Overhead Power Lines

Transcription

1 F. Kiessling P. Nefzger J.F. Nolasco U. Kaintzyk Overhead Power Lines Planning, Design, Construction With 402 Figures and 193 Tables Springer

2 Contents 1 Overall planning Symbols Development stages of a transmission project Transmission planning Objective Planning stages Planning aspects regarding transmission lines Planning methods Data acquisition and preparation Formulation and preselection of alternatives Electrical studies Economic studies and final evaluation Planning criteria General Criteria for steady-state conditions Criteria for temporary and transient conditions Evolution and selection of voltage levels Evolution of transmission voltages Introduction of transmission voltages Conductor selection Selection of line configuration Direct current transmission Aspects of DC transmission components Economic comparison of DC and AC lines Technical comparison of AC and DC transmission Practical use of DC transmission Transmission with higher order phase lines Options Properties of multiple-phase systems Present experience Investments Licences and permit procedures Underground transmission versus overhead lines Application and planning aspects Environmental constraints Technical limitations Comparative investments Perspectives Results of overall planning References 22 2 Electric requirements and design Symbols Overhead lines as components of electric systems Surge impedance and surge impedance load (natural power) Stability Voltage regulation and maximum permissible losses 30

3 XII Contents Capability of a line Reliability and availability Reactive power compensation Power transmitted versus right-of-way width Current-related phenomena Normal and emergency conditions Ohmic losses Short circuit condition Voltage and current-related phenomena Introduction Electrical and magnetic fields Effects on humans and animals Effects on electronic devices Corona phenomena and related effects General Calculation of voltage gradients on individual conductors Calculation of voltage gradient by approximate formulae Radio noise or radio interference (RI) Audible noise (AN) Impact of line design on voltage- and current-depending phenomena Line performance and insulation requirements Introduction Power frequency voltages and temporary overvoltages Slow-front overvoltages Fast-front overvoltages Principles of insulation coordination General principles Insulation design for permanent power frequency voltages Insulation design for slow-front overvoltages Insulation design for fast-front overvoltage Live-line maintenance Clearances Clearance requirements Types of electrical clearances Calculation of electrical clearances Required withstand voltages of air gaps Voltages to be considered Summary of formulae for electrical clearances Empirical data for clearances Internal and external clearances Introduction Design principles Load cases for the calculation of clearances Maximum conductor temperature at no-wind condition Ice load without wind Wind load assumptions Insulator and conductor position under wind action Definition of wind action Calculation of swing angle Time distribution of swing angles Determination of swing angles by measurements 6o Conductor and insulator position according to standards... 65

4 Contents XIII Midspan clearances Minimum clearances within a span or at a tower Clearances to ground and obstacles Examples Electrical clearances for a 110 kv overhead line Electrical clearances for a 380 kv overhead line Electrical clearances for a 500 kv overhead line Clearances to obstacles for line design, empirical approach Time distribution of swing angles Tower top geometry according to statistic considerations Tower top geometry according to European standards Tower top geometry according to Brazilian practice References 75 3 Electric parameters Symbols Introduction Resistance Positive-sequence impedance Introduction Inductance and inductive Reactance Zero-sequence impedance Introduction Simplified approach for the determination of zero-sequence impedances Capacitance and capacitive reactance General considerations Single-circuit lines Double-circuit lines Admittance Electric representation of lines Goals and basic conditions Short- and medium-length lines Long-length transmission lines Representation by exponential functions Representation by hyperbolic functions The equivalent II-circuit of a long line References 97 4 Lightning protection Symbols 9 C J 4.1 Significance of lightning Formation of lightning strokes Mechanism of lightning discharge Impulse behaviour of lightning discharges Electric characteristics of the discharges 1( Frequency and intensity of lightning strokes Keraunic levels and earth flash density Magnitude of lightning stroke currents Direct and indirect lightning strokes Arrangement and efficiency of earth wires Theoretical background Effective shielding by earth wires 107

5 XIV Contents Surge arresters Assessment of lightning performance of overhead lines 4.5 Earthing in view of lightning protection j Significance of earthing for lightning protection Surge impedance of earthing systems 4.6 References 5 Earthing r 5.0 Symbols 5.1 Purpose of earthing 5.2 Definitions and basic principles Requirements Standards Safety of persons Thermal short-circuit strength Mechanical strength and corrosion resistance H Currents to be considered 1^" 5.4 Earthing for personal safety purposes 1^1 5.5 Operational earthing 1" 5.6 Lightning protection earthing Rating for short-term currents Soil resistivity and conductivity Calculation of earthing resistance Spherical electrode Earthing rods Horizontally arranged electrode wires (counterpoises) Measurements of soil resistivity Basic principles Measuring methods Measurement of earthing resistance Earthing resistance in non-homogeneous soils Soil resistivity in a two-layer soil structure Computation of earthing resistance in a two-layer soil structure Computation of earthing resistance by means of the apparent resistivity Computation of earthing resistance of three-dimensional structures Example for computation of earthing resistance Practical rules for installation of earthing systems Radial and ring-type earthing counterpoises Vertically or obliquely driven earthing rods Bonding between earthing electrodes Earthing connections References Requirements on loading and strength 143 fi.o Symbols Mechanical design of the overhead line system Components and elements of an overhead line Reliability Calculation of reliability Strength coordination and selection of reliability Effect of maximum load intensity on a high number of components Use factor and its effect on the design X

6 Contents XV 6.2 Strengths of line components and elements Strength limits Rating of individual components and elements Damage and failure limits Wind loads Wind measurements Determination of meteorological reference wind velocities Evaluation of wind measurements Effect of the terrain roughness Variation of reference wind velocity with height Wind action on line components and elements Ice loads Atmospheric icing Ice observations and measurements Determination of reference ice loads Basic relations Evaluation of ice load information Reference ice load Loading of supports and load cases Combined wind and ice loads Probability of occurrence and combination of parameters Determination of design parameters Ice load Wind load Effective drag factors and ice densities Wind action on the ice covered conductor Climatic loads according to relevant standards Standards for overhead power lines Wind loads Wind load model according to IEC Wind model according to the European standard EN Wind models according to EN Comparison of wind load models with measurements Ice loads Ice load model according to IEC Ice load model according to EN Ice load model according to EN Combined wind and ice action Model according to IEC Model according to EN Combined wind and ice action according to EN Loads at construction, operation and maintenance Introduction Requirements according to IEC Requirements according to EN and EN Failure containment and other special loads Introduction Provisions according to IEC Provisions according to EN Statistical distributions Introduction Normal distribution (Gaussian distribution) 188

7 XVI Contents Log-normal distribution ]OQ Gumbel distribution,qd 6.10 References,,, 7 Selection of conductors 1Q(. 7.0 Symbols ^ 7.1 Conductor types and design Introduction (f Conductor designation Progress in technical development um Materials ' ' '.'.'.'.'.'.'.'.'.'.'.'.' Aluminium Aluminium-magnesium-silicon alloys 9m Steel wires..'.'.[' Aluminium-clad steel wires 9()? Copper and copper alloys 2() Thermal resistant aluminium alloys, n Wire testing f' Introduction [ [ Dimensions and surfaces ' Testing the tensile strength. f Wrapping and twisting test t ' Testing zinc mass, cladding thickness'and uniformity 204 (" Testing resistivity Conductors made of wires with the'same material '. 204 ' i-o-l AH aluminium conductors AH aluminium alloy conductors Aluminium-clad steel conductors.,, Copper, copper alloy and steel conductors i ' ' 1-7 Composite conductors Configuration and design Characteristic data Production Joints Shipment...[ Conductor testing Classification of tests Extent of sample tests G Tensile breaking strength Test of creep behaviour A Special conductor designs Self-damping conductors Vibration resistant conductors

8 Contents XVII Low noise conductors Conductors with treated surfaces Design with regard to current loading Introduction and requirements Principles for determination of conductor temperature Design with regard to current carrying capacity Design with regard to short-circuit current Design based on economic considerations Line capacity as a function of the weather conditions Design with regard to stresses caused by voltages Introduction and requirements Design with respect to the electric parameters Design with respect to conductor surface gradients and corona effects Corona losses Mechanical design of conductors Introduction and requirements Stresses under extreme load conditions Stresses under everyday conditions Impact of the conductor tensile load on line investment Conductor creep Recommendations for selection of conductor tensile stresses References Earth wire selection Symbols Types of earth wires Electric and thermal design Requirements Earth wire design under short-circuit conditions Temperature limits of earth wires in case of short circuits Fault clearing and reclosing operations Examples of earth wire current carrying capacity in case of short circuits Mechanical design Loss of mechanical strength during heating process Establishing tensile stresses and forces Steps for selection of conventional earth wires Earth wires comprising optical fibres (OPGW) Generalities and design Installation conditions Accessories Tests References Insulators Symbols Introduction Ceramic insulators Insulator types and their application Raw materials Production Glass insulators Raw materials and production 265

9 XVIII Contents Insulator types and application Composite insulators Raw materials, design and production Types of composite insulators and their application Comparison of insulator types Tests on insulator units Basic information Tests on ceramic and glass insulators Type tests Sample tests Routine tests Tests on composite insulators Basic information Test of the structural design and type test Sample and routine tests Design of insulator sets Suspension insulator sets Tension insulator sets Requirements for insulator sets Electric requirements for AC lines Particularities for DC lines Audible noise (AN) performance Mechanical design Operational performance of insulator strings Introduction Voltage stresses Behaviour of individual insulator types Behaviour under pollution layers Formation of pollution layers Simulation of pollution layers Pollution levels Assessment of pollution levels by means of local measurements Measures to maintain insulation capacity Testing of insulator sets Basic information and assumptions Standard atmospheric conditions Artificial rain Testing arrangements Power frequency voltage test Fast-front and slow-front overvoltage tests Power arc behaviour Radio interference strength test Corona onset or extinction voltage test Example for insulator selection References Overhead line fittings Definitions Fittings for conductors Conductor attachment at suspension insulator sets Conductor attachments at dead-end terminations Turn buckles 309

10 Contents XIX Connectors 3( Spacers for bundle conductors Vibration dampers for single conductors Spacer dampers for bundle conductors Fittings for insulator sets Rating and tests General Electric requirements Mechanical requirements Corrosion protection Selection of material Tests References Conductor vibrations Symbols Overview and types of vibration Aeolian vibrations Basic physical aspects, mathematic-mechanic model of a.lino Conductor free-span amplitude Conductor strains and stresses Bending stiffness of a conductor Origin of vibrations Consequences of vibrations Consequences for line design Verification of vibration intensity and effectiveness of damping measures Evaluation of vibration measurements Subspan oscillations Origin and consequences Remedy measures Galloping Origin and consequences Remedy measures Short-circuit oscillations Origin and consequences Remedy measures References Supports Symbols Support types and their applications Definitions Tasks of supports in an overhead line Suspension supports Angle suspension supports Angle supports Strain and angle-strain supports Dead-end supports Special supports Support design and application Selection of support design Self-supporting lattice stool towers 357

11 XX Contents Self-supporting steel poles Steel-reinforced concrete poles Wood poles Guyed supports Crossarmless supports Tower top geometry Requirements Electrical clearances according to relevant standards Clearance between conductors Equal cross sections, alike materials and equal sags of conductors Conductors with different cross sections, materials or sags Clearances at supports Basic design requirements Introduction Static design Design values and verification methods Load cases and partial factors Combination of loads Extreme wind load Wind load at minimum temperature Uniform and unbalanced ice loads without wind Combined wind and ice load Construction and maintenance loads Security loads Partial factors for actions on supports Partial factors for materials Lattice steel towers Structural design Structural design of members Connections Walkways Production Corrosion protection Materials Materials for angle sections and plates Material for bolts Analysis of member forces Calculation of the member forces at a plane system Basic procedure Forces in the leg members Forces in bracings, loaded by horizontal forces Forces in bracings, loaded by asymmetrical vertical forces Forces in bracings, loaded by torsional moments Total forces in bracings Forces in horizontal members at tower waist Forces in horizontal bracings within the tower body Forces in leg extensions Forces in crossarm members Analysis of member forces at a three-dimensional system Basic approach of the finite element method Application to three-dimensional truss structure systems Comparison of computations at plane and three-dimensional systems. 396

12 Contents XXI General format of verification of members and connections Design of compression members Effective cross section properties for compression members Flexural buckling of axially compressed members Flexural torsional buckling of centrally compressed members Bending and axial compression forces Design of compound members Member connected by batten plates Laced box-type members Design of tensile-loaded members Members axially loaded in tension Axial tensile force and bending Design of connections Design for bending due to transverse loads Design of redundant members Deformation Calculation of foundation loads Application of computer programs for calculation of lattice steel towers Upgrading the support strength Example: Static calculation of a 110 kv suspension support Example: Calculation guy wire and mast loads in a guyed-v tower Steel poles Structural design Analysis of loads Rating Example for design of a conical solid-wall steel pole Steel-reinforced concrete poles Selection of cross sections Spun concrete poles Vibrated concrete poles Structural design Production Rating Example for design of a spun concrete pole Basic data Calculation of loads Verification of cross sections Wood poles Application and design Rating Treatment of wood poles Loading and failing tests Introduction Foundations for support under test Material for the tower under tost Fabrication of the prototype tower under test Strain measurements Assembly and erection Tost loads Load application Load procedure Load measurement 461

13 XXII Contents Deflections Acceptance and failures Destruction test Disposition of test tower 4f > Test report 4(i References 4(i6 13 Foundations 13.0 Symbols Requirements and preconditions Types of subsoils Classification of soil Undisturbed natural soil Rock Filled-up soil Subsoil investigation Purpose of subsoil investigation Methods for obtaining soil samples Type of samples Trial pits Exploratory borings Soil investigation by drilling probes Probes Types of probes Driven probes Standard penetration test Van-type probes Compression probes Evaluation of soil investigation Classification and description of soil types Classification of rock Concrete-aggressive water and soils Borehole log Graphical representation Design and calculation of foundations Type of foundation and load Soil characteristics Compact foundations Definition Monoblock foundations Monoblock foundations without base enlargement, Monoblock foundation with base enlargement Slab foundations Single grillage foundation Single pile foundations Foundation of self-supporting timber poles Separate foundations Definition Stepped block foundations Auger-bored and excavated foundations Separate grillage foundations Pile foundations

14 Contents XXIII Steel reinforced pad and chimney foundation Foundations in rock Anchoring of leg member stubs Foundation for guyed towers Acting loads Central footings Foundations for guy wires Field tests Testing of foundations Definitions and object Categories of tests Foundation installation Testing equipment Testing procedure Test evaluation and acceptance criteria Uplift load tests on construction and test, piles References Sag and tension calculations Symbols Basis Sags described by the catenary curve Conductor sagging curve as a parabola Span with differing attachment levels Conductor state change equation Span with concentrated loads Span with tension insulator sets at both ends Conductor forces and sags in a tensioning section Introduction Conductor state in spans with end points movable in line direction Conductor stresses and sags in case of inverted V-insulator sets Conductor state change equation for a tensioning section Computer program for conductor state change in a tensioning section Approximate formulae of sags at ice load in one span only Clearances to ground and to objects Requirements Calculation of clearance to ground Calculation of the clearance to a crossed road Calculation of clearance to a crossed line References Route selection and detailed line design Symbols Introduction Basic information Preliminary activities Route selection and licences Introduction General aspects and guidelines Alternative lino designs Conversion of existing linos Underground transmission 577

15 XXIV Contents Regulatory controls and permit procedures Introduction Permits Regulations, approvals and procedures Compensations Environmental impact assessment Outline of the process Environmental impact studies Existing environmental situation without the line project Reference alternative Environmental impacts of a new line Route selection and line design in view of visual impact Introduction Conceptual approaches Assessment through qualitative methods Assessment through quantitative methods Routing for minimum visual impact Visualization of new lines Design of components to reduce visual impact Route selection in view of people Route selection and line design in view of ecological systems Introduction Impacts on avifauna Impacts on wild animals Impacts on vegetation Conservation and wilderness areas Route selection in view of land use Introduction Agricultural areas Forestry Industrial areas and infrastructure developments Urban areas Survey on site Steps of survey Survey procedures and instruments adopted Direct survey in the terrain Indirect line survey Terrain data banks Survey of angle points and line alignment Survey of terrain profile Location of supports Survey of existing lines Line design and establishing of plans Clearances Determination of support locations, tower types and heights Evaluation of the profile survey Basis and relevant parameters 60J Manual tower spotting Tower spotting and optimization by means of data processing Documentation of linos Data processing for line design and administration Data processing systems for planning of overhead lines 611

16 Coiiioiiis X.W Establishing t.lio longitudinal profile Establishing the plan layout (ill Graphical Information System with integrated data bank Administration of plans, lists and documents References Construction Symbols Construction planning Introduction Construction time schedule Mobilisation and stockyard Transportation Means of transport Access roads Fences, gates and cattle-guards Construction of foundations Introduction Concrete foundations black and slab foundations Augerbored foundations Driven pile foundations Common ink's Steel piles Steel piles grouted by mortar 62S Testing Grillage foundations Anchor foundations Concrete for foundations Ready-mixed and site-mixed concrete Constituent, materials Requirements on concrete and concrete properties Ready-mixed concrete Site-mixed concrete Handling and placing the concrete 63M Curing the concrete 63* Methods for verification of concrete properties Quality supervision and quality management Installation of earthing (ill) 16.5 Setting of tower stubs or bases (ill Methods and tools Inclination of angle and dead-end towers (i] Erection of supports Introduction Assembly and erection by elevation Tower erection using a crane Tower erection by means of a gin polo (i Procedures tilli Erection with a gin polo outside the lower (i. 1.3 Erection with gin polo in the tower centre Erection with ;> gin pule in the tower ;it ;i leu member (>ls Erection of guyed towers 61s Hoisting of a crossarin using a gin pole 61*

17 XXVI Contents Tower erection using helicopters Manual method Use of an auxiliary mast Erection by cranes Bolts and torques Installation of insulator sets and hardware Insulator sets Joints Conductor stringing General requirements Stringing methods Conductor stringing equipment Requirements Pulling ropes Rope connections Stringing blocks Puller for conductor stringing Tensioner Reel stands Conductor stringing Preparations Stringing procedure Sagging the conductors Terminating the conductors Clipping-in of conductors Installation of jumper loops Installation of dampers and bundle spacers Conductor replacement Stringing conductors with optical fibres Installation of conductors adjacent to or crossing energized lines Determination of initial sags Requirements Position of the conductor on stringing blocks and in clamps Impact of conductor creep Example: Sagging data for an overhead line in a mountainous area References Commissioning, operation and line management Symbols Commissioning Introduction Supervision of approval, design and manufacturing stage Supervision and acceptance of construction Final inspection and acceptance Quality assurance Performance tests Measurements of tower earthing resistance Power losses and electrical resistance of conductors Line energization test Electrical and magnetic fields (EMF) Vibration performance measurements Energization and commence of operation 686

18 Contents XXVII 17.2 Operation Real-time monitoring of conductor ampacity Targets and benefits Direct methods Indirect methods Examples and experience Thunderstorm monitoring and forecast Ice observations Galloping alerting system Insulator contamination and performance Asset management Definitions Introduction and targets Risk management of line assets Net present value of annual expenditures Planned expenditures Risk of failure Consequences of a failure Overhead line asset management process Data base Management options Example on management of risk of failure Basic data Calculation of planned expenditures and risks Management options and assessment Maintenance Introduction Inspection Reasons and procedures for inspections Inspection classification and frequency Foundations and stubs Supports including corrosion protection Conductors Joints and fittings Insulators Clearances Corrective maintenance Strategy Refurbishment and upgrading of foundations Renewal of coating, replacement of tower components Repair of conductors Replacement of insulators, fittings, dampers and spacers Tasks and priorities Dead-line work Livo-line work Clearing of right-of-way, trimming of trees Access roads Earthing Investigation of line failures General Causes of failure Investigation procedures 720

19 XXVIII Contents Experience on line failures Reliability and availability Introduction and definitions Energy availability, general description and guidelines Availability Determination of energy availability, example Line refurbishment, upgrading and uprating Definitions Uprating Current uprating Uprating by reconductoring or voltage increase Replacement of earth wire by optical cables (OPGW) Upgrading Introduction Upgrading of a 380/220 kv river crossing in Germany Upgrading of a 380/110 kv line in view of increased ice loads References 731 Index 735

20 1 Overall planning 1.0 Symbols Symbols Signification AAI Aluminium cross section of the conductor ^AC, IDC Current of AC or DC line K2C Investment of a double circuit overhead line ii'ic Investment of a single circuit overhead line Kic Investment of a four-circuit overhead line n-2 Number of subconductors per bundle L r N Rated voltage U\c, Uoc Voltage of an AC or DC line P\c Power of a three-phase AC lino FDC Power of a DC bipolar line S Power angle 1.1 Development stages of a transmission project Overhead transmission of electric power has been along the years and will still continue one of the most important elements of today's electric power systems. Power transmission from generating stations to industrial sites and to substations is the fundamental object of the transmission systems. This function is accomplished by overhead transmission lines that connect the power plants into the transmission network, interconnect, various areas of transmission networks, interconnect one electric utility with another, or deliver the electric power from various areas within the transmission network to the distribution substations, from which the distribution systems supply residential and commercial consumers. The planning studies take a leading role in the definition of an electric system or in its expansion. Due to the several variables involved in the process, the planning activities have to start several years before a new installation or an expansion of an existing one is planned to be implemented. So, a transmission line project may be considered as being initiated with some planning activities long before its execution can be started. Several stages are usually necessary inside a power utility before a new transmission system from its conception until its completion is energized. The conception of a transmission line and of the associated substations starts in the long-term planning with initial system evaluations and continues with further steps of medium-term planning and finally with the detailed definition of the line and then the granting of operation licence and approval. For completing the preliminary studies of a new line, some complementary studios of performance assessment are carried out such as (see [ ]): - Reactive, compensation needs, - Load flows and stability, - Transposition needs. - Switching surge overvoltages and - Reliability evaluation. Finally, the line owner proceeds to the lino basic design and then the detailed design, with all associated activities. The last stages consist in establishing the rights-of-way. performing and approving environmental impact studies and providing indemnification to the landowners affected by the new line in order to obtain their agreement. Only