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Project Scope

Fortescue as part of the Pilbara Transmission Project (PTP) engaged Partum to undertake the design of the 220kV transmission line including:

  • 98kM of 220kV overhead transmission line (38km wind region D and 60km wind region C) from North Star Junction station (20km from Iron Bridge mine) to Kanyirri Station (Port Hedland).
  • Single circuit with double overhead Optic Fibre Ground Wire (OPGW) for the entire line length.
  • Zero degree shielding angle for the entire line.
  • Earthworks design for construction of pads and track access for all poles.

Challenges Overcome

  • Design poles to optimise the span length and reduce the overall number of poles and stays.
  • Design Line route with limited corridor with rail lines and comms tower restrictions.
  • Position poles and stays to avoid numerous services and constraint along the line route including underground fibre optic, heritage areas and telecom.
  • Design pole Geometry to achieve zero degree Shielding angle.
  • Maintaining 3.1m flash over distance of conductor under no wind conditions from any structure.
  • Maintaining switching, lighting and power frequency clearance at wind conditions.
  • Tight project timeframes.

Solution

  • Extensive pole optioneering process was performed to determine a feasible pole height. Achieved >500m spans for single circuit 220kV line
  • Selection of limited common pole heights (30.8m / 36m / 40m) and strength rating across the line to increase efficiency with procurement and construction.
  • Positioned poles to avoid exceeding a selected maximum moment at the base of the pole to ensure a standard and cost-effective foundation type is suitable.
  • Different cross arm lengths were selected for each phase to ensure that phase conductor falls directly under the OPGW. CDEGS modelling performed to validate design.
  • 3D model prepared to ensure minimum 3.1m phase to earth/structure clearance is achieved.
  • Design incorporated special insulator hangers on crossarms to ensure lightning/switching and power frequency clearances maintained.
  • Pole locations were selected to maintain required set back from all the underground and above ground services and heritage areas.
  • Working collaboratively with the client with frequent meetings and status reporting.

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