Overhead Electric Power Lines: Theory and practice
2: Department of Electrical Engineering, Jadavpur University, India
In order to fulfill the tremendous worldwide demand for electrification, power line professionals will need to adopt rapid, reliable and sustainable solutions. For example, in a fast-developing country like India, which had the largest population without electricity in 2014 and 1.34 billion inhabitants in 2017, the demand for electrification is immense. In recent years, a new program facilitated 0.73 million new household connections per month and almost 19000 villages per year. Wide-spread experience in geographical, geological, social and economic diversity leaves no doubt that overhead power lines (OHL) are the only way to provide electricity to communities where underground lines are technically unfeasible or too expensive. This book presents the technology and recent research into OHL in a concise and systematic way. After brief introductory sections, chapters cover line support, foundation and mechanical sag, corona discharge, overhead line insulators and conductors, earthing and earth wire, lightning and surge protection, insulation and coordination, route selection, commissioning, operation and maintenance. This book is a must-read for researchers and experts involved with utilities and particularly for anyone associated with the installation, electrification, operation and maintenance of overhead lines in transmission and distribution networks.
Inspec keywords: insulators; lightning protection; earthing; surge protection; insulation co-ordination; transmission line theory; power system management; power system planning; overhead line mechanical characteristics; overhead line conductors
Other keywords: overhead line insulator; earth wire; mechanical sag; maintenance; line support; insulation coordination; transmission line fundamentals; earthing; commissioning; conductor; overhead electric power lines; corona; surge protection; lightning protection; route selection; operation
Subjects: Power line supports, insulators and connectors; Power system protection; Power system management, operation and economics; Insulation and insulating coatings; Overhead power lines; Power system planning and layout; Network and transmission line calculations; General electrical engineering topics
- Book DOI: 10.1049/PBPO193E
- Chapter DOI: 10.1049/PBPO193E
- ISBN: 9781839533112
- e-ISBN: 9781839533129
- Page count: 361
- Format: PDF
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Front Matter
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1 Introduction
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With the advancement of technology, worldwide power demand is increasing. Power consumption has become the measure of technological progress of a country. With this, power system network has undergone various changes in terms of different technical parameters. Diversity has entered in generation, transmission and distribution. Transmission and distribution are still based on overhead lines mostly in AC form and partly in DC form. Power engineers are to cope with this ever changing complexity of the overhead lines. Changes in the overhead line technology are rapid and gradual aiming for long-term sustainability. This book attempts to present all aspects of overhead electric power lines to fulfil the need of advanced students and professionals working in this field. It focuses on fundamentals, line support, corona, line insulators, conductors, earthing, lightning and surge protection, insulation coordination, planning, commissioning and management.
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2 Transmission line fundamentals
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This chapter describes fundamentals of electric power lines. Different line parameters are presented. Resistance, inductance and capacitance have been derived. Skin effect and proximity effect have been described. Based on line parameters, classification of power line has been done followed by modelling of different parts of power system. A two-port network model of transmission lines has been presented. Transmission parameters, characteristics impedance, image impedance, surge impedance loading, etc. have been presented. Useful parameters of wave propagation have been shown. Comparison of AC overhead lines with DC lines and underground lines has been made. Modelling of synchronous generator and transformer has also been presented. Voltage regulation has been discussed with respect to transmission system. Different useful voltage compensation methods have been described.
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3 Line support, foundation and mechanical sag
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This chapter presents different aspects of line support, foundation and mechanical sag of transmission line. It starts with introduction and then describes the design aspects with respect to distribution system and then with respect to transmission system. Components of overhead lines have been described. Different types of line supports have been presented. Different feature of wooden pole, steel pole, concrete pole and lattice tower have been presented. Foundation methods have been presented for different line support. Classification of foundation has been made. Different types of monoblock and compact foundations have been presented. Tests for supports have been highlighted. Mechanical sag with tension for overhead lines has been presented. Effects of ice and wind on sag have been described.
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4 Corona
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This chapter deals with corona associated with high voltage (HV) or extra high voltage (EHV) overhead lines. Corona is defined, and relationship with electric field is described. Critical corona is explained. Power loss occurred due to corona in transmission system has been presented. Frequency and voltage dependencies of coronal loss have been explained. Other factors related to corona are mentioned. Practices followed for reducing corona loss have been presented.
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5 Overhead line insulator
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This chapter describes different aspects of overhead insulators. Properties of line insulators have been described. Materials used for manufacturing overhead line (OHL) insulators have been presented. Different types of insulators used in OHL application have been discussed. Requirement of string has been mentioned. Voltage distribution across different discs of string has been shown, and string efficiency has been derived. Design features of insulators for overhead application have been presented. Selection factors for insulator have been mentioned for transmission and distribution line applications. Fittings of insulator in OHLs have been described. Failure and testing of OHL insulator have been discussed. Different useful standards for this aspect have been referred.
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6 Conductor
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This chapter deals with conductor used in overhead electric lines. It describes electrical, thermomechanical and other properties of line conductors. The conductors are classified followed by their description. Stranded and bundled conductors are described. Materials used in conductor have been presented. Conductors of the same material and composite conductor have been described. Different aspects of hollow conductor, conductor with optical fibre cable, phase and earth conductors have been presented. Different types of jumper have been mentioned. Covered conductors or overhead cables have been included. Conductor fittings and installation care have been described. Common stringing methods followed by different electrical properties have been discussed. Ground clearance, stringing chart, conductor vibration, damper, spacer, etc. have also been presented.
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7 Earthing and earth wire
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This chapter deals with earthing and earth wire used in overhead electric lines. Effect of electric current on human body has been mentioned. Resistance properties of soil have been described. Measurement techniques for earth resistance have been presented. Different earthing procedures and materials suitable for earthing have been presented. Limitation of ungrounded system and advantages of earthed system have been presented. Different types of system grounding have been presented. Fault current for different earthing systems have been described. Harmonic suppression system (HSS) and earthing transformer have been described. Common grounding practices have been mentioned. Different properties of earth wire and its selection guidelines have been presented. Design features of earth wires have been included. Practices for tower earthing have been described. Earthing for personal safety has also been described. Pipe earthing, counterpoise earthing, grounding in pole support, earthing of guard wire, etc. have been described.
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8 Lightning and surge protection
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Lightning protection practices followed in overhead lines. Overhead lines are exposed to open air and therefore, they are subject to over-voltages due to both external and internal causes. Lightning is the main cause of the occurrence of overvoltage in overhead lines. Different types of transients are experienced by overhead lines. Transients faced by lines may be divided into two following broad categories: 1. DC transients 2. AC transients. Lightning is unidirectional voltage waveform of very high peak. Both direct and indirect lightning strokes have severe adverse effect on transmission lines. It can cause breaking of insulators, lines and other members hampering the service of the electric power system. Thyrite-type lightning arrester is used for diverting very high voltages. Multiple numbers of disc separated by gap are placed in stack and enclosed in porcelain container. Gap reduces flow of current at normal condition. Surge absorber absorbs energy from travelling waves and reduces their high ampli-tude. The capacitor-based voltage transformer is used for measurement of high voltage. Dissipation factor is the measure of dielectric strength of insulating medium. Dissipation factor is measured using bridge circuit. Schering bridge is commonly used for measurement of dissipation factor. Lightning has been protected by earth wires while other overvoltages are protected by surge arresters, surge absorber and other protective devices.
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9 Insulation coordination
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This chapter deals with coordination of insulation levels for overhead lines. As overhead lines operate at different voltage levels and connected with other parts of power system network, knowledge of power frequency nominal voltage levels has been presented. Then lightning of other transient over voltages has been presented. Concept of basic insulation levels has been provided mentioning its necessity. Then insulation coordination factors have been mentioned. Coordination with respect to insulation level of apparatus has been presented. Coordination with arresters has been described. Insulation coordination between overhead lines and connected substations has been discussed. At the end of the chapter, some useful standards have been listed for further study.
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10 Route selection, commissioning, operation and maintenance
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This chapter deals with route selection, commissioning, operation and maintenance of overhead power transmission lines. It starts with route selection followed by general considerations of understanding of purpose, resource and objective, covered area, geographical and geological diversity, political map, climatic statistics, cost study, etc. Different aspects of establishing new lines, alternate lines, lines conversion have been discussed. Linking with underground lines has been discussed. Different aspects of planning and construction like survey, planning, design, foundation, installation, erection, commissioning, responsibility and issues, check-up, test, energization, etc. have been discussed. Supervision and quality assurance in commissioning and commencement of operation have been discussed thoroughly. Operation and maintenance, post-commissioning planning and management, operation management, maintenance management, asset management, risk management have been discussed followed by uprating, upgrading and extension of line.
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Back Matter
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