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- ELECTRIC POWER TRANSMISSION
AND DISTRIBUTION
S. Sivanagaraju
Associate Professor
Department of Electrical Engineering
JNTU College of Engineering
Anantapur, Andhra Pradesh
S. Satyanarayana
Professor and Head
Department of Electrical Engineering
Tenali Engineering College
Tenali, Andhra Pradesh
Delhi • Chennai • Chandigarh
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- Contents
Preface
Acknowledgement
1 Transmission and Distribution: An Introduction
1.1 Overview
1.2 Various Levels of Power Transmission
1.3 Conventional Sources of Electrical Energy
1.3.1 Hydro Power Stations
1.3.2 Thermal Power Stations
1.3.3 Nuclear Power Stations
1.3.4 Diesel Power Stations
1.4 Load Forecasting
1.4.1 Purpose of Load Forecasting
1.4.2 Classification of Load Forecasting
1.4.3 Forecasting Procedure
1.4.4 Load Characteristics
1.5 Load Modelling
1.5.1 Characteristics of Load Models
1.6 Star-Connected Loads
1.6.1 Constant Power Model
1.6.2 Constant Current Model
1.6.3 Constant Impedance Model
1.7 Deregulation
1.7.1 Need for Restructuring
1.7.2 Motivation for Restructuring the Power Industry
1.8 Distribution Automation
2 Transmission-Line Parameters
2.1 Introduction
2.2 Conductor Materials
2.3 Types of Conductors
2.4 Bundled Conductors
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- 2.5 Resistance
2.6 Current Distortion Effect
2.6.1 Skin Effect
2.6.2 Proximity Effect
2.6.3 Spirality Effect
2.7 Inductance
2.7.1 Inductance of a Conductor Due to Internal Flux
2.7.2 Inductance of a Conductor Due to External Flux
2.8 Inductance of a Single-Phase Two-Wire System
2.9 Flux Linkages With One Sub-Conductor of a Composite
Conductor
2.10 Inductance Of a Single-Phase System (With Composite
Conductors)
2.11 Inductance of Three-Phase Lines
2.11.1 Equivalent (Symmetrical) Spacing
2.11.2 Unsymmetrical Spacing (Untransposed)
2.11.3 Transposition of Overhead Lines
2.11.4 Unsymmetrical Spacing (Transposed)
2.12 Inductance of Three-Phase Double Circuit Line
2.12.1 Inductance of Three-Phase Double-Circuit Line with
Symmetrical Spacing (Hexagonal)
2.12.2 Inductance of a Three-Phase Transposed Double-Circuit Line
with Unsymmetrical Spacing
2.13 Capacitance
2.14 Potential Difference Between Two Points Due to a Charge
2.15 Capacitance of a Single-Phase Line (Two-Wire Line)
2.16 Potential Difference Between Two Conductors of a Group of
Charged Conductors
2.17 Capacitance of Three-Phase Lines
2.17.1 Equilateral Spacing
2.17.2 Capacitance of an Unsymmetrical Three-Phase System
(Transposed)
2.18 Capacitance of a Three-Phase Double-Circuit Line
2.18.1 Hexagonal Spacing
2.18.2 Flat Vertical Spacing (Unsymmetrical Spacing)
2.19 Effect of Earth on Transmission Line Capacitance
2.19.1 Capacitance of a Single Conductor
2.19.2 Capacitance of a Single-Phase Transmission Line
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- 2.19.3 Capacitance of Three-Phase Line
3 Performance of Short and Medium Transmission Lines
3.1 Introduction
3.2 Representation of Lines
3.3 Classification of Transmission Lines
3.4 Short Transmission Line
3.4.1 Effect of Power Factor On Regulation and Efficiency
3.5 Generalised Network Constants
3.6 A, B, C, D Constants for Short Transmission Lines
3.7 Medium Transmission Line
3.7.1 Load End Capacitance Method
3.7.2 Nominal-T Method
3.7.3 Nominal-π Method
4 Performance of Long Transmission Lines
4.1 Introduction
4.2 Rigorous Solution
4.3 Interpretation of the Long Line Equations
4.3.1 Propagation Constant
4.3.2 Wave Length and Velocity of Propagation
4.4 Evaluation of Transmission Line Constants
4.5 Regulation
4.6 Equivalent Circuit Representation of Long Lines
4.6.1 Representation of a Long Line by Equivalent- π Model
4.6.2 Representation of a Long Line by Equivalent-T Model
4.7 Tuned Transmission Lines
4.8 Characteristic Impedance
4.9 Surge Impedance Loading (Sil)
4.10 Ferranti Effect
4.11 Constant Voltage Transmission
4.12 Charging Current in Lines
4.12.1 Power Loss Due to Charging Current (or Open-Circuited Line)
4.13 Line Loadability
4.14 Power Flow Through a Transmission Line
4.15 Circle Diagram
4.15.1 Receiving-End Phasor Diagram
4.15.2 Receiving-End Power Circle Diagram
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- 4.15.3 Analytical Method for Receiving-End Power Circle Diagram
4.15.4 Sending-End Power Circle Diagram
4.15.5 Analytical Method for Sending-End Power Circle Diagram
5 Transmission Line Transients
5.1 Introduction
5.2 Types of System Transients
5.3 Travelling Waves on a Transmission Line
5.4 The Wave Equation
5.5 Evaluation of Surge Impedance
5.6 Importance of Surge Impedance
5.7 Travelling Wave
5.8 Evaluation of Velocity of Wave Propagation
5.9 Reflection and Refraction Coefficient (Line Terminated Through
a Resistance)
5.9.1 Line Open-Circuited at the Receiving End
5.9.2 Line Short-Circuited at the Receiving End
5.10 Line Connected to A Cable
5.11 Reflection and Refraction at A T-Junction
5.12 Reactance Termination
5.12.1 Line Terminated Through Capacitance
5.12.2 Line Terminated Through Inductance
5.13 Bewley’s Lattice Diagram
5.14 Attenuation of Travelling Waves
6 Corona
6.1 Introduction
6.2 Theory of Corona Formation (Corona Discharge)
6.3 Electric Stress
6.4 Critical Disruptive Voltage
6.5 Visual Critical Voltage
6.6 Power Loss Due to Corona
6.7 Factors Affecting Corona Loss
6.7.1 Electrical Factors
6.7.2 Atmospheric Factors
6.7.3 Factors Related to the Conductors
6.8 Methods For Reducing Corona Loss
6.9 Advantages and Disadvantages of Corona
6.10 Effect of Corona on Line Design
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- 6.11 Radio Interference
6.12 Audio Noise
6.13 Interference with Communication Lines
6.13.1 Electromagnetic Effect
6.13.2 Electrostatic Effect
6.14 Corona Phenomena in HVDC Lines
7 Mechanical Design of Transmission Line
7.1 Introduction
7.2 Factors Affecting Mechanical Design
7.3 Line Supports
7.3.1 Wooden Poles
7.3.2 Tubular Steel Poles
7.3.3 RCC Poles
7.3.4 Latticed Steel Towers
7.4 Sag
7.4.1 Calculation of Sag at Equal Supports
7.4.2 Effect of Ice Covering and Wind Pressure
7.4.3 Safety Factor
7.4.4 Calculation of Sag at Different Level Supports
7.5 Stringing Chart
7.6 Effects and Prevention of Vibrations (Vibrations and Dampers)
7.7 Sag Template
7.8 Conductor Spacing and Ground Clearance
8 Overhead Line Insulators
8.1 Introduction
8.2 Insulator Materials
8.3 Types of Insulators
8.3.1 Pin Type Insulators
8.3.2 Suspension Type Insulator
8.3.3 Strain Insulator
8.3.4 Shackle Type Insulator
8.4 Potential Distribution Over a String of Suspension Insulators
8.4.1 Mathematical Expression for Voltage Distribution
8.5 String Efficiency
8.6 Methods of Improving String Efficiency
8.6.1 Selection of m
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- 8.6.2 Grading of Units
8.6.3 Guard Ring or Static Shielding
8.7 Arcing Horn
8.8 Testing of Insulators
8.8.1 Flashover Tests
8.8.2 Performance Test
8.8.3 Routine Tests
8.9 Causes of Failure of Insulators
9 Underground Cables
9.1 Introduction
9.2 General Construction of a Cable
9.3 Types of Cables
9.3.1 Low Tension Cables
9.3.2 High Tension Cables
9.3.3 Super Tension Cables
9.3.4 Extra High Tension Cables
9.4 Advantages and Disadvantages of Underground Cables Over
Overhead Lines
9.5 Properties of Insulating Materials for Cables
9.5.1 Insulating Materials
9.6 Insulation Resistance of Cables
9.7 Capacitance of a Single-Core Cable
9.8 Dielectric Stress in a Cable
9.9 Economical Core Diameter
9.10 Grading of Cables
9.10.1 Capacitance Grading
9.10.2 Intersheath Grading
9.10.3 Practical Aspects of Cable Grading
9.11 Power Factor in Cables (Dielectric Power Factor)
9.12 Capacitance of a Three-Core Cable
9.12.1 Measurement of Cc and Cs
9.13 Heating of Cables
9.13.1 Generation of Heat Within the Cables
9.14 Thermal Characteristics
9.14.1 Current Capacity
9.15 Testing of Cables
9.15.1 Acceptance Tests at Works
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- 9.15.2 Sample Tests at Working
9.15.3 Performance Tests
9.15.4 Tests On Oil-Filled and Gas-Filled Cables
9.15.5 Tests When Installed
9.15.6 Tests On Pressurized Cables
9.16 Laying of Cables
9.16.1 Direct System
9.16.2 Draw-In System
9.16.3 Solid Systems
9.17 Cable Faults
9.18 Determination of Maximum Current Carrying Capacity of Cables
10 Power Factor Improvement
10.1 Introduction
10.2 Power Factor
10.2.1 Causes of Low Power Factor
10.2.2 Effects or Disadvantages of Low Power Factor
10.3 Advantages of Power Factor Improvement
10.4 Methods of Improving Power Factor
10.4.1 Static Capacitor
10.4.2 Synchronous Condenser
10.4.3 Phase Advancers
10.5 Most Economical Power Factor When the Kilowatt Demand is
Constant
10.6 Most Economical Power Factor When the kVA Maximum
Demand is Constant
11 Voltage Control
11.1 Introduction
11.2 Necessity of Voltage Control
11.3 Generation and Absorption of Reactive Power
11.4 Location of Voltage Control Equipment
11.5 Methods of Voltage Control
11.5.1 Excitation Control
11.5.2 Shunt Capacitors and Reactors
11.5.3 Series Capacitors
11.5.4 Tap Changing Transformers
11.5.5 Booster Transformers
11.5.6 Synchronous Condensers
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- 11.6 Rating of Synchronous Phase Modifier
12 Electric Power Supply Systems
12.1 Introduction
12.2 Comparison of Conductor Efficiencies for Various Systems
12.2.1 Overhead Lines
12.2.2 Cable Systems
12.3 Choice of System Frequency
12.4 Choice of System Voltage
12.5 Advantages of High-Voltage Transmission
12.6 Effect of Supply Voltage
12.7 Economic Size of Conductor (Kelvin’s Law)
12.7.1 Modification of Kelvin’s Law
12.7.2 Practical Limitations to the Application of Kelvin’s Law
13 Substations
13.1 Introduction
13.2 Factors Governing the Selection of Site
13.3 Classification of Substation
13.3.1 According to Service
13.3.2 According to Design
13.4 Merits and Demerits of Indoor and Outdoor Substations
13.5 Substation Equipment
13.6 Types of Bus Bar Arrangements
13.6.1 Single Bus Bar
13.6.2 Single-Bus Bar System with Sectionalization
13.6.3 Double Bus Bar with Single Breaker
13.6.4 Double Bus Bar with Two Circuit Breakers
13.6.5 Breakers and a Half with Two Main Buses
13.6.6 Main and Transfer Bus Bar
13.6.7 Double Bus Bar with Bypass Isolator
13.6.8 Ring Bus
13.7 Pole and Plinth-Mounted Transformer Substations
13.8 Optimal Substation Location
13.8.1 Perpendicular Bisector Rule
13.9 Basic Terms of Earthing
13.10 Grounding or Neutral Earthing
13.11 Earthing of Substations
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- 13.12 Methods of Neutral Grounding
13.12.1 Solid Grounding or Effective Grounding
13.12.2 Resistance Grounding
13.12.3 Reactance Grounding
13.12.4 Peterson-Coil Grounding
13.12.5 Grounding Transformer
13.13 Grounding Grid
14 Distribution Systems
14.1 Introduction
14.2 Primary and Secondary Distribution
14.2.1 Primary Distribution
14.2.2 Secondary Distribution
14.3 Design Considerations in a Distribution System
14.4 Distribution System Losses
14.4.1 Factors Effecting Distribution-System Losses
14.4.2 Methods for the Reduction of Line Losses
14.5 Classification of Distribution System
14.5.1 Type of Current
14.5.2 Type of Construction
14.5.3 Type of Service
14.5.4 Number of Wires
14.5.5 Scheme of Connection
14.6 Radial Distribution System
14.7 Ring or Loop Distribution System
14.8 Interconnected Distribution System
14.9 Dc Distribution
14.9.1 Distributor Fed at One End with Concentrated Loads
14.9.2 Distributor Fed at Both Ends with Concentrated Loads
14.9.3 Uniformly Loaded Distributor Fed at One End
14.9.4 Uniformly Distributed Load Fed at Both Ends at the Same
Voltage
14.9.5 Uniformly Distributed Load Fed at Both Ends at Different
Voltages
14.10 Ring Distribution
14.10.1 Advantages of Using Interconnector
14.11 Stepped Distributor
14.12 Ac Distribution
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- 14.12.1 Power Factor Referred to the Receiving-End
14.12.2 Power Factor Referred to Respective Load Voltages
14.13 Ac Three-Phase Distribution
15 EHV and HVDC Transmission Lines
15.1 Introduction
15.2 Need of EHV Transmission Lines
15.3 Advantages and Disadvantages of EHV Lines
15.4 Methods of Increasing Transmission Capability of EHV Lines
15.5 HVDC Transmission System
15.6 Comparison Between AC and DC Transmission Systems
15.6.1 Economic Advantages
15.6.2 Technical Advantages
15.7 Advantages and Disadvantages of HVDC Systems
15.8 HVDC Transmission System
15.8.1 Monopolar Link
15.8.2 Bipolar Link
15.8.3 Homopolar Link
15.9 Rectification
15.10 Three-Phase Bridge Converter
15.11 Inversion
15.12 Components of HVDC Transmission System
15.13 Harmonic Filters
15.14 Application of HVDC Transmission System
16 Flexible AC Transmission Systems
16.1 Introduction
16.2 Facts
16.3 Facts Controllers
16.3.1 Shunt-Connected Controllers
16.3.2 Series-Connected Controllers
16.3.3 Combined Shunt and Series-Connected Controllers
16.4 Control of Power Systems
16.4.1 FACTS Devices
16.4.2 Benefits of Control of Power Systems
16.4.3 FACTS Technology: Opportunities
16.5 Basic Relationship For Power-Flow Control
16.5.1 Shunt Compensator
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- 16.5.2 Thyristor-Controlled Reactor (TCR)
16.5.3 Thyristor-Switched Capacitor (TSC)
16.5.4 Series Compensator
16.5.5 Unified Power-Flow Controller (UPFC)
16.6 “Facts” for Minimizing Grid Investments
16.7 Voltage Stability
16.7.1 Voltage Stability – What is it?
16.7.2 Derivation of Voltage Stability Index
Appendix 1: Datasheets
Appendix 2: Answers to Problems
Appendix 3: Answers to Odd Questions
Appendix 4: Solutions Using MATLAB Programs
Glossary
Bibliography
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-
TO MY PARENTS
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- Preface
Electric Power Transmission and Distribution has been
designed for undergraduate courses in electrical and
electronics engineering in Indian universities. Tailored
to provide an elementary knowledge of power systems, a
foundation in electric circuits and engineering is a pre-
requisite for starting this course. The organization of the
topics and the pace at which they unfold have been
planned to enable students to proceed from the basic
concepts to the difficult ones with ease. The text can
ideally be taught at the sixth or seventh semester, and
can also be used as a reference book by BE, BTech and
AMIE students.
The contents of this book have been developed with
emphasis on clarity, with equal stress on the basic
concepts as well as advanced ideas, in detail over sixteen
chapters.
Chapter 1 introduces the conventional sources of
electrical energy, and explains about the load forecasting
and its various aspects, the various levels of power
transmission, and the need as well as the motivation for
restructuring the power industry.
Chapter 2 explains the four transmission line
parameters, namely, resistance and inductance in a
series combination and a shunt combination of
capacitance and conductance. Materials used for the
manufacture of conductors and the various types of
conductors are explained in detail. It is explained in
detail about the current distortion effect and the effect of
earth on transmission line capacitance to give a lucid
understanding of the constituent elements of the
transmission system.
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- Chapters 3 and 4 are devoted to the construction and
performance analysis of overhead transmission lines.
Classification of transmission lines, network constraints,
long line equations, regulation concepts, surge
impedance, Ferranti effect, and line loadability are dealt
comprehensively. Power circle diagrams used to
calculate the maximum power-transfer capacity, and
synchronous phase-modifier capacity are also discussed.
Chapter 5 describes the power system transients due
to surges. The travelling wave equation used to describe
the phenomena of incident and reflected waves, the
evaluation of surge impedance, its importance and the
analysis of the travelling wave under different
conditions, such as with open-circuited and short-
circuited end lines, are highlighted in this chapter.
Chapter 6 is devoted to the corona phenomenon. The
formation and effects of the corona, factors affecting
corona loss, and corona interference with
communication lines are examined.
Chapter 7 describes the mechanical design of overhead
lines. Different line supports, sag calculations with
reference to both equal and unequal supports, effect of
ice and wind-loading on sag calculations, string charts,
vibrations and dampers, and sag templates are all
covered in this chapter. This chapter gives an idea of the
different types of line supports and their design for
overhead lines.
Chapter 8 is devoted to the description of overhead
insulators. Insulating materials, types of insulators,
stringing efficiency and methods for its improvement,
arcing horns, and the various methods for testing
insulators are discussed. This chapter also gives a
selection of the ideal type of insulator for various given
voltages.
Chapter 9 gives the general construction of
underground cables, elaborates upon their various types,
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- and explains their properties, advantages and
disadvantages. The power factor, heating, testing and
laying of cables are also discussed.
Chapter 10 is concerned with power factor
improvement. The causes and demerits of lower power
factor are followed by a discussion of the methods for
their improvement. The most economical power factor is
also expounded suitably.
Chapter 11 discusses the necessity of voltage control,
the various sources of reactive power generation and
absorption of reactive power, the methods of voltage
control and rating of synchronous phase modifier. These
concepts help to choose the rating of the capacitors for
power factor improvement as well as for voltage control.
Chapter 12 discusses the economics of power-system
designing. The choice of system frequency, system
voltage and the advantage of high voltage transmission
are elucidated here. The calculation of economical size of
conductors using Kelvin’s law, and the limitations of the
applications of Kelvin’s law are illustrated to give the
student a holistic understanding of the methods of
calculating the ideal size of conductors for different load
levels.
Chapter 13 discusses the different types of substations,
the substation equipment and types of bus-bar
arrangements. Various types of neutral grounding
systems are also discussed in this chapter. Based on the
requirement and available budget, selection of bus-bar
arrangements and suitable earthing methods, are
described.
Chapter 14 gives a description of the different types of
distribution systems, distribution-system losses, and
their classification. We also look at voltage drop
calculations of various types of DC and AC distributors in
this chapter, to gain an insight into the designing of a
suitable type of distributor for a given system.
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- Chapter 15 is designed to give an idea of the EHV and
HVDC transmission systems including the need,
advantages and disadvantages of EHV and HVDC
transmission systems. The different types of HVDC
systems, three-phase bridge converters, components of
HVDC transmission systems, and harmonic filters form a
part of this chapter.
Chapter 16, the concluding chapter of the book,
introduces the flexible AC transmission systems
technology and provides basic definitions of the various
types of FACTS controllers, control of power systems and
an overview of FACTS controller circuits. It also includes
a brief discussion on voltage stability.
In-text Learning Aids
Each chapter opens with chapter objectives which are
listed and an introduction. Worked-out solutions follow
each section and serve to reinforce what the student has
learnt. ‘Test yourself’ questions, designed to act as rapid
review tests, are placed at strategic points within the
chapters. Each chapter concludes with ‘chapter at a
glance’, ‘multiple choice questions’ with answers, ‘review
questions’ and practice problems, and are aimed to
augment the student’s understanding of the topics
discussed.
An appendix containing datasheets, MATLAB
programs as illustrative resolution of complex problems,
and answers to odd questions added as a concluding
section to the book, serve to further clarify and sum up
the discussed concepts, enabling the student to solve
problems with ease.
We appreciate the efforts of all those who provided
inputs that helped us to develop and improve the text.
We are committed to improving the text further in its
future editions, and encourage you to contact us with
your comments and suggestions.
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- S. SIVANAGARAJU
S.SATYANARAYANA
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- Acknowledgements
We would like to express our gratitude towards the
people mentioned below, who have helped us in many
ways to shape this book:
To our college administration for providing us a conducive
atmosphere to carry out this work.
To our department colleagues, especially, whose valuable inputs with
regard to the content and discussions pertaining to various topics,
immensely helped us to maintain the quality of this book.
For the services rendered by our students, especially D. Ravi Teja, for
the successful outcome of this book.
To all those who have, either directly or indirectly, helped us in
translating our effort into reality.
S. SIVANAGARAJU
S. SATYANARAYANA
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