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Dr.G.Nageswara Rao
Professor , EEE Department
Lakireddy Bali Reddy College of Engineering
(LBRCE)
Course Outcomes: At the end of the course, the student will be able to:
CO1: Understand the operation of non-renewable electrical power generating
stations (Understand-L2)
CO2: Illustrate the economic aspects of power generation (Apply-L3)
CO3: Understand the a.c distribution system and performance of insulated
cables (Understand-L2)
CO4: Evaluate the electrical and mechanical parameters of transmission lines
(Apply-L3)
CO5: Analyze operation of overhead line insulators and phenomena of corona
(Understand-L2)
Course Educational Objective:
This course enables the student to learn different types of non-
renewable power generation methods, the economic aspects of
power generation, tariff methods and design aspects of
transmission lines.
2
3
UNIT-I: POWER GENERATION METHODS
Introduction to typical layout of an electrical power system, present power
scenario in India, Generation of electric power: non-renewable sources
(Qualitative): Hydro station, Steam power plant, Nuclear power plant and
Gas turbine plant.
UNIT-II: ECONOMICS OF GENERATION
Introduction, definitions of connected load, maximum demand, demand
factor, load factor, diversity factor, Load duration curve, number and size
of generator units. Base load and peak load plants. Cost of electrical
energy-fixed cost, running cost, Tariff on charge to customer.
UNIT-III: AC DISTRIBUTION & CABLES
AC Distribution: Introduction, AC distribution, Single phase, 3-phase-
3wire, 3 phase 4 wire system, bus bar arrangement, Selection of site and
layout of substation.
Insulated Cables: Introduction, insulation, insulating materials, extra
high voltage cables, grading of cables, insulation resistance of a cable,
capacitance of a single core and three core cables, overhead lines versus
underground cables, types of cables.
4
Unit-IV: ELECTRICAL AND MECHANICAL DESIGN OF
TRANSMISSION LINES
Transmission line sag calculation: The catenary curve, sag tension
calculations, supports at different levels, stringing Chart, inductance and
capacitance calculations of transmission lines: line conductors,
inductance and capacitance of single phase and three phase lines with
symmetrical and unsymmetrical spacing, Composite conductors-
transposition, bundled conductors, and effect of earth on capacitance.
UNIT-V: CORONA& INSULATORS
Corona: Introduction, disruptive critical voltage, corona loss, Factors
affecting corona loss and methods of reducing corona loss, Disadvantages
of corona, interference between power and Communication lines,
Numerical problems.
Overhead Line Insulators: Introduction, types of insulators, Potential
distribution over a string of suspension insulators, Methods of equalizing
the potential, testing of insulators.
5
TEXT BOOKS:
1. Soni, Gupta & Bahtnagar, Power Systems Engineering, Dhanpat Rai &
Sons, 2016.
2. C.L. Wadhwa, Electrical Power Systems, 6th Edition, New
AgeInternational,2009.
REFERENCE BOOKS:
1. M.V.Deshpande, Elements of Electrical Power Station Design, 3rd,
Wheeler Pub.1997.
2. C.L. Wadhwa, Generation, Distribution and Utilization of Electrical
Energy, 3rd Edition, New AgeInternational,2015. 3. V K Mehta & Rohit
Mehta, Principles of Power Systems (Multicolor Edition), 24/e, S.Chand
Publishing, 4th Edition ,2005.
W.D.Stevenson, Elements of Power System Analysis, 4th Edition,
McGraw Hill, 1982.
https://www.slideshare.net/raoakhil/thermal-power-plants-237930541
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8 February 2024 Department of EEE 7
8 February 2024 Department of EEE 8
 Electricity sector in India is growing at a rapid pace.
 The present peak demand is about 1,15,000 MW and the Installed
Capacity is 1,52,380 MW using generation from thermal (63%), hydro (25
%), Nuclear (9 %) and renewables (9 %)
8 February 2024 Department of EEE 9
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8 February 2024 Department of EEE 11
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14
Basic Principal of Steam Power Plant
The heat produced for burning of coal & with the help
of water steam is produced. This produced steam flow
towards turbine i.e. kinetic energy is converted into
mechanical energy. The input steam drives the prime
mover or turbine, simultaneously the generator also
start to rotate. At that time mechanical energy is
converted into electrical energy.
Thermal Power Plant
15
Selection of Site for Thermal Power Plant
1. Supply of Fuel: The Steam power station should be located near the coal
mine so that transportation cost of fuel is minimum. If the land is not available
near to coal mines then provide adequate facilities for transportation of fuel.
2. Available of Water: A huge amount of water is required in boiler &
condenser, so that the plant should be located near the river, lake etc.
3. Transportation Facility: For steam power station provide better
transportation facility for the transportation of man, machinery etc.
4. Cost & Type of Land: The Steam Power Station should be located where
the cost of land is chief & also future extension is possible.
5. Near to Load Center: In order to reduce transmission & distribution losses
the plant should be located near to load center.
6. Distance from Populated Area: As the thermal power plant produces flue
gases, these gases will effect to live human being, so that the plant should be
located away from thickly populated area.
7. Disposal Facility Provided: As the thermal power plant produces ash, while
burning of coal. So, disposal of ash facility should be provided.
8. Availability of labour: Skilled and unskilled labour should be available
nearly.
General Layout of
Thermal Power Plant
17
Flow Diagram of
Steam Thermal Power Plant
18
The Basic Components
1. Boiler
(i) fire tube boiler and (ii) water tube boiler
1. Steam turbine
2. Generator
3. Condenser
4. Cooling towers
5. Circulating water pump
6. Boiler feed pump
7. Forced or induced draught fans
8. Ash precipitators
19
Boiler
A boiler is a closed vessel in which the water or fluid is heated
Steam turbine
A steam turbine is a device which extracts thermal energy from the
pressurized steam. The energy must be used to organize mechanical
work on a rotating output shaft.
Generator
A generator is a device which is used to convert the mechanical
form of energy into the electrical energy.
Condenser
A condenser is a device used to converts the gaseous substance into
the liquid state substance with the help of cooling.
Cooling towers
A cooling tower is a heat rejection device, which discards the waste
heat into the atmosphere with help of the cooling water stream to a
lower temperature.
20
Circulating water pump
Circulating pump is a special device used to circulate the liquids,
gases and slurries present in the closed circuit. The main purpose of
the circulating pump is circulating the water in a cooling system or
hydronic heating.
Boiler feed pump
A boiler feed pump is a specific type of pump which is used to feed
the water into the steam boiler. The condition of water supply
depends on the boiler produce the condensation of the steam.
Forced draught fans: Forced draught fans are used to provide a
positive pressure to a system.
Induced draught fans
Induced draught fans are used to provide a negative pressure or
vacuum in a slack or system
Ash precipitators: Precipitators are devices used to remove the fine
particles like smoke and dust. By using the force of induced
electrostatic charge minimally close the flow of gases through the
unit.
21
Working Principle Of Thermal Power Plant
Water is used as the working fluid in the thermal power plant. We can see
coal based and nuclear power plants in this category. From the working of
the power plant energy, later from the fuel gets transferred into the form of
electricity. With the help of high pressure and high steams a steam turbine
in a thermal power plant is rotates, the rotation must be transfer to the
generator to produce power.
When turbine blades are rotated with the high pressure and high
temperature at that case the steam loses its energy. So it results in the low
pressure and low temperature at the outlet of the turbine. Steam must be
expanded upto the point where it reaches the saturation point. So from the
steam, there is no heat addition or removal that takes place. Entropy of the
steam remains same. So we can notice the change in the pressure and
volume and temperature along with the entropy diagrams. If the condition
comes to the low pressure and low temperature steam back to the original
state, from that we can produce continuous electricity.
22
To compress the gaseous state liquids at that case large amount of
energy is required. So before the compression we need to convert the fluids
into liquid state. For this purpose condenser is required and heat is rejected
to the surroundings and converts the steam into liquid state. During this
process the temperature and volume of the fluid changes take place hardly,
so it turns into liquid state. And the fluid turns to the original state. To bring
the fluid to the original state external heat is added. To the heat exchanger
heat is added which is called as boiler. Then the pressure of the fluid must
remain same. In heat exchanger tubes it expands freely. Due to increase in
temperature the liquid state is transformed into the vapour state and the
temperature remains same. So know we complete the thermodynamic cycle
in the thermal power plant. It is known as Rankine cycle. By repeating the
cycle we can produce the power continuously.
With the help of boiler furnace heat is added to the boiler. Then the
fuel must reacts with the air and produces heat. The fuel must be either
nuclear or coal. In this process if we use coal as a fuel we can observe lot of
pollutants before ejects in to the air clean or removed the particles and send
into surroundings. The process is done in various steps. By using the electro
static precipitator the ash particles are removed. So with the help of the stack
clean exhaust must be send outside.
23
Working Principle
24
Advantages:
1.Cost of fuel: Fuel used in thermal power station (TPS) is cheaper
than cost of fuel used in diesel & nuclear power station.
2.Capital cost: Capital cost of TPS is less than hydro & nuclear
power station.
3.Near load center: TPS can be located near load center. The coal
can be transport from coal mines to power plant. As it is located load
centre it reduces transmission cost and losses in it.
4.Space required: Less space required as compared to hydro power
station.
5.Generating capacity: TPS build/construct of high generating
capacity, so used as a base load power plant.
6.Time required for completion of project: Time required for
completion of Thermal power project is very less as compare to
hydroelectric power station.
25
Disadvantages:
1. Air pollution: It produces air pollution due to smoke and ash produced during combustion
of fuel.
2. Starting Time: TPP cannot be put into service immediately like hydroelectric power
plant. As thermal power plant required few hours (6-7 hour) to generate steam at high
pressure and high temperature.
3. Handling of fuel: Handling of coal and disposal of ash is quite difficult.
4. Fuel transportation cost: When power plant are located away from coal mines i.e. near
load centre at that time fuel transportation cost is more.
5. Preparation for fuel: There is more expenditure for preparation of coal (raw coal to
pulverized coal).
6. Space required: Large amount of space is required for storage of fuel and ash as compare
to Nuclear power plant.
7. Efficiency: It is less efficient power plant overall efficiency is maximum 30 %.
8. Stand by losses: Stand by losses is more as furnace is required to keep in operation even
when there is no load.
9. Maintenance cost: High maintenance and operating cost because number of axillaries
plant are required such as coal and ash handling plant, pulverizing plant, condensing plant
and water purification plant etc.
10. Availability of fuel: Less availability of high grade coal.
11. Simplicity and cleanness: Layout of thermal power plant is complicated than
hydroelectric power plant due to coal and ash.
12. Life: Life of thermal power plant is less than hydro power plant.
13. Cost per unit (cost of generation) is high
26
Cooling Tower
In water tube boilers the water flows through tubes and hot combustion
gases flow over these tubes. Whereas in fire tube boilers the tubes are
surrounded by water and hot combustion gases flow through these tubes.
28
8 February 2024 Department of EEE 29
Surface Condenser
30
31
Principle And Working Of Surface Condenser
The Basic working principle of a surface condenser is the transfer of heat from a
higher-temperature body to a lower-temperature body. In this, the steam (high-
temperature body) liberates its heat to the cooling water tubes (low-temperature
body). In the process of heat transfer, the hot steam gets converted to water.
The steam enters from the exhaust Steam inlet and comes in contact with the water
carrying tubes. The water in the tubes has a circulating flow. As soon as the
exhaust steam comes in contact with the water-cooled tubes, the process of heat
transfer begins. The heat from the steam is removed and converted into a liquid
which Is known as condensate. This condensate is then removed from the
cylindrical vessel through a valve located at the bottom of the cylinder.
In thermal power stations, water is heated more than its boiling point to generate
steam which in turn is used to rotate the turbine. After passing through the turbine
the steam is fed into a surface condenser where it is converted into water and then
reused.
8 February 2024 Department of EEE 32
Jet Condenser Surface Condenser
Both steam & cooling water are
mixed together
Both steam & cooling water are
not mixed together
Manufacturing cost is low Manufacturing cost is high
Occupies less area Occupies large area
The air pump requires large power The air pump requires less power
A small quantity of cooling water
is required
A large quantity of cooling water
is required
33
Advantages
The following are the advantages of surface condenser
1. Its vacuum efficiency is high
2. They are mainly used in large plants area
3. It uses low-quality water
4. It also uses impure water for cooling purpose
5. The pressure ratio & steam are directly proportional.
Disadvantages
The following are the disadvantages of surface condenser
1. Water required is in the large amount
2. Complex in construction
3. High maintenance
4. It occupies a large area.
Applications
The following are the applications of surface condenser
1. Refrigeration of vacuum
2. Evaporation of vacuum
3. Systems like Desalination
8 February 2024 Department of EEE 34
35
Hydroelectric power plant has the following parts
Dam or weir: it contains the river water, forming a reservoir behind it and thus creating a
water drop that is used to produce energy. Dams can be made of earth or concrete.
Spillways: They release part of the impounded water without passing through the turbines;
water can then be used for irrigation purposes. They are located on the main wall of the
dam and can be at the top or at the bottom. Most of the water goes into a plunge pool at
the toe of the dam, to prevent scour damage by the falling water.
Water intakes: they let in the impounded water towards the turbines through a penstock.
Water intakes have gates to control the amount of water that reaches the turbines and grids
to filter out any debris such as trunks, branches, etc.
Powerhouse: it houses the hydraulic and electrical equipment (turbines, generators,
transformers) and the service area with control and testing rooms. It has inlet and outlet
gates to ensure the equipment area can be dry in case of repairs or disassembling
equipment.
Turbines: they harness the energy of the water that goes through them to rotate around a
shaft. There are three main types of turbines: Pelton, Francis and Kaplan turbines (propeller
type).
Transformers: electrical devices to increase or decrease the voltage in an alternating current
circuit.
Electrical power transmission lines: cables to transmit the electricity generated.
36
GAS POWER PLANT LAYOUT
8 February 2024 Department of EEE 37
Gas Turbine Power Plant
A generating station which employs a gas turbine as the prime mover for
the generation of electrical energy is known as a gas turbine power plant. In
a gas turbine power plant, air is used as the working fluid. The air is
compressed by the compressor and is led to the combustion chamber where
heat is added to the air, thus raising its temperature. We will understand the
gas turbine power plant layout and learn the diagram.
Heat is added to the compressed air either by burning fuel in the
chamber or by the use of air heaters. The hot and high-pressure air from the
combustion chamber is then passed to the gas turbine where it expands and
does the mechanical work. The gas turbine drives the alternator which
converts mechanical energy into electrical energy.
It may be mentioned here that compressor, gas turbine and the
alternator are mounted on the same shaft so that a part of the mechanical
power of the turbine can be utilised for the operation of the compressor.
Gas turbine power plants are being used as standby plants for hydro-electric
stations, as a starting plant for driving auxiliaries in power plants etc.
8 February 2024 Department of EEE 38
The main components of the Gas Turbine Power Plant are :
(i) Compressor
(ii) Regenerator
(iii) Combustion chamber
(iv) Gas turbine
(v) Alternator
(vi) Starting motor
(i) Compressor: The compressor used in the plant is generally of rotatory
type. The air at atmospheric pressure is drawn by the compressor via the filter
which removes the dust from the air. The rotatory blades of the compressor
push the air between stationary blades to raise its pressure. Thus air at high
pressure is available at the output of the compressor.
(ii) Regenerator: A regenerator is a device which recovers heat from the
exhaust gases of the turbine. The exhaust is passed through the regenerator
before wasting to the atmosphere. A regenerator consists of a nest of tubes
contained in a shell as seen in the below power plant layout. The compressed
air from the compressor passes through the tubes on its way to the combustion
chamber. In this way, compressed air is heated by the hot exhaust gases.
39
(iii) Combustion chamber: The air at high pressure from the compressor is
led to the combustion chamber via the regenerator. In the combustion
chamber, heat is added to the air by burning oil. The oil is injected through
the burner into the chamber at high pressure to ensure atomisation of oil and
its thorough mixing with air. The result is that the chamber attains a very high
temperature (about 3000 F). The combustion gases are suitably cooled to
1300F to 1500F and then delivered to the gas turbine.
iv) Gas turbine: The products of combustion consisting of a mixture of gases
at high temperature and pressure are passed to the gas turbine.These gases in
passing over the turbine blades expand and thus do the mechanical work. The
temperature of the exhaust gases from the turbine is about 900F.
(v) Alternator: The gas turbine is coupled to the alternator as seen in the gas
turbine plant layout. The alternator converts mechanical energy of the turbine
into electrical energy. The output from the alternator is given to the bus-bars
through the transformer, circuit breakers and isolators.
(vi) Starting motor: Before starting the turbine, the compressor has to be
started. For this purpose, an electric motor is mounted on the same shaft as
that of the turbine. The motor is energised by the batteries. Once the unit
starts, a part of the mechanical power of the turbine drives the compressor
and there is no need of motor now
40
Gas turbine power plant Advantages:
(i) It is simple in design as compared to steam power station since no boilers and
their auxiliaries are required.
(ii) It is much smaller in size as compared to the steam power station of the same
capacity. This is expected since the gas turbine power plant does not require a
boiler, feed water arrangement etc.
(iii) The initial and operating costs are much lower than that of the equivalent steam
power station.
(iv) It requires comparatively less water as no condenser is used.
(v) The maintenance charges are quite small.
(vi) Gas turbines are much simpler in construction and operation than steam
turbines.
(vii) It can be started quickly form cold conditions.
(viii) There are no standby losses. However, in a steam power station, these losses
occur because the boiler is kept in operation even when the steam turbine is
supplying no load.
41
Gas turbine power plant Disadvantages:
(i) There is a problem with starting the unit. It is because before starting the turbine,
the compressor has to be operated for which power is required from some external
source. However, once the unit starts, the external power is not needed as the turbine
itself supplies the necessary power to the compressor.
(ii) Since a greater part of power developed by the turbine is used in driving the
compressor, the net output is low.
(iii) The overall efficiency of such plants is low (about 20%) because the exhaust
gases from the turbine contain sufficient heat.
(iv) The temperature of the combustion chamber is quite high (3000F) so that its life
is comparatively reduced.
44
1. Discuss the different sources of energy available in nature.
2. Draw the schematic diagram of a modern steam power station and explain its
operation
3. What is a steam power station ? Discuss its advantages and disadvantages.
4. What factors are taken into account while selecting the site for a steam
power station ?
5. Draw a neat schematic diagram of a hydro-electric plant and explain the
functions of various components.
6. Explain the functions of the following :
(i) dam (ii) spillways (iii) surge tank (iv) headworks (v) draft tube
7. Draw the schematic diagram of a nuclear power station and discuss its
operation
8. Explain with a neat sketch the various parts of a nuclear reactor
9. Discuss the factors for the choice of site for a nuclear power plant.
10. Explain the working of a gas turbine power plant with a schematic diagram.
11. Give the comparison of steam power plant, hydro-electric power plant, gas
power plant and nuclear power plant
12. Discuss the advantages and disadvantages of a gas power station.
CHAPTER REVIEW QUESTIONS
45
1
Hydro Electric Power Plant
Site Selection for Hydro Power Plant
2
01. Availability of water
Water is the main source of hydroelectric power plants. A huge amount of water should be
available so that the power plant can be built with a high head. The quantity of the water
available will be estimated on the basis of the measurement of streamflow over a certain
period or previous rainfall records.
02. Storage of water
There will be a wide variation of rainfall during the year. This makes it necessary to store
water for continuous generation of power throughout the year.
03. Head of water
The head of the water depends upon the topography of the area. If the head is more then
potential energy will be more.
04. Choice of the dam
The important consideration in the choice of the dam is safety and economics. Failure of the
dam may result in substantial loss of life and property. The dam must satisfy the stability
test for shock loads and unusual floods.
05. Distance from the power station to load center
The distance should be less between the power station and load center so that the cost of
transmission of power becomes less.
06. Accessibility of the site
The plant should be easily accessible by rain and load for transportation of plant equipment.
3
Hydro Electric Power Plant
4
01. Reservoir: The purpose of this reservoir is to store the water which will be further used to
generate electricity. The water will be stored during the rainy season. By storing water we get
potential energy.
02. Dam: dam will be constructed across the river or lakes to provide the head of the water.
These are classified based on their function, material, shape, and structural design.
03. Spillway: This spillway is the safety wall for the dam. It discharges the existing amount of
water from the reservoir into the rivers. That means spillway is required to reduce overtopping.
It keeps the reservoir level below the predetermined value.
04. Intake: Intake acts as a filter in Hydro Electric power plants. It removes unwanted material
from the water. In this stage, the potential energy will be converted into kinetic energy.
05. Penstock: This is the channel between the dam and turbine which helps to increase the
kinetic energy of the water. It is made up of stainless steel.
06. Surge tank: It acts as a pressure release wall for the water. It reduces the water hammer
effect. That means it holds the water whenever there is no requirement of load on the turbines,
and similarly, it discharges water whenever there is a requirement of load on the turbines.
07. Prime mover/turbine: For this reason, the kinetic energy will be converted into
mechanical energy, which is responsible for the rotation of the shaft of the turbines. Commonly
used turbines are Kaplan, Francis, Pelton, cross flow, etc.
08. Alternators / Generators: These are normally located near the foot of the dam. Water is
brought to alternators with the help of penstock. In this region, the mechanical energy is
converted to electrical energy. Thus final power will get in this stage.
5
Working Principle
 In a hydro electric power plant, water is stored in the dam reservoir
which has potential energy.
 This potential energy is converted into kinetic energy when water from
the dam is allowed to flow through the pipes.
 This kinetic energy is converted into mechanical energy allowing the
water flowing in pipe to drive the turbine.
 At last, the mechanical energy by rotating the turbine is converted to
electrical energy in the generator which is coupled to the turbine.
 The dam creates the head of the water from which water flows.
 Penstock carries the water from the Dam to the turbine, and it provides
kinetic energy.
 The fast flowing water through the penstock pushes turbine blades.
 The water forces on turbine plates and rotates the generator rotor, which
in turn generates electricity.
6
Advantages
1. Electricity can be produced at a constant rate once the dam is constructed
2. The gates of the dam can be shut down if electricity is not needed, which
stops electricity generation. Hence by doing this, we can save water for
further use in future when the demand for electricity is high.
3. One of the biggest advantages of hydroelectric power plants is that they are
designed to last many decades, and so they can contribute to the generation of
electricity for years.
4. Large dams often become tourist attractions because the lake that forms in the
reservoir area behind the dam can be used for leisure or water sports.
5. The water from the lake of the dam can be used for irrigation purposes in
farming.
6. Since the water is released to produce electricity, the build-up of water in the
dam is stored to produce extra energy until needed.
7. Hydroelectric energy generation does not pollute the atmosphere because the
hydroelectric power plant does not produce greenhouse gases.
8. Hydropower plants can be considered a reliable energy generation source.
Since hydropower totally depends on water present on this planet, this energy
source will remain inexhaustible because of the water cycle as it continuously
keeps on maintaining balance on the Earth.
7
Disadvantages
1. It is not an easy task to assemble a hydropower plant because the dams are
extremely expensive to build, and they require extremely high standards and
calculations for their construction.
2. It becomes important that the hydropower plant must serve for many decades
because of its high cost of construction, and this totally depends on the availability
of water resources.
3. If flooding happens due to natural calamities or the failure of dams, it would
impact a large area of land, which means that the natural environment can be
destroyed.
4. People are forcibly removed from the particular area where a hydropower plant
is going to be assembled. This affects the day-to-day life of people living in that
area.
5. A serious geological damage can be caused due to the construction of large
dams.
6. To construct a hydro plant, it is important to block the running water source due
to which the fishes can’t arrive at their favourable place, and as the water stops
streaming, the areas along the riverside start to vanish out which eventually
influences the life of creatures that depend on fish for food.
8
Different types of modern hydro power plants
1. Pumped storage hydropower plants
2. Reversible turbine pump hydropower plants
3. Underground hydropower plants
4. Tidal power plants
Types of Pumped Storage Plants
1. Daily, weekly or seasonal storage plants
2. High, medium or low head plants
3. According to the type of turbine used in the plant
4. Pure or mixed storage hydropower plants
5. Horizontal or vertical storage plants
8-Feb-24 9
Pumped Storage Plants
Pumped Storage Hydropower Plants:
To supply the peak loads, hydropower plants has to have the installed capacity of high
loads of which remains idle during the off-peak hours.
The more the demands of variable power supply, it is necessary to devise some way to
achieve the economical loading of the power
plant by levelling up the load curve.
The following are some of the ways:
(a) Commercial Method: To sell electric current at a higher rate during peak hours than
during off-peak hours.
(b) Technical method: The following are the two methods:
(i) By installing special peak load power plants
(ii) By storing energy produced during off-peak hours. Such a system is known
as Pumped Storage Plants.
Purpose of Pumped Storage Hydropower Plants:
This type of plants combined with steam power stations reduces the power load
fluctuations to narrow limits.
In some cases, the storage plant consists of pump and motor with no turbines.
The pump increases the head in the feeder reservoir of a separate hydro-electric plant
while motor improves the power factor in the electric supply network.
11
Advantages:
The pump storage plants entail the following advantages :
1.There is substantial increase in peak load capacity of the plant at
comparatively low capital cost.
2.Due to load comparable to rated load on the plant, the operating
efficiency of the plant is high.
3.There is an improvement in the load factor of the plant.
4.The energy available during peak load periods is higher than that of
during off peak periods so that in spite of losses incurred in pumping there
is over-all gain.
5. Load on the hydro-electric plant remains uniform.
6.The hydro-electric plant becomes partly independent of the stream flow
conditions.
12
8-Feb-24 1
NUCLEAR
POWER PLANT
Dr.G.Nageswara Rao
Professor , EEE Department
Lakireddy Bali Reddy College of Engineering (LBRCE)
NUCLEAR BINDING ENERGY
Nuclei are made up of protons and neutron, but the mass of a
nucleus is always less than the sum of the individual masses of the
protons and neutrons which constitute it. The difference is a
measure of the nuclear binding energy which holds the nucleus
together. The enormity of the nuclear binding energy can perhaps be
better appreciated by comparing it to the binding energy of an
electron in an atom. The comparison of the alpha particle binding
energy with the binding energy of the electron in a hydrogen atom is
shown below. The nuclear binding energies are on the order of a
million times greater than the electron binding energies of atoms.
Fusion is the process where two light nuclei combine together releasing
vast amounts of energy.
Fission is the splitting of a heavy, unstable nucleus into two lighter
nuclei
Fission and Fusion
(Hydrogen Bomb) (Atom Bomb or Atomic Bomb)
4
Fission Reaction Fusion Reaction
A fission reaction is splitting up of a large atom or a
molecule into two or more smaller ones.
Fusion is the process of combination of two or more
lighter atoms or molecules into larger ones.
Fission reaction doesn’t occur normally in nature. Fusion reaction process occurs in the stars, like in the sun,
etc.
This reaction produces highly radioactive substances. Few number of radioactive particles are developed by the
process of a fusion reaction.
Neutrons must be slowed down by moderation to increase
their capture probability in fission reactors.
This process requires high-temperature, high-density
environment.
This process consumes a very little amount of energy to
break up the atoms.
High amount of energy is consumed to combine protons
so that the nuclear forces can overcome the electrostatic
repulsion.
The energy released during the process of fission is much
larger than that of the released energy in other chemical
reactions.
The energy released by the process of fusion is around 3-4
times much greater than that of the energy liberated by the
process of fission.
Fission process is utilized in the nuclear power plant. Fusion process is one of the experimental technologies for
the production of power.
Uranium is one of the primary fuels used for the process
of fission in power plants.
The isotopes of hydrogen such as the Deuterium &
Tritium are some of the primary fuels used in the
experimental process of fusion power plants.
A fission bomb is one kind of nuclear weapon which is
also known as Atom Bomb or Atomic Bomb.
Hydrogen Bomb is one class of fusion bomb.
Differences between Fission and Fusion
6
Nuclear Power Plant
Nuclear reactor is used to produce heat and heat exchanger performs to convert water into
steam by using the heat generated in nuclear reactor. This steam is fed into steam turbine
and condensed in condenser. Now steam turbine is turn to run an electric generator or
alternator which is coupled to steam turbine and thereby producing electric energy.
SELECTION OF SITE
1. Availability of water: At the power plant site an ample quantity of water should be
available for condenser cooling and made up water required for steam generation. Therefore
the site should be nearer to a river, reservoir or sea.
2. Distance from load center: The plant should be located near the load center. This will
minimize the power losses in transmission lines.
3. Distance from populated area: The power plant should be located far away
From populated area to avoid the radioactive hazard.
4. Accessibility to site: The power plant should have rail and road transportation facilities.
5. Waste disposal: The wastes of a nuclear power plant are radioactive and there should be
sufficient space near the plant site for the disposal of wastes.
8
The working principle of nuclear power plant depends upon mainly four
components.
1.Nuclear Reactor
2.Heat Exchanger
3.Steam Turbine
4.Alternator
1. Nuclear Reactor:-
Nuclear reactor is the main component of nuclear power plant and nuclear fuel is
subjected to nuclear fission. Nuclear fission is a process where a heavy nucleus is
spitted into two or more smaller nuclei. . A heavy isotope generally uranium-235(U-
235) is used as a nuclear fuel in the nuclear reactor because it has the ability to control
the chain reaction in the nuclear reactor. Nuclear fission is done by bombarding
uranium nuclei with slow moving neutrons. The energy released by the fission of nuclei
is called nuclear fission energy or nuclear energy. By the braking of uranium atom,
tremendous amount of heat energy and radiation is formed in the reactor and the chain
reaction is continuously running until it is controlled by a reactor control chain reaction.
A large amount of fission neutrons are removed in this process, only small amount of
fission uranium is used to generate the electrical power.
The nuclear reactor is cylindrical type shape. Main body of reactor is enclosed by reactor core,
reflector and thermal shielding. It prevent reactor wall from getting heated. It is also used to protect
alpha ( α), bita (β) , gama (γ) rays and neutrons which are bounce back at the time of fission within the
reactor. Mainly Nuclear reactor consists, some fuel rods of uranium, moderator and control rods. Fuel
rods are made of the fission materials and released large number of energy at the time of bombarding
with slow moving neutrons. Moderator consists full of graphite which is enclosed by the fuel rods.
Moderator maintains the chain reaction by releasing the neutrons in a suitable manner before they
mixed with the fissile materials. Control rods are made of boron-10 and cadmium or hafnium which is
a highly neutron absorber and it is inserted into the nuclear reactor. When control rods are push down
into the reactor core, it absorbs most of fission neutrons and power of the reactor is reduced. But when
it is pulling out from the reactor, it releases the fission neutrons and power is increased. Real practice,
this arrangement depends upon according to the requirement of load. A coolant, basically sodium
metal is used to reduce the heat produce in the reactor and it carries the heat to the heat exchanger.
2. Heat Exchanger:-Coolant is used to raise the heat of the heat exchanger which is utilised in raising
the steam. After that, it goes back to the reactor.
3. Steam Turbine:-Steam is coming from the heat exchanger to fed into the steam turbine through the
valve. After that the steam is exhausted to the condenser. This condensed steam is fed to the heat
exchanger through feed water pump.
4. Alternator:-Steam turbine is coupled to an alternator which converts mechanical energy to
electrical energy. The output of alternator produces electrical energy to bus bars via major electrical
apparatus like transformer, circuit breakers, isolators etc.
BLOCK DIAGRAM OF NUCLEAR REACTOR
Main Components of a Nuclear Reactor
The Core: It contains all the fuel and generates the heat required for energy
production.
The Coolant: It passes through the core, absorbing the heat and transferring into
turbines.
The Turbine: Transfers energy into the mechanical form.
The Cooling Tower: It eliminates the excess heat that is not converted or
transferred.
Moderator: Moderators are used for reducing the speed of fast neutrons released
from the fission reaction and making them capable of sustaining a nuclear chain
reaction. Usually, water, solid graphite, and heavy water are used as a moderator in
nuclear reactors. Commonly-used moderators include regular (light) water (in
74.8% of the world’s reactors), solid graphite (20% of reactors), heavy water (5% of
reactors).
The Containment: The enveloping structure that separates the nuclear reactor from
the surrounding environment.
Neutron Poison: A neutron poison (also called a neutron absorber or a nuclear
poison) is a substance with a large neutron absorption cross-section.
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Monitoring Nuclear Fuel
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Fuel assembly (fuel bundle, fuel element)
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Fuel Assembly Manufacturing (Fuel rod to fuel assembly)
Materials
Pellet: UO2, UO2 containing gadolinia
Cladding: Zirconium alloy
Guide thimble tube: Zirconium alloy
Spacer: Zirconium alloy and inconel
Top/Bottom nozzle: Stainless steel
Type 14×14 15×15 17×17
10ft 12ft 12ft 12ft
Section size
(mm) 197 214 214
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(a) Schematic of nuclear fuel rod assembly 2 (b) Simplified schematic of a TN-32
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ADVANTAGES OF NUCLEAR POWER PLANTS
1. Since the requirement of fuel is very small, so the cost of fuel transportation,
storage etc. is small.
2. Nuclear power plant needs less space as compared to any other power station of
the same size. Example: A 100 MW nuclear power station needs 38 - 40 acres of
land whereas the same capacity coal based thermal power plant needs 120-130
acres of land.
3. This type of power plant is very economical to produce large electric power.
4. Nuclear power plant can be located near load centre because bulk amount of fuel
(like water, coal) is not required.
5. Nuclear power is most economical to generate large capacities of power like 100
MVA or more. It produces huge amount of energy in every nuclear fission process.
6. Using a small amount of fuel, this plant produces large electrical energy.
7. This plant is very reliable in operation.
8. Since, the large number of nuclear fuel is available in this world. So, a nuclear
power plant can generate electrical energy thousands of years continuously.
9. Nuclear Power Plant is very neat and clean as compared to a steam power plant.
10. The operating cost is low at this power plant but it is not affected for higher load
demand. Nuclear power plant always operates a base load plant and load factor
will not be less than 0.8.
DISADVANTAGES OF NUCLEAR POWER PLANTS
1. Initial installation cost is very high as compared to the other power
station.
2. Nuclear fuel is very much expensive and it is difficult to recover.
3. Capital cost is higher in respect of other power station.
4. Good technical knowledge is required to operate such type plant. So,
salary bill and other maintenance cost will be higher to operate such of
a plant.
5. There is a chance to spread of radioactive pollution from this type of
plant.
6. Nuclear Reactor does not response efficiently with the fluctuating load
demand. So, it is not suited for varying the load.
7. Cooling water requirement is twice than a coal based steam power
plant.
Types of Nuclear Reactors
Most nuclear reactors in the United States and in Europe use fuel composed of natural uranium
that is enriched with uranium 235, and ordinary water as a coolant. These reactors are known as
light-water reactors. There are two basic types: the pressurized water reactor and the boiling water
reactor.
Pressurized Water Reactor is the most common type of nuclear reactor used for the generation
of electricity. It uses ordinary water as both the moderator (to slow neutrons) and the coolant (to
transfer heat). It has two separate cooling circuits: one which flows through the core of the reactor
(the primary), and one which is used to drive the turbine (the secondary).
Boiling Water Reactor is similar in some ways to the more common pressurized water reactor.
This design also uses ordinary water as both the moderator (to slow neutrons) and the coolant (to
transfer heat). In the boiling water reactor, however, a single cooling circuit is used and the
cooling water boils inside the reactor.
CANDU (CANadian Deuterium Uranium), is also used to generate power. Developed by Canada,
this reactor uses only natural uranium as a fuel, but is moderated and cooled using heavy water.
Since the complex enrichment process can be skipped, this type is very popular in developing
nations. It is also known as a pressurized heavy water reactor.
23
CANDU Reactor
25
Nuclear Waste
Nuclear waste refers to any radioactive material produced by medical, research, nuclear
power facilities, or nuclear weapons programs. Nuclear waste can be grouped in two
categories: low-level and high-level. Low-level wastes are slightly contaminated materials.
A major source of low-level waste is mill-tailings from uranium ore processing. High-level
wastes are comprised mainly of spent fuel from nuclear reactors. A small amount of high-
level waste is very toxic.
26
The major concern about nuclear waste is its disposal. Nuclear waste must be stored until the
radioactivity has dropped to safe levels without contaminating the surrounding environment. The
disposal of low-level waste is done by some form of shallow land burial. The disposal of high-level
waste is a more complex problem. The waste is highly toxic and must be stored for several centuries.
Currently there are no long-term storage facilities for high-level waste in the United States.
27
Radioactive waste disposal
The dispose of nuclear waste in the Euopean Union
Dumping of Radioactive Materials at Sea
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Nuclear Explosion
8-Feb-24 32
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Nuclear Explosion
35
YouTube Channel: GUDIPUDI FAMILY
https://www.slideshare.net/slideshows/power-generation-methodspower-generation-power-
plants/266214209
Introduction, definitions of connected load, maximum
demand, demand factor, load factor, diversity factor,
Load duration curve, number and size of generator
units. Base load and peak load plants. Cost of electrical
energy-fixed cost, running cost, Tariff on charge to
customer.
4
Important Terms and Factors
Connected load: It is the sum of continuous ratings of all the equipment's
connected to supply system.
Maximum demand : It is the greatest demand of load on the power station
during a given period.
Demand factor. It is the ratio of maximum demand on the power station to its
connected load i.e.,
Demand factor =Maximum demand / Connected load
The value of demand factor is usually less than 1.
Average load: The average of loads occurring on the power station in a given
period (day or month or year) is known as average load or average demand.
Daily average load =No. of units (kWh) generated in a day/24 hours
Monthly average load =No. of units (kWh) generated in a month/Number of
hours in a month
Yearly average load = No. of units (kWh) generated in a year/8760 hours
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Residential Customers
Chittoor, Anantapur, Kurnool, YSR Kadapa, SPSR Nellore
districts - Southern Power Company.
Srikakulam, Vizianagaram, Visakhapatnam, East Godavari,
West Godavari districts - Eastern Power Company.
Krishna, Guntur and Prakasam Districts -Central Power
Company.
https://aptransco.co.in
34
35
Grid Map
37
TARIFF
The rate at which electrical energy is supplied to a consumer is known
as tariff
Objectives of tariff. Like other commodities, electrical energy
is also sold at such a rate so that it not only returns the cost but
also earns reasonable profit. Therefore, a tariff should include
the following items :
(i) Recovery of cost of producing electrical energy at the power
station.
(ii) Recovery of cost on the capital investment in transmission
and distribution systems.
(iii) Recovery of cost of operation and maintenance of supply
of electrical energy e.g., metering equipment, billing etc.
(iv) A suitable profit on the capital investment.
Characteristics of a Tariff
(i) Proper return : The tariff should be such that it ensures the proper return from
each consumer. In other words, the total receipts from the consumers must be equal
to the cost of producing and supplying electrical energy plus reasonable profit.
(ii) Fairness : The tariff must be fair so that different types of consumers are
satisfied with the rate of charge of electrical energy. Thus a big consumer should
be charged at a lower rate than a small consumer. It is because increased energy
consumption spreads the fixed charges over a greater number of units, thus
reducing the overall cost of producing electrical energy.
(iii) Simplicity : The tariff should be simple so that an ordinary consumer can
easily understand it. A complicated tariff may cause an opposition from the public
which is generally distrustful of supply companies.
(iv) Reasonable profit : The profit element in the tariff should be reasonable. An
electric supply company is a public utility company and generally enjoys the
benefits of monopoly.
(v) Attractive : The tariff should be attractive so that a large number of consumers
are encouraged to use electrical energy. Efforts should be made to fix the tariff in
such a way so that consumers can pay easily.
Types of Tariff
1. Simple tariff. When there is a fixed rate per unit of energy consumed, it is
called a simple tariff or uniform rate tariff. In this type of tariff, the price
charged per unit is constant i.e., it does not vary with increase or decrease in
number of units consumed. The consumption of electrical energy at the
consumer’s terminals is recorded by means of an energy meter. This is the
simplest of all tariffs and is readily understood by the consumers.
Disadvantages
(i) There is no discrimination between different types of consumers since
every consumer has to pay equitably for the fixed charges.
(ii) The cost per unit delivered is high.
(iii) It does not encourage the use of electricity.
2. Flat rate tariff. When different types of consumers are charged at different
uniform per unit rates, it is called a flat rate tariff. In this type of tariff, the
consumers are grouped into different classes and each class of consumers is
charged at a different uniform rate. The different classes of consumers are made
taking into account their diversity and load factors. The advantage of such a
tariff is that it is more fair to different types of consumers and is quite simple in
calculations.
Disadvantages
(i) Since the flat rate tariff varies according to the way the supply is used, separate
meters are required for lighting load, power load etc. This makes the application of
such a tariff expensive and complicated.
(ii) A particular class of consumers is charged at the same rate irrespective of the
magnitude of energy consumed. However, a big consumer should be charged at a
lower rate as in his case the fixed charges per unit are reduced.
3. Block rate tariff. When a given block of energy is charged at a specified rate
and the succeeding blocks of energy are charged at progressively reduced rates, it is
called a block rate tariff. In block rate tariff, the energy consumption is divided into
blocks and the price per unit is fixed in each block. The price per unit in the first
block is the highest** and it is progressively reduced for the succeeding blocks of
energy. For example, the first 30 units may be charged at the rate of 60 paise per
unit ; the next 25 units at the rate of 55 paise per unit and the remaining additional
units may be charged at the rate of 30 paise per unit.
The advantage of such a tariff is that the consumer gets an incentive to consume
more electrical energy. This increases the load factor of the system and hence the
cost of generation is reduced. However, its principal defect is that it lacks a measure
of the consumer’s demand. This type of tariff is being used for majority of
residential and small commercial consumers.
4. 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.
Total charges = Rs (b × kW + c × kWh)
where, b = charge per kW of maximum demand
c = charge per kWh of energy consumed
This type of tariff is mostly applicable to industrial consumers who have
appreciable maximum demand.
Advantages
(i) It is easily understood by the consumers.
(ii) It recovers the fixed charges which depend upon the maximum demand of
the consumer but are independent of the units consumed.
Disadvantages
(i) The consumer has to pay the fixed charges irrespective of the fact whether
the has consumed or not consumed the electrical energy.
(ii) There is always error in assessing the maximum demand of the consumer
5. Maximum demand tariff. It is similar to two-part tariff with the only
difference that the maximum demand is actually measured by installing
maximum demand meter in the premises of the consumer. This removes
the objection of two-part tariff where the maximum demand is assessed
merely on the basis of the rateable value. This type of tariff is mostly
applied to big consumers. However, it is not suitable for a small consumer
(e.g., residential consumer) as a separate maximum demand meter is
required.
6. Power factor tariff. The tariff in which power factor of the consumer’s
load is taken into consideration is known as power factor tariff. In an a.c.
system, power factor plays an important role. A low power factor
increases the rating of station equipment and line losses.
7. Three-part tariff. When the total charge to be made from the
consumer is split into three parts viz., fixed charge, semi-fixed charge
and running charge, it is known as a three-part tariff. i.e.,
Total charge = Rs (a + b × kW + c × kWh)
where a = fixed charge made during each billing period.
It includes interest and depreciation on the cost of secondary
distribution and labour cost of collecting revenues,
b = charge per kW of maximum demand,
c = charge per kWh of energy consumed.
Cost of Electrical Energy
The total cost of electrical energy generated can be divided into three parts, namely
(i) Fixed cost (ii) Semi-fixed cost (iii) Running or operating cost
(i) Fixed cost. It is the cost which is independent of maximum demand and units
generated. The fixed cost is due to the annual cost of central organisation, interest on capital
cost of land and salaries of high officials. The annual expenditure on the central organisation
and salaries of high officials is fixed since it has to be met whether the plant has high or low
maximum demand or it generates less or more units. Further, the capital investment on the
land is fixed and hence the amount of interest is also fixed.
(ii) Semi-fixed cost. It is the cost which depends upon maximum demand but is
independent of units generated. The semi-fixed cost is directly proportional to the maximum
demand on power station and is on account of annual interest and depreciation on capital
investment of building and equipment, taxes, salaries of management and clerical staff. The
maximum demand on the power station determines its size and cost of installation. The
greater the maximum demand on a power station, the greater is its size and cost of
installation.
(iii) Running cost. It is the cost which depends only upon the number of units
generated. The running cost is on account of annual cost of fuel, lubricating oil,
maintenance, repairs and salaries of operating staff.
51
POWER SYSTEMS
-I
Dr.G.Nageswara Rao
Professor
Lakireddy Bali Reddy College of Engineering
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AC DISTRIBUTION
Bus Bar
The conducting material or a conductor used to collect power
from the input terminals of an electrical system and distribute
it to various output circuits is known as an electrical bus bar
or bus system. It acts as a junction, where the incoming
power and outgoing power meets. It is used to collect all the
electrical power in one place. It is available in the form of
rectangular strips, round tubes, round bars, and square bars
made up of aluminium, copper, and brass.
Distribution System
The part of power system which distributes electric power for local
use is known as distribution system.
Distribution system generally consists of feeders, distributors and the servicemains. Fig
showsthe single line diagram of a typical low tensiondistribution system.
(i)Feeders. A feeder is a conductor which connects the sub-station (or localised generating
station) to thearea wherepower isto be distributed. Generally, no tappings are takenfrom
the feeder so that current in it remains the same throughout. The main consideration in the
design of a feeder is the current carrying capacity.
(ii)Distributor.Adistributor isa conductor from whichtappings are taken for supplytothe
consumers. In Fig. AB, BC, CD and DA are the distributors. The current through a
distributor is not constant because tappings are taken at various places along its length.
While designing a distributor, voltage drop along its length is the main consideration
since the statutory limit of voltage variations is ± 6% of rated value at the consumers’
terminals.
(iii)Servicemains.Aservicemainsisgenerally a smallcable whichconnectsthe distributor to
the consumers’ terminals.
Classification of Distribution Systems
(i) Nature of current. According to nature of current, distribution system may be classified as
(a) d.c. distribution system (b) a.c. distribution system.
Now-a-days, a.c. system is universally adopted for distribution of electric power as it is simpler
and more economical than direct current method.
(ii)Type of construction. According to type of construction, distribution system may be
classified as
(a) overhead system (b) underground system.
The overhead systemis generally employed for distribution as it is 5 to 10 times cheaper
than the equivalent underground system.Ingeneral, the underground systemisusedat places
where overhead construction is impracticable or prohibited by the local laws.
(iii)Schemeof connection. According to schemeof connection, the distribution systemmay be
classified as
(a) Radial system (b) ring main system (c) inter-connected system.
Eachschemehas its own advantages and disadvantages.
A.C. distribution calculations differ from those of d.c. distribution
in the following respects :
(i) In case of d.c. system, the voltage drop is due to resistance alone. However, in
a.c. system, the voltage drops are due to the combined effects of resistance,
inductance and capacitance.
(ii) In a d.c. system, additions and subtractions of currents or voltages are done
arithmetically but in case of a.c. system, these operations are done vectorially.
(iii) In an a.c. system, power factor (p.f.) has to be taken into account. Loads
tapped off form the distributor are generally at different power factors. There are
two ways of referring power factor viz
(a) It may be referred to supply or receiving end voltage which is regarded as the
reference vector.
(b) It may be referred to the voltage at the load point itself.
A.C. Distribution
The a.c. distribution system isclassified into
(i) primary distribution systemand (ii) secondary distribution system
Primary distribution system: It is that part of a.c. distribution system which
operates at voltages somewhat higher than general utilisation and handles large blocks of
electrical energy than the average low-voltage consumer uses. The voltage used for
primary distribution depends upon the amount of power to be conveyed and the distance
of the substation required to be fed. The most commonly used primary distribution voltages
are 11 kV, 6·6 kV and 3·3 kV. Due to economic considerations, primary distribution is
carried out by 3- phase, 3-wire system. Fig. shows a typical primary distribution system.
Electric power from the generating station is transmitted at high voltage to the substation
located in or near the city. At this substation, voltage is stepped down to 11 kV with the
help of step-down transformer. Power is supplied to various substations for distribution or to
big consumersat this voltage. This forms the high voltage distribution or primary distribution.
Secondary distribution system.
It is that part of a.c. distribution system which includes the range of voltages at which the
ultimate consumer utilises the electrical energy delivered to him. The secondary distribution
employs 400/230 V,3-phase, 4-wire system.
Fig. shows a typical secondary distribution system. The primary distribution circuit delivers
power to various substations, called distribution substations. The substations are situated near
the consumers’ localities and contain stepdown transformers.
At each distribution substation, the voltage is stepped down to 400V and power is delivered
by 3-phase,4-wire a.c. system.
The voltage between any two phases is 400 V and between any phase and neutral is 230V.
The single phase domestic loads are connected between any one phase and the neutral,
whereas 3-phase 400 V motor loads are connected across 3-phase lines directly.
Overhead Versus Underground System
(i) Public safety. The underground system is more safe than overhead system because all distribution
wiring is placed underground and there are little chances of any hazard.
(ii)Initial cost. The underground system is more expensive due to the high cost of trenching, conduits,
cables, manholes and other special equipment. The initial cost of an underground system may be five to
ten times than that of an overhead system.
(iii)Flexibility. Theoverhead system is much more flexible than the underground system. In the latter case,
manholes, duct lines etc., are permanently placed once installed and the load expansion can only be
met by laying new lines. However, on an overhead system, poles, wires, transformers etc., can be easily
shifted to meet the changes in load conditions.
(iv) Faults. The chances of faults in underground system are very rare as the cables are laid
underground and are generally provided with better insulation.
(v)Appearance. The general appearance of an underground system is better as all the distribution lines
are invisible. This factor is exerting considerable public pressure on electric supply companies to switch
over to underground system.
(vi)Fault location and repairs. In general, there are little chances of faults in an underground system.
However, if a fault does occur, it is difficult to locate and repair on this system. On an overhead system,
the conductors are visible and easily accessible so that fault locations and repairs can be easily made.
(vii)Current carrying capacity and voltage drop. An overhead distribution conductor has a
considerably higher current carrying capacity than an underground cable conductor of the
same material and cross-section. On the other hand, underground cable conductor has much
lower inductive reactance than that of an overhead conductor because of closer spacing of
conductors.
(viii)Useful life. The useful life of underground system is much longer than that of an overhead
system. An overhead system may have a useful life of 25 years, whereas an underground
systemmay have a useful life of more than 50 years.
(ix)Maintenance cost. The maintenance cost of underground system is very low as compared
with that of overhead system because of less chances of faults and service interruptions from
wind, ice, lightning as well as from traffic hazards.
(x)Interference with communication circuits. An overhead system causes electromagnetic
interference with the telephone lines. The power line currents are superimposed on speech
currents, resulting in the potential of the communication channel being raised to an undesirable
level. However, there is no suchinterference with the underground system.
Requirements of a Distribution System
(i)Proper voltage. One important requirement of a distribution system is that voltage variations at consumer’s
terminals should be as low as possible. The changes in voltage are generally caused due to the variation of load
on the system. Low voltage causes loss of revenue, inefficient lighting and possible burning out of motors. High
voltage causes lamps to burn out permanently and may cause failure of other appliances. Therefore, a good
distribution system should ensure that the voltage variations at consumers terminals are within permissible limits. The
statutory limit of voltage variations is ± 6% of the rated value at the consumer’s terminals. Thus, if the declared
voltage is 230 V, then the highest voltage of the consumer should not exceed 244 V while the lowest voltage of the
consumer should not be less than 216 V.
(ii)Availability of power ondemand. Powermustbe available to theconsumersinany amount that theymay require
from time to time. For example, motors may be started or shut down, lights may be turned on or off, without
advance warning to the electric supply company. As electrical energy cannot be stored, therefore, the distribution
system must be capable of supplying load demands of the consumers. This necessitates that operating staff must
continuouslystudyload patterns to predict inadvancethosemajorload changesthat follow theknown schedules.
(iii)Reliability. Modern industry is almost dependent on electric power for its operation. Homes and office buildings
are lighted, heated, cooled and ventilated by electric power. This calls for reliable service. Unfortunately, electric
power, like everything else that is man-made, can never be absolutely reliable. However, the reliability can be
improved to a considerable extent by (a) interconnected system (b) reliable automatic control system (c) providing
additional reserve facilities.
Design Considerations in Distribution System
Good voltage regulation of a distribution network is probably the most
important factor responsible for delivering good service to the consumers. For this
purpose, design of feeders and distributors requires careful consideration.
(i)Feeders. A feeder is designed from the point of view of its current carrying
capacity while the voltage drop consideration is relatively unimportant. It is
because voltage drop in a feeder can be compensated by means of voltage
regulating equipment at the substation.
(ii)Distributors. A distributor is designed from the point of view of the voltage
drop in it. It is because a distributor supplies power to the consumers and there is
a statutory limit of voltage variations at the consumer’s terminals (± 6% of rated
value). The size and length of the distributor should be such that voltage at the
consumer’s terminals is within the permissible limits.
Connection Schemes of Distribution S
ystem
All distribution of electrical energy is done by constant voltage system
(i) Radial System. In this system, separate feeders radiate from a single substation and
feed the distributors at one end only. Fig.1 shows a single line diagram of a radial system for
d.c. distribution where a feeder OC supplies a distributor AB at point A. Obviously, the
distributor is fed at one end only i.e., point A is this case. Fig.2 shows a single line diagram of
radial system for a.c. distribution. The radial system is employed only when power is
generated at low voltage and the substation is located at the centre of the load. This is the
simplest distribution circuit and has the lowest initial cost. However, it suffers from
the following drawbacks :
(a) The end of the distributor nearest to the feeding point will be heavily loaded.
(b)The consumers are dependent on a single feeder and single distributor. Therefore, any fault
on the feeder or distributor cuts off supply to the consumers who are on the side of the fault
away from the substation.
(c)Theconsumersat thedistant endof thedistributor would be subjectedto seriousvoltage
fluctuations when theload onthedistributor changes.Due to these limitations, this systemis
used for short distancesonly.
(ii) Ring main system. In this system, the primaries of distribution transformers form a
loop. The loop circuit starts from the substation bus-bars, makes a loop through the area to be
served, and returns to the substation. Fig. shows the single line diagram of ring main system
for a.c. distribution where substation supplies to the closed feeder LMNOPQRS.
The distributors are tapped from different points M, O and Q of the feeder
through distribution transformers. Thering main systemhas the following advantages :
(a) There are less voltage fluctuations at consumer’s terminals.
(b)The systemis very reliable as each distributor is fed via two feeders. In the event of fault
onanysectionof thefeeder, thecontinuity of supply is maintained.For example, suppose
that fault occurs at any point Fof section SLMof the feeder. Then section SLMof the
feeder can be isolated for repairs and at the same time continuity of supply is maintained to
all the consumers via the feeder SRQPONM.
(iii) Interconnected system. When the feeder ring is energised by two or more than two
generating stations or substations, it is called inter-connected system. Fig. shows the single line
diagram of interconnected system where the closed feeder ring ABCD is supplied by two
substations S1 and S2 at points D and C respectively. Distributors are connected to points O, P
,
Q and Rof the feeder ring through distribution transformers. The interconnected system has the
following advantages :
(a) It increases the service reliability.
(b) Any area fed from one generating station during peak load hours can be fed from the
other generating station. Thisreducesreserve power capacityand increasesefficiency of the
system.
SELF- TEST
1. Fill in the blanks by inserting appropriate words/figures.
(i) The underground systemhas ............. initial cost than the overhead system.
(ii) A ring main systemof distribution is ............. reliable than the radial system.
(iii) The distribution transformer links the primary and ............. distribution systems
(iv) The most common systemfor secondary distribution is ............ 3-phase, ............. wire system.
(v) The statutory limit for voltage variations at the consumer’s terminals is ............. % of rated
value.
(vi) The service mains connect the ............. and the .............
(vii) Theoverhead systemis ............. flexible than underground system.
ANSWERSTO SELF-TEST
(i) more (ii) more (iii) secondary (iv) 400/230 V,4 (v) = 6 (vi) distributor, consumer
terminals (vii) more
CHAPTER UNITEND QUESTIONS
1. What do youunderstand by distribution system?
2. Draw a single line diagram showing a typical distribution system.
3. Define and explain the terms : feeder, distributor and service mains.
4. Discuss the relative merits and demerits of underground and overhead systems.
5. Explain the following systemsof distribution :
(i) Radial system
(
i
i
) R
ing main system
(iii) Interconnected system
6. Discuss briefly the design considerations in distribution system.
7.With a neat diagram, explain the complete a.c. system for distribution of
electrical energy.
Methods of Solving A.C. Distribution Problems
(i)w.r.t. receiving or sending end voltage
(ii)w.r.t. to load voltage itself.
(i) Power factors referred to receiving end voltage
Example: A 3-phase, 400V distributor AB is loaded as shown in Fig.14.8. The 3-phase load at
point C takes 5A per phase at a p.f. of 0·8 lagging. At point B, a 3-phase, 400 V induction
motor is connected which has an output of 10 H.P. with an efficiency of 90% and p.f. 0·85
lagging. If voltage at point B is to be maintained at 400 V, what should be the voltage at
point A ? The resistance and reactance of the line are 1Ω and 0·5Ωper phase per kilometre
respectively
Solution. It is convenient to consider one phase only. Fig shows the single line diagram of the distributor.
Impedance of the distributor per phase per kilometre = (1 + j 0·5)
CHAPTER REVIEW TOPICS
1. How does a.c. distribution differ from d.c. distribution ?
2. What is the importance of load power factors in a.c. distribution ?
3. Describe briefly how will you solve a.c. distribution problems ?
4. Write short notes on the following :
(i) Difference between d.c. and a.c. distribution
(ii) Systems of a.c. distribution
5. Discuss about feeder, distributor and service main.
1. Fill in the blanks by inserting appropriate words/figures.
(i) The most common system for secondary distribution is 400/..... V, 3-phase, ......... wire
system.
(ii) In a 3-phase, 4-wire a.c. system, if the loads are balanced, then current in the neutral wire
is .........
(iii) Distribution transformer links the ............ and ........... systems.
(iv) The 3-phase, 3-wire a.c. system of distribution is used for .......... loads.
(v) For combined power and lighting load, .............. system is used.
2. Pick up the correct words/figures from brackets and fill in the blanks.
(i) 3-phase, 4-wire a.c. system of distribution is used for .............. load. (balanced,
unbalanced)
(ii) In a.c. system, additions and subtractions of currents are done ..............
(vectorially, arithmetically)
(iii) The area of X-section of neutral is generally .............. that of any line conductor. (the
same, half)
(iv) For purely domestic loads, .............. a.c. system is employed for distribution
ASSIGNMENT QUESTIONS
i) What are the different distribution system adopted in power system?
ii)What are the advantages of ring main distribution system?
iii) What are the types of dc distribution system are there? Explain.
iv) A single phase distributor 2 km.long supplies a load of 120 A at 0.8 p.f. lagging
at its far end and a load of 80 A at 0.9 p.f. lagging at its mid point. Both power factor
are referred to the voltage at the far end. The resistance and reactance per km. go
and return are 0.05Ω and 0.1 Ω respectively. The voltage at the far end is maintained
at 230 v, calculate
i) Voltage at the sending end.
ii) Phase angle between voltage at the two end.
ANSWERS TO SELF-TEST
1. (i) 230, 4 (ii) zero (iii) primary, secondary (iv) balanced (v) 3-phase 4-wire.
2. (i) unbalanced (ii) vectorially (iii) half (iv) single phase 2-wire.
Bus Bar Arrangements
 During the distribution of electrical power to various output circuits, two or more wires
are connected to a single wire.
 The improper electrical connection gets opened and the insulation of the wire may get
damaged due to heat generation in the wires.
 This condition may lead to an open circuit, which is too dangerous for the distribution of
power.
 In such cases, to avoid open-circuit conditions, the multiple wires are connected
properly using an electric bus system.
 The bus bar is an electrical component used in electrical distribution systems to collect
current from the input terminals of an electrical system and distributes it to various
output circuits.
 It is used as a junction between the input power and output power.
 It distributes the power to various output circuits with more flexibility.
Busbar Arrangements in Substations
Main and Transfer Busbar Arrangement
Selection and location of site for substation
1. It should be located nearer or at the center of the gravity of load.
2. It should provide safe and reliable arrangement
3. Maintenance of regulation clearances (deals with political issues)
4. Facilities for carrying out repairs and maintenance.
5. Immediate facilities against abnormalities such as possibility of
explosion or fire etc.
6. Good design and construction
7. Provision of suitable switchgear and protective gear etc.
8. Land cost
9. Number of incoming and out
10. Transfer of power
11. Short-circuit levels
12. Types of substation (objective/function)
13. It should be away from airport and terrorist zones
14. Physical amenities should be available for engineers such as
transportation, schools, houses, hospitals, communication services,
availability of drinking water etc.
15.Drainage facility for rainwater
16.Should be easily operated and maintained
17.Should involve minimum capital cost
18.Provision for future expansion
Selection and rating of S/s equipment
• Surge arrester
• CT
• PT
• Isolator
• Circuit breaker
• Transformer
• Busbar
• Shunt capacitor
• Earth switch
• Relays
• Auxiliaries
UNIT-III
UNDERGROUND CABLES
Dr.G.Nageswara Rao
Professor
EEE Department
LBRCE
Underground Cable: Consists of one or more conductors covered with
suitable insulation and surrounded by a protecting cover.
Requirements :
(i) The conductor used in cables should be tinned stranded copper or aluminium
of high conductivity. Stranding is done so that conductor may become
flexible and carry more current.
(ii) The conductor size should be such that the cable carries the desired load
current without overheating and causes voltage drop within permissible
limits.
(iii)The cable must have proper thickness of insulation in order to give high
degree of safety and reliability at the voltage for which it is designed
(iv) The cable must be provided with suitable mechanical protection so that it
may withstand the rough use in laying it.
(v) The materials used in the manufacture of cables should be such that there is
complete chemical and physical stability throughout.
1. Better general appearance
2. Less liable to damage through storms or lighting
3. Low maintenance cost
4. Less chances of faults
5. Small voltage drops
1. Greater installation cost
2. Insulation problems at high voltages compared with equivalent
overhead system
Advantages & Disadvantages
Requirements of the insulating materials used for cable are:
1. High insulation resistance.
2. High dielectric strength.
3. Good mechanical properties i.e., tenacity and elasticity.
4. It should not be affected by chemicals around it.
5. It should be non-hygroscopic because the dielectric strength of any
material goes very much down with moisture content
Vulcanized rubber insulated cables are used for wiring of houses, buildings and
factories for low power work.
There are two main groups of synthetic rubber material :
(i) general purpose synthetics which have rubber-like properties
(ii) special purpose synthetics which have better properties than the rubber
e.g. fire resisting and oil resisting properties.
The four main types are:
(i) butyl rubber, (ii) silicon rubber, (iii) neoprene, and (iv) styrene rubber.
Polyvinyl Chloride (PVC)
PVC material has many grades.
General Purpose Type: It is used both for sheathing and as an insulating material. In this
compound monomeric plasticizers are used. It is to be noted that a V.R. insulated PVC
sheathed cable is not good for use.
Hard Grade PVC: These are manufactured with less amount of plasticizer as compared with
general purpose type. Hard grade PVC are used for higher temperatures for short duration
of time like in soldering and are better than the general purpose type. Hard grade cannot be
used for low continuous temperatures.
Heat Resisting PVC: Because of the use of monomeric plasticizer which volatilizes at
temperature 80°C–100°C, general purpose type compounds become stiff. By using
polymeric plasticizers it is possible to operate the cables continuously around 100°C.
PVC compounds are normally costlier than the rubber compounds and the polymeric
plasticized compounds are more expensive than the monomeric plasticized ones. PVC is
inert to oxygen, oils, alkalis and acids and, therefore, if the environmental conditions are
such that these things are present in the atmosphere, PVC is more useful than rubber.
Impregnated Paper
A suitable layer of the paper is lapped on the conductor depending upon the operating
voltage. It is then dried by the combined application of heat and vacuum. This is carried
out in a hermetically sealed steam heated chamber. The temperature is 120°–130°C before
vacuum is created.
Protective Coverings
A cotton braid is applied over the insulated conductor and is then impregnated with a
compound, which is water and weather proof. The rubber insulated cables are covered with
a lead alloy sheath and is used for fixed installation inside or outside buildings in place of
braided and compound finished cable in conduit.
Polythene
This material can be used for high frequency cables. This has been used to a limited extent
for power cables also. The thermal dissipation properties are better than those of
impregnated paper and the impulse strength compares favorably with an impregnated paper-
insulated cable. The maximum operating temperature of this cable under short circuits is
100°C.
Construction
1. Cores or Conductors. A cable may have one or more than one core
(conductor) depending upon the type of service for which it is intended. The
conductors are made of tinned copper or aluminium and are usually stranded in
order to provide flexibility to the cable.
2. Insulation. Each core or conductor is provided with a suitable thickness of
insulation, the thickness of layer depending upon the voltage to be withstood by
the cable. The commonly used materials for insulation are impregnated paper,
varnished cambric or rubber mineral compound.
3. Metallic sheath. In order to protect the cable from moisture, gases or other
damaging liquids(acids or alkalies) in the soil and atmosphere, a metallic sheath
of lead or aluminium is provided over the insulation.
4. Bedding. Over the metallic sheath is applied a layer of bedding which
consists of a fibrous material like jute or hessian tape. The purpose of bedding
is to protect the metallic sheath against corrosion and from mechanical injury
due to armouring.
5. Armouring. Over the bedding, armouring is provided which consists of one
or two layers of galvanised steel wire or steel tape. Its purpose is to protect the
cable from mechanical injury while laying it and during the course of handling.
Armouring may not be done in the case of some cables.
6. Serving. In order to protect armouring from atmospheric conditions, a layer
of fibrous material (like jute) similar to bedding is provided over the
armouring.This is known as serving.
Types of Cables
Classified in two ways according to
(i) Type of insulating material used in their manufacture
(ii) Voltage for which they are manufactured.
Latter method of classification is :
(i) Low-tension (L.T.) cables — upto 1000 V
(ii) High-tension (H.T.) cables — upto 11,000 V
(iii) Super-tension (S.T.) cables — from 22 kV to 33 kV
(iv) Extra high-tension (E.H.T.) cables — from 33 kV to 66 kV
(v) Extra super voltage cables — beyond 132 kV
A cable may have one or more than one core depending upon the type of service for which it
is intended. It may be (i)single-core (ii) two-core (iii) three-core (iv) four-core etc.
Fora 3-phase service, either 3-single-core cables or three-core cable can be used depending
upon the operating voltage and load demand
Cables for 3-Phase Service
1. Belted cables — upto 11 kV
2. Screened cables — from 22 kV to 66 kV
3. Pressure cables — beyond 66 kV
Belted cables
Screened cables
Pressure cables
Single core conductor channel oil filled cable
Single core sheath channel oil filled cable
Three core oil filled cable
Three core pressure cable
Unit-IV
ELECTRICAL AND MECHANICAL DESIGN OF
TRANSMISSIONLINES
Transmission line sag calculation.
Inductance and Capacitance calculations of transmission
lines: line conductors, inductance and capacitance of single
phase and three phase lines with symmetrical and
unsymmetrical spacing, Composite conductors
transposition, bundled conductors, and effect of earth on
capacitance
Structure Types and Voltages
• The difference in level between points of
supports and the lowest point on the conductor is
called sag.
Sag Template
The sag template is used for allocating the position and height of
the supports correctly on the profile. The sag template decided the
limitations of vertical and wind load. It also limits the minimum
clearance angle between the sag and the ground for safety purpose.
The sag template is usually made up of transparent celluloid,
perplex, or sometimes cardboard. The following curves are marked
on it.
1. Hot Template Curve or Hot Curve
2. Ground Clearance Curve
3. Support Foot or Tower Curve
4. Cold Curve or Uplift Curve
Hot Curve – The hot curve is obtained by plotting the sag at maximum
temperature against span length. It shows where the supports must be located to
maintain the prescribed ground clearance.
Ground Clearance Curve – The clearance curve is below the hot curve. It is
drawn parallel to the hot curve and at a vertical distance equal to the ground
clearance as prescribed by the regulation for the given line.
Support Foot Curve – This curve is drawn for locating the position of the
supports for tower lines. It shows the height from the base of the standard support
to the point of attachment of the lower conductor. For wood or concrete line, pole
line this curve is not required to be drawn since they can be put in any convenient
position.
Cold Curve or Uplift Curve – Uplift curve is obtained by plotting the sag at a
minimum temperature without wind price against span length. This curve is drawn
to determine whether uplift of conductor occurs on any support. The uplift
conductor may occur at low temperature when one support is much lower than
either of the adjoining ones
(i) supports are at equal levels
(ii) supports are at unequal levels
P1: A transmission line has a span of 150 m between level supports.
The conductor has a cross-sectional area of 2 cm2. The tension in the
conductor is 2000 kg. If the specific gravity of the conductor material
is 9·9 gm/cm3 and wind pressure is 1·5 kg/m length, calculate the sag.
What is the vertical sag?
P2: A transmission line has a span of 214 metres between level supports. The
conductors have a cross-sectional area of 3·225 cm2. Calculate the factor of
safety under the following conditions :
Vertical sag = 2·35 m ; Wind pressure = 1·5 kg/m run
Breaking stress = 2540 kg/cm2 ; Wt. of conductor = 1·125 kg/m run
P3: The towers of height 30 m and 90 m respectively support a transmission
line conductor at water crossing. The horizontal distance between the
towers is 500 m. If the tension in the conductor is 1600 kg, find the
minimum clearance of the conductor and water and clearance mid-way
between the supports. Weight of conductor is 1·5 kg/m. Bases of the towers
can be considered to be at water level.
Fig. shows the conductor suspended between two supports
A and B at different levels with O as the lowest point on
the conductor.
Here, l = 500 m ; w = 1·5 kg ; T = 1600 kg.
Difference in levels between supports,
h = 90 − 30 = 60 m.
Let the lowest point O of the conductor be at a distance x1
from the support at lower level (i.e., support A) and at a
distance x2 from the support at higher level (i.e., support
B).
Obviously,
x1 + x2 = 500 m ………………...(i)
P4: An overhead transmission line at a river crossing is supported from two
towersat heights of 40 m and 90 m above water level, the horizontal distance
between the towers being 400m. If the maximum allowable tension is 2000 kg,
find the clearance between the conductor and water at a point mid-way between
the towers. Weight of conductor is 1 kg/m.
STRINGING CHART
Stringing chart is basically a graph between Sag, Tension with
Temperature. As we want low Tension and minimum sag in our
conductor but that is not possible as sag is inversely proportional to
tension. It is because low sag means a tight wire and high tension
whereas a low tension means a loose wire and increased sag.
Therefore, we make compromise between two but if the case of
temperature is considered and we draw graph then that graph is
called Stringing chart.
Electrical Design of Overhead Lines
 An a.c. transmission line has resistance, inductance and
capacitance uniformly distributed along its length.
 These are known as constants or parameters of the line.
 The performance of a transmission line depends to a considerable
extent upon these constants.
 For instance, these constants determine whether the efficiency
and voltage regulation of the line will be good or poor.
 Therefore, a sound concept of these constants is necessary in
order to make the electrical design of a transmission line a
technical success.
Constants of a Transmission Line
A transmission line has resistance, inductance and capacitance
uniformly distributed along the whole length of the line
(i) Resistance. It is the opposition of line conductors to current flow.
(i) Inductance. When an alternating current flows through a
conductor, a changing flux is set up which links the conductor.
Due to these flux linkages, the conductor possesses inductance.
(iii)Capacitance. As any two conductors of an overhead transmission
line are separated by air which acts as an insulation, therefore,
capacitance exists between any two overhead line conductors. The
capacitance between the conductors is the charge per unit
potential difference
Skin Effect
When a conductor is carrying steady direct current (d.c.), this current is uniformly
distributed over the whole X-section of the conductor. However, an alternating
current flowing through the conductor does not distribute uniformly, rather it has
the tendency to concentrate near the surface of the conductor. This is known as
skin effect.
The tendency of alternating current to concentrate near the surface of a conductor
is known as skin effect.
Due to skin effect, the effective area of cross-section of the conductor through
which current flows is reduced. Consequently, the resistance of the conductor is
slightly increased when carrying an alternating current. The cause of skin effect
can be easily explained. A solid conductor may be thought to be consisting of a
large number of strands, each carrying a small part of the current. The *inductance
of each strand will vary according to its position. Thus, the strands near the centre
are surrounded by a greater magnetic flux and hence have larger inductance than
that near the surface. The high reactance of inner strandscauses the alternating
current to flow near the surface of conductor. This crowding of current near the
conductor surface is the skin effect.
The skin effect depends upon the following factors :
(i) Nature of material
(ii) Diameter of wire − increases with the diameter of
wire.
(iii) Frequency − increases with the increase in
frequency.
(iv) Shape of wire − less for stranded conductor than
the solid conductor.
It may be noted that skin effect is negligible when the
supply frequency is low (< 50 Hz) and conductor
diameter is small (< 1cm).
DEFINITION: The ionization of air surrounding the high voltage
transmission lines causing the conductors to glow, producing a
hissing noise with violet glow color , is called Corona Discharge or
Corona Effect.
Corona Effect in Transmission Lines:
This phenomenon occurs when the electrostatic field across
the transmission line conductors produces the condition of
potential gradient. The air gets ionized when the potential
gradient at the conductor surface reaches the value of
30kV/cm at normal pressure and temperature.
In transmission lines, conductors are surrounded by the air. Air
acts as a dielectric medium. When the voltage of air
surrounding the conductor exceeds the value of 30kV/cm,
the charging current starts to flow through the air, that is air
has been ionized. The ionized air act as a virtual conductor,
producing a hissing sound with a luminous violet glow.
Advantages & Disadvantages of Corona Effect
Advantages:
The main advantages of corona effects are:
1. Due to corona across the conductor, the sheath of air
surrounding the conductor becomes conductive which rises the
conductor diameter virtually. This virtual increase in the
conductor diameter reduces the maximum potential gradient or
maximum electrostatic stress. Thus, the probability of flash-over is
reduced.
2. Effects of transients produced by lightning or electrical
surges are also reduced due to the corona effect. As, the
charges induced on the line by surge or other causes, will be
partially dissipated as a corona loss. In this way, corona protects
the transmission lines by reducing the effect of transients that
Disadvantages:
1. The glow appear across the conductor which shows the
power loss occur on it.
2. The audio noise occurs because of the corona effect which
causes the power loss on the conductor.
3. The vibration of conductor occurs because of corona effect.
4. The corona effect generates the ozone because of which the
conductor becomes corrosive.
5. The corona effect produces the non-sinusoidal signal thus the
non-sinusoidal voltage drops occur in the line.
6. The corona power loss reduces the efficency of the line.
7. The radio and TV interference occurs on the line because of
corona effect.
Factors Affecting Corona Discharge
1. Supply Voltage: As the electrical corona discharge mainly depends upon
the electric field intensity produced by the applied system voltage. Therefore,
if the applied voltage is high, the corona discharge will cause excessive
corona loss in the transmission lines. On contrary, the corona is negligible in the
low-voltage transmission lines, due to the inadequate amount of electric field
required for the breakdown of air.
2.Conductor Surface: The corona effect depends upon the shape, material
and conditions of the conductors. The rough and irregular surface i.e.,
unevenness of the surface, decreases the value of breakdown voltage. This
decrease in breakdown voltage due to concentrated electric field at rough
spots, give rise to more corona effect. The roughness of conductor is usually
caused due to the deposition of dirt, dust and scratching. Raindrops, snow,
fog and condensation accumulated on the conductor surface are also
sources of surface irregularities that can increase corona.
3. Air Density Factor: Air density factor also determines the corona loss in
transmission lines. The corona loss in inversely proportional to air density factor.
Power loss is high due to corona in Transmission lines that are passing through a
hilly area because in a hilly area the density of air is low.
4.Spacing between Conductors: If the distance between two conductors is
very large as compared to the diameter of conductor, the corona effect may
not happen. It is because the larger distance between conductors reduces the
electro-static stress at the conductor surface, thus avoiding corona formation.
5.Atmosphere: In the stormy weather, the number of ions is more than normal
weather. The decrease in the value of breakdown voltage is followed by the
increase in the number of ions. As a result of it, corona occurs at much less
voltage as compared to the breakdown voltage value in fair weather.
How Corona Effect is Reduced:
It has been observed that the intense corona effects are observed at a working voltage
of 33 kV or above. On the sub-stations or bus-bars rated for 33 kV and higher voltages,
highly ionized air may cause flash-over in the insulators or between the phases, causing
considerable damage to the equipment, if careful designing is not made to reduce the
corona effect. The corona effect can be reduced by the following methods:
1. By Increasing Conductor Size: The voltage at which corona occurs can be raised by
increasing conductor size. Hence, the corona effect may be reduced. This is one of the
reasons that ACSR conductors which have a larger cross-sectional area are used in
transmission lines.
2. By Increasing Conductor Spacing: The corona effect can be eliminated by increasing
the spacing between conductors, which raises the voltage at which corona occurs.
However, increase in conductor spacing is limited due to the cost of supporting structure
as bigger cross arms and supports to accompany the increase in conductor spacing,
increases the cost of transmission system.
3. By Using Corona Ring: The intensity of electric field is high at the point where the
conductor curvature is sharp. Therefore, corona discharge occurs first at the sharp points,
edges, and corners. In order to, mitigate electric field, corona rings are employed at the
terminals of very high voltage equipment.
Corona rings are metallic rings of toroidal shaped, which are fixed at
the end of bushings and insulator strings. This metallic ring distributes the
charge across a wider area due to its smooth round shape which
significantly reduces the potential gradient at the surface of the
conductor below the critical disruptive value and thus preventing
corona discharge.
Important points:
 Disruptive voltage is the minimum voltage at which the breakdown
of air occurs and corona starts.
 Visual critical voltage is the minimum voltage at which visible
corona begins.
CORONA RING
Thank You
Insulators
 An insulator gives support to the overhead line conductors on the poles to
prevent the current flow toward earth. In the transmission lines, it plays an
essential role in its operation.
 The designing of an insulator can be done using different materials like rubber,
wood, plastic, mica, etc.
 The special materials used in the electrical system are glass, ceramic, PVC,
steatite, polymer, etc.
 But the most common material used in the insulator is porcelain and also
special composition, steatite, glass materials are also used.
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POWER SYSTEMS-1 Complete notes examples

  • 1. 1 Dr.G.Nageswara Rao Professor , EEE Department Lakireddy Bali Reddy College of Engineering (LBRCE)
  • 2. Course Outcomes: At the end of the course, the student will be able to: CO1: Understand the operation of non-renewable electrical power generating stations (Understand-L2) CO2: Illustrate the economic aspects of power generation (Apply-L3) CO3: Understand the a.c distribution system and performance of insulated cables (Understand-L2) CO4: Evaluate the electrical and mechanical parameters of transmission lines (Apply-L3) CO5: Analyze operation of overhead line insulators and phenomena of corona (Understand-L2) Course Educational Objective: This course enables the student to learn different types of non- renewable power generation methods, the economic aspects of power generation, tariff methods and design aspects of transmission lines. 2
  • 3. 3 UNIT-I: POWER GENERATION METHODS Introduction to typical layout of an electrical power system, present power scenario in India, Generation of electric power: non-renewable sources (Qualitative): Hydro station, Steam power plant, Nuclear power plant and Gas turbine plant. UNIT-II: ECONOMICS OF GENERATION Introduction, definitions of connected load, maximum demand, demand factor, load factor, diversity factor, Load duration curve, number and size of generator units. Base load and peak load plants. Cost of electrical energy-fixed cost, running cost, Tariff on charge to customer. UNIT-III: AC DISTRIBUTION & CABLES AC Distribution: Introduction, AC distribution, Single phase, 3-phase- 3wire, 3 phase 4 wire system, bus bar arrangement, Selection of site and layout of substation. Insulated Cables: Introduction, insulation, insulating materials, extra high voltage cables, grading of cables, insulation resistance of a cable, capacitance of a single core and three core cables, overhead lines versus underground cables, types of cables.
  • 4. 4 Unit-IV: ELECTRICAL AND MECHANICAL DESIGN OF TRANSMISSION LINES Transmission line sag calculation: The catenary curve, sag tension calculations, supports at different levels, stringing Chart, inductance and capacitance calculations of transmission lines: line conductors, inductance and capacitance of single phase and three phase lines with symmetrical and unsymmetrical spacing, Composite conductors- transposition, bundled conductors, and effect of earth on capacitance. UNIT-V: CORONA& INSULATORS Corona: Introduction, disruptive critical voltage, corona loss, Factors affecting corona loss and methods of reducing corona loss, Disadvantages of corona, interference between power and Communication lines, Numerical problems. Overhead Line Insulators: Introduction, types of insulators, Potential distribution over a string of suspension insulators, Methods of equalizing the potential, testing of insulators.
  • 5. 5 TEXT BOOKS: 1. Soni, Gupta & Bahtnagar, Power Systems Engineering, Dhanpat Rai & Sons, 2016. 2. C.L. Wadhwa, Electrical Power Systems, 6th Edition, New AgeInternational,2009. REFERENCE BOOKS: 1. M.V.Deshpande, Elements of Electrical Power Station Design, 3rd, Wheeler Pub.1997. 2. C.L. Wadhwa, Generation, Distribution and Utilization of Electrical Energy, 3rd Edition, New AgeInternational,2015. 3. V K Mehta & Rohit Mehta, Principles of Power Systems (Multicolor Edition), 24/e, S.Chand Publishing, 4th Edition ,2005. W.D.Stevenson, Elements of Power System Analysis, 4th Edition, McGraw Hill, 1982. https://www.slideshare.net/raoakhil/thermal-power-plants-237930541
  • 6. 6
  • 7. 8 February 2024 Department of EEE 7
  • 8. 8 February 2024 Department of EEE 8  Electricity sector in India is growing at a rapid pace.  The present peak demand is about 1,15,000 MW and the Installed Capacity is 1,52,380 MW using generation from thermal (63%), hydro (25 %), Nuclear (9 %) and renewables (9 %)
  • 9. 8 February 2024 Department of EEE 9
  • 10. 8 February 2024 Department of EEE 10
  • 11. 8 February 2024 Department of EEE 11
  • 12. 8 February 2024 Department of EEE 12
  • 13. 8 February 2024 Department of EEE 13
  • 14. 14 Basic Principal of Steam Power Plant The heat produced for burning of coal & with the help of water steam is produced. This produced steam flow towards turbine i.e. kinetic energy is converted into mechanical energy. The input steam drives the prime mover or turbine, simultaneously the generator also start to rotate. At that time mechanical energy is converted into electrical energy. Thermal Power Plant
  • 15. 15 Selection of Site for Thermal Power Plant 1. Supply of Fuel: The Steam power station should be located near the coal mine so that transportation cost of fuel is minimum. If the land is not available near to coal mines then provide adequate facilities for transportation of fuel. 2. Available of Water: A huge amount of water is required in boiler & condenser, so that the plant should be located near the river, lake etc. 3. Transportation Facility: For steam power station provide better transportation facility for the transportation of man, machinery etc. 4. Cost & Type of Land: The Steam Power Station should be located where the cost of land is chief & also future extension is possible. 5. Near to Load Center: In order to reduce transmission & distribution losses the plant should be located near to load center. 6. Distance from Populated Area: As the thermal power plant produces flue gases, these gases will effect to live human being, so that the plant should be located away from thickly populated area. 7. Disposal Facility Provided: As the thermal power plant produces ash, while burning of coal. So, disposal of ash facility should be provided. 8. Availability of labour: Skilled and unskilled labour should be available nearly.
  • 17. 17 Flow Diagram of Steam Thermal Power Plant
  • 18. 18 The Basic Components 1. Boiler (i) fire tube boiler and (ii) water tube boiler 1. Steam turbine 2. Generator 3. Condenser 4. Cooling towers 5. Circulating water pump 6. Boiler feed pump 7. Forced or induced draught fans 8. Ash precipitators
  • 19. 19 Boiler A boiler is a closed vessel in which the water or fluid is heated Steam turbine A steam turbine is a device which extracts thermal energy from the pressurized steam. The energy must be used to organize mechanical work on a rotating output shaft. Generator A generator is a device which is used to convert the mechanical form of energy into the electrical energy. Condenser A condenser is a device used to converts the gaseous substance into the liquid state substance with the help of cooling. Cooling towers A cooling tower is a heat rejection device, which discards the waste heat into the atmosphere with help of the cooling water stream to a lower temperature.
  • 20. 20 Circulating water pump Circulating pump is a special device used to circulate the liquids, gases and slurries present in the closed circuit. The main purpose of the circulating pump is circulating the water in a cooling system or hydronic heating. Boiler feed pump A boiler feed pump is a specific type of pump which is used to feed the water into the steam boiler. The condition of water supply depends on the boiler produce the condensation of the steam. Forced draught fans: Forced draught fans are used to provide a positive pressure to a system. Induced draught fans Induced draught fans are used to provide a negative pressure or vacuum in a slack or system Ash precipitators: Precipitators are devices used to remove the fine particles like smoke and dust. By using the force of induced electrostatic charge minimally close the flow of gases through the unit.
  • 21. 21 Working Principle Of Thermal Power Plant Water is used as the working fluid in the thermal power plant. We can see coal based and nuclear power plants in this category. From the working of the power plant energy, later from the fuel gets transferred into the form of electricity. With the help of high pressure and high steams a steam turbine in a thermal power plant is rotates, the rotation must be transfer to the generator to produce power. When turbine blades are rotated with the high pressure and high temperature at that case the steam loses its energy. So it results in the low pressure and low temperature at the outlet of the turbine. Steam must be expanded upto the point where it reaches the saturation point. So from the steam, there is no heat addition or removal that takes place. Entropy of the steam remains same. So we can notice the change in the pressure and volume and temperature along with the entropy diagrams. If the condition comes to the low pressure and low temperature steam back to the original state, from that we can produce continuous electricity.
  • 22. 22 To compress the gaseous state liquids at that case large amount of energy is required. So before the compression we need to convert the fluids into liquid state. For this purpose condenser is required and heat is rejected to the surroundings and converts the steam into liquid state. During this process the temperature and volume of the fluid changes take place hardly, so it turns into liquid state. And the fluid turns to the original state. To bring the fluid to the original state external heat is added. To the heat exchanger heat is added which is called as boiler. Then the pressure of the fluid must remain same. In heat exchanger tubes it expands freely. Due to increase in temperature the liquid state is transformed into the vapour state and the temperature remains same. So know we complete the thermodynamic cycle in the thermal power plant. It is known as Rankine cycle. By repeating the cycle we can produce the power continuously. With the help of boiler furnace heat is added to the boiler. Then the fuel must reacts with the air and produces heat. The fuel must be either nuclear or coal. In this process if we use coal as a fuel we can observe lot of pollutants before ejects in to the air clean or removed the particles and send into surroundings. The process is done in various steps. By using the electro static precipitator the ash particles are removed. So with the help of the stack clean exhaust must be send outside.
  • 24. 24 Advantages: 1.Cost of fuel: Fuel used in thermal power station (TPS) is cheaper than cost of fuel used in diesel & nuclear power station. 2.Capital cost: Capital cost of TPS is less than hydro & nuclear power station. 3.Near load center: TPS can be located near load center. The coal can be transport from coal mines to power plant. As it is located load centre it reduces transmission cost and losses in it. 4.Space required: Less space required as compared to hydro power station. 5.Generating capacity: TPS build/construct of high generating capacity, so used as a base load power plant. 6.Time required for completion of project: Time required for completion of Thermal power project is very less as compare to hydroelectric power station.
  • 25. 25 Disadvantages: 1. Air pollution: It produces air pollution due to smoke and ash produced during combustion of fuel. 2. Starting Time: TPP cannot be put into service immediately like hydroelectric power plant. As thermal power plant required few hours (6-7 hour) to generate steam at high pressure and high temperature. 3. Handling of fuel: Handling of coal and disposal of ash is quite difficult. 4. Fuel transportation cost: When power plant are located away from coal mines i.e. near load centre at that time fuel transportation cost is more. 5. Preparation for fuel: There is more expenditure for preparation of coal (raw coal to pulverized coal). 6. Space required: Large amount of space is required for storage of fuel and ash as compare to Nuclear power plant. 7. Efficiency: It is less efficient power plant overall efficiency is maximum 30 %. 8. Stand by losses: Stand by losses is more as furnace is required to keep in operation even when there is no load. 9. Maintenance cost: High maintenance and operating cost because number of axillaries plant are required such as coal and ash handling plant, pulverizing plant, condensing plant and water purification plant etc. 10. Availability of fuel: Less availability of high grade coal. 11. Simplicity and cleanness: Layout of thermal power plant is complicated than hydroelectric power plant due to coal and ash. 12. Life: Life of thermal power plant is less than hydro power plant. 13. Cost per unit (cost of generation) is high
  • 27. In water tube boilers the water flows through tubes and hot combustion gases flow over these tubes. Whereas in fire tube boilers the tubes are surrounded by water and hot combustion gases flow through these tubes.
  • 28. 28
  • 29. 8 February 2024 Department of EEE 29 Surface Condenser
  • 30. 30
  • 31. 31 Principle And Working Of Surface Condenser The Basic working principle of a surface condenser is the transfer of heat from a higher-temperature body to a lower-temperature body. In this, the steam (high- temperature body) liberates its heat to the cooling water tubes (low-temperature body). In the process of heat transfer, the hot steam gets converted to water. The steam enters from the exhaust Steam inlet and comes in contact with the water carrying tubes. The water in the tubes has a circulating flow. As soon as the exhaust steam comes in contact with the water-cooled tubes, the process of heat transfer begins. The heat from the steam is removed and converted into a liquid which Is known as condensate. This condensate is then removed from the cylindrical vessel through a valve located at the bottom of the cylinder. In thermal power stations, water is heated more than its boiling point to generate steam which in turn is used to rotate the turbine. After passing through the turbine the steam is fed into a surface condenser where it is converted into water and then reused.
  • 32. 8 February 2024 Department of EEE 32 Jet Condenser Surface Condenser Both steam & cooling water are mixed together Both steam & cooling water are not mixed together Manufacturing cost is low Manufacturing cost is high Occupies less area Occupies large area The air pump requires large power The air pump requires less power A small quantity of cooling water is required A large quantity of cooling water is required
  • 33. 33 Advantages The following are the advantages of surface condenser 1. Its vacuum efficiency is high 2. They are mainly used in large plants area 3. It uses low-quality water 4. It also uses impure water for cooling purpose 5. The pressure ratio & steam are directly proportional. Disadvantages The following are the disadvantages of surface condenser 1. Water required is in the large amount 2. Complex in construction 3. High maintenance 4. It occupies a large area. Applications The following are the applications of surface condenser 1. Refrigeration of vacuum 2. Evaporation of vacuum 3. Systems like Desalination
  • 34. 8 February 2024 Department of EEE 34
  • 35. 35 Hydroelectric power plant has the following parts Dam or weir: it contains the river water, forming a reservoir behind it and thus creating a water drop that is used to produce energy. Dams can be made of earth or concrete. Spillways: They release part of the impounded water without passing through the turbines; water can then be used for irrigation purposes. They are located on the main wall of the dam and can be at the top or at the bottom. Most of the water goes into a plunge pool at the toe of the dam, to prevent scour damage by the falling water. Water intakes: they let in the impounded water towards the turbines through a penstock. Water intakes have gates to control the amount of water that reaches the turbines and grids to filter out any debris such as trunks, branches, etc. Powerhouse: it houses the hydraulic and electrical equipment (turbines, generators, transformers) and the service area with control and testing rooms. It has inlet and outlet gates to ensure the equipment area can be dry in case of repairs or disassembling equipment. Turbines: they harness the energy of the water that goes through them to rotate around a shaft. There are three main types of turbines: Pelton, Francis and Kaplan turbines (propeller type). Transformers: electrical devices to increase or decrease the voltage in an alternating current circuit. Electrical power transmission lines: cables to transmit the electricity generated.
  • 37. 8 February 2024 Department of EEE 37 Gas Turbine Power Plant A generating station which employs a gas turbine as the prime mover for the generation of electrical energy is known as a gas turbine power plant. In a gas turbine power plant, air is used as the working fluid. The air is compressed by the compressor and is led to the combustion chamber where heat is added to the air, thus raising its temperature. We will understand the gas turbine power plant layout and learn the diagram. Heat is added to the compressed air either by burning fuel in the chamber or by the use of air heaters. The hot and high-pressure air from the combustion chamber is then passed to the gas turbine where it expands and does the mechanical work. The gas turbine drives the alternator which converts mechanical energy into electrical energy. It may be mentioned here that compressor, gas turbine and the alternator are mounted on the same shaft so that a part of the mechanical power of the turbine can be utilised for the operation of the compressor. Gas turbine power plants are being used as standby plants for hydro-electric stations, as a starting plant for driving auxiliaries in power plants etc.
  • 38. 8 February 2024 Department of EEE 38 The main components of the Gas Turbine Power Plant are : (i) Compressor (ii) Regenerator (iii) Combustion chamber (iv) Gas turbine (v) Alternator (vi) Starting motor (i) Compressor: The compressor used in the plant is generally of rotatory type. The air at atmospheric pressure is drawn by the compressor via the filter which removes the dust from the air. The rotatory blades of the compressor push the air between stationary blades to raise its pressure. Thus air at high pressure is available at the output of the compressor. (ii) Regenerator: A regenerator is a device which recovers heat from the exhaust gases of the turbine. The exhaust is passed through the regenerator before wasting to the atmosphere. A regenerator consists of a nest of tubes contained in a shell as seen in the below power plant layout. The compressed air from the compressor passes through the tubes on its way to the combustion chamber. In this way, compressed air is heated by the hot exhaust gases.
  • 39. 39 (iii) Combustion chamber: The air at high pressure from the compressor is led to the combustion chamber via the regenerator. In the combustion chamber, heat is added to the air by burning oil. The oil is injected through the burner into the chamber at high pressure to ensure atomisation of oil and its thorough mixing with air. The result is that the chamber attains a very high temperature (about 3000 F). The combustion gases are suitably cooled to 1300F to 1500F and then delivered to the gas turbine. iv) Gas turbine: The products of combustion consisting of a mixture of gases at high temperature and pressure are passed to the gas turbine.These gases in passing over the turbine blades expand and thus do the mechanical work. The temperature of the exhaust gases from the turbine is about 900F. (v) Alternator: The gas turbine is coupled to the alternator as seen in the gas turbine plant layout. The alternator converts mechanical energy of the turbine into electrical energy. The output from the alternator is given to the bus-bars through the transformer, circuit breakers and isolators. (vi) Starting motor: Before starting the turbine, the compressor has to be started. For this purpose, an electric motor is mounted on the same shaft as that of the turbine. The motor is energised by the batteries. Once the unit starts, a part of the mechanical power of the turbine drives the compressor and there is no need of motor now
  • 40. 40 Gas turbine power plant Advantages: (i) It is simple in design as compared to steam power station since no boilers and their auxiliaries are required. (ii) It is much smaller in size as compared to the steam power station of the same capacity. This is expected since the gas turbine power plant does not require a boiler, feed water arrangement etc. (iii) The initial and operating costs are much lower than that of the equivalent steam power station. (iv) It requires comparatively less water as no condenser is used. (v) The maintenance charges are quite small. (vi) Gas turbines are much simpler in construction and operation than steam turbines. (vii) It can be started quickly form cold conditions. (viii) There are no standby losses. However, in a steam power station, these losses occur because the boiler is kept in operation even when the steam turbine is supplying no load.
  • 41. 41 Gas turbine power plant Disadvantages: (i) There is a problem with starting the unit. It is because before starting the turbine, the compressor has to be operated for which power is required from some external source. However, once the unit starts, the external power is not needed as the turbine itself supplies the necessary power to the compressor. (ii) Since a greater part of power developed by the turbine is used in driving the compressor, the net output is low. (iii) The overall efficiency of such plants is low (about 20%) because the exhaust gases from the turbine contain sufficient heat. (iv) The temperature of the combustion chamber is quite high (3000F) so that its life is comparatively reduced.
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  • 44. 44 1. Discuss the different sources of energy available in nature. 2. Draw the schematic diagram of a modern steam power station and explain its operation 3. What is a steam power station ? Discuss its advantages and disadvantages. 4. What factors are taken into account while selecting the site for a steam power station ? 5. Draw a neat schematic diagram of a hydro-electric plant and explain the functions of various components. 6. Explain the functions of the following : (i) dam (ii) spillways (iii) surge tank (iv) headworks (v) draft tube 7. Draw the schematic diagram of a nuclear power station and discuss its operation 8. Explain with a neat sketch the various parts of a nuclear reactor 9. Discuss the factors for the choice of site for a nuclear power plant. 10. Explain the working of a gas turbine power plant with a schematic diagram. 11. Give the comparison of steam power plant, hydro-electric power plant, gas power plant and nuclear power plant 12. Discuss the advantages and disadvantages of a gas power station. CHAPTER REVIEW QUESTIONS
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  • 47. Site Selection for Hydro Power Plant 2 01. Availability of water Water is the main source of hydroelectric power plants. A huge amount of water should be available so that the power plant can be built with a high head. The quantity of the water available will be estimated on the basis of the measurement of streamflow over a certain period or previous rainfall records. 02. Storage of water There will be a wide variation of rainfall during the year. This makes it necessary to store water for continuous generation of power throughout the year. 03. Head of water The head of the water depends upon the topography of the area. If the head is more then potential energy will be more. 04. Choice of the dam The important consideration in the choice of the dam is safety and economics. Failure of the dam may result in substantial loss of life and property. The dam must satisfy the stability test for shock loads and unusual floods. 05. Distance from the power station to load center The distance should be less between the power station and load center so that the cost of transmission of power becomes less. 06. Accessibility of the site The plant should be easily accessible by rain and load for transportation of plant equipment.
  • 49. 4 01. Reservoir: The purpose of this reservoir is to store the water which will be further used to generate electricity. The water will be stored during the rainy season. By storing water we get potential energy. 02. Dam: dam will be constructed across the river or lakes to provide the head of the water. These are classified based on their function, material, shape, and structural design. 03. Spillway: This spillway is the safety wall for the dam. It discharges the existing amount of water from the reservoir into the rivers. That means spillway is required to reduce overtopping. It keeps the reservoir level below the predetermined value. 04. Intake: Intake acts as a filter in Hydro Electric power plants. It removes unwanted material from the water. In this stage, the potential energy will be converted into kinetic energy. 05. Penstock: This is the channel between the dam and turbine which helps to increase the kinetic energy of the water. It is made up of stainless steel. 06. Surge tank: It acts as a pressure release wall for the water. It reduces the water hammer effect. That means it holds the water whenever there is no requirement of load on the turbines, and similarly, it discharges water whenever there is a requirement of load on the turbines. 07. Prime mover/turbine: For this reason, the kinetic energy will be converted into mechanical energy, which is responsible for the rotation of the shaft of the turbines. Commonly used turbines are Kaplan, Francis, Pelton, cross flow, etc. 08. Alternators / Generators: These are normally located near the foot of the dam. Water is brought to alternators with the help of penstock. In this region, the mechanical energy is converted to electrical energy. Thus final power will get in this stage.
  • 50. 5 Working Principle  In a hydro electric power plant, water is stored in the dam reservoir which has potential energy.  This potential energy is converted into kinetic energy when water from the dam is allowed to flow through the pipes.  This kinetic energy is converted into mechanical energy allowing the water flowing in pipe to drive the turbine.  At last, the mechanical energy by rotating the turbine is converted to electrical energy in the generator which is coupled to the turbine.  The dam creates the head of the water from which water flows.  Penstock carries the water from the Dam to the turbine, and it provides kinetic energy.  The fast flowing water through the penstock pushes turbine blades.  The water forces on turbine plates and rotates the generator rotor, which in turn generates electricity.
  • 51. 6 Advantages 1. Electricity can be produced at a constant rate once the dam is constructed 2. The gates of the dam can be shut down if electricity is not needed, which stops electricity generation. Hence by doing this, we can save water for further use in future when the demand for electricity is high. 3. One of the biggest advantages of hydroelectric power plants is that they are designed to last many decades, and so they can contribute to the generation of electricity for years. 4. Large dams often become tourist attractions because the lake that forms in the reservoir area behind the dam can be used for leisure or water sports. 5. The water from the lake of the dam can be used for irrigation purposes in farming. 6. Since the water is released to produce electricity, the build-up of water in the dam is stored to produce extra energy until needed. 7. Hydroelectric energy generation does not pollute the atmosphere because the hydroelectric power plant does not produce greenhouse gases. 8. Hydropower plants can be considered a reliable energy generation source. Since hydropower totally depends on water present on this planet, this energy source will remain inexhaustible because of the water cycle as it continuously keeps on maintaining balance on the Earth.
  • 52. 7 Disadvantages 1. It is not an easy task to assemble a hydropower plant because the dams are extremely expensive to build, and they require extremely high standards and calculations for their construction. 2. It becomes important that the hydropower plant must serve for many decades because of its high cost of construction, and this totally depends on the availability of water resources. 3. If flooding happens due to natural calamities or the failure of dams, it would impact a large area of land, which means that the natural environment can be destroyed. 4. People are forcibly removed from the particular area where a hydropower plant is going to be assembled. This affects the day-to-day life of people living in that area. 5. A serious geological damage can be caused due to the construction of large dams. 6. To construct a hydro plant, it is important to block the running water source due to which the fishes can’t arrive at their favourable place, and as the water stops streaming, the areas along the riverside start to vanish out which eventually influences the life of creatures that depend on fish for food.
  • 53. 8 Different types of modern hydro power plants 1. Pumped storage hydropower plants 2. Reversible turbine pump hydropower plants 3. Underground hydropower plants 4. Tidal power plants Types of Pumped Storage Plants 1. Daily, weekly or seasonal storage plants 2. High, medium or low head plants 3. According to the type of turbine used in the plant 4. Pure or mixed storage hydropower plants 5. Horizontal or vertical storage plants
  • 55. Pumped Storage Hydropower Plants: To supply the peak loads, hydropower plants has to have the installed capacity of high loads of which remains idle during the off-peak hours. The more the demands of variable power supply, it is necessary to devise some way to achieve the economical loading of the power plant by levelling up the load curve. The following are some of the ways: (a) Commercial Method: To sell electric current at a higher rate during peak hours than during off-peak hours. (b) Technical method: The following are the two methods: (i) By installing special peak load power plants (ii) By storing energy produced during off-peak hours. Such a system is known as Pumped Storage Plants. Purpose of Pumped Storage Hydropower Plants: This type of plants combined with steam power stations reduces the power load fluctuations to narrow limits. In some cases, the storage plant consists of pump and motor with no turbines. The pump increases the head in the feeder reservoir of a separate hydro-electric plant while motor improves the power factor in the electric supply network.
  • 56. 11 Advantages: The pump storage plants entail the following advantages : 1.There is substantial increase in peak load capacity of the plant at comparatively low capital cost. 2.Due to load comparable to rated load on the plant, the operating efficiency of the plant is high. 3.There is an improvement in the load factor of the plant. 4.The energy available during peak load periods is higher than that of during off peak periods so that in spite of losses incurred in pumping there is over-all gain. 5. Load on the hydro-electric plant remains uniform. 6.The hydro-electric plant becomes partly independent of the stream flow conditions.
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  • 58. 8-Feb-24 1 NUCLEAR POWER PLANT Dr.G.Nageswara Rao Professor , EEE Department Lakireddy Bali Reddy College of Engineering (LBRCE)
  • 59. NUCLEAR BINDING ENERGY Nuclei are made up of protons and neutron, but the mass of a nucleus is always less than the sum of the individual masses of the protons and neutrons which constitute it. The difference is a measure of the nuclear binding energy which holds the nucleus together. The enormity of the nuclear binding energy can perhaps be better appreciated by comparing it to the binding energy of an electron in an atom. The comparison of the alpha particle binding energy with the binding energy of the electron in a hydrogen atom is shown below. The nuclear binding energies are on the order of a million times greater than the electron binding energies of atoms.
  • 60. Fusion is the process where two light nuclei combine together releasing vast amounts of energy. Fission is the splitting of a heavy, unstable nucleus into two lighter nuclei Fission and Fusion (Hydrogen Bomb) (Atom Bomb or Atomic Bomb)
  • 61. 4 Fission Reaction Fusion Reaction A fission reaction is splitting up of a large atom or a molecule into two or more smaller ones. Fusion is the process of combination of two or more lighter atoms or molecules into larger ones. Fission reaction doesn’t occur normally in nature. Fusion reaction process occurs in the stars, like in the sun, etc. This reaction produces highly radioactive substances. Few number of radioactive particles are developed by the process of a fusion reaction. Neutrons must be slowed down by moderation to increase their capture probability in fission reactors. This process requires high-temperature, high-density environment. This process consumes a very little amount of energy to break up the atoms. High amount of energy is consumed to combine protons so that the nuclear forces can overcome the electrostatic repulsion. The energy released during the process of fission is much larger than that of the released energy in other chemical reactions. The energy released by the process of fusion is around 3-4 times much greater than that of the energy liberated by the process of fission. Fission process is utilized in the nuclear power plant. Fusion process is one of the experimental technologies for the production of power. Uranium is one of the primary fuels used for the process of fission in power plants. The isotopes of hydrogen such as the Deuterium & Tritium are some of the primary fuels used in the experimental process of fusion power plants. A fission bomb is one kind of nuclear weapon which is also known as Atom Bomb or Atomic Bomb. Hydrogen Bomb is one class of fusion bomb.
  • 63. 6 Nuclear Power Plant Nuclear reactor is used to produce heat and heat exchanger performs to convert water into steam by using the heat generated in nuclear reactor. This steam is fed into steam turbine and condensed in condenser. Now steam turbine is turn to run an electric generator or alternator which is coupled to steam turbine and thereby producing electric energy. SELECTION OF SITE 1. Availability of water: At the power plant site an ample quantity of water should be available for condenser cooling and made up water required for steam generation. Therefore the site should be nearer to a river, reservoir or sea. 2. Distance from load center: The plant should be located near the load center. This will minimize the power losses in transmission lines. 3. Distance from populated area: The power plant should be located far away From populated area to avoid the radioactive hazard. 4. Accessibility to site: The power plant should have rail and road transportation facilities. 5. Waste disposal: The wastes of a nuclear power plant are radioactive and there should be sufficient space near the plant site for the disposal of wastes.
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  • 65. 8 The working principle of nuclear power plant depends upon mainly four components. 1.Nuclear Reactor 2.Heat Exchanger 3.Steam Turbine 4.Alternator 1. Nuclear Reactor:- Nuclear reactor is the main component of nuclear power plant and nuclear fuel is subjected to nuclear fission. Nuclear fission is a process where a heavy nucleus is spitted into two or more smaller nuclei. . A heavy isotope generally uranium-235(U- 235) is used as a nuclear fuel in the nuclear reactor because it has the ability to control the chain reaction in the nuclear reactor. Nuclear fission is done by bombarding uranium nuclei with slow moving neutrons. The energy released by the fission of nuclei is called nuclear fission energy or nuclear energy. By the braking of uranium atom, tremendous amount of heat energy and radiation is formed in the reactor and the chain reaction is continuously running until it is controlled by a reactor control chain reaction. A large amount of fission neutrons are removed in this process, only small amount of fission uranium is used to generate the electrical power.
  • 66. The nuclear reactor is cylindrical type shape. Main body of reactor is enclosed by reactor core, reflector and thermal shielding. It prevent reactor wall from getting heated. It is also used to protect alpha ( α), bita (β) , gama (γ) rays and neutrons which are bounce back at the time of fission within the reactor. Mainly Nuclear reactor consists, some fuel rods of uranium, moderator and control rods. Fuel rods are made of the fission materials and released large number of energy at the time of bombarding with slow moving neutrons. Moderator consists full of graphite which is enclosed by the fuel rods. Moderator maintains the chain reaction by releasing the neutrons in a suitable manner before they mixed with the fissile materials. Control rods are made of boron-10 and cadmium or hafnium which is a highly neutron absorber and it is inserted into the nuclear reactor. When control rods are push down into the reactor core, it absorbs most of fission neutrons and power of the reactor is reduced. But when it is pulling out from the reactor, it releases the fission neutrons and power is increased. Real practice, this arrangement depends upon according to the requirement of load. A coolant, basically sodium metal is used to reduce the heat produce in the reactor and it carries the heat to the heat exchanger. 2. Heat Exchanger:-Coolant is used to raise the heat of the heat exchanger which is utilised in raising the steam. After that, it goes back to the reactor. 3. Steam Turbine:-Steam is coming from the heat exchanger to fed into the steam turbine through the valve. After that the steam is exhausted to the condenser. This condensed steam is fed to the heat exchanger through feed water pump. 4. Alternator:-Steam turbine is coupled to an alternator which converts mechanical energy to electrical energy. The output of alternator produces electrical energy to bus bars via major electrical apparatus like transformer, circuit breakers, isolators etc.
  • 67. BLOCK DIAGRAM OF NUCLEAR REACTOR
  • 68. Main Components of a Nuclear Reactor The Core: It contains all the fuel and generates the heat required for energy production. The Coolant: It passes through the core, absorbing the heat and transferring into turbines. The Turbine: Transfers energy into the mechanical form. The Cooling Tower: It eliminates the excess heat that is not converted or transferred. Moderator: Moderators are used for reducing the speed of fast neutrons released from the fission reaction and making them capable of sustaining a nuclear chain reaction. Usually, water, solid graphite, and heavy water are used as a moderator in nuclear reactors. Commonly-used moderators include regular (light) water (in 74.8% of the world’s reactors), solid graphite (20% of reactors), heavy water (5% of reactors). The Containment: The enveloping structure that separates the nuclear reactor from the surrounding environment. Neutron Poison: A neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section.
  • 71. 8-Feb-24 14 Fuel assembly (fuel bundle, fuel element)
  • 73. 8-Feb-24 16 Fuel Assembly Manufacturing (Fuel rod to fuel assembly) Materials Pellet: UO2, UO2 containing gadolinia Cladding: Zirconium alloy Guide thimble tube: Zirconium alloy Spacer: Zirconium alloy and inconel Top/Bottom nozzle: Stainless steel Type 14×14 15×15 17×17 10ft 12ft 12ft 12ft Section size (mm) 197 214 214
  • 74. 8-Feb-24 17 (a) Schematic of nuclear fuel rod assembly 2 (b) Simplified schematic of a TN-32
  • 76. ADVANTAGES OF NUCLEAR POWER PLANTS 1. Since the requirement of fuel is very small, so the cost of fuel transportation, storage etc. is small. 2. Nuclear power plant needs less space as compared to any other power station of the same size. Example: A 100 MW nuclear power station needs 38 - 40 acres of land whereas the same capacity coal based thermal power plant needs 120-130 acres of land. 3. This type of power plant is very economical to produce large electric power. 4. Nuclear power plant can be located near load centre because bulk amount of fuel (like water, coal) is not required. 5. Nuclear power is most economical to generate large capacities of power like 100 MVA or more. It produces huge amount of energy in every nuclear fission process. 6. Using a small amount of fuel, this plant produces large electrical energy. 7. This plant is very reliable in operation. 8. Since, the large number of nuclear fuel is available in this world. So, a nuclear power plant can generate electrical energy thousands of years continuously. 9. Nuclear Power Plant is very neat and clean as compared to a steam power plant. 10. The operating cost is low at this power plant but it is not affected for higher load demand. Nuclear power plant always operates a base load plant and load factor will not be less than 0.8.
  • 77. DISADVANTAGES OF NUCLEAR POWER PLANTS 1. Initial installation cost is very high as compared to the other power station. 2. Nuclear fuel is very much expensive and it is difficult to recover. 3. Capital cost is higher in respect of other power station. 4. Good technical knowledge is required to operate such type plant. So, salary bill and other maintenance cost will be higher to operate such of a plant. 5. There is a chance to spread of radioactive pollution from this type of plant. 6. Nuclear Reactor does not response efficiently with the fluctuating load demand. So, it is not suited for varying the load. 7. Cooling water requirement is twice than a coal based steam power plant.
  • 78. Types of Nuclear Reactors Most nuclear reactors in the United States and in Europe use fuel composed of natural uranium that is enriched with uranium 235, and ordinary water as a coolant. These reactors are known as light-water reactors. There are two basic types: the pressurized water reactor and the boiling water reactor. Pressurized Water Reactor is the most common type of nuclear reactor used for the generation of electricity. It uses ordinary water as both the moderator (to slow neutrons) and the coolant (to transfer heat). It has two separate cooling circuits: one which flows through the core of the reactor (the primary), and one which is used to drive the turbine (the secondary). Boiling Water Reactor is similar in some ways to the more common pressurized water reactor. This design also uses ordinary water as both the moderator (to slow neutrons) and the coolant (to transfer heat). In the boiling water reactor, however, a single cooling circuit is used and the cooling water boils inside the reactor. CANDU (CANadian Deuterium Uranium), is also used to generate power. Developed by Canada, this reactor uses only natural uranium as a fuel, but is moderated and cooled using heavy water. Since the complex enrichment process can be skipped, this type is very popular in developing nations. It is also known as a pressurized heavy water reactor.
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  • 82. 25 Nuclear Waste Nuclear waste refers to any radioactive material produced by medical, research, nuclear power facilities, or nuclear weapons programs. Nuclear waste can be grouped in two categories: low-level and high-level. Low-level wastes are slightly contaminated materials. A major source of low-level waste is mill-tailings from uranium ore processing. High-level wastes are comprised mainly of spent fuel from nuclear reactors. A small amount of high- level waste is very toxic.
  • 83. 26 The major concern about nuclear waste is its disposal. Nuclear waste must be stored until the radioactivity has dropped to safe levels without contaminating the surrounding environment. The disposal of low-level waste is done by some form of shallow land burial. The disposal of high-level waste is a more complex problem. The waste is highly toxic and must be stored for several centuries. Currently there are no long-term storage facilities for high-level waste in the United States.
  • 84. 27 Radioactive waste disposal The dispose of nuclear waste in the Euopean Union
  • 85. Dumping of Radioactive Materials at Sea
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  • 95. Introduction, definitions of connected load, maximum demand, demand factor, load factor, diversity factor, Load duration curve, number and size of generator units. Base load and peak load plants. Cost of electrical energy-fixed cost, running cost, Tariff on charge to customer.
  • 96. 4 Important Terms and Factors Connected load: It is the sum of continuous ratings of all the equipment's connected to supply system. Maximum demand : It is the greatest demand of load on the power station during a given period. Demand factor. It is the ratio of maximum demand on the power station to its connected load i.e., Demand factor =Maximum demand / Connected load The value of demand factor is usually less than 1. Average load: The average of loads occurring on the power station in a given period (day or month or year) is known as average load or average demand. Daily average load =No. of units (kWh) generated in a day/24 hours Monthly average load =No. of units (kWh) generated in a month/Number of hours in a month Yearly average load = No. of units (kWh) generated in a year/8760 hours
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  • 125. Residential Customers Chittoor, Anantapur, Kurnool, YSR Kadapa, SPSR Nellore districts - Southern Power Company. Srikakulam, Vizianagaram, Visakhapatnam, East Godavari, West Godavari districts - Eastern Power Company. Krishna, Guntur and Prakasam Districts -Central Power Company. https://aptransco.co.in
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  • 133. TARIFF The rate at which electrical energy is supplied to a consumer is known as tariff Objectives of tariff. Like other commodities, electrical energy is also sold at such a rate so that it not only returns the cost but also earns reasonable profit. Therefore, a tariff should include the following items : (i) Recovery of cost of producing electrical energy at the power station. (ii) Recovery of cost on the capital investment in transmission and distribution systems. (iii) Recovery of cost of operation and maintenance of supply of electrical energy e.g., metering equipment, billing etc. (iv) A suitable profit on the capital investment.
  • 134. Characteristics of a Tariff (i) Proper return : The tariff should be such that it ensures the proper return from each consumer. In other words, the total receipts from the consumers must be equal to the cost of producing and supplying electrical energy plus reasonable profit. (ii) Fairness : The tariff must be fair so that different types of consumers are satisfied with the rate of charge of electrical energy. Thus a big consumer should be charged at a lower rate than a small consumer. It is because increased energy consumption spreads the fixed charges over a greater number of units, thus reducing the overall cost of producing electrical energy. (iii) Simplicity : The tariff should be simple so that an ordinary consumer can easily understand it. A complicated tariff may cause an opposition from the public which is generally distrustful of supply companies. (iv) Reasonable profit : The profit element in the tariff should be reasonable. An electric supply company is a public utility company and generally enjoys the benefits of monopoly. (v) Attractive : The tariff should be attractive so that a large number of consumers are encouraged to use electrical energy. Efforts should be made to fix the tariff in such a way so that consumers can pay easily.
  • 135. Types of Tariff 1. Simple tariff. When there is a fixed rate per unit of energy consumed, it is called a simple tariff or uniform rate tariff. In this type of tariff, the price charged per unit is constant i.e., it does not vary with increase or decrease in number of units consumed. The consumption of electrical energy at the consumer’s terminals is recorded by means of an energy meter. This is the simplest of all tariffs and is readily understood by the consumers. Disadvantages (i) There is no discrimination between different types of consumers since every consumer has to pay equitably for the fixed charges. (ii) The cost per unit delivered is high. (iii) It does not encourage the use of electricity. 2. Flat rate tariff. When different types of consumers are charged at different uniform per unit rates, it is called a flat rate tariff. In this type of tariff, the consumers are grouped into different classes and each class of consumers is charged at a different uniform rate. The different classes of consumers are made taking into account their diversity and load factors. The advantage of such a tariff is that it is more fair to different types of consumers and is quite simple in calculations.
  • 136. Disadvantages (i) Since the flat rate tariff varies according to the way the supply is used, separate meters are required for lighting load, power load etc. This makes the application of such a tariff expensive and complicated. (ii) A particular class of consumers is charged at the same rate irrespective of the magnitude of energy consumed. However, a big consumer should be charged at a lower rate as in his case the fixed charges per unit are reduced. 3. Block rate tariff. When a given block of energy is charged at a specified rate and the succeeding blocks of energy are charged at progressively reduced rates, it is called a block rate tariff. In block rate tariff, the energy consumption is divided into blocks and the price per unit is fixed in each block. The price per unit in the first block is the highest** and it is progressively reduced for the succeeding blocks of energy. For example, the first 30 units may be charged at the rate of 60 paise per unit ; the next 25 units at the rate of 55 paise per unit and the remaining additional units may be charged at the rate of 30 paise per unit. The advantage of such a tariff is that the consumer gets an incentive to consume more electrical energy. This increases the load factor of the system and hence the cost of generation is reduced. However, its principal defect is that it lacks a measure of the consumer’s demand. This type of tariff is being used for majority of residential and small commercial consumers.
  • 137. 4. 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. Total charges = Rs (b × kW + c × kWh) where, b = charge per kW of maximum demand c = charge per kWh of energy consumed This type of tariff is mostly applicable to industrial consumers who have appreciable maximum demand. Advantages (i) It is easily understood by the consumers. (ii) It recovers the fixed charges which depend upon the maximum demand of the consumer but are independent of the units consumed. Disadvantages (i) The consumer has to pay the fixed charges irrespective of the fact whether the has consumed or not consumed the electrical energy. (ii) There is always error in assessing the maximum demand of the consumer
  • 138. 5. Maximum demand tariff. It is similar to two-part tariff with the only difference that the maximum demand is actually measured by installing maximum demand meter in the premises of the consumer. This removes the objection of two-part tariff where the maximum demand is assessed merely on the basis of the rateable value. This type of tariff is mostly applied to big consumers. However, it is not suitable for a small consumer (e.g., residential consumer) as a separate maximum demand meter is required. 6. Power factor tariff. The tariff in which power factor of the consumer’s load is taken into consideration is known as power factor tariff. In an a.c. system, power factor plays an important role. A low power factor increases the rating of station equipment and line losses.
  • 139. 7. Three-part tariff. When the total charge to be made from the consumer is split into three parts viz., fixed charge, semi-fixed charge and running charge, it is known as a three-part tariff. i.e., Total charge = Rs (a + b × kW + c × kWh) where a = fixed charge made during each billing period. It includes interest and depreciation on the cost of secondary distribution and labour cost of collecting revenues, b = charge per kW of maximum demand, c = charge per kWh of energy consumed.
  • 140. Cost of Electrical Energy The total cost of electrical energy generated can be divided into three parts, namely (i) Fixed cost (ii) Semi-fixed cost (iii) Running or operating cost (i) Fixed cost. It is the cost which is independent of maximum demand and units generated. The fixed cost is due to the annual cost of central organisation, interest on capital cost of land and salaries of high officials. The annual expenditure on the central organisation and salaries of high officials is fixed since it has to be met whether the plant has high or low maximum demand or it generates less or more units. Further, the capital investment on the land is fixed and hence the amount of interest is also fixed. (ii) Semi-fixed cost. It is the cost which depends upon maximum demand but is independent of units generated. The semi-fixed cost is directly proportional to the maximum demand on power station and is on account of annual interest and depreciation on capital investment of building and equipment, taxes, salaries of management and clerical staff. The maximum demand on the power station determines its size and cost of installation. The greater the maximum demand on a power station, the greater is its size and cost of installation. (iii) Running cost. It is the cost which depends only upon the number of units generated. The running cost is on account of annual cost of fuel, lubricating oil, maintenance, repairs and salaries of operating staff.
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  • 143. 51
  • 144. POWER SYSTEMS -I Dr.G.Nageswara Rao Professor Lakireddy Bali Reddy College of Engineering
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  • 149. Bus Bar The conducting material or a conductor used to collect power from the input terminals of an electrical system and distribute it to various output circuits is known as an electrical bus bar or bus system. It acts as a junction, where the incoming power and outgoing power meets. It is used to collect all the electrical power in one place. It is available in the form of rectangular strips, round tubes, round bars, and square bars made up of aluminium, copper, and brass.
  • 150. Distribution System The part of power system which distributes electric power for local use is known as distribution system.
  • 151. Distribution system generally consists of feeders, distributors and the servicemains. Fig showsthe single line diagram of a typical low tensiondistribution system. (i)Feeders. A feeder is a conductor which connects the sub-station (or localised generating station) to thearea wherepower isto be distributed. Generally, no tappings are takenfrom the feeder so that current in it remains the same throughout. The main consideration in the design of a feeder is the current carrying capacity. (ii)Distributor.Adistributor isa conductor from whichtappings are taken for supplytothe consumers. In Fig. AB, BC, CD and DA are the distributors. The current through a distributor is not constant because tappings are taken at various places along its length. While designing a distributor, voltage drop along its length is the main consideration since the statutory limit of voltage variations is ± 6% of rated value at the consumers’ terminals. (iii)Servicemains.Aservicemainsisgenerally a smallcable whichconnectsthe distributor to the consumers’ terminals.
  • 152. Classification of Distribution Systems (i) Nature of current. According to nature of current, distribution system may be classified as (a) d.c. distribution system (b) a.c. distribution system. Now-a-days, a.c. system is universally adopted for distribution of electric power as it is simpler and more economical than direct current method. (ii)Type of construction. According to type of construction, distribution system may be classified as (a) overhead system (b) underground system. The overhead systemis generally employed for distribution as it is 5 to 10 times cheaper than the equivalent underground system.Ingeneral, the underground systemisusedat places where overhead construction is impracticable or prohibited by the local laws. (iii)Schemeof connection. According to schemeof connection, the distribution systemmay be classified as (a) Radial system (b) ring main system (c) inter-connected system. Eachschemehas its own advantages and disadvantages.
  • 153. A.C. distribution calculations differ from those of d.c. distribution in the following respects : (i) In case of d.c. system, the voltage drop is due to resistance alone. However, in a.c. system, the voltage drops are due to the combined effects of resistance, inductance and capacitance. (ii) In a d.c. system, additions and subtractions of currents or voltages are done arithmetically but in case of a.c. system, these operations are done vectorially. (iii) In an a.c. system, power factor (p.f.) has to be taken into account. Loads tapped off form the distributor are generally at different power factors. There are two ways of referring power factor viz (a) It may be referred to supply or receiving end voltage which is regarded as the reference vector. (b) It may be referred to the voltage at the load point itself.
  • 154. A.C. Distribution The a.c. distribution system isclassified into (i) primary distribution systemand (ii) secondary distribution system Primary distribution system: It is that part of a.c. distribution system which operates at voltages somewhat higher than general utilisation and handles large blocks of electrical energy than the average low-voltage consumer uses. The voltage used for primary distribution depends upon the amount of power to be conveyed and the distance of the substation required to be fed. The most commonly used primary distribution voltages are 11 kV, 6·6 kV and 3·3 kV. Due to economic considerations, primary distribution is carried out by 3- phase, 3-wire system. Fig. shows a typical primary distribution system. Electric power from the generating station is transmitted at high voltage to the substation located in or near the city. At this substation, voltage is stepped down to 11 kV with the help of step-down transformer. Power is supplied to various substations for distribution or to big consumersat this voltage. This forms the high voltage distribution or primary distribution.
  • 155.
  • 156. Secondary distribution system. It is that part of a.c. distribution system which includes the range of voltages at which the ultimate consumer utilises the electrical energy delivered to him. The secondary distribution employs 400/230 V,3-phase, 4-wire system. Fig. shows a typical secondary distribution system. The primary distribution circuit delivers power to various substations, called distribution substations. The substations are situated near the consumers’ localities and contain stepdown transformers. At each distribution substation, the voltage is stepped down to 400V and power is delivered by 3-phase,4-wire a.c. system. The voltage between any two phases is 400 V and between any phase and neutral is 230V. The single phase domestic loads are connected between any one phase and the neutral, whereas 3-phase 400 V motor loads are connected across 3-phase lines directly.
  • 157.
  • 158. Overhead Versus Underground System (i) Public safety. The underground system is more safe than overhead system because all distribution wiring is placed underground and there are little chances of any hazard. (ii)Initial cost. The underground system is more expensive due to the high cost of trenching, conduits, cables, manholes and other special equipment. The initial cost of an underground system may be five to ten times than that of an overhead system. (iii)Flexibility. Theoverhead system is much more flexible than the underground system. In the latter case, manholes, duct lines etc., are permanently placed once installed and the load expansion can only be met by laying new lines. However, on an overhead system, poles, wires, transformers etc., can be easily shifted to meet the changes in load conditions. (iv) Faults. The chances of faults in underground system are very rare as the cables are laid underground and are generally provided with better insulation. (v)Appearance. The general appearance of an underground system is better as all the distribution lines are invisible. This factor is exerting considerable public pressure on electric supply companies to switch over to underground system. (vi)Fault location and repairs. In general, there are little chances of faults in an underground system. However, if a fault does occur, it is difficult to locate and repair on this system. On an overhead system, the conductors are visible and easily accessible so that fault locations and repairs can be easily made.
  • 159. (vii)Current carrying capacity and voltage drop. An overhead distribution conductor has a considerably higher current carrying capacity than an underground cable conductor of the same material and cross-section. On the other hand, underground cable conductor has much lower inductive reactance than that of an overhead conductor because of closer spacing of conductors. (viii)Useful life. The useful life of underground system is much longer than that of an overhead system. An overhead system may have a useful life of 25 years, whereas an underground systemmay have a useful life of more than 50 years. (ix)Maintenance cost. The maintenance cost of underground system is very low as compared with that of overhead system because of less chances of faults and service interruptions from wind, ice, lightning as well as from traffic hazards. (x)Interference with communication circuits. An overhead system causes electromagnetic interference with the telephone lines. The power line currents are superimposed on speech currents, resulting in the potential of the communication channel being raised to an undesirable level. However, there is no suchinterference with the underground system.
  • 160. Requirements of a Distribution System (i)Proper voltage. One important requirement of a distribution system is that voltage variations at consumer’s terminals should be as low as possible. The changes in voltage are generally caused due to the variation of load on the system. Low voltage causes loss of revenue, inefficient lighting and possible burning out of motors. High voltage causes lamps to burn out permanently and may cause failure of other appliances. Therefore, a good distribution system should ensure that the voltage variations at consumers terminals are within permissible limits. The statutory limit of voltage variations is ± 6% of the rated value at the consumer’s terminals. Thus, if the declared voltage is 230 V, then the highest voltage of the consumer should not exceed 244 V while the lowest voltage of the consumer should not be less than 216 V. (ii)Availability of power ondemand. Powermustbe available to theconsumersinany amount that theymay require from time to time. For example, motors may be started or shut down, lights may be turned on or off, without advance warning to the electric supply company. As electrical energy cannot be stored, therefore, the distribution system must be capable of supplying load demands of the consumers. This necessitates that operating staff must continuouslystudyload patterns to predict inadvancethosemajorload changesthat follow theknown schedules. (iii)Reliability. Modern industry is almost dependent on electric power for its operation. Homes and office buildings are lighted, heated, cooled and ventilated by electric power. This calls for reliable service. Unfortunately, electric power, like everything else that is man-made, can never be absolutely reliable. However, the reliability can be improved to a considerable extent by (a) interconnected system (b) reliable automatic control system (c) providing additional reserve facilities.
  • 161. Design Considerations in Distribution System Good voltage regulation of a distribution network is probably the most important factor responsible for delivering good service to the consumers. For this purpose, design of feeders and distributors requires careful consideration. (i)Feeders. A feeder is designed from the point of view of its current carrying capacity while the voltage drop consideration is relatively unimportant. It is because voltage drop in a feeder can be compensated by means of voltage regulating equipment at the substation. (ii)Distributors. A distributor is designed from the point of view of the voltage drop in it. It is because a distributor supplies power to the consumers and there is a statutory limit of voltage variations at the consumer’s terminals (± 6% of rated value). The size and length of the distributor should be such that voltage at the consumer’s terminals is within the permissible limits.
  • 162. Connection Schemes of Distribution S ystem All distribution of electrical energy is done by constant voltage system (i) Radial System. In this system, separate feeders radiate from a single substation and feed the distributors at one end only. Fig.1 shows a single line diagram of a radial system for d.c. distribution where a feeder OC supplies a distributor AB at point A. Obviously, the distributor is fed at one end only i.e., point A is this case. Fig.2 shows a single line diagram of radial system for a.c. distribution. The radial system is employed only when power is generated at low voltage and the substation is located at the centre of the load. This is the simplest distribution circuit and has the lowest initial cost. However, it suffers from the following drawbacks : (a) The end of the distributor nearest to the feeding point will be heavily loaded. (b)The consumers are dependent on a single feeder and single distributor. Therefore, any fault on the feeder or distributor cuts off supply to the consumers who are on the side of the fault away from the substation. (c)Theconsumersat thedistant endof thedistributor would be subjectedto seriousvoltage fluctuations when theload onthedistributor changes.Due to these limitations, this systemis used for short distancesonly.
  • 163.
  • 164. (ii) Ring main system. In this system, the primaries of distribution transformers form a loop. The loop circuit starts from the substation bus-bars, makes a loop through the area to be served, and returns to the substation. Fig. shows the single line diagram of ring main system for a.c. distribution where substation supplies to the closed feeder LMNOPQRS. The distributors are tapped from different points M, O and Q of the feeder through distribution transformers. Thering main systemhas the following advantages : (a) There are less voltage fluctuations at consumer’s terminals. (b)The systemis very reliable as each distributor is fed via two feeders. In the event of fault onanysectionof thefeeder, thecontinuity of supply is maintained.For example, suppose that fault occurs at any point Fof section SLMof the feeder. Then section SLMof the feeder can be isolated for repairs and at the same time continuity of supply is maintained to all the consumers via the feeder SRQPONM.
  • 165.
  • 166. (iii) Interconnected system. When the feeder ring is energised by two or more than two generating stations or substations, it is called inter-connected system. Fig. shows the single line diagram of interconnected system where the closed feeder ring ABCD is supplied by two substations S1 and S2 at points D and C respectively. Distributors are connected to points O, P , Q and Rof the feeder ring through distribution transformers. The interconnected system has the following advantages : (a) It increases the service reliability. (b) Any area fed from one generating station during peak load hours can be fed from the other generating station. Thisreducesreserve power capacityand increasesefficiency of the system.
  • 167.
  • 168. SELF- TEST 1. Fill in the blanks by inserting appropriate words/figures. (i) The underground systemhas ............. initial cost than the overhead system. (ii) A ring main systemof distribution is ............. reliable than the radial system. (iii) The distribution transformer links the primary and ............. distribution systems (iv) The most common systemfor secondary distribution is ............ 3-phase, ............. wire system. (v) The statutory limit for voltage variations at the consumer’s terminals is ............. % of rated value. (vi) The service mains connect the ............. and the ............. (vii) Theoverhead systemis ............. flexible than underground system. ANSWERSTO SELF-TEST (i) more (ii) more (iii) secondary (iv) 400/230 V,4 (v) = 6 (vi) distributor, consumer terminals (vii) more
  • 169. CHAPTER UNITEND QUESTIONS 1. What do youunderstand by distribution system? 2. Draw a single line diagram showing a typical distribution system. 3. Define and explain the terms : feeder, distributor and service mains. 4. Discuss the relative merits and demerits of underground and overhead systems. 5. Explain the following systemsof distribution : (i) Radial system ( i i ) R ing main system (iii) Interconnected system 6. Discuss briefly the design considerations in distribution system. 7.With a neat diagram, explain the complete a.c. system for distribution of electrical energy.
  • 170. Methods of Solving A.C. Distribution Problems (i)w.r.t. receiving or sending end voltage (ii)w.r.t. to load voltage itself.
  • 171. (i) Power factors referred to receiving end voltage
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  • 181.
  • 182. Example: A 3-phase, 400V distributor AB is loaded as shown in Fig.14.8. The 3-phase load at point C takes 5A per phase at a p.f. of 0·8 lagging. At point B, a 3-phase, 400 V induction motor is connected which has an output of 10 H.P. with an efficiency of 90% and p.f. 0·85 lagging. If voltage at point B is to be maintained at 400 V, what should be the voltage at point A ? The resistance and reactance of the line are 1Ω and 0·5Ωper phase per kilometre respectively Solution. It is convenient to consider one phase only. Fig shows the single line diagram of the distributor. Impedance of the distributor per phase per kilometre = (1 + j 0·5)
  • 183.
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  • 194. CHAPTER REVIEW TOPICS 1. How does a.c. distribution differ from d.c. distribution ? 2. What is the importance of load power factors in a.c. distribution ? 3. Describe briefly how will you solve a.c. distribution problems ? 4. Write short notes on the following : (i) Difference between d.c. and a.c. distribution (ii) Systems of a.c. distribution 5. Discuss about feeder, distributor and service main.
  • 195. 1. Fill in the blanks by inserting appropriate words/figures. (i) The most common system for secondary distribution is 400/..... V, 3-phase, ......... wire system. (ii) In a 3-phase, 4-wire a.c. system, if the loads are balanced, then current in the neutral wire is ......... (iii) Distribution transformer links the ............ and ........... systems. (iv) The 3-phase, 3-wire a.c. system of distribution is used for .......... loads. (v) For combined power and lighting load, .............. system is used. 2. Pick up the correct words/figures from brackets and fill in the blanks. (i) 3-phase, 4-wire a.c. system of distribution is used for .............. load. (balanced, unbalanced) (ii) In a.c. system, additions and subtractions of currents are done .............. (vectorially, arithmetically) (iii) The area of X-section of neutral is generally .............. that of any line conductor. (the same, half) (iv) For purely domestic loads, .............. a.c. system is employed for distribution
  • 196. ASSIGNMENT QUESTIONS i) What are the different distribution system adopted in power system? ii)What are the advantages of ring main distribution system? iii) What are the types of dc distribution system are there? Explain. iv) A single phase distributor 2 km.long supplies a load of 120 A at 0.8 p.f. lagging at its far end and a load of 80 A at 0.9 p.f. lagging at its mid point. Both power factor are referred to the voltage at the far end. The resistance and reactance per km. go and return are 0.05Ω and 0.1 Ω respectively. The voltage at the far end is maintained at 230 v, calculate i) Voltage at the sending end. ii) Phase angle between voltage at the two end. ANSWERS TO SELF-TEST 1. (i) 230, 4 (ii) zero (iii) primary, secondary (iv) balanced (v) 3-phase 4-wire. 2. (i) unbalanced (ii) vectorially (iii) half (iv) single phase 2-wire.
  • 197. Bus Bar Arrangements  During the distribution of electrical power to various output circuits, two or more wires are connected to a single wire.  The improper electrical connection gets opened and the insulation of the wire may get damaged due to heat generation in the wires.  This condition may lead to an open circuit, which is too dangerous for the distribution of power.  In such cases, to avoid open-circuit conditions, the multiple wires are connected properly using an electric bus system.  The bus bar is an electrical component used in electrical distribution systems to collect current from the input terminals of an electrical system and distributes it to various output circuits.  It is used as a junction between the input power and output power.  It distributes the power to various output circuits with more flexibility.
  • 198. Busbar Arrangements in Substations
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  • 201. Main and Transfer Busbar Arrangement
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  • 204. Selection and location of site for substation 1. It should be located nearer or at the center of the gravity of load. 2. It should provide safe and reliable arrangement 3. Maintenance of regulation clearances (deals with political issues) 4. Facilities for carrying out repairs and maintenance. 5. Immediate facilities against abnormalities such as possibility of explosion or fire etc. 6. Good design and construction 7. Provision of suitable switchgear and protective gear etc. 8. Land cost 9. Number of incoming and out
  • 205. 10. Transfer of power 11. Short-circuit levels 12. Types of substation (objective/function) 13. It should be away from airport and terrorist zones 14. Physical amenities should be available for engineers such as transportation, schools, houses, hospitals, communication services, availability of drinking water etc. 15.Drainage facility for rainwater 16.Should be easily operated and maintained 17.Should involve minimum capital cost 18.Provision for future expansion
  • 206. Selection and rating of S/s equipment • Surge arrester • CT • PT • Isolator • Circuit breaker • Transformer • Busbar • Shunt capacitor • Earth switch • Relays • Auxiliaries
  • 207.
  • 208.
  • 210. Underground Cable: Consists of one or more conductors covered with suitable insulation and surrounded by a protecting cover. Requirements : (i) The conductor used in cables should be tinned stranded copper or aluminium of high conductivity. Stranding is done so that conductor may become flexible and carry more current. (ii) The conductor size should be such that the cable carries the desired load current without overheating and causes voltage drop within permissible limits. (iii)The cable must have proper thickness of insulation in order to give high degree of safety and reliability at the voltage for which it is designed (iv) The cable must be provided with suitable mechanical protection so that it may withstand the rough use in laying it. (v) The materials used in the manufacture of cables should be such that there is complete chemical and physical stability throughout.
  • 211. 1. Better general appearance 2. Less liable to damage through storms or lighting 3. Low maintenance cost 4. Less chances of faults 5. Small voltage drops 1. Greater installation cost 2. Insulation problems at high voltages compared with equivalent overhead system Advantages & Disadvantages
  • 212. Requirements of the insulating materials used for cable are: 1. High insulation resistance. 2. High dielectric strength. 3. Good mechanical properties i.e., tenacity and elasticity. 4. It should not be affected by chemicals around it. 5. It should be non-hygroscopic because the dielectric strength of any material goes very much down with moisture content Vulcanized rubber insulated cables are used for wiring of houses, buildings and factories for low power work. There are two main groups of synthetic rubber material : (i) general purpose synthetics which have rubber-like properties (ii) special purpose synthetics which have better properties than the rubber e.g. fire resisting and oil resisting properties. The four main types are: (i) butyl rubber, (ii) silicon rubber, (iii) neoprene, and (iv) styrene rubber.
  • 213. Polyvinyl Chloride (PVC) PVC material has many grades. General Purpose Type: It is used both for sheathing and as an insulating material. In this compound monomeric plasticizers are used. It is to be noted that a V.R. insulated PVC sheathed cable is not good for use. Hard Grade PVC: These are manufactured with less amount of plasticizer as compared with general purpose type. Hard grade PVC are used for higher temperatures for short duration of time like in soldering and are better than the general purpose type. Hard grade cannot be used for low continuous temperatures. Heat Resisting PVC: Because of the use of monomeric plasticizer which volatilizes at temperature 80°C–100°C, general purpose type compounds become stiff. By using polymeric plasticizers it is possible to operate the cables continuously around 100°C. PVC compounds are normally costlier than the rubber compounds and the polymeric plasticized compounds are more expensive than the monomeric plasticized ones. PVC is inert to oxygen, oils, alkalis and acids and, therefore, if the environmental conditions are such that these things are present in the atmosphere, PVC is more useful than rubber.
  • 214. Impregnated Paper A suitable layer of the paper is lapped on the conductor depending upon the operating voltage. It is then dried by the combined application of heat and vacuum. This is carried out in a hermetically sealed steam heated chamber. The temperature is 120°–130°C before vacuum is created. Protective Coverings A cotton braid is applied over the insulated conductor and is then impregnated with a compound, which is water and weather proof. The rubber insulated cables are covered with a lead alloy sheath and is used for fixed installation inside or outside buildings in place of braided and compound finished cable in conduit. Polythene This material can be used for high frequency cables. This has been used to a limited extent for power cables also. The thermal dissipation properties are better than those of impregnated paper and the impulse strength compares favorably with an impregnated paper- insulated cable. The maximum operating temperature of this cable under short circuits is 100°C.
  • 216. 1. Cores or Conductors. A cable may have one or more than one core (conductor) depending upon the type of service for which it is intended. The conductors are made of tinned copper or aluminium and are usually stranded in order to provide flexibility to the cable. 2. Insulation. Each core or conductor is provided with a suitable thickness of insulation, the thickness of layer depending upon the voltage to be withstood by the cable. The commonly used materials for insulation are impregnated paper, varnished cambric or rubber mineral compound. 3. Metallic sheath. In order to protect the cable from moisture, gases or other damaging liquids(acids or alkalies) in the soil and atmosphere, a metallic sheath of lead or aluminium is provided over the insulation.
  • 217. 4. Bedding. Over the metallic sheath is applied a layer of bedding which consists of a fibrous material like jute or hessian tape. The purpose of bedding is to protect the metallic sheath against corrosion and from mechanical injury due to armouring. 5. Armouring. Over the bedding, armouring is provided which consists of one or two layers of galvanised steel wire or steel tape. Its purpose is to protect the cable from mechanical injury while laying it and during the course of handling. Armouring may not be done in the case of some cables. 6. Serving. In order to protect armouring from atmospheric conditions, a layer of fibrous material (like jute) similar to bedding is provided over the armouring.This is known as serving.
  • 218. Types of Cables Classified in two ways according to (i) Type of insulating material used in their manufacture (ii) Voltage for which they are manufactured. Latter method of classification is : (i) Low-tension (L.T.) cables — upto 1000 V (ii) High-tension (H.T.) cables — upto 11,000 V (iii) Super-tension (S.T.) cables — from 22 kV to 33 kV (iv) Extra high-tension (E.H.T.) cables — from 33 kV to 66 kV (v) Extra super voltage cables — beyond 132 kV A cable may have one or more than one core depending upon the type of service for which it is intended. It may be (i)single-core (ii) two-core (iii) three-core (iv) four-core etc. Fora 3-phase service, either 3-single-core cables or three-core cable can be used depending upon the operating voltage and load demand
  • 219. Cables for 3-Phase Service 1. Belted cables — upto 11 kV 2. Screened cables — from 22 kV to 66 kV 3. Pressure cables — beyond 66 kV
  • 222. Pressure cables Single core conductor channel oil filled cable Single core sheath channel oil filled cable Three core oil filled cable Three core pressure cable
  • 223.
  • 224. Unit-IV ELECTRICAL AND MECHANICAL DESIGN OF TRANSMISSIONLINES Transmission line sag calculation. Inductance and Capacitance calculations of transmission lines: line conductors, inductance and capacitance of single phase and three phase lines with symmetrical and unsymmetrical spacing, Composite conductors transposition, bundled conductors, and effect of earth on capacitance
  • 225. Structure Types and Voltages
  • 226.
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  • 228. • The difference in level between points of supports and the lowest point on the conductor is called sag.
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  • 231. Sag Template The sag template is used for allocating the position and height of the supports correctly on the profile. The sag template decided the limitations of vertical and wind load. It also limits the minimum clearance angle between the sag and the ground for safety purpose. The sag template is usually made up of transparent celluloid, perplex, or sometimes cardboard. The following curves are marked on it. 1. Hot Template Curve or Hot Curve 2. Ground Clearance Curve 3. Support Foot or Tower Curve 4. Cold Curve or Uplift Curve
  • 232.
  • 233. Hot Curve – The hot curve is obtained by plotting the sag at maximum temperature against span length. It shows where the supports must be located to maintain the prescribed ground clearance. Ground Clearance Curve – The clearance curve is below the hot curve. It is drawn parallel to the hot curve and at a vertical distance equal to the ground clearance as prescribed by the regulation for the given line. Support Foot Curve – This curve is drawn for locating the position of the supports for tower lines. It shows the height from the base of the standard support to the point of attachment of the lower conductor. For wood or concrete line, pole line this curve is not required to be drawn since they can be put in any convenient position. Cold Curve or Uplift Curve – Uplift curve is obtained by plotting the sag at a minimum temperature without wind price against span length. This curve is drawn to determine whether uplift of conductor occurs on any support. The uplift conductor may occur at low temperature when one support is much lower than either of the adjoining ones
  • 234. (i) supports are at equal levels (ii) supports are at unequal levels
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  • 242. P1: A transmission line has a span of 150 m between level supports. The conductor has a cross-sectional area of 2 cm2. The tension in the conductor is 2000 kg. If the specific gravity of the conductor material is 9·9 gm/cm3 and wind pressure is 1·5 kg/m length, calculate the sag. What is the vertical sag?
  • 243. P2: A transmission line has a span of 214 metres between level supports. The conductors have a cross-sectional area of 3·225 cm2. Calculate the factor of safety under the following conditions : Vertical sag = 2·35 m ; Wind pressure = 1·5 kg/m run Breaking stress = 2540 kg/cm2 ; Wt. of conductor = 1·125 kg/m run
  • 244.
  • 245. P3: The towers of height 30 m and 90 m respectively support a transmission line conductor at water crossing. The horizontal distance between the towers is 500 m. If the tension in the conductor is 1600 kg, find the minimum clearance of the conductor and water and clearance mid-way between the supports. Weight of conductor is 1·5 kg/m. Bases of the towers can be considered to be at water level.
  • 246. Fig. shows the conductor suspended between two supports A and B at different levels with O as the lowest point on the conductor. Here, l = 500 m ; w = 1·5 kg ; T = 1600 kg. Difference in levels between supports, h = 90 − 30 = 60 m. Let the lowest point O of the conductor be at a distance x1 from the support at lower level (i.e., support A) and at a distance x2 from the support at higher level (i.e., support B). Obviously, x1 + x2 = 500 m ………………...(i)
  • 247.
  • 248. P4: An overhead transmission line at a river crossing is supported from two towersat heights of 40 m and 90 m above water level, the horizontal distance between the towers being 400m. If the maximum allowable tension is 2000 kg, find the clearance between the conductor and water at a point mid-way between the towers. Weight of conductor is 1 kg/m.
  • 249.
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  • 251. STRINGING CHART Stringing chart is basically a graph between Sag, Tension with Temperature. As we want low Tension and minimum sag in our conductor but that is not possible as sag is inversely proportional to tension. It is because low sag means a tight wire and high tension whereas a low tension means a loose wire and increased sag. Therefore, we make compromise between two but if the case of temperature is considered and we draw graph then that graph is called Stringing chart.
  • 252. Electrical Design of Overhead Lines  An a.c. transmission line has resistance, inductance and capacitance uniformly distributed along its length.  These are known as constants or parameters of the line.  The performance of a transmission line depends to a considerable extent upon these constants.  For instance, these constants determine whether the efficiency and voltage regulation of the line will be good or poor.  Therefore, a sound concept of these constants is necessary in order to make the electrical design of a transmission line a technical success.
  • 253. Constants of a Transmission Line A transmission line has resistance, inductance and capacitance uniformly distributed along the whole length of the line (i) Resistance. It is the opposition of line conductors to current flow. (i) Inductance. When an alternating current flows through a conductor, a changing flux is set up which links the conductor. Due to these flux linkages, the conductor possesses inductance. (iii)Capacitance. As any two conductors of an overhead transmission line are separated by air which acts as an insulation, therefore, capacitance exists between any two overhead line conductors. The capacitance between the conductors is the charge per unit potential difference
  • 254. Skin Effect When a conductor is carrying steady direct current (d.c.), this current is uniformly distributed over the whole X-section of the conductor. However, an alternating current flowing through the conductor does not distribute uniformly, rather it has the tendency to concentrate near the surface of the conductor. This is known as skin effect. The tendency of alternating current to concentrate near the surface of a conductor is known as skin effect. Due to skin effect, the effective area of cross-section of the conductor through which current flows is reduced. Consequently, the resistance of the conductor is slightly increased when carrying an alternating current. The cause of skin effect can be easily explained. A solid conductor may be thought to be consisting of a large number of strands, each carrying a small part of the current. The *inductance of each strand will vary according to its position. Thus, the strands near the centre are surrounded by a greater magnetic flux and hence have larger inductance than that near the surface. The high reactance of inner strandscauses the alternating current to flow near the surface of conductor. This crowding of current near the conductor surface is the skin effect.
  • 255. The skin effect depends upon the following factors : (i) Nature of material (ii) Diameter of wire − increases with the diameter of wire. (iii) Frequency − increases with the increase in frequency. (iv) Shape of wire − less for stranded conductor than the solid conductor. It may be noted that skin effect is negligible when the supply frequency is low (< 50 Hz) and conductor diameter is small (< 1cm).
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  • 290. DEFINITION: The ionization of air surrounding the high voltage transmission lines causing the conductors to glow, producing a hissing noise with violet glow color , is called Corona Discharge or Corona Effect.
  • 291. Corona Effect in Transmission Lines: This phenomenon occurs when the electrostatic field across the transmission line conductors produces the condition of potential gradient. The air gets ionized when the potential gradient at the conductor surface reaches the value of 30kV/cm at normal pressure and temperature. In transmission lines, conductors are surrounded by the air. Air acts as a dielectric medium. When the voltage of air surrounding the conductor exceeds the value of 30kV/cm, the charging current starts to flow through the air, that is air has been ionized. The ionized air act as a virtual conductor, producing a hissing sound with a luminous violet glow.
  • 292. Advantages & Disadvantages of Corona Effect Advantages: The main advantages of corona effects are: 1. Due to corona across the conductor, the sheath of air surrounding the conductor becomes conductive which rises the conductor diameter virtually. This virtual increase in the conductor diameter reduces the maximum potential gradient or maximum electrostatic stress. Thus, the probability of flash-over is reduced. 2. Effects of transients produced by lightning or electrical surges are also reduced due to the corona effect. As, the charges induced on the line by surge or other causes, will be partially dissipated as a corona loss. In this way, corona protects the transmission lines by reducing the effect of transients that
  • 293. Disadvantages: 1. The glow appear across the conductor which shows the power loss occur on it. 2. The audio noise occurs because of the corona effect which causes the power loss on the conductor. 3. The vibration of conductor occurs because of corona effect. 4. The corona effect generates the ozone because of which the conductor becomes corrosive. 5. The corona effect produces the non-sinusoidal signal thus the non-sinusoidal voltage drops occur in the line. 6. The corona power loss reduces the efficency of the line. 7. The radio and TV interference occurs on the line because of corona effect.
  • 294. Factors Affecting Corona Discharge 1. Supply Voltage: As the electrical corona discharge mainly depends upon the electric field intensity produced by the applied system voltage. Therefore, if the applied voltage is high, the corona discharge will cause excessive corona loss in the transmission lines. On contrary, the corona is negligible in the low-voltage transmission lines, due to the inadequate amount of electric field required for the breakdown of air. 2.Conductor Surface: The corona effect depends upon the shape, material and conditions of the conductors. The rough and irregular surface i.e., unevenness of the surface, decreases the value of breakdown voltage. This decrease in breakdown voltage due to concentrated electric field at rough spots, give rise to more corona effect. The roughness of conductor is usually caused due to the deposition of dirt, dust and scratching. Raindrops, snow, fog and condensation accumulated on the conductor surface are also sources of surface irregularities that can increase corona.
  • 295. 3. Air Density Factor: Air density factor also determines the corona loss in transmission lines. The corona loss in inversely proportional to air density factor. Power loss is high due to corona in Transmission lines that are passing through a hilly area because in a hilly area the density of air is low. 4.Spacing between Conductors: If the distance between two conductors is very large as compared to the diameter of conductor, the corona effect may not happen. It is because the larger distance between conductors reduces the electro-static stress at the conductor surface, thus avoiding corona formation. 5.Atmosphere: In the stormy weather, the number of ions is more than normal weather. The decrease in the value of breakdown voltage is followed by the increase in the number of ions. As a result of it, corona occurs at much less voltage as compared to the breakdown voltage value in fair weather.
  • 296. How Corona Effect is Reduced: It has been observed that the intense corona effects are observed at a working voltage of 33 kV or above. On the sub-stations or bus-bars rated for 33 kV and higher voltages, highly ionized air may cause flash-over in the insulators or between the phases, causing considerable damage to the equipment, if careful designing is not made to reduce the corona effect. The corona effect can be reduced by the following methods: 1. By Increasing Conductor Size: The voltage at which corona occurs can be raised by increasing conductor size. Hence, the corona effect may be reduced. This is one of the reasons that ACSR conductors which have a larger cross-sectional area are used in transmission lines. 2. By Increasing Conductor Spacing: The corona effect can be eliminated by increasing the spacing between conductors, which raises the voltage at which corona occurs. However, increase in conductor spacing is limited due to the cost of supporting structure as bigger cross arms and supports to accompany the increase in conductor spacing, increases the cost of transmission system. 3. By Using Corona Ring: The intensity of electric field is high at the point where the conductor curvature is sharp. Therefore, corona discharge occurs first at the sharp points, edges, and corners. In order to, mitigate electric field, corona rings are employed at the terminals of very high voltage equipment.
  • 297. Corona rings are metallic rings of toroidal shaped, which are fixed at the end of bushings and insulator strings. This metallic ring distributes the charge across a wider area due to its smooth round shape which significantly reduces the potential gradient at the surface of the conductor below the critical disruptive value and thus preventing corona discharge. Important points:  Disruptive voltage is the minimum voltage at which the breakdown of air occurs and corona starts.  Visual critical voltage is the minimum voltage at which visible corona begins.
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  • 302. Insulators  An insulator gives support to the overhead line conductors on the poles to prevent the current flow toward earth. In the transmission lines, it plays an essential role in its operation.  The designing of an insulator can be done using different materials like rubber, wood, plastic, mica, etc.  The special materials used in the electrical system are glass, ceramic, PVC, steatite, polymer, etc.  But the most common material used in the insulator is porcelain and also special composition, steatite, glass materials are also used.