FOR DAE THIRD-YEAR ELECTRICAL TECHNOLOGY
Developed by:
(ACADEMICS WING)
TEVTA PUNJAB, 96 H, GULBERG,
LAHORE
PREFACE
The world is currently facing a crucial moment in its history, where energy
consumption and its impact on the environment are becoming more and more
pressing issues. The way we generate and consume energy has a significant
impact on our planet, and it's up to us to ensure that we use it efficiently and
responsibly.
This book is an exploration of power plants and energy conservation. It aims
to provide readers with an understanding of the different types of power
plants, their workings, and their impact on the environment. Furthermore, the
book focuses on energy conservation measures that can be implemented in
homes, businesses, and industries to reduce energy consumption and lessen
the burden on the planet.
This book is intended for anyone interested in understanding the basics of
power plants and energy conservation. Whether you are a student, a
researcher, a policy-maker, or an ordinary citizen, this book will provide you
with the knowledge and tools to make informed decisions and take
responsible actions towards a sustainable future.
Compiled by:
Engr. Muhammad Faheem Akram Dharala
(Instructor)
Government College of Technology, Multan
Engr. Amad Ali
(Instructor)
Government College of Technology, Multan
Contents
CHAPTER 1 SOURCES OF POWER ........................................................................ 7
1.1 Introduction to different sources of power ............................................ 7
1.2 Salient features of systems of power sources ........................................ 7
1.2.1 The type and capacity of the power sources ................................... 8
1.2.2 The configuration and interconnection of the power sources ........ 8
1.2.3 The control and management of the power sources ...................... 8
1.2.4 The integration and interaction with the load and the grid ............ 8
1.3 Comparison of different sources, Thermal, Hydel, Nuclear, Solar, Tidal,
Wind Magneto Dynamic and Geothermal. ................................................... 8
1.3.1 Thermal Power ................................................................................. 9
1.3.2 Hydropower (Hydel) ....................................................................... 10
1.3.3 Nuclear Power ................................................................................ 11
1.3.4 Solar Power .................................................................................... 13
1.3.5 Tidal Power..................................................................................... 14
1.3.6 Wind Power .................................................................................... 15
1.3.7 Magneto Hydrodynamic (MHD) Power ......................................... 16
1.3.8 Geothermal Power ......................................................................... 17
1.4 Solar Power System............................................................................... 19
1.4.1 Calculation of load for solar PV system design .............................. 20
1.4.2 Planning for installation of solar panel up to 3 KW ....................... 21
1.4.3 Testing of solar power plant .......................................................... 23
1.5 Wind power system .............................................................................. 24
1.5.1 Parts of wind power plant .............................................................. 27
CHAPTER 2 THERMAL POWER STATION ............................................................ 36
2.1 Introduction to thermal power station ................................................. 36
2.2 Selection of fuels and site ..................................................................... 37
2.2.1 Selection of Fuel ............................................................................. 37
2.2.2 Selection of Site.............................................................................. 39
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2.3 Types of thermal power stations and their working............................. 40
2.3.1 Coal-fired power plants: ................................................................ 40
2.3.2 Oil-fired power plants: ................................................................... 41
2.3.3 Gas-fired power plants:.................................................................. 42
2.3.4 Combined Cycle Thermal Power Plants: ........................................ 43
2.4 Parts of thermal power station and their working with schematic
diagram ....................................................................................................... 44
2.4.1 Coal and ash handling .................................................................... 44
2.4.2 Steam generating plant .................................................................. 45
2.4.3 Steam turbine................................................................................. 46
2.4.4 Alternator ....................................................................................... 46
2.4.5 Feed Water..................................................................................... 46
2.4.6 Cooling arrangement ..................................................................... 46
2.5 Boilers and their types .......................................................................... 47
2.5.1 Working principle of boiler ............................................................ 47
2.5.2 Types of steam boiler ..................................................................... 47
2.6 Steam turbine working principle and construction .............................. 50
2.6.1 Working principle ........................................................................... 50
2.6.2 Construction of steam turbine ....................................................... 50
2.7 Types of steam turbine ......................................................................... 51
2.7.1 Impulse Turbine ............................................................................. 51
2.7.2 Reaction Turbine ............................................................................ 52
2.8 Selection and capacity of steam turbine............................................... 54
2.9 Construction of turbo generators ......................................................... 55
2.9.1 Working Principle ........................................................................... 55
2.9.2 Construction ................................................................................... 55
2.9.3 Ratings ............................................................................................ 56
2.10 Function and application of condenser in a steam turbine power station
..................................................................................................................... 56
2.10.1 Function of Condensers ............................................................... 56
2.10.2 Types of Condensers .................................................................... 56
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2.10.3 Applications of Condensers in Steam Turbine Power Stations: .. 58
2.11 Water circulation system in a thermal power station ........................ 59
2.11.1 Boiler ............................................................................................ 59
2.11.2 Turbine ......................................................................................... 60
2.11.3 Condenser .................................................................................... 60
2.11.4 Feed water pump ......................................................................... 60
2.11.5 Feed water heater ........................................................................ 60
2.11.6 Economizer................................................................................... 61
2.12 Introduction to diesel engine power station ...................................... 61
2.12.1 Major Components of a diesel power station ............................. 62
2.12.2 Site Selection for diesel power plant: .......................................... 64
2.13 Working of a diesel Engine, two strokes, four strokes and their
comparison ................................................................................................. 65
2.13.1 Two Stroke Diesel Engine ............................................................. 65
2.13.2 Four Stroke Diesel Engine ............................................................ 67
2.13.3 Comparison of Two Stroke and Four Stroke Diesel Engines ........ 72
2.14 Cooling system of diesel engine .......................................................... 72
CHAPTER 3 NUCLEAR POWER STATIONS.......................................................... 79
3.1 Introduction to Nuclear power station ................................................. 79
3.2 Main parts of nuclear power station with schematic diagram ............. 81
3.3 Principle of nuclear energy, atomic structure, atomic, number........... 83
3.3.1 Principle of nuclear energy ............................................................ 83
3.3.2 Atomic Structure ............................................................................ 83
3.4 Kinetic energy and isotopes, fuel (Nuclear) .......................................... 85
3.4.1 Kinetic energy................................................................................. 85
3.4.2 Isotopes .......................................................................................... 86
3.4.3 Radio Activity ................................................................................. 87
3.4.4 Half Life .......................................................................................... 87
3.4.5 Binding Energy and Mass Defect ................................................... 88
3.4.6 Nuclear Fuel ................................................................................... 89
3.5 Nuclear fission and fusion ..................................................................... 90
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3.5.1 Nuclear Fusion................................................................................ 90
3.5.2 Nuclear Fission ............................................................................... 92
3.6 Heavy water and its importance ........................................................... 94
3.7 Nuclear reactor ..................................................................................... 95
3.8 Types of a nuclear reactor .................................................................... 96
3.8.1 Boiling Water Reactor: ................................................................... 97
3.8.2 Pressurized Water Reactor ............................................................ 99
3.8.3 Heavy Water Cooled and Moderated type (CANDU) reactors .... 100
3.8.4 Gas Cooled Reactors .................................................................... 101
3.8.5 Liquid Metal Cooled Reactors ...................................................... 103
3.8.6 Homogeneous Reactors ............................................................... 104
3.8.7 Fast Breed Reactors ..................................................................... 105
3.9 Site selection for nuclear power plant ................................................ 105
3.10 Nuclear power stations in Pakistan................................................... 106
CHAPTER 4 HYDEL POWER STATION ............................................................... 114
4.1 Introduction to Hydel Power station .................................................. 114
4.2 Classification of Hydel Power Station ................................................. 115
4.2.1 Classification of hydroelectric power plants w.r.t head .............. 115
4.2.2 Classification of hydroelectric power plants w.r.t availability of
water flow ............................................................................................. 118
4.2.3 Classification of hydroelectric power plants w.r.t loading .......... 119
4.3 Merits & demerits of Hydel Power Station ......................................... 120
4.4 Selection of site for Hydel Power Station ........................................... 121
4.5 General arrangement and operation of Hydel Power Station ............ 122
4.6 Types of Hydel turbines and their characteristic ................................ 125
4.6.1 Impulse Turbines .......................................................................... 126
4.6.2 Reaction Turbines ........................................................................ 128
4.7 Governing of Turbines ......................................................................... 129
4.8 Comparison between turbines ........................................................... 130
4.9 Hydro- electric generation in Pakistan ................................................ 131
CHAPTER 5 GAS TURBINE POWER STATION ................................................... 139
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5.1 Introduction to Gas Power station ...................................................... 139
5.2 Construction & working of simple gas turbine ................................... 141
5.2.1 Construction ................................................................................. 141
5.2.2 Working of simple gas turbine ..................................................... 145
5.2.3 Terms and Definitions .................................................................. 149
5.3 Layout of a gas turbine station ........................................................... 150
5.4 Introduction to combined cycle power station .................................. 151
5.5 Gas turbine and combined cycle plants in Pakistan ........................... 155
5.5.1 Gas Turbine Power Plants ............................................................ 155
5.5.2 Combined Cycle Power Plants ..................................................... 155
5.6 Environmental effects of Gas Turbine Plant and measures to improve the
situation .................................................................................................... 156
5.6.1 Environmental Effects of Gas Turbine Plants............................... 156
5.6.2 Measures to Improve the Situation ............................................. 156
CHAPTER 6 TARIFFS AND ECONOMICS............................................................ 164
6.1 Introduction to economics consideration ........................................... 164
6.1.1 Cost of Generation ....................................................................... 164
6.1.2 Fixed or capital cost ..................................................................... 164
6.1.3 Running or operation cost ........................................................... 166
6.2 Factors influencing cost of generation, load factor, demand factor,
diversity factor .......................................................................................... 168
6.2.1 Some Important Terms ................................................................ 171
6.2.2 Measures to reduce cost of electricity ........................................ 172
6.3 Different load curves ........................................................................... 173
6.4 Depreciation of plant cost and method of charging ........................... 176
6.4.1 Straight line method .................................................................... 176
6.4.2 Sinking fund method .................................................................... 177
6.5 Types of Tariffs .................................................................................... 178
6.5.1 Objectives of tariff........................................................................ 179
6.5.2 Desirable Characteristics of a Tariff ............................................. 179
6.5.3 Types of Tariff .............................................................................. 180
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6.6 Calculations on tariffs ......................................................................... 184
6.7 Fundamentals of load management. .................................................. 190
6.7.1 Techniques of Power Load Management .................................... 192
CHAPTER 7 CONSERVATION OF ENERGY ....................................................... 202
7.1 Introduction & necessity of energy conservation ............................... 202
7.1.1 Necessity of Energy Conservation................................................ 204
7.2 Sources of energy loss and major Items of energy consumption ....... 204
7.3 Ways to limit energy losses................................................................. 206
7.4 Power Factor ....................................................................................... 210
7.4.1 Power Triangle ............................................................................. 212
7.4.2 Causes of Low Power Factor ..................................................... 213
7.4.3 Disadvantages of Low Power Factor ............................................ 214
7.4.4 Power Factor Improvement ......................................................... 215
7.4.5 Power Factor Improvement Equipment ................................... 216
7.4.6 Importance of Power Factor Improvement ............................ 220
7.5 Calculations of power factor improvement in the context of energy
conservation ............................................................................................. 221
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Sources of Power
CHAPTER 1 SOURCES OF POWER
Chapter objectives:





After studying this chapter, a student will be able to
Understand the Introduction of different sources of power.
Understand the difference between conventional, nonconventional, indigenous and non-indigenous sources of
energy.
Understand the ccomparison of different sources, Thermal,
Hydel, Nuclear, Solar, Tidal, Wind Magneto Dynamic and
Geothermal.
Understand Solar Power System types, design and testing.
Wind Power System types, design and testing.
1.1 Introduction to different sources of power
Electric power is the rate of doing work or transferring energy. It is measured
in watts (W) or kilowatts (kW). Electric power sources supply energy to electric
systems by moving the electrons in a circuit and thereby creating an electric
current. This power is mainly divided into two categories being known as AC
power and DC power. The most common sources for the transfer of electrical
power are batteries and grid (mains) electricity. There are many sources of
power that can be used to generate electricity, such as solar, wind, hydro,
nuclear, geothermal, and tidal. These sources have different advantages and
disadvantages in terms of cost, availability, environmental impact and
reliability. In this chapter, we shall introduce the different sources of power
and their salient features.
1.2 Salient features of systems of power sources
The systems of power sources can be classified into two main categories:
renewable and non-renewable. Renewable sources are those that can be
replenished naturally or by human activities, such as solar, wind, hydro,
biomass and geothermal. Non-renewable sources are those that are finite and
cannot be replaced once they are used up, such as coal, oil, gas and nuclear.
These sources are also categorized as indigenous and non-indigenous sources.
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Indigenous sources are sources that are found within the local environment of
a particular region or area and have been traditionally used by the population
of that area to produce electricity. Examples of indigenous fuels include wood,
charcoal, peat, and dung. Non-indigenous sources, on the other hand, are
sources that are not typically found within the local environment of a
particular region or area. These fuels are often imported from other regions
or countries and effect the cost of power system. The salient features of power
sources are:
1.2.1 The type and capacity of the power sources
Different power sources have different characteristics, such as voltage,
current, frequency, power factor, efficiency, reliability, and environmental
impact. The type and capacity of the power sources determine the
performance and cost of the system.
1.2.2 The configuration and interconnection of the power sources
The power sources can be connected in series, parallel, or hybrid modes to
achieve different objectives, such as voltage regulation, load sharing, fault
tolerance, and redundancy. The configuration and interconnection of the
power sources also affect the stability and security of the system.
1.2.3 The control and management of the power sources
The power sources need to be controlled and managed to ensure optimal
operation and coordination. The control and management functions include
monitoring, protection, regulation, synchronization, dispatching, and load
balancing. The control and management can be done locally or remotely, using
wired or wireless communication technologies.
1.2.4 The integration and interaction with the load and the grid
The system of power sources needs to be integrated and interact with the load
and the grid to meet the demand and supply requirements. The integration
and interaction involve aspects such as power quality, harmonics, voltage
sag/swell, frequency deviation, islanding, grid support, and grid services.
1.3 Comparison of different sources, Thermal, Hydel,
Nuclear, Solar, Tidal, Wind Magneto Dynamic and
Geothermal.
Changing one form of energy into a different form is called energy
conservation. Total amount of energy remains same during this process.
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Power generation is an energy conversion process that transforms the
available source of energy into electrical energy.
Figure 1.1. A Simple Energy Conservation Process
The source of energy can be a fossil fuel, such as coal, oil or natural gas, a
renewable resource, such as wind, solar or hydro, or a nuclear fuel, such as
uranium or thorium. The process of power generation involves several steps,
depending on the type of source and the technology used. In this section, we
will compare the different power sources based on their salient features
mentioned above.
1.3.1 Thermal Power
Thermal power plants utilize heat to generate electricity. This heat is usually
derived from the burning of fossil fuels such as coal, oil, or natural gas. These
types of power plants are currently the primary source of electricity
worldwide. However, they also contribute to greenhouse gas emissions and
other environmental concerns. Thus, there is an increasing focus on
alternative and renewable energy sources.
Merits:
a. High Reliability: Thermal power plants are highly reliable and have
a high operational efficiency, ensuring uninterrupted power supply
to the grid.
b. Large Capacity: Thermal power plants can generate a large amount
of electricity and are capable of meeting the power demands of
both industrial and domestic consumers.
c. Flexibility: Thermal power plants are highly flexible and can easily
adapt to changes in power demand.
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d. Cost-Effective: Thermal power plants are relatively cost-effective
to build and operate compared to other power generation
technologies.
e. Low Maintenance Costs: Thermal power plants have low running
and maintenance costs and require minimal downtime for
maintena-nce.
Demerits:
a. Environmental Impact: Thermal power plants are known to emit
large amounts of greenhouse gases, including carbon dioxide,
which contributes to global warming and climate change.
b. Water Consumption: Thermal power plants require large amounts
of water for cooling purposes, which can lead to water shortages in
areas with limited water resources.
c. Land Use: Thermal power plants require a large amount of land,
which can be a challenge in densely populated areas.
d. Health Hazards: Thermal power plants can emit harmful pollutants
such as sulfur dioxide, nitrogen oxides, and particulate matter,
which can have negative health impacts on nearby communities.
e. Fuel Dependence: Thermal power plants rely on fossil fuels such as
coal, oil, and natural gas, which are finite resources and subject to
price volatility in the global market.
1.3.2 Hydropower (Hydel)
Hydropower or hydel power is generated from the energy of flowing water, by
capturing its kinetic energy using turbines. Typically, dam projects are built to
store this water for power generation. This type of power source is widely
available, renewable, and emits comparatively fewer greenhouse gases.
However, the construction of large hydropower projects can have significant
land and aquatic ecosystem impacts.
Merits:
a. Renewable Energy: Hydroelectric power plants produce electricity
using a renewable energy source - water, which means that it is
sustainable, and there are no harmful emissions to the
environment.
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b. Cost-Effective: Hydroelectric power plants have a lower cost of
operation compared to thermal and nuclear power plants, which
can save consumers money on their electricity bills.
c. Large Capacity: Hydroelectric power plants can generate large
amounts of electricity, making them an excellent option for
meeting the power demands of both industrial and domestic
consumers.
d. Long Life Span: Hydroelectric power plants have a long life span,
typically lasting up to 100 years, which makes them a good
investment for long-term energy generation.
e. Flood Control: Hydroelectric power plants can also help to control
floods in river systems by regulating the flow of water.
Demerits:
a. Environmental Impact: The construction of hydroelectric power
plants can have negative impacts on the environment and local
ecosystems, such as altering the natural flow of rivers and streams
and disrupting fish and wildlife habitats.
b. Limited Site Availability: Hydroelectric power plants require
specific topography, such as high rainfall and steep terrain, which
can limit their availability in certain locations.
c. Upfront Cost: The initial cost of building hydroelectric power plants
can be relatively high compared to other power generation
technologies.
d. Dependence on Water Resources: Hydroelectric power plants rely
on a steady and sufficient supply of water, which can be affected
by droughts and changes in climate patterns.
e. Sedimentation: Over time, sediment buildup in the reservoirs of
hydroelectric power plants can reduce their capacity, leading to
decreased efficiency in energy generation.
1.3.3 Nuclear Power
Nuclear power plants generate electricity by harnessing the heat produced by
nuclear fission reactions. These involve splitting heavy atomic nuclei to release
a large amount of energy. Nuclear power is often described as a low-carbon
energy source since it does not generate significant greenhouse gas emissions.
Nevertheless, the handling and disposal of radioactive waste materials pose
safety challenges.
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Merits:
a. High Energy Density: Nuclear power plants have a very high energy
density, meaning that they can generate a large amount of
electricity using a small amount of fuel.
b. Low Greenhouse Gas Emissions: Nuclear power plants emit very
low amounts of greenhouse gases, making them a good option for
reducing carbon emissions and mitigating climate change.
c. Energy Security: Nuclear power plants can provide energy security
by reducing dependence on imported fossil fuels and ensuring a
reliable source of electricity.
d. Low Operating Costs: Nuclear power plants have relatively low
operating costs compared to other forms of energy production,
such as natural gas or coal-fired power plants.
e. Reliable Power: Nuclear power plants are highly reliable and can
operate continuously for long periods, providing a stable source of
electricity.
Demerits:
a. Risk of Nuclear Accidents: Nuclear power plants have the potential
for catastrophic accidents, such as the Chernobyl disaster and the
Fukushima Daiichi nuclear disaster, which can have devastating
environmental and health consequences.
b. Radioactive Waste: Nuclear power plants generate radioactive fuel
waste that is hazardous to human health and the environment,
which must be carefully managed and stored for thousands of
years.
c. High Capital Costs: The construction of nuclear power plants is very
expensive, requiring large upfront capital investments, which can
make it difficult for some countries to finance.
d. Proliferation Risks: The technology used to generate electricity in
nuclear power plants can also be used to produce nuclear
weapons, creating a proliferation risk.
e. Decommissioning Challenges: Nuclear power plants have a finite
operational life, and the decommissioning process can be complex
and expensive, requiring long-term management of radioactive
materials.
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1.3.4 Solar Power
Solar power is derived from sunlight, which can be captured and converted
into electricity in two main ways: directly using photovoltaic (PV) technology
or indirectly through solar thermal systems. These power sources are
renewable and produce minimal environmental impact. However, solar power
generation is subject to the availability of sunlight, and the technology’s
widespread deployment is limited by factors such as high costs and the need
for large land areas.
Merits:
a. Renewable Energy: Solar power is green energy source. meaning
that it is sustainable, and there are no harmful emissions to the
environment.
b. Low Operating Costs: Solar panels have low operating costs, and
solar energy is essentially free, which can save consumers money
on their electricity bills.
c. Scalability: Solar power can be scaled up or down, making it
suitable for both large and small-scale energy generation.
d. Low Maintenance: Solar panels require minimal maintenance, and
their lifespan can range from 20 to 30 years.
e. Energy Security: Solar power can also provide energy security by
reducing dependence on imported fossil fuels and ensuring a
reliable source of electricity.
Demerits:
a. Intermittent Energy Production: Solar power is an intermittent
energy source, meaning that it is affected by weather conditions
and cannot produce electricity 24/7, which can make it difficult to
meet peak energy demands.
b. High Upfront Costs: The initial cost of installing solar panels can be
high, making it challenging for some consumers to invest in solar
energy.
c. Land Use: Solar power requires a large amount of land to generate
significant amounts of electricity, which can be a challenge in
densely populated areas.
d. Limited Efficiency: Solar panels have limited efficiency in
converting sunlight into electricity, which means that they require
large surface areas to generate significant amounts of electricity.
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e. Environmental Impact: The production of solar panels can have
negative environmental impacts, such as the emission of
greenhouse gases during manufacturing and the disposal of panels
after their lifespan.
1.3.5 Tidal Power
Tidal power is generated from the kinetic energy of moving water caused by
the ocean’s tides. It is a predictable and renewable source of electricity. Tidal
power can be generated using tidal stream generators, tidal barrages, or tidal
lagoons. However, the technology is relatively expensive, and potential
environmental impacts need to be carefully assessed.
Merits:
a. Renewable Energy: Tidal power is a renewable and green energy
source, meaning that it is sustainable, and there are no harmful
emissions to the environment.
b. Predictable Energy Production: Tidal power is a predictable source
of energy, as the tides are cyclical and can be accurately predicted,
which allows for efficient energy production planning.
c. High Energy Density: Tidal power has a very high energy density,
which means that it can generate large amounts of electricity from
a relatively small amount of space.
d. Long Lifespan: Tidal power systems can have a lifespan of up to 75
years, making them a reliable source of energy.
e. Low Operating Costs: Once installed, tidal power systems have low
operating costs, which can save consumers money on their
electricity bills.
Demerits:
a. Limited Availability: Tidal power can be generated in areas with
large tidal fluctuations, which limits its availability and potential
use.
b. High Capital Costs: The installation of tidal power systems can be
expensive, requiring significant upfront capital investments, which
can make it challenging for some countries to finance.
c. Environmental Impact: Tidal power systems can have negative
environmental impacts, such as altering the natural flow of water,
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affecting marine ecosystems, and interfering with the migration
patterns of marine animals.
d. Limited Efficiency: Tidal power systems have limited efficiency in
converting the energy of ocean tides into electricity, which means
that large systems are required to generate significant amounts of
electricity.
e. Maintenance and Repair: Tidal power systems require regular
maintenance and repair due to the harsh oceanic environment,
which can increase operating costs and affect system reliability.
1.3.6 Wind Power
Wind power generates electricity by harnessing the kinetic energy in wind
using turbines. It is a clean and renewable source of electricity. Advancements
in wind power technology have led to reduced costs, making it an increasingly
viable alternative to conventional power sources. However, wind power is
dependent upon wind conditions, which can be unpredictable, and the
construction of wind farms can impact local ecosystems.
Merits:
a. Renewable Energy: Wind power is a renewable energy source,
meaning that it is sustainable, and there are no harmful emissions
to the environment.
b. Low Operating Costs: Wind turbines have low operating costs, and
wind energy is essentially free, which can save consumers money
on their electricity bills.
c. Scalability: Wind power can be scaled up or down, making it
suitable for both large and small-scale energy generation.
d. Energy Security: Wind power provide energy security by reducing
dependence on imported fossil fuels and ensuring a reliable source
of electricity.
e. Land Use: Wind turbines require relatively little land compared to
other renewable energy sources such as solar, allowing for their
installation in a range of locations.
Demerits:
a. Intermittent Energy Production: Wind power is intermittent
energy source, meaning that it is affected by weather conditions
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and cannot produce electricity 24/7, which can make it difficult to
meet peak energy demands.
b. Visual and Noise Pollution: Wind turbines can also generate noise
pollution, which can be a concern for people living near them.
c. High Upfront Costs: The initial cost of installing wind turbines can
be high, making it challenging for some consumers to invest in wind
energy.
d. Environmental Impact: The construction of wind turbines can have
negative environmental impacts, such as the disruption of wildlife
habitats and the potential harm to migratory birds and bats.
e. Land Use Conflicts: Wind turbines can sometimes conflict with
other land uses, such as agriculture and wildlife conservation,
which can limit their potential installation in some areas.
1.3.7 Magneto Hydrodynamic (MHD) Power
MHD power generation is a technique that uses the motion of an ionized gas
or liquid metal (the “plasma”) through a magnetic field to produce electricity
it works on Faraday’s law of electromagnetic induction. The principle behind
MHD generation is the conversion of the kinetic energy of the conductive fluid
(or working fluid) into electrical energy. This technology yields high energy
conversion efficiencies and requires minimal fuel usage, making it an
attractive and clean energy source.
A working fluid (such as a plasma) is passed through a duct or channel
surrounded by a magnetic field. The magnetic field interacts with the moving
charges in the working fluid, inducing an electric field perpendicular to both
the magnetic field and the flow direction of the fluid. As the working fluid flows
through the channel, the electric field induces an electric current in the fluid,
which can be harnessed to generate electricity. The generated electricity can
be extracted from the system through electrodes placed in contact with the
fluid. However, technical challenges and costs remain significant barriers to its
wide-scale deployment.
Merits:
a. High Efficiency: MHD systems have the potential for high
conversion efficiency, as they can convert up to 50% of the energy
in a fuel into electricity.
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b. Fuel Flexibility: MHD can operate on a range of fuels, including
fossil fuels and nuclear energy sources, making it a versatile
technology.
c. Low Emissions: MHD systems have low emissions, making them a
cleaner source of energy than conventional power generation
technologies.
d. Longevity: MHD systems have a long lifespan, and the materials
used in their construction are durable and can withstand high
temperatures.
e. Minimal Maintenance: MHD systems require minimal
maintenance, reducing the operating costs of the technology.
Demerits:
a. High Capital Costs: The installation of MHD systems can be
expensive, requiring significant upfront capital investments, which
can make it challenging for some countries to finance.
b. Limited Availability: MHD systems are not yet widely available or
commercialized, making it difficult to access the technology in
some regions.
c. Technological Challenges: The development of MHD technology
requires overcoming significant technological challenges, such as
the need to develop stronger magnets and better conductive fluids.
d. Environmental Impact: While MHD systems have low emissions,
the extraction and production of the fuels they use can have
negative environmental impacts.
e. Scalability: MHD systems are currently limited in their scalability,
making them less suitable for large-scale energy production.
1.3.8 Geothermal Power
Geothermal power is generated from the Earth’s natural heat stored in its
interior. Hot water or steam extracted from underground is used to drive
turbines, thus producing electricity. Geothermal power plants have minimal
environmental impact and provide a consistent electricity supply. However,
geothermal resources are limited to certain geographic locations, and the high
costs of drilling and infrastructure can be prohibitive.
Merits:
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a. Renewable Energy: Geothermal energy is a renewable energy source,
meaning that it is sustainable and there are no harmful emissions to
the environment.
b. Low Operating Costs: Once installed, geothermal power plants have
low operating costs, and geothermal energy is essentially free, which
can save consumers money on their electricity bills.
c. Scalability: Geothermal power can be scaled up or down, making it
suitable for both large and small-scale energy generation.
d. Energy Security: Geothermal energy can provide energy security by
reducing dependence on imported fossil fuels and ensuring a reliable
source of electricity.
e. Environmental Benefits: Geothermal power plants have low
emissions, and the use of geothermal energy can help reduce
greenhouse gas emissions and other air pollutants.
Demerits:
a. Limited Resource Availability: Geothermal energy resources are not
uniformly distributed, and suitable sites for geothermal power plants
are limited.
b. High Upfront Costs: The initial cost of drilling and installing
geothermal power plants can be high, making it challenging for some
consumers to invest in geothermal energy.
c. Environmental Impacts: The construction and operation of
geothermal power plants can have negative environmental impacts,
such as the potential for groundwater contamination, land
subsidence, and seismic activity.
d. Land Use Conflicts: Geothermal power plants can sometimes conflict
with other land uses, such as agriculture and wildlife conservation,
which can limit their potential installation in some areas.
e. Technology Limitations: Some geothermal resources have low
temperatures and may require advanced technologies for efficient
energy production, limiting the potential for their widespread use.
A simple comparison of different power generation sources is given in table 1.
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Table 1. Comparison of Different Power Systems
Source
Renewable Cost
Availability Environmental Reliability
impact
Solar
Yes
High
Variable
Low
Low
Wind
Yes
High
Variable
Low
Low
Hydro
Yes
Low
Seasonal
Moderate
High
Biomass
Yes
Low
Constant
Moderate
High
Geothermal
Yes
High
Constant
Low
High
Tidal
Yes
High
Periodic
Low
Moderate
Coal
No
Low
Constant
High
High
Oil
No
High
Constant
High
High
Gas
No
High
Constant
Moderate
High
Nuclear
No
High
Constant
Low
High
1.4 Solar Power System
A solar power system is a system that uses the energy from the sun to produce
electricity or heat. There are two main types of solar power systems:
photovoltaic (PV) and concentrated solar power (CSP). Photovoltaic systems
convert sunlight directly into electric current using semiconductor materials
that exhibit the photovoltaic effect. Concentrated solar power systems use
mirrors or lenses and tracking devices to focus a large area of sunlight onto a
small spot, where it is converted into heat that drives a turbine or engine. Both
types of systems can be installed on rooftops, ground-mounted, or integrated
into buildings or vehicles. The advantages of solar power systems include their
renewable and clean nature, their potential to reduce greenhouse gas
emissions and dependence on fossil fuels, and their decreasing costs and
increasing efficiency over time. The challenges of solar power systems include
their variability and intermittency depending on the weather and time of day,
their need for storage or backup solutions, and their integration into the
existing grid and energy markets.
PV Solar panels have following different types.
a. Monocrystalline solar panels: Made from a single crystal of silicon,
these panels are highly efficient and can produce more electricity per
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square foot than other types of solar panels. They are also more
expensive than other types of panels.
b. Polycrystalline solar panels: These panels are made from multiple
crystals of silicon and are less expensive than monocrystalline panels.
They are slightly less efficient, but still a good option for residential
and commercial installations.
c. Thin-film solar panels: Made from a thin layer of semiconductor
material, these panels are the least expensive and least efficient type
of solar panel. They are lightweight and flexible, making them a good
option for portable or off-grid applications.
1.4.1 Calculation of load for solar PV system design
Process for the calculation of load for solar PV system design comprises off
following steps.
a. Determining the electrical load: This involves calculating the total
amount of electrical energy required by the appliances, devices, and
equipment that will be connected to the solar PV system. This can be
done by reviewing the product specifications of each device and
adding up their power consumption in Watts (W) or kilowatts (kW).
b. Estimating daily energy consumption: Once the electrical load has
been determined, the next step is to estimate the daily energy
consumption. This is done by multiplying the total power
consumption by the number of hours that each device or appliance is
expected to run each day.
c. Accounting for system efficiency: It's important to consider the
efficiency of the solar PV system when calculating the load. This can
be done by multiplying the estimated daily energy consumption by a
factor of 1.3 to account for system losses and inefficiencies.
d. Adjusting for climate conditions: The amount of solar energy that can
be harvested by a solar PV system will depend on the climate
conditions of the location. The average solar insolation (or solar
irradiance) can be used to estimate the amount of energy that can be
harvested by the solar PV system each day. This information can be
obtained from publicly available solar maps or databases.
e. Sizing the solar PV system: Based on the estimated daily energy
consumption and the amount of solar energy that can be harvested,
the size of the solar PV system can be calculated. This involves
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selecting the appropriate solar panel size, number of panels, and
battery capacity to meet the estimated daily energy demand.
1.4.2 Planning for installation of solar panel up to 3 KW
Main and first step for the solar system planning is calculation of load. Load of
a house is given in Table 2 and we want to design a solar system for this load
with a battery backup of 1 day. So, we shall calculate following three important
things.
a) Rating of Inverter.
b) Battery capacity and connections.
c) Rating of Solar Panels.
After calculating these, we’ll decide how to connect batteries and solar panels.
Table 2. Load and energy profile of a house
Sr.
No
Name of
Appliance
Quantity
Operating
Hours
Power
(W)
Energy
(Wh)
1
Fridge
1
6
250
1500
2
Fan
4
6
300
1800
3
Led TV
1
5
50
250
4
Led Bulb
10
8
300
2400
5
Microwave oven
1
0.25
850
213
1750
6163
Total
a) Rating of inverter
Inverter is always selected by keeping in view the peak load and multiply it
with 1.3 to add the future load growth. Required inverter size for our proposed
load will be
Inverter Capacity = Peak load x 1.3
= 1750 x 1.3
= 2275 Watt
Nearest suitable inverter available in market in 2.5 KW.
b) Battery capacity and connections
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Batteries are selected keeping in view the supported battery voltage of
inverter. Generally, 2.5KW inverters support 24V DC.
Battery Capacity =
Wh required x Backuptime in days
System Efficiency x DOD x V
6163 x 1
0.85 x 0.8 x 24
=378Ah
Where DOD represents the depth of discharge. Generally deep cycle batteries
have 80 to 90% DOD and V represents the voltage of battery bank. So, our
required battery capacity will be 400 Ah and we shall connect two 12V, 200 Ah
batteries in series.
c) Rating of solar panels
There are several things to consider for the optimum selection of solar panels
as like geographic location, solar peak hours, efficiency of solar panels and
energy consumption of devices etc. Average solar peak hours per day in
Pakistan are 8. Let’s calculate the capacity of solar panels.
Solar Panel Capacity =
Wh required
Sun Peak Hours x Efficiency
6163
8 x 0.25
= 3082 W
So, we shall use approximately 6 solar panels of 520 watt for this system. Now,
we shall check the input voltage range of selected inverter. For example, a
2.5kW inverter has input voltage range of 145 V to 280 V while maximum
voltage of 520 watt solar panel are 54 v. So, we shall make two parallel strings
each comprising of three solar panels in series.
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Figure 1.2. Design of solar system
1.4.3 Testing of solar power plant
Testing of a solar power plant is essential to ensure that the system operates
efficiently and effectively, producing the desired amount of electricity. Here
are some steps that are typically involved in testing a solar power plant.
a) Pre-commissioning tests
Before the solar power plant is commissioned, various tests need to be carried
out to ensure that the plant is ready for operation. These tests include
checking the wiring, measuring the voltage and current, and ensuring that all
the components are functioning correctly.
b) Performance testing
Once the solar power plant is operational, it is essential to evaluate its
performance. Performance testing involves measuring the power output of
the solar panels, inverters, and other components to ensure that they are
operating correctly.
c) Environmental testing
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Solar power plants are exposed to various environmental conditions, including
extreme temperatures, humidity, and wind. It is important to test the system's
ability to withstand these conditions and continue to function optimally.
d) Maintenance testing
Regular maintenance of the solar power plant is necessary to ensure that it
continues to operate efficiently. Maintenance testing involves checking the
various components of the system and identifying any issues that need to be
addressed.
e) Monitoring and control
Monitoring and control systems are essential for ensuring that the solar power
plant operates efficiently. These systems enable operators to monitor the
system's performance in real-time, detect any issues, and take appropriate
action to address them.
Overall, the testing of a solar power plant involves a combination of precommissioning tests, performance testing, environmental testing,
maintenance testing, and monitoring and control. By carrying out these tests,
operators can ensure that the system operates efficiently and effectively,
producing the desired amount of electricity.
1.5 Wind power system
A wind power system harnesses the power of wind to generate electricity. It
typically consists of a wind turbine, a tower or pole to support the turbine, a
generator, and a controller or inverter to convert the electrical output of the
turbine to the appropriate voltage and frequency for use in homes or
businesses.
The wind turbine is designed to capture the kinetic energy of the wind and
convert it into mechanical energy by rotating the blades of the turbine. The
mechanical energy is then converted to electrical energy by the generator,
which produces a current that can be used to power appliances, lights, and
other electrical devices.
Wind power systems come in various sizes, from small systems that can
generate a few hundred watts to large systems that can generate several
megawatts of power. They are typically installed in areas with high wind
speeds, such as hilltops, ridges, or coastal regions.
Wind power systems offer several advantages, such as being a clean and
renewable source of energy, reducing reliance on fossil fuels, and reducing
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greenhouse gas emissions. However, they also have some limitations, such as
the change of wind speed and direction, which can affect the efficiency and
reliability of the system.
Overall, wind power systems can be a cost-effective and sustainable option for
generating electricity, especially in areas with high wind resources. Proper
planning, installation, and maintenance are important to ensure the safe and
efficient operation of the system.
a) Horizontal-axis wind turbines (HAWT)
HAWT is the most commonly used type of wind turbine. It consists of a rotor
that has blades attached to a horizontal axis that rotates around a vertical
mast. The rotor faces into the wind, and the blades spin like propellers. The
rotational motion is transferred to a gearbox and a generator that converts
the mechanical energy into electrical energy. HAWTs are suitable for largescale applications, such as wind farms, as they can generate a significant
amount of electricity with high efficiency.
b) Vertical-axis wind turbines (VAWT)
VAWTs have a rotor that spins around a vertical axis. They can be classified
into two types: Savonius and Darrieus turbines. Savonius turbines have a
curved, S-shaped rotor that resembles a cylinder cut in half. The curved blades
catch the wind and rotate the rotor. Darrieus turbines have a straight rotor
that consists of multiple airfoil-shaped blades that rotate around a central
shaft. VAWTs are suitable for small-scale applications and urban areas, where
space is limited.
c) Offshore wind turbines
Offshore wind turbines are installed in bodies of water, such as oceans or seas.
They are designed to withstand harsh weather conditions and strong winds.
Offshore turbines can be either HAWT or VAWT, but HAWT is more commonly
used due to its higher efficiency. Offshore wind turbines can generate more
energy than onshore turbines as the wind speed and consistency is generally
higher over water bodies.
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Figure 1.3. Horizontal Axis Wind Turbines
Figure 1.4. Vertical Axis Wind Turbines
d) Hybrid wind turbines
Hybrid wind turbines combine two or more types of wind turbines to enhance
their efficiency and performance. For instance, a hybrid turbine can have a
HAWT on top of a VAWT, where the HAWT operates in high wind speed
conditions, and the VAWT operates in low wind speed conditions. Hybrid
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turbines can also have a solar panel or a battery system integrated with the
turbine to provide a more stable power output.
In conclusion, wind turbines come in various types and designs, each with its
own advantages and limitations. The choice of wind turbine depends on
factors such as wind speed, application, available space, and environmental
conditions.
1.5.1 Parts of wind power plant
A wind power plant consists of several components that work together to
generate electricity from wind. In this response, we will discuss the major
components of a wind power plant in detail:
a. Wind Turbines
The wind turbines are the most critical components of a wind power plant.
They convert the kinetic energy of wind into mechanical energy that is used to
rotate the turbine blades. Wind turbines can be categorized into two main
types, Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines
(VAWT). HAWTs are more commonly used in wind power plants, as they are
more efficient and generate higher electricity outputs. The number of wind
turbines in a wind power plant can vary, depending on the capacity of the plant
and the available wind resources.
b. Tower
The tower is the structure that supports the wind turbines. It is usually made
of steel and can vary in height depending on the wind resources and the size
of the wind turbines. The tower height can range from 30 meters to 150
meters, and the diameter can range from 3 to 6 meters. The tower must be
strong enough to withstand the weight of the turbine and the rotational forces
created by the wind.
c. Foundation
The foundation is the base on which the tower is erected. It must be strong
enough to support the weight of the tower and the wind turbine. The
foundation can vary in size and shape depending on the soil conditions and the
tower height. The foundation can be a shallow or deep foundation, and it can
be made of concrete or steel.
d. Rotor Blades
The rotor blades are the components that capture the kinetic energy of the
wind and convert it into mechanical energy. The blades can vary in size and
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shape depending on the turbine capacity and the wind resources. The rotor
blades can be made of various materials, such as fiberglass, carbon fiber, or
wood. They are designed to be aerodynamically efficient and must withstand
the stresses created by the wind.
e. Gearbox
The gearbox is a component that transfers the rotational energy from the rotor
to the generator. It increases the rotational speed of the rotor to match the
speed required by the generator. The gearbox is usually located inside the
nacelle, which is the compartment at the top of the tower that houses the
gearbox, generator, and other components.
f. Generator
The generator is the component that converts the mechanical energy into
electrical energy. The generator is usually located inside the nacelle and can
be either a synchronous or asynchronous generator. The generator output
voltage is usually in the range of 690V to 33kV, depending on the capacity of
the wind turbine and the grid requirements.
g. Power Electronics
The power electronics are the components that control the electrical output
of the generator. They are responsible for regulating the voltage and
frequency of the output to match the grid requirements. The power
electronics can include components such as inverters, transformers, and
switchgear.
h. Control System
The control system is responsible for monitoring and controlling the operation
of the wind turbine. It includes sensors that measure the wind speed,
direction, and temperature. The control system can adjust the pitch angle of
the rotor blades to optimize the performance of the turbine based on the wind
conditions. It also includes safety systems that can shut down the turbine in
case of emergency or high wind speeds.
i. Substation
The substation is the component that connects the wind power plant to the
grid. It includes transformers that step up the voltage of the generator output
to match the grid voltage. The substation also includes switchgear that
protects the plant from overloads and faults. The substation can be located
on-site or off-site, depending on the distance to the grid connection point.
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Figure 1.5. Wind Power Plant
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Sample Multiple Choice Questions
1. Which of the following is not a renewable source of energy
(a) Solar
(b) Wind
(c) Coal
(d) Hydro
2. What is the main disadvantage of thermal power plants
(a) They are not widely available
(b) They emit significant greenhouse gases
(c) They require large land areas
(d) They have high installation costs
3. How is nuclear power generated
(a) By harnessing the energy of water
(b) By capturing sunlight
(c) By burning fossil fuels
(d) By nuclear fission reactions
4. What is the main advantage of tidal power
(a) It is a predictable
(b) It does not require large land areas
(c) It produces no environmental impact
d) It is not affected by weather conditions
5. What is a solar power system
(a) System that uses energy from wind
(b) System that uses energy from the sun
(c) System that uses energy from water
(d) System that uses energy from coal
6. What are the two main types of solar power systems
(a) Wind power and hydro power
(b) Photovoltaic and concentrated solar power
(c) Geothermal power and biomass power
(d) Nuclear power and fossil fuel power
7. What is the advantage of solar power systems
(a) They are cheap and widely available
(b) They are easy to install
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(c) They are renewable and clean
(d) They are not affected by weather conditions
8. What is the disadvantage of solar power systems
(a) They are expensive
(b) Energy production is not sufficient
(c) They are variable and intermittent
(d) They are harmful to the environment
9. What are the types of PV solar panels
(a) Monocrystalline and polycrystalline
(b) Monocrystalline and thick-film
(c) Polycromide and intracrystalline
(d) Monocrystalline and amorphous
10. Which type of solar panel is the most efficient and expensive
(a) Monocrystalline solar panels
(b) Polycrystalline solar panels
(c) Thin-film solar panels
(d) Concentrated solar power panels
11. Which type of wind turbine is most commonly used in large-scale
applications
(a) Horizontal-axis wind turbines (HAWT)
(b) Vertical-axis wind turbines (VAWT)
(c) Offshore wind turbines
(d) Hybrid wind turbine
12. What component of a wind power plant captures the kinetic energy of
the wind and converts it into mechanical energy
(a) Tower
(b) Generator
(c) Rotor blades
(d) Gearbox
13. Which type of wind turbine is suitable for small-scale applications and
urban areas with limited space
(a) Horizontal-axis wind turbines (HAWT)
(b) Vertical-axis wind turbines (VAWT)
(c) Offshore wind turbines
(d) Hybrid wind turbines
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14. What component of a wind power plant is responsible for stepping up
the voltage of the generator output to match the grid voltage
(a) Generator
(b) Control system
(c) Power electronics
(d) Substation
15. Which component of a solar power system focuses sunlight onto a small
spot to produce heat
(a) Photovoltaic panels
(b) Mirrors or lenses in a CSP
(c) Semiconductor materials
(d) Solar tracking devices
16. What is the depth of discharge (DOD) of a typical deep cycle battery
(a) 50-60%
(b) 70-80%
(c) 80-90%
(d) 100%
17. What is the purpose of including an inverter in a solar power system
(a) To convert sunlight into electric current
(b) To focus sunlight onto a small spot
(c) To convert direct current into alternating current
(d) To store excess solar energy in batteries
18. What design feature allows thin-film solar panels to be suitable for
portable or off-grid applications
(a) High efficiency
(b) Low cost
(c) Lightweight and flexible
(d) High power output per square foot
19. In wind power systems, what component is housed in the nacelle
(a) Rotor blades
(b) Tower
(c) Foundation
(d) Generator
20. What is MHD
(a) Magnetohydrodynamic
(b) Magnetomotive Force
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(b) Modern Hydrogen Dynamics
(d) Mega Hydro Dam
21. All available fuels are source of
(a) Coal
(b) Thermal Energy
(c) Nuclear Energy
(d) Chemical Energy
22. MHD works on principle of
(a) Fleming
(b) Faraday
(c) Edison
(d) Tesla
23. To convert water energy into electric energy, _____ is used with
generator
(a) Steam Turbine
(b) Wind Turbine
(c) Water Turbine
(d) Heat Exchanger
24. ________ power plants are installed far from load centers.
(a) Hydro Electric
(b) Thermal
(c) Wind
(d) Diesel
25. ________ is less for a nuclear power plant.
(a) Age
(b) Initial cost
(c) Security
(d) Per unit cost
Answer to MCQ’s
1.
c
2.
b
3.
d
4.
a
5.
b
6.
b
7.
c
8.
c
9.
a
10.
a
11.
a
12.
c
13.
b
14.
d
15.
b
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16.
c
17.
c
18.
c
19.
d
20.
a
21.
b
22.
b
23.
c
24.
a
25.
d
Sample Short Questions
1. What is electrical power?
2. Name some sources of power that can be used to generate electricity?
3. What are the salient features of systems of power sources?
4. Define hydroelectric energy?
5. Define nuclear power generation?
6. Define thermal power generation?
7. Define geothermal generation?
8. What are indigenous sources of energy?
9. What are non-indigenous sources of energy?
10. What is the difference between renewable and non-renewable
energy?
11. What are the two main types of solar power systems?
12. How do photovoltaic systems convert sunlight into electricity?
13. What are concentrated solar power systems known for?
14. What advantages do solar power systems offer?
15. What challenges do solar power systems face?
16. Name the three types of PV solar panels.
17. What is the main difference between photovoltaic and concentrated
solar power systems?
18. What factors are considered in the calculation of load for a solar PV
system design?
19. What are the testing methods of solar power plant?
20. What are the main components of a wind power system?
21. What are the two main types of wind turbines?
22. What advantages do wind power systems offer compared to
conventional power sources?
23. What is the main limitation of wind power systems?
24. What is the difference between horizontal-axis wind turbines and
vertical-axis wind turbines?
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25. Where are offshore wind turbines typically installed?
26. What are hybrid wind turbines, and why are they used?
Sample Long Questions
1.
2.
3.
4.
5.
Compare different sources of electrical power?
Write a detailed note on solar power generation?
What are the planning considerations for a solar power plant?
Describe different types of wind turbines in detail?
Write a note on construction of wind turbine?
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CHAPTER # 02
Thermal Power Station
CHAPTER 2 THERMAL POWER STATION
Chapter objectives:
After studying this chapter, a student will be able to
 Understand the Introduction to thermal power station.
 Understand the types of thermal power stations and their
working.
 Understand the working of different parts of thermal power
station and their working with schematic diagram.
 Understand the types of boilers.
 Understand the types, selection criteria and working of steam
turbines.
 Understand the cconstruction of turbo generators.
 Understand the function and application of condenser in a
steam turbine power station.
 Understand the water circulation system in a thermal power
station.
 Understand the introduction of diesel engine power station.
 Understand the working and construction of a diesel eengine,
two strokes, four strokes and their comparison.
2.1 Introduction to thermal power station
A thermal power station, also known as a coal-fired power station, is a type of
power plant that generates electricity by burning coal to produce steam. The
steam is then used to drive a steam turbine, which in turn drives a generator
that produces electricity. Thermal power stations are one of the most common
types of power plants in the world, and they provide a significant portion of
the electricity used globally.
The process of generating electricity in a thermal power station begins with
the coal being delivered to the station and stored in coal bunkers. From there,
the coal is transported to a coal pulverizer, which grinds the coal into a fine
powder. The pulverized coal is then blown into the boiler, where it is burned
at high temperatures to produce heat. This heat is used to boil water in the
boiler, creating steam that is used to drive the steam turbine.
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The steam turbine is connected to a generator, which converts the mechanical
energy from the turbine into electrical energy. The electricity generated by the
generator is then transmitted through power lines to homes, businesses, and
other users of electricity.
Thermal power stations require large amounts of water for the steam
generation process. The water is typically sourced from a nearby river, lake, or
ocean and is treated to remove impurities before being used in the power
plant. The process of cooling the steam after it has passed through the turbine
also requires large amounts of water, which is typically returned to the source
in a cooled state.
One of the major environmental concerns associated with thermal power
stations is the emission of greenhouse gases, primarily carbon dioxide, which
contributes to global warming. Other pollutants, such as sulfur dioxide and
nitrogen oxide, can also be emitted by the burning of coal and can contribute
to acid rain and other environmental problems.
In recent years, there has been a shift towards cleaner forms of energy, such
as wind and solar power, as well as the development of technologies such as
carbon capture and storage, which aim to capture and store carbon dioxide
emissions from thermal power stations. Despite these developments, thermal
power stations continue to play a significant role in meeting the world's energy
needs, particularly in developing countries where access to electricity is
limited.
2.2 Selection of fuels and site
2.2.1 Selection of Fuel
The primary fuel used in thermal power stations is coal, which is burned to
produce heat that is used to generate steam. However, other types of fuels
can also be used, depending on the availability and cost of the fuel, as well as
environmental considerations. Some of the fuels that can be used in thermal
power stations include:
a. Coal
Coal is a fossil fuel that is formed from the remains of plants that lived millions
of years ago. It is a black or brownish-black sedimentary rock that is primarily
composed of carbon, along with small amounts of other elements such as
sulfur, nitrogen, and oxygen. Coal is one of the most widely used fuels for
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power generation, accounting for about 38% of global electricity generation in
2020.
Peat is considered very low grade coal which contains very high carbon
content and not suitable to be used in power plants. There are four main types
of coal that are commonly used in power generation, classified according to
their degree of metamorphism, or the amount of heat and pressure they have
been subjected to over time. These types are:
Anthracite: Anthracite is the highest grade of coal, with a high carbon content
and low moisture content. It is very hard and has a high heat output, making
it an excellent fuel for power generation. Anthracite is relatively rare and
expensive compared to other types of coal.
Bituminous: Bituminous coal is the most common type of coal used in power
generation, with a moderate carbon content and higher moisture content than
anthracite. It is softer and more brittle than anthracite and is divided into subbituminous and bituminous coal depending on its carbon content. Bituminous
coal is used in power plants that require a balance between heat output and
cost.
Subbituminous: Subbituminous coal has a lower carbon content and higher
moisture content than bituminous coal. It is often brownish or black in color
and has a dull, matte finish. Subbituminous coal is used in power plants that
have lower efficiency requirements, such as in developing countries.
Lignite: Lignite is the lowest grade of coal, with a low carbon content and high
moisture content. It is often brown in color and has a woody texture. Lignite is
typically used in power plants that have very low efficiency requirements, or
as a backup fuel source.
b. Natural Gas
Natural gas is a clean-burning fuel that produces fewer emissions than coal. It
is often used in combined-cycle power plants, where the exhaust heat from a
gas turbine is used to generate steam for a steam turbine.
c. Oil
Oil can also be used as a fuel in thermal power stations, although it is less
common than coal or natural gas. Oil-fired power plants are typically used as
backup power sources or for peak demand periods.
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d. Biomass
Biomass is a renewable fuel source that is derived from organic matter, such
as wood chips, agricultural waste, or municipal solid waste. Biomass can be
burned in a boiler to produce steam, which is then used to generate electricity.
The choice of fuel used in a thermal power station depends on a number of
factors, including cost, availability, and environmental impact. Coal remains
the most common fuel used in thermal power stations, although there is
increasing interest in using cleaner fuels such as natural gas and biomass.
2.2.2 Selection of Site
Selecting the right site for a thermal power plant is a critical process that
involves careful consideration of a variety of factors. Here are some of the key
factors that are typically considered when selecting a site for a thermal power
plant:
a. Availability of fuel
The primary fuel for a thermal power plant is coal, so the site should be located
near coal mines or have easy access to a reliable supply of coal.
b. Water availability
Thermal power plants require large quantities of water for cooling purposes,
so the site should be located near a reliable water source, such as a river or
lake.
c. Land availability
The site should have sufficient land to accommodate the power plant and any
associated infrastructure, such as transmission lines and substations.
d. Environmental factors
The site should be evaluated for any potential environmental impacts, such as
air pollution, water pollution, and impacts on wildlife and habitats.
e. Transportation infrastructure
The site should have good transportation infrastructure, such as highways,
railroads, and ports, to facilitate the transport of fuel and equipment to the
site and the transport of electricity from the power plant to customers.
f. Local community
The site should be located in an area that is compatible with the local
community and does not have significant negative impacts on the health,
safety, or quality of life of nearby residents.
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g. Economic factors
The site should be economically viable and have a low cost of production,
including factors such as labor costs, taxes, and regulatory costs.
Overall, selecting the right site for a thermal power plant is a complex process
that requires careful evaluation of a wide range of factors. A comprehensive
site selection study is typically conducted to evaluate potential sites and
identify the most suitable location for the power plant.
2.3 Types of thermal power stations and their working
2.3.1 Coal-fired power plants:
Figure 2.6. Coal Fired Thermal Power Plant
Coal-fired power plants work by burning coal to produce heat, which is then
used to generate steam. The steam turns a turbine connected to a generator,
which produces electricity. To start the process, coal is first pulverized into a
fine powder and then blown into the boiler, where it is burned to produce
heat. The heat generated by the burning coal is used to convert water into
steam, which is then directed to the turbine. The turbine spins the generator,
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which produces electricity. The steam is then condensed back into water and
returned to the boiler to be heated again, completing the cycle. The electricity
produced by the generator is sent to a transformer, which increases the
voltage so it can be transmitted over long distances via power lines. Coal-fired
power plants require a constant supply of coal, which is transported to the
plant by rail or truck. They also require a source of cooling water, which is
typically drawn from nearby lakes, rivers, or oceans. The cooling water is
circulated through the power plant to absorb heat, and then released back
into the environment. Coal-fired power plants generate large amounts of
carbon dioxide and other pollutants, which contribute to climate change and
air pollution. A typical coal fired power plant is given in figure 2.1.
2.3.2 Oil-fired power plants:
Figure 2.7. Oil fired thermal power plant
Oil-fired power plants work by burning oil to produce heat, which is then used
to generate steam. The steam turns a turbine connected to a generator, which
produces electricity. To start the process, oil is first stored in tanks and then
pumped into the boiler, where it is burned to produce heat. The heat
generated by the burning oil is used to convert water into steam, which is then
directed to the turbine. The turbine spins the generator, which produces
electricity. The steam is then condensed back into water and returned to the
boiler to be heated again, completing the cycle. The electricity produced by
the generator is sent to a transformer, which increases the voltage so it can
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be transmitted over long distances via power lines. Oil-fired power plants
require a constant supply of oil, which is transported to the plant by tanker
trucks or ships. They also require a source of cooling water, which is typically
drawn from nearby lakes, rivers, or oceans. The cooling water is circulated
through the power plant to absorb heat, and then released back into the
environment. Oil-fired power plants generate fewer pollutants than coal-fired
power plants but are still a significant source of greenhouse gases and other
air pollutants. A typical oil fired power plant is given in figure 2.2.
2.3.3 Gas-fired power plants:
Figure 2.8. Gas fired thermal power plant
Gas-fired power plants work by burning natural gas to produce heat, which is
then used to generate electricity. To start the process, natural gas is first
extracted from underground wells and transported to the power plant via
pipeline. At the power plant, the natural gas is burned in a boiler to produce
heat. The heat generated by the burning natural gas is used to convert water
into steam, which is then directed to a turbine. The turbine spins a generator,
which produces electricity. The steam is then condensed back into water and
returned to the boiler to be heated again, completing the cycle. The electricity
produced by the generator is sent to a transformer, which increases the
voltage so it can be transmitted over long distances via power lines. Gas-fired
power plants require a constant supply of natural gas, which is transported to
the plant via pipeline. They also require a source of cooling water, which is
typically drawn from nearby lakes, rivers, or oceans. The cooling water is
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circulated through the power plant to absorb heat, and then released back
into the environment. Gas-fired power plants generate fewer pollutants than
coal-fired power plants and oil-fired power plants, making them a cleaner
source of electricity. A typical gas fired power plant is given in figure 2.3.
2.3.4 Combined Cycle Thermal Power Plants:
Figure 2.9. Combined cycle thermal power plant
Combined cycle power plants work by using both gas turbines and steam
turbines to generate electricity. The process begins by burning natural gas in a
gas turbine, which produces hot exhaust gases. The hot exhaust gases are then
directed to a heat recovery steam generator, where they heat water to
produce steam. The steam is then directed to a steam turbine, which
generates additional electricity. The steam is then condensed back into water
and returned to the heat recovery steam generator to be heated again. The
electricity produced by the gas turbine and steam turbine is sent to a
transformer, which increases the voltage so it can be transmitted over long
distances via power lines. Combined cycle power plants require a constant
supply of natural gas, which is transported to the plant via pipeline. They also
require a source of cooling water, which is typically drawn from nearby lakes,
rivers, or oceans. The cooling water is circulated through the power plant to
absorb heat, and then released back into the environment. Combined cycle
power plants are highly efficient, as they capture waste heat from the gas
turbine to produce additional electricity. They generate fewer pollutants than
other types of power plants, making them a cleaner source of electricity. A
typical combined cycle power plant is given in figure 2.4.
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2.4 Parts of thermal power station and their working with
schematic diagram
Steam power station simply involves the conversion of heat of coal combustion
into electrical energy, yet it embraces many arrangements for proper working
and efficiency. The schematic arrangement of a modern steam power station
is shown in figure 2.5.The whole arrangement can be divided into the following
parts for the sake of simplicity:
1. Coal and ash handling
2. Steam generating plant
3. Steam turbine
4. Alternator
5. Feed water
6. Cooling arrangement
2.4.1 Coal and ash handling
The coal is transported to the power station by road or rail and is stored in the
coal storage plant. Storage of coal is primarily a matter of protection against
coal strikes, failure of transportation system and general coal shortages. From
the coal storage plant, coal is delivered to the coal handling plant where it is
pulverized (crushed into small pieces) in order to increase its surface exposure,
thus promoting rapid combustion without using large quantity of excess air.
The pulverized coal is fed to the boiler by belt conveyors. The coal is burnt in
the boiler and the ash produced after the complete combustion of coal is
removed to the ash handling plant and then delivered to the ash storage plant
for disposal. The removal of the ash from the boiler furnace is necessary for
proper burning of coal.
It is worthwhile to give a passing reference to the amount of coal burnt and
ash produced in a modern thermal power station. A 100 MW station operating
at 50% load factor may burn about 20,000 tons of coal per month and ash
produced may be to the tune of 10% to of coal fired i.e., 2,000 to 3,000 tons.
In fact, in a thermal station, about 50% to 60% of the total operating cost
consists of fuel purchasing and its handling.
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Figure 2.5. Schematic arrangement of thermal power plant
2.4.2 Steam generating plant
The steam generating plant consists of a boiler for the production of steam
and other auxiliary equipment for the utilization of flue gases.
a) Boiler: The heat of combustion of coal in the boiler is utilized to convert
water into steam at high temperature and pressure. The flue gases from the
boiler make their journey through super heater, economizer, and air preheater and are finally exhausted to atmosphere through the chimney.
b) Super heater: The steam produced in the boiler is wet and is passed through
a super heater where it is dried and superheated (steam temperature
increased above that of boiling point of water) by the flue gases on their way
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to chimney. Superheating provides two principal benefits. Firstly, the overall
efficiency is increased. Secondly, too much condensation in the last stages of
turbine (which would cause blade corrosion) is avoided. The superheated
steam from the super heater is fed to steam turbine through the main valve.
c) Economizer: An economizer is essentially a feed water heater and derives
heat from the flue gases for this purpose. The feed water is fed to the
economizer before supplying to the boiler. The economizer extracts a part of
heat of flue gases to increase the feed water temperature.
d) Air preheater: An air preheater increases the temperature of the air
supplied for coal burning by deriving heat from flue gases. Air is drawn from
the atmosphere by a forced draught fan and is passed through air 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 meter of boiler surface.
2.4.3 Steam turbine
The dry and superheated steam from the super heater is fed to the steam
turbine through main valve. The heat energy of steam when passing over the
blades of turbine is converted into mechanical energy. After giving heat energy
to the turbine, the steam is exhausted to the condenser which condenses the
exhausted steam by means of cold water circulation.
2.4.4 Alternator
The steam turbine is coupled to an alternator. The alternator converts
mechanical energy of turbine into electrical energy. The electrical output from
the alternator is delivered to the bus bars through transformer, circuit
breakers and isolators.
2.4.5 Feed Water
The condensate from the condenser is used as feed water to the boiler. Some
water may be lost in the cycle which is suitably made up from external source.
The feed water on its way to the boiler is heated by water heaters and
economizer. This helps in raising the overall efficiency of the plant.
2.4.6 Cooling arrangement
In order to improve the efficiency of the plant, the steam exhausted from the
turbine is condensed* by means of a condenser. Water is drawn from a natural
source of supply such as a river, canal or lake and is circulated through the
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condenser. The circulating water takes up the heat of the exhausted steam
and itself becomes hot. This hot water coming out from the condenser is
discharged at a suitable location down the river. In case the availability of
water from the source of supply is not assured throughout the year, cooling
towers are used. During the scarcity of water in the river, hot water from the
condenser is passed on to the cooling towers where it is cooled. The cold water
from the cooling tower is reused in the condenser.
2.5 Boilers and their types
A boiler is a closed vessel that heats a fluid (typically water). The fluid does not
always boil. The heated or vaporized fluid exits the boiler and is used in a
variety of processes or heating applications, including cooking, water or
central heating, and boiler-based power generation. Boilers and most
specifically steam boilers are an important component of thermal power
plants.
2.5.1 Working principle of boiler
The boiler operates on the principle that water is heated in a closed vessel and
then converted into steam as a result of the heating. This steam has a lot of
kinetic energy at high pressures. Water is fed to the boiler and then heated to
its boiling point by using heat from the furnace. This water is converted into
high-pressure steam as a result of heating. The generated steam is routed
through the steam turbines. When high-pressure steam strikes the turbine, it
causes it to rotate. A generator is connected to the turbine, and the generator
begins to rotate along with the turbine, producing electricity.
2.5.2 Types of steam boiler
Boilers are classified into several types based on several factors such as
pressure and temperature, fuel type, form of heating, heating method and
size/capacity etc. However, the most common fuel type is petrol, oil, or
electricity to operate. Both gas and oil boilers work in the same way. Mainly
tere are two types of boiler that are most important and these are
a) Water tube boiler
b) Fire tube boiler
a) Water tube boiler
A water tube Boiler is a type of pressure vessel used to create steam under
pressure by passing hot water through it. It works by heating water above its
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normal boiling point which turns into vapor and then exits the boiler at higher
pressure than when it was entered.
Figure 2.6. Water tube boiler
The main components of a water tube Boiler consist of tubes filled with water,
a furnace where fuel is burned to heat up the water, and a drum connected to
the top of the furnace containing air and other gases. Advantages of this type
of boiler over fire-tube boilers include greater efficiency, easier access to
parts, better control of flue gas temperature and composition, and improved
safety features such as automatic blow down valves. However, they can be
more expensive initially and require more frequent inspection and
maintenance. La-Mont boiler, Benson boiler, Yarrow boiler and Wilcox boiler
are some examples of water tube boilers.
Advantages
a. The tubes of these boilers are exposed outside the shell, any
part inside the tubes can easily accessed without having to remove
the entire unit from service. This makes repairs faster and cheaper.
b. Automatic blow down valve systems help prevent explosions
due to excessive build ups in pressure.
c. The temperature of the exhaust gasses can be controlled
precisely.
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d. Improved design for high pressure applications
Disadvantages
a. Water tubes are more prone to corrosion and scale formation
than fire tubes.
b. The large number of small diameter tubes in a water-tube
boiler makes it difficult to maintain proper circulation if one or
two tubes become blocked by debris or ash. 3. Due to the high
pressure inside the boiler, any leakage of steam could cause
serious safety hazards such as explosions or fires.
c. These boilers have low efficiency as compared to fire tube
boilers.
b) Fire tube boiler
Fire tube Boilers are one of the most common types of boilers available. Fire
tube boilers consist of a series of small diameter tubes called fires into which
fuel is burned to create high temperature gas flowing inside the tubes. In order
to maximize energy output from the system, these tubes must be kept as long
and straight as possible.
Figure 2.7. Fire tube boiler
To achieve this, these tubes may be supported by stay rods or a stay arm
arrangement. As the gas flows through the tubes, it transfers its heat to the
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surrounding water, thus creating saturated steam. Fire tube boilers are
typically designed to work under both low and high pressure conditions.
Additionally, these boilers often feature automatic controls and safety devices
to ensure proper operation and prevent any potential hazards. Overall, fire
tube boilers offer many advantages including efficient use of space, easy
maintenance, and versatility across various industries. Lancashire boiler,
Cochran boiler, Velcon boiler and locomotive boiler are some examples of fire
tube boilers.
Advantages
a. These are relatively low in cost.
b. Their operation is easy.
c. These can handle high pressures and temperatures.
d. These boilers have flexibility in design.
e. Efficiency of these boilers are high.
Disadvantages
a. These boilers have problem of water contamination due to ash
deposits from combustion products.
b. These have limited steam output compared to water tube
boilers.
c. Cleaning and maintenance of these boilers is difficult.
2.6 Steam turbine working principle and construction
A steam turbine is a machine that converts thermal energy from pressurized
steam into mechanical energy, which can be used to generate electricity or
drive machinery. The steam turbine is an essential component of a power
plant that uses steam as a working fluid to generate electricity.
2.6.1 Working principle
The working principle of a steam turbine is based on the conversion of thermal
energy into mechanical energy through the use of high-pressure steam.
2.6.2 Construction of steam turbine
The construction of a steam turbine can vary depending on its type and size.
However, the basic components of a steam turbine include a rotor, stator, and
nozzles. The rotor is the rotating part of the steam turbine that converts the
energy of the steam into mechanical energy. It is typically made of highstrength materials such as steel and is designed to withstand the stresses and
strains associated with high-speed rotation.
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The stator is the stationary part of the steam turbine that contains a series of
stationary blades. These blades guide the steam onto the rotor blades and are
designed to optimize the energy transfer from the steam to the rotor. The
stator also contains a series of fixed guide vanes that direct the steam flow
into the rotor blades.
The nozzles are the components that convert the high-pressure, hightemperature steam into a high-velocity jet. The steam is directed through the
nozzles and onto the rotor blades, where it imparts energy to the rotor and
causes it to rotate.
2.7 Types of steam turbine
There are two basic types of steam turbines: impulse turbines and reaction
turbines.
2.7.1 Impulse Turbine
An impulse steam turbine is a type of steam turbine that uses the impulse
force of high-velocity steam jets to generate mechanical energy. The impulse
steam turbine consists of two main components: the stationary nozzles and
the moving rotor blades.
The stationary nozzles are designed to direct the high-pressure steam onto the
rotor blades in the form of a high-velocity jet. The nozzles are arranged in a
row or series and are stationary during the operation of the turbine. The
nozzles are carefully designed to ensure that the steam jet exits the nozzle at
a high velocity and with a precise angle of deflection so that it can impinge on
the rotor blades at the correct angle and with the correct amount of force.
The moving rotor blades are mounted on a shaft, which rotates as a result of
the force generated by the steam jet. The blades are aerodynamic and curved
so that they can efficiently deflect the steam jet and convert its kinetic energy
into rotational energy. The rotor blades are typically arranged in a series of
disks, with each disk having several rows of blades.
During operation, steam is generated in a boiler and is sent to the turbine
through a series of pipes. The steam enters the turbine and is directed onto a
set of stationary nozzles. The nozzles create a high-velocity steam jet that
impinges on the rotor blades. The force of the steam jet causes the rotor to
rotate, generating mechanical energy. The steam then exits the turbine and is
condensed back into water.
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Impulse steam turbines are typically used in applications that require low to
medium power outputs, such as in small-scale power plants or in industrial
settings. They are generally more compact and efficient than other types of
steam turbines, making them ideal for use in applications where space is
limited. However, they are limited in their power output and are not suitable
for large-scale power generation.
Figure 2.8. Impulse steam turbine
2.7.2 Reaction Turbine
A reaction steam turbine is a type of steam turbine that operates on the
principle of the reaction force of high-pressure steam. It consists of a series of
stationary blades and moving blades that are mounted on a rotor.
The stationary blades, also called nozzles, are arranged in a circular pattern
around the rotor. They are designed to direct the high-pressure steam onto
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the moving blades at a specific angle and with a specific velocity. The nozzles
are designed to have a convergent shape, which accelerates the steam as it
passes through them and converts its pressure energy into kinetic energy.
Figure 2.9. Reaction steam turbine
The moving blades, also known as buckets, are mounted on the rotor and are
designed to rotate as the steam flows through them. The buckets are curved
to take advantage of the reaction force of the steam as it flows over them. The
steam flows over the curved surfaces of the buckets, which deflects the steam
in the opposite direction and generates a reaction force that causes the rotor
to rotate. The curved shape of the buckets also helps to maintain a constant
flow of steam through the turbine.
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As the rotor rotates, it generates mechanical energy that can be used to drive
a generator or other machinery. The steam that has passed through the
moving blades is then exhausted out of the turbine and either condensed back
into water or passed through a condenser to reuse the steam.
Reaction steam turbines are generally used in applications that require high
power outputs, such as in large-scale power plants. They are more efficient
than impulse turbines and can handle a wider range of steam pressures and
temperatures. However, they are also more complex and expensive to
manufacture and maintain.
2.8 Selection and capacity of steam turbine
The selection and capacity of a steam turbine depend on several factors,
including the application, the available steam pressure and flow rate, and the
desired power output.
The first step in selecting a steam turbine is to determine the power output
required for the application. This can be calculated based on the electrical load
or mechanical load that the turbine will be driving. Once the power output is
determined, the steam conditions, such as pressure and temperature, need to
be identified to match the output requirement.
The steam turbine capacity is determined based on the steam flow rate and
pressure. The steam flow rate is usually expressed in terms of mass flow rate
(kg/hr) or volume flow rate (m3/hr). The pressure and temperature of the
steam also affect the capacity of the turbine, with higher pressure and
temperature steam resulting in higher turbine capacity.
Another important factor in the selection of a steam turbine is the type of
turbine needed for the application. There are two basic types of steam
turbines: impulse turbines and reaction turbines. Impulse turbines are suitable
for applications with high steam pressures and low to medium flow rates,
while reaction turbines are better suited for applications with low steam
pressures and high flow rates.
In addition to these factors, other considerations that need to be taken into
account when selecting a steam turbine include the availability of space, the
availability of cooling water, and the level of maintenance required. It is also
important to consider the manufacturer and their reputation for producing
reliable and efficient steam turbines.
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Overall, selecting the right steam turbine requires careful consideration of
several factors, including the application, steam conditions, type of turbine
needed, and other operational considerations. By taking these factors into
account, it is possible to select a steam turbine that meets the power output
and operational requirements of the application while providing reliable and
efficient performance.
2.9 Construction of turbo generators
Turbo alternators are a type of electrical generator that is driven by a steam
turbine. These generators are commonly used in power plants to convert the
mechanical energy generated by the steam turbine into electrical energy.
2.9.1 Working Principle
The working principle of a turbo alternator is based on the conversion of
mechanical energy into electrical energy. When steam is generated in a boiler,
it is sent to the steam turbine, which rotates the rotor of the turbo alternator.
As the rotor rotates, the windings generate a magnetic field that induces an
electrical current in the stator coils. This electrical current is then transmitted
to the power grid, where it can be used to power homes, businesses, and other
electrical devices.
2.9.2 Construction
A turbo alternator consists of several components, including a rotor, a stator,
and an exciter. The rotor is mounted on the shaft of the steam turbine and
rotates at high speeds, typically between 3000 and 3600 revolutions per
minute (RPM). The stator, which is stationary, consists of a series of wire coils
that are wound around an iron core. The exciter is a small generator that is
used to provide the initial electrical current to the rotor.
The rotor of a turbo alternator is typically constructed from a series of
laminated steel discs that are stacked on top of each other. The discs are
mounted on the shaft of the steam turbine and are separated by air gaps to
reduce friction and prevent electrical short circuits. The rotor is also equipped
with a series of copper windings that are embedded in the laminated steel
discs. These windings are connected to the slip rings, which allow the electrical
current generated by the rotor to be transmitted to the stator.
The stator of a turbo alternator is constructed from a series of wire coils that
are wound around an iron core. The coils are arranged in a circular pattern and
are connected to the power grid through the bus bars. When the rotor rotates,
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the magnetic field generated by the windings induces an electrical current in
the stator coils, which is then transmitted to the power grid.
2.9.3 Ratings
The ratings of a turbo alternator are typically expressed in terms of its capacity
and efficiency. The capacity of a turbo alternator is determined by its power
output, which is typically measured in megawatts (MW). The efficiency of a
turbo alternator is determined by its ability to convert the mechanical energy
generated by the steam turbine into electrical energy, and is typically
expressed as a percentage.
In conclusion, turbo alternators play a crucial role in the production of
electrical energy in power plants. Their construction, ratings, and working
principle make them an essential component of the power generation
process. The efficient and reliable operation of turbo alternators is critical to
ensuring a steady supply of electrical power to meet the needs of modern
society.
2.10 Function and application of condenser in a steam
turbine power station
A condenser is a crucial component of a steam turbine power station that
helps to increase the efficiency of the power generation process. It is designed
to remove the waste heat from the steam that has passed through the turbine
and convert it back into water, which can be reused in the boiler. Cooling
water for condenser comes from spray ponds or cooling towers present in
thermal power stations. In this article, we will explore the different types of
condensers, their functions, and their applications in steam turbine power
stations.
2.10.1 Function of Condensers
The main function of a condenser is to remove the waste heat from the steam
that has passed through the turbine and convert it back into water. This is
important because steam turbines operate most efficiently when they are
exposed to a constant flow of cool water. By removing the waste heat from
the steam, condensers help to maintain a constant temperature within the
turbine, which maximizes its efficiency and prolongs its lifespan.
2.10.2 Types of Condensers
There are two main types of condensers used in steam turbine power stations:
surface condensers and jet condensers.
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a) Surface condensers
Surface condensers are the most common type of condenser used in steam
turbine power stations. They work by passing the steam through a set of tubes
that are immersed in a large tank of cool water. As the steam passes through
the tubes, it gives up its heat to the water, which then flows out of the tank
and into a cooling tower. The cooled water is then pumped back into the
condenser to repeat the process.
Figure 2.10. Surface condenser
b) Jet condensers
Jet condensers, on the other hand, work by directing a stream of cool water
directly into the steam. The water jet breaks up the steam and causes it to
condense back into water, which is collected in a receiver tank. Jet condensers
are generally used in small-scale power stations, as they are less efficient than
surface condensers. A typical jet condenser is given in figure 2.11.
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2.10.3 Applications of Condensers in Steam Turbine Power
Stations:
Condensers are a critical component of steam turbine power stations, as they
help to increase the efficiency of the power generation process. By removing
the waste heat from the steam, they help to maintain a constant temperature
within the turbine, which maximizes its efficiency and prolongs its lifespan.
Additionally, condensers can help to reduce the amount of water used in the
power generation process by recycling the steam back into the boiler.
Figure 2.11. Jet condenser
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2.11 Water circulation system in a thermal power station
A water circulation system is an essential component in the generation of
electricity in a thermal power station. This system circulates water throughout
the power station to provide the necessary cooling and heating needed for the
generation of steam, which drives the turbines to generate electricity. This
article will provide a comprehensive overview of the water circulation system,
including the components and their functions.
The water circulation system in a thermal power station consists of boiler,
turbine, condenser, feed water pump, feed water heater, economizer and air
preheater. These components work together to transfer water through the
power station, converting it into steam and then condensing it back into water
for reuse. Water circulation system of a thermal power plant is given in figure
2.12.
Figure 2.12. Water circulation system
2.11.1 Boiler
The first component of the water circulation system is the boiler. The boiler
heats water to produce steam. The heated water is fed into the boiler, where
it is pressurized and heated to a high temperature to produce steam. The
boiler contains a series of tubes that allow the hot gases produced by the
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combustion of coal, oil, or gas to pass through and heat the water in the tubes.
The function of the reheater is to improve the overall thermal efficiency of the
power plant by increasing the temperature of the steam before it enters the
low-pressure turbine, which in turn increases the power output of the turbine.
2.11.2 Turbine
The second component of the water circulation system is the turbine. The
steam produced in the boiler is directed to the turbine, where it drives the
generator to produce electricity. The turbine consists of a rotor and a series of
blades. The steam flows over the blades, causing the rotor to rotate, which
generates electricity. Generally, there are two types of steam turbines named
as low pressure steam turbine and high pressure steam turbine. Steam enters
from high pressure to low pressure steam turbine by passing through
reheater.
2.11.3 Condenser
The third component of the water circulation system is the condenser. The
steam that has passed through the turbine is directed to the condenser, where
it is condensed back into water. The condenser is a large, heat-exchange
device that uses cold water to cool the steam, causing it to condense back into
water. The cooled water is then sent back to the feed water pump.
2.11.4 Feed water pump
The forth component of the water circulation system is the feed water pump.
The feed water pump pumps the condensed water back to the boiler, where
it is reheated and used again in the generation of steam. The pump provides a
continuous flow of water to the boiler to ensure that it is continuously
supplied with water.
2.11.5 Feed water heater
Before entering into economizer, feed water is passed through feed water
heater. There are two types of feed water heater, open heaters and closed
heaters. The feed water heater works by using the heat from the steam leaving
the turbine to heat the water that is supplied to the boiler. The steam is passed
through a series of tubes in the feed water heater, while the water is passed
through a separate set of tubes in the same heat exchanger. The heat from
the steam is then transferred to the water, which is heated to a temperature
that is just below the boiling point. This preheated water is then supplied to
the boiler, where it is further heated to produce steam.
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2.11.6 Economizer
After feed water heater, water is passed through economizer. An economizer
is a component in a steam power plant that is designed to recover the heat
from the flue gases that exit the boiler. The economizer is essentially a heat
exchanger that transfers heat from the flue gases to the water that is supplied
to the boiler. By recovering the heat from the flue gases, the economizer
reduces the amount of fuel required to produce steam, thereby improving the
overall thermal efficiency of the power plant.
Economizers are an important component in a steam power plant, as they help
to improve the overall efficiency of the plant by reducing the amount of fuel
required to produce steam. They are typically located between the boiler and
the air preheater, and can be used in conjunction with other components such
as feed water heaters and air preheaters to further improve the thermal
efficiency of the power plant.
2.12 Introduction to diesel engine power station
Figure 2.13. Block diagram of a diesel power plant
A diesel engine power station is a type of power plant that uses diesel engines
to convert fuel into electrical energy. These power stations are generally used
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as a source of backup power or for generating electricity in remote locations
where other types of power plants are not feasible. Block diagram of a diesel
power plant is given in figure 2.13.
2.12.1 Major Components of a diesel power station
a. Diesel engine
This is the heart of the power plant, where the combustion of diesel fuel takes
place. The diesel engine consists of a cylinder, piston, connecting rod,
crankshaft, fuel injection system, air intake system, exhaust system, cooling
system, lubrication system and governor. The diesel engine operates on the
principle of compression ignition, where air is compressed in the cylinder and
then injected with diesel fuel at high pressure. The fuel-air mixture ignites
spontaneously and expands, pushing the piston down and rotating the
crankshaft.
b. Alternator
This is the device that converts the mechanical energy of the diesel engine into
electrical energy. The alternator consists of a rotor, stator, slip rings, brushes
and exciter. The rotor is attached to the crankshaft of the diesel engine and
rotates along with it. The stator is a stationary part that surrounds the rotor
and contains coils of wire. When the rotor spins, it induces an alternating
current (AC) in the stator coils. The slip rings and brushes transfer the AC
output to the external circuit. The exciter is a small generator that provides
direct current (DC) to the rotor coils to create a magnetic field.
c. Control panel
This is the device that monitors and controls the operation of the power plant.
The control panel consists of various instruments, switches, meters, relays and
circuit breakers. The control panel displays the parameters such as voltage,
current, frequency, power factor, speed, temperature and pressure of the
power plant. It also regulates the load distribution, synchronization,
protection and safety of the power plant.
d. Fuel supply system
This is the system that stores and supplies diesel fuel to the diesel engine. The
fuel supply system consists of a fuel tank, fuel pump, fuel filter, fuel injector
and fuel pipes. The fuel tank stores enough diesel fuel for continuous
operation of the power plant. The fuel pump delivers the fuel from the tank to
the engine at a constant pressure. The fuel filter removes any impurities or
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water from the fuel before it reaches the injector. The fuel injector sprays a
fine mist of fuel into the cylinder at high pressure and precise timing.
e. Air intake system:
This is the system that supplies fresh air to the diesel engine for combustion.
The air intake system consists of an air filter, turbocharger, intercooler and
intake manifold. The air filter removes any dust or dirt from the air before it
enters the engine. The turbocharger is a device that uses exhaust gases to spin
a turbine and compress more air into the engine. This increases the power
output and efficiency of the engine. The intercooler is a device that cools down
the compressed air before it enters the intake manifold. This reduces the
temperature and increases the density of the air.
f. Exhaust system
This is the system that removes the exhaust gases from the diesel engine after
combustion. The exhaust system consists of an exhaust manifold, silencer,
muffler and chimney. The exhaust manifold collects the exhaust gases from
each cylinder and directs them to the silencer. The silencer reduces the noise
level of the exhaust gases by absorbing some of their sound waves. The
muffler further reduces the noise level by reflecting some of their sound waves
back into the exhaust pipe. The chimney discharges the exhaust gases into the
atmosphere at a high elevation.
g. Cooling system
This is the system that maintains the optimum temperature of the diesel
engine by removing excess heat from it. The cooling system consists of a water
pump, a radiator, a fan, a thermostat and cooling pipes. The water pump
circulates water through the engine block, where it absorbs heat from the
cylinders. The radiator transfers heat from the water to the surrounding air by
means of fins. The fan blows air over the radiator to enhance heat transfer.
The thermostat regulates the flow of water according to the temperature of
the engine.
h. Lubrication system
This is the system that reduces friction and wear between moving parts of the
diesel engine by supplying oil to them. The lubrication system consists of an
oil pump, an oil filter, an oil cooler, an oil pressure gauge and oil pipes. The oil
pump delivers oil from the oil sump to the engine at a constant pressure. The
oil filter removes any impurities or metal particles from the oil before it
reaches the engine. The oil cooler lowers the temperature of oil.
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i. Governor
The governor of a diesel engine generator is a device that regulates the speed
and fuel supply of the engine according to the load and frequency
requirements. The governor ensures that the generator operates at a constant
speed and delivers stable power output. There are different types of
governors, such as mechanical, electronic, and electronic control units (ECU),
each with its own advantages and disadvantages. The function of the governor
is essential for the efficient and reliable operation of a diesel power plant.
2.12.2 Site Selection for diesel power plant:
The site selection of a diesel power plant is an important decision that affects
the performance, cost and environmental impact of the plant. There are
several factors that need to be considered for the site selection, such as:
a. Availability of fuel
The site should have easy access to the fuel supply, preferably by rail or road,
to minimize the transportation cost and ensure uninterrupted operation. The
fuel storage capacity should also be adequate to meet the peak demand and
emergency situations. The relative weightage of this factor is high, as it directly
affects the operational cost and reliability of the plant.
b. Load center
The site should be close to the load center, or the area where the electricity is
consumed, to reduce the transmission losses and voltage drop. The load
center should also have a stable and predictable demand pattern, to avoid
frequent load fluctuations and overloading of the plant. The relative
weightage of this factor is medium, as it affects the efficiency and stability of
the plant.
c. Land availability:
The site should have enough land area to accommodate the plant layout,
auxiliary buildings, fuel storage, cooling system, waste disposal and other
facilities. The land should also have suitable topography, soil condition and
drainage system to support the plant construction and operation. The relative
weightage of this factor is low, as it affects the initial cost and environmental
impact of the plant.
d. Water availability:
The site should have sufficient water supply for cooling, lubrication and other
purposes. The water source should be reliable, clean and free from
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contamination. The water consumption and discharge should also comply
with the environmental regulations and standards. The relative weightage of
this factor is low, as it affects the cooling efficiency and environmental impact
of the plant.
e. Environmental factors:
The site should have minimal impact on the surrounding environment, such as
noise, air pollution, water pollution and visual intrusion. The site should also
comply with the local zoning laws, land use regulations and environmental
policies. The relative weightage of this factor is low, as it affects the social
acceptance and legal compliance of the plant.
2.13 Working of a diesel Engine, two strokes, four strokes
and their comparison
Diesel engines operate by compressing air and fuel within the engine cylinder
to a high pressure and temperature, causing combustion to occur. This
combustion generates heat and pressure, which in turn drives a piston to
move within the cylinder, converting the chemical energy of the fuel into
mechanical energy.
2.13.1 Two Stroke Diesel Engine
A two stroke diesel engine is a type of internal combustion engine that uses
compression ignition to burn diesel fuel in a two-stroke cycle. Unlike a fourstroke engine, a two-stroke engine has only two piston movements: one up
and one down. This means that every revolution of the crankshaft produces a
power stroke, making the engine more efficient and powerful than a fourstroke engine of the same size. However, a two-stroke engine also has some
disadvantages, such as higher emissions, lower durability and more noise.
The working of a two stroke diesel engine can be explained by the following
strokes:
a) Compression stroke
In this stroke, the piston moves up from the bottom dead center (BDC) to the
top dead center (TDC), compressing the air in the cylinder. The air
temperature rises to above the auto-ignition temperature of diesel fuel, which
is around 500°C. As the piston reaches the TDC, a small amount of diesel fuel
is injected into the cylinder by a fuel injector. The fuel instantly ignites due to
the high temperature and pressure of the air, creating a rapid expansion of
hot gases that push the piston down.
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Figure 2.14. Compression stroke
b) Power stroke
In this stroke, the piston moves down from the TDC to the BDC, converting the
chemical energy of the fuel into mechanical energy. The piston is connected
to a crankshaft by a connecting rod, which converts the linear motion of the
piston into rotational motion. The crankshaft then drives a flywheel or a
gearbox that transfers the power to the desired application.
Figure 2.15. Power stroke
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As the piston approaches the BDC, an exhaust port opens on the side of the
cylinder wall, allowing some of the exhaust gases to escape. At the same time,
a fresh charge of air enters through an intake port on the opposite side of the
cylinder wall, which is connected to an air compressor or a turbocharger. The
fresh air helps to scavenge out the remaining exhaust gases and prepare the
cylinder for the next compression stroke.
The cycle then repeats itself as long as fuel is supplied to the engine. Therefore,
a two-stroke diesel engine is mainly used for applications that require high
power output and low weight, such as marine propulsion, locomotives and
generators. However, due to its environmental and regulatory challenges, it is
being replaced by more advanced four-stroke engines in many sectors.
Advantages:
a. It can generate twice as much power as a four-stroke engine of
the same size and speed.
b. A two-stroke engine does not require valves, camshafts or valve
timing mechanisms, which reduces its complexity and cost.
c. A two-stroke engine has more uniform torque output
throughout its speed range, which makes it suitable for
applications that require high torque at low speeds.
Disadvantages:
a. A two-stroke engine does not burn all of its fuel completely,
resulting in more unburned hydrocarbons, carbon monoxide
and particulate matter in its exhaust.
b. A two-stroke engine has more friction and wear due to its
higher speed and pressure.
c. It also requires more lubrication and cooling to prevent
overheating and seizure.
2.13.2 Four Stroke Diesel Engine
A four-stroke diesel engine is a type of internal combustion engine that
converts the chemical energy of diesel fuel into mechanical work. It consists
of four main phases: intake, compression, power and exhaust. In this article,
we will explain each stroke in detail and provide some insights into the
advantages and disadvantages of this engine.
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a) Intake Stroke
Figure 2.16. Intake stroke
In this phase, the piston moves down from the top dead center (TDC) to the
bottom dead center (BDC), creating a low-pressure area in the cylinder. The
intake valve opens and fresh air is drawn into the cylinder through the air filter
and intake manifold. The amount of air entering the cylinder depends on the
throttle position and the engine speed. The intake valve closes at the end of
this stroke.
b) Compression Stroke
In this phase, the piston moves up from the BDC to the TDC, compressing the
air in the cylinder. The intake valve closes and the compression ratio increases.
The temperature and pressure of the air rise to a high level, making it ready
for ignition.
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Figure 2.17. Compression stroke
c) Power Stroke
The third stroke is the power stroke. In this phase, when the piston reaches
near the TDC, fuel is injected into the cylinder through a fuel injector. The fuel
atomizes and mixes with the hot compressed air, causing spontaneous
combustion. The rapid expansion of the burning gases pushes the piston down
from the TDC to the BDC, generating power. The crankshaft converts the linear
motion of the piston into rotational motion
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.
Figure 2.18. Power stroke
d) Exhaust Stroke
The fourth stroke is the exhaust stroke. This is the last stroke of this cycle. In
this phase, the piston moves up from the BDC to the TDC, expelling the exhaust
gases from the cylinder. The exhaust valve opens and the exhaust gases are
released through the exhaust manifold and the muffler. After this the cycle of
engine repeats from intake to exhaust.
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Figure 2.19. Exhaust stroke
Advantages:
The four stroke diesel engine has several advantages over other types of
engines, such as
a. Efficiency of four stroke is high.
b. Emission is low.
c. Maintenance cost is low.
Disadvantages:
However, it also has some disadvantages.
a. Initial cost is higher.
b. Heavier in weight.
c. Louder in noise.
d. Lower power-to-weight ratio.
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2.13.3 Comparison of Two Stroke and Four Stroke Diesel Engines
Two-stroke diesel engines are generally simpler in design and require fewer
parts than four-stroke engines. They are also more lightweight and have a
higher power-to-weight ratio. However, they are less efficient and emit more
pollutants compared to four-stroke engines.
Four-stroke diesel engines are generally more complex and require more parts
than two-stroke engines. They are also heavier and have a lower power-toweight ratio. However, they are more efficient and emit fewer pollutants
compared to two-stroke engines.
2.14 Cooling system of diesel engine
The cooling system of a diesel engine is used to remove heat from the engine
and maintain the engine operating temperature within a safe range. The
cooling system generally comprises of a radiator, a water pump, a thermostat,
and a cooling fan.
The water pump circulates coolant, which is a mixture of water and antifreeze,
through the engine and the radiator. The radiator transfers the heat from the
coolant to the surrounding air, thereby cooling the coolant. The thermostat
regulates the flow of coolant through the engine, ensuring that the engine
temperature remains within the optimal range. The cooling fan helps to
increase the flow of air through the radiator, thereby improving the cooling
efficiency.
Figure 2.20. Cooling system of diesel engine
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Sample Multiple Choice Questions
1. Power plants that convert water in boilers into steam by generating
heat energy using a thermal source are called
(a) Thermal Power Plants
(b) Nuclear Power Plants
(c) Solar Power Plants
(d) Diesel Power Plant
2. A machine which converts the energy contained in steam into
mechanical energy is called;
(a) Boiler
(b) Steam turbine
(c) Generator
(d) Condenser
3. The steam Power station has large sections
(a) Boiler
(b) Turbine
(c) Generator
(d) All of these
4. A thermal (steam) power plant consists of these major parts
(a) Boiler and Team Turbine
(b) Boiler and generator
(c) Steam turbine and generator
(d) Boiler, Steam turbine and generator
5. The primary purpose of a thermal power plant is to
(a) Generating electric power
(b) Generation of steam for industrial purposes other than power
generation
(c) Both a & b
(d) None of these
6. A boiler is a device which;
(a) Produces pressurized steam
(b) Converts water to steam
(c) both c and b
(d) Converts steam to water
7. Boiler is used in
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(a) In steam power station
(b) In hydel power station
(c) Both a & b
(d) None of these
8. The types of boiler are
(a) Fire tube boiler
(b) Water tube boiler
(c) Both a & b
(d) None of these
9. In a water tube boiler
(a) Water is inside the tubes
(b) Fire takes place inside the tubes
(c) Fire takes place outside the tubes
(d) Both a & c
10. Economizers are used to heat
(a) Gas
(b) Water
(c) Steam
(d) Feed water
11. By heating the feed water in the economizer
(a) Flue gases are used
(b) Boiler efficiency increases
(c) Fuel is saved.
(d) All of these
12. A steam power plant has an economizing function
(a) Saving in water consumption
(b) Heating feed water by using flue gasses
(c) Preventing wastage of steam
(d) All of these
13. This advantage is achieved by the use of economizer in a steam power
plant
(a) Steam pressure is increased
(b) Fuel is saved
(c) Boiler efficiency is increased
(d) Both b & c
14. Heating the feed water with flue gases saves fuel
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(a) 2 percent
(b) 5 to 15 percent
(c) 20 percent
(d) None of these
15. Steam is passed through this before sending from the boiler to the
turbine
(a) Pre-heater
(b) economizer
(c) Super heaters
(d) Cooling tower
16. The aim to pass the steam through the super heater is
(a) drying
(b) protecting the turbine blades from rusting
(c) Both a & b
(d) None of these
17. ----------- is passed through the superheater
(a) Dry steam
(b) Cold water
(c) Moist steam
(d) Very hot water
18. The superheater is fitted
(a) Outside the boiler before the turbine
(b) Inside the condenser
(c) Inside the boiler
(d) At the outlet of the turbine
19. A steam condenser is essentially a device
(a) Water cooler
(b) Steam cooler
(c) Gas cooler
(d) Fuel cooler
20. The steam coming out of the steam turbine goes
(a) In economizer
(b) In boiler
(c) In preheater
(d) In condenser
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21. Turbo alternators are ------pole machines
(a) Two
(b) Four
(c) Both a & b
(d) Eight
22. ------Turbine in which the pressure remains constant as the steam
passes over the moving blades
(a) Impulse
(b) Reaction
(c) Gas
(d) Water
23. A diesel engine power plant has an important part
(a) Diesel engine
(b) Generator
(c) Both a & b
(d) None of these
24. ------- Power plants can be installed in less time
(a) Thermal
(b) Hydro
(c) Diesel
(d) Gas
25. This method is used for cooling large diesel engines
(a) Air cooling system
(b) Forced water cooling system
(c) Hydrogen cooling system
(d) None of these
26. Diesel power plant has higher initial cost than steam power plant;
(a) Very less
(b) less
(c) High
(d) Very High
27. Environmental impact of thermal power station effects the;
(a) Human life
(b) Animal life
(c) Plant life
(d) All
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28. Which fuel used in thermal power plant produces pollution?
(a) Coal
(b) Oil
(c) Gas
(d) All of these
Answer to MCQ’s
1.
a
2.
b
3.
d
4.
d
5.
a
6.
c
7.
a
8.
c
9.
a
10.
d
11.
d
12.
d
13.
d
14.
b
15.
c
16.
c
17.
a
18.
a
19.
b
20.
d
21.
b
22.
a
23.
c
24.
c
25.
b
26.
c
27.
d
28.
d
Sample Short Questions
1.
2.
3.
4.
5.
6.
7.
What is meant by thermal power plant?
Write the names of types of thermal power plant.
Name the types of power plant based on the fuel used.
Name the types of power station based on the nature of load.
At which locations are thermal power plants operating in Pakistan?
What are the main objectives of a thermal power plant?
What are the important considerations for setting up a thermal power
plant?
8. Write the advantages of thermal power plant.
9. Describe the disadvantages of thermal power plant.
10. Which location is preferred for thermal power plant?
11. Define fuel and name the types of fuel used in thermal plant.
12. What are the types of furnaces used in thermal power plants?
13. Name the four major parts of a thermal or steam power plant.
14. What is meant by cool handling?
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15. Why is coal ground and used in the form of saffron or powder?
16. What is a combustion chamber?
17. What is the advantage of using economizer in steam power plant?
18. Air pre-heater is used for purpose? What is the benefit of this?
19. For what purpose is super heater used? Where does the fuel for it
come from?
20. What is meant by bower? Write the names of its two basic types.
21. What is meant by Fire Tube Boiler? Write the names of its two types.
22. What is meant by water tube boiler?
23. Define steam condenser and what are the different types?
24. Define jet condenser.
25. What is a Diesel Engine Power station?
26. Where are diesel engine power stations installed?
27. Write the names of important parts of diesel power plant.
28. What is a crankshaft?
29. What is a flywheel and what is its function?
30. Write the names of important parts of diesel engine.
31. What is meant by inlet valve?
Sample Long Questions
1.
2.
3.
4.
Write a note on type of fuel used in thermal power plants?
Write some merits and demerits of thermal power plants?
State requirement of site selection for thermal power plants?
Explain working of thermal power plants by drawing a component
block diagram?
5. State different types of boiler used in thermal power plants?
6. Explain different types of turbines used in thermal power plants?
7. Write a detailed note on turbo alternators?
8. Explain different types of condensers used in thermal power plant?
9. Compare two stroke and four stroke diesel engine?
10. Explain working and components of a diesel power station with the
help of diagram?
11. What are the site selection requirements for a diesel power plant?
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CHAPTER 3 NUCLEAR POWER STATIONS
Chapter objectives:






After studying this chapter, a student will be able to
Understand the Introduction of nuclear power station and its
main parts using schematic diagram.
Understand working principle of nuclear energy in context with
atomic structure, atomic number, mass number for materials
used for nuclear energy.
Understand the concept of nuclear fusion and fission.
Understand different types of nuclear reactors.
Understand the construction and different components of a
nuclear reactor.
Understand salient features of nuclear power station working
in Pakistan.
3.1 Introduction to Nuclear power station
Nuclear power station is a facility that uses nuclear fission to generate
electricity. Nuclear fission is a process in which the nuclei of certain atoms,
such as uranium or plutonium, are split into smaller fragments, releasing
energy and neutrons. The neutrons can then cause more fission reactions in a
chain reaction that sustains itself. The energy released by the fission reactions
is used to heat water and produce steam, which drives a turbine and a
generator to produce electricity.
A nuclear power station consists of several components, such as the reactor
core, the coolant system, the control rods, the containment building, the
steam generator, the turbine, the generator, and the cooling tower. The
reactor core is where the fission reactions take place and where the fuel rods
are located. The fuel rods contain pellets of enriched uranium or plutonium
that provide the fissile material for the reactions. The coolant system
circulates a fluid, such as water or gas, through the reactor core to remove
heat and prevent overheating. The control rods are made of materials that
absorb neutrons and can be inserted or withdrawn from the reactor core to
regulate the rate of the fission reactions and control the power output. The
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containment building is a reinforced concrete structure that surrounds the
reactor core and protects it from external events and radiation leaks. The
steam generator is a heat exchanger that transfers heat from the coolant
system to a secondary circuit of water that turns into steam. The turbine is a
device that converts the kinetic energy of the steam into mechanical energy
that rotates a shaft. The generator is a device that converts the mechanical
energy of the shaft into electrical energy that can be transmitted to the grid.
The cooling tower is a structure that cools down the water from the secondary
circuit and releases it back into the environment or recycles it for reuse.
Nuclear power station is a complex and sophisticated technology that requires
careful design, operation, and maintenance. It has many advantages and
disadvantages that need to be weighed against each other and compared with
other sources of energy.
Advantages:
a. Nuclear power station can provide reliable and low-carbon
electricity that can reduce greenhouse gas emissions and
dependence on fossil fuels.
b. They produce large amounts of energy without emitting
greenhouse gases or air pollutants.
c. It is a clean and reliable source of electricity that can help
mitigate climate change and reduce dependence on fossil fuels.
d. They have low operating costs and high capacity factors,
meaning that they can run continuously and efficiently for long
periods of time.
Disadvantages:
a. Nuclear power station poses significant challenges and risks,
such as nuclear waste management, nuclear proliferation,
nuclear accidents, and public acceptance.
b. They produce radioactive waste that needs to be safely stored
and disposed of. 3. Their waste can remain hazardous for
thousands of years and can cause environmental and health
problems if not handled properly.
c. They are vulnerable to accidents and attacks that can result in
catastrophic consequences.
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3.2 Main parts of nuclear power station with schematic
diagram
A nuclear power station consists of two major portions: the nuclear island and
the conventional island. The nuclear island contains the components that are
directly involved in the nuclear fission process, such as the reactor, the steam
generators, the pressurizer, the reactor coolant pumps, and the safety
systems. The conventional island contains the components that are common
to other types of power plants, such as the turbine, the generator, the
condenser, and the cooling system. The main parts of a nuclear power station
and their functions are given below.
Figure 3.1. Nuclear Power Plant
a. Nuclear reactor
The nuclear reactor is the heart of a nuclear power station. It is a device that
initiates and controls a sustained nuclear chain reaction. The reactor contains
fuel rods that are filled with uranium pellets. The uranium atoms undergo
fission when they are hit by neutrons, releasing more neutrons and heat. The
heat is transferred to the coolant, which is usually deuterium water (D2O) that
flows through and around the fuel rods. The coolant also acts as a moderator,
which slows down the neutrons to sustain the chain reaction. The reactor also
has control rods that can be inserted or withdrawn to adjust the reaction rate.
The control rods are made of materials that absorb neutrons, such as boron
or cadmium.
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b. Steam generators
Steam generators are heat exchangers that convert feed water into steam
from heat produced in the reactor core. They are used in pressurized water
reactors (PWRs), which are the most common type of reactors in the United
States. In PWRs, the coolant is kept under high pressure to prevent it from
boiling in the reactor. The coolant passes through tubes inside the steam
generators, where it transfers heat to a secondary water circuit. The
secondary water boils and becomes steam, which is then sent to the turbine.
c. Pressurizer
A pressurizer is a device that maintains the pressure of the coolant in PWRs. It
is connected to the primary coolant circuit and contains a heater and a spray
nozzle. The heater increases the temperature of the coolant, which expands
and raises its pressure. The spray nozzle releases cold water into the
pressurizer, which contracts and lowers its pressure. By adjusting the heater
and the spray nozzle, the pressurizer keeps the pressure of the coolant within
a certain range.
d. Reactor coolant pumps
Reactor coolant pumps are devices that circulate the coolant through the
reactor core and the steam generators. They ensure that enough heat is
removed from the fuel rods and that enough steam is produced for the
turbine. They also prevent hot spots from forming in the reactor core, which
could damage the fuel rods or cause a meltdown.
e. Safety systems
Safety systems are components that protect the reactor from accidents or
malfunctions. They include emergency core cooling systems, containment
systems, backup power sources, radiation monitoring systems, and control
room systems. Emergency core cooling systems provide additional coolant to
cool down the reactor core in case of a loss of coolant accident (LOCA), which
could result from a leak or a rupture in the primary circuit. Containment
systems prevent radioactive materials from escaping into the environment in
case of an accident. They consist of barriers such as concrete walls, steel liners,
and air filters that surround the reactor vessel and other components. Backup
power sources provide electricity to operate essential systems in case of a loss
of external power supply. Radiation monitoring systems measure and record
radiation levels inside and outside the plant and alert operators if they exceed
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safe limits. Control room systems allow operators to monitor and control all
aspects of plant operation and safety.
f. Turbine
A turbine is a device that converts steam into mechanical energy. It consists of
blades attached to a shaft that rotates when steam passes through them. The
turbine is connected to a generator by a coupling.
g. Generator
A generator is a device that converts mechanical energy into electrical energy.
It consists of coils of wire that rotate inside a magnetic field created by
magnets or electromagnets. The rotation induces an electric current in the
coils, which is then transmitted to transformers.
h. Condenser
A condenser is a device that converts steam back into water after it passes
through the turbine. It consists of tubes surrounded by cold water that cools
down and condenses the steam. The condensed water is then pumped back
to the steam generators as feed water.
i. Cooling system
The cooling system of a nuclear power plant is a vital component that ensures
the safe and efficient operation of the reactor. The cooling system has two
main functions: to transfer heat from the reactor core to the steam turbines
that generate electricity, and to remove and dump surplus heat from the
steam cycle to the environment. The cooling system can use water or air as
the cooling medium, depending on the availability and suitability of water
sources near the plant site.
3.3 Principle of nuclear energy, atomic structure, atomic,
number
3.3.1 Principle of nuclear energy
The principle of nuclear energy is based on the process of nuclear fission, in
which the nucleus of an atom is split into two smaller nuclei, releasing a large
amount of energy in the process. This energy is harnessed to produce heat,
which is used to generate electricity in nuclear power plants.
3.3.2 Atomic Structure
Atomic structure refers to the arrangement of protons, neutrons and electrons
in an atom. The number and configuration of these subatomic particles
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determine the chemical and physical properties of an element. The atomic
structure of an atom consists of a nucleus and an electron cloud. The nucleus
contains protons and neutrons, which have positive and neutral charges
respectively. The electron cloud contains electrons, which have negative
charges and orbit around the nucleus. For example, an atom of uranium has
92 protons and 92 electrons, and can have different numbers of neutrons
depending on the isotope. The most common isotope of uranium is uranium238, which has 146 neutrons in its nucleus.
Figure 3.2. Atomic structure of Uranium
a) Atomic Number
The atomic number of an atom is the number of protons in its nucleus. It
determines the identity and chemical properties of the element. It is denoted
by letter Z. For example, hydrogen has an atomic number of 1, helium has an
atomic number of 2, and so on. Radioactive materials are elements that have
unstable nuclei and emit radiation. The atomic number of a radioactive
element can change during radioactive decay, when it emits an alpha or beta
particle and transforms into a different element. For example, uranium-238
has an atomic number of 92, but when it emits an alpha particle, it becomes
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thorium-234, which has an atomic number of 90. Atomic number is written on
the upper side of atom.
b) Atomic Mass
The atomic mass of an atom is the total numbers of its protons and neutrons.
It is usually measured in atomic mass units (amu), where one amu is equal to
1/12 of the mass of a carbon-12 atom. It is denoted by letter A. Radioactive
materials are atoms that have unstable nuclei and can decay into other atoms
by emitting radiation. The atomic mass of a radioactive atom can change
during the decay process, as some mass is converted into energy according to
Einstein's equation E = mc^2. Atomic mass is usually written on the down side
of symbol.
Figure 3.3 Uranium U238
3.4 Kinetic energy and isotopes, fuel (Nuclear)
3.4.1 Kinetic energy
Kinetic energy is the energy that an object has because of its motion. The
faster an object moves, the more kinetic energy it has. The amount of kinetic
energy also depends on the mass of the object. A heavier object moving at the
same speed as a lighter object has more kinetic energy. Some examples of
kinetic energy are:
- A car driving on a highway has kinetic energy because it is moving fast.
- A baseball thrown by a pitcher has kinetic energy because it is flying through
the air.
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- A roller coaster at the top of a hill has potential energy, which is stored energy
due to its position. As it goes down the hill, it converts potential energy into
kinetic energy because it gains speed.
- A wind turbine has kinetic energy because its blades are spinning due to the
wind.
3.4.2 Isotopes
Isotopes are variants of an element that have the same number of protons in
the nucleus but different numbers of neutrons. This means that isotopes of
the same element have the same atomic number but different mass numbers.
For example, water (H2O) is made up of two hydrogen atoms and one oxygen
atom. Hydrogen has three naturally occurring isotopes: rotium (H-1),
deuterium (H-2), and tritium (H-3).
Figure 3.4 Isotopes of hydrogen
Protium is the most common isotope of hydrogen, with one proton and no
neutrons in its nucleus. Deuterium has one proton and one neutron in its
nucleus, and tritium has one proton and two neutrons in its nucleus.
Therefore, water can have different isotopes depending on the type of
hydrogen present. The most common form of water is H2O, which contains
two protium atoms. However, water can also contain deuterium (D) or tritium
(T) in place of protium.
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In nuclear materials, isotopes play a significant role. For example, uranium has
three isotopes: uranium-234, uranium-235, and uranium-238. Uranium-235 is
important in nuclear energy because it can undergo nuclear fission, which
releases a significant amount of energy. In contrast, uranium-238 is not fissile
but can be used to produce plutonium-239, which is fissile.
3.4.3 Radio Activity
Radioactivity is the process by which unstable atomic nuclei emit particles
and/or electromagnetic radiation in order to achieve greater stability. This
emission of radiation can take the form of alpha particles, beta particles, and
gamma rays. Radioactive materials can be found in nature or artificially
produced, and they can be used in a variety of applications such as medical
diagnosis and treatment, power generation, and scientific research.
a) Alpha
Alpha particles are made up of two protons and two neutrons and have a
positive charge. They are relatively large and heavy and can be stopped by a
piece of paper or even by skin. Alpha radiation is formed when an atomic
nucleus emits an alpha particle during radioactive decay.
b) Beta
Beta particles are electrons that are emitted from the nucleus of an atom
during radioactive decay. They have a negative charge and are smaller and
lighter than alpha particles. Beta radiation can penetrate deeper into materials
than alpha radiation and can be stopped by a sheet of aluminum. Beta
radiation is formed when a neutron in the nucleus of an atom is converted into
a proton, and an electron and an antineutrino are emitted.
c) Gamma
Gamma rays are high-energy electromagnetic radiation that is emitted from
the nucleus of an atom during radioactive decay. They are similar to X-rays but
are more energetic and have higher frequency. Gamma radiation can
penetrate through most materials, and thick layers of concrete or lead are
required to stop them. Gamma radiation is formed when a nucleus in an
excited state releases energy in the form of a photon.
3.4.4 Half Life
The half-life of a nuclear element is the time it takes for half of its atoms to
decay into another element. The decay process can be described by nuclear
equations that show the changes in the atomic number and mass number of
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the nuclides involved. For example, uranium-238 undergoes alpha decay to
form thorium-234, as shown by the equation:
U238 (92) → Th234 (90) + α4 (2)
In this equation, we see that the atomic number decreases by two and the
mass number decreases by four, as an alpha particle (a helium nucleus) is
emitted. The half-life of uranium-238 is about 4.5 billion years, which means
that after 4.5 billion years, half of the uranium-238 atoms will have decayed
into thorium-234 atoms.
Another example of nuclear decay is carbon-14, which undergoes beta decay
to form nitrogen-14, as shown by the equation:
C14 6 → N14 7 + β0 −1
In this equation, we see that the atomic number increases by one and the mass
number remains unchanged, as a beta particle (an electron) is emitted. The
half-life of carbon-14 is about 5730 years, which means that after 5730 years,
half of the carbon-14 atoms will have decayed into nitrogen-14 atoms.
3.4.5 Binding Energy and Mass Defect
The binding energy is the amount of energy required to separate the
constituent parts of a nucleus. It is the energy released when protons and
neutrons come together to form a nucleus, and is a measure of the stability of
the nucleus.
The mass defect is the difference between the mass of a nucleus and the sum
of the masses of its constituent protons and neutrons. This mass defect is due
to the conversion of some of the mass into energy during the formation of the
nucleus. This relationship between mass and energy is described by Einstein's
famous equation, E=mc², where E is the energy, m is the mass, and c is the
speed of light.
The equation relating binding energy to mass defect can be derived from
Einstein's equation. The mass defect (∆m) can be calculated by subtracting the
sum of the masses of the individual protons and neutrons from the mass of
the nucleus. The binding energy (BE) can then be calculated using the
equation:
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BE = ∆mc²
Where c is the speed of light, and ∆m is the mass defect. This equation shows
that the binding energy of a nucleus is directly proportional to its mass defect,
which in turn is related to the stability of the nucleus.
3.4.6 Nuclear Fuel
Nuclear fuel is the material that is used in nuclear reactors to produce heat
and electricity by nuclear fission. There are different types of nuclear fuel,
depending on the design and purpose of the reactor. The most common type
of nuclear fuel is uranium dioxide, which is a ceramic compound of uranium
and oxygen. Nuclear fuel can be used using these three methods.
1) Slugs
2) Clade Plates
3) Loose Powder
Some important nuclear fuels are given below.
a. Uranium Dioxide
Uranium dioxide is formed into pellets and loaded into metal tubes called fuel
rods or fuel pins. The fuel rods are arranged into fuel assemblies, which are
inserted into the reactor core. The uranium dioxide used in most reactors is
enriched, meaning that it has a higher concentration of uranium-235 than
natural uranium, which is about 0.7%. Enrichment increases the probability of
fission and allows the use of light water as both coolant and moderator in lightwater reactors (LWRs), which are the most widely used type of reactors for
commercial power generation.
b. Natural Uranium
Another type of nuclear fuel is natural uranium, which does not require
enrichment but requires a different type of reactor that uses heavy water or
graphite as moderator. Heavy water and graphite slow down the neutrons
more effectively than light water, making fission possible with natural
uranium.
c. Plutonium
Plutonium is a radioactive chemical element with the symbol Pu and the
atomic number 94. It is a silvery metal that tarnishes in air and can form
compounds with other elements. Plutonium has several isotopes, but the
most important one for nuclear power and weapons is plutonium-239.
Plutonium-239 is produced by bombarding uranium-238 with neutrons in a
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nuclear reactor. Plutonium-239 has a half-life of 24,110 years, which means it
takes that long for half of its atoms to decay into other elements. Plutonium239 undergoes nuclear fission, which means it can split into smaller atoms and
release a large amount of energy. This energy can be used to generate
electricity in a nuclear power plant or to create a powerful explosion in a
nuclear weapon.
d. Thorium
Thorium is a naturally occurring radioactive element that has potential as a
nuclear fuel. Its atomic symbol is Th, and its atomic number is 90. Thorium is
a fertile material, which means that it can be converted into fissile material
through nuclear reactions. When thorium is bombarded with neutrons, it can
be converted into uranium-233, which is a fissile material.
Thorium has a long half-life of 14.05 billion years, which means that it decays
very slowly. This makes it an attractive fuel for nuclear reactors because it
produces less radioactive waste compared to other nuclear fuels. Thorium is
also more abundant in the earth's crust than uranium, which means it has the
potential to provide a more sustainable source of nuclear energy.
There are different types of thorium-based nuclear fuels that have been
proposed, including thorium dioxide (ThO2) and thorium-uranium mixed
oxide (ThUO2). These fuels have the potential to produce energy through
different types of nuclear reactors, including thermal reactors and fast
reactors.
3.5 Nuclear fission and fusion
Nuclear reactions occur when the nucleus of an atom undergoes a change,
resulting in the formation of a new element or isotope. These reactions can be
classified into different types based on the type of particles involved and the
type of energy released or absorbed. Generally, there are four types of nuclear
reactions.
1. Nuclear Fission
2. Nuclear Fusion 3. Elastic Scattering 4. Neutron
Capture
We will discuss only nuclear fission and fusion in this chapter.
3.5.1 Nuclear Fusion
Nuclear fusion is a process in which atomic nuclei come together to form a
heavier nucleus, releasing a tremendous amount of energy in the process. This
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process is the source of energy for stars, including our Sun, and is also being
researched as a potential future source of clean energy for human use.
The basic principle of nuclear fusion is to bring together two atomic nuclei to
form a heavier nucleus, accompanied by the release of energy. This process
requires very high temperatures and pressures to overcome the natural
repulsion between the positively charged nuclei. In the Sun, the temperature
and pressure at the core are so high that hydrogen nuclei (protons) can fuse
together to form helium nuclei, releasing energy in the form of light and heat.
One simple example of nuclear fusion is the fusion of two hydrogen nuclei
(protons) to form a helium nucleus. This process releases a tremendous
amount of energy in the form of light and heat. The reaction can be written as
follows:
2H --> He + energy
This reaction is what powers the Sun and other stars, as the continuous fusion
of hydrogen nuclei produces a steady flow of energy that radiates outward,
providing heat and light.
Figure 3.5 Nuclear Fission
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Another example of nuclear fusion is the fusion of deuterium and tritium, two
isotopes of hydrogen, to form helium and a neutron. This reaction is of
particular interest for potential energy generation because it is relatively easy
to achieve in laboratory conditions, and produces a large amount of energy.
The reaction is displayed in figure 3.5 and can be written as follows:
2D + 3T --> 4He + n + energy
3.5.2 Nuclear Fission
Nuclear fission is a process in which a heavy atomic nucleus, such as uranium
or plutonium, splits into two or more smaller nuclei of roughly equal mass.
This process releases a large amount of energy, as well as gamma rays and
several neutrons. The neutrons can then induce fission in other nuclei,
creating a chain reaction that can be controlled for power generation or
uncontrolled for explosive purposes.
The phenomenon of nuclear fission was discovered in 1938 by German
physicists Otto Hahn and Fritz Strassmann, who bombarded uranium with
neutrons and observed barium as a product. The interpretation of this result
was provided by Lise Meitner and Otto Frisch, who proposed that the uranium
nucleus had split into two fragments and released energy according to
Einstein's equation E = mc2. This discovery opened a new era of nuclear
physics and technology, with both beneficial and destructive applications.
The energy released by nuclear fission is due to the difference in binding
energy per nucleon between the initial and final nuclei. Binding energy is the
energy required to separate a nucleus into its constituent protons and
neutrons. Generally, nuclei with intermediate mass numbers have higher
binding energy per nucleon than nuclei with very low or very high mass
numbers. Therefore, when a heavy nucleus splits into two lighter nuclei, the
total binding energy increases and the excess energy is converted into kinetic
energy of the fission products and radiation.
The amount of energy released by a single fission event depends on the
specific nuclides involved, but it is typically around 200 MeV (million electron
volts) per fission. For comparison, the energy released by the combustion of
one molecule of methane is about 0.001 eV (electron volt). This means that
nuclear fission is about 200 million times more energetic than chemical
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reactions. To illustrate this further, one kilogram of uranium-235 can produce
as much energy as about three million kilograms of coal.
Nuclear fission can occur spontaneously or can be induced by bombarding a
nucleus with a particle or a photon. Spontaneous fission is rare and occurs only
in very heavy isotopes, such as uranium-238 or plutonium-240. Induced fission
is more common and can be achieved by using neutrons, protons, deuterons,
alpha particles or gamma rays. However, neutrons are the most effective
particles for inducing fission, because they do not need to overcome the
electrostatic repulsion from the positively charged nucleus.
Example of nuclear fission is when neutron is bombard on uranium-235 and
then it converts into uranium-236 which has low half-life and turns in to
Barium Ba-144 and Krypton Kr-89 while releasing three neutrons for further
reaction as shown in figure 3.6.
U-235+n → U-236 → Ba-144+Kr-89+3n
Figure 3.6 Nuclear Fission
Nuclear weapons are devices that use uncontrolled chain reactions to create
massive explosions. Nuclear weapons use different types of initiators (devices
that produce neutrons) and reflectors (materials that bounce back neutrons)
to start and amplify the chain reaction in a very short time. Nuclear weapons
also use different types of explosives (chemicals that compress the fissile
material) and tampers (materials that hold together the fissile material) to
achieve high densities and temperatures for efficient fission.
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3.6 Heavy water and its importance
Heavy water, also known as deuterium oxide, is a form of water in which the
hydrogen atoms are replaced with their heavier isotope, deuterium. It is used
in nuclear power plants as a moderator and coolant, and its importance in the
nuclear industry cannot be overstated.
In a nuclear power plant, the fuel, typically uranium-235, undergoes fission,
which releases a large amount of energy in the form of heat. This heat is used
to generate steam, which turns turbines and generates electricity. However,
the fission process also produces high-energy neutrons, which can cause the
fuel to undergo further fission, releasing even more energy. This is called a
chain reaction.
To control the chain reaction and prevent it from becoming uncontrolled and
potentially dangerous, a moderator is used to slow down the neutrons. This is
where heavy water comes in. Heavy water has a greater ability to slow down
neutrons compared to regular water, which makes it an ideal moderator. It
allows for a more efficient use of fuel and safer operation of the reactor.
Heavy water is also used as a coolant in nuclear power plants. The heat
generated by the fuel needs to be removed to prevent the fuel from
overheating and potentially melting down. Heavy water is an excellent coolant
because it has a high boiling point and does not react with the fuel or the
reactor materials.
The production of heavy water is a complex process and requires a significant
amount of energy. It can be produced through the process of electrolysis, in
which a current is passed through water to separate the deuterium from the
regular hydrogen atoms. Alternatively, it can be produced through the process
of hydrogen-water exchange, in which regular water is exposed to a hydrogen
gas that has been enriched with deuterium.
The importance of heavy water in the nuclear industry cannot be overstated.
It is a critical component of nuclear power plants, allowing for the safe and
efficient production of electricity. Additionally, heavy water can be used in
research reactors, which are used for scientific experiments and medical
isotope production.
However, heavy water also has some potential drawbacks. It is more expensive
to produce than regular water, which can increase the cost of nuclear power.
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Additionally, heavy water can pose a potential risk if it were to leak or spill, as
it is toxic and can potentially cause health problems if ingested.
3.7 Nuclear reactor
Nuclear reactors are devices used to produce energy by harnessing the power
of nuclear fission. They work by splitting atoms of certain radioactive
materials, releasing energy in the form of heat, which is then used to generate
electricity. A nuclear reactor consists of several major components, each of
which plays a critical role in the safe and efficient operation of the reactor.
Figure 3.7. Nuclear reactor
1. Reactor Core
The reactor core is the heart of the nuclear reactor, where the nuclear fuel is
housed and the fission reaction takes place. The core typically consists of fuel
rods, which contain pellets of enriched uranium or other nuclear fuels. These
fuel rods are arranged in a precise configuration to ensure a controlled chain
reaction.
2. Moderator
The moderator is a material that slows down the high-energy neutrons
produced by the fission reaction, allowing them to interact more effectively
with other fuel atoms and sustain the chain reaction. The most common
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moderator used in nuclear reactors is water, but other materials such as
graphite, heavy water, or beryllium can also be used.
3. Reflector
The reflector is a material that surrounds the reactor core and reflects
neutrons back into the core, increasing the likelihood of a fission reaction.
Reflectors are typically made of a material such as graphite or beryllium.
4. Shielding
Shielding is a layer of material that surrounds the reactor core and other
components of the reactor to protect workers and the environment from
radiation. The shielding can be made of materials such as concrete, lead, or
steel.
5. Control Rods
Control rods are rods made of a material such as boron or cadmium that can
absorb neutrons and slow down or stop the fission reaction. These rods are
inserted or removed from the reactor core to control the rate of the reaction.
6. Coolant
The coolant is a substance used to transfer heat away from the reactor core
and generate steam for electricity generation. The coolant can be a liquid such
as water, or a gas such as helium. The choice of coolant depends on the design
of the reactor and the operating conditions.
7. Reactor Vessel
The reactor vessel is a heavy-duty steel container that houses the reactor core,
coolant, and other major components of the reactor. The vessel is designed to
withstand the high temperatures and pressures generated by the fission
reaction and to contain any potential leaks or accidents.
3.8 Types of a nuclear reactor
There are two main types of nuclear power plants: Thermal Reactor and Fast
Reactors. In thermal reactors, speed of neutron is controlled by using
moderators while in fast reactors neutrons continue chain reaction with
default speed of their emission. Generally, in thermal reactors energy of
neutron is 0.03 eV while in fast reactors it can go up to 1000 eV. Reactors are
further categorized based on fuel, moderator, coolant and core utilization.
Types of Nuclear Reactors w.r.t Fuel
In terms of fuel used, there are two types of nuclear reactors:
a) Uranium-based reactors
b) Plutonium-based reactors
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Types of Nuclear Reactors w.r.t moderator
In terms of moderator used, there are three types of nuclear reactors:
a) Graphite-moderated reactors
b) Heavy water-moderated reactors
c) Light water-moderated reactors
Types of Nuclear Reactors w.r.t coolant
In terms of coolant used, there are two types of nuclear reactors:
a) Gas-cooled reactors
b) Liquid-cooled reactors
Types of Nuclear Reactors w.r.t core
In terms of core used, there are two types of nuclear reactors:
a) Homogeneous reactors
b) Heterogeneous reactors
Details of some important types of nuclear reactors is given below.
3.8.1 Boiling Water Reactor:
A Boiling Water Reactor (BWR) is a type of nuclear reactor that generates
electricity by using nuclear fission to heat water, producing steam that drives
a turbine and generates electricity.
Working of BWR
In a BWR, fuel rods containing uranium-235 pellets are placed in the reactor
core. Neutrons from the fuel rods initiate a chain reaction, causing the
uranium atoms to split and release energy in the form of heat. The heat
produced by the nuclear reaction is transferred to the water in the reactor
vessel, which is converted to steam. The steam then drives the turbine, which
is connected to a generator, producing electricity.
Unlike Pressurized Water Reactors (PWRs), which use a separate loop for
cooling the steam and the reactor core, BWRs use the same water for both
purposes. The steam produced by the reactor core is directly used to drive the
turbine, and then condensed back into water in a separate condenser, which
is then pumped back into the reactor vessel.
Advantages of BWRs:
a. BWRs have a simple design and require fewer components than
PWRs, making them cheaper to build and maintain.
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b. BWRs have a higher thermal efficiency than PWRs, as the steam
produced by the reactor core is directly used to drive the
turbine, without any intermediate heat exchange process.
c. BWRs can be used to generate electricity using natural
uranium, whereas PWRs require enriched uranium.
Disadvantages of BWRs:
a. BWRs produce a smaller amount of electricity than PWRs of
similar size, due to the lower temperature and pressure of the
steam produced by the reactor core.
b. BWRs have a higher risk of radiation exposure to workers and
the environment, as the reactor coolant is also used as a
working fluid in the turbine and generator, increasing the risk
of radioactive contamination.
c. BWRs produce more radioactive waste than PWRs, due to the
direct contact of the reactor coolant with the fuel rods.
Figure 3.8. Boiling water reactor
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3.8.2 Pressurized Water Reactor
A pressurized water nuclear reactor (PWR) is a type of light-water nuclear
reactor that uses ordinary water as both coolant and neutron moderator.
PWRs are the most common type of nuclear power plants in the world,
accounting for about 65% of the commercial reactors in the United States and
more than 300 globally.
The working principle of a PWR is based on heating water under high pressure
to prevent it from boiling. The water in the primary circuit is heated by the
energy released by the fission of uranium atoms in the fuel rods. The heated
water then flows to a steam generator, where it transfers its thermal energy
to a secondary circuit of water that turns into steam. The steam then drives a
turbine that spins an electric generator to produce electricity. The steam is
then condensed back to water and returned to the steam generator, while the
water in the primary circuit is pumped back to the reactor core to be reheated.
Figure 3.9. Pressurized water reactor
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Advantages of PWRs:
a. They have a high thermal efficiency compared to other types of
reactors, as they operate at high temperatures and pressures.
b. They have a negative temperature coefficient of reactivity,
which means that as the temperature increases, the reactivity
decreases, making them more stable and safe.
c. They can use enriched uranium or mixed oxide (MOX) fuel,
which reduces the amount of nuclear waste and extends the
fuel cycle.
d. They have a long operational life span, as some PWRs can
operate for up to 60 years with proper maintenance and
upgrades.
Disadvantages of PWRs:
a. High capital cost due to the need for a strong pressure vessel
and a pressurizer.
b. Low efficiency of plant due to the generation of only saturated
steam in the secondary circuit.
c. Corrosion problems and radiation damage of the fuel and
cladding materials.
3.8.3 Heavy Water Cooled and Moderated type (CANDU) reactors
Heavy water cooled and moderated reactors, also known as CANDU (Canadian
Deuterium Uranium) reactors, are a type of nuclear reactor commonly used in
Canada and other countries around the world. These reactors use heavy water
(deuterium oxide) as both the coolant and moderator, which helps slow down
neutrons and increase the likelihood of fission.
CANDU reactors are typically large, cylindrical structures made of reinforced
concrete and steel. The core of the reactor contains fuel rods made of uranium
dioxide, which are arranged in bundles and surrounded by a structure of heavy
water-filled tubes called "pressure tubes". The fuel bundles and pressure
tubes are housed within a cylindrical vessel called the calandria, which is also
filled with heavy water. The calandria is surrounded by a layer of heavy water
called the "shield tank", which helps to absorb radiation and protect the
environment.
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CANDU reactors operate by using the heat generated by fission to create
steam, which drives a turbine and generates electricity. The heavy water
coolant is pumped through the pressure tubes and absorbs heat from the fuel
rods. The heated water then passes through a heat exchanger, where it
transfers its heat to a separate system of lighter water, which is used to create
steam. The steam is then directed to a turbine, which drives a generator and
produces electricity.
Unlike many other types of reactors, CANDU reactors use natural uranium as
fuel instead of enriched uranium. This means that the fuel does not need to
be processed before being loaded into the reactor, which reduces the risk of
nuclear proliferation. In addition, the use of heavy water as both the coolant
and moderator allows for greater flexibility in reactor design and operation, as
well as increased safety and efficiency.
Figure 3.10. CANDU reactor
3.8.4 Gas Cooled Reactors
Gas cooled nuclear reactors are a type of nuclear power plant that use gas as
a coolant instead of water or liquid metal. The gas, usually carbon dioxide or
helium, flows through the reactor core and carries away the heat generated
by the nuclear fission reactions. The heat is then transferred to a secondary
circuit where it is used to produce steam and drive a turbine generator.
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The main advantages of gas cooled nuclear reactors are that they can operate
at higher temperatures and lower pressures than water cooled reactors, which
improves their thermal efficiency and reduces the risk of coolant loss. They
also have lower corrosion and erosion problems, and can use natural uranium
as fuel without enrichment.
The main disadvantages of gas cooled nuclear reactors are that they require
more fuel and more complex fuel assemblies than water cooled reactors,
which increases their cost and waste production. They also have lower power
density and higher neutron leakage, which reduces their neutron economy
and fuel utilization.
There are two main types of gas cooled nuclear reactors: gas cooled graphite
moderated reactors (GCR) and high temperature gas cooled reactors (HTGR).
GCRs use graphite as a moderator to slow down the neutrons and sustain the
chain reaction.
Figure 3.11. Gas cooled reactors
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3.8.5 Liquid Metal Cooled Reactors
Liquid Metal cooled nuclear reactors are a type of nuclear reactor that use
liquid metal as the coolant instead of water or gas. The main advantages of
liquid metal coolants are that they have high thermal conductivity, low
pressure, and can operate at higher temperatures than water-cooled reactors.
This allows for higher efficiency, smaller size, and lower risk of accidents.
The most common liquid metal coolants used in nuclear reactors are sodium,
lead, and lead-bismuth eutectic (LBE). Sodium has the highest thermal
conductivity and the lowest melting point of the three, but it also reacts
violently with water and air, which poses a safety challenge. Lead and LBE have
higher melting points and lower thermal conductivity than sodium, but they
are more compatible with water and air, and have better neutron properties.
Figure 3.12. Liquid metal cooled reactors
The construction and working of a liquid metal cooled nuclear reactor depends
on the type of reactor design and the choice of coolant. However, a general
description is as follows: The reactor core consists of fuel rods that contain
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fissile material such as uranium or plutonium. The fuel rods are arranged in a
lattice inside a pressure vessel. The liquid metal coolant flows through the
gaps between the fuel rods and carries away the heat generated by the fission
reactions. The coolant then passes through a heat exchanger, where it
transfers its heat to a secondary fluid, such as water or gas. The secondary
fluid then drives a turbine and a generator to produce electricity. The coolant
then returns to the reactor core to complete the cycle.
3.8.6 Homogeneous Reactors
Homogeneous nuclear reactors are a type of nuclear reactor that uses a single,
homogeneous mixture of fuel and coolant. Unlike traditional nuclear reactors,
which use fuel rods and coolant channels, homogeneous reactors rely on a
liquid fuel that is mixed with the coolant and circulated through the reactor
core. This design offers several advantages, including increased efficiency and
simplified fuel processing, but it also presents unique challenges in terms of
reactor stability and safety.
Homogeneous reactors typically use a liquid fuel mixture that is composed of
uranium or plutonium dissolved in a solvent such as molten salt, liquid metal,
or water. This fuel is mixed with the coolant and circulated through the core
of the reactor in a continuous loop. As the fuel undergoes fission, it releases
heat that is absorbed by the coolant, which is then used to produce steam and
generate electricity.
One of the key advantages of homogeneous reactors is their ability to achieve
high fuel utilization, meaning that a greater proportion of the fuel is burned
before it is removed from the reactor. This is because the fuel is distributed
evenly throughout the reactor, allowing for more efficient use of the
fissionable material. In addition, homogeneous reactors do not require the use
of fuel rods or other complex fuel assemblies, which simplifies the fuel
processing and reduces the overall cost of the reactor.
However, homogeneous reactors also pose several unique challenges in terms
of reactor stability and safety. For example, the continuous mixing of the fuel
and coolant can make it difficult to control the rate of fission and maintain a
stable reactor. In addition, the use of liquid fuels can create safety concerns
related to the handling and storage of radioactive materials.
Homogeneous reactors have been used in a variety of applications, including
research and medical isotope production, as well as for military purposes.
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3.8.7 Fast Breed Reactors
Fast breeder nuclear reactors are a type of nuclear reactor that uses fast
neutrons to sustain nuclear fission and breed new fuel. Unlike traditional
thermal reactors, which use slow neutrons, fast breeders are designed to
produce more fuel than they consume, making them a potentially valuable
source of sustainable energy. However, the technology is complex and has
faced significant technical and economic challenges over the years.
Fast breeder reactors operate by using fast neutrons to convert fertile
materials, such as depleted uranium or thorium, into fissionable material, such
as plutonium or uranium-233. This process is called breeding, and it allows the
reactor to produce more fuel than it consumes. The fuel is typically arranged
in a liquid metal or ceramic form and cooled using a liquid metal, such as
sodium or lead.
One of the key advantages of fast breeders is their high fuel efficiency. Unlike
thermal reactors, which use only a small percentage of the available fuel, fast
breeders can utilize nearly all of the fuel, making them much more efficient.
In addition, the process of breeding allows the reactor to produce more fuel
than it consumes, which could potentially provide a long-term source of
sustainable energy.
However, fast breeders also pose significant technical challenges. The use of
fast neutrons requires a complex and expensive fuel cycle, and the coolant can
be highly reactive and corrosive, which can lead to safety concerns. In
addition, the production of plutonium in fast breeders has raised concerns
about nuclear proliferation and the potential for weaponization.
More recently, there has been renewed interest in fast breeders as a potential
source of sustainable energy. For example, India has developed a prototype
fast breeder reactor, the Prototype Fast Breeder Reactor, which is expected to
begin commercial operation in 2023. Russia has also announced plans to build
a new fast breeder reactor, the Brest-OD-300, which is expected to begin
operation in the mid-2020s.
3.9 Site selection for nuclear power plant
The site selection of a nuclear power plant installation is a complex and
multidimensional process that involves various technical, economic,
environmental and social factors. Some of the important factors that need to
be considered are:
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a. Safety
The site should be located in a region that has low seismic activity, low flood
risk, low population density and adequate distance from major urban centers.
The site should also have sufficient emergency planning zones and evacuation
routes in case of accidents.
b. Cooling
The site should have access to a reliable and sufficient source of cooling water,
such as a river, lake or sea. The cooling water should have low salinity, low
temperature and low turbidity to avoid corrosion, fouling and thermal
pollution.
c. Grid connection
The site should be close to the existing or planned transmission lines and
substations that can accommodate the power output and voltage level of the
nuclear power plant. The site should also have good road and rail access for
the transportation of equipment and materials.
d. Land availability
The site should have enough land area to accommodate the nuclear power
plant facilities, such as the reactor building, turbine hall, cooling towers, waste
storage and disposal facilities. The site should also have enough buffer zone
to provide protection from external hazards and interference.
e. Public acceptance
The site should have the support and consent of the local communities and
stakeholders that may be affected by the nuclear power plant installation. The
site should also comply with the relevant laws and regulations of the country
and region.
3.10 Nuclear power stations in Pakistan
Pakistan is one of the few countries in the world that has developed and
operates civil nuclear power plants. The country has six commercial reactors
that provide about 7.5% of its electricity generation, and plans to build more
in the future. The Pakistan Atomic Energy Commission (PAEC) is the sole
authority responsible for the design, construction and operation of these
plants.
The first nuclear power plant in Pakistan was Karachi 1 (K1), a 90 MWe
pressurized heavy water reactor (PHWR) supplied by Canada and inaugurated
in 1972. It was shut down in 2021 after 49 years of service. The second plant
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was Chashma 1 (C1), a 300 MWe pressurized water reactor (PWR) supplied by
China and started up in 2000. It was followed by three more units of the same
type at the same site: Chashma 2 (C2) in 2011, Chashma 3 (C3) in 2016 and
Chashma 4 (C4) in 2017. The sixth and latest plant is Karachi 2 (K2), a 1100
MWe PWR also supplied by China and connected to the grid in 2021. Another
unit of the same type, Karachi 3 (K3), is under construction and expected to
start operation in 2022.
Pakistan's nuclear power plants are under international safeguards and use
enriched uranium fuel imported from China. The country also has a small
indigenous nuclear fuel cycle, including uranium mining and milling,
conversion, enrichment and fabrication facilities, as well as research reactors
and reprocessing plants. However, these facilities are not part of the civil
nuclear program and are used for military purposes.
Pakistan's nuclear power program faces several challenges, such as financing,
safety, security, waste management and public acceptance. The country has
faced international isolation and sanctions due to its development of nuclear
weapons outside the Nuclear Non-Proliferation Treaty. However, it has also
received support and cooperation from China, which considers Pakistan a
strategic partner and a counterbalance to India. Pakistan is a member of the
International Atomic Energy Agency and has signed several agreements with
it for technical assistance and nuclear safety.
Pakistan has ambitious plans to expand its nuclear power capacity to meet its
growing energy demand and reduce its dependence on fossil fuels. The
country aims to have 32 nuclear power plants with a total capacity of 40,000
MW by 2050, which would account for about 20% of its electricity generation.
Some of the potential sites for new plants are Mianwali, Kundian, Dera Ghazi
Khan, Jhangar and Naukundi. Pakistan is also interested in developing small
modular reactors and thorium-based reactors for remote areas and industrial
applications.
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Sample Multiple Choice Questions
1. It is used as fuel in nuclear power stations
(a) Coal
(b) Diesel
(c) Gas
(d) Uranium
2. One kilogram of uranium can generate as much electricity as ------- burning
of high grade coal
(a) 1500 ton
(b) 2000 ton
(c) 3000 ton
(d) 4500 ton
3. Nuclear power plants are generally used as follows
(a) Base load
(b) Peak load
(c) Variable load
(d) Both b & c
4. Nuclear power plants are not suitable for this type of load operation
(a) Base load
(b) High load
(c) Variable load
(d) Both a & b
5. Nuclear power plant has
(a) Initial cost too high
(b) Very low per unit cost
(c) Running cost too low
(d) All of these
6. Initial cost of a nuclear power plant is
(a) Very low
(b) Medium
(c) Very high
(d) Suitable
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7. In a nuclear power plant, this cost is negligible
(a) Construction of reactor
(b) Transport of fuel
(c) Fuel to be used
(d) All of these
8. The process of splitting or dividing of uranium atoms is called
(a) Fission
(b) Fusion
(c) Chain Reaction
(d) Radiation
9. Work of the coolant is
(a) Gaining heat
(b) Generating heat
(c) Absorbing neutrons
(d) Generating a chain reaction
10. The total number of protons and neutrons of an atom is called
(a) Atomic number
(b) Mass number
(c) Atomic weight
(d) None of these
11. --------- are the primary isotopes of uranium
(a) U234
(b) U235
(c) U238
(d) All of these
12. This isotope of uranium is used for nuclear fission reactions
(a) U234
(b) U235
(c) U233
(d) U238
13. The charge on Alfa particles is
(a) Positive
(b) Negative
(c) Both a & b
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(d) Neutral
14. The charge on Beta particles is
(a) Positive
(b) Negative
(c) Both a & b
(d) Neutral
15. During uranium enrichment, the amount of uranium in raw uranium is
increased from 0.7% to this percentage
(a) Up to one percent
(b) Up to three to four percent
(c) Up to 10 percent
(d) Up to 30 to 40 percent
16. This method is being used to enrich uranium at the Kahuta plant in
Pakistan
(a) Thermal diffusion method
(b) Gaseous permeability method
(c) Centrifugal method
(d) Electromagnetic method
17. ------ is the chemical name for heavy water
(a) Hydrogen peroxide
(b) Hydroxide
(c) Deuterium Oxide
(d) None of these
18. ----- is used to send neutrons escaping out of the reactor core back into
the core
(a) Moderator
(b) Coolant
(c) Shielding
(d) Reflector
19. Graphite and beryllium materials are used in nuclear reactors
(a) As moderators
(b) As reflectors
(c) As shielding
(d) Both a & b
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20. In addition to graphite, beryllium and heavy water, this material can also
be used as a moderator
(a) Light water
(b) Helium gas
(c) Carbon and nitrogen
(d) All of these
21. Control rods in nuclear reactors are made of this material
(a) Zirconium
(b) Boron
(c) Beryllium
(d) Lead
22. Basic types of nuclear reactors are
(a) Thermal reactor
(b) Fast reactor
(c) Both a and b
(d) None of these
23. The most important problem occurs in nuclear power stations
(a) Control of the plant
(b) Disposal of nuclear waste
(c) Access to the plant
(d) Availability of water
24. This power plant has the highest cost
(a) Hydro
(b) Thermal
(c) Nuclear
(d) Diesel
25. Nuclear power station in Pakistan is working at
(a) Karachi
(b) Chashma
(c) Kahuta
(d) All of these
26. Pakistan's second nuclear power plant has been installed at this location
(a) Gwadar
(b) Karachi
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(c) Sibbi
(d) Chashma
Answer to MCQ’s
1.
d
2.
c
3.
a
4.
b
5.
a
6.
c
7.
c
8.
a
9.
a
10.
b
11.
b
12.
b
13.
a
14.
b
15.
b
16.
c
17.
c
18.
d
19.
d
20.
d
21.
b
22.
c
23.
b
24.
c
25.
b
26.
d
Sample Short Questions
1. What is meant by nuclear power station?
2. Write the advantages of nuclear power station.
3. Write down the disadvantages of nuclear power station.
4. What is the principle of nuclear energy based on?
5. Write the names of the main parts of Nuclear Par Station.
6. What are Alfa particles?
7. What are Beta particles?
8. What are gamma rays?
9. What is meant by nuclear reaction?
10. What is meant by chain reaction?
11. Write the names of any four to four elements.
12. What is meant by fashion?
13. What is meant by fusion?
14. What are moderators and what materials are used as moderators?
15. What is meant by reactor core?
16. What is meant by coolant or cooling system? Which materials are
used as coolant in a nuclear reactor?
17. On what principle does the gas permeation method for uranium
enrichment work?
18. What is meant by centrifuge? Explain its use.
19. What is meant by heavy water?
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20. Define nuclear reactor.
21. Write the names of the main parts of a nuclear reactor.
22. On what basis can reactors be divided into opposite types?
23. Name the types of reactors based on neutron energy.
24. Write the names of types of thermal reactors.
25. Write four advantages of pressurized water reactor.
26. Name the main parts of a pressurized water reactor.
27. What words is CANDU an abbreviation for?
28. What considerations are taken into account while selecting a site for
a nuclear power plant?
29. Where are the nuclear power plants working in Pakistan?
30. Define gas led reactor.
31. How far has Pakistan succeeded in enriching uranium?
Sample Long Questions
1. Write a detailed note on nuclear power station and its main parts
using schematic diagram?
2. Describe nuclear fusion?
3. Describe nuclear fission?
4. Write a note on boiling water reactor?
5. Write a note on pressurized water reactor?
6. Write a note on CANDU reactor?
7. Write a note on gas cooled reactor?
8. Write a note on Liquid metal cooled reactor?
9. Write a note on homogeneous reactor?
10. Write a note on fast breeder reactor?
11. Describe the construction and working of a nuclear reactor?
12. Describe salient features of nuclear power station working in
Pakistan?
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CHAPTER 4 HYDEL POWER STATION
Chapter objectives:
After studying this chapter, a student will be able to
 Understand different types of hydro- electric power stations.
 Understand working of Hydel power stations.
 Understand requirements of site selection for installation of
hydel power plant.
 Understand general arrangements and operation of hydel
power station.
 Understand types of hydel turbines and their characteristics.
 Understand about hydro-electric power plants working in
Pakistan along with their capacities.
4.1 Introduction to Hydel Power station
Hydel power stations, also known as hydroelectric power stations, are facilities
that generate electricity using the kinetic energy of falling or flowing water.
This type of power station is a popular form of renewable energy and has been
in use for over a century. It is an efficient and clean source of electricity that
produces minimal pollution and carbon emissions.
The concept behind hydel power stations is simple - moving water can be used
to turn turbines, which drive generators to produce electricity. In a hydel
power station, water is usually stored in a reservoir behind a dam, and when
released, flows through the turbines and drives the generators.
The development of hydel power stations started in the late 19th century
when water wheels were used to power mills and factories. The first hydel
power station was built in 1878 in Northumberland, England, and used
turbines to generate electricity. Over the years, the technology behind hydel
power stations has advanced, leading to more efficient and powerful systems.
Hydel power stations are found in many parts of the world, including countries
like China, Pakistan, Canada, Brazil, and the United States. In fact, hydel power
accounts for around 16% of the world's total electricity generation. In some
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countries, hydel power is the primary source of electricity, with Norway and
Iceland generating over 99% of their electricity from hydel power stations.
Advantages:
a. Hydroelectric power is renewable and clean. It does not
produce greenhouse gases or air pollutants that contribute to
climate change or health problems.
b. Hydroelectric power is inexpensive in the long run. Once the
infrastructure is built, the maintenance costs are low and the
energy production is reliable and stable.
c. Hydroelectric power can be used for irrigation and flood
control. The reservoirs created by dams can provide water for
agriculture and prevent flooding downstream.
d. Hydroelectric power can be adjusted to meet the demand. The
turbines can be turned on or off quickly to respond to changes
in electricity consumption.
Disadvantages:
a. Hydroelectric power can have negative impacts on the
environment and wildlife. The construction of dams and
reservoirs can alter the natural flow of rivers, affect fish
migration, destroy habitats, and displace people and
communities.
b. Hydroelectric power is dependent on local hydrology and
climate. The availability and quality of water can vary
depending on rainfall, drought, evaporation, and
sedimentation.
c. Hydroelectric power is expensive to build and may face public
opposition.
4.2 Classification of Hydel Power Station
Hydroelectric power plants are a form of renewable energy generation that
harnesses the power of flowing water to produce electricity. These plants are
classified based on several factors, including their head, water flow
availability, and loading type.
4.2.1 Classification of hydroelectric power plants w.r.t head
Hydroelectric power plants can also be classified based on the head, which
refers to the vertical distance between the water level at the upstream of the
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plant and the water level at the downstream of the plant. The head is an
important parameter that affects the efficiency and design of a hydroelectric
power plant.
Here are the three main types of hydroelectric power plants based on the
head:
1. High head
High head hydroelectric power plants typically have a head of more than 80
meters. These plants are usually located in mountainous regions where there
is a significant drop in elevation over a short distance. The high head results in
a high potential energy that can be converted to electricity efficiently. These
plants usually have a smaller capacity, typically less than 50 MW.
Figure 4.1. High head power plant
2. Medium head
Medium head hydroelectric power plants typically have a head between 20
and 80 meters. These plants are often located on medium-sized rivers or at
the base of dams. They can have a capacity ranging from a few megawatts to
several hundred megawatts. The medium head allows for efficient electricity
generation without requiring a large amount of water flow.
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Figure 4.2. Medium head power plant
3. Low head
Low head hydroelectric power plants typically have a head of less than 20
meters. These plants are often located on low-gradient rivers and canals. They
require a large water flow to generate electricity efficiently. Low head
hydroelectric power plants can have a capacity ranging from a few kilowatts
to several megawatts.
In addition to these three main types, there are also hydroelectric power
plants that are classified as ultra-low head, which have a head of less than 2
meters. These plants are usually located in areas with a large water flow, such
as tidal estuaries or irrigation canals. They require innovative designs and
technologies to efficiently convert the kinetic energy of water into electricity.
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Figure 4.3. Low head power plant
4.2.2 Classification of hydroelectric power plants w.r.t availability
of water flow
Hydroelectric power plants can be classified based on the available water flow,
which can have a significant impact on their design and operation. Here are
the three main types of hydroelectric power plants based on water flow:
1. Run off river power plants without pondage
These are the type of hydroelectric generation plant that do not have any
water storage facility. They use the natural flow of the river to produce
electricity, but they cannot control the amount or timing of the water
availability. This makes them an intermittent and unreliable energy source,
especially during dry seasons or low run off periods. These plants are suitable
for locations where there is no possibility of creating a reservoir or a pond
behind a dam, and where the environmental or social impacts of such
structures are undesirable.
2. Run off river power plants with pondage
Run off river power plants with pondage are a type of hydroelectric power
generation that use the natural flow of water from a river to produce
electricity. Unlike conventional dams, they do not create large reservoirs that
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can affect the environment and the people living nearby. Instead, they have a
small pond or basin that can store some water and regulate the flow to the
turbines. This allows them to adjust to the fluctuations in demand and supply
of electricity. Run off river power plants with pondage are more flexible and
reliable than run off river power plants without pondage, which depend
entirely on the availability of water in the river. However, they also require
more civil works and maintenance than the latter. Run off river power plants
with pondage are suitable for locations where there is a high variation in water
flow throughout the year, and where there is enough space for building a pond
or basin.
3. Reservoir Hydroelectric Power Plants
Reservoir power plants are a type of hydroelectric power plants that use dams
to store water in a reservoir. The stored water can be released through
turbines to generate electricity when needed. Reservoir power plants have
several advantages, such as providing a reliable and flexible source of
renewable energy, regulating water flow and preventing floods, and creating
recreational opportunities for fishing and boating. However, reservoir power
plants also have some drawbacks, such as displacing people and wildlife,
affecting water quality and temperature, and emitting greenhouse gases from
decomposing organic matter.
4.2.3 Classification of hydroelectric power plants w.r.t loading
Hydroelectric power plants can also be classified based on their loading, which
refers to the amount of electrical power that they are generating at any given
time. Here are the three main types of hydroelectric power plants based on
loading:
1. Base Load Hydroelectric Power Plants
These types of hydroelectric power plants are designed to operate at a
constant output level, typically at or near their maximum capacity. They are
used to provide a stable and reliable source of electricity to meet the baseline
demand of the electric grid. Base load hydroelectric power plants are usually
large in size and have a high efficiency, which allows them to generate
electricity at a lower cost than other types of power plants.
2. Peak Load Hydroelectric Power Plants
These types of hydroelectric power plants are designed to operate at a high
output level for short periods of time, typically during periods of peak
electricity demand. They are used to provide additional power to the electric
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grid when demand exceeds the capacity of the base load power plants. Peak
load hydroelectric power plants are typically smaller in size than base load
plants and may have a lower efficiency.
3. Pumped-Storage Hydroelectric Power Plants
These types of hydroelectric power plants are designed to operate as both
base load and peak load plants. During periods of low electricity demand,
water is pumped from a lower reservoir to an upper reservoir. When
electricity demand is high, the water is released from the upper reservoir
through turbines to generate electricity. Pumped-storage hydroelectric power
plants can be used to balance the load on the electric grid and are usually
operated during periods of peak demand.
4.3 Merits & demerits of Hydel Power Station
There are several merits and demerits of a hydel power station. Some of these
are given below:
Merits of Hydel Power Station
a. Hydroelectric power is a renewable source of energy, which
means it does not deplete natural resources and can be used
indefinitely.
b. Once a hydroelectric power plant is built, it has low operating
costs compared to other types of power plants.
c. Hydroelectric power plants have a long life span of up to 50-100
years.
d. Hydroelectric power plants do not produce greenhouse gas
emissions, which makes them a clean energy source.
e. Hydroelectric power plants can be quickly turned on or off,
making them an ideal source of energy for meeting peak
electricity demands.
Demerits of Hydel Power Station
a. Hydroelectric power plants can have a significant impact on the
local ecosystem and wildlife, particularly if they involve dam
construction and reservoir creation.
b. Building a hydroelectric power plant can be expensive,
particularly if it involves dam construction and reservoir
creation.
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c. Hydroelectric power plants depend on a steady supply of
water, which can be affected by droughts or other changes in
climate.
d. There is always a risk of dam failure or other equipment failures
associated with hydroelectric power plants, which can have
serious consequences.
e. The construction of hydroelectric power plants can lead to the
displacement of communities living in the affected areas.
4.4 Selection of site for Hydel Power Station
Hydel power stations are facilities that use water to generate electricity. They
are one of the most economical and environmentally friendly sources of
renewable energy. However, they require careful planning and design to
ensure optimal performance and minimal impact on the natural environment.
One of the most important aspects of hydel power station development is the
selection of site.
The selection of site for hydel power station depends on several factors, such
as:
a. Water availability
The site should have a reliable and sufficient supply of water throughout the
year. The water availability can be estimated from the rainfall data, runoff
data, and mass curve analysis of the catchment area. The water availability
determines the capacity and output of the hydel power station.
b. Water storage
The site should have adequate storage capacity to store water during periods
of excess rainfall and release it during periods of low rainfall. The storage
capacity can be calculated from the mass curve analysis and the variation of
water demand. The storage capacity affects the cost and reliability of the hydel
power station.
c. Water head
The site should have a high water head, which is the difference in elevation
between the water source and the turbine. The water head determines the
potential energy of the water and the efficiency of the hydel power station. A
higher water head requires less water flow and reduces the size and cost of
the turbine and penstock.
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d. Accessibility of the site
The site should be easily accessible by road or rail for transportation of
materials, equipment, and personnel. The accessibility of the site affects the
construction time and cost of the hydel power station.
e. Distance from load center
The site should be close to the load center, which is the area where the
electricity is consumed. The distance from load center affects the transmission
loss and cost of the hydel power station. A shorter distance reduces the
voltage drop and line losses and improves the power quality and stability.
f. Environmental aspects
The site should have minimal impact on the environment, such as wildlife,
vegetation, soil, water quality, and social aspects. The environmental aspects
can be assessed by conducting environmental impact assessment (EIA) studies
and obtaining necessary permits and clearances from relevant authorities. The
environmental aspects affect the public acceptance and sustainability of the
hydel power station.
g. Geology
The geology of the site is another important factor to consider when selecting
a site for a hydropower plant. The site should have a stable geological
structure that can support the weight of the dam, reservoir, and other
infrastructure. The presence of faults, landslides, or other geological hazards
can pose a significant risk to the safety and stability of the plant.
4.5 General arrangement and operation of Hydel Power
Station
A hydroelectric power plant is a renewable source of energy that uses the
potential energy of water stored in a dam or a reservoir to generate electricity.
It is the most used power plant in many countries. The basic principle of
operation is as follows.
Height difference is created by building a dam in front of water reservoir and
then water from the reservoir flows through a pipe called a penstock and
reaches a water turbine. The water turbine converts the kinetic energy of the
water into mechanical energy, which drives a generator. The generator
converts the mechanical energy into electrical energy, which is then
transmitted to the grid or consumers. One can determine the power
availability from a hydroelectric power plant using equation given below.
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P = 981 x ρ x q x g x h
Where
ρ= water density (kg/m3) which is typically 1000 kg/m3 for water.
q= water flow (m3/s)
g= acceleration of gravity which is 9.81 m/s2
h= head (m)
A hydroelectric power plant is a complex system that consists of various
components that work together to convert the energy of falling water into
electricity. Each component plays a crucial role in the operation of the plant,
and any failure in one component can affect the entire system's performance.
In this article, we will discuss the different components of a hydroelectric
power plant.
Figure 4.4. General arrangement of a hydroelectric power station
1. Forebay
Forebay is a term used to describe a reservoir or pond that regulates the flow
of water into a hydroelectric power plant or a canal. Forebays are usually
located near the intake structure of the plant or canal and help to control the
water level and prevent debris from entering the system. Forebays can also
provide recreational opportunities such as fishing, boating and swimming.
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2. Dam
The dam is the most visible and essential component of a hydroelectric power
plant. It is a massive concrete or earthen structure that is built across a river
or stream to create a reservoir. The dam's primary function is to store water
and control its flow to the turbines. The height of the dam determines the
head, which is the potential energy available to generate electricity.
3. Intake Structure
The intake structure is a structure located at the bottom of the dam that
collects water from the reservoir and channels it towards the turbines. The
intake structure may contain trash racks and screens to prevent debris from
entering the turbines.
4. Penstock
The penstock is a large pipe that carries water from the intake structure to the
turbines. The penstock is usually made of steel or concrete and is designed to
withstand high pressure and velocity. The diameter of the penstock depends
on the volume of water flow and the head.
5. Surge Tank
A surge tank is a device that is used to control the pressure fluctuations in a
fluid system. A surge tank can absorb or release fluid to balance the pressure
changes caused by events such as pump start-up or shut-down, valve opening
or closing, or sudden demand changes. A surge tank can also provide
additional storage capacity for the system and prevent water hammer or
cavitation. A surge tank can be classified into three types: simple surge tank,
throttled surge tank, and differential surge tank. Each type has its own
advantages and disadvantages depending on the system requirements and
design.
6. Turbines
The turbines are the heart of the hydroelectric power plant. They are located
at the end of the penstock and convert the potential energy of falling water
into mechanical energy. There are different types of turbines used in
hydroelectric power plants, such as Pelton, Francis, and Kaplan. The type of
turbine used depends on the head and volume of water flow.
7. Draft Tube
A draft tube is a component of a hydroelectric power plant that connects the
outlet of the turbine to the tailrace, where the water is discharged. The draft
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tube has a diverging shape that reduces the velocity of the water and increases
its pressure, thus improving the efficiency of the turbine. The draft tube also
allows the turbine to be placed above the tailrace level, which facilitates
maintenance and reduces excavation costs. There are different types of draft
tubes, such as conical, elbow, or moody, depending on the shape and crosssection of the tube.
8. Tailrace
The tailrace is an important component of a hydroelectric power plant. It is
the channel that carries the water away from the turbine after it has been used
to generate electricity. The tailrace connects the power station to the natural
watercourse, such as a river or a lake. The tailrace affects the efficiency and
performance of the power plant, as it determines the net head available for
power generation. The net head is the difference between the water level in
the upstream reservoir and the water level in the tailrace. A lower tailrace
level means a higher net head and more power output. Therefore, it is
desirable to design the tailrace to minimize its resistance and friction losses,
and to avoid backwater effects from the downstream watercourse.
9. Generator
The generator is connected to the turbine and converts the mechanical energy
of the turbine into electrical energy. The generator is usually a large and heavy
machine and requires a stable foundation to operate correctly.
10. Transformer
The transformer is a device that increases the voltage of the electricity
generated by the generator to a level suitable for transmission. The
transformer is usually located near the generator and is connected to the
power grid through transmission lines.
11. Switchgear
The switchgear is a device that controls the flow of electricity from the
generator to the transformer and then to the transmission lines. The
switchgear includes circuit breakers, relays, and other protective devices that
prevent damage to the equipment in case of a fault.
4.6 Types of Hydel turbines and their characteristic
Hydroelectric power plants are a significant source of renewable energy, and
turbines are the key components that convert the potential energy of falling
water into mechanical energy. There are different types of turbines used in
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hydroelectric power plants, and they can be broadly classified into two
categories: impulse turbines and reaction turbines.
4.6.1 Impulse Turbines
Impulse turbines are used in hydroelectric power plants where there is a high
head and low flow rate of water. These turbines work by directing a jet of
water onto a set of buckets or vanes, which then spin the turbine shaft. There
are three types of impulse turbines: Pelton wheel, Turgo, and Crossflow.
a. Pelton wheel Turbines
Pelton turbines are the most commonly used impulse turbines in hydroelectric
power plants. They are used in high head applications, and their design allows
for maximum efficiency in the conversion of water energy into mechanical
energy. The Pelton turbine consists of a set of buckets mounted on a wheel,
with each bucket split in the middle. The jet of water is directed onto the
buckets, and the split design allows the water to be deflected and exit the
bucket cleanly, resulting in high efficiency.
Figure 4.5. Pelton wheel turbine
b. Turgo Turbines
Turgo turbines are also impulse turbines that are used in high head
applications. They are similar to Pelton turbines, but instead of having buckets,
they have cups. The cups are arranged in a circular pattern around the turbine
shaft, and the water jet is directed onto the cups, causing the turbine to spin.
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Turgo turbines are more compact than Pelton turbines, making them suitable
for sites where space is limited.
Figure 4.6. Turgo turbine
c. Cross flow Turbines
Crossflow turbines are also impulse turbines that are used in low head
applications. They consist of a vertical axis turbine with blades that are
arranged in a circular pattern. The water flows into the turbine from the top
and exits through the sides, causing the turbine to spin. Crossflow turbines are
less efficient than Pelton and Turgo turbines but are suitable for sites where
there is a low head and high flow rate.
Figure 4.7. Cross flow turbine
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4.6.2 Reaction Turbines
Reaction turbines are used in hydroelectric power plants where there is a low
head and high flow rate of water. These turbines work by directing water onto
a set of blades, which then spin the turbine shaft. There are two types of
reaction turbines: Francis and Kaplan.
a. Francis Turbines
Francis turbines are the most commonly used reaction turbines in
hydroelectric power plants. They are used in medium to high head
applications and have an efficiency range of 85% to 95%. Francis turbines
consist of a set of curved blades that are arranged around the turbine shaft.
The water flows into the turbine and passes through the blades, causing the
turbine to spin. Francis turbines are suitable for sites where the head is
between 30 and 600 meters.
Figure 4.8. Francis turbine
b. Kaplan Turbines
Kaplan turbines are also reaction turbines that are used in low head
applications. They consist of a propeller-like blade that is adjustable, allowing
for greater efficiency in different flow conditions. The water flows into the
turbine and passes through the blades, causing the turbine to spin. Kaplan
turbines are suitable for sites where the head is less than 30 meters.
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Figure 4.9. Kaplan turbine
4.7 Governing of Turbines
Hydroelectric turbines are an essential part of hydropower generation
systems, which convert the potential energy of falling water into mechanical
energy that can be used to generate electricity. To ensure the safe and
efficient operation of hydroelectric turbines, it is essential to have a proper
governing system in place. A governing system is a set of control mechanisms
and devices that regulate the speed, output, and stability of the turbine and
generator.
There are several different types of governing systems used in hydroelectric
turbines, but the basic principles are similar. The governing system consists of
three main components: the speed governor, the hydraulic power unit, and
the control valve.
The speed governor is responsible for maintaining the rotational speed of the
turbine at a constant level. It does this by monitoring the speed of the turbine
and adjusting the position of the control valve accordingly. The governor is
typically an electronic or hydraulic device that senses changes in the speed of
the turbine and sends signals to the control valve to open or close as
necessary.
The hydraulic power unit provides the pressure required to operate the
control valve. It consists of a hydraulic pump, a reservoir, and a set of valves
that control the flow of hydraulic fluid to the control valve. The hydraulic
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power unit is responsible for supplying the necessary pressure to the control
valve to ensure that it operates smoothly and accurately.
The control valve is the device that regulates the flow of water through the
turbine. It is typically a large, multi-stage valve that is designed to operate
under high pressure and flow conditions. The control valve is controlled by the
speed governor and the hydraulic power unit, and it is responsible for
adjusting the flow of water through the turbine to maintain a constant speed
and output.
In addition to these three main components, a governing system may also
include other devices such as pressure sensors, temperature sensors, and
vibration sensors. These devices are used to monitor the performance of the
turbine and provide feedback to the governing system so that it can make
appropriate adjustments.
Overall, a well-designed governing system is essential for the safe and efficient
operation of hydroelectric turbines. It ensures that the turbine operates at a
constant speed and output, which maximizes the efficiency of the hydropower
generation system. Additionally, it helps to prevent damage to the turbine and
other components of the system, which can reduce maintenance costs and
improve overall system reliability.
4.8 Comparison between turbines
Hydroelectric power plants use turbines to convert the potential energy of
falling water into mechanical energy that can be used to generate electricity.
There are two main types of turbines used in hydroelectric power plants:
reaction turbines and impulse turbines. While both types of turbines serve the
same basic function, they operate on different principles and have distinct
advantages and disadvantages. Here is a detailed comparison between the
two:
a. Operating Principle
The main difference between reaction and impulse turbines is their operating
principle. Impulse turbines use the kinetic energy of a high-velocity jet of
water to drive the turbine blades, while reaction turbines use the pressure and
momentum of a high-pressure water flow to drive the turbine blades.
b. Design
Impulse turbines have a series of buckets or blades mounted around the
circumference of the turbine wheel. Water enters the turbine through a nozzle
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and is directed onto the blades, causing the wheel to rotate. Reaction turbines
have curved blades that are mounted on a shaft, with water entering the
turbine from the sides and passing over the blades to generate the rotational
force.
c. Efficiency
Impulse turbines are generally more efficient than reaction turbines at low
head and high flow rates. They operate at high rotational speeds, which allows
them to extract more energy from the water flow. On the other hand, reaction
turbines are more efficient at high head and low flow rates, as they are
designed to operate under high pressure conditions.
d. Size
Impulse turbines are typically smaller than reaction turbines because they
operate at higher rotational speeds and can generate more power in a smaller
space. Reaction turbines require a larger area to accommodate the curved
blades and the high-pressure water flow.
e. Maintenance
Impulse turbines are generally easier to maintain than reaction turbines
because they have fewer moving parts and are less complex. However, they
require more frequent cleaning and inspection due to the accumulation of
debris in the bucket or blade passages. Reaction turbines require more
maintenance due to the complexity of the curved blades and the hydraulic
control systems.
f. Cost
Impulse turbines are generally less expensive to manufacture and install than
reaction turbines due to their smaller size and simpler design. Reaction
turbines are more expensive to manufacture and install due to their larger size
and more complex design.
4.9 Hydro- electric generation in Pakistan
Hydroelectric power is one of the major sources of electricity generation in
Pakistan. The country is blessed with a number of large rivers, including the
Indus, Jhelum, Chenab, and Sutlej, which provide abundant water resources
for hydroelectric power generation.
Currently, Pakistan has an installed capacity of around 9,000 MW of
hydroelectric power, which accounts for around one-third of the country's
total installed capacity. The majority of the hydroelectric power plants in
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Pakistan are located in the northern regions, particularly in the mountainous
areas of Khyber Pakhtunkhwa and Gilgit-Baltistan.
The Tarbela Dam, located on the Indus River in Khyber Pakhtunkhwa, is the
largest hydroelectric power station in Pakistan, with an installed capacity of
4,888 MW. The Mangla Dam, located on the Jhelum River in Azad Jammu and
Kashmir, is the second-largest hydroelectric power station in Pakistan, with an
installed capacity of 1,100 MW.
In addition to these large power stations, there are also several small and
medium-sized hydroelectric power plants scattered throughout the country.
These include the Ghazi-Barotha Hydropower Project, located on the Indus
River near Islamabad, which has an installed capacity of 1,450 MW, and the
Allai Khwar Hydropower Project, located in Khyber Pakhtunkhwa, which has
an installed capacity of 121 MW.
Pakistan has ambitious plans to further develop its hydroelectric power sector
in order to meet its growing electricity demand and reduce its dependence on
imported fossil fuels. The government has set a target of increasing the
country's installed hydroelectric capacity to 30,000 MW by 2030, which would
require significant investment in new hydroelectric power projects.
One of the major challenges facing the hydroelectric power sector in Pakistan
is the issue of water scarcity, particularly during the dry summer months when
water levels in the rivers are low. Climate change is expected to exacerbate
this problem, leading to more frequent droughts and reduced water
availability for hydropower generation.
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Sample Multiple Choice Questions
1. A power station in which the potential energy of water at a higher level is
used to generate electrical energy
(a) Thermal Power Station
(b) Tidal Power Station
(c) Hydel Power Station
(d) Nuclear Power Station
2. A means of generating electricity that requires more land than other
methods
(a) Thermal Power Plant
(b) Nuclear Power Plant
(c) Hydro Power Plant
(d) Diesel Power Plant
3. Pakistan has a large hydel power station at
(a) Tarbela
(b) Mangala
(c) Warsak
(d) All
4. A hydel power station can be installed where
(a) Fuel is available in abundance
(b) Water is available in abundance with adequate head
(c) Both a & b
(d) None of these
5. It is the primary source of water
(a) Rain
(b) Snow-fall
(c) River & canals
(d) Both a & b
6. They are usually mounted on the same shaft
(a) Turbine and generator
(b) Turbine and exciter
(c) Generator and exciter
(d) Turbine, generator and exciter
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7. The water level in a storage reservoir or water storage pond is called
(a) Headrace
(b) Tailrace
(c) Penstock
(d) None of these
8. The outlet through which the water discharged from the turbine is called
(a) Headrace
(b) Tailrace
(c) Penstock
(d) Breaking jet
9. The purpose of a lake is to store water and provide --------(a) Electricity
(b) Area
(c) Head
(d) Fishes
10. All the area behind the dam where water collects from rain and
snowmelt
(a) Lake
(b) Catchment area
(c) Plant area
(d) Flood area
11. Long tunnels are used for the plant
(a) Thermal
(b) Nuclear
(c) Hydel
(d) Tidal
12. This part is not used in hydel power plants
(a) Search tank
(b) Forebay
(c) Compressor
(d) Penstock
13. A sudden load increase on the generator may cause penstock
(a) Vacuum
(b) High pressure
(c) Water hammer
(d) All of these
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14. It provides optimal regulation of water pressure in the system during
load changes in a hydel power station
(a) Governor
(b) Penstock
(c) Search tank
(d) None of these
15. The power generated in a hydropower plant depends on
(a) Lake and water
(b) Water volume and head
(c) Height of head
(d) Speed of water
16. Power is delivered from hydropower plants to consumers
(a) From transmission lines
(b) From distribution lines
(c) From microwaves
(d) None of these
17. A hydropower plant that takes water directly from a river is called a runof-river plant
(a) Without pond
(b) With pond
(c) Storage
(d) None of these
18. It acts as a natural surge tank in the run-off river plant containing pond
(a) Penstock
(b) Hydel turbine
(c) Forebay
(d) Dam
19. Power plants which operate at the lower part of the load curve are called
(a) Base load plant
(b) Peak load plant
(c) Pump storage power plant for peak load
(d) None of these
20. There are hydel power plants depending on the load
(a) Base load plants
(b) Peak load plants
(c) None of these
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(d) Both a and b
21. Pump storage hydel plant has ------ponds
(a)One
(b) Two
(c)Three
(d) Four
22. Power plants which operate at head which is less than 30 meters, are
called
(a) Low head plants
(b) Medium head plants
(c) High head plants
(d) None of these
23. It is a type of modern hydraulic turbine
(a) Impulse turbine
(b) Reaction turbine
(c) Both a and b
(d) None of these
24. A turbine which is driven by the force of water is called
(a) Impulse Turbine
(b) Reaction Turbine
(c) Pelton wheel
(d) None of these
25. This turbine does not require nozzles
(a) Impulse
(b) Reaction
(c) Both a and b
(d) None of these
26. A turbine whose blades are adjustable is called
(a) Propeller type
(b) Kaplan
(c) Francis
(d) None of these
27. Francis Turbine are actually
(a) Reaction turbine
(b) Impulse Turbine
(c) Axial flow turbine
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(d) Both a & c
28. Generators are used at low head hydel power plants
(a) Low speed
(b) Large diameter
(c) Both a & b
(d) Small diameter
29. A sudden increase in load on the generator of a hydel power plant can
prevent it from decelerating
(a) By increasing the excitation
(b) By increasing the amount of water
(c) By increasing the number of poles
(d) None of these
30. Hydroelectric generators have number of poles
(a)Two
(b) Four
(c)Six
(d) More than six
Answer to MCQ’s
1.
c
2.
c
3.
d
4.
b
5.
c
6.
a
7.
a
8.
b
9.
a
10.
a
11.
c
12.
c
13.
c
14.
a
15.
b
16.
a
17.
a
18.
c
19.
a
20.
d
21.
b
22.
a
23.
b
24.
c
25.
a
26.
b
27.
c
28.
c
29.
a
30.
d
Sample Short Questions
1. What is meant by hydel power station?
2. Which is the ideal place to build a dam for hydel power station?
3. What purposes does a hydroelectric power station serve?
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4.
5.
6.
7.
8.
On what principle does a hydroelectric power plant work?
How electric power is generated by hydel power generation method.
At which locations are the hydel power plants operating in Pakistan?
Write the advantages of hydel power plant.
What are the types of hydel power plants depending on the load
demand? Enter the name.
9. Name the types of hydel power plants depending on the availability of
head of water?
10. Write four disadvantages of pond-less run-of-river plant.
11. What is meant by reservoir or storage power plant?
12. What are base load plots?
13. Define pack load plants.
14. Write the names of types of hydel power plants depending on available
head of water.
15. What is the water head in low, medium and high head plants?
16. What is Penstock? Write the names of its types depending on the
temperature.
17. What is meant by tail race?
18. What is hydel turbine?
19. Name the types of reaction turbines depending on the direction of
water flow.
20. What is a Francis turbine and for what purpose is it used?
21. What is meant by governing of turbine?
22. Name the largest hydroelectric power plant in Pakistan and where is it
located?
Sample Long Questions
1.
2.
3.
4.
5.
6.
Enlist different types of hydro- electric power stations?
Write some merits and demerits of hydel power stations?
Explain requirements of site selection for installation of hydel
power plant?
Explain general arrangements and operation of hydel power
station with the help of suitable diagram.
Describe different types of hydel turbines.
Name hydro-electric power plants working in Pakistan along
with their capacities.
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Gas Turbine Power Station
CHAPTER 5 GAS TURBINE POWER STATION
Chapter objectives:
After studying this chapter, a student will be able to
 Understand the Gas power station.
 Understand the construction and working to simple gas turbine.
 Understand the layout of a gas turbine station.
 Understand the combined cycle power station.
 Understand the gas power stations in Pakistan.
 Understand the combined cycle power station in pakistan.
5.1 Introduction to Gas Power station
A gas turbine power station is an electric power station or plant that uses a
gas turbine as the prime mover to generate electrical energy. Gas turbine
power plants are generally inexpensive and may be put into service quickly. It
takes up a smaller area. This plant has a lesser capacity and is used mostly for
peak load service. Gas turbine power plants are extremely promising for areas
where liquid or gaseous fuel is abundant. Gas turbine installations consume a
fraction of the water that steam turbine installations do.
Gas turbine technology has advanced rapidly during the last decade, owing
primarily to extensive research. The size of gas turbine plants used in big
systems typically ranges from 10 to 25 MW, with the maximum amount
employed being around 50 MW. The thermal efficiency of a gas turbine plant
is between 22% and 25%.
In some cases, gas turbines are the least expensive type of plant available. In
these cases, they are employed as intermittent or peak load plants in
conjunction with base load plants. They are especially beneficial and cost
effective when the amount of energy required is a tiny portion of the total
energy to be supplied by the entire system and the load factor is less than 15%.
Because a portion of the mechanical power generated by the turbine is wasted
driving the compressor, gas turbine power plant efficiency is low (up to 25%).
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A diesel power plant varies from a diesel engine in that the fuel is burned in a
combustion chamber or combustor located outside the prime mover. A gas
turbine power plant is often used to generate electricity as a single load or
alternating current facility. Aside from the aviation and maritime industries,
these plants are also employed in the oil and gas industries. These plants are
ideal for places where there is an abundance of petrol or liquid fuel.
Gas turbine power plants are available in the different capacities. Such plants
are being installed in Pakistan to meet the increasing needs of electricity. At
present, Kotri 130MW, Shahdara 86MW, Faisalabad 200MW, Kot Addu
800MW, Karachi 225MW gas power plants are working in Pakistan.
A gas turbine power station or plant is shown in the figure 5.1.
Figure 5.1. Gas turbine power station
Advantages of gas turbine plant
a. It is smaller and lighter than a comparable steam power unit.
b. The starting and operating costs of the plant are lower than
those of an equivalent steam power station.
c. The plant consumes less water than a condensing steam
power plant.
d. The plant can be started quickly and loaded efficiently.
e. There are no standby losses in a gas turbine power plant.
Disadvantages of gas turbine plant
a. The compressor is operated from a major amount of the
turbine's produced work. As a result, the network output of
the facility is low.
b. Service circumstances get difficult as the temperature of the
combustion products rises too high, even at low pressures.
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c. These plants have a limited capacity and create a lot of noise.
d. Fuel is expensive, and its efficiency ranges from 22 to 25%.
The turbine also drives the compressor, resulting in reduced
effort with some power consumption.
5.2 Construction & working of simple gas turbine
A fundamental gas turbine plant employs a gas turbine as the prime mover
and solid gas as the driving medium.
5.2.1 Construction
The gas turbine generates electricity by utilizing the energy of burned gases
and high-pressure air that expands through a series of fixed and movable
blade rings. As a result, it resembles a steam turbine. A compressor is
necessary to obtain a high pressure of working fluid, which is required for
expansion.
Because the amount of working fluid and speed required are greater, a
centrifugal or axial compressor is typically used. The compressor is connected
to the turbine shaft since it is powered by the turbine. If the working fluid were
expanded in a turbine after compression, assuming no losses in either
component, the power developed by the turbine would be exactly equal to
that absorbed by the compressor, and the work done would be zero. However,
increasing the volume of the working fluid at constant pressure, or raising the
pressure at constant volume, can enhance the turbine's power output. Adding
heat after compression to raise the temperature of the working fluid may
accomplish either of these. To raise the temperature of the working fluid, a
combustion chamber is necessary, where combustion of air and fuel occurs,
raising the temperature of the working fluid.
As a result, a basic gas turbine cycle contains of
a. Compressor
b. Combustion chamber or Combustor
c. Turbine.
Because the compressor is linked to the turbine shaft, it absorbs some of the
power generated by the turbine, lowering efficiency. The network is thus the
difference between turbine work and compressor work necessary to drive it.
The following auxiliary equipment are also utilized to operate the major
elements of a gas turbine plant.
a. Starting motor or engine
b. Oil or gas system
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c. Fuel Control System
d. Auxiliary lubricating oil pump
e. Duct system
f. Oil coolers and filters
g. Inlet and exhaust silencers
h. Plant control panel
i. Alarm and shutdown automatic devices etc.
A basic gas turbine plant is shown in the figure 5.1.
Figure 5.1. Gas turbine power plant
a. Compressor
A compressor is a device that draws in common air and compresses it. It's
known as a compressor. Because of the large flow rates of turbines and the
comparatively low pressure ratios, rotary compressors are required. There are
two types of compressors that are typically used: centrifugal and axial flow.
The centrifugal compressor is made up of two parts: an impeller (which
rotates) and a diffuser (which is fixed). The impeller gives high kinetic energy
to the air, which the diffuser transforms into pressure energy. A pressure ratio
of 2 to 3 is feasible with a single stage compressor and up to 20 with a threestage compressor. Compressors can have a single or dual inlet. Single inlet
compressors are designed to handle air volumes ranging from 15 to 300
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m3/min, whereas twin inlets are preferred for capacities greater than 300
m3/min. Centrifugal compressors have an efficiency of 80 to 90%. Due to
losses, the efficiency of a multistage compressor is lower than that of a single
stage.
The axial flow compressor is made up of a sequence of rotor and stator stages
with decreasing diameters as the air flows through it. The blades are attached
to the rotor, which is attached to the shaft. The stator casing holds the stator
blades in place. The stator blades direct air flow from the previous rotor stage
to the next rotor stage. The air flows along the rotor's axis. As the air flows
past the rotor, some of its kinetic energy is turned into pressure. For a pressure
ratio of 5, the number of stages necessary can be as much as sixteen or more.
Because it is critical to retain the specified profile of the aero foil blades, a
good air filter is absolutely important for cleaning the air before it enters the
compressor. The accumulation of dust particles on the blade surfaces
significantly lowers efficiency. It has been discovered that reducing the inlet
air temperature by 15 to 20°C yields over 25% more output with a 5% increase
in efficiency in both types of compressors.
b. Combustion chamber or combustor
The place at which fuel combustion occurs. A combustor is another name for
the combustion chamber. The combustion process that occurs inside the
combustion chamber is critical because it provides energy that is later
transformed into work by the turbine. As a result, the combustion chamber
should ensure extensive mixing of fuel and air, as well as combustion products
and air, in order to produce complete combustion and equal temperature
distribution in the combustion gases. Because combustion losses have a direct
effect on the thermal efficiency of the gas turbine cycle, combustion should
take place at a high efficiency. Furthermore, pressure losses in the combustion
chamber should be minimized, and the combustion chamber should be large
enough and long enough to allow complete burning of the fuel.
The temperature in the combustion chamber is initially too high. The problem
is avoided by introducing a sufficient volume of air to sustain stable
combustion conditions, and then cooling the combustion products to a
temperature acceptable for use in gas turbines by introducing secondary air.
The total amount of air required for combustion is the sum of the primary and
secondary air supplied.
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The combustion chamber is cylindrical in shape, with a nozzle supplying fuel
and a compressor supplying high-pressure air. In the combustion chamber,
fuel is combined with heated air. The combustion of the fuel produces
extremely hot gases (about 3000°F). These gases's temperatures are
decreased to around 1400°F. There is a risk of the turbine blades melting if this
is not done. These high-temperature gases are introduced into the turbine,
where they expand and spin it. Combustor is depicted in the below figure 5.2.
Figure 5.2. Arrangement of combustor
A conical sleeve with a nozzle at the tip is enclosed within the cylindrical shell.
The sleeve contains the fuel spray and has openings for air intake. Inside the
cell, an igniting device is mounted. Fuel pumps are used to deliver fuel to the
combustion engine. The gases created by the combustion of the fuel in the
combustor are not pumped directly into the gas turbine, as this would cause
the turbine blades to melt. Air from the sleeve's later perforations reduces the
temperature of these hot gases to 650 °C from 800 °C, allowing them to work
easily in the gas turbine.
c. Gas turbine
A gas turbine is a mechanism that converts the kinetic energy of gases into
mechanical energy. When the blades are constructed to withstand higher
stresses, faster blade speeds can produce a high work output each stage. More
turbine stages are always preferable in gas turbine power plants since they
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help to alleviate tensions in the blades and extend the turbine's total life. More
stages are desired with stationary power plants because weight is not a
primary issue in the design, as it is in aircraft turbine-plants. Because gas
turbine blades are constantly exposed to high-temperature gases, cooling is
critical for their longevity. There are various methods for cooling the blades.
The most popular method is air cooling. The air is directed via the perforations
in the blade.
A turbine is made up of blades or vanes positioned on a shaft and contained
in a shell. It powers the turbine, compressor, and generator, which are all
connected by a single shaft. When the combustor's high pressure and
temperature gases enter the gas turbine, they expand and cause the turbine
to rotate.
Although the structures of steam turbines and gas turbines are similar, the
blades of gas turbines are made of different materials so that the high
temperature gases do not damage the blades. As a result, the hot gases can
spread across them and activate the rotor. The compressor and generator are
connected to the shaft of the gas turbine. In practise, 65 to 70% of the
turbine's output is used to drive the compressor, while only 30 to 35% is used
to generate electricity. The temperature of the gas turbine's output gases
ranges from 475 to 550 °C, which is used to generate steam in the combined
cycle boiler. Gas turbines have multiple stages. This extends the life and
efficiency of the turbine.
5.2.2 Working of simple gas turbine
When the equipment is turned on, the compressor draws in ambient air, which
is then raised to a static pressure several times that of the atmosphere (and at
a higher temperature). Fuel is injected into the combustor, where it burns in
the stream of air supplied from the compressor. The combustion products
(burned high temperature gases) are pushed into the turbine, where they
expand and produce motive force to drive the turbine rotor. The power
generated by the gases going through the turbine is utilized to power the
compressor and auxiliaries, while the remainder is used to generate electrical
energy (which drives the generator). The gases leave the turbine at
atmospheric pressure after expanding. The compressor can be positioned on
the same shaft as the turbine or linked to it. The temperature of the exhaust
gases ranges between 475 and 550°C.
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It is vital to notice that a portion of the air is given ahead of the burning fuel in
the compressor. This is done to cool the very hot combustion products, which
are around 1,600°C, down to a temperature range of around 650 to 800°C. In
the above simple system, approximately 65% of the generated power is used
to drive the compressor, therefore the net output is only about 20% of the
energy intake in the form of fuel.
Classification of gas turbine power plant:
The cycle of operation divides gas turbine power plants used in the electric
power industry into two classes.
(i)
Open cycle gas turbine.
(ii)
Closed cycle gas turbine.
a. Open Cycle Gas Turbine Power Plant
A simple open cycle gas turbine, as shown in Fig. 5.5, consists of a compressor,
combustion chamber, and turbine. The compressor takes in and compresses
outside air. Heat is added to the air in the combustion chamber by burning the
fuel, raising its temperature.
Figure 5.3. Open cycle gas turbine
The hot gases exiting the combustion chamber are then directed to the
turbine, where they expand and perform mechanical work. The turbine's
power is used to drive the compressor and other accessories, while the
remainder is used to generate electricity. Because ambient air enters the
compressor and turbine gases are discharged into the atmosphere, the
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working medium must be replaced on a constant basis. This sort of cycle is
known as an open cycle gas turbine plant, and it is widely employed in the
majority of gas turbine power plants due to its numerous intrinsic benefits.
Advantages
a. Once the starting motor has gotten the turbine up to rated
speed and the fuel has been ignited, the gas turbine will be
accelerated from cold start to full load without any warm-up
period.
b. The weight per kW developed is lower.
c. The combustion chamber may use almost any hydrocarbon
fuel, from high octane gasoline to heavy diesel oils.
Disadvantages
a. As a significant portion of the power generated by the turbine
is required to drive the compressor, the efficiency of the open
cycle plant declines rapidly.
b. The system is sensitive to component efficiency, notably
compressor efficiency. The open cycle plant is sensitive to
changes in the temperature, pressure, and humidity of the
surrounding air.
b. Closed Cycle Gas Turbine Power Plant
The closed cycle gas turbine plant was invented and developed in Switzerland.
J. Ackeret and C. Keller proposed this sort of machine in 1935, and the first
plant was erected in 1944 in Zurich. It operated on air and produced a useable
output of 2 MW. Since then, a number of closed cycle gas turbine plants have
been developed around the world, the largest of which has a capacity of 17
MW and has been in operation since 1967 at Gelsenkirchen, Germany. The
working fluid (air or any other suitable gas) exiting the compressor in a closed
cycle gas turbine plant is heated in a heater by an external source at constant
pressure. The gas turbine is fed by the high-temperature, high-pressure air
emitted by the external heater. Before moving to the compressor, the fluid
from the turbine is cooled to its original temperature in the cooler using an
external cooling source. The working fluid is utilised continuously in the
system without changing phases, and the heat exchanger provides the
appropriate heat to the working fluid.
Figure 5.4 depicts the component arrangement of the closed cycle gas turbine
plant.
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Figure 5.4. Closed cycle gas turbine
Closed cycle is only preferred to open cycle when using an inferior type of fuel
or solid fuel and there is adequate cooling water available at the planned plant
site.
However, closed cycle gas turbine plants have not yet been used to generate
power. This is primarily due to the constraints imposed by heat exchanger unit
size. The utilisation of a large number of parallel heat exchangers would
effectively negate the economic benefit of greater plant capacity. The air
backpressure, which limits the unit rating, is an intrinsic disadvantage of open
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cycle. This disadvantage can be overcome in a closed cycle plant by increasing
the cycle's backpressure. Because the air heater limits the unit rating, typical
closed cycle gas turbine facilities can only take advantage of this to a limited
extent. This disadvantage does not apply to closed cycle plants powered by a
nuclear reactor. With the use of a nuclear reactor as a gas heating source, the
heat exchangers in the closed cycle plant can be omitted, and the previously
indicated limitation (number of heat exchangers) is removed.
The combination of fast breeder reactors and gas turbines is projected to be a
very feasible option for power generation in the future. This is due to the
superior breeding qualities of the helium-cooled fast reactors, which provide
continuation of low fuel cost, while the use of a closed cycle gas turbine plant
is predicted to lower the facility's capital expenditure. Cost is roughly related
to weight as well. Turbo equipment is substantially less expensive than steam
plants.
Advantages
a. The air backpressure at the turbine exhaust is an inherent
drawback of open cycle gas turbines. Backpressure can be
increased in closed cycle gas turbine systems. Because of the
backpressure control, the unit rating can be increased in
proportion to the backpressure.
b. The closed cycle prevents turbine blade degradation from
polluted gases and compressor blade fouling from dust
c. The necessity for incoming air filtration, which is a major issue
in open cycle plants, is completely eliminated.
Disadvantages
a. The system is reliant on external means since a large amount
of cooling water is required in the pre-cooler.
b. Higher internal pressures necessitate a more intricate design
of all components, as well as the use of high quality materials,
which raises the plant's cost.
5.2.3 Terms and Definitions
a. Work Ratio
It is defined as the ratio of network output to total turbine work performed.
b. Thermal efficiency
It is defined as the network output to total fuel energy input ratio. The higher
the temperature of the working medium, the greater the turbine's thermal
efficiency.
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c. Air Ratio
It is defined as the amount of air entering the compressor inlet per unit of
turbine network output. The size of a gas turbine plant is determined by the
rate of air flow in relation to useful horse power production. The smaller the
plant, the lower the air rate. The air rate is reduced by intercooling and
reheating. The air rate will drop as the compressor and turbine efficiencies
improve. A rise in compressor input temperature reduces the net output of
the turbine and so raises the air rate.
d. Pressure Ratio
It is defined as the ratio of absolute pressure at the compressor outlet to
absolute ambient pressure at the compressor inlet.
e. Compression efficiency or machine efficiency
It is linked to compressors and is defined as the ratio of the work required for
optimal compression to the work required by the compressor for a given
pressure ratio.
5.3 Layout of a gas turbine station
The turbine house, which houses the plant's primary components and auxiliary
equipment, is the major structure in a gas turbine plant. In many ways, the
turbine house is comparable to the turbine house of a steam plant. Near the
turbine housing, fuel oil tanks or gas pipe systems are constructed. Heat
exchangers are also installed outside the building in specific setups.
Except for the intercoolers, heat exchangers, waste heat exchangers, and
connecting ductwork, all rotational sections of the plant, which account for a
very small portion of the total volume of the plant, are correctly integrated.
These machines take up the majority of the entire plant space.
Its air filters clean the air before supplying it to the compressor. The low
pressure compressor receives air from the air filters. The compressed air is
then routed through the intercooler to the high pressure (H.P) compressor.
The high pressure compressor released air enters the heat exchanger. The
heated air is then sent into the combustion chamber to accelerate the
combustion process. As illustrated in Figure 5.5, the combustion gases in the
combustion chamber are expanded first into the high pressure turbine and
then into the low pressure turbine.
The structure of the plant is also important so that the plant's efficiency does
not lose more than 20% of the generated power due to tiny bends, pipes, and
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ducts. This is why gas and air circuits are meticulously built. Layout of a gas
turbine station is depicted in the below figure.
Figure 5.5. Layout of a gas turbine power station
5.4 Introduction to combined cycle power station
When the heat contained in a gas turbine's exhaust gases is transferred to a
steam power plant's steam boiler, steam is created and used to drive the
steam turbine. A combined cycle power station is one that consists of a gas
power station and a steam power station that uses a combined cycle. They can
be utilized for peak load by operating a gas power plant station in conjunction
with other types of power stations such as steam and hydel power stations
(i.e. in the form of combined cycle). The gas turbine plant's ability to start
quickly has made it very popular. The combined cycle system was introduced
for these reasons. Its goal is to improve plant efficiency.
Exhaust gas temperatures in a basic gas turbine plant range from 475 to 550
degrees Celsius. Furthermore, exhaust gases contain around 16% oxygen,
compared to 21% in ambient air. As a result, these hot gases can be utilized to
speed up combustion in the boiler furnace or to heat the feed water. At the
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moment, the most efficient system is a combination system with a gas turbine
cycle.
The combined cycle improves thermal efficiency while increasing generated
power. Furthermore, the utilisation of combined cycle lowers the requirement
for extra equipment which further lowers the cost of plant. For combined
cycle, the three approaches listed below are commonly employed.
a. To use flue gases of gas turbine plant to heat feed water.
b. To use flue gases as combustion air in the steam boiler.
c. To use gases from a supercharged boiler to expand in the gas turbine.
a. To use flue gases of gas turbine plant to heat feed water
The temperature of the flue gases from the gas turbine is between 475 and
550 degrees Celsius. These gases are used to heat the boiler's feed water. This
reduces the boiler's fuel use. In some boilers, these gases serve the same
purpose as the gases produced by fuel combustion. In this instance, such
boilers do not require any fuel.
Figure 5.6. Use of flue gases to heat feed water in gas power plant
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b. To use flue gases as combustion air in the steam boiler
In this situation, gas turbine exhaust gases (Flue gases) are used as preheating
air for the boiler. The oxygen content in gas turbine discharge gases is around
16%. This amount of oxygen is sufficient to speed up the combustion process
in the boiler. This increases the boiler's efficiency. The combined cycle boosts
the plant's heating rate by up to 5%.
Figure 5.7. Use of flue gases as combustion air in the steam boiler
c. To use gases from a supercharged boiler to expand in the gas turbine
A steam generator or boiler with a supercharged furnace is utilized in place of
a gas turbine's combustion chamber in this combined cycle approach. The
compressor supplies air to the supercharged boiler, and the supercharged
boiler's exhaust gases (flue gases) are used in the gas turbine. Instead of a
combustor, a supercharged furnace boiler is employed for this purpose. Hot
gases emitted from the boiler enter the gas turbine and expand, causing the
turbine to rotate. While exiting, these gases also heat the feed water
connected to the boiler. This boosts a typical boiler's efficiency while lowering
its volume by 50%.
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Figure 5.8. Use of gases from a supercharged boiler to expand in the gas turbine
Advantages of Combined Cycle
The benefits of a combined cycle are as below.
a. The combined cycle power plant has a higher efficiency than a turbine
cycle or steam cycle plant. The combined cycle power plant's efficiency
will be in the range of 45% to 50%.
b. Compared to a reciprocating engine, it has fewer moving components
and produces less vibration.
c. The combined cycle plant can start and stop fast and easily.
d. A combined cycle uses less cooling water than a steam plant producing
the same amount of energy.
Disadvantages of Combined Cycle:
The following are the disadvantages of combined cycle.
a. Higher cost
b. Longer Startup time
c. Power demands are less responsive
d. A shrill whining sound
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5.5 Gas turbine and combined cycle plants in Pakistan
Gas turbine and combined cycle power plants are two major types of power
plants in Pakistan. In this article, we will discuss different gas-fired gas turbine
power plants and combined cycle power plants in Pakistan.
5.5.1 Gas Turbine Power Plants
a. Guddu Thermal Power Station
Guddu Thermal Power Station is a gas-fired power plant located in the
province of Sindh. It has a total capacity of 1,650 MW and consists of six gas
turbines, each with a capacity of 210 MW, and one steam turbine with a
capacity of 220 MW. The gas turbines at Guddu Thermal Power Station use
natural gas as their primary fuel. The plant was commissioned in the 1980s
and has since undergone several upgrades to improve its efficiency.
b. Nandipur Power Plant
Nandipur Power Plant is a gas-fired power plant located near the city of
Gujranwala in Punjab. It has a total capacity of 425 MW and consists of two
gas turbines, each with a capacity of 175 MW, and one steam turbine with a
capacity of 75 MW. The gas turbines at Nandipur Power Plant use a
combination of natural gas and diesel as their primary fuels. The plant was
commissioned in 2015 and is equipped with advanced control systems for
efficient operation.
5.5.2 Combined Cycle Power Plants
a. Balloki Power Plant
Balloki Power Plant is a combined cycle power plant located in the province of
Punjab. It has a total capacity of 1,223 MW and consists of two gas turbines,
each with a capacity of 409 MW, and one steam turbine with a capacity of 405
MW. The gas turbines at Balloki Power Plant use natural gas as their primary
fuel. In a combined cycle power plant, the exhaust heat from the gas turbines
is used to generate steam, which is then used to power a steam turbine,
resulting in higher efficiency compared to a gas turbine power plant. The plant
was commissioned in 2018 and is equipped with advanced combustion
technology for low emissions.
b. Haveli Bahadur Shah Power Plant
Haveli Bahadur Shah Power Plant is a combined cycle power plant located near
the city of Jhang in Punjab. It has a total capacity of 1,230 MW and consists of
three gas turbines, each with a capacity of 409 MW, and one steam turbine
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with a capacity of 3 MW. The gas turbines at Haveli Bahadur Shah Power Plant
use natural gas as their primary fuel. The plant was commissioned in 2018 and
is equipped with advanced control systems for efficient operation.
5.6 Environmental effects of Gas Turbine Plant and
measures to improve the situation
Gas turbine plants are widely used for power generation due to their high
efficiency and low emissions. However, like any other industrial activity, gas
turbine plants can have environmental effects. In this article, we will discuss
the environmental effects of gas turbine plants and measures that can be
taken to improve the situation.
5.6.1 Environmental Effects of Gas Turbine Plants
a. Air Pollution
Gas turbine plants emit pollutants such as carbon dioxide (CO2), nitrogen
oxides (NOx), sulfur dioxide (SO2), and particulate matter (PM). These
pollutants contribute to the formation of smog, acid rain, and respiratory
illnesses.
b. Water Pollution
Gas turbine plants consume large amounts of water for cooling purposes,
which can affect water quality and aquatic life. The discharged water can also
contain chemicals and metals that can harm the environment.
c. Noise Pollution
Gas turbine plants can produce noise pollution that can be disruptive to
nearby communities and wildlife.
5.6.2 Measures to Improve the Situation
a. Use of Cleaner Fuels
Gas turbine plants can use cleaner fuels such as natural gas, which produces
fewer emissions compared to coal or oil. The use of cleaner fuels can
significantly reduce the environmental effects of gas turbine plants.
b. Use of Advanced Technology
Advanced technology such as Selective Catalytic Reduction (SCR) and Gas
Turbine Inlet Air Cooling (GTIAC) can reduce NOx emissions and increase the
efficiency of gas turbine plants.
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c. Water Conservation
Gas turbine plants can conserve water by using alternative cooling methods
such as dry cooling or hybrid cooling systems. These methods can reduce
water consumption and minimize the environmental effects of gas turbine
plants.
d. Noise Mitigation
Gas turbine plants can use noise barriers and sound-absorbing materials to
reduce noise pollution and minimize the impact on nearby communities and
wildlife.
e. Environmental Impact Assessments
Before the construction of a gas turbine plant, an environmental impact
assessment should be conducted to identify potential environmental effects
and measures that can be taken to mitigate them.
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SAMPLE MULTIPLE CHOICE QUESTIONS
1. Gas tubines are used as prime movers
(a) In thermal power station
(b) In gas power station
(c) Both a & b
(d) None of these
2. A gas tubine consists of
(a) Compressor
(b) Combustion chamber
(c) Turbine
(d) All of these
3. Turbines use in gas turbine plants are
(a) Impulse
(b) Reaction
(c) Both a & b
(d) None of these
4. Gas turbine and compressor are usually mounted
(a) Separately
(b) On same shaft
(c) Nearly
(d) Away from each other
5. The second name of combustion chamber is
(a) Burner
(b) Combustor
(c) Fuel pump
(d) Stove
6. Advantage/s of gas turbine power station is/are
(a) Simple design
(b) Compact in size
(c) High Efficiency
(d) Both a & b
7. The disadvantage/s of gas turbine power plants is/are
(a) Produces noise
(b) Low efficiency
(c) Both a & b
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(d) Low operating speed of turbine
8. Compressor used in gas turbine is ----multistage compressor
(a) Centrifugal
(b) Rotary
(c) Axial
(d) All of these
9. Number of air inlet in centrifugal compressor is/are
(a) One
(b) Two
(c) One or Two
(d) Always more than two
10. Gas plant has
(a) High Efficiency
(b) High running cost
(c) Limited per unit capacity
(d) All of these
11. The place in which fuel is burned is called
(a) Combustion Chamber or combustor
(b) Burner
(c) Gas turbine
(d) Boiler
12. After mixing fuel with this, then It is used in gas turbine power plant
(a) Pure oxygen
(b) Common air
(c) Hydrogen
(d) SF6
13. When air is compressed through compressor in gas turbine plant, then it is
increased
(a) Temperature
(b) Pressure
(c) Both a & b
(d) Volume
14. Temperature of hot gasses in combustion chamber of gas turbine is
(a) 700 degree Fahrenheit
(b) 1400 degree Fahrenheit
(c) 3000 degree Fahrenheit
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(d) 2100 degree Fahrenheit
15. Blades of gas turbine are manufactured from this material
(a) Stainless Steel
(b) Carbon steel
(c) Pure copper
(d) High nickel alloy steel
16. The working of simple gas power plant depends on
(a) Open Cycle
(b) Closed Cycle
(c) Both a & b
(d) None of these
17. A cycle in which same air or gas is used again and again in compressor, is
called
(a) Open Cycle
(b) Closed Cycle
(c) Both a & b
(d) None of these
18. This is not used in Open cycle gas turbine power plant
(a) Compressor
(b) Heat Exchanger
(c) Normal Air
(d) Gaseous Fuel
19. It is essential for closed cycle power plant
(a) Large Heat Exchanger
(b) More cooling water
(c) Large Air
(d) Both a & b
20. Closed cycle gas turbine plant in comparison of open cycle plant has
(a) More complex
(b) Large size
(c) Simple
(d) Both a & b
21. In combined cycle, gasses exhaust from gas turbine are used in
(a) Compressor
(b) Turbine
(c) Boiler
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(d) Generator
22. Combined cycle power plant are more suitable for following loads
(a) Base Load
(b) Peak Load
(c) Both a & b
(d) Intermediate Load
23. In combined cycle, which another plant is installed with gas plant
(a) Steam Turbine Plant
(b) Pump Storage Hydel Plant
(c) Diesel engine plant
(d) None of these
24. The efficiency of gas turbine plant increases with the use of
(a) Combustor
(b) Compressor
(c) Combined Cycle
(d) Generator
25. Hot gasses exhaust from gas turbine plant consists of following
(a) Nitrogen Oxides
(b) Sulphur Diode
(c) Carbon monoxide
(d) All of these
Answrer to MCQ’s
1.
b
2.
d
3.
c
4.
b
5.
6.
d
7.
c
8.
d
9.
c
10. d
11.
a
12.
b
13.
c
14.
c
15. d
16.
c
17.
b
18.
b
19.
d
20. d
21.
c
22.
c
23.
a
24.
c
25. d
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SAMPLE SHORT QUESTIONS
1. Define gas turbine power plant.
2. Write the advantages of gas turbine power plant.
3. Write the disadvantages of gas turbine power plant.
4. Where are gas turbine power plants operating in Pakistan?
5. What is meant by simple gas turbine plant?
6. Draw a diagram of a simple gas turbine plant.
7. What is the function of a compressor in a gas turbine plant?
8. What is used to drive the compressor in a gas turbine power plant?
9. Define gas turbine.
10. Gas turbine plants are used for what purpose?
11. Write three reasons for using gas turbine plants on peak load.
12. How is gas turbine different from diesel engine?
13. Write four advantages of gas turbine plant over steam turbine plant.
14. What is meant by open cycle of a gas turbine plant?
15. What is the efficiency of open cycle gas turbine plants?
16. Write three disadvantages of open cycle gas turbine plant as compared
to closed cycle plant.
17. What is meant by closed cycle of gas turbine plant?
18. Write four advantages of closed cycle gas turbine power plant over
open cycle.
19. Write three disadvantages of closed cycle gas turbine power plant as
compared to open cycle.
20. What is the main difference between open and closed cycle gas turbine
power plants?
21. What is meant by combined cycle?
22. Define combined cycle power station.
23. Write any four advantages of combined cycle plant.
24. Which stations are we operating in the combined cycle system in
Pakistan?
25. Give a brief overview of Faisalabad Gas Power Plant.
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26. Which acidic components are released from the gas turbine power
plant and are harmful to human life and the environment?
27. Write down the effects of carbon monoxide on human health.
28. How is nitrogen oxide formed in a gas power station?
29. What are the damages caused by the production of nitrogen oxide?
30. How is sulfur dioxide formed in a gas power station and what is the
damage caused by it?
SAMPLE LONG QUESTIONS
1. Enlist advantages and disadvantages of Gas turbine stations?
2. Describe different types of gas power plant?
3. Sketch block diagram of a gas turbine power station and explain its
important components?
4. List different gas turbine and combined cycle power stations working
in Pakistan?
5. Describe combined cycle power station?
6. Describe environmental effects of gas turbine stations and measures
to improve the situation?
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Tariffs and Economics
CHAPTER 6 TARIFFS AND ECONOMICS
Chapter objectives:
After studying this chapter, a student will be able to
 Understand the Power Plant economics consideration.
 Understand the different factors influencing cost of generation.
 Understand the different load curves.
 Understand the depreciation of plant cost and method of
charging.
 Understand the types of tariffs.
 Understand the fundamentals of load managements.
6.1 Introduction to economics consideration
The technique of determining the per unit (i.e., one kWh) cost of producing
electrical energy is known as power generation economics. The economics of
power generating have become increasingly important in this rapidly evolving
field of power plant engineering. A consumer will only utilize electricity if it is
provided at a reasonable cost. As a result, power engineers must devise costeffective techniques of producing electric power so that consumers are
enticed to utilize electrical means.
6.1.1 Cost of Generation
Cost of generation refers to the cost of generating electrical power. Cost of
generation depends on the following two factors.
a. Fixed or Capital cost
b. Running or operation cost.
6.1.2 Fixed or capital cost
The capital or fixed cost refers to the long-term investment made in the plant's
complete installation. The following are the most critical capital cost factors:
a. Initial price
b. Interest
c. Depreciation
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d. Taxes
e. Insurance
a. Initial price
The initial cost of a power station includes the cost of land, the cost of
construction, the cost of purchasing machinery, the cost of installing the plant,
and overhead expenses. Overhead costs include transportation, storage, and
interest while the plant is being built. The cost of the plant's equipment is
typically represented in terms of the plant's installed kilowatt capacity.
b. Interest
Interest is the expense of borrowing money. A power plant is built with a large
sum of money. This money is usually obtained from banks or other financial
institutions, and the supply firm is responsible for paying the annual interest
on it. Even though the corporation has used its reserve cash, interest must still
be compensated for because the money could have earned interest if stored
in a bank.
As a result, the cost of producing electrical energy must include the interest
payable on the initial investment. Interest rates change depending on market
conditions and other variables.
c. Depreciation
Depreciation refers to the loss in the value of power plant equipment and
buildings caused by continuous usage. If the power station equipment were to
survive forever, the sole expense would have been interest on the capital
investment.
In practice, however, each power station has a useful life of fifty to sixty years.
From the moment the power station is established, its equipment gradually
deteriorates due to wear and tear, resulting in a progressive decrease in the
plant's value. Annual depreciation refers to the annual decrease in the value
of a plant. Because of depreciation, the plant must be replaced by a new one
at the end of its useful life. As a result, an appropriate amount must be set
away each year so that when the plant retires, the money received through
depreciation equals the cost of replacement. It is evident that annual
depreciation costs must be considered when calculating the cost of
production. There are various ways to calculate annual depreciation charges.
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d. Taxes
Municipalities, provincial governments, and the federal government all levy
taxes based on the actual worth of capital invested, the quantity of sales, or
both. A property tax is also levied on the site where the plant is built, based
on the assessed monetary value of the land. Other taxes outside property tax
include income tax, sales tax, social security, unemployment, and excess
profits, among others.
These investment costs only include taxes based on the real capital invested
in the facility, whereas other taxes are levied on an operating cost basis.
e. Insurance
Insurance is bought to cover against predicted accidents to labour and
equipment, as well as natural disasters such as earthquakes, floods, and
storms. Annual premiums are charged by insurance companies for this
purpose. If the organization is large enough, it will create its own insurance
fund, which will come in helpful in the event of an accident.
6.1.3 Running or operation cost
Operating or running costs are expenses incurred while a plant is in operation
or in an active state. Some of these expenses are variable, while others are
set. These costs vary with the plant's output. The following are examples of
operating expenses:
a. Fuel cost
b. Labor cost
c. Maintenance cost
d. Supplies
e. Monitoring
f. Operating Taxes
Running or operation costs are not factored into investment because they vary
depending on the size of the unit. Aside from that, the type of plant has an
impact. Hydro, thermal, and nuclear power plants, for example, have very
varied operating costs. There is no fuel in hydel, yet it is 70 to 75 percent more
expensive in thermal. The fuel cost of a nuclear power plant is modest, but the
operating and maintenance costs are rather high. On the contrary, the diesel
power plant's fuel cost is fairly high while its maintenance cost is quite cheap.
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a. Fuel cost
The cost of fuel in any power plant is referred to as fuel cost. The fuel cost
accounts for 70 to 75 percent of the total operating cost of a thermal power
plant. The type of fuel is also crucial because the cost of solid, liquid, or gas
fuel varies. Aside from that, fuel transportation costs and the distance
between the fuel source and the plant are crucial considerations.
Furthermore, thermal efficiency has an impact on this figure. It also involves
spending on pollution-control equipment. As a result, in order to cut fuel costs,
the plant's efficiency must be improved.
b. Labor Cost
The cost of labor required to run the power plant is referred to as labor cost.
A thermal power plant requires more labor because it utilizes coal as fuel, but
a hydel power plant of the same power requires less labor. As a result, labor
costs play a significant part in operating costs. Although most labor is now
done by automated machines, a traditional thermal power plant still requires
more manpower due to fuel unloading, storage, monitoring of boiler and
combustion chamber equipment, gauging units, and switchyard. Working
demands greater effort.
c. Maintenance Cost
To avoid breakdown, any plant requires extensive upkeep. Maintenance
comprises adequate inspection, cleaning, greasing, adjusting, and overhauling
of plant equipment at appropriate and regular intervals, and the expenses
incurred are referred to as maintenance costs.
By doing so, the possibility of the plant breaking down during operation is
reduced or eliminated. The cost of maintenance materials is also included in
the cost of maintenance. A fixed percentage of money is sometimes set aside
for maintenance. A thermal power station requires more maintenance than a
hydroelectric plant, and a nuclear power plant requires more maintenance
than a conventional power plant.
d. Supplies
All things not covered by fuel or maintenance are covered by supplies and are
subject to supply costs. Makeup water, water treatment chemicals, tool
lubricating oils and greases, paints, tools, and cleaning cloths, to name a few.
The cost of thermal power plant supplies is the greatest. This cost rises with
the plant's age because the plant's efficiency declines with age.
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e. Supervision
The cost of supervision includes the salaries of supervisory employees such as
the chief engineer, resident engineer, chemist, supervisors, labour welfare
officer, store in charge, cashier officer, and a few more. The cost of supervision
is a minor percentage of the total operating cost, but it is extremely beneficial
in maintaining plant performance. The cost of thermal plant supervision is
higher than that of hydro plant monitoring, and the cost of nuclear power
plant supervision is the greatest.
f. Operating Taxes
Operating taxes are levied on the amount of output rather than the amount
of investment. It includes income tax, social security, and employee security,
among other things. These taxes are in addition to the initial capital gains tax.
6.2 Factors influencing cost of generation, load factor,
demand factor, diversity factor
The following factors influence cost of generation.
a. Load factor
Load factor is the ratio of average load to maximum load at any particular time.
That is,
Load Factor = Average Load
=
Average Demand
Maximum Load
Maximum Demand
The load factor is always less than unity because the average load or demand
is always less than the maximum load or demand. (i.e. one). For example, if a
power plant's peak load is 100 MW and its average load is 35 MW, the load
factor will be 0.35. In such a circumstance, the facility will be idle for an
extended period of time, and its production costs will be significant.
If the load factor is high, it indicates that the plant is being used to its full
potential. As a result, the cost of production per unit is reduced. If the time
period selected is a day, the load factor will be daily. The load factor will be
one month if the duration is one month. Similarly, if the time is a year, the load
factor will be annual as well.
The load factor for 1 day can be found as,
Load Factor = A Energy consumed during 24 Hours
Maximum demand x 24 Hours
Load factors for different types of consumers are as follows:
(i) Residential load
10-15%
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(ii) Commercial load
25-30%
(iii) Municipal load
25%
(iv) Industrial load
(a) Small scale industries
30-50%
(b) Medium size industries
55-60%
(c) Heavy Industries
70-80%
Base load plants often have a high load factor, whereas peak load plants
typically have a low load factor.
b. Demand Factor
1.
The demand factor is the ratio of a system's or user maximal
demand to the entire load connected to the system.
Demand Factor = Maximum Demand
Connected Load
Its value is usually less than 1. The maximum load consumed by a consumer at
any one time is referred to as the maximum demand, whereas the total load
(in KW) linked to a consumer's premises is referred to as the connected load.
Because all appliances and loads in the system are almost never turned on at
the same time, the demand factor is used to determine the maximum demand
in KW or KVA of all appliances consuming electricity that are used at any given
time that is less than the total KW or KVA rating of these devices.
For example, if a house has ten 100-watt bulbs installed, the installed load is
1000 watts. If same client lights 9 bulbs at the same time, his maximum
demand is 900 watts. As a result, the demand factor will be 900/1000, or 0.90.
The maximum demand defines the required plant capacity, hence the demand
factor determines the required equipment capacity.
c. Diversity Factor
The ratio between the sum of the individual maximum demand of all
consumers and the maximum demand of the power station is called the
diversity factor.
Diversity Factor = Sum of Individual Maximum Demand
Maximum demand of power station
Because not all consumers utilize or turn on their complete load at the same
time, the size of a power plant does not have to be the same as the size of the
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load linked to that power plant. As a result, the term "diversity factor" is
utilized.
When the diversity factor is more than one, the maximum demands on the
power plant are reduced in comparison to individual needs. This decreases the
plant's original cost and the unit cost of production.
d. Capacity Factor (or Plant Factor)
Every power plant has a reserve capacity to meet potential extra load
requirements, therefore the plant's total installed capacity is typically more
than its actual requirements. (I.e. maximum demand). As a result, the capacity
factor or plant factor is defined as follows.
The ratio between the average load and the rated capacity of the power plant
is called power plant factor.
Capacity Factor = Average Demand
Rated Capacity of power plant
OR
The ratio of the actual energy produced in kilowatt hours of a plant in a given
time and the maximum energy produced by the plant in the same time
according to the capacity of the plant is called the plant capacity factor.
Capacity Factor = Actual Energy produced in KWh
Maximum Possible energy produced
If the plant's rated capacity equals the peak load, the load factor and capacity
factor will be numerically equal. The difference between load factor and
capacity factor indicates reserve capacity.
e. Plant use factor
It is defined as the ratio of energy produced in a given time to the maximum
feasible energy produced during the actual number of hours the plant was
operational.
Plant Use Factor = E
Cxt
Where
E = Energy produced (KWh) in a given period.
C = Capacity of Plant in KW
t = actual number of hours the plant has been in operation.
f. Reserve Factor
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The ratio between the Load factor and capacity factor is called the reserve
factor.
Diversity Factor = Load Factor
Capacity Factor
The "connected load" of each consumer is the sum of the continuous ratings
of all the equipment and outlets on the consumer's circuits. The maximum
demand is the highest load that a consumer can use at any given time. It is
never greater than or equal to the linked load.
g. Utilization Factor
The ratio between the maximum demand at the plant and the rated capacity
of the power plant is called utilization factor.
Utilization Factor = Maximum demand at the power station
Rated capacity of power station
6.2.1 Some Important Terms
a. Connected load
It is the sum of the ratings in kilowatts (kW) of equipment installed in the
consumer's premises.
For example, if a consumer has connections for four 60 watt (W) lamps, a
power point rated at 500 W, and a radio rated at 60 W, the total connected
load of the consumer is as follows:
Total Load = 4 × 60 +500 + 60 = 240 + 500+ 60 = 800 W
b. Maximum Demand
It is the maximum load that a consumer can use at any time. It may be less or
equal to the connected load.
If all of the gadgets installed in the consumer's home operate at full capacity
at the same time, the maximum demand equals the connected load. However,
because no device ever runs at full load at the same time, the actual maximum
demand is usually less than the connected load. A power station's maximum
demand is the maximum load it can handle in a given period.
c. Installed Capacity
The total available capacity of the plant to supply the load of system is called
the installed capacity.
d. Firm Power
That Power which is available in both normal and emergency situations is
called firm power.
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e. Cold Reserve
The reserve generating capacity of a power plant which is available for service
but not in operation is called cold reserve.
f. Hot Reserve
The generating capacity of a power plant which is available in active condition
or running condition but no load is applied to it is called hot reserve.
g. Spinning Reserve:
The generating capacity of a power plant which is connected to the bus bar
and ready to take load is called Spinning Reserve.
6.2.2 Measures to reduce cost of electricity
The cost per unit of energy is determined by the actual investment in the plant,
the distribution infrastructure, and plant maintenance, as well as running or
operation costs. In reality, any plant's reserve capacity raises the cost of
electricity.
Furthermore, the cost of energy produced by the plant is affected by frequent
fluctuations in load. If the load changes deviate too much from the typical, the
manufacturing cost rises. The cost of producing power is divided into two
sections. One of these fixed expenses is tied to plant investment. It has nothing
to do with the amount of energy produced, but the other part, running
charges, is tied to the amount of energy produced.
As a result, the following methods can help to reduce the cost of electricity.
a. By employing a plant with a simple design that does not require a large
number of skilled personnel to operate.
b. Lowering production costs can also be accomplished through greater
manpower utilization and by utilizing a plant with a higher load factor.
c. By using a good type of fuel, which decreases production cost. Avoid using
plants with large reserves.
d. Lowering production costs can be accomplished appropriate plant size and
number of units also have an impact. A few large units instead of numerous
tiny units result in lower production costs.
e. By integrating power systems or connecting multiple plants together via
the national grid, production costs can be decreased since units can be
switched on or off when the load is low.
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f. By enhancing power plant efficiency, maintaining regular monitoring and
scheduled maintenance to reduce breakdown and extend the plant's life.
g. By selecting equipment with sufficient capacity and longevity.
6.3 Different load curves
Load is a curve that represents the load requirements in terms of time at any
generating station. The capacity and peak load of the plant can be determined
using the load curve. A curve that shows load requirements or power demand
within an hour is known as an hourly load curve, a curve that shows load
requirements during a day is known as a daily (i.e. 24 hour) load curve and a
curve that shows load requirements within a week (i.e. seven days) is known
as a weekly load curve. A monthly load curve is one that shows load
requirements for a month, whereas a yearly load curve shows annual (i.e. 8760
hours) load requirements or power consumption.
The power station's load is not constant, rather it changes all the time. Peak
load is the maximum electricity demand at a specific time of day. The size and
cost of the plant can be calculated based on the maximum demand at the
station. On a graph paper, if time is represented on the x-axis and load needs
or power demand are shown on the y-axis, then the varying load requirements
at different times should be shown as a curve on the x-axis and y-axis,
respectively, and such curve is called a load curve. A load curve is depicted
below.
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Figure 6.1. Power demand VS Time
The following data is derived from daily load curves.
a. It displays load variations throughout the day.
b. The number of units produced in a day is represented by the area
under the curve.
c. The peak of the curve represents the maximum demand at the
power station on a given day.
d. When the area under the load curve is divided by the number of
hours, the power station displays the average load or average
demand for that day.
e. The load factor represents the ratio of the area under the load curve
to the total area of the entire rectangle.
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Figure 6.2. Daily load curve
The entire capacity of the power plant can be calculated using the
aforementioned information and the load curve. Because the load curve
changes daily and according to seasons, it is required to establish distinct
load curves for winter and summer, and the annual output requirements of
the power station are determined based on these load curves.
The figure above depicts the load changes that occur during the day. The curve
shows that the largest load on the power system is 25 kW from 8 a.m. to 2
p.m., and the minimum load is 3 kW from 6 p.m. to 6 a.m. If the loads in this
curve are organised in descending order, the resulting curve, which is depicted
below, is known as the load duration curve. The load duration curve simplifies
the selection of base load and peak load power plant.
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Figure 6.3. Load duration curve
6.4 Depreciation of plant cost and method of charging
Each year, depreciation causes the value of the plant's equipment and other
property to decrease. In order to ensure that the collected amount is equal to
the cost of replacing the plant by the time the plant's life cycle is complete, a
reasonable amount must be set aside each year.
The methods that are frequently used to determine the annual depreciation
charge are as follows:
a. Straight line method.
b. Sinking fund method.
6.4.1 Straight line method
According to this system, a fixed depreciation charge is applied annually based
on the property's useful life and overall depreciation. The total depreciation
divided by the property's useful life will, of course, equal the annual
depreciation charge. So, if an item's initial cost is Rs. 1,000,000 and its scrap
value is Rs. 10,000 after a 20-year useful life,
Annual depreciation charge = Total depreciation = 1,00,000 - 10,000 = Rs 4,500
Useful life
20
In general, the straight line method's annual depreciation charge can be
represented as:
Annual depreciation charge = P - S
n
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Where
P = Initial cost of equipment.
n = Useful life of equipment in years.
S = Scrap or salvage value after the useful life of the plant.
Because the annual depreciation charge can be easily calculated from the total
depreciation and useful life of the equipment, the straight line method is
extremely simple and easy to apply. The method is depicted graphically in Fig.
6.4. The initial value P of the equipment is clearly reduced uniformly through
depreciation to the scrap value S over the useful life of the equipment. The
depreciation curve is straight, indicating that the annual depreciation charge
is constant.
However, there are two flaws in this method. To begin with, the assumption
of a constant depreciation charge each year is incorrect. Second, it does not
take into account any interest that may be drawn during the accumulation
process.
Figure 6.4. Straight line method
6.4.2 Sinking fund method
A fixed depreciation charge is made every year in this method, and interest is
compounded on it annually. The constant depreciation charge is calculated so
that the total of annual installments plus interest accruals equals the cost of
replacing equipment after its useful life.
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Let
P = Initial value of equipment
n = Useful life of equipment in years
S = Scrap value after useful life
r = Annual rate of interest stated as a decimal
Cost of replacement = P - S
Assume that an amount of q is set aside as a depreciation charge each year,
with interest compounded on it, so that an amount of P - S is available after n
years. At the end of n years, an amount q with an annual interest rate of r
becomes q (1 + r) n.
Now, the amount q accumulated at the end of the first year will earn
compound interest for n-1 years and will become q (1 + r) n - 1 i.e.,
Amount q collected after the completion of first year equals to
= q (1 + r) n - 1
Amount q collected after the completion of 2nd year equals to
= q (1 + r) n - 2
Amount q collected after the completion of 3rd year equals to
= q (1 + r) n - 3
Similarly amount q collected after the completion of n - 1 year becomes
= q (1 + r) n - (n -1)
= q (1 + r)

Total fund after n years = q (1 + r)n - 1 + q (1 + r)n - 2 +……………+ q (1 +r)
= q [(1 + r) n - 1 + (1 + r) n - 2 +………+ (1 + r)]
This is a G.P. series and its total amount is given by:
q (1 + r) n - 1
The uniform annual depreciation charge is given by the value of q. The
parenthetical term in equation is also known as the "sinking fund factor."
Sinking fund factor = ________r
(1 + r) n - 1
6.5 Types of Tariffs
Tariff is the rate at which electrical energy is supplied to a consumer. A power
station's electrical energy is distributed to a large number of consumers.
Consumers can be convinced to use electricity if it is sold at a reasonable price.
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The rate at which electrical energy is sold, naturally attracts the attention of
the electric supply company. The supply company must ensure that the tariff
not only recovers the total cost of producing electrical energy but also
generates a profit on the capital investment. However, the profit must be
marginal, where electric supply companies are part of the public sector and
are frequently criticized. In this topic, various types of tariffs will be discussed,
with special emphasis on their benefits and drawbacks.
Although the tariff should include the total cost of producing and supplying
electrical energy, as well as a profit, it cannot be the same for all types of
consumers. It is because the cost of producing electrical energy is heavily
influenced by the amount of electrical energy consumed by the user and his
load conditions. As a result, in order to be fair, different types of consumers
(e.g., industrial, domestic, and commercial) must be taken into account when
determining tariffs. This complicates the problem of determining an
appropriate rate.
6.5.1 Objectives of tariff
Electrical energy, like other commodities, is sold at a price that not only covers
the cost but also earns a reasonable profit. As a result, a tariff should include
the following provisions:
a. Recovering the cost of generating electricity at the power station.
b. Cost recovery for capital investments in transmission and distribution
systems.
c. Cost recovery for the operation and maintenance of electrical energy
supply, such as metering equipment, billing, and so on.
d. A reasonable return on the capital investment.
6.5.2 Desirable Characteristics of a Tariff
The following desirable properties must be present in a tariff
a. Proper return
The tariff should be set in such a way that suitable return is ensured from each
consumer. In other words, total consumer receipts must equal the cost of
generating and supplying electrical energy plus a reasonable profit. This will
allow the electric utility to provide consumers with consistent and dependable
service.
b. Fairness
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The tariff must be equitable in order for various types of consumers to be
satisfied with the rate of charge for electrical energy. As a result, a large
consumer should be levied less than a small consumer. Because increased
energy consumption spreads fixed charges over a greater number of units, the
overall price for generating electrical energy is reduced. Similarly, a consumer
whose load conditions do not deviate significantly from the ideal (i.e., nonvariable) should be charged less than one whose load conditions deviate
significantly from the ideal.
c. Simplicity
The tariff should be simple enough for the average consumer to understand.
A complicated tariff may elicit opposition from a public that is generally deeply
distrustful of supply companies.
d. Reasonable profit
The tariff's profit component should be reasonable. An electric supply
company is a public utility company that benefits from monopoly. As a result
of the market's lack of competition, the investment is relatively safe. This
implies that profit should be limited.
e. Attractive
The tariff should be fascinating enough to encourage a large number of
consumers to use electrical energy. Efforts should be made to set the tariff in
a way that allows consumers to pay easily.
6.5.3 Types of Tariff
Tariffs are classified into several types. However, the following are the most
commonly used tariff types:
a. Simple tariff.
b. Flat rate tariff.
c. Block rate tariff.
d. Two-part tariff.
e. Maximum demand tariff.
f. Power factor tariff.
a. Simple tariff
A simple tariff or uniform rate tariff is one that has a fixed rate per unit of
energy consumed. The price charged per unit in this tariff is constant, meaning
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it does not differ with the number of units consumed. An energy meter is used
to record the consumption of electrical energy at the consumer's terminals.
This is the most basic tariff and is easily understood by consumers.
Disadvantages
There is no disparity between different types of consumers because all
consumers must pay the fixed charges equally.
(i) The price per delivered unit is high.
(ii) It discourages the use of electricity.
b. Flat rate tariff
A flat rate tariff is used when different types of consumers are billed at
different uniform per unit rates. In this tariff, consumers are divided into
different classes, and each class is charged at a different uniform rate. For
example, the flat rate per kWh for lighting load may be 60 paise, whereas the
flat rate per kWh for power load may be slightly less (say, 50 paise per kWh).
The various classes of consumers are created with their diversity and load
factors in mind. The benefit of such a tariff is that it is more equitable to
different types of consumers and is relatively simple to calculate.
Disadvantages
(i) Because the flat rate tariff varies depending on how the supply is used,
separate meters for lighting load, power load, and so on are required.
As a result, implementing such a tariff is both costly and complicated.
(ii) A specific class of consumers is charged the same rate regardless of the
amount of energy consumed. A large consumer, on the other hand,
should be charged at a lower rate because the fixed charges per unit
are lowered in this case.
c. Block rate tariff
A block rate tariff is used when a given block of energy is charged at a specific
rate and subsequent blocks of energy are charged at progressively lower rates.
The energy consumption is divided into blocks in a block rate tariff, and the
price per unit is fixed in each block. The price per unit in the first block is the
highest, and it gradually decreases in subsequent blocks of energy. For
example, the first 30 units could be charged at a rate of 60 paise per unit, the
next 25 at a rate of 50 paisa per unit, and the remaining units at a rate of 30
paisa per unit.
Advantage
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The benefit of such a tariff is that it incentivizes consumers to consume more
electrical energy. This increases the system's load factor, lowering the cost of
generation.
Disadvantage
Its major flaw is that it lacks a measure of consumer demand. This tariff is used
by the vast majority of residential and small commercial customers.
d. Two-part tariff
When the rate of electrical energy is charged on the basis of maximum
demand of the consumer and the units consumed, it is called a two-part tariff.
In two-part tariff, the total charge to be made from the consumer is split into
two components viz., fixed charges and running charges. The fixed charges
depend upon the maximum demand of the consumer while the running
charges depend upon the number of units consumed by the consumer. Thus,
the consumer is charged at a certain amount per kW of maximum demand
plus a certain amount per kWh of energy consumed i.e.
A two-part tariff is used when the rate of electrical energy is charged based on
the consumer's maximum demand and the units consumed. The total charge
to the consumer is divided into two components in a two-part tariff: fixed
charges and running charges. The fixed charges are determined by the
consumer's maximum demand, whereas the running charges are determined
by the number of units consumed. As a result, the consumer is charged a
certain amount per kW of peak demand plus a certain amount per kWh of
energy consumed, i.e.
Total charges = R.S (B x kW + C x kWh)
Where,
B = charges per kW of maximum demand
C = charges per kWh of energy consumed
This tariff is typically applied to industrial consumers with high maximum
demand.
Advantages
(i) It is simple for customers to understand.
(ii) It recovers the fixed charges that are based on the consumer's
maximum demand but are independent of the units consumed.
Disadvantages
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The consumer must pay the fixed charges whether or not he has
consumed electrical energy.
(ii) There is always error in estimating the maximum demand of the
consumer.
e. Maximum demand tariff
It is identical to a two-part tariff with the exception that the maximum demand
is actually evaluated by installing a maximum demand meter in the consumer's
premises. This eliminates the objection to a two-part tariff in which maximum
demand is determined solely on the basis of ratable value. This tariff is mostly
applied to large consumers. However, because a separate maximum demand
meter is required, it is not appropriate for a small consumer (e.g., a residential
consumer).
f. Power factor tariff
Power factor tariff refers to the tariff that takes the power factor of the
consumer's load into account. The power factor is critical in an alternating
current system. A low power factor raises the rated capacity of station
equipment and increases line losses. As a result, a consumer with a low power
factor must be penalized. The following are the various kinds of power factor
tariffs.
(i) k VA maximum demand tariff
It is a two-part tariff in a modified form. In this case, the fixed charges are
calculated based on maximum demand in kVA rather than kW. Because kVA is
inversely proportional to power factor, a consumer with a low power factor
must contribute more to the fixed charges. This tariff has the advantage of
encouraging consumers to operate their appliances and machinery at a higher
power factor.
(ii) Sliding scale tariff
This is also referred to as the average power factor tariff. In this case, the
reference is an average power factor, say 0.8 lagging. If the consumer's power
factor falls below this level, appropriate additional charges are imposed. If, on
the other hand, the power factor is greater than the reference, the consumer
is entitled to a discount.
(iii) kW and kVAR tariff
(i)
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This type charges for both active power (kW) and reactive power (kVAR)
supplied. A consumer with a low power factor will use more reactive power
and thus pay more charges.
6.6 Calculations on tariffs
Example 6.1. A consumer has a maximum demand of 100 kW at 40% load
factor. If the tariff is Rs. 100 per kW of maximum demand plus 10 paise per
kWh, find the overall cost per kWh.
Solution:
Units consumed/year = Max. Demand  L.F. Hours in a year
= (100)  (0·4)  8760 = 3, 50,400 kWh
Annual charges = Annual M.D. charges + Annual energy charges
= Rs (100  100 + 0·1  3, 50,400)
= Rs 45,040
Overall cost/kWh = Rs
45,040
= Re 0·1285 = 12·85 paisa
=3,50,400
Example 6.2. The maximum demand of a consumer is 40 A at 220 V and his
total energy consumption is 8760 kWh. If the energy is charged at the rate of
20 paise per unit for 1000 hours use of the maximum demand per annum plus
10 paise per unit for additional units, calculate: (i) annual bill (ii) equivalent
flat rate.
Solution.
Assume the load factor and power factor to be unity.

Maximum demand =
(i)
220  40  1  8  8 kW
1000
Units consumed in 1000 hrs = 4·4 x 1000 = 4400 kWh
Charges for 4400 kWh
= Rs 0·2 x 4400 = Rs 880
Remaining units
= 8760 - 4400 = 4360 kWh
Charges for 6560 kWh = Rs 0·1 4360 = Rs 436
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(i)
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Tariffs and Economics

Total annual bill = Rs (880 + 436) = Rs. 1316
Equivalent flat rate = Rs. (1316/8760) = Re 0 150  15.0 paisa
Example 6.3. The following two tariffs are offered:
(a)
Rs 100 plus 30 paisa per unit ;
(b)
A flat rate of 60 paisa per unit ;
At what consumption is first tariff economical?
Solution.
Let x be the number of units at which charges due to both tariffs become
equal. Then,
100 + 0·3x = 0·6x
or
0·3x = 100

x = 100/0·3 = 333·33 units
Therefore, tariff (a) is economical if consumption is more than 333.33 units.
Example 6.4. A supply is offered on the basis of fixed charges of Rs 60 per
annum plus 6 paisa per unit or alternatively, at the rate of 12 paisa per unit for
the first 400 units per annum and 10 paisa perunit for all the additional units.
Find the number of units taken per annum for which the cost under the two
tariffs becomes the same.
Solution.
Let x (> 400) be the number of units taken per annum for which the annual
charges due to both tariffs become equal.
Annual charges due to first tariff = Rs (60 + 0·06x)
Annual charges due to second tariff = Rs [(0·12 400) + (x  400)  0·1]
= Rs (8 + 0·1x)
As the charges in both cases are equal,

60 + 0·06x = 8 + 0·1x
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
0·1x -0·06x = 60 -8

0·04x = 52

x = 52/0·04

x  1300 kWh
Example 6.5. An electric supply company having a maximum load of 100
MW generates 36 x 107 units per annum and the supply consumers have an
aggregate demand of 150 MW. The annual expenses including capital charges
are:
For fuel = Rs 90 lakhs
Fixed charges concerning generation = Rs 28 lakhs
Fixed charges concerning transmission and distribution = Rs 32 lakhs
Assuming 90% of the fuel cost is essential to running charges and the loss in
transmission anddistribution as 15% of kWh generated, deduce a two part tariff
to find the actual cost of supply to the consumers.
Solution.
Annual fixed charges
For generation = Rs 28  105
For transmission and distribution= Rs 32  105
For fuel (10% only) = Rs 0·1  90  105 = Rs 9  105
Total annual fixed charge = Rs (28 + 32 + 9)  105
= Rs 69  105
This cost has to be spread over the a g g re g at e maximum
demand of all the consumers i.e., 75 MW.
 Cost per kW of maximum demand = (69  105) / (150  103) = Rs. 46
Annual running charges
Cost of fuel (90%) = Rs 0·9  90  105 = Rs. 81  105
Units delivered to consumers = 85% of units generated
= 0·85  36  107 = 30·6  107 kWh
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This cost is to be spread over the units delivered to the consumers.
 Cost / kWh = (81  105) / (30·6  107) = Re 0  0265  2.65 paisa
 Tariff is Rs 46 per kW of maximum demand plus 2.65 paisa per kWh.
Example 6.6. A generating station has a maximum demand of 150 MW and
a yearly load factor of 40%. Generating costs inclusive of station capital costs
are Rs. 60 per annum per kW demand plus 4 paise per kWh transmitted. The
annual capital charges for transmission system are Rs 20, 00,000 and for
distribution system Rs 15, 00,000; the respective diversity factors being 1·2
and 1·25. The efficiency of transmission system is 90% and that of the
distribution system inclusive of substation losses is 85%. Find the yearly cost
per kW demand and cost per kWh supplied:
(i) at the substation
(ii) at the consumers premises.
Solution.
Maximum demand = 150 MW = 150,000 kW
Annual load factor = 40% = 0·4
Cost at substation.
The cost per kW of maximum demand is to be determined from the total annual
fixed charges associated with the supply of energy at the substation. The cost
per kWh shall be determined from the running charges.
Annual fixed charges
Generation cost = Rs 60  150  103 = Rs 9  106
Transmission cost = Rs 2  106
Total annual fixed charges at the substation = Rs (9 + 2)  106 = Rs 13  106
Aggregate of all maximum demands by the various substations
= Max. demand on generating station  Diversity factor
= (150  103)  1·2 = 180  103 kW
The total annual fixed charges have to be spread over the aggregate
maximum demands by various substations i.e., 180  103 kW.
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Annual cost per kW of maximum demand = (13  106) / (180  103) = Rs. 72.22
Running Charges.
It is given that cost of 1 kWh transmitted to substation is 4 paisa.
As thetransmission efficiency is 90%, therefore, for every kWh transmitted, 0·9
kWh reaches the sub- station.
 C o s t /kWh at substation = 4/0·9 = 4·45 paisa
Hence at sub-station, the cost is Rs 72·22 per annum per kW maximum demand
plus 4·45 paisa per kWh.
Cost at consumer’s premises.
The total annual fixed charges at consumer’s premises is the sum of annual fixed
charges at substation (i.e. Rs 13  106) and annual fixed charge for distribution
(i.e., Rs 1·5  106).
 Total annual fixed charges at consumer’s premises= Rs (13 + 1·5) 106 = Rs
14.5  106
Aggregate of maximum demands of all consumers
= Max. Demand on Substation  Diversity factor
= (180  103)  1·25 = 225 103 kW
 Annual cost per kW of maximum demand
= Rs (14.5  106)/( 225 103)= Rs. 64.44
As the distribution efficiency is 85%, therefore, for each kWh delivered from
substation, only 0·85 kWh reaches the consumer’s premises.
 Cost per kWh at consumer’s premises
= (Cost per kWh at substation)/ (0.85) = (4.45)/ (0.85) = 5·23 paisa per kWh
Hence at consumer’s premises, the cost is Rs. 64.44 per annum per kW
maximum demand plus 5·23 paisa per kWh.
Example 6.7. Calculate annual bill of a consumer whose maximum demand is
200 kW, p. f. = 0·8 lagging and load factor = 60%. The tariff used is Rs 150 per
kVA of maximum demand plus 30 paisa per kWh consumed.
Solution.
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Units consumed/year = Max. Demand  L.F.  Hours in a year
= (200)  (0·6) (8760) kWh
= 10·512  105 kWh
Max. Demand in kVA = 100/p.f. = 200/0·8 = 250
Annual bill = Max. Demand charges + Energy charges
= Rs 150  250 + Rs 0·3  10·512  105
= Rs 37500 + Rs 315360
= Rs 352860
Example 6.8. A factory has a maximum load of 480 kW at 0·8 p.f. lagging
with an annual consumption of 100,000 units. The tariff is Rs 100 per kVA of
maximum demand plus 20 paisa per unit. Calculate the flat rate of energy
consumption. What will be annual saving if p. f. is raised to unity?
Solution.
Maximum demand in kVA at a p.f. of 0·8 = 480/0·8 = 600
Annual bill = Demand charges + Energy charges
= Rs 100  600 + Rs 0·2 100,000
= Rs 60,000 + Rs 20000 = Rs 80,000
Flat rate/unit = (80,000)/( 100,000)  Rs 0  80  80 paise
When p.f. is raised to unity, the maximum demand in
kVA
= 480/1 = 480
Annual bill = Rs 100  480 + Rs 0·2 100,000
= Rs 48,000 + Rs 20,000 = Rs 68,000
Annual saving = Rs (80,000  68,000) = Rs 12000
Example 6.9. The tariff in force is Rs 300 per kVA of maximum demand and
16 paisa per unit consumed. If the load factor is 30%, find the overall cost per
unit at (i) unity p. f. and (ii) 0·7 p. f.
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Solution.
Suppose the maximum demand is 1 kVA.
When p.f. is unity
300  100
Max. Demand charge/unit =
= 11·4 paisa
8760  0  30
Energy charge/unit = 16 paisa
Overall cost/unit = 11·4 + 16 = 27·4 paisa
When p.f. is 0·7
Max. Demand charge/unit = 300  100
8760  0 30  0  7
Energy charge/unit = 16 paisa
= 16.3 paisa
Overall cost/unit = 16.3 + 16 = 32·3 paisa
6.7 Fundamentals of load management.
Electricity is distinguished by the fact that its production and consumption
occur almost simultaneously. Furthermore, large amounts of electricity
cannot be stored. This means that power generation must adjust to changing
demand, which is influenced by climate, economic growth, and customer
consumption habits. These variables cause demand to fluctuate at different
times. The utility must invest in generation plant and equipment to maintain
adequate net peaking capability in accordance with the system maximum
demand. There will be a significant imbalance in power supply and demand if
utilities do not impose any system measures. Excessive or insufficient
investment will result in idle assets or power shortages, which will be
unpleasant for both suppliers and customers.
Load management is a new concept in electricity distribution that aims to
create a more efficient supply network system. A control system of this type
should meet the needs of consumers at the lowest possible peak loading. Load
management is becoming increasingly popular around the world. Direct load
management systems have progressed through the experimental stage and
are now used in a wide range of supply network systems. The economic
grounds for implementing these systems have been established all over the
world. Load management is a process that, in conjunction with electricity
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conservation, reduces total electricity consumption, whereas load
management is intended for consumption control over a specific time period.
Load management is referred to as a set of objectives designed to control and
modify the patterns of demand of a power utility's various consumers. This
control and modification entitles the supply system to meet demand in the
most cost-effective manner at all times. Load management approaches the
consumption pattern rather than reducing overall electricity consumption. It
could be used on both the demand and supply sides of the energy equation:
a. Supply Side Load Management
b. Demand Side Load Management
a. Supply Side Load Management
This management is referred to as the action taken on the supply side to meet
demand. In the 1970s, this idea was very popular. If society demanded more
power, power companies would simply build more generation facilities to
meet the demand. This was the crux of the idea.
The continuous supply of electricity to consumers at low cost using existing
sources as per their demand with optimal load factor during normal and
emergency conditions without the need for shutdowns, e.g. Due to a lack of
water at hydel power plants during the winter, production is reduced. The
thermal power plants are then used to full capacity. Similarly, diesel and petrol
plants are used in conjunction with thermal plants. Only thermal plants
operate at normal loads, with the output of diesel or gas plants supplementing
demand during peak hours. This allows the supply company to better meet
the requirements of its consumers.
b. Demand Side Load Management
This management describes the planning and execution of activities aimed at
influencing customers in such a way that the shape of the utility's power load
curve can be modified to produce power in an optimal manner. Peak clipping
and load shifting from peak to off-peak periods are used to accomplish these
goals. Demand side load management encompasses not only technical or
economic measures, but also social ones, because it is directly related to
behavioral issues.
These actions seek to guarantee the proper distribution of loads on the
distribution system according to consumer loads at optimum power factor
during peak hours so that the system is not overloaded and the equipment
continues to operate properly, e.g. tube wells, mills, and small factories during
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peak hours are restricted for certain hours to ensure uninterrupted power
supply to domestic consumers. Thus, load changes are handled in ways that
not only protect the supply company's interests but also meet consumer
expectations. Increasing the power factor on the load side is another measure
to protect the system from overloading.
6.7.1 Techniques of Power Load Management
The number of supply side constraints influences the selection of the load
shape objective. Some of these constraints include whether or not the system
is energy constrained, the system's reliability, the need for scheduled
maintenance, and the state of the distribution and transmission system. Load
shape changes are classified into three types.
a. Peak Clipping
b. Valley Filling
c. Load Shifting
a. Peak Clipping
Peak clipping is the practice of reducing load during peak periods in order to
achieve the load profile desired by the utility. This voltage reduction on the
part of consumers is directly controlled by the utility and is typically enforced
during peak times, i.e. when consumer usage of electric appliances is at its
peak. Figure 6.5 depicts the peak clipping technique's effect on the shape of
the load profile.
Figure 6.5. Peak clipping
This direct control may be utilized to reduce capacity needs, operating costs,
and reliance on critical fuel. Peak clipping becomes critical, particularly for
utilities that lack sufficient generating capacity during peak hours.
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b. Valley Filling
The second most common type of load profile shape change technique is
valley filling. It increases load during off-peak hours. Figure 6.6 depicts the
shape of a load profile created using the valley filling technique.
Figure 6.6. Valley filling
c. Load Shifting
The third technique of load shape change is load shifting which moves peak
loads to off peak time periods without necessarily changing overall
consumption. Load shifting combines the benefits of peak clipping and valley
filling by moving existing loads from on peak hours to off peak hours as in
figure.
Figure 6.7. Load Shifting
The third load shape change technique is load shifting, which shifts peak loads
to off-peak times without affecting overall consumption. Load shifting
combines the advantages of peak clipping and valley filling by shifting existing
loads from on peak to off peak hours, as shown in figure 6.7.
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When the accumulative cost of electricity is less than the average cost of
electricity, this technique is best suited to utilities and customers. Adding load
at the right price can lower the average cost of electricity for all consumers
while also improving system load factors. Off-peak industrial production,
which replaces loads served by fossil fuels with electricity, is one of the most
efficient strategies of valley filling.
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Sample Multiple Choice Questions
1. What is meant by tariff
(a) Estimation of load
(b) Rate of electricity received from consumer
(c) Both a & b
(d) None of these
2. This is the most important factor in all works of engineering
(a) Cost
(b) Economics
(c) Weather
(d) Both a & b
3. These are the relative parameters of power plant design
(a) Reliable
(b) Low fixed cost
(c) Low running cost
(d) All of these
4. Cost of generation of any power plant depends on
(a) Fixed Cost
(b) Running cost
(c) Both a & b
(d) None of these
5. The difference between borrow amount and return amount is called
(a) Depreciation cost
(b) Initial cost
(c) Interest
(d) Running cost
6. The decrease in the value of equipments with time is called
(a) Maintenance
(b) Over hauling
(c) Depreciation
(d) Re-conditioning
7. The running cost of this power plant is the lowest
(a) Wind
(b) Thermal
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(c) Hydal
(d) Gas turbine
8. These are included in the maintenance of power plant
(a) Suitable inspection of plant
(b) Cleanliness and Greasing
(c) Adjustment and over-hauling of equipments
(d) All of these
9. When the age of power plant increases, its efficiency
(a) Increases
(b) Decreases
(c) Remains constant
(d) None of these
10. A good supervision of power plant is that under which
(a) Less breakdown occurs
(b) Age of power plant increases
(c) Both a & b
(d) None of these
11. The cost of generationof power plant will be low, if it has
(a) High load factor
(b) High diversity factor
(c) Low load factor
(d) Both a & b
12. Which factor effects the cost of generation
(a) Load factor
(b) Demand factor
(c) Diversity & Power plant factor
(d) All of these
13. If the load factor of power plant is high, then per unit cost of generation
will be
(a) Very Low
(b) Low
(c) High
(d) Very high
14. The demand in this season is maximum on the power system of Pakistan
(a) Winter
(b) Summer
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(c) Rainny
(d) Autumn
15. The value of load factor is always
(a) Less than one
(b) One
(c) More than one
(d) Infinite
16. The calculate the load factor, its duration is
(a) One day
(b) One Week or one month
(c) One year
(d) All of these
17. A curve which indicates load of power plant with respect to time is called
(a) Daily curve
(b) Month curve
(c) Yearly curve
(d) Load Curve
18. Load curves are prepared for such duration
(a) One year
(b) One month
(c) One day
(d) All of these
19. It is easy to decide through load curve
(a) Size of generating units
(b) Total installed capacity of plant
(c) Operating schedule of generator
(d) All of these
20. Load management means control of power use in peak hours with
(a) Fines
(b) Incentives
(c) Inducements
(d) All of these
21. This tariff is not used for household load because their maximum
demand is less
(a) Flat rate tariff
(b) Two part tariff
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(c) Block rate tariff
(d) All of these
22. If a consumer is closed his factory for some duration, still he has to pay
(a) Fixed Charges
(b) Running charges
(c) Both a & b
(d) None of these
23. Two part tariff is received on such basics
(a) Total units consumed
(b) Maximum demand (KW)
(c) Both a & b
(d) Maximum demand (KVA)
24. Average power factor tariff is also called
(a) Sliding scale tariff
(b) Maximum demand tariff
(c) Block rate tariff
(d) Flat rate tariff
25. Which plant has high depreciation charges
(a) Hydal
(b) Thermal
(c) Nuclear
(d) Gas turbine
Answrer to MCQ’s
1.
b
2.
d
3.
d
4.
c
5.
c
6.
c
7.
a
8.
d
9.
b
10.
c
11.
d
12.
d
13.
b
14.
b
15.
a
16.
d
17.
d
18.
d
19.
d
20.
d
21.
b
22.
a
23.
c
24.
a
25.
b
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Sample Short Questions
1. What is meant by cost of generation?
2. What is meant by the initial price of Power station?
3. What is meant by interest in the capital cost?
4. What is meant by depreciation?
5. What is meant by operating cost or running cost?
6. What is meant by fuel cast?
7. What is meant by maintenance cost?
8. What is meant by operating taxes in operating cost?
9. Name the factors effecting cost of generation.
10. Define load factor and write its formula.
11. Why does cost of generation increases as load factor decreases?
12. What is meant by power plant factor? Write its formula.
13. What is meant by connected load?
14. What do we mean by maximum demand?
15. What is meant by demand factor?
16. What is meant by plant use factor or plant operating factor?
17. What is meant by Utilization factor?
18. What is the main purpose of load management?
19. What is meant by supply side load management?
20. What is meant by load side load management?
21. Define load curve and for what purpose it is used?
22. Define monthly load curve.
23. Define annual load curve.
24. What is flat rate tariff?
25. What is meant by two part tariff?
26. What is meant by maximum demand tariff?
27. What is power factor tariff?
28. What is the main purpose of power factor tariff?
29. What is KVA Maximum Demand Tariff?
30. What is the main purpose of average power factor?
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Sample Long Questions
1. Write a note on different factors influencing cost of generation, load
factor, demand factor, diversity factor?
2. Draw different load curves?
3. What is depreciation of plant? Write it’s method of charging?
4. What are the different types of tariffs?
5. What are the techniques used for power load management?
Sample Numerical Problems
1. A consumer has a maximum demand of 200 MW at 60% load factor. If
the tariff is Rs 40 per kW of maximum demand plus 20 paise per kWh,
find the overall cost per kWh.
2. The maximum demand of a consumer is 50A at 220 V and his total
energy consumption is 9750 kWh. If energy is charged at the rate of 40
paise per kWh for 500 hours use of maximum demand plus 10 paise
per unit for all additional units, estimate his annual bill and the
equivalent flat rate.
3. A consumer has an annual consumption of 4 x 105 units. The tariff is Rs
50 per kW of maximum demand plus 20 paise per kWh.
4. Find the annual bill and the overall cost per kWh if the load factor is
35%.
5. What is the overall cost per kWh if the consumption were reduced by
25% with the same load factor ?
6. Daily load of an industry is 400 kW for first one hour, 300 kW for next
seven hours, 100 kW for next eight hours and 2 kW for remaining time.
If tariff in force is Rs. 100 per kW of maximum demand per annum plus
5 paise per kWh, find the annual bill.
7. A consumer requires one million units per year and his annual load
factor is 50%. The tariff in force is Rs. 200 per kW per annum plus 20
paise per unit consumed. Estimate the saving in his energy costs if he
improves the load factor to 100%.
8. An industrial undertaking has a connected load of 200 kW. The
maximum demand is 160 kW. On an average, each machine works for
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60 per cent time. Find the yearly expenditure on the electricity if the
tariff is Rs 10,000 + Rs 1000 per kW of maximum demand per year + Re
1 per kWh.
9. An industrial consumer has a maximum demand of 240 kW and
maintains a load factor of 80%. The tariff in force is Rs. 60 per kVA of
maximum demand plus 16 paise per unit. If the average p.f. is 0·8
lagging, calculate the total energy consumed per annum and the
annual bill.
10. A customer is offered power at Rs 100 per annum per kVA of maximum
demand plus 10 paise per unit. He proposes to install a motor to carry
his estimated maximum demand of 400 b.h.p. (metric). The motor
available has a power factor of 0·83 at full load. How many units will
be required at 30% load factor and what will be the annual bill? The
motor efficiency is 90%.
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Conservation of Energy
CHAPTER 7 CONSERVATION OF ENERGY
Chapter objectives:
After studying this chapter, a student will be able to
 Understand the different energy conservation.
 Understand the sources of energy losses.
 Understand the methods to limit the energy losses.
 Understand the power factor.
 Understand the methods to improve power factor.
7.1 Introduction & necessity of energy conservation
Energy is the most basic requirement for a country's economic success. Many
modern-day processes come to a standstill when the supply of energy runs
out. It is nearly impossible to measure the exact scale of the role that energy
has played in the development of modern society. The present availability of
vast amounts of energy has resulted in a shorter working day, increased
agricultural and industrial output, a healthier and more balanced diet, and
improved transportation facilities.
In reality, there is a close association between Efforts to reduce energy use are
referred to as energy conservation. Energy conservation can be accomplished
by combining more efficient energy use with less energy use and/or less
consumption from traditional energy sources. Increased financial capital,
environmental quality, national security, personal security, and human
comfort can all be attributed to energy saving. Individuals and organizations
that use energy directly seek to preserve energy in order to minimize energy
expenses and enhance economic security. To maximize profit, industrial and
commercial users can improve energy efficiency.
According to standard economic theory, technological advancements increase
energy efficiency rather than decrease energy demand. It's said to happen in
two ways. For starters, better energy efficiency makes energy use more
affordable, promoting increased use. Second, higher energy efficiency leads to
increased economic growth, which drives up overall energy consumption. This
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is not to say that better fuel economy is useless, increased fuel efficiency
allows for greater productivity and a higher standard of living.
The goal of efforts to reduce the amount of energy necessary to deliver
products and services is efficient energy usage, also known as energy
efficiency. Insulating a dwelling, for example, enables a building to consume
less heating and cooling energy to achieve and maintain a comfortable
temperature. When compared to standard incandescent light bulbs, installing
fluorescent lights or natural skylights use less energy to achieve the same level
of illumination. Compact fluorescent lights consume two-thirds less energy
and can last six to ten times longer than incandescent bulbs. Energy efficiency
gains are often obtained by implementing a more efficient technology or
manufacturing process.
Energy saved equals energy generated. As a result, energy conservation
techniques can result in significant energy savings. Energy savings can be
viewed as a secondary source of energy. This will also assist to reduce pollution
in the environment.
Limiting your energy consumption reduces your environmental impact. The
longer we wait to make meaningful changes, the more dangerous global
warming and climate change become to our daily lives. When we use fossil
fuels, we emit a massive amount of greenhouse gases. These gasses, which
include carbon dioxide, accumulate faster than the atmosphere can absorb
them, preventing the Earth from maintaining a steady temperature.
Global warming refers to the planet's rising temperatures. Climate change
refers to the consequences of warming. Changes in sea level, cold snaps,
droughts, hurricanes, melting glaciers, and wildfires are examples of these
negative effects. Fortunately, we can cut greenhouse gas emissions by
lowering our energy consumption.
First, as our supply of fossil fuels diminishes, they will become less easily
available. Drilling and mining will become more difficult and, as a result, more
expensive. This additional cost raises the consumer's cost as well.
We can minimize our reliance on fossil fuels as consumers by consuming less
energy and looking for new ways to increase our energy sustainability options,
such as solar, wind, and hydroelectric power. The more we rely on renewable
energy sources, the longer fossil fuels will persist and the rate at which their
prices will rise will slow.
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Utility expenses are another way that energy conservation can help you save
money. A few easy modifications, ranging from the sorts of equipment you
use to your electricity plan, can have a substantial impact on how much your
energy bills will cost you. The more you do to conserve energy, the more your
electricity, natural gas, and even water bills will reflect those improvements.
As your efforts accumulate, you will begin to see big savings.
7.1.1 Necessity of Energy Conservation
As a country's energy consumption rises, boosting efficiency is the only way to
partially balance the energy deficit. Power consumption losses are decreased
with high efficiency. Industrial production rises, resulting in energy savings.
Energy conservation essentially implies preventing energy from being
squandered without regard for the impact on production.
Today, there is a major energy deficit all across the world. Given the growing
demand for energy, despite limited resources and means, it is critical to
identify big areas of energy consumption in order to reduce the quantity of
energy used inefficiently through investigating energy conservation in many
domains. Energy saving measures are one of the most effective approaches to
close the growing gap between power demand and supply. Energy
conservation is one such technique that can help to alleviate energy scarcity.
7.2 Sources of energy loss and major Items of energy
consumption
The main sources of energy losses are as follows.
a. Light energy loss
b. Heat energy loss
c. Electric energy loss
d. Fuel Losses
a. Light Energy Loss
Lamps transform electrical energy into light energy. LED lamps, energy savers,
floor lamps, and other types of lighting provide more light while using less
power. Some lamps, such as incandescent bulbs, produce less light despite
using more energy. Because of their inefficiency, such bulbs waste energy.
Fluorescent and vapor lamps produce a lot of light, but the chokes that come
with them reduce the power factor. Because most lights lack red light, it is
difficult to identify the proper color, and in the light of some lamps, the
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revolving machinery seems to be motionless or rotating in the other direction,
posing a risk of injury.
It is critical to note that old, broken, and dirty fixtures and reflectors, among
other things, cause light loss, e.g. 10% light loss owing to an old 100 watt
incandescent lamp, 10% due to dust on the lamp's surface. If an additional
20% of energy is lost owing to percentage light loss and unclean fixtures, the
total energy loss is 40%. Regularly cleaning the external surfaces of lamps,
fixtures, reflectors, and globes reduces energy loss and increases light output.
b. Heat Energy Loss
In the condenser attached to the steam turbine, around 50 to 60 percent of
the heat energy created by burning thermal energy sources such as coal, oil,
or natural gas is lost to fresh water. Similarly, the thermal energy generated
by the nuclear fission process is lost along with the cooling water. This thermal
energy is lost without doing any meaningful work when hot water is
discharged directly into a river, sea, or cold water lake, or when hot water is
sent directly through a cooling tower.
The temperature of the exhaust gases from the boiler in thermal power plants
is around 175°C, while the temperature of the exhaust gases from the gas
turbine can reach 550°C. It is possible to calculate how much heat energy is
lost to the atmosphere. Waste heat energy can be used in this manner. Waste
heat energy from gas turbines can also be recovered by employing a combined
cycle to power a steam boiler or a supercharged boiler. Similarly, if the hot
steam created by a steam turbine is delivered to another engine capable of
operating at high temperatures, the heat produced by the fossil fuel can be
better utilized. The steam turbine's exhaust heat energy can also be used to
generate steam in the boiler.
Significant heat energy is wasted in industries as a result of poor design,
inadequate control, and rough handling of electric furnaces. Heat energy loss
happens in homes and hotels during cooking, water heating, and room
heating, among other things, but it is far less than heat energy loss in industry.
c. Electric Energy Loss
Electric energy losses are several types of losses that occur in the power
system from generation to transmission, distribution, and utilization.
Distribution losses are connected with transformer losses from generation to
consumers. A portion of the energy is lost in the form of electric energy losses
caused by the operation of motors at the user's premises, which include
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copper loss, iron or core loss, magnetization loss, and eddy current loss,
among other things. Low power factor is also a significant source of energy
loss in the distribution system. Aside from that, induction motors,
transformers, chokes, and induction heating devices, among other things,
reduce power factor.
Induction motors are used in 90% of industry, and they turn electrical energy
into mechanical energy. Electric motors utilize around 80% of the electrical
energy consumed in manufacturing. A significant quantity of electrical energy
is lost as a result of losses caused by the use of a large number of electric
motors. If the efficiency and power factor of these motors are enhanced, a
large quantity of lost electric energy can be avoided.
d. Fuel Loss
In our country, conventional fuel reserves such as coal, oil, and natural gas are
limited. They will only last for a specific amount of time if they are utilized
excessively. The necessity of the hour is to use these fuels with extreme
caution and to reap the greatest benefits from their utilization. Fuel
consumption in industry is normally minimal, but it is considerable in thermal
power plants. Electric power (electricity) is generated in a thermal power plant
or a gas power plant by using fuel to drive a turbine. After rotating the turbine,
a considerable portion of the heat energy generated by fuel combustion is
discharged into the atmosphere.
The temperature of exhaust gases from boilers in thermal power plants is
around 175°C, while the temperature of exhaust gases from gas turbines can
reach 550°C. It is possible to calculate how much heat energy is lost to the
atmosphere. This is a waste of fuel as well as a waste of heat energy. Fuel
losses are the losses of fuel in the form of heat energy. The release of heat
energy in the form of gases from thermal power plants into the atmosphere
always reduces the efficiency of the thermal power plant. The hot exhaust
gases from a gas turbine plant can be delivered to a boiler to generate steam
and electric power when run as a combined cycle. The plant's efficiency
improves as a result.
7.3 Ways to limit energy losses
Energy can be saved by limiting energy losses using the methods listed below.
a. Light Energy conservation
b. Heat Energy conservation
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c. Electric Energy conservation
d. Fuel Energy conservation
a. Light Energy Conservation
To achieve savings in light energy or to increase lighting efficiency, the
following measures can be taken:
(i) Excess lights should be switched off, and spare lights should be turned
off when not in use. The light can be delivered only at the appropriate
work plane or spot by carefully arranging the lighting scheme, and the
surrounding waste can be avoided. Reflectors, sunshades, and other
such items can be useful in this regard. Instead of traditional blasts,
electronic squares should be employed. If conventional chokes are
utilized, capacitors should be used in conjunction with them to
maintain a higher power factor.
(ii) Lighting levels in stores, passageways, and warehouses are typically
excessive. Energy can be conserved by eliminating some lamps from
such locations and dimming the lighting. Light energy saving can be
accomplished by utilizing more efficient lights that produce light with
colors that are more similar to natural light.
(iii) Dust on lit surfaces also reduces light. The finest light, however, can be
obtained through regular cleaning. To improve light reflection, the
surfaces of ceilings, walls, floors, and furniture in rooms should be
clean, bright, and smooth. In this situation, more light can be obtained
by employing fewer light energy sources. To improve their
performance, lamps, reflectors, and shades should be kept clean.
(iv) When using incandescent lighting, high efficiency lamps should be
used. Replacing incandescent lamps with fluorescent lamps, energy
savers, or LEDs can result in higher light energy saving, efficiency, and
luminance. Fluorescent lamps with various ratings and designs are now
routinely available in the market under the brand name "energy saver."
Their initial investment is substantial. However, in terms of energy
saving, their performance and lifespan are quite good. As a result, their
utilization results in energy savings.
(v) Lamps should not be used where work can be done by daylight.
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b. Heat Energy Conservation
The following procedures can be used to conserve heat energy released from
an installation in the form of steam, hot water, or hot air.
(i) A co-generation system is one in which the useful energy produced by
the usage of a fuel is used in two ways, i.e. the heat energy released
after producing one form of energy is used to produce another type of
energy. Mechanical effort is turned into electrical energy by an electric
generator in a generation system, and the released heat is utilized in
an industrial process or in some other way rather than being
squandered.
(ii) Primary goal of production is to generate electricity, but in addition to
steam, hot water and hot air are available for usage in residential
structures, hotels, swimming pools, and huge commercial buildings in
cold climates. In this approach, the goal of energy conservation is met
by putting heat energy to good use rather of waste it.
(iii) Heat energy can also be conserved by using a combined cycle system.
Because the efficiency of the gas turbine cycle is low, this method is
commonly employed to raise the total thermal efficiency of the gas
turbine cycle.
(iv) Heat pipes can be used to reuse wasted heat energy, resulting in
energy savings. A heat pipe is a sort of heat exchanger that transfers
heat from hot gas to working fluid with great efficiency, i.e. the flue gas
transmits its heat to the working fluid in this type of heat exchanger.
(v) A heat pump system can also help to save energy by conserving heat.
Heat energy is delivered at a cheap cost to places that demand heating,
such as buildings, using heat pumps.
(vi) Good cooking practices can also help you save energy. Heat energy
savings can also be realized by proper furnace design, monitoring, and
operation. Vapor absorption refrigeration systems can also conserve
heat energy. The waste heat of gas or steam is employed in this
method to preserve fruits and vegetables at a minimal cost.
c. Electric Energy Conservation
Electric energy can be conserved in the following ways.
(i) Energy savings can be obtained by lowering electric energy losses
within plants and factories by enhancing the power factor with the help
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of capacitors. A low power factor has an impact on the entire system,
requiring the power supply company to supply more current to offer
the same power, resulting in increased energy losses in the lines.
(ii) Energy loss can be decreased by using a higher transmission voltage.
When a high voltage, such as 220 or 500 kV, is used to transmit a
specific power over a long distance, the current at these voltages is
extremely low. As a result, the energy loss 12 R is decreased. If the
correct size conductor is used for the lines, the efficiency of the lines
increases utilizing Kelvin's law. Thus, energy savings result from energy
decrease. Losses occurring inside the transformer can be minimized to
a large extent by employing transformers with correct ratings and high
efficiency appropriate to the load and operating them at higher loads.
(iii) Energy savings can also be realized by selecting the proper design of
the distribution system that delivers the supply to the users, such as
using a ring main system or a selective system instead of a radial
system. If the entire feeder is not out of power due to a malfunction or
repair, the system's efficiency increases, resulting in less energy loss.
(iv) Except for lighting loads, all standard industrial control and power
devices, such as switches, circuit breakers, contactors, and thermal
relays, can be improved by modifying the power flow circuit design.
Proper monitoring, maintenance, right use, and improved control of all
plant equipment also gives information that can save energy. Most
loads in industries are motors, if standard motors of the correct size
are used, motor losses can be avoided, saving a lot of lost energy.
Motor size and motor load are very essential when it comes to saving
energy through motor utilization. Over and under voltage also affects
the performance of motors. Motor manufacturers allow up to 10%
variation in voltage. Therefore, the efficiency of the motors can be
increased by providing them with the correct rated voltage.
(v) Regular motor maintenance and repair improves their efficiency.
Cleaning, cooling arrangement, protection from chemical vapors and
moisture, periodic overhauling and lubrication, and so on are all part
of maintenance and repair. Motor performance is also affected by
adequate alignment, installation, and connection. Variable frequency
drives, slip power recovery systems, and fluid couplings can all be used
to save energy.
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(vi) Pump selection errors also result in significant energy losses. A pump's
efficiency is 85% at rated flow and drops to 65% at half flow. As a result,
effective pump selection can also result in energy savings.
d. Fuel energy conservation:
Saving fuel energy is critical because fossil fuel stocks are limited and quickly
declining. The following steps can be done to achieve this goal.
(i) Instead of utilizing conventional fuel excessively, fuel savings can be
gained by using it sparingly and only when necessary. When renewable
energy sources are used instead of conventional ones, significant
savings in the utilization of available conventional fuels can be realized.
(ii) Overall efficiency is increased by using a thermal plant with a gas
turbine as a combined cycle, and so fuel energy consumption is
lowered. If natural gas is widely available, it should be used instead of
coal and oil in thermal and steam power facilities. Reusing hot gases
from gas turbines instead of releasing them into the atmosphere can
save fuel.
(iii) Regular cleaning of thermal power plant burners improves efficiency
and saves energy. The generation of the plant grows as the load factor
of the plant increases. As a result, boosting the load factor saves fuel
as well. Fuel savings are accomplished by upgrading the boiler design
and boosting its thermal efficiency.
(iv) By burning the fuel fully in the correct ratio of coal and air in the
combustion chamber, using coal as fuel can reduce fuel consumption.
It is preferable to utilize pulverized coal.
(v) Regular and proper maintenance of diesel and petrol engines can also
help to save oil. Proper savings can be obtained by limiting oil leaks,
using filtered oil, and pre-heating the oil for proper combustion.
(vi) Fuel usage can be reduced as much as feasible by increasing reliance
on hydroelectric and nuclear power generation.
7.4 Power Factor
Power factor is defined as the cosine of the angle between voltage and current
in an alternating current circuit. There is always a phase difference between
voltage and current in an alternating current circuit. The power factor of the
circuit is denoted by the term cos . When an inductive circuit is used, the
current lags behind the voltage, and the power factor is said to be lagging. In a
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capacitive circuit, however, current leads voltage, and power factor is said to
be leading.
Consider an inductive circuit that receives a lagging current from a supply
diagram.
Figure 7.1. Phasor diagram
The circuit current I can be divided into two perpendicular components:
a I cos  in phase with V and
b I sin 90o out of phase with V.
Component I cos is referred to as the active or wattful component,
Whereas, component I sin  is referred to as the reactive or wattless
component.
The reactive component measures the power factor. If the reactive
component is minimal, the phase angle is small, and hence the power factor
cos  is high. As a result, a circuit with a low reactive current (i.e., I sin ) will
have a high power factor and vice versa. It should be noted that the power
factor's value can never be more than unity.
It is common practice to use the words 'lagging' or 'leading' in conjunction with
the numerical value of power factor to indicate whether the current lags or
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leads the voltage. As an example, if the circuit has a power factor of 0.5 and
the current lags the voltage, we can express power factor as 0.5 lagging. Power
factor is sometimes represented as a percentage. Thus, a power factor of 0.8
may be stated as 80% lagging.
7.4.1 Power Triangle
Power factor analysis can also be performed in terms of the
power drawn by the alternating current circuit. If we multiply each side of the
current triangle oab of Fig. 7.1 by the voltage V, we get the power triangle OAB
shown in Fig. 7.2,
Where
OA = VI cos  and indicates the active power in watts or kW.
AB = VI sin  and indicates the reactive power in VAR or kVAR.
OB = VI and indicates the apparent power in VA or kVA.
Figure 7.2. Power triangle
The power triangle has the following points:
The apparent power in an alternating current circuit consists of two
components, active and reactive power, which are at right angles to each
other.
OB2 = OA2 + AB2
or
(apparent power)2 = (active power)2 + (reactive power)2
or
(kVA)2 = (kW)2 + (kVAR)2
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Power factor, cos  =
Conservation of Energy
OA
OB
=
𝐀𝐜𝐭𝐢𝐯𝐞 𝐏𝐨𝐰𝐞𝐫
𝐀𝐩𝐩𝐚𝐫𝐞𝐧𝐭 𝐏𝐨𝐰𝐞𝐫
=
KW
KVA
As a result, a circuit's power factor can also be defined as the ratio of active
power to apparent power. This is a completely general definition that may be
used to every instance, regardless of waveform.
The low power factor is caused by lagging reactive power. The power triangle
clearly shows that the lower the reactive power component, the higher the
power factor of the circuit.
kVAR = kVA sin  = kW sin 
cos 
kVAR = kW tan 
The power triangle is flipped for leading currents. This fact holds the key to
improving the power factor. If a device that consumes leading reactive
power (e.g., a capacitor) is connected in parallel with the load, the load's
lagging reactive power is partially neutralized, enhancing the load's power
factor.
The power factor of a circuit can be expressed in one of three ways:
Power factor = cos  = cosine of angle between V and I
R
𝐑𝐞𝐬𝐢𝐬𝐭𝐚𝐧𝐜𝐞
a)
Power factor = cos  =
b)
Power factor, cos  = (VI Cos  )/ VI
Z
=
𝐈𝐦𝐩𝐞𝐝𝐞𝐧𝐜𝐞
=
𝐀𝐜𝐭𝐢𝐯𝐞 𝐏𝐨𝐰𝐞𝐫
𝐀𝐩𝐩𝐚𝐫𝐞𝐧𝐭 𝐏𝐨𝐰𝐞𝐫
The reactive power is not utilized in the circuit and does not perform any
beneficial work. It simply flows back and forth in the circuit in both
directions. Reactive power is not measured by a wattmeter.
7.4.2 Causes of Low Power Factor
Low power factor is bad from an economic standpoint. In most cases, the
power factor of the entire load on the supply system is less than 0.8. Low
power factor can be caused by the following factors:
a. The majority of A.C. motors are induction type (1 and 3 induction
motors) with low lagging power factor. These motors have a power factor
that is extremely low on light load (0.2 to 0.3) and rises to 0.8 or 0.9 at full
load.
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b. Arc lamps, electric discharge lamps and industrial heating furnaces work at
low lagging p.f.
c. The electricity system's load varies, being high in the morning and evening
and low at other times. The supply voltage is increased during the low load
period, which raises the magnetization current. As a result, the power factor
is reduced.
7.4.3 Disadvantages of Low Power Factor
The power factor is important in alternating current circuits because
it determines how much power is utilized.
P = VL IL cos 
(For single phase supply)
IL = P / (VL cos 
P=
...(i)
3 VL IL cos 
IL = P / (
(For 3 phase supply)
3 VL cos 
...(ii)
The load current is inversely proportional to the power factor for fixed power
and voltage, as shown above. Lower the power factor, greater the load
current, and vice versa. A power factor less than unity leads in the following
drawbacks
a. Large kVA rating of equipment
Electrical equipment (such as alternators, transformers, and switchgear) is
always rated in kVA.
Now,
kVA = kW
cos 
The kVA rating of the equipment is clearly inversely proportional to the power
factor. The higher the kVA rating, the lower the power factor. As a result, at low
power factor, the kVA rating of the equipment must be increased, making the
equipment larger and more expensive.
b. Greater conductor size
At low power factor, the wire must carry greater current to transmit or
distribute a set quantity of power at constant voltage. This involves the use of
big conductors. Consider the scenario of a single phase a.c. motor with a full
load input of 10 kW and a terminal voltage of 250 V. The input full load current
at unity p.f. would be 10,000/250 = 40 A. At 0.8 p.f., the kVA input would be
10/0.8 = 12.5, and the current input would be 12,500/250 = 50 A. If the motor
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is operated at a low power factor of 0.8, the cross-sectional area of the supply
cables and motor wires must be calculated using a current of 50 A rather than
the 40 A required at unity power factor.
c. Large copper losses
The high current at low power factor creates increased I2R losses in all supply
system elements. As a result, efficiency suffers.
d. Poor voltage regulation:
The high current at low lagging power factor generates larger voltage dips in
alternators, transformers, transmission lines, and distributors. As a result, the
voltage available at the supply end is reduced, reducing the performance of
utilization devices. Extra equipment (such as voltage regulators) is necessary
to keep the receiving end voltage within allowable limits.
e. Reduced handling capacity of system:
The lagging power factor decreases the handling capacity of all system
elements. This is due to the reactive component of current, which prevents
full utilization of installed capacity.
The preceding explanation leads to the conclusion that a low power factor in
the supply system is an unwanted trait.
7.4.4 Power Factor Improvement
The low power factor is mostly owing to the fact that most power loads are
inductive and hence require lagging currents. To increase the power factor,
connect some leading-edge device in parallel with the load. A capacitor is one
such device. The capacitor draws a leading current and partially or totally
neutralizes the lagging reactive component of the load current. This raises the
load's power factor.
Figure 7.3. Power factor improvement
Consider a single phase load with lagging current I and a power factor cos 1
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as illustrated in Figure 7.3 to demonstrate the power factor enhancement
provided by a capacitor.
The capacitor C is linked in series with the load. The capacitor takes current IC,
which is 90o ahead of the supply voltage. As illustrated in the phasor diagram
of Fig. 7.3 (iii), the resulting line current I is the phasor sum of I and IC, and its
angle is 2. It is obvious that 2 is less than 1, hence cos 2 is bigger than cos
1. So, the power factor of the load is increased. The following points are
noteworthy:
(i) After p.f. correction, the current I is less than the current I.
(ii) Because the capacitor merely reduces the lagging reactive
component, the active or wattful component stays constant before
and after p.f. correction.
I cos 1 = I  cos 2

(iii) After p.f. improvement, the lagging reactive component is lowered
and equals the difference between the lagging reactive component of
the load (I sin 1) and the capacitor current (IC), i.e.,
I  sin 2 = I sin 1  IC
As
(iv)

I cos 1 = I  cos 2
VI cos 1 = VI  cos 2
[Multiplying by V]
As a result of the improved power factor, active power (kW) stays
same.
(v)
I  sin 2 = I sin 1  IC

VI  sin 2 = VI sin 1  VIC
[Multiplying by V]
i.e., Net kVAR after p.f. correction = Lagging kVAR before p.f.
correction leading kVAR of equipment
7.4.5 Power Factor Improvement Equipment
Normally, the power factor of a big generating station's total load is in
the range of 0.8 to 0.9. However, it can be lower at times, and in such
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instances, it is normally preferable to take particular measures to boost the
power factor. This can be accomplished using the following tools:
a. Static capacitors.
b. Synchronous condenser.
c. Phase advancers.
Figure 7.4. Power factor improvement in Y and delta connections
a. Static capacitor
Power factor can be enhanced by connecting capacitors in parallel with lagging
power factor devices. The capacitor (also known as a static capacitor) draws a
leading current and partially or entirely neutralizes the load current's lagging
reactive component. This increases the load's power factor. For three-phase
loads, the capacitors can be linked in either a delta or a star configuration, as
shown in Figure 7.4. In factories, static capacitors are almost often employed
to improve power factor.
Advantages
a. They bear few losses.
b. Because there are no moving parts, they require less
maintenance.
c. Because they are light and do not require a foundation, they
are simple to install.
d. They can operate in normal air circumstances.
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Disadvantages
a. They have a limited service life of 8 to 10 years.
b. They are readily damaged if the voltage exceeds the rated
value.
c. Once the capacitors have been destroyed, it is uneconomical
to repair them.
b. Synchronous condenser
When over-excited, a synchronous motor takes a leading current and hence
behaves like a capacitor. A synchronous condenser is an over-excited
synchronous motor that runs without load. When such a machine is linked in
parallel with the power supply, it draws a leading current, which somewhat
neutralizes the load's lagging reactive component. As a result, the power
factor improves.
Figure 7.5. P.f improvement using synchronous condenser
Figure 7.5 depicts the power factor improvement achieved using the
synchronous condenser approach. At low lagging power factor cos L, the
3load takes current IL. The synchronous condenser accepts an impedance
Im that leads the voltage by an angle m. The resulting current I is the phasor
sum of Im and IL and follows the voltage by an angle. It is obvious that  is
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smaller than L, hence cos  is bigger than cos L. As a result, the power factor
is increased from cos L to cos . Synchronous condensers are commonly
utilized to increase power factor at huge bulk supply substations.
The reactive power consumed by a synchronous motor is determined by two
factors: The direct current field excitation and the mechanical load produced
by the motor. A synchronous motor with maximal excitation and zero load
consumes the most leading power.
Advantages
a. The magnitude of the current drawn by the motor can be
adjusted by altering the field excitation. This aids in attaining
stable control of power factor.
b. The motor windings are extremely thermally stable to short
circuit currents.
c. The problems are easily remedied.
Disadvantages
a. The motor suffers from significant losses.
b. The expense of maintenance is substantial.
c. It makes noise.
d. The cost is higher than that of static capacitors of the same
rating, except at capacities exceeding 500 kVA.
e. Because synchronous motors do not have self-starting torque,
an auxiliary equipment must be provided for this purpose.
c. Phase advancers
Induction motors depend on phase advancers to improve their power factor.
An induction motor's low power factor is caused by the fact that its stator
winding draws exciting current that is 90o behind the supply voltage. If the
exciting ampere turns can be supplied by another alternating current source,
the stator winding will be relieved of exciting current and the motor's power
factor will be enhanced.
The phase advancer, which is just an A.C. exciter, does this task. The phase
advancer is positioned on the same shaft as the main electric motor and is
linked to the motor's rotor circuit. At slip frequency, it provides exciting
ampere turns to the rotor circuit. The induction motor can be made to operate
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on leading power factor like an over-excited synchronous motor by giving
more ampere turns than required.
The primary benefits of phase advancers are as follows. For starters, because
the exciting ampere turns are supplied at slip frequency, the lagging kVAR
drawn by the motor is significantly reduced. Second, phase advancers are
useful in situations when synchronous motors are not feasible. The main
drawback of phase advancers is that they are not cost effective for motors with
less than 200 horsepower.
Advantages
a. Because the exciting ampere turns are delivered at slip
frequency, the lagging kVAR drawn by the motor is sufficiently
reduced. (fs).
b. The Phase Advancer is easily applicable where the use of
synchronous motors is prohibited.
Disadvantage
a. For motors with less than 200 horsepower (about 150kW),
using a Phase Advancer is not cost effective.
7.4.6 Importance of Power Factor Improvement
As explained below, improving power factor is essential for both
consumers and generating stations.
a. For consumers
Electricity prices for a consumer's maximum demand in kVA plus the units
consumed must be paid. If the consumer improves his power factor, his
maximum kVA demand decreases, resulting in an annual savings owing to
maximum demand costs. Although power factor enhancement necessitates
additional annual spending due to p.f. correction equipment, it results in a net
annual savings for the consumer.
b. For generating stations
Power factor increase is as important to a generating station as it is to a
consumer. A power station's generators are rated in kVA, while the useful
output is determined by kW output. Because station output is kW = kVA X cos
, the number of units delivered by it is determined by the power factor. The
higher the generating station's power factor, the more kWh it contributes to
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the system. This ultimately results in the conclusion that higher power factor
improves the power station's earning capability.
7.5 Calculations of power factor improvement in the
context of energy conservation
Example 7.1. Let us illustrate the power relations in an A.C. circuit with an
example. Suppose a circuit draws a current of 10 A at a voltage of 220 V and
its p.f. is 0·8 lagging. Then,
Apparent power = VI = 220 x 10 = 2200 VA
Active power = VI cos = 220 x 10 x 0·8 = 1760 W
Reactive power = VI sin = 220 x 10 x 0·6 = 1320 VAR
The circuit receives an apparent power of 2200 VA and is able to
convert only 1760 watts into active power. The reactive power is 1320 VAR and
does no useful work. It merely flows into and out of the circuit periodically. In
fact, reactive power is a liability on the source because the source has to supply
the additional current.
Example 7.2 An alternator is supplying a load of 600 kW at a p.f. of 0·6
lagging. If the power factor is raised to unity, how many more kilowatts can
alternator supply for the same kVA loading?
Solution:
kVA = kW/ cos  kVA
kW at 0·6 p.f. = 600 kW
kW at 1 p.f. = 1000 x 1 = 1000 kW
Hence, Increased power supplied by the alternator = 1000 - 600 = 400 kW
When the p.f. of the alternator is unity, the 1000 kVA are also 1000 kW and the
engine driving the alternator has to be capable of developing this powertogether
with the losses in the alternator. But when the power factor of the load is 0·6,
the power is only 600 kW. Therefore, the engine is developing only 600 kW,
though the alternator is supplying its rated output of 1000 kVA.
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Example 7.3 A 3-phase, 10 kW induction motor has a p.f. of 0·75 lagging. A
bank of capacitors is connected in delta across the supply terminals and p.f.
raised to 0·9 lagging. Determine the kVAR rating of the capacitors connected
in each phase.
Solution:
Original p.f., cos 1 = 0·75 lag ;
Motor input, P = 10 kW
Final p.f., cos 2 = 0·9 lag
;
Efficiency,  = 100 % (assumed)
 = cos1 (0·75)
= 41·41o
1
;
tan  =1 tan 41·41º = 0·8819
 = cos1 (0·9)
= 25·84o
2
;
tan  =2 tan 25·84º = 0·4843
Leading kVAR taken by the condenser bank
= P (tan 1  tan 2)
= 10 (0·8819  0·4843) = 3·98 kVAR
 Rating of capacitors connected in each phase
= 3·98/3 = 1·327 kVAR
Example 7.4. The load on an installation is 400 kW, 0·8 lagging p.f. which
works for 3000 hours per annum. The tariff is Rs 100 per kVA plus 20 paise per
kWh. If the power factor is improved to 0·9 lagging by means of loss-free
capacitors costing Rs 60 per kVAR, calculate the annual saving effected. Allow
10% per annum for interest and depreciation on capacitors.
Solution:
Load, P = 400 kW
cos 1 = 0·8 ;
tan 1 = tan (cos1 0·8) = 0·75
cos 2 = 0·9 ;
tan 2 = tan (cos1 0·9) = 0·4843
Leading kVAR taken by the capacitors
= P (tan 1  tan 2) = 400 (0·75 
0·4843) = 106.28
Annual cost before p.f. correction
Max. kVA demand = 400/0·8 = 500
kVA demand charges = Rs 100  500 = Rs 50,000
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Units consumed/year = 400  3000 = 12,00,000 kWh
Energy charges/year = Rs 0·2  12,00,000 = Rs 2,40,000
Total annual cost = Rs (50,000 + 2,40,000) = Rs 2,90,000
Annual cost after p.f. correction
Max. kVA demand = 400/0·9 = 444·44
kVA demand charges = Rs 100  444.44 = Rs 44444
Energy charges = Same as before i.e., Rs 2,40,000
Capital cost of capacitors = Rs 60  106·28 = Rs 6376.8
Annual interest and depreciation = Rs 0·1  6376.8 = Rs
637.68
Total annual cost = Rs (44,444 + 2,40,000 + 637.68) = Rs
285081.8

 Annual saving = Rs (2,90,000  2,85,081.8) = Rs
4918.2
Example 7.5 A supply system feeds the following loads
(i) a lighting load of 250 kW
(ii) a load of 200 kW at a p.f. of 0·707 lagging
(iii) a load of 400 kW at a p.f. of 0·8 leading
(iv) a load of 250 kWat a p.f. 0·6 lagging
(v) a synchronous motor driving a 270 kW d.c. generator and having an overall
efficiency of 90%.
Calculate the power factor of synchronous motor so that the station power
factormay become unity.
Solution:
The lighting load works at unity p.f. and, therefore, its lagging kVAR is zero.
The lagging kVAR are taken by the loads (ii) and (iv), whereas loads (iii) and (v)
take the leading kVAR. For station power factor to be unity, the total lagging
kVAR must be neutralised by the total leading kVAR. We know that kVAR = kW
tan .
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 Total lagging kVAR taken by loads (ii) and (iv)
= 200 tan (cos1 0·707) + 250 tan (cos1 0·6)
= 200  1 + 250  1·33 = 532.5
Leading kVAR taken by the load (iii) = 400 tan (cos1 0·8)
= 400  0·75 = 300
 Leading kVAR to be taken by synchronous motor = 532.5  300
= 232.5 kVAR
Motor input = output/efficiency = 270/0·9 = 300 kW
If  is the phase angle of synchronous motor, then,
tan  = kVAR/kW = 232.5/300 = 0·775


leading
 = tan1 0·775 = 37·77o
 p.f. of synchronous motor = cos  = cos 37·77o = 0·79
Therefore, in order that the station power factor may become unity, the
synchronous motor should be operated at a p.f. of 0·79 leading.
Example 7.6. A factory takes a load of 400 kW at 0·85 p.f. lagging for 2000
hours per annum. The traiff is Rs 150 per kVA plus 5 paise per kWh consumed.
If the p.f. is improved to 0·9 lagging bymeans of capacitors costing Rs 420 per
kVAR and having a power loss of 100 W per kVA, calculate the annual saving
effected by their use. Allow 10% per annum for interest and depreciation.
Solution:
Factory load, P1 = 400 kW
cos 1 = 0·85 ;
tan 1 = 0·62
cos 2 = 0·9 ;
tan 2 = 0·4843
Suppose the leading kVAR taken by the capacitors is x.
Capacitor Loss =
100 x
1000
= 0.1 x kW
Total power, P2 = (400 + 0·1 x) kW
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Leading kVAR taken by the capacitors is
x = P1 tan 1  P2 tan 2
= 400  0·62  (400 + 0·1x)  0·4843
or
x = 248  193.72  0·04843 x

x = 54·28/1·04843 = 51·773 kVAR
Annual cost before p.f. improvement
Max. kVA demand = 400/0.85 = 470.588
kVA demand charges = Rs 150  470.588 = Rs 70588.2
Units consumed/year = 400  2000 = 8,00,000 kWh
Energy charges = Rs 0·05  8,00,000 = Rs 40,000
Total annual cost = Rs (70588.2 + 40,000) = Rs 110588.2
Annual cost after p.f. improvement
Max. kVA demand = 400/0·9 = 444.44
kVA demand charges = Rs 150  444·44 = Rs 66,666
Energy charges = same as before i.e., Rs 40,000
Annual interest and depreciation = Rs 420  51·773  0·1 = Rs
2174.466
Annual energy loss in capacitors = 0·1 x  2500 = 0·1  51·773 
2000
= 10354.6 kWh
Annual cost of losses occurring in capacitor= Rs 0·05 
10354.6 = Rs 517.73
Total annual cost = Rs (66,666 + 40,000 + 2174.466 +
517.73) = Rs 109358.196
Annual saving = Rs (110588.2 109358.196) = Rs 1230.004
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Example 7.7. A factory load consists of the following:
An induction motor of 100 H.P. (74.6 kW) with 0·8 p.f. and efficiency
0·85.
(ii) a synchronous motor of 50 H.P. (37.3 kW) with 0·9 p.f. leading and
efficiency 0·9.
(iii) Lighting load of 20 kW at unity p.f.
Find the annual electrical charges if the tariff is Rs 60 per kVA of maximum
demand per annum plus 5 paisa per kWh; assuming the load to be steady for
2000 hours in a year.
(i)
Solution:
Input power to induction motor = 74·6/0·85 = 87·76 kW
Lagging kVAR taken by induction motor = 87·76 tan (cos1 0·8) = 65.82
Input power to synchronous motor = 37·3/0·9 = 41·44 kW
Leading kVAR taken by synchronous motor = 41·44 tan (cos1 0·9) = 20.07
Since lighting load works at unity p.f., its lagging kVAR = 0.
Net lagging kVAR = 65.82  20 = 45·82
Total active power = 87·76 + 41·44 + 20 = 149·2 kW
Total KVA = √(149 · 2 )2 − (45 · 82)2
= 156.077 kVA
Annual kVA demand charges = Rs 60  156.077 = Rs 9,364.636
Energy consumed/year = 149·2 2000 = 2,98,400 kWh
Annual Energy charges = Rs 0·05  2,98,400 = Rs 14,920
Total annual bill = kVA demand charges + Energy charges
= Rs (9,364.636 + 14,920) = Rs 24,284.636
Example 7.8. An industrial load consists of
(i) A synchronous motor of 200 metric h.p.
(ii) Induction motors aggregating 400 metric h.p, 0·707 power factor lagging
and 82% efficiency and
(iii) Lighting load aggregating 60 kW.
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The tariff is Rs 100 per annum per kVA maximum demand plus 6 paise per kWh.
Find the annual saving in cost if the synchronous motor operates at 0·8 p.f.
leading, 93% efficiency instead of 0·8 p.f. Lagging at 93% efficiency.
Solution:
The annual power bill will be calculated under two conditions viz., (a) when
synchro- nous motor runs with lagging p.f. and (b) when synchronous motor
runs with a leading p.f.
(a) When synchronous motor runs at p.f. 0·8 lagging. We shall find the
combined kW and thencalculate total kVA maximum demand using the
relation:
Total KVA = √(kW)2 − (kVA)2
200 𝑥 735.5
Input to Synchronous Motor =
1000 𝑥 0.93
= 158.172 kW
Lagging kVAR taken by the synchronous motor
= 158.172 tan (cos1 0·8) = 158.172  0·75 =
118.63 kVAR
400 𝑥 735.5
Input to Induction Motors =
1000 𝑥 0.82
= 358.78 kW
Lagging kVAR taken by induction motors
= 358.78 tan (cos1 0·707) = 358.78  1 = 358.78
kVAR
Since lighting load works at unity p.f., its lagging kVAR is zero.

Total lagging kVAR = 118.63 + 358.78 = 477·41 kVAR
Total active power = 158.172 + 358.78 + 60 = 576·952 kW
Total KVA = √(576 · 952 )2 − (477 · 41 )2
= 748.86 kVA
Annual kVA demand charges = Rs 100  748.86 = Rs 74,886
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Energy consumed/year = 576·952  8760 = 5054.099.52 kWh
Annual energy charges = Rs 0·06  5054.099.52 = Rs 303245.9712
Total annual bill = Rs (74,886 + 303245.9712) = Rs 378131.9712
When synchronous motor runs at p.f. 0·8 leading. As the synchronous
motor runs at leading p.f. of 0·8 (instead of 0·8 p.f. lagging), therefore, it
takes now 118.63 leading kVAR. The lagging kVAR taken by induction motors
are the same as before i.e., 358.78.
(b)

Net lagging kVAR = 358.78 118.63 = 240·15
Total active power = Same as before i.e., 576·952 kW
Total KVA = √(576 · 952 )2 − (240 · 15)2
= 624.936 kVA
Annual kVA demand charges = Rs 100  624.936 = Rs 62493.6
Annual energy charges = Same as before i.e., Rs 303245.9712
Total annual bill = Rs (62493.6 + 303245.9712) = Rs
365737.5712
Annual saving = Rs (378131.9712 365737.5712) = Rs
12392.4
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Sample Multiple Choice Questions
1. The meaning of energy conservation is
(a) The wastage of energy
(b) The saving of energy
(c) Less use of energy
(d) The control of energy
2. The sun is the natural source of ---------- energy
(a) Heat
(b) Light
(c) Both a & b
(d) Nuclear energy
3. The mostly heat energy is obtained from
(a) Sun
(b) Fossil Fuel
(c) Geothermal
(d) Wind
4. The sources of energy losses are
(a) Light energy loss
(b) Heat energy loss
(c) Electric energy loss & Fuel loss
(d) All of these
5. The following procedure is used to limit the energy loss
(a) Light energy conservation
(b) Heat energy conservation
(c) Electric energy conservation
(d) All of these
6. The advantages of heat energy over other energies are
(a) Easy control
(b) High efficiency
(c) Clean environment
(d) All of these
7. When electricity is use with high efficiency
(a) Reduces losses
(b) Increases industrial production
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(c) Both a & b
(d) None of these
8. The regular maintenance and repair of motors causes saving in
(a) Energy
(b) Light
(c) Heat
(d) Water
9. The per unit cost of electricity is increasing due to
(a) Line losses
(b) Theft of electricity
(c) Expensive contract of purchasing electricity with private sector
(d) All of these
10. The ratio between resistance and impedance is called
(a) Farm Factor
(b) Peak Factor
(c) Power Factor
(d) Reflection factor
11. In AC, The ------- of angle between current and voltage is called power
factor
(a) Sin
(b) Cos
(c) Tan
(d) Cot
12. The apparent power is measured in
(a) VA
(b) KVA
(c) Both a & b
(d) KW
13. When the current remains behind voltage in AC circuit, the power factor is
(a) Lagging
(b) Leading
(c) Unity
(d) None of these
14. When the current remains ahead of voltage in AC circuit, the power factor
is
(a) Lagging
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(b) Leading
(c) Unity
(d) None of these
15. KW is equal to
(a) KVA Sin 
(b) KVA Cos 
(c) KVAR Sin 
(d) KVAR Cos 
16. KVAR is equal to
(a) KVA Sin 
(b) KVA Cos 
(c) KVAR Sin 
(d)
17. The capacitor supplies
(a) Leading KVA
(b) Leading KW
(c) Lead Current
(d) Both a & c
18. The formula to find KVAR
(a) KW Tan 
(b) KW Cos 
(c) KW Sin 
(d) None of these
19. The formula to find KW
(a) KVA Sin 
(b) KVA Cos 
(c) KVA Tan 
(d) None of these
20. No Load over excited motor is called
(a) Capacitor
(b) Synchronous Condenser
(c) Both a & b
(d) None of these
21. By increasing power factor reduces
(a) Corona Losses
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(b) Iron Losses
(c) Both a & b
(d) Power Losses
22. The power factor in DC Supply is always
(a) Zero
(b) Unity
(c) Lagging
(d) Leading
23. The improvement in power factor gives advantage to
(a) Supply company only
(b) Industrial consumers only
(c) Both a & b
(d) Household consumers
24. To improve Power factor, -------- is/are are used
(a) Static Capacitor
(b) Synchronous motor
(c) Phase advancer
(d) All of these
25. The Phase advancer is used for the improvement of
(a) Load Factor
(b) Demand Factor
(c) Power factor
(d) User Factor
ANSWERS OF MCQ’s
1.
b
2.
c
3.
b
4.
d
5.
d
6.
d
7.
c
8.
a
9.
d
10.
c
11. b
12. c
13. a
14. b
15.
b
16. a
17. d
18. a
19. b
20.
b
21. d
22. b
23. c
24. d
25.
c
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Sample Short Questions
1. What is meant by energy conservation?
2. What is the necessity of energy conservation?
3. Write the names of different sources of energy losses. Also write the
names of methods to limit energy losses.
4. How can light energy loss be reduced?
5. What is meant by heat energy loss?
6. Which power plant has the highest heat energy loss?
7. What is meant by electric energy loss?
8. Write any four measures for fuel energy conservation.
9. What is meant by power factor?
10. Power factor is determined by which formula?
11. What is meant by lagging and leading power factor?
12. What is the difference between real and reactive power?
13. What is the effect of increasing or decreasing the power factor on the
real power?
14. What is the effect on reactive power of reducing power factor?
15. What is meant by reactive component or magnetising component of
current?
16. A 100 kVA generator is supplying a load having a power factor of 0.8
Lagging. How many kilowatt loads can this generator supply?
17. How does the supply company suffer financial loss due to reduce
power factor?
18. What is the effect of reduction in power factor of transmission and
distribution systems on the distribution committee?
19. If the power is kept constant and the power factor is reduced, what is
the effect on the size of the conductor?
20. Write the causes or sources of low power factor.
21. What is the loss to an industrial user due to reduction in power factor,
mention any four?
22. Write any four advantages of improving power factor in a power plant.
23. What is the standard power factor limit in Pakistan?
24. Name the methods of improving power factor with the help of
capacitors with reference to the supplier.
25. Write down the disadvantages of a static capacitor.
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26. Write the advantages of synchronous condenser.
27. Write are the disadvantages of synchronous condenser.
28. What is the purpose of Phase Advancer?
29. What are the benefits of phase advancer?
30. What are the disadvantages of phase advancer?
Sample Long Questions
1.
2.
3.
4.
Write in detail different sources of Energy losses?
Explain methods to limit energy losses?
Describe effects of low power factor on energy losses.
Describe different methods to improve power factor?
Sample Numerical Problems
1. What should be the kVA rating of a capacitor which would raise the
power factor of load of 200 kW from 0·5 lagging to 0·9 lagging?
2. A 3-phase, 50 Hz, 3300 V star connected induction motor develops 300
H.P. (223·8 kW), the power factor being 0·707 lagging and the
efficiency 0·86. Three capacitors in delta are connected across the
supply terminals and power factor raised to 0·9 lagging.
Calculate:
a. the kVAR rating of the capacitor bank.
b. the capacitance of each unit.
3. A 3-phase, 50 Hz, 3000 V motor develops 500 H.P. (373 kW), the power
factor being 0·75 lagging and the efficiency 0·93. A bank of capacitors
is connected in delta across the supply terminals and power factor
raised to 0·95 lagging. Each of the capacitance units is built of five
similar 600-V capacitors. Determine the capacitance of each capacitor.
4. A factory takes a load of 600 kW at 0·8 p.f. (lagging) for 2500 hours per
annum and buys energy on tariff of Rs 100 per kVA plus 10 paise per
kWh. If the power factor is improved to 0·9 lagging by means of
capacitors costing Rs 60 per kVAR and having a power loss of 100 W
per kVA, calculate the annual saving effected by their use. Allow 10%
per annum for interest and depreciation on the capacitors.
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5. A station supplies 300 kVA at a lagging power factor of 0·8. A
synchronous motor is connected in parallel with the load. If the
combined load is 300 kW with a lagging p.f. of 0.9.
Determine:
a. The leading kVAR taken by the motor.
b. kVA rating of the motor.
c. p.f. at which the motor operates.
6. A generating station supplies power to the following :
a. A lighting load of 200 kW;
b. An induction motor 600 h.p. (447·6 kW) p.f. 0·8 lagging, efficiency
92%;
c. A rotary converter giving 160 A at 400 V at an efficiency of 0·95.
d. What must be the power factor of the rotary convertor in order that
power factor of the supply station may become unity?
7. A 3-phase, 400 V synchronous motor having a power consumption of
60 kW is connected in parallel with an induction motor which takes
250 kW at a power factor of 0·8 lagging.
a. Calculate the current drawn from the mains when the power factor
of the synchronous motor is unity.
b. At what power factor should the synchronous motor operate so that
the current drawn from the mains is minimum?
8. A factory load consists of the following :
a. An induction motor of 170 h.p. (126·82 kW) with 0·7 p.f. lagging and
80% efficiency.
b. A synchronous motor of 120 h.p. (89·52 kW) with 0·85 p.f. leading at
90% efficiency.
c. A lighting load of 60 kW.
Find the annual electric charges if the tariff is Rs 100 per annum per
kVA maximum demand plus 8 paisa per kWh; assuming the load to be
steady throughout the year.
9. A 3-phase synchronous motor having a mechanical load (including
losses) of 130 kW is connected in parallel with a load of 530 kW at 0·8
p.f. lagging. The excitation of the motor is adjusted so that the kVA
input to the motor becomes 150 kVA. Determine the new power factor
of the whole system.
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10. A 3-phase synchronous motor is connected in parallel with a load of
720 kW at 0·7 power factor lagging and its excitation is adjusted till it
raises the total p.f. to 0.9 lagging. Mechanical load on the motor
including losses is 160 kW. Find the power factor of the synchronous
motor.
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