water tubes is high, so
rate of heat transfer also becomes high resulting in greater efficiency.They produce high pressure , easily
accessible and can respond quickly to changes in steam demand.These are also classified as vertical,horizontal
and inclined tube depending on the arrangement of the tubes.These are of less weight and less liable to
explosion.Large heating surfaces can be obtained by use of large number of tubes.We can attain pressure as
high as 125 kg/sq cm and temperatures from 315 to 575 centigrade. (Ref. 2)
Fig. 8.2 Water tube boilers
NTPC Durgapur has two water tube boilers and total boiler drum length is 11 m.Each of them is situated at
height of 52m from the ground.

17. 17
Table no.1: Boiler Drum Specifications
Inner diameter 1600mm
Thickness 100mm
Outside diameter 1800mm
Overall length 11500mm
Steam Capacity 12.6 cu.m
Number of boiler drums 02
Boiler drum height from the ground 52m
Orientation of water tubes Vertical
8.2 Air preheater:
The remaining heat of flue gases is utilised by air preheater.It is a device used in steam boilers to transfer heat
from the flue gases to the combustion air before the air enters the furnace. Also known as air heater; air-heating
system. It is not shown in the lay out.But it is kept at a place near by where the air enters in to the boiler. The
purpose of the air preheater is to recover the heat from the flue gas from the boiler to improve boiler efficiency
by burning warm air which increases combustion efficiency, and reducing useful heat lost from the flue. As a
consequence, the gases are also sent to the chimney or stack at a lower temperature, allowing simplified design
of the ducting and stack. It also allows control over the temperature of gases leaving the stack (to meet
emissions regulations, for example).After extracting heat flue gases are passed to elctrostatic
precipitator.NTPC Durgapur has regenerative type of air preheater.

18. 18
Fig.8.3 Air preheater
8.3 Economiser:
Flue gases coming out of the boiler carry lot of heat.Function of economiser is to recover some of the heat
from the heat carried away in the flue gases up the chimney and utilize for heating the feed water to the boiler.It
is placed in the passage of flue gases in between the exit from the boiler and the entry to the chimney.The use
of economiser results in saving in coal consumption,increase in steaming rate and high boiler efficiency but
needs extra investment and increase in maintenance costs and floor area required for the plant.This is used in
all modern plants.In this a large number of small diameter thin walled tubes are placed between two
headers.Feed water enters the tube through one header and leaves through the other.The flue gases flow outside
the tubes usually in counter flow.
Fig.8.4 Economiser
8.4 Superheater:

19. 19
Most of the modern boliers are having superheater and reheater arrangement. Superheater is a component of
a steam-generating unit in which steam,after it has left the boiler drum, is heated above its saturation
temperature. The amount of superheat added to the steam is influenced by the location, arrangement, and
amount of superheater surface installed, as well as the rating of the boiler. The superheater may consist of one
or more stages of tube banks arranged to effectively transfer heat from the products of
combustion.Superheaters are classified as convection , radiant or combination of these.
Fig.8.5 Superheater
8.5 Electrostatic precipitator:
It is a device which removes dust or other finely divided particles from flue gases by charging the particles
inductively with an electric field, then attracting them to highly charged collector plates. Also known as
precipitator. The process depends on two steps. In the first step the suspension passes through an electric
discharge (corona discharge) area where ionization of the gas occurs. The ions produced collide with the
suspended particles and confer on them an electric charge. The charged particles drift toward an electrode of
opposite sign and are deposited on the electrode where their electric charge is neutralized. The phenomenon
would be more correctly designated as electrodeposition from the gas phase.
The use of electrostatic precipitators has become common in numerous industrial applications. Among the
advantages of the electrostatic precipitator are its ability to handle large volumes of gas, at elevated
temperatures if necessary, with a reasonably small pressure drop, and the removal of particles in the
micrometer range. Some of the usual applications are: (1) removal of dirt from flue gases in steam plants; (2)
cleaning of air to remove fungi and bacteria in establishments producing antibiotics and other drugs, and in

20. 20
operating rooms; (3) cleaning of air in ventilation and air conditioning systems; (4) removal of oil mists in
machine shops and acid mists in chemical process plants; (5) cleaning of blast furnace gases; (6) recovery of
valuable materials such as oxides of copper, lead, and tin; and (7) separation of rutile from zirconium sand.
Fig.8.6 ESP
8.6 Condenser:
Steam after rotating steam turbine comes to condenser.Condenser refers here to the shell and tube heat
exchanger (or surface condenser) installed at the outlet of every steam turbine in Thermal power stations of
utility companies generally. These condensers are heat exchangers which convert steam from its gaseous to
its liquid state, also known as phase transition. In so doing, the latent heat of steam is given out inside the
condenser. Where water is in short supply an air cooled condenser is often used. An air cooled condenser is
however significantly more expensive and cannot achieve as low a steam turbine backpressure (and therefore
less efficient) as a surface condenser.
The purpose is to condense the outlet (or exhaust) steam from steam turbine to obtain maximum efficiency
and also to get the condensed steam in the form of pure water, otherwise known as condensate, back to steam
generator or (boiler) as boiler feed water.
The steam turbine itself is a device to convert the heat in steam to mechanical power. The difference between
the heat of steam per unit weight at the inlet to turbine and the heat of steam per unit weight at the outlet to
turbine represents the heat given out (or heat drop) in the steam turbine which is converted to mechanical

21. 21
power. The heat drop per unit weight of steam is also measured by the word enthalpy drop. Therefore the more
the conversion of heat per pound (or kilogram) of steam to mechanical power in the turbine, the better is its
performance or otherwise known as efficiency. By condensing the exhaust steam of turbine, the exhaust
pressure is brought down below atmospheric pressure from above atmospheric pressure, increasing the steam
pressure drop between inlet and exhaust of steam turbine. This further reduction in exhaust pressure gives out
more heat per unit weight of steam input to the steam turbine, for conversion to mechanical power. Most of
the heat liberated due to condensing, i.e., latent heat of steam, is carried away by the cooling medium. (water
inside tubes in a surface condenser, or droplets in a spray condenser (Heller system) or air around tubes in an
air-cooled condenser).
Condensers are classified as (i) Jet condensers or contact condensers (ii) Surface condensers.
In jet condensers the steam to be condensed mixes with the cooling water and the temperature of the condensate
and the cooling water is same when leaving the condenser; and the condensate can't be recovered for use as
feed water to the boiler; heat transfer is by direct conduction.
In surface condensers there is no direct contact between the steam to be condensed and the circulating cooling
water. There is a wall interposed between them through heat must be convectively transferred.The temperature
of the condensate may be higher than the temperature of the cooling water at outlet and the condnsate is
recovered as feed water to the boiler.Both the cooling water and the condensate are separetely with
drawn.Because of this advantage surface condensers are used in thermal power plants.Final output of
condenser is water at low temperature is passed to high pressure feed water heater,it is heated and again passed
as feed
water to the boiler.Since we are passing water at high temperature as feed water the temperature inside the
boiler does not decrease and boiler efficiency also maintained.

22. 22
Fig.8.7 Condenser
8.7 Cooling tower:
The condensate (water) formed in the condeser after condensation is initially at high temperature.This hot
water is passed to cooling towers.It is a tower- or building-like device in which atmospheric air (the heat
receiver) circulates in direct or indirect contact with warmer water (the heat source) and the water is thereby
cooled. A cooling tower may serve as the heat sink in a conventional thermodynamic process, such as
refrigeration or steam power generation, and when it is convenient or desirable to make final heat rejection to
atmospheric air. Water, acting as the heat-transfer fluid, gives up heat to atmospheric air, and thus cooled, is
recirculated through the system, affording economical operation of the process.
Two basic types of cooling towers are commonly used.One transfers the heat from warmer water to cooler air
mainly by an evaporation heat-transfer process and is known as the evaporative or wet cooling tower.
Fig.8.8 Cooling tower

23. 23
Evaporative cooling towers are classified according to the means employed for producing air circulation
through them:atmospheric, natural draft, and mechanical draft. The other transfers the heat from warmer water
to cooler air by a sensible heat-transfer process and is known as the non evaporative or dry cooling tower.
Nonevaporative cooling towers are classified as air-cooled condensers and as air-cooled heat exchangers, and
are further classified by the means used for producing air circulation through them. These two basic types are
sometimes combined, with the two cooling processes generally used in parallel or separately, and are then
known as wet-dry cooling towers.
Evaluation of cooling tower performance is based on cooling of a specified quantity of water through a given
range and to a specified temperature approach to the wet-bulb or dry-bulb temperature for which the tower is
designed. Because exact design conditions are rarely experienced in operation, estimated performance curves
are frequently prepared for a specific installation, and provide a means for comparing the measured
performance with design conditions.
Fig.8.9 Cooling tower fans

24. 24
Fig.8.10 Sectional view of cooling tower
8.8 Turbine:
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it
into rotary motion. Because the turbine generates rotary motion, it is particularly suited to be used to drive an
electrical generator – about 80% of all electricity generation in the world is by use of steam turbines. The
steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency
through the use of multiple stages in the expansion of the steam, which results in a closer approach to the
idealreversibleprocess.
Non condensing or backpressure turbines are most widely used for process steam applications. The exhaust
pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly
found at refineries, district heating units, pulp and paper plants, and desalination facilities.
Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam in a
partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser.
Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow
exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is
added. The steam then goes back into an intermediate pressure section of the turbine and continues its
expansion.

25. 25
Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from
various stages of the turbine, and used for industrial process needs or sent to boiler feedwater heaters to
improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled.
Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.
To maximize turbine efficiency the steam is expanded, generating work, in a number of stages. These stages
are characterized by how the energy is extracted from them and are known as either impulse or reaction
turbines. Most steam turbines use a mixture of the reaction and impulse designs: each stage behaves as either
one or the other, but the overall turbine uses both. Typically, higher pressure sections are impulse type and
lower pressure stages are reaction type.
An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain
significant kinetic energy, which the rotor blades, shaped like buckets, convert into shaft rotation as the steam
jet changes direction.As the steam flows through the nozzle its pressure falls from inlet pressure to the exit
pressure (atmospheric pressure, or more usually, the condenser vacuum). Due to this higher ratio of expansion
of steam in the nozzle the steam leaves the nozzle with a very high velocity. The steam leaving the moving
blades is a large portion of the maximum velocity of the steam when leaving the nozzle. The loss of energy
due to this higher exit velocity is commonly called the "carry over velocity" or "leaving loss"
Fig.8.11 Turbine
In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of
turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the
rotor. Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the
entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed
of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the

26. 26
stator and decelerating through the rotor, with no net change in steam velocity across the stage but with a
decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.
When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass line to
allow superheated steam to slowly bypass the valve and proceed to heat up the lines in the system along with
the steam turbine. Also a turning gear is engaged when there is no steam to the turbine to slowly rotate the
turbine to ensure even heating to prevent uneven expansion. After first rotating the turbine by the turning gear,
allowing time for the rotor to assume a straight plane (no bowing), then the turning gear is disengaged .
Problems with turbines are now rare and maintenance requirements are relatively small. Any imbalance of the
rotor can lead to vibration, which in extreme cases can lead to a blade letting go and punching straight through
the casing. It is, however, essential that the turbine be turned with dry steam. If water gets into the steam and
is blasted onto the blades (moisture carryover) rapid impingement and erosion of the blades can occur, possibly
leading to imbalance and catastrophic failure. Also, water entering the blades will likely result in the
destruction of the thrust bearing for the turbine shaft. To prevent this, along with controls and baffles in the
boilers to ensure high quality steam, condensate drains are installed in the steam piping leading to the
turbine.(Ref. 4)
Fig.8.12 Types of turbines
8.9 Alternator:
An alternator is an electromechanical device that converts mechanical energy to alternating current electrical
energy. The A.C Generator or alternator is based upon the principle of electromagnetic induction & consists a
stationary part called Stator & a rotating part called Rotor. The armature windings are placed in the stator.
Field winding is placed in the Rotor & DC supply is given to the field winding. When rotor is rotated, the lines
of magnetic flux (viz magnetic field) cut through the stator windings. This induces an electromagnetic force
(e.m.f) in the stator windings.

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The magnitude of e.m.f (E) = 4.44  f N volts
 = Strength of magnetic field in webers
N = Number of turns in a coil of stator winding
f = Frequency in Hz = P n/120
where n = revolutions of rotor
P = Number of poles. For same frequency increase in number of poles decrease the
machine speed & vice versa. Hence low speed hydro turbines have 14 to 20 poles & high speed steam turbines
have generally 2 poles.
There are three basic requirements for the generation of voltage /e.m.f / electricity. These are magnetism,
motion and conductors. When a coil moves relative to a magnetic field, a voltage is produced; generatio n
systems are based on this concept.
When a conductor cuts through a magnetic field, a current is produced in that conductor. These two concepts
are very closely connected. Keep in mind that it makes no difference if the magnetic field is stationary and the
conductor moves or whether the conductor is stationary and the magnetic field moves. The important aspect
is that there is relative motion/ there must be a relative motion between two windings of the Generator.
The simplest generator consists of a loop of wire rotating between two permanent magnet poles. An AC
synchronous generator is significantly more complex than the simple generator of a wire loop rotating between
two permanent magnets. An AC synchronous generator consists of four main components and/or systems field
(rotor),armature (stator),exciter and automatic Voltage Regulator.
Essentially the process of generating voltage goes in the following order. The exciter provides DC current to
the rotor windings. DC current through these wires creates magnetic flux. Magnetic flux generates an AC
voltage in the nearby stator windings when there is relative motion between the two. The regulator then senses
this output and controls the exciter current. In generators, the rotor (the source of the magnetic field) rotates
inside a stationary armature called a stator. One reason for using a stationary armature and a rotating magnetic
field is the difficulty of taking 3-phase current from a rotating armature. The rotor is rotated by a prime mover.
The Turbine has been used as a prime mover for Generators; that is why it is called as TG (Turbo Generator).
The rotor contains magnetic poles with windings wrapped around them to form coils. These coils are called
field coils or field windings because they create a magnetic field when excited with a DC current. Typically,
the generator field windings contain many turns. A magnetic field radiates out from the rotor as lines of
magnetic flux. As the rotor rotates, so does the magnetic field. When this moving magnetic field comes across
a stator winding, an AC voltage is produced. The magnetic field is strongest at the center of the north and
south poles where the lines of magnetic flux are concentrated. Therefore, the closer a pole is to a stator winding,

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the higher the voltage produced in that stator winding. It is important to note voltage is a function of flux
change per time, not only the proximity to the field.
Fig.8.13 An Alternator
Table No.2: Alternator ratings (Ref. 5)
Parameter Rating
Rated Power 81250 KVA
RPM 3000
Insulation Class F
Stator voltage 11500 V
Rotor voltage 186.6 V
Stator current 4879.1 A
Rotor current 1550 A

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Power factor 0.8
Phase connection Y
Frequency 50 Hz
Cooling hydrogen Temp. 42. oC
8.10 Fanor draught system:
In a boiler it is essential to supply a controlled amount of air to the furnace for effective combustion of fuel
and to evacuate hot gases formed in the furnace through the various heat transfer area of the boiler. This can
be done by using a chimney or mechanical device such as fans which acts as pump.(Ref. 3)
8.10.1 Natural draught
When the required flow of air and flue gas through a boiler can be obtained by the stack (chimney) alone, the
system is called natural draught. When the gas within the stack is hot, its specific weight will be less than the
cool air outside; therefore the unit pressure at the base of stack resulting from weight of the column of hot gas
within the stack will be less than the column of extreme cool air. The difference in the pressure will cause a
flow of gas through opening in base of stack. Also the chimney is form of nozzle, so the pressure at top is very
small and gases flow from high pressure to low pressure at the top.
8.10.2 Mechanized draught
There are 3 types of mechanized draught systems:
 Forced draught: – In this system a fan called Forced draught fan is installed at the inlet of the boiler.
This fan forces the atmospheric air through the boiler furnace and pushes out the hot gases from the
furnace through superheater, reheater, economiser and air heater to stacks.
 Induced draught: – Here a fan called ID fan is provided at the outlet of boiler, that is, just before the
chimney. This fan sucks hot gases from the furnace through the superheaters, economiser, reheater and
discharges gas into the chimney. This results in the furnace pressure lower than atmosphere and affects
the flow of air from outside to the furnace.
 Balanced draught:-In this system both FD fan and ID fan are provided. The FD fan is utilized to draw
control quantity of air from atmosphere and force the same into furnace. The ID fan sucks the product
of combustion from furnace and discharges into chimney. The point where draught is zero is called
balancing point.
8.11 ASH HANDLING PLANT:

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The furnace is a dry bottom furnace characterized by a huge amount of fly ash (about 80%) removed
by the suction of Induced Duct fan (I.D Fan) and about 20% bottom ash that falls through furnace
bottom. The exit temperature of gases must be less than ash fusion temperature. Different components of
ash handling plant are ash hopper, scraper conveyor, clinker grinder, Electrostatic Precipitator (ESP),
flushing apparatus, sump, ash slurry pump, ash pond, etc.The various processes that take place in Ash
Handling Plant are:
8.11.1 Removal ofBottom-Ash: The ash collected in bottom hopper is quenched by spraying water
andcontinuously discharging water through impounded scraper conveyor. The ash is then transported to
respective clinker grinder to reduce the lump size.
Fig.8.14 Ash Handling Plant
The crushed ash falls below ash sluice trench and then transported to ash slurry pump by gravity associated
with high pressure water jet.
8.11.2 Removal of fly-Ash: Fly ash collected in each of the E.S.P hopper, economizer hopper, air pre
heater hopper and stack hopper drops continuously toflushing apparatus where water mixes with ash
and the resulting slurry drops into ash sluice trench. The ash slurry is later transported to ash slurry sump
in the same way as bottom ash.

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8.11.3 DisposalofAshSlurry: Three ash slurry pumps have provided for disposal of slurry sump to the
disposal area .Each set comprise two stage of pumping. Two streams of disposal pipe lines of 250dia and
length about 3 km are provided for three slurry pump sets, out of which one pipe line will be stand by.
Chapter 9
SWITCHYARD
Fig.9.1 Switchyard
9.1 SWITCHYARD EQUIPMENTS:
 Isolators
 Current transformer
 CVT
 Lightening arrestor
 Earthing switch

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 Wave traps
 Power transformers
 Bus reactor
 Circuit Breaker
 Relays
9.1.1 Isolator
 Operates under No Load Condition
 Interlocked with Breakers and Earth Switches
 Local as well as Remote Operation possible
 Isolates Sections for Maintenance
 Used to select Bus Bars
Fig. 9.2 Isolator
9.1.2 CT
 To step-down the high magnitude of current to a safe value to incorporate protection .
 Current Transformers are used for the instrumentation of power systems.

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Fig. 9.3 Current Transformer
It provides a simple, inexpensive and yet accurate means of sensing current flow in power conductors.
9.1.3 CVT
 The Capacitor Voltage Transformer (CVT) is used for supplying voltage signal to the measuring
instruments and protective relays.
 This is also used as coupling capacitor for Power Line Carrier Communication (PLCC).
o Primary voltage is applied to a series of capacitors group. The voltage across one of the
capacitor is taken to Aux PT. The secondary of the Aux PT is taken for measurement and
protection.
Fig. 9.4 CVT
9.1.4 Lighting arrestor
• To discharge the high voltage surges in the power system due to Lightning to the ground.

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• Not in circuit in normal operation.
 Offers low resistance at abnormal voltages
The earthing screen and ground wires can well protect the electrical system against direct lightning strockes
but they fail to provide protection against travelling waves which may reach the terminal apparatus . The
lightning arresters or surge diverters provide protection against such surges.
A lightning arresters or surge diverter is a protective device which conducts the high voltage surges on the
power system to the ground.
It consists of a spark gap in series with a non linear resistor. One end of diverter is connected to the terminal
of the equipment to be protected and the other end is effectively grounded. The length of gap is so set that
normal line voltage is not enough to cause an arc across the gap but a dangerously high voltage will break
down the air insulation and form an arc. The property of non linear resistance is that its resistance decreases
as the voltage (or current) increase and vice-versa.
A lightning arrestor is used for to protect the insulation on system from damaging effect of lighting. When a
lighting surge travels down the power system to the arrestor, the current from surge is diverted to ground and
the system is protected.
Fig. 9.5 Surge Arrester
9.1.5 Earthing Switch
 These are also called as Grounding Switches.

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 Used To ground the Sections required for
maintenance .
 To ground induction voltages.
 Interlocked with Breakers and Isolators.
 Motor driven as well as Hand driven.
9.1.6 Wavetrap
 Wave trap is used for protection of the transmission lines and communication & data transmission
between the Substations.
 Major part of PLCC i.e. Power Line Carrier Communication.
 Sends inter-trip signal to the other end CBs so that fault can be isolated at the earliest time.
9.1.7 Circuit Breaker
Device capable of making and breaking an electrical circuit under normal and abnormal conditions.Main
Parts of a Circuit Breaker :-
 Fixed Contact
 Movable Contact
 Operating Mechanism and control circuit
 Arc quenching medium
Types of circuit breakers
 Oil CB
 Air Blast CB
 Vacuum CB
 SF6 CB

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Circuit breakers are mechanical devices designed to close or open contact members, thus closing or opening
of an electrical circuit under normal or abnormal conditions.Automatic circuit breakers, which are usually
employed for the protection of electrical circuits, are equipped with a trip coil connected to a relay or other
means, designed to open the breaker automatically under abnormal condition, such as over current. The
automatic circuit breakers perform the following duties:
(a) It carries the full-load current continuously without overheating or damages,
(b) It opens and closes the circuit on no load,
(c) It makes and brakes the normal operating current and
(d) It makes and brakes the shorts-circuits currents of magnitude upto which it designed.
Fig.9.6 Circuit Breaker
9.1.8 Bus bar
When a number of lines operating at the same voltage have to be directly connected electrically, bus bars are
used as the common electrical component. Bus bars are copper or aluminium bars ( generally of rectangular
X section ) and operate at constant voltage. The incoming and outgoing lines in a substation are connected to
the bus bars. The most commonly used bus bar arrangements in substations are :
 Single bus bar arrangement.
 Single bus bar system with sectionalisation.
 Double bus bar arrangement.

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Fig. 9.7 Bus Bars
9.1.9 Relays
It is an electrical device designed to initiate isolation of a part of electrical installation, or to operate an alarm
signal, in the event of an abnormal condition or a fault.
9.1.10 Transformers
A transformer is a device that transfers electrical energy from one circuit to another through inductively
coupled electrical conductors. A changing current in the first circuit (the primary) creates a changing magnetic
field; in turn, this magnetic field induces a changing voltage in the second circuit (the secondary). By adding
a load to the secondary circuit, one can make current flow in the transformer, thus transferring energy from
one circuit to the other.
The secondary induced voltage VS, of an ideal transformer, is scaled from the primary VP by a factor equal to
the ratio of the number of turns of wire in their respective windings:
By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped
up by making NS more than NP or stepped down, by making it less.
Transformers are some of the most efficient electrical 'machines', with some large units able to transfer 99.75%
of their input power to their output.Transformers come in a range of sizes from a thumbnail-sized coupling
transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect
portions of national power grids. All operate with the same basic principles, though a variety of designs exist
to perform specialized roles throughout home and industry
Transformers are used to step up and step down the voltage or current in the substations.

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Fig.9.8 Generator transformer
Fig. 9.9 Station transformer
Chapter 10
CONTROL ROOM

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Fig.10 Control panel and monitors
Control room or control unit is for the controlling of equipments like alternator,switchyard its components and
their protection.This unit also helps in identifying type of faults in the system and eradicate it from the system. It
also tells us about the power factor and the ratings as well as the characteristics of an alternator.The panels of
the control unit are always has three push buttons namely accept (A),test (T) and reset (R).This unit plays a
vital role in any plant as after generation,controlling is done by this unit.
CONCLUSION

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The first phase of practical training has proved to be quiet fruitful. It provided an opportunity for encounter
with such huge machines like turbines and generators.
The architecture of the power plant the way various units are linked and the way working of whole plant is
controlled make the student realize that engineering is not just learning the structured description and working
of various machines, but the greater part is of planning proper management.
It also provides an opportunities to learn low technology used at proper place and time can cave a lot of labour
e.g. wagon tippler (CHP).
But there are few factors that require special mention. Training is not carried out into its tree sprit. It is
recommended that there should be some project specially meant for students where presence of authorities
should be ensured. There should be strict monitoring of the performance of students and system of grading
be improved on the basis of work done.
However training has proved to be quite fruitful. It has allowed an opportunity to get an exposure of the
practical implementation to theoretical fundamentals.
REFERENCES

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1. Generation of electrical energy “B R Gupta” page no. 5 and 83
2. http://powerelectrical.blogspot.com/2007/03/thermal-power-plant-layout-and.html
3. indianpowersector.com/home/power-station/thermal-power-plant/
4 . http://powerplantstechnology.blogspot.in/2010/04/steam-turbine-use-in-power-plant.html
5.Materials provided at NSPCL Durgapur