Handbook
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SA/SNZ HB 331:2020
[Current]Overhead line design handbook
The objective of this Handbook is to provide guidance for both transmission and distribution lines in relation to the application of AS/NZS 7000:2016. Typical distribution voltages are 230/400 V, 230/460 V [referred to as low voltage (LV)] and 6.6 kV, 11 kV, 12.7 kV, 19.1 kV, 22 kV [referred to as high voltage (HV)]. Typical sub-transmission voltages are 33 kV, 66 kV, 110 kV, 132 kV and transmission voltages are 220 kV, 275 kV, 330 kV, 400 kV and 500 kV.
Published: 17/01/2020
Pages: 303
Table of contents
Cited references
Content history
Table of contents
Header
About this publication
Preface
1 Scope and general
1.1 Scope
1.2 Significant changes to this Handbook
1.3 Structure of Handbook
1.4 Referenced documents
2 Design philosophies
2.1 Basic methodology
2.2 Reliability levels
2.3 Design working and service life
2.4 Security levels
2.5 Limit state design principles
2.6 Guidelines on strength coordination (AS/NZS 7000 Clause 2.7)
2.7 Commentary on AS/NZS 7000 Appendix D — Guidelines on service life of overhead lines
2.8 Service life of other line material and components
2.8.1 General
2.8.2 Composite poles
2.8.3 Annealing
2.8.4 Corrosion
2.8.5 Crossarms
3 Safety in design principles
3.1 General
3.2 Safe design considerations for overhead lines
4 Electrical requirements
4.1 Clearance and spacing for overhead lines
4.2 Electric and magnetic fields
4.3 Hand reach clearance
5 Conductors and overhead earthwires (ground wires)
5.1 Selection of conductor
5.2 Electrical requirements
5.2.1 Steady-state thermal current rating
5.2.2 Short-circuit thermal current rating
5.2.3 Corona effect
5.2.4 Conductor long-term electrical performance
5.3 Mechanical strength
5.3.1 General
5.3.2 Conductor limit states
5.3.3 Conductor fatigue and conductor everyday load horizontal tension
5.4 Economic considerations
5.4.1 General considerations
5.4.2 Kelvin’s law for conductor selection (distribution conductors)
5.5 Selection of conductors for hostile environment
5.6 Conductor thermal limits
5.6.1 General
5.6.2 Maximum design operating temperatures
5.7 Conductor permanent elongation
5.7.1 General
5.7.2 Empirical guidelines for temperature compensation for creep
5.8 Conductor fault ratings
5.8.1 General
5.8.2 Annealing
5.8.3 Sag-tension calculation
5.9 Selection of serviceability conductor tension
6 Insulators
6.1 Insulator design
6.2 Design for pollution
6.3 Mechanical design of insulators
7 Basis of structural design
7.1 Determination of height
7.2 Loading on structures
7.2.1 General
7.2.2 Vertical loads
7.2.3 Transverse loads
7.2.4 Longitudinal loads
7.3 Limit state design
8 Action on lines
8.1 Introduction
8.2 Wind loading
8.3 Conductor tension governing conditions
8.4 Establishment of load cases
8.4.1 Objective
8.4.2 Load combinations
8.4.2.1 General
8.4.2.2 Line security and wind return period
8.4.3 Failure containment
8.4.3.1 General
8.4.3.2 Failure containment condition
8.4.3.3 Residual static load (RSL)
8.4.4 Snow and ice loading
8.4.5 Personnel access, construction and maintenance loads
8.4.5.1 General
8.4.5.2 Construction and maintenance loading types
8.4.5.3 Man-standing loads
8.4.5.4 Fall arrest loads
8.4.6 High voltage live working
8.4.6.1 General
8.4.6.2 Electrical safety considerations
8.4.6.3 Mechanical safety considerations
8.4.6.4 Other considerations
8.4.7 Short-circuit forces
8.4.8 Earthquake loads
8.4.9 Differential settlement of structure foundations
8.4.10 Design measures to provide for mine subsidence
8.4.11 Serviceability loads
8.4.11.1 General
8.4.11.2 Load factors and tolerances
8.5 Simplified wind loading application table
8.6 Commentary on Appendix B — Wind loads
8.6.1 Australia
8.6.2 New Zealand
8.6.3 Synoptic wind regions
8.6.4 Downdraft wind regions (Australia Zone II, Zone III and New Zealand Region A7)
8.6.5 Tornadoes
8.6.6 Wind pressures
8.6.6.1 General
8.6.6.2 Wind pressures on lattice steel towers
8.6.6.3 Wind pressure on poles
8.6.6.4 Wind pressures on conductors
8.6.6.5 Wind pressures on insulators and fittings
8.6.7 Topographical effects
8.6.8 Escarpments
8.7 Local effects
8.7.1 Channelling effects
8.7.2 Funnelling effects
8.7.3 Katabatic wind effects
8.7.4 Extensive fetch distances
8.7.5 Air turbulence near airports
9 Supports
9.1 Pole strength
9.2 Serviceability limits and deflection design
9.3 Failure rate of structures
9.4 Commentary on AS/NZS 7000 Appendix F — Timber poles
9.4.1 Paragraph F1, General
9.4.2 Paragraph F3, Characteristic strengths and elastic moduli
9.4.3 Paragraph F5, Design capacity
9.5 Concrete poles
9.5.1 Design of concrete poles
9.5.2 Biaxial bending of rectangular concrete poles
9.5.3 Testing of concrete poles
9.5.4 Hollow pole manufacture related design issues
9.5.5 Pole handling stresses
9.5.6 Equipotential bonding
10 Foundation design
10.1 General
10.2 Geotechnical parameters of soils and rocks
10.3 Footing design of directly embedded overhead line poles for lateral loads and moments
10.3.1 General
10.3.2 Serviceability limit state bearing strength fb
10.3.3 Strength limit state bearing strength fbu
10.3.4 Serviceability limit state shear strength
10.3.5 Design method
10.3.5.1 Direct embedment
10.3.5.2 Bearing block foundation
10.3.5.3 Derivation of embedment formula
10.3.5.4 Tables of minimum embedment depths
10.4 Additional comment on foundation capacity of direct buried poles
10.4.1 Introduction
10.4.2 Background
10.4.3 Foundation limit states
10.4.4 General philosophy
10.4.5 Methods of assessment
10.4.6 Site and geotechnical investigations
10.4.7 Soil testing
10.4.8 Soil classification and mapping
10.4.9 Foundation capacity using Brinch Hansen (1961)
10.4.10 Foundation strength factors
10.4.11 Comparison of different methods
10.4.12 Brinch Hansen method
10.4.13 Full scale testing
10.4.14 Stayed poles
10.4.15 Limits of simple embedment depth
10.4.16 Rigid pole rotation
10.4.17 Pole shape
10.4.18 Acceptable lateral deflection
10.4.18.1 For lattice towers
10.4.18.2 For poles
10.4.19 Loading duration
10.4.20 Foundation strengthening methods
10.4.20.1 General
10.4.20.2 Grass verge
10.4.20.3 Effect of asphaltic concrete footpath
10.4.20.4 Concrete footpath
10.4.20.5 Blocking
10.4.20.6 Blocking at top only
10.4.20.7 Gravel collar
10.4.20.8 Cement stabilized backfill
10.4.20.9 Comparison of improvement types
10.4.21 Sloping ground
10.4.22 Trenches and excavations
10.4.23 Land instability
10.4.24 Liquefaction
10.4.25 References
10.5 Foundation design for lattice steel towers
11 Earthing
11.1 Introduction
11.2 New Zealand requirements
11.3 Design for touch and step potential for conductive structures
11.4 Replacing a non-conductive pole with a conductive pole
11.5 SWER earthing
11.6 Risk-based approach to earthing for Australia
11.6.1 Risk-based earthing examples
11.6.2 Example 1 — HV distribution earth
11.6.3 Example 2 — Conductive distribution pole in an urban area
11.7 Risk-based approach to earthing for New Zealand
11.7.1 Examples of risk treatment options
11.7.1.1 Installing an underslung earth wire on the line
11.7.1.2 Installing a gradient control conductor and an asphalt layer around the pole
11.7.1.3 Installing an insulating barrier around the pole to prevent people from touching the pole
11.7.1.4 Replacement of the concrete pole with a wood pole
11.7.1.5 Installation of a ground fault neutralizer
12 Line equipment — Overhead line fittings
13 Overhead line design process
13.1 Steps in the design process
13.2 Design inputs/parameters
13.3 Route selection process
13.3.1 Introduction
13.3.2 Risk management principles
13.3.3 Prudent avoidance principle
13.3.4 Aesthetic considerations
13.3.5 Electric and magnetic fields
13.3.5.1 Prudent avoidance
13.3.5.2 Transmission lines
13.3.5.2.1 General
13.3.5.2.2 Distance
13.3.5.2.3 Conductor configuration
13.3.5.2.4 Line compaction
13.3.5.2.5 Phase arrangement
13.3.5.2.6 Split phasing
13.3.5.2.7 Current reduction
13.3.5.2.8 Shielding and cancellation loops
13.3.5.2.9 Undergrounding
13.3.5.2.10 Land development and easements
13.3.5.3 Distribution lines
13.3.5.3.1 General
13.3.5.3.2 Siting
13.3.5.3.3 Design
13.3.5.3.4 Magnetic field modelling and profiles
13.3.5.3.5 LV Standards
13.3.5.3.6 11 kV Standards
13.3.5.3.7 33 kV Overhead standards
13.3.5.3.8 110 kV Standards
13.4 Seek route approvals
13.5 Conduct route survey
13.5.1 General
13.5.2 Determination of transmission line easement width
13.5.2.1 General
13.5.2.2 Case 1 — Common structure on easement
13.5.2.2.1 General
13.5.2.2.2 Wb1— Maximum conductor blowout
13.5.2.2.3 Wc — Circuit/phase spacing
13.5.2.2.4 Wi — Insulator swing
13.5.2.3 Case 2 — Multiple circuits across easement
13.5.3 Vegetation clearances
13.5.3.1 General
13.5.3.2 Vegetation management principles
13.5.3.3 Vegetation management risk guidelines
13.5.3.4 Vegetation clearance zones
13.5.3.5 Special considerations for high reliability lines (e.g. transmission lines) or lines with long spans
13.5.3.6 Special consideration for overhead lines in heavy or dense vegetation
13.6 Electrical design
13.6.1 Conductor and earthwires
13.6.2 Determination of conductor rating
13.6.3 Design for lightning performance
13.6.3.1 General
13.6.3.2 Estimation of line outages due to lightning
13.6.4 Transpositions
13.6.5 Radiofrequency interference (RFI) and television interference (TVI)
13.6.6 Electrical and mechanical design for insulators
13.6.6.1 Insulator selection
13.6.6.2 Design for pollution
13.6.6.3 Design for power frequency voltages (wet withstand requirement)
13.6.6.4 Design for switching surge voltages
13.6.6.5 Selection of insulators to meet electrical performance
13.6.7 Earthing systems
13.6.7.1 General
13.6.7.2 Distribution earthing systems
13.6.7.3 Multiple earthed neutral (MEN)
13.6.7.4 Common multiple earthed neutral (CMEN)
13.6.7.5 Separate earthed system
13.6.7.6 Earthing and insulation of stay wires
13.6.8 Earthing structures for touch and step potential
13.6.8.1 General
13.6.8.2 Definitions
13.6.8.3 Non-conductive structures
13.6.8.4 Conductive structures
13.6.9 Earth potential rise
13.6.9.1 General
13.6.9.2 Comparison of grading ring configurations
13.7 Structure suite
13.7.1 General
13.7.2 Tower top geometry
13.8 Layout design process
13.8.1 General
13.8.2 Site information
13.8.3 Structure placement (spotting)
13.8.4 Actual weight span to wind span ratio
13.8.5 Allowable weight span to wind span ratio
13.8.6 Weight span to wind span ratio variation with conductor tension
13.8.7 Conformance under all design wind conditions
13.8.8 Using computer programs for layout design
13.8.9 Modelling of wire system
13.8.9.1 General
13.8.9.2 Ruling span method (RS) modelling — Usefulness and practicality of method
13.8.9.3 Finite element (FE) modelling ignoring interaction between wires — Usefulness and practicality of method
13.8.9.4 Finite element (FE) modelling accounting for interaction between wires — Usefulness and practicality of method
13.8.10 Layout design output
13.9 Structural and mechanical design
13.9.1 General
13.9.2 Design verification
13.9.3 Detail design documentation
13.10 Construction approvals
13.11 Design support for construction
13.12 As-constructed documentation
14 Design process for a single circuit 132 kV overhead line
14.1 General
14.2 Line layout
14.3 Performance and design inputs
14.3.1 Environmental conditions
14.3.2 Relevant mechanical and electrical design Standards
14.3.3 Conductor rating
14.3.4 Maximum conductor temperatures
14.3.5 Fault current and clearing times
14.3.5.1 General
14.3.5.2 Earthwires
14.3.6 Lightning performance
14.3.7 Earthing resistance
14.3.8 Power frequency performance
14.3.9 Switching surge performance
14.3.10 Insulation
14.3.11 Maximum surface voltage gradient
14.3.12 Maximum electric and magnetic field levels
14.3.13 Electrical clearances
14.3.14 Mechanical design
14.3.15 Corrosion resistance of structures and materials
14.3.16 Foundations and stays
14.3.17 Vibration damping
14.3.18 Joints and terminations
14.3.19 Design within easements
14.3.20 Step and touch potentials
14.3.21 Low frequency induction
14.3.22 Other design considerations
14.4 Selection of conductor
14.4.1 General
14.4.2 Conductor ratings
14.4.3 Conductor sags and tensions
14.4.4 Calculation of pole height
14.4.5 Concrete pole selection
14.4.6 Wood pole selection
14.4.7 Overall comparison between conductors
14.4.8 Final selection of conductor
14.5 Electrical design
14.5.1 Electrical clearances between conductors
14.5.1.1 Example 1 — Determining midspan separation using disc insulators
14.5.1.2 Example 2 — Determination of midspan separation using post insulators
14.5.2 Swing angle calculations at structure
14.5.2.1 General
14.5.2.2 Example 1 — Swing angle for low wind condition
14.5.2.3 Example 2 — Swing angle for high wind condition
14.5.3 Blowout calculations
14.5.4 Lightning outage predictions
14.5.5 Magnetic field calculations
14.5.6 Electrical design of transmission line insulation, under pollution, clean and wet conditions
14.6 Mechanical design of insulator — Transmission line insulators
14.6.1 Worked examples for transmission line insulators
14.6.1.1 Example 1 — Determining strength of insulation for ceramic disc insulator on Oxygen conductor
14.6.1.2 Example 2 — Determining strength of insulation for long rod composite insulator on Paw Paw conductor
14.6.1.3 Example 3 — Determining strength of insulation for composite line post insulator on Oxygen conductor
14.6.1.4 Concluding comments
14.6.1.5 Example 4 — Determining strength of insulation for suspension composite insulator to support Oxygen conductor
14.6.1.6 Concluding comments
14.6.1.7 Example 5 — Determining strength of tension ceramic disc insulators for a terminal tower (more rigorous approach)
14.7 Structural design
14.7.1 General
14.7.2 Pole tip load calculation for structure 3 (un-stayed angle on concrete pole)
14.7.3 Selection of pole
14.7.3.1 General steps
14.7.3.2 Selection of concrete pole strength
14.7.4 Pole tip load calculation for structures 1 and 3 (stayed termination on concrete pole — see Figure 14.3)
14.7.4.1 General
14.7.4.2 Second iteration for a two stay design
14.7.4.3 Pole design checks
14.7.4.4 Check critical sections of the pole for bending stress
14.7.4.5 Consideration of compressive load in stayed concrete pole
14.7.4.6 Pole footing design
14.7.4.7 Stay anchor design
14.7.4.8 Use of stay insulators
14.7.5 Pole tip load calculation for structure 5 (un-stayed timber pole — see Figure 14.3)
14.7.6 Pole tip load calculation for structure 7 (stayed timber pole — see Figure 14.3)
14.8 Earthing design for 132 kV concrete and wood poles
14.8.1 General
14.8.2 Selection of overhead earthwires
14.8.3 Ground earthing design
14.8.4 Design for step and touch potentials
15 Miscellaneous worked examples using AS/NZS 7000
15.1 Worked examples for various line components
15.1.1 Electrical clearances between conductors
15.1.1.1 Example 1 — Single circuit 19/3.25 AAC at 33 kV on pin insulators with a span of 200 m
15.1.1.2 Example 2 — Upper circuit 33 kV on pin insulators with a span of 200 m located directly above an 11 kV lower circuit
15.1.1.3 Example 3 — Separation where conductors go from vertical to flat or triangular
15.2 Insulator worked examples
15.2.1 Transmission insulator example
15.2.2 Distribution insulator examples
15.2.2.1 Example 1 — Determining strength of tension ceramic disc insulator used for Moon conductor
15.2.2.2 Example 2 — Determining strength of a ceramic line post insulator used to support Moon conductor in a clamp top insulator
15.2.2.3 Example 3 — Determining the strength of a ceramic pin insulator used to support Saturn conductor
15.2.3 Determining component strength of pin insulator
15.2.4 Crossarm analysis of 11 kV construction
15.2.5 Selection of timber crossarm
15.2.6 Selection of steel crossarm
15.2.7 Summary
15.3 Limit state design worked examples
15.3.1 General
15.3.2 Pole tip load calculation
15.3.3 Selection of pole
15.3.3.1 Wood pole
15.3.3.1.1 Considerations for un-stayed wood pole
15.3.3.1.2 Consideration for stayed pole
15.3.3.2 Steel pole
15.4 Multiple span calculations
15.5 Distribution worked example 1
15.5.1 General
15.5.2 Design data
15.5.3 Design calculations
15.6 Distribution worked example 2
15.6.1 General
15.6.2 Design data
15.6.3 Ultimate conductor loads
15.6.4 Failure containment loads
15.7 Seismic loads worked example
15.7.1 General
15.7.2 Example of a typical distribution pole mounted transformer station
15.7.2.1 Design parameters
15.7.2.2 Frequency and modal response of PSC poles
15.7.2.2.1 Conductor vertical load
15.7.2.2.2 Structure vertical load
15.7.2.2.3 Transformer vertical load
15.7.2.2.4 Seismic load
15.7.2.3 Equivalent tip loads
15.7.2.4 Seismic displacements
16 Special topics
16.1 General
16.2 Non-conventional conductors
16.3 Aerodynamic conductors
16.4 High temperature low sag conductors
16.5 Special conductor constructions
16.6 References
17 Conductor clashing
17.1 General
17.2 Primary conductor clashing
17.3 Secondary conductor clashing
18 Designs and constructions for bushfire prone areas
18.1 Vegetation clearing
18.2 Increase in conductor height and separation
18.3 Conductor tension and vibration dampers
18.4 Insulated conductors
18.5 Temperatures during extreme bushfire conditions and appropriate line materials
18.6 Poles installed in bushfire prone areas
18.7 Fire resistant coatings on steel and wood poles
18.8 Concrete poles
18.9 Inspection and risk management
19 Low voltage aerial bundled cable
19.1 General
19.2 Supports
19.3 Cable tension
19.4 Clearances
19.5 Facade cable
19.6 Mechanical design
19.7 Clearances
19.8 References
20 High voltage aerial bundled cable
20.1 General
20.2 Mechanical
20.3 Electrical
20.4 Clearances
20.5 References
21 Covered conductor systems
21.1 General
21.2 Covered conductor (CC)
21.3 Covered conductor thick (CCT)
21.4 Clearances
21.5 References
21.6 Spacer covered conductor system
21.7 Clearances
21.8 Design guidelines for covered conductors
21.9 References
22 Stays
22.1 Glossary of terms
22.2 Applications
22.3 Stay capacity
22.4 Bollard capacity
22.4.1 Un-stayed bollard
22.4.2 Stayed bollard
22.5 Stayed structure analysis
22.6 Sidewalk stay analysis
22.7 Structures in compression
22.8 Stay layout
22.8.1 Intermediate structures
22.8.2 Flying angle structures
22.8.3 Termination structures
22.8.4 Strain structures
22.8.5 Tension equalization
22.9 Electrical design
23 Overhead lines in traffic corridors or proximity to other services
23.1 Pole locations in traffic corridors
23.1.1 General
23.1.2 Special considerations for slip based poles
23.1.3 Safety by design for poles in clear zones
23.2 Railway and tramway crossings
23.3 Waterway crossings
23.3.1 Example— New crossings Koolkhan to Maclean #2 66 kV
23.4 Coordination with other services
23.5 Aerial lines in the vicinity of aircraft
23.5.1 General
23.5.2 Aerial lines in areas other than take-off and landing areas
23.6 Marking of overhead lines
23.6.1 General
23.6.2 Types of markers
23.6.3 Permanent markers
23.6.4 Temporary markers
23.6.5 Over crossing markers
23.7 Rural activities in proximity to line
23.8 Country line road crossings
23.9 Blasting near overhead lines
23.9.1 Potential effects of blasting near overhead lines
23.9.2 Managing risk of blasting near overhead lines
24 Application of surge arresters
25 Line equipment — overhead line fittings
25.1 Fittings
25.2 Twisted connectors
25.3 Tongues and thick tongues
25.4 Round pins and hexagonal pins
25.5 Yoke plates and Y-clevises
25.6 Security devices
25.7 Arcing holes and horns
25.8 Sag/sector links
25.9 The effect on tensile load of maintenance loads
25.10 Maintenance holes
25.11 Live line collars
25.12 Trunnion maintenance holes
25.13 Landing spans insulator orientation
25.14 Vibration dampers
25.15 Spiral vibrations dampers
25.16 Helical fittings or wraps
25.17 Departure angle
26 Climbing and working at heights
26.1 General
26.2 Reference standards for climbing and working at heights
26.3 Methods for accessing work positions
26.3.1 General considerations
26.3.2 Use of elevating work platforms (EWP)
26.3.3 Climbing pole structures
26.3.4 Climbing lattice steel tower structures
26.4 Fall arrest systems
26.4.1 General
26.4.2 “Restrained fall” fall arrest
26.4.3 “Limited free fall” fall arrest
26.4.4 “Free fall” fall arrest
26.5 Use of static lines
26.6 Double lanyard restraint
26.7 Specific structure design provisions
Amendment control sheet
Bibliography
Cited references in this standard
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