Projects

Power: Dugald River Substation and Transmission Line

PROJECT OVERVIEW

The $280 million Granville Harbour Wind Farm is currently under construction near Zeehan, on the picturesque west coast of Tasmania. When complete, the wind farm will host 31 wind turbines that will produce up to 112 megawatts of clean, renewable energy available to Tasmanians; diversifying the state’s energy generation mix. This is enough electricity to power around 46,000 homes.

The wind farm will be connected to the Tasmanian grid via a new 12.5km transmission line that will join up to a connection point at the existing Reece Dam.

Zinfra were engaged by TasNetworks to design and construct the 11km Single Circuit 220kV Steel Pole Transmission Line, a 220kV Switching Station, and a 1.5km Dual Circuit 220kV Lattice Steel Tower Transmission Line across the Reece Dam wall connecting into the Hydro Tasmania Reece Power Station. Scope of works include:

• Clearing, stock piling and site development: Clearing of site vegetation;
  • Construction of temporary and permanent access tracks;
  • Benching and levelling of proposed construction area;
  • Stockpiling of construction aggregate.
• Switching Station design and construction:
  • 6 x 220kV disconnectors;
  • 3 x 220kV circuit breakers;
  • Associated post insulators & solid bus;
  • 12 x Capacitive Voltage Transformers (CVTs);
  • New conduit systems to new equipment;
  • New Pre-fabricated control building;
  • New fence arrangement;
  • New access track & associate internal pathways;
  • Associated secondary cabling and equipment;
  • Associated primary conductor and compression fittings.
• Transmission line design and construction:
  • 11km single and 1.5km dual circuit 220kV transmission line to the new Dual OPGW Circuit Pieman Switching Station;
  • Two new circuits with hard tee at the Farrell – Reece No.1 and No.2 translines adjacent to the Reece Power Station;
  • Pole and tower foundation designs allowing for foundation type selection based on confirmed ground conditions;
  • Pole and tower erection;
  • All associated stringing activities.

PROJECT DELIVERY

Challenging Weather Conditions

Occurring on the Tasmanian west coast, the project area receives a high monthly rainfall average exceeding 200mm. Construction of all-weather access tracks and hardstands resulted in nil inclement weather days being submitted for foundations despite these high rainfalls including the wettest month on record.

Environmentally Sensitive Area

The approved alignment for the line was designed to follow existing roadways and easements to minimise clearing of vegetation and impacts on sensitive environments. As such, the construction methodology focused on utilising helicopter stringing techniques to further minimise any impact to vegetation. Where practicable the height of vegetation for the clearance zone was increased towards the structures where wires were higher and in low areas such as gullies and creeks where there was increased ground clearance (as the line spans between elevated terrain points).

An avifauna management plan was also developed specifically to protect native species that may be present on site. All on-site personnel were trained to identify all threatened species likely to be encountered on site.

Constrained Tower Sites

A 3D modelling of tower 89A’s location was undertaken to provide optimum benching requirements to accommodate the tower and maintain access to the existing tower 90.

Poor Ground Conditions

Poor ground conditions were encountered along the transmission line which required special designs including the addition of large piers to achieve bearing capacity. A design and construction of micropile pole foundations also offered significant savings to the client over alternative latent condition foundations.

A high ground water table was also encountered at numerous structure foundations which required the optimisation of tower foundation types and micropiling. This provided further cost savings to the client.

PROJECT OUTCOMES

With over 33,795 hours worked to date (Jul 2019), the project has successfully maintained 0 LTI or environmental incidents.

To date, the project has achieved full EPA compliance during monthly audits with the project progressing to schedule despite latent conditions being encountered at numerous pole locations and high rainfalls.