400kV Overhead Line Construction

400kV Overhead Line Construction

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Tim Inglehearn

Contents

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Overhead line components

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Typical tower types

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Overhead line construction

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Reinstatement

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Inspection and maintenance

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Substations

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Overhead Line Components 

Support

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Conductors

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Insulators

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Spacers

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Dampers

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Earth wire

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Jumpers (on tension towers)

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Typical Tower Types Suspension Tower

Tension Tower (angled or deviation towers)

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Typical Tower Types Termination Tower at a Sealing End Compound or Substation

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Typical Tower Types Span Lengths and Tower Heights 

Short support: lower height; more supports per kilometre

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Tall support: greater height; fewer supports

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Clearance and ‘sag’; higher voltages require greater clearance/increased insulation

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Sum of adjacent ‘spans’

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Typical tower height: around 50m

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Typical tower span: 360m 6

Overhead Line Construction Access, Working Areas and Ground Preparation 

Temporary metal trackways or stone tracks dependent on landowners requirements

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Localised vegetation clearance and excavation where tower foundations needed, minor soil storage as a result

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Drainage/dewatering works might be required depending on ground conditions/watertable

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Every tower requires its own working area – protected by temporary Heras fencing 7

Overhead Line Construction Machinery Required 

Excavator for foundations and any drainage works

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Delivery of materials to site

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Crane to assemble towers

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Winch and tensioner

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Overhead Line Construction Tower Foundations – Excavated or Piled 

Foundation type dependent on ground conditions

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Excavated foundations encased in mass concrete

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Piled foundations also use concrete

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Stub legs installed and remainder of tower built up by crane 9

Overhead Line Construction Tower Construction and Cranage 

Fabricated from rolled steel angles and delivered to site in numbered parts (similar to flatpack furniture)

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Most parts are bolted together

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Sections e.g. crossarms assembled at ground level and raised into position using a crane

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All steelwork is galvanised for protection (will last approx. 20 years)

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Installation of insulators and fittings

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Overhead Line Construction Stringing conductors 

Draw wires winched through

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Conductors are winched into position

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Conductors pulled through suspension towers

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Winch and tensioner placed at tension towers

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Additional fittings (spacers etc.) installed 11

Reinstatement 

At end of construction, temporary access tracks and working areas are removed (unless otherwise agreed with the landowner)

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Land returned to original condition

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Inspection and Maintenance 

Inspection is carried out every year

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Towers are repainted approx. every 18 years depending on condition

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Replacement fittings during routine inspection, if required

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Reconductoring takes place approx. every 40 years

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Substations 

Transform voltages (400/132 kV)

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Switch connections in and out of the network

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Manage power flows

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Connection points

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Switches, transformers, compensation equipment

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Permanent land-take and vehicle access required

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Transformers delivered as abnormal loads - existing roads may need widening etc. 14

Any Questions?

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