Lecture Note 2_2023A Power Systems II (PWRS 201).pdf

Power Systems II
(PWRS 201)
Introduction to Power Generation
BNPWE1
Lecturer: Mrs N Loji
1

Generating Stations
Hydro-electric Power Station
• A hydro-electric power station is a generating station which utilizes the potential energy of water at a high level for
the generation of electrical energy.
• Hydro-electric power stations are generally located in hilly areas where dams can be built conveniently and large
water reservoirs can be obtained. In a hydro-electric power station, water head is created by constructing a dam
across a river or lake. From the dam, water is led to a water turbine.
• The water turbine captures the energy in the falling water and changes the hydraulic energy (i.e., product of head
and flow of water) into mechanical energy at the turbine shaft. The turbine drives the alternator which converts
mechanical energy into electrical energy.
2
Figure 1: Schematic diagram of

Generating Stations
3
Figure 1: Schematic diagram of
Figure 1b: Diagram of a

Generating Stations
Advantages of hydro-electric power stations
(i) It requires no fuel as water is used for the generation of electrical energy.
(ii) It is quite neat and clean as no smoke or ash is produced.
(iii) It requires very small running cost because water its source of energy is available free of
charge.
(iv) It is comparatively simple in construction and requires less maintenance.
(v) It does not require a long starting time like a thermal power station. In can be put into
service instantly.
(vi) It is robust and has a longer lifespan.
(vii) In addition to the generation of electrical energy, they also help in irrigation and
controlling floods. 4

Generating Stations
Disadvantages of hydro-electric power stations
(i) It is a capital intensive project with low rate of return.
(ii) Power generation is dependent on the quantity of water available due to dependence on
weather conditions.
(iii) It requires high cost of transmission lines as the plant is located in hilly areas which are
quite far away from the consumers.
Choice of Site for Hydro-electric Power Stations
The following points should be considered before selecting a hydro-electric power station
site:
(a) Availability of water. The primary requirement of a hydro-electric power station is the
availability of huge quantity of water, such plants should be built at a place where adequate
water is available at a good head.
5

Generating Stations
Disadvantages of hydro-electric power stations
(b) Storage of water. There are wide variations in water supply from a river or canal during
the year. This makes it necessary to store water by constructing a dam in order to ensure the
generation of power throughout the year. The storage helps in equalising the flow of water so
that any excess quantity of water at a certain period of the year can be made available during
times of very low flow in the river. This leads to the conclusion that site selected for a hydro-
electric plant should provide adequate facilities for erecting a dam and storage of water.
(c) Cost and type of land. The cost of the land for the construction of the plant should be
reasonable and it bearing capacity should be adequate to withstand the weight of heavy
equipment to be installed.
(d) Transportation facilities. The site selected for a hydro-electric plant should be
accessible by rail and road so that necessary equipment and machinery could be easily
transported.
It is clear from the above mentioned factors that ideal choice of site for such a plant is near a
river in hilly areas where dam can be conveniently built and large reservoirs can be obtained.
6

Generating Stations
Constituents of Hydro-electric Plant
The constituents of a hydro-electric plant are: (1) hydraulic structures (2) water turbines and
(3) electrical equipment. We shall discuss these items in turn.
1) Hydraulic structures. Hydraulic structures in a hydro-electric power station include dam,
spillways, headworks, surge tank, penstock and accessory works.
2) Water turbines. Water turbines are used to convert the energy of falling water into
mechanical energy. The principal types of water turbines are: (i) Impulse turbines (ii) Reaction
turbines
(i) Impulse turbines. Such turbines are used for high heads.
(ii) Reaction turbines. Reaction turbines are used for low and medium heads. The two
types of reaction turbines are:
(a) Francis turbines (b) Kaplan turbines
3) Electrical equipment. The electrical equipment of a hydro-electric power station includes:
alternators, transformers, circuit breakers and other switching and protective devices. 7

Generating Stations
8
Figure 1c: 1MW Francis Turbine / Hydropower Turbine Generator

Generating Stations
The power generated by a hydro power station in kilowatt can be determine with the formula:
(kW)
Where: P = power, measured in Watts (W). m = mass flow rate in kg/s, g = the gravitational
constant, which is 9.81m/s2, H = the head. η = the product of all of the component efficiencies,
which are normally the turbine, mechanical and generator efficiency
• Power is the rate of producing energy. Power is measured in Watts (W) or kiloWatts (kW).
Energy is what is used to do work and is measured in kilowatt-hours (kWh) or megawatt-
hours (MWh).
How much water is used by generators to produce power in hydroelectric power stations?
The amount of water utilized depends on the power generated and the head of water
available.
• The potential energy, ”E” in joules, of water available is given by
• E= m x g x h. : where, m = mass of water in kg, g = water acceleration in m/s, h is
the head of the water in the dam, in metres square. 9

Generating Stations
Example 1. A hydro-electric generating station is supplied from a reservoir of capacity 5 x 106
cubic metres at a head of 200 metres. Find the total energy available in kWh if the overall
efficiency is 75%.
10

Generating Stations
Example 2. It has been estimated that a minimum run off of approximately 94 m3/sec will be
available at a hydro power station project with a head of 39 m. Determine (i) firm
capacity/total capacity (ii) yearly gross output. Assume the efficiency of the plant to be 80%.
11

Generating Stations
Example 3. Water for a hydro-electric power station is obtained from a reservoir with a head
of 100 metres. Calculate the electrical energy generated per hour per cubic metre of water if
the hydraulic efficiency be 0·86 and electrical efficiency 0·92.
12

Generating Stations
Example 4. Calculate the average power in kW that can be generated in a hydro-
electric power station from the following data:
• Catchment area = 5 × 109 m2 ;
• Mean head, H = 30 m
• Annual rainfall, F = 1·25 m ;
• Yield factor, K = 80%
• Overall efficiency, ηoveall = 70%
If the load factor is 40%, what is the rating of generators installed?
13

Generating Stations
Example 5. A hydro-electric power station has a reservoir of area 2·4 square kilometres and
capacity 5 × 106 m3. The effective head of water is 100 metres. The penstock, turbine and
generation efficiencies are respectively 95%,90% and 85%.
(i) Calculate the total electrical energy that can be generated from the power station.
(ii) If a load of 15,000 kW has been supplied for 3 hours, find the fall in reservoir level.
15

Generating Stations
TUTORIAL PROBLEMS
1. A hydro-electric station has an average available head of 100 metres and reservoir capacity
of 50 million cubic metres. Calculate the total energy in kWh that can be generated,
assuming hydraulic efficiency of 85% and electrical efficiency of 90%. [Ans: 10·423 ×
106 kWh]
2. A hydroelectric plant has a reservoir of area 2 sq. kilometres and of capacity 5 million
cubic meters. The net head of water at the turbine is 50 m. If the efficiencies of turbine and
generator are 85% and 95% respectively, calculate the total energy in kWh that can be
generated from this station. If a load of 15000 kW has been supplied for 4 hours, find the
fall in reservoir. [Ans: 5·5 x 105 kWh ; 27·8 cm]
17

Generating Stations
Diesel Power Station
Diesel power station is a power generating station that uses diesel engine as the prime mover
for the generation of electrical energy.
• In a diesel power station, diesel engine is used as the prime mover. The diesel burns inside
the engine and the products of this combustion act as the “working fluid” to produce
mechanical energy.
• The diesel engine drives the alternator which converts mechanical energy into electrical
energy. This power plant generation cost is considered too high due to the price of diesel,
therefore, such power stations are only used to produce small power.
• Although thermal power stations and hydro-electric plants are invariably used to generate
bulk power at cheaper cost, yet diesel power stations are popularly used at places where
demand of power is less, sufficient quantity of coal and water is not available and the
transportation facilities are inadequate.
• This power plant is also used as standby set for continuity of supply to high priority points
such as hospitals, radio stations, cinema houses and telephone exchanges. 18

Generating Stations
Advantages
(i) The design and layout of the plant are quite simple.
(ii) It occupies less space as the number and size of the auxiliaries is small.
(iii) It can be located at any place.
(iv) It can be started quickly and can pick up load in a short time.
(v) There are no standby losses.
(vi) It requires less quantity of water for cooling.
(vii) The overall cost is much less than that of thermal power station of the same capacity.
(viii) The thermal efficiency of the plant is higher than that of a thermal power station.
(ix) It requires less operating staff/worker. 19

Generating Stations
Disadvantages
(i) The plant has high running charges as the fuel (i.e., diesel) used is costly.
(ii) The plant does not work satisfactorily under overload conditions for a longer period.
(iii) The plant can only generate small power.
(iv) The cost of lubrication is generally high.
(v) The maintenance charges are generally high.
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Generating Stations
21
Figure 2: Schematic diagram
of Diesel Power Plant

Generating Stations
Example 6. A diesel power station has fuel consumption of 0·28 kg per kWh, the calorific
value of fuel being 10,000 kcal/kg. Determine (i) the overall efficiency, and (ii) efficiency of
the engine if alternator efficiency is 95%.
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Generating Stations
Example 7. A diesel power station has the following data:
Fuel consumption/day = 1000 kg
Units generated/day = 4000 kWh
Calorific value of fuel = 10,000 kcal/kg
Alternator efficiency = 96%
Engine mechanical efficiency = 95%
Calculate:
(i) Specific fuel consumption,
(ii) Overall efficiency, and
(iii) Thermal efficiency of engine.
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Generating Stations
Example 8. A diesel engine power plant has one 700 kW and two 500 kW generating units.
The fuel consumption is 0·28 kg per kWh and the calorific value of fuel oil is 10 200 kcal/kg.
Calculate: (i) The fuel oil required for a month of 30 days and (ii) Overall efficiency. Plant
capacity factor = 40%.
25

Generating Stations
26
NB: Convert the units has
been converted to kcal here

Generating Stations
Gas Turbine Power Plant
A gas turbine power plant is a power generating station employs gas turbine as the prime
mover for the generation of electrical energy.
• In a gas turbine power plant, air is used as the working fluid. The air is compressed by a
compressor and is led to the combustion chamber where heat is added to the air, therefore
raising its temperature.
• Heat is added to the compressed air either by burning fuel in the chamber or by the use of air
heaters. The hot and high pressure air from the combustion chamber is then passed to the gas
turbine where it expands and does the mechanical work. The gas turbine thereafter drives the
alternator which converts mechanical energy into electrical energy.
• The compressor, gas turbine and the alternator are mounted on the same shaft so that a part
of mechanical power of the turbine can be utilised for the operation of the compressor.
• Gas turbine power plants are typically used as standby plants for hydro-electric stations, as a
starting plant for driving auxiliaries in power plants.
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Generating Stations
Advantages of Gas Turbine Power Plant
(i) It is simple in design as compared to thermal power station since no boilers and their
auxiliaries are required.
(ii) It is much smaller in size as compared to thermal power station of the same capacity. This
is expected since gas turbine power plant does not require boiler, feed water arrangement.
(iii) The initial and operating costs are much lower than that of equivalent thermal power
station.
(iv) It requires comparatively less water as no condenser is used.
(v) The maintenance charges are quite small.
(vi) Gas turbines are much simpler in construction and operation than thermal turbines.
(vii)There are no standby losses. However, in a thermal power station, these losses occur
because boiler is kept in operation even when the thermal turbine is supplying no load.
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Generating Stations
Disadvantages of Gas Turbine Power Plant
(i) There is a problem for starting the unit. It is because before starting the turbine, the
compressor has to be operated for which power is required from some external source.
However, once the unit starts, the external power is not needed as the turbine itself
supplies the necessary power to the compressor.
(ii) In gas turbine power plant, the net output of the plant is very low. It is because a greater
part of the power generated by the turbine is used in driving the compressor.
(iii) The overall efficiency of this plant is low (about 20%) because the exhaust gases from the
turbine contain sufficient heat.
(iv) The temperature of the combustion chamber is very high (about 1700 °C). Hence, its life
is comparatively reduced.
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Generating Stations
Schematic Design of Gas Turbine Power Plant
• The main components of the plant are: (i) Compressor (ii) Regenerator (iii) Combustion
chamber (iv) Gas turbine (v) Alternator (vi) Starting motor
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of Gas Turbine Power Plant

Generating Stations
(i) Compressor: The compressor used in the plant is generally of rotatory type. The air at
atmospheric pressure is drawn by the compressor via the filter which removes the dust
from the air. The rotatory blades of the compressor push the air between stationary blades
to raise its pressure. Therefore, air at high pressure is available at the output of the
compressor.
(ii) Regenerator: The regenerator is a device which recovers heat from the exhaust gases of
the turbine and pass it through it shell before the gases are released into the atmosphere. It
consists of a nest of tubes contained in a shell. The compressed air from the compressor
passes through the tubes on its way to the combustion chamber. In this way, the
compressed air is heated by the hot exhaust gases.
(iii) Combustion chamber: The air at high pressure from the compressor is led to the
combustion chamber via the regenerator. In the combustion chamber, heat* is added to the
air by burning oil. The oil is injected through the burner into the chamber at high pressure
to ensure atomisation 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 cooledto 1300oF to 1500oF and then delivered to the gas turbine. 31

Generating Stations
(iv) Gas turbine: The products of combustion consisting of a mixture of gases at high
temperature and pressure are passed to the gas turbine. These gases in passing over the turbine
blades expand, hence do the mechanical work. The temperature of the exhaust gases from the
turbine is about 480 oC.
(v) 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.
(vi) Starting motor: The compressor has to be started before starting the turbine. Therefore,
an electric motor is mounted on the same shaft as that of the turbine. When the motor is
energized by the batteries, the unit starts, and a part of mechanical power of the turbine drives
the compressor thereafter there is no need of the motor again.
32

Generating Stations
Nuclear Power Station
• A nuclear power station is a power generating station in which nuclear energy is converted
into electrical energy.
• In nuclear power station, heavy elements such as Uranium (U235) or Thorium (Th232) are
subjected to nuclear fission (the breaking up of nuclei of heavy atoms into two nearly equal
parts with release of huge amount of energy) in a special apparatus known as a reactor.
• The heat energy the fission released is utilized to raise steam at high temperature and
pressure. The steam turns a 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.
33

Generating Stations
Advantages Nuclear Power Station
(i) The amount of fuel required is quite small. Therefore, there is a considerable saving in the
cost of fuel transportation.
(ii) A nuclear power plant requires less space as compared to any other type of the same
capacity.
(iii) It has low running charges as a small amount of fuel is used for producing bulk electrical
energy.
(iv) This type of plant is very economical for producing bulk electric power.
(v) It can be located near the load centres because it does not require large quantities of water.
Therefore, the cost of primary distribution is reduced.
(vi) There are large deposits of nuclear fuels available all over the world. Therefore, such
plants can ensure continued supply of electrical energy for thousands of years.
(vii) It ensures reliability of operation.
34

Generating Stations
Disadvantages Nuclear Power Station
(i) The capital cost on a nuclear plant is very high as compared to other types of plants.
(ii) The construction and commissioning of the plant requires greater technical know-how.
(iii) The maintenance costs are high due to high salaries of specially trained personnel
employed to handle the plant.
(iv) The fission by-products are generally radioactive and may cause a dangerous amount of
radioactive pollution.
(v) 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 sea-shore.
35

Generating Stations
Schematic Design of Nuclear Power Station
• The whole arrangement can be divided into the following main stages: (i) Nuclear reactor
(ii) Heat exchanger (iii) Steam turbine (iv) Alternator.
36
of Nuclear Power Plant

Generating Stations
(i) Nuclear reactor: It is an apparatus in which nuclear fuel (U235) is subjected to nuclear
fission. It controls the chain reaction that starts once the fission is done. If the chain
reaction is not controlled, the result will be an explosion due to the fast increase in the
energy released.
A nuclear reactor is a cylindrical pressure vessel and it contain fuel rods of Uranium, moderator and
control rods (See Fig. 4b). The fuel rods constitute the fission material and release huge amount of
energy when bombarded with slow moving neutrons. The moderator consists of graphite rods which
enclose the fuel rods. The moderator slows down the neutrons before they bombard the fuel rods. The
control rods made of cadmium are inserted into the reactor. Cadmium, a strong neutron absorber,
regulates the supply of neutrons for nuclear fission. When the control rods are pushed in deep enough,
they absorb most of fission neutrons and hence few neutrons are available for the chain reaction, which
therefore stops the fission.
However, as they are being withdrawn, more and more of these fission neutrons cause fission and hence
the intensity of chain reaction (or heat produced) is increased. Therefore, by pulling out the control rods,
power of the nuclear reactor is increased, whereas by pushing them in, it is reduced. In actual practice,
the lowering or raising of the control rods is accomplished automatically according to the load
requirement. The heat produced in the reactor is removed by the coolant, generally a sodium metal. The
coolant carries the heat to the heat exchanger.
37

Generating Stations
38
Figure 4b: Schematic diagram of a Nuclear Reactor

Generating Stations
(i) Nuclear reactor: It is an apparatus in which nuclear fuel (U235) is subjected to nuclear
fission.
(ii) Heat exchanger. The heat exchanger is utilized to raise the steam to high temperature and
pressure. After giving up heat, it again feed the reactor.
(iii) Steam turbine: The steam produced in the heat exchanger is directed 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.
(iv) 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
transformer, circuit breakers and isolators.
39

Generating Stations
Selection of Site for Nuclear Power Station
The following points should be consider while selecting the site for a nuclear power station:
(i) Availability of water. Sufficient water is required for cooling purposes, thus, the plant site
should be located where ample quantity of water is available, e.g., across a river or by sea-
side.
(ii) Disposal of waste. The waste produced by fission in a nuclear power station is generally
radioactive which must be disposed off properly to avoid health hazards. The waste should
either be buried in a deep trench or disposed off in sea quite away from the sea shore.
Therefore, the site selected for such a plant should have adequate arrangement for the disposal
of radioactive waste.
(iii) Distance from populated areas. The site selected for a nuclear power station should be quite
away from the populated areas as there is a danger of presence of radioactivity in the
atmosphere near the plant. However, as a precautionary measure, a dome is used in the plant
which does not allow the radioactivity to spread by wind or underground waterways.
(iv) Transportation facilities. The site selected for a nuclear power station should have adequate
facilities in order to transport the heavy equipment during erection and to facilitate the
movement of the workers employed in the plant. 40

Generating Stations
41
Figure 5: A typical
Nuclear Power Plant

Generating Stations
Tutorial Questions
(i) The major heat loss in a steam power station occurs in ........
(ii) The thermal efficiency of a thermal power station is about ........
(iii) Cooling towers are used where ........
(iv) Economisers are used to heat .........
(v) In a hydro-electric plant, spillways are used ........
(vi) Diesel power plants are used as ........ plants. (base load, standby)
(vii) For high head hydro-electric plants, the turbine used is ........
(viii) Francis and Kaplan turbines are used for ........ heads.
(ix) Surge tank is provided for the protection of ........
(x) Of all the plants, minimum quantity of fuel is required in ........ plant.
44

Generating Stations
Tutorial Questions
1. What is a power generating station?
2. What is a thermal power station? Discuss its advantages and disadvantages.
3. Draw the schematic diagram of a thermal power station and explain its operation.
4. Explain the important components of a thermal power station.
5. What factors are taken into account while selecting the site for a thermal power station?
6. Discuss the advantages and disadvantages of a hydro-electric plant.
7. Draw a neat schematic diagram of a hydro-electric plant and explain the functions of
various components.
8. Explain the essential factors which influence the choice of site for a hydro-electric plant.
9. Explain the functions of the following :
(i) dam (ii) surge tank (iii) reaction turbines (iv) impulse turbine (v) penstock.
45

Generating Stations
Tutorial Questions
10. Discuss the advantages and disadvantages of a diesel power station.
11. Draw the schematic diagram of a nuclear power station and discuss its operation.
12. Explain with a neat sketch the various parts of a nuclear reactor.
13. Discuss the factors for the choice of site for a nuclear power plant.
14. Explain the working of a gas turbine power plant with a schematic diagram.
15. Give the comparison of thermal power plant, hydro-electric power plant, diesel power
plant and nuclear power plant on the basis of operating cost, initial cost, efficiency,
maintenance cost and availability of source of power.
46

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