POWER GENERATION AND TRANSMISSION employs (see Fig. 1.

1) an alternator coupled to a prime

mover. The prime mover is driven by the energy obtained
TOPICS from various sources
1:POWER GENERATION
2: EXCITATION
3:ECONOMICS OF POWER SUPPLY
4:POWER FACTOR IMPROVEMENT
5:OVERHEAD TRANSMISSION LINE
6:SWITCH GEARS
7:UNDERGROUND CABLES

such as burning of fuel, pressure of water, force of wind etc.

TOPIC 1 For example, chemical energy of a fuel (e.g., coal) can be
used to produce steam at high temperature and pressure. The
POWER GENERATION AND TRANSMISSION
steam is fed to a prime mover which may be a steam engine
Energy exists in different forms in nature but the most important form is or a steam turbine. The turbine converts heat energy of steam
the electrical energy. into mechanical energy which is further converted into
electrical energy by the alternator. Similarly, other forms of
The conversion of energy available in different forms in nature into energy can be converted into electrical energy by employing
electrical energy is known as generation of electrical energy. suitable machinery and equipment.
The stages of electrical energy production and consumption
Calorific Value
1: Generation It is the amount of heat produced by the complete combustion
↓ of a unit weight of fuel
2: Transmission
↓ Calorific value indicates the amount of heat available from a
4: Distribution fuel.
↓
5: Consumption LIQUID FUEL AND SOLID FUELS
The following are the advantages of liquid fuels over the
solid fuels :
Reasons why electrical energy is superior to all other forms of i. Easier to handle and require less storage space.
energy ii. The combustion of liquid fuels is uniform.
iii. The solid fuels have higher percentage of moisture and
Electrical energy is superior to all other forms of energy due to the consequently they burn with great difficulty. However,
following reasons : liquid fuels can be burnt with a fair degree of ease and
1.Convenient form. Electrical energy is a very convenient form of attain high temperature very quickly compared to solid
energy. It can be easily converted into other forms of energy. I.e fuels.
Electrical energy can be converted to light simply by using bulb iv. The waste product of solid fuels is a large quantity of ash
2.Easy control. The electrically operated machines have simple and and its disposal becomes a problem. However, liquid fuels
convenient starting, control and operation. For instance, an electric leave no or very little ash after burning.
motor can be started or stopped by turning on or off a switch. v. The firing of liquid fuels can be easily controlled. This
3.Greater flexibility. It can be easily transported from one place to permits to meet the variation in load demand easily.
another with the help of conductors.
4.Cheapness. Electrical energy is much cheaper than other forms of The following are the advantages of solid fuels over the
energy. Thus it is overall economical to use this form of energy for liquid fuels :
domestic, commercial and industrial purposes. i. In case of liquid fuels, there is a danger of
5.Cleanliness. Electrical energy is not associated with smoke, fumes or explosion.
poisonous gases. Therefore, its use ensures cleanliness and healthy ii. Liquids fuels are costlier as compared to solid fuels.
conditions. iii. Sometimes liquid fuels give unpleasant odours
6.High transmission efficiency. The electrical energy can be transmitted during burning.
conveniently and efficiently from the centres of generation to the iv. Liquid fuels require special types of burners for
consumers with the help of overhead conductors known as transmission
lines to the consumers in any part of the nation.
burning.
v. Liquid fuels pose problems in cold climates since the
oil stored in the tanks is to be heated in order to
avoid the stoppage of oil flow.
NOTE: All these forms of energy can be converted into electrical
energy by the use of suitable arrangements. The arrangement essentially

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SOURCES OF ELECTRICAL ENERGY 1.Steam Power Station (Thermal Station)
These sources of energy are : It is a generating station which converts
1.The Sun heat energy of coal combustion into
2.The Wind electrical energy
3.Water A steam power station basically works on the Rankine cycle.
4. Fuels Steam is produced in the boiler by utilizing the heat of coal
4. Nuclear energy. combustion. The steam is then expanded in the prime mover
(i.e., steam turbine) and is condensed in a condenser to be fed
into the boiler again. The steam turbine drives the alternator
a)The Sun. The Sun is the primary source of energy. The heat energy
which converts mechanical energy of the turbine into electrical
radiated by the Sun can be focussed over a small area by means of
energy. This type of power station is suitable where coal and
reflectors. This heat can be used to raise steam and electrical energy
water are available in abundance and a large amount of
can be produced with the help of turbine-alternator combination.
electric power is to be generated.
However, this method has limited application because it requires a large
area for the generation of even a small amount of electric power
Advantages
it cannot be used in cloudy days or at night
it is an uneconomical method. i)The fuel (i.e., coal) used is quite cheap.
b)The Wind. This method can be used where wind flows for a ii)Less initial cost as compared to other generating stations.
considerable length of time. The wind energy is used to run the wind iii)It can be installed at any place
mill which drives a small generator. In order to obtain the electrical irrespective of the existence of coal. The
energy from a wind mill continuously, the generator is arranged to coal can be trans- ported to the site of
charge the batteries. These batteries supply the energy when the wind the plant by rail or road.
stops. This method has the advantages that maintenance and
generation costs are negligible. However, the drawbacks of this iv)It requires less space as compared to the hydroelectric
method are power station.
i)variable output, v)The cost of generation is lesser than that of the diesel power
ii) unreliable because of uncertainty about wind pressure and station.
iii) power generated is quite small.
Disadvantages
c)Water. When water is stored at a suitable place, it possesses potential i)It pollutes the atmosphere due to the production of large
energy because of the head created. This water energy can be converted amount of smoke and fumes.
into mechanical energy with the help of water turbines. The water ii)It is costlier in running cost as compared to hydroelectric
turbine drives the alternator which converts mechanical energy into plant.
electrical energy. This method of generation of electrical energy has
become very popular because it has low production and maintenance Schematic Arra ngement of Stea m Power Station
costs.
d)Fuels. The main sources of energy are fuels viz., solid fuel as coal,
liquid fuel as oil and gas fuel as natural gas. The heat energy of these
fuels is converted into mechanical energy by suitable prime movers
such as steam engines, steam turbines, internal combustion engines etc.
The prime mover drives the alternator which converts mechanical
energy into electrical energy.
e)Nuclear energy. Towards the end of Second World War, it was
discovered that large amount of heat energy is liberated by the fission
of uranium and other fissionable materials. It is estimated that heat
produced by 1 kg of nuclear fuel is equal to that produced by 4500
tonnes of coal. The heat produced due to nuclear fission can be utilised
to raise steam with suitable arrangements

GENERATING STATIONS
The production of electrical energy is made possible power producing
units, known as Power plants or Electric power generating stations.
Bulk electric power is produced by special plants known as generating
stations or power plants.

Classification of power generation stations

1.Steam power generation station
2.Hydroelectric power generation stations The schematic arrangement of a modern
3.Diesel power station steam power station is shown in Fig. 2.1.
4.Nuclear power station The whole arrangement can be divided
5.Geothermal power station into the following stages for the sake of

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simplicity : condenser. Water is drawn from a natural source of supply
1. Coal and ash handling arrangement such as a river, canal or lake and is circulated through the
2. Steam generating plant condenser. The circulating water takes up the heat of the
3. Steam turbine exhausted steam and itself becomes hot. This hot water
4. Alternator coming out from the condenser is discharged at a suitable
5. Feed water location down the river. In case the availability of water from
6. Cooling arrangement the source of supply is not assured throughout the year,
cooling towers are used. During the scarcity of water in the
1.Coal and ash handling plant. The coal is transported to the power river, hot water from the condenser is passed on to the
station by road or rail and is stored in the coal storage plant. Storage of cooling towers where it is cooled. The cold water from the
coal is primarily a matter of protection against coal strikes, failure of cooling tower is reused in the condenser.
transportation system and general coal shortages. From the coal storage
plant, coal is delivered to the coal handling plant where it is pulverised Choice of Site for Steam Power Stations
(i.e., crushed into small pieces) in order to increase its surface In order to achieve overall economy, the following points
exposure, thus promoting rapid combustion without using large should be considered while selecting a site for a steam power
quantity of excess air. station :
2.Steam generating plant. The steam generating plant consists of a i)Supply of fuel - The steam power station should be located
boiler for the production of steam and other auxiliary equipment for the near the coal mines so that transportation cost of fuel is
utilisation of flue gases. minimum.
i)Boiler. The heat of combustion of coal in the boiler is utilised to ii)Availability of water. -such a plant should be located at the
convert water into steam at high temperature and pressure. The flue bank of a river or near a canal where there is huge amount of
gases from the boiler make their journey through super- heater, water to ensure the continuous supply of water.
economizer, air pre-heater and are finally exhausted to atmosphere iii)Transportation facilities. -adequate transportation
through the chimney. facilities must exist i.e., the plant should be well connected to
ii)Superheater. The steam produced in the boiler is wet and is passed other parts of the country by rail, road. etc.
through a super heater where it is dried and superheated (i.e., steam iv)Cost and type of land. The steam power station should be
temperature increased above that of boiling point of water) by the flue located at a place where land is cheap and further extension, if
gases on their way to chimney. The superheated steam from the super necessary, is possible. Moreover, the bearing capacity of the
heater is fed to steam turbine through the main valve. ground should be adequate so that heavy equipment could be
iii)Economiser. An economizer is essentially a feed water heater and installed.
derives heat from the flue gases for this purpose. The feed water is fed v)Nearness to load centres. In order to reduce the
to the economizer before supplying to the boiler. The economizer transmission cost, the plant should be located near the centre
extracts a part of heat of flue gases to increase the feed water of the load.
temperature.
iii)Air preheater. An air preheater increases the temperature of the air vi)Distance from populated area. the plant should be located
supplied for coal burning by deriving heat from flue gases. Air is drawn at a considerable distance from the populated areas to avoid
from the atmosphere by a forced draught fan and is passed through air the effects of polution
preheater before supplying to the boiler furnace. The air preheater
extracts heat from flue gases and increases the temperature of air used
for coal combustion. The principal benefits of preheating the air are :
increased thermal efficiency and increased steam capacity per square
metre of boiler surface. Equipment of Steam Power Station
3.Steam turbine. The dry and superheated steam from the super heater The most important constituents of a steam power station are :
is fed to the steam turbine through main valve. The heat energy of 1. Steam generating equipment
steam when passing over the blades of turbine is converted into 2. Condenser
mechanical energy. After giving heat energy to the turbine, the steam is 3. Prime mover
exhausted to the condenser which condenses the exhausted steam by 4. Water treatment plant
means of cold water circulation. 5. Electrical equipment.
4.Alternator. The steam turbine is coupled to an
1.Steam generating equipment. This is an important part of
alternator. The alternator converts mechanical
steam power station. It is con- cerned with the generation of
energy of turbine into electrical energy. The
superheated steam and includes such items as boiler, boiler
electrical output from the alternator is delivered to
furnace, superheater, economiser, air pre-heater and other heat
the bus bars through transformer, circuit breakers
reclaiming devices.
and isolators. i)Boiler. A boiler is closed vessel in which water is converted
5.Feed water. The condensate from the condenser is used as feed water into steam by utilising the heat of coal combustion. Steam
to the boiler. Some water may be lost in the cycle which is suitably boilers are broadly classified into the following two types :
made up from external source. The feed water on its way to the boiler is (a) Water tube boilers
heated by water heaters and economiser. This helps in raising the (b) Fire tube boilers
overall effi- ciency of the plant.
In a water tube boiler, water flows through the tubes and the
6.Cooling arrangement. In order to improve the efficiency of the plant,
hot gases of combustion flow over these tubes.
the steam exhausted from the turbine is condensed* by means of a

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 On the other hand, in a fire tube boiler, the hot products of combustion helps in converting heat energy of steam into mechanical
pass through the tubes surrounded by water. Water tube boilers have a energy in the prime mover. Secondly, the condensed steam
number of advantages over fire tube boilers viz., require less space, can be used as feed water to the boiler. There are two types of
smaller size of tubes and drum, high working pressure due to small drum, condensers, namely :
less liable to explosion etc. Therefore, the use of water tube boilers has i)Jet condenser
become universal in large capacity steam power stations.
ii) Surface condenser
In a jet condenser, cooling water and exhausted steam are
ii)Boiler furnace. A boiler furnace is a chamber in which fuel is burnt
mixed together. Therefore, the temperature of cooling water
to liberate the heat energy. In addition, it provides support and
and condensate is the same when leaving the condenser.
enclosure for the combustion equipment i.e., burners. The boiler
Advantages of this type of condenser are : low initial cost, less
furnace walls are made of refractory materials such as fire clay, silica,
floor area required, less cooling water required and low
kaolin etc. There are following three types of construction of furnace
maintenance charges. However, its disadvantages are :
walls :
condensate is wasted and high power is required for pumping
(a) Plain refractory walls water.
(b) Hollow refractory walls with an arrangement for air cooling In a surface condenser, there is no direct contact between
(c) Water walls. cooling water and exhausted steam. It consists of a bank of
horizontal tubes enclosed in a cast iron shell. The cooling
1)Super heater. A superheater is a device which superheats the steam i.e., water flows through the tubes and exhausted steam over the
it raises the tempera- ture of steam above boiling point of water. This surface of the tubes. The steam gives up its heat to water and
increases the overall efficiency of the plant. is itself condensed. Advantages of this type of condenser are :
The steam produced in the boiler is led through the superheater where it condensate can be used as feed water, less pumping power
is superheated by the heat of flue gases. required and creation of better vacuum at the turbine exhaust
Super heaters are mainly classified into two types according to the .However, disadvantage of vantages of this type of condenser
system of heat transfer from flue gases to steam viz. are : high initial cost, requires large floor area and high
maintenance charges.
(a) Radiant superheater
(b) Convection superheater
3.Prime movers. The prime mover converts steam energy into
The radiant super heater is placed in the furnace between the water
mechanical energy. There are two types of steam prime
walls and receives heat from the burning fuel through radiation process.
movers viz., steam engines and steam turbines. A steam
On the other hand, a convection super heater is placed in the boiler tube
turbine has several advantages over a steam engine as a prime
bank and receives heat from flue gases entirely through the convection
mover viz., high efficiency, simple construction, higher
process.
speed, less floor area requirement and low maintenance cost.
Therefore, all modern steam power stations employ steam
i)Economiser. It is a device which heats the feed water on its way to turbines as prime movers.
boiler by deriving heat from the flue gases. This results in raising boiler Steam turbines are generally classified into two types according
efficiency, saving in fuel and reduced stresses in the boiler due to to the action of steam on moving blades viz.
higher temperature of feed water. (i) Impulse turbines
ii)Air Pre-heater. Super heaters and economisers generally cannot fully (ii) Reactions turbines
extract the heat from flue gases. Therefore, pre-heaters are employed In an impulse turbine, the steam expands completely in the
which recover some of the heat in the escaping gases. The function of stationary nozzles (or fixed blades), the pressure over the
an air pre-heater is to extract heat from the flue gases and give it to the moving blades remaining constant. In doing so, the steam
air being supplied to furnace for coal combustion. This raises the attains a high velocity and impinges against the moving
furnace temperature and increases the thermal efficiency of the plant. blades. This results in the impulsive force on the moving
from flue gases to air, air pre-heaters are divided into the following blades which sets the rotor rotating. In a reaction turbine, the
two classes : steam is partially expanded in the stationary nozzles, the
(a) Recuperative type remaining expansion takes place during its flow over the
moving blades. The result is that the momentum of the steam
(b) Regenerative type causes a reaction force on the moving blades which sets the
rotor in motion.
The recuperative type air-heater consists of a group of steel tubes. The
flue gases are passed through the tubes while the air flows externally to 4.Water treatment plant. Boilers require clean and soft water
the tubes.
for longer life and better efficiency. However, the source of
Thus heat of flue gases is transferred to air. The regenerative type air
boiler feed water is generally a river or lake which may
pre-heater consists of slowly moving drum made of corrugated metal
plates. The flue gases flow continuously on one side of the drum and contain suspended and dissolved impurities, dissolved gases
air on the other side. This action permits the transference of heat of flue etc. Therefore, it is very important that water is first purified
gases to the air being supplied to the furnace for coal combustion. and softened by chemical treatment and then delivered to the
boiler.
2:Condensers. A condenser is a device which condenses the steam at the
The water from the source of supply is stored in storage
exhaust of turbine. It serves two important functions. Firstly, it creates
tanks. The suspended impurities are removed through
a very low *pressure at the exhaust of turbine, thus permitting
expansion of the steam in the prime mover to a very low pressure. This sedimentation, coagulation and filtration. Dissolved gases are

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 removed by aeration and degasification. The water is then ‘softened’ by Disadvantages
removing temporary and permanent hardness through different It involves high capital cost due to construction of dam.
chemical processes. The pure and soft water thus available is fed to the There is uncertainty about the availability of huge amount of
boiler for steam generation. water due to dependence on weather conditions.
Skilled and experienced hands are required to build the plant.
5.Electrical equipment. A modern power station contains numerous It requires high cost of transmission lines as the plant is located
electrical equipment. However, the most important items are : in hilly areas which are quite away from the consumers.
i)Alternators. Each alternator is coupled to a steam turbine and Schema tic Arrang ement of Hydr oele ctric Power
converts mechanical energy of the turbine into electrical energy. The Station
alternator may be hydrogen or air cooled. The necessary excitation is
provided by means of main and pilot exciters directly coupled to the
alternator shaft.
ii)Transformers. A generating station has different types of
transformers, viz.,

i. main step-up transformers which step-up the generation

voltage for transmission of power.
ii. station transformers which are used for general service (e.g.,
lighting) in the power station.
iii. auxiliary transformers which supply to individual unit-
auxiliaries.
ii)Switchgear. It houses such equipment which locates the fault on the Although a hydro-electric power station simply involves the
system and isolate the faulty part from the healthy section. It contains conversion of hydraulic energy into electrical energy, yet it
circuit breakers, relays, switches and other control devices embraces many arrangements for proper working and
efficiency. The sche- matic arrangement of a modern hydro-
electric plant is shown in Fig. 2.2.
2.HYDRO-ELECTRIC POWER STATION The dam is constructed across a river or lake and water from
A generating station which utilises the potential energy of water at a the catchment area collects at the back of the dam to form a
high level for the generation of electrical energy. The Hydro-electric reservoir. A pressure tunnel is taken off from the reservoir
power stations are generally located in hilly areas where dams can be and water brought to the valve house at the start of the
built conveniently and large water reservoirs can be obtained. In a penstock. The valve house contains main sluice valves and
hydroelectric power station, water head is created by constructing a automatic isolating valves. The former controls the water flow
dam across a river or lake. From the dam, water is led to a water to the power house and the latter cuts off supply of water
turbine. The water turbine captures the energy in the falling water and when the penstock bursts. From the valve house, water is
changes the hydraulic energy (i.e., product of head and flow of water) taken to water turbine through a huge steel pipe known as
into mechanical energy at the turbine shaft. The turbine drives the penstock. The water turbine converts hydraulic energy into
alternator which converts mechanical energy into electrical energy. mechanical energy. The turbine drives the alternator which
Hydro-electric power stations are becoming very popular because the converts mechanical energy into electrical energy.
reserves of fuels (i.e., coal and oil) are depleting day by day. They have A surge tank (open from top) is built just before the valve
the added importance for flood control, storage of water for irrigation house and protects the penstock from bursting in case the
turbine gates suddenly close* due to electrical load being
and water for drink- ing purposes.
thrown off. When the gates close, there is a sudden stopping of
Advantages water at the lower end of the penstock and consequently the
i. It requires no fuel as water is used for the generation of electrical penstock can burst like a paper log. The surge tank absorbs this
energy. pressure swing by increase in its level of water.
ii. It is quite neat and clean as no smoke or ash is produced.
iii. It requires very small running charges because water is the source
of energy which is avail- able free of cost. Choice of Site for Hydroelectric Power Stations
iv. It is comparatively simple in construction and requires less The following points should be taken into account while
maintenance. selecting the site for a hydro-electric power station :
v. It does not require a long starting time like a steam power station. In i)Availability of water. such plants should be built at a place
fact, such plants can be put into service instantly. (e.g., river, canal) where adequate water is available at a good
vi. It is robust and has a longer life. head.
vii. Such plants serve many purposes. In addition to the generation of Ii)Storage of water-The site selected for a hydro-electric plant
electrical energy, they also help in irrigation and controlling should provide adequate facilities for erecting a dam and
floods. storage of water. in order to ensure the generation of power
viii. Although such plants require the attention of highly skilled persons throughout the year.
at the time of construction, yet for operation, a few experienced iii)Cost and type of land. The land for the construction of the
persons may do the job well. plant should be available at a reasonable price. Further, the
bearing capacity of the ground should be adequate to
withstand the weight of heavy equipment to be installed.
iv)Transportation facilities. The site selected for a hydro-

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electric plant should be accessible by rail and road so that necessary tank (See Fig. 2.3) are provided for the protection of
equipment and machinery could be easily transported. penstocks. Automatic butterfly valve shuts off water flow
through the penstock promptly if it ruptures. Air valve
Constituents of Hydroelectric Plant
maintains the air pressure inside the penstock equal to outside
The constituents of a hydro-electric plant are
atmospheric pressure. When water runs out of a penstock
(1) hydraulic structures
faster than it enters, a vacuum is created which may cause the
(2) water turbines and
penstock to collapse. Under such situations, air valve opens
(3)electrical equipment. We shall discuss these items in turn.
and admits air in the penstock to maintain inside air pressure
1.Hydraulic structures. Hydraulic structures in a hydro-electric power equal to the outside air pressure.
station include : 1.Water turbines.
i)Dam. A dam is a barrier which stores water and creates water head.
Dams are built of concrete or stone masonary, earth or rock fill. The
type and arrangement depends upon the top topography of the site.
ii)Spillways. – used to discharge surplus water from the storage
reservoir into the river on the down-stream side of the dam. There are
times when the river flow exceeds the storage capacity of the reservoir.
Such a situation arises during heavy rainfall in the catchment area.
Spillways are constructed of concrete piers on the top of the dam. Gates
are provided between these piers and surplus water is discharged over
the crest of the dam by opening these gates.
iii)Headworks. The head works consists of the diversion structures at
the head of an intake. They generally include booms and racks for Water turbines are used to convert the
diverting floating debris, sluices for by-passing debris and sediments energy of falling water into mechanical
and valves for controlling the flow of water to the turbine. The flow of energy. The principal types of water
water into and through headworks should be as smooth as possible to turbines are :
avoid head loss and cavitation. For this purpose, it is necessary to avoid
sharp corners and abrupt contractions or enlargements. (i) Impulse turbines

(ii) Reaction turbines

i)Impulse turbines. Such turbines are used for high heads. In

an impulse turbine, the entire pressure of water is converted
into kinetic energy in a nozzle and the velocity of the jet
drives the wheel. The example of this type of turbine is the
Pelton wheel (See Fig. 2.4). It consists of a wheel fitted with
elliptical buckets along its periphery. The force of water jet
strik- ing the buckets on the wheel drives the turbine. The
quantity of water jet falling on the turbine is controlled by
means of a needle or spear (not shown in the figure) placed in
the tip of the nozzle. The movement of the needle is
controlled by the governor. If the load on the turbine
decreases, the governor pushes the needle into the nozzle,
thereby reducing the quantity of water striking the buckets.
iv)Surge tank. - A surge tank is a small reservoir or tank (open at the
Reverse action takes place if the load on the turbine increases.
top) in which water level rises or falls to reduce the pressure swings in
the conduit. ii)Reaction turbines. Reaction turbines are used for low and
A surge tank is located near the beginning of the conduit. medium heads. In a reaction turbine, water enters the runner
When the turbine is running at a steady load, there are no surges in the partly with pressure energy and partly with velocity head. The
flow of water through the conduit i.e., the quantity of water flowing in important types of reaction turbines are :
the conduit is just sufficient to meet the turbine requirements. (a) Francis turbines
Open conduits leading water to the turbine require no* protection. (b) Kaplan turbines
However, when closed conduits are used, protection becomes
necessary to limit the abnormal pressure in the conduit. For this reason, A Francis turbine is used for low to medium heads. It consists
closed conduits are always provided with a surge tank. of an outer ring of stationary guide blades fixed to the turbine
However, when the load on the turbine decreases, the governor closes the casing and an inner ring of rotating blades forming the runner.
gates of turbine, reducing water supply to the turbine. The excess water The guide blades control the flow of water to the turbine.
at the lower end of the conduit rushes back to the surge tank and Water flows radially inwards and changes to a downward
increases its water level. Thus the conduit is prevented from bursting. direction while passing through the runner. As the water
passes over the “rotating blades” of the runner, both pressure
v)Penstocks. Penstocks are open or closed conduits which carry water and velocity of water are reduced. This causes a reaction force
to the turbines. They are generally made of reinforced concrete or steel. which drives the turbine.
Concrete penstocks are suitable for A Kaplan turbine is used for low heads and large quantities
Various devices such as automatic butterfly valve, air valve and surge of water. It is similar to Francis tur- bine except that the

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 runner of Kaplan turbine receives water axially. Water flows radially Fig. 2.6 shows the schematic arrangement of a typical diesel
inwards through regulating gates all around the sides, changing power station. Apart from the diesel- generator set, the
direction in the runner to axial flow. This causes a reaction force which plant has the following auxiliaries :
drives the turbine. i)Fuel supply system. It consists of storage tank, strainers, fuel
Diesel Power Station transfer pump and all day fuel tank. The fuel oil is supplied at
A generating station in which diesel engine is used as the prime mover the plant site by rail or road. This oil is stored in the storage
for the generation of electrical energy tank. From the storage tank, oil is pumped to smaller all day
In a diesel power station, diesel engine is used as the prime mover. The tank at daily or short intervals. From this tank, fuel oil is
diesel burns inside the engine and the products of this combustion act as passed through strainers to remove suspended impurities. The
the “working fluid” to produce mechanical energy. The diesel engine clean oil is injected into the engine by fuel injection pump.
drives the alternator which converts mechanical energy into electrical
energy. As the generation cost is considerable due to high price of diesel, ii)Air intake system. This system supplies necessary air to the
therefore, such power stations are only used to produce small power. engine for fuel combustion. It consists of pipes for the supply
Although steam power stations and hydro-electric plants are invariably of fresh air to the engine manifold. Filters are provided to
used to generate bulk power at cheaper cost, yet diesel power stations remove dust particles from air which may act as abrasive in
are finding favour at places where demand of power is less, sufficient the engine cylinder.
quantity of coal and water is not available and the transportation iii)Exhaust system. This system leads the engine exhaust gas
facilities are inadequate. outside the building and dis- charges it into atmosphere. A
silencer is usually incorporated in the system to reduce the
Advantages noise level.
i. i.The design and layout of the plant are quite simple.
ii. ii.It occupies less space as the number and size of the auxiliaries is iv)Cooling system. The heat released by the burning of fuel in
small. the engine cylinder is partially converted into work. The
remainder part of the heat passes through the cylinder walls,
iii. It can be located at any place. piston, rings etc. and may cause damage to the system. In order
iv. It can be started quickly and can pick up load in a short time. to keep the temperature of the engine parts within the safe
v. There are no standby losses. operating limits, cooling is provided. The cooling system
vi. It requires less quantity of water for cooling. consists of a water source, pump and cooling towers. The pump
vii. The overall cost is much less than that of steam power station of the circulates water through cylinder and head jacket. The water
same capacity. takes away heat form the engine and itself becomes hot
viii. The thermal efficiency of the plant is higher than that of a steam v)Lubricating system. This system minimises the wear of
power station. rubbing surfaces of the engine. It comprises of lubricating oil
ix. It requires less operating staff. tank, pump, filter and oil cooler. The lubricating oil is drawn
from the lubricating oil tank by the pump and is passed through
Disadvantages filters to remove impurities. The clean lubricating oil is
i. The plant has high running charges as the fuel (i.e., diesel) used is delivered to the points which require lubrication. The oil coolers
incorporated in the system keep the temperature of the oil low.
costly.
ii. The plant does not work satisfactorily under overload conditions Vi)Engine starting system. This is an arrangement to rotate
for a longer period. the engine initially, while starting, until firing starts and the
iii. The plant can only generate small power. unit runs with its own power. Small sets are started manually
iv. The cost of lubrication is generally high. by handles but for larger units, compressed air is used for
v. The maintenance charges are generally high. starting. In the latter case, air at high pressure is admitted to a
Schematic Arrangement of Diesel Power Station few of the cylinders, making them to act as reciprocating air
motors to turn over the engine shaft. The fuel is admitted to
the remaining cylinders which makes the engine to start under
its own power.

Nuclear Power Station

A generating station in which nuclear energy is converted into
electrical energy is known as a nuclear power station.
In nuclear power station, heavy elements such as Uranium
(U235) or Thorium (Th232) are subjected to nuclear fission in a
special apparatus known as a reactor. The heat energy thus
released is utilised in raising steam at high temperature and
pressure. The steam runs the steam turbine which converts
steam energy into mechanical energy. The turbine drives the
alternator which converts mechanical energy into electrical
energy.
The most important feature of a nuclear power station is that
huge amount of electrical energy can be produced from a
relatively small amount of nuclear fuel as compared to other
conventional types of power stations. It has been found that

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 complete fission of 1 kg of Uranium (U235) can produce as much energy i. Nuclear reactor
as can be produced by the burning of 4,500 tons of high grade coal. Al- ii. Heat exchanger
though the recovery of principal nuclear fuels (i.e., Uranium and
iii. Steam turbine
Thorium) is difficult and expensive, yet the total energy content of the
estimated world reserves of these fuels are considerably higher than those iv. Alternator
of conventional fuels, viz., coal, oil and gas. At present, energy crisis is i)Nuclear reactor. It is an apparatus in which nuclear fuel
235
gripping us and, therefore, nuclear energy can be successfully employed (U ) is subjected to nuclear fission. It controls the chain
for producing low cost electrical energy on a large scale to meet the reaction* that starts once the fission is done. If the chain
growing commercial and industrial demands. reaction is not controlled, the result will be an explosion due
to the fast increase in the energy released.
Advantages
A nuclear reactor is a cylindrical stout pressure vessel and
i. The amount of fuel required is quite small. Therefore, there is a houses fuel rods of Uranium, moderator and control rods (See
considerable saving in the cost of fuel transportation. Fig. 2.8). The fuel rods constitute the fission material and
ii. A nuclear power plant requires less space as compared to any release huge amount of energy when bombarded with slow
other type of the same size. moving neutrons. The modera- tor consists of graphite rods
iii. It has low running charges as a small amount of fuel is used for which enclose the fuel rods. The moderator slows down the
producing bulk electrical energy. neutrons before they bombard the fuel rods. The control rods
iv. This type of plant is very economical for producing bulk electric are of cadmium and are inserted into the reactor. Cadmium is
power. strong neutron absorber and thus regulates the supply of
v. It can be located near the load centres because it does not require neutrons for fission. When the control rods are pushed in
large quantities of water and need not be near coal mines. deep enough, they absorb most of fission neutrons and
Therefore, the cost of primary distribution is reduced. hence few are available for chain reaction which, therefore,
vi. There are large deposits of nuclear fuels available all over the world. stops. However, as they are being withdrawn, more and
Therefore, such plants can ensure continued supply of electrical more of these fission neutrons cause fis- sion and hence the
energy for thousands of years. intensity of chain reaction (or heat produced) is increased.
vii. It ensures reliability of operation. Therefore, by pulling out the control rods, power of the
nuclear reactor is increased, whereas by pushing them in, it is
Disadvantages
reduced. In actual practice, the lowering or raising of control
i. The fuel used is expensive and is difficult to recover.
rods is accom- plished automatically according to the
ii. The capital cost on a nuclear plant is very high as compared to
other types of plants. requirement of load. The heat produced in the reac- tor is
iii. The erection and commissioning of the plant requires greater removed by the coolant, generally a sodium metal. The
technical know-how. coolant carries the heat to the heat exchanger.
iv. The fission by-products are generally radioactive and may cause a
dangerous amount of radioactive pollution.
v. Maintenance charges are high due to lack of standardization.
Moreover, high salaries of specially trained personnel employed to
handle the plant further raise the cost.
vi. Nuclear power plants are not well suited for varying loads as the
reactor does not respond to the load fluctuations efficiently.
vii. The disposal of the by-products, which are radioactive, is a big
problem. They have either to be disposed off in a deep trench or in
a sea away from seashore.

SCHEMATIC ARRANGEMENT OF NUCLEAR POWER

STATION

i)Heat exchanger. The coolant gives up heat to the heat

exchanger which is utilised in raising the steam. After giving
up heat, the coolant is again fed to the reactor.
ii)Steam turbine. The steam produced in the heat exchanger is
led to the steam turbine through a valve. After doing a useful
work in the turbine, the steam is exhausted to condenser. The
condenser condenses the steam which is fed to the heat
exchanger through feed water pump.
iii)Alternator. The steam turbine drives the alternator which
converts mechanical energy into electrical energy. The output
from the alternator is delivered to the bus-bars through trans-
former, circuit breakers and isolators.
The schematic arrangement of a nuclear power station is shown in Fig.
2.7. The whole arrangement can be divided into the following main
stages:

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Selection of Site for Nuclear Power Station Advantages
The following points should be kept in view while selecting the site for i)It is simple in design as compared to steam power station
a nuclear power station : since no boilers and their auxiliaries are required.
ii)It is much smaller in size as compared to steam power
station of the same capacity. This is expected since gas
i)Availability of water. As sufficient water is required for cooling turbine power plant does not require boiler, feed water
purposes, therefore, the plant site should be located where ample arrangement etc.
quantity of water is available, e.g., across a river or by sea-side. iii)The initial and operating costs are much lower than that of
ii)Disposal of waste. The waste produced by fission in a nuclear power equivalent steam power station.
station is generally radioactive which must be disposed off properly to iv)It requires comparatively less water as no condenser is
avoid health hazards. The waste should either be buried in a deep used.
trench or disposed off in sea quite away from the sea shore. Therefore, v)The maintenance charges are quite small.
the site selected for such a plant should have adequate arrangement for vii)Gas turbines are much simpler in construction and
the disposal of radioactive waste. operation than steam turbines.
viii)It can be started quickly form cold conditions.
iii)Distance from populated areas. The site selected for a nuclear ix)There are no standby losses. However, in a steam power
power station should be quite away from the populated areas as there is station, these losses occur because boiler is kept in operation
a danger of presence of radioactivity in the atmosphere near the plant. even when the steam turbine is supplying no load.
However, as a precautionary measure, a dome is used in the plant Disadvantages
which does not allow the radioactivity to spread by wind or i)There is a problem for starting the unit. It is because before
underground waterways. starting the turbine, the compressor has to be operated for
which power is required from some external source. How-
iv)Transportation facilities. The site selected for a nuclear power station ever, once the unit starts, the external power is not needed as
should have adequate facilities in order to transport the heavy the turbine itself supplies the necessary power to the
equipment during erection and to facilitate the movement of the compressor.
workers employed in the plant. ii)Since a greater part of power developed by the turbine is
From the above mentioned factors it becomes apparent that ideal choice used in driving the compressor, the net output is low.
for a nuclear power station would be near sea or river and away from iii)The overall efficiency of such plants is low (about 20%)
thickly populated areas because the exhaust gases from the turbine contain sufficient
heat.
iv)The temperature of combustion chamber is quite high
(3000oF) so that its life is comparatively reduced.
Schematic Arrangement of Gas Turbine Power Plant
The schematic arrangement of a gas turbine power plant is
shown in Fig. 2.9. The main components of the plant are :
i)Compressor
ii)Regenerator
iii)Combustion chamber
iv)Gas turbine
v)Alternator
vi) Starting motor

a)Compressor. The compressor used in the plant is generally

of rotatory type. The air at atmospheric pressure is drawn by
G as Turbin e Power Plant the compressor via the filter which removes the dust from air.
A generating station which employs gas turbine as the prime mover for The rotatory blades of the compressor push the air between
the generation of electrical energy stationary blades to raise its pressure. Thus air at high
In a gas turbine power plant, air is used as the working fluid. The air is pressure is available at the output of the compressor.
compressed by the compressor and is led to the combustion chamber
where heat is added to air, thus raising its tempera- ture. Heat is added to
the compressed air either by burning fuel in the chamber or by the use b)Regenerator. A regenerator is a device which recovers
of air heaters. The hot and high pressure air from the combustion heat from the exhaust gases of the turbine. The exhaust is
chamber is then passed to the gas turbine where it expands and does the passed through the regenerator before wasting to atmosphere.
mechanical work. The gas turbine drives the alternator which converts A regenerator consists of a nest of tubes contained in a shell.
mechanical energy into electrical energy. The compressed air from the compressor passes through the
It may be mentioned here that compressor, gas turbine and the tubes on its way to the combustion chamber. In this way,
alternator are mounted on the same shaft so that a part of mechanical compressed air is heated by the hot exhaust gases.
power of the turbine can be utilised for the operation of the compressor.
Gas turbine power plants are being used as standby plants for hydro- c)Combustion chamber. The air at high pressure from the
electric stations, as a starting plant for driving auxiliaries in power compressor is led to the combustion chamber via the
plants etc. regenerator. In the combustion chamber, heat* is added to the

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air by burning oil. The oil is injected through the burner into the
chamber at high pressure to ensure a atomization of oil and its thorough
mixing with air. The result is that the chamber attains a very high
temperature (about 3000oF). The combustion gases are suitably cooled
to 1300oF to 1500oF and then delivered to the gas turbine.

d)Gas turbine. The products of combustion consisting of a mixture of

gases at high tempera- ture and pressure are passed to the gas turbine.
These gases in passing over the turbine blades expand and thus do the
mechanical work. The temperature of the exhaust gases from the turbine
is about 900oF.

e)Alternator. The gas turbine is coupled to the alternator. The

alternator converts mechanical energy of the turbine into electrical
energy. The output from the alternator is given to the bus-bars through
transformer, circuit breakers and isolators.
f)Starting motor. Before starting the turbine, compressor has to be
started. For this purpose, an electric motor is mounted on the same shaft
as that of the turbine. The motor is energised by the batteries. Once the
unit starts, a part of mechanical power of the turbine drives the
compressor and there is no need of motor now.

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