E4014 Construction Surveying

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E4014 Construction Surveying

• Transmission Line Surveys

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Objectives

• provide an understanding of the principles
  involved and methods used for surveying
  transmission lines

• describe factors that affect the location of
  transmission lines
• describe the basic principles of the survey and
  design of transmission lines

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Objectives (cont)

• understand the survey design required for a
  rural extension line

• display a knowledge of the surveys required for
  high voltage lines

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Introduction

• Three main types of transmission lines

• (a) rural extension of the distribution network
  
• ( low high voltage )
• (b) extra high voltage lines carried on towers
• similar design principles apply to types (a) and
  (b)
• factors are more critical and methods more
  accurate for type (b)

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Introduction

• Third type of transmission line
• ( c ) urban distribution network

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Power Supply System

• Generation
• Transmission
• Distribution

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Power Supply System

• Generation

• electrical energy is generated at the power
  stations using 3-phase a.c. generators
• voltage and frequency are controled producing a
  moderate voltage of, say, 13.8 kV

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Power Supply System

• Transmission

• high voltage transmission lines are used to
  transfer electrical energy from the power
  stations to the load centres
• usually 3-phase overhead conductors suspended
  from insulators attached to towers, and called
  PRIMARY TRANSMISSION lines
• 275kV used in Qld, 330kV in NSW and 500kV in Vic

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Power Supply System

• Transmission (cont)
• power transformers are used at generating
  stations to step up or step down the voltages
• choice of transmission voltage depends on the
  power to be transmitted and the distance involved

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Single Wire Earth Return System ( SWER )

• Low cost, low maintenance method of supplying
  power to isolated (country) areas

• An isolating transformer separates the main high
  voltage system ( 11kV or 33kV ) from the SWER
  line ( 12.7kV to 19.1kV )
• separates the different earthing systems
• a single conductor overhead line feeds a
  distribution transformer, which steps-down the
  voltage to 2 circuits of 250V, or 1 circuit of
  500V

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Single Wire Earth Return System ( SWER )

• The SWER system uses a unique method of passing
  the return current through the earth
• the resistivity of the earth must be within a
  certain range for the system to work effectively

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Basic Principles of Transmission Line Design

• Ideal route between the point of power production
  and the point of consumption is a straight line
• Design Parameters and regional constraints affect
  the location of power lines

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Design Parameters

• Height of Poles or Towers
• Span Length
• Foundations
• Angles

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Design Parameters

• Height of Poles or Towers

• minimum height of transmission lines above the
  ground, for road crossings etc is laid down by an
  Act of Parliament
• most economic design attains this ground
  clearance and no more
• more height increases span length, but
• increases cost of pole or tower
• increases depth of pole, or
• increases foundation costs of tower

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Design Parameters

• Span Length

• aim is to have as few poles or towers per
  kilometre
• poles should be placed to maximise span length,
  whilst maintaining the minimum clearance

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Design Parameters

• Foundations

• location of poles or towers may affect the type
  of foundations required
• cost of towers in 1978
• normal foundations - 4 legs, 5m deep, 0.5m
  deep 2500
• special foundation - unstable soil 5000
• rock anchor - rocky ground 5000
• piled - mangroves, coastal flats 10000

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Design Parameters

• Angles

• the pole or tower must be able to withstand the
  tension of an indirect pull
• poles will need to guyed on the half angle
• angle towers can be up to 20000 more expensive
  than an ordinary support tower
• essential to keep bends to a minimum

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Design Parameters

• Summary of Design Parameters

• Height of Poles or Towers
• Span Length
• Foundations
• Angles

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Constraints

• Built up areas
• topography
• mountains, forests, rivers, swamps, flood zones
• recreational areas
• national parks, development areas

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Constraints (cont)

• mining areas
• cultivation areas
• future uses
• highways, railways, airstrips
• environment
• aesthetics, erosion

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Rural Extension Surveys

• Extend the power transmission network to small
  settlements and farm dwellings
• may carry high or low voltage
• low voltage lt 650 volts
• high voltage gt 650 volts
• normal extension is 11kV or 22kV high tension line

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Rural Extension Surveys

• Proposed extension is designed by an electrical
  engineer and plotted on existing topographical
  and cadastral maps
• shows location of all properties to be served
• shows proposed location of transformers etc

• actual route location and design functions are
  carried out in the field by the SURVEYOR

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Rural Extension Surveys

• Aim for
• minimum number of poles per kilometre
• minimum number of bends
• minimum ground clearance (6m at 49C)
• minimum clearance over
• road cuttings
• railways
• telephone wires

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Rural Extension Surveys

• minimum cut angle between telephone and power
  lines is 45 and parallel lines must be a minimum
  of 30m apart to avoid interference and power loss
• before undergrounding of power and telephone
  lines power lines were often placed 30 - 100m
  away from the phone line which was often in the
  road reserve
• advantages - easy connections to sheds and houses
  set back from road
• disadvantages - cultivation, access

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Rural Extension SurveysSurvey Design

• Basic survey problem is to obtain a profile of
  the land over which the transmission line is to
  traverse and to negotiate obstacles unforeseen in
  the proposed design - trees, hedges, buildings
  etc.
• clinometer and chain
• total station
• GPS

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Rural Extension SurveysSurvey Design

• traverse along proposed centreline from the last
  pole position
• note chainage and RL of grade changes and
  features
• continue past the next pole position

• plot profile
• horizontal and vertical scales are different
• governed by sag templates provided by Electricity
  Authority

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Rural Extension SurveysSurvey Design
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Rural Extension SurveysSurvey Design

• by using the sag template the position of the
  next pole is determined

• place a peg at the pole position
• only after the chainage and RL of the point have
  been compared to the plot
• surveyor should do a reconnaissance survey of the
  route before hand so that the topography is known
  to some extent

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Rural Extension SurveysSurvey Design

• angles are read
• where a bend occurs
• where a spur or branch line occurs

• place a peg at the bend and at the half angle
• poles will have to be guyed

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Rural Extension SurveysSurvey Design

• if line is traversing private property and
  easements are required, then occupation is also
  located
• running chainage to fence, angle along fence and
  distance along fence to cadastral corner

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Rural Extension SurveysSurvey Design

• surveyor has measured
• the profile of the line
• the running chainages and RLs
• the angles at bends

• an accurate plot of the final design is made for
  construction, easement and record purposes

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High Voltage Lines on Towers

• Basic design factors are the same
• the following are critical
• cost factor
• foundations
• length of route
• aesthetics and environment

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High Voltage Lines on TowersInitial Design

• most suitable route is chosen based on
• voltage, conductor, tower specification
• topographical maps
• cadastral maps
• town planning schemes
• aerial photos
• local Authorities advice
• other Government Departments advice
• ground reconnaissance

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High Voltage Lines on TowersInitial Design

• report on the route is prepared
• costing
• scheduling
• approval
• environmental impact assessment
• comments of interested Public Authorities

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High Voltage Lines on TowersInitial Design

• route maps are prepared
• 110 000
• latest cadastral information
• number of lines proposed
• easement widths
• current land use

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High Voltage Lines on TowersInitial Design

• contact is made with the owners and occupiers
• negotiate easements and access tracks
• property owners ( and other interested parties )
  may object
• property owners may state their intended future
  use of the land

• if objections justify an amendment then the
  centre line may be re-routed

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High Voltage Lines on Towers Survey of the Route

• high accuracy required
• control survey for whole of the route
• centre lines are cleared, surveyed and marked
• further public reaction may be forthcoming and
  the route may be deviated again
• keep lines to a minimum height for aesthetic
  reasons

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High Voltage Lines on Towers Survey of the Route

• surveyor locates towers and access tracks
• appreciate land usage and erosion
• report all relevant circumstances particularly
  those affecting overall location

• field data must show enough data for the towers
  to be located and their positions to be checked
  in the office

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Urban Distribution Network

• Transmission lines are entirely located in the
  road or street reserve
• span length is not as important
• poles are place to service as many consumers as
  possible
• design and survey is usually carried out by
  electrical engineers and their staff
• underground transmission conduits
• at least 5 times more expensive