The Granville Harbour Wind Farm will capitalise on Tasmania’s enviable wind potential while helping the state achieve its target of 100 per cent renewable energy by 2022. Zinfra, one of Australia's leading utility infrastructure service providers, was responsible for designing and constructing the transmission line connecting the wind farm to the grid, giving the wind farm a physical connection to Tasmania’s energy network and bringing the state closer to delivering a new source of clean energy to households and businesses. Zinfra was able to make light work of the challenging conditions to deliver another successful grid connection project, showcasing its experience and expertise in the renewables sector.
Situated near Zeehan, on the picturesque west coast of Tasmania, the $280 million Granville Harbour Wind Farm will produce up to 112MW of clean, renewable energy when complete – enough to power around 46,000 homes.
The 31-turbine wind farm is connected to the Tasmanian grid via a 12.5km transmission line that joins up to a connection point at the existing Reece Dam.
Zinfra was 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.
Works commenced in September 2018 and included: vegetation management; construction of temporary and permanent access tracks; benching and levelling of the construction area; design and construction of transmission line foundations; supply and erection of poles and towers; and all associated stringing activities.
The switching station plant included disconnectors, circuit breakers, capacitive voltage transformers and a prefabricated control building to house the protection and control systems.
A QUALITY OUTCOME IN CHALLENGING CONDITIONS
Stephen Mayoh, Senior Project Manager at Zinfra, said that he was proud of his team for completing the project on time despite the challenging conditions. “It was a tight timeframe when you take into account the weather conditions that you get on the west coast. We also overcame several other challenges and still met the timeframe, which was a great result,” Mr Mayoh said.
Occurring on the Tasmanian west coast, the project area receives a high monthly rainfall average exceeding 200mm. The construction of all-weather access tracks and hardstands allowed the foundation construction to continue despite these high rainfalls, including the wettest month on record for 50 years. Mr Mayoh said that the transmission line also traversed environmentally sensitive areas.
“The approved alignment for the line was designed to follow existing roadways and easements to minimise impacts on sensitive environments,” Mr Mayoh said. “Helicopter stringing, a technique we use for when we’re stringing the wires, helped us further minimise any impact to vegetation. Where practical 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). A fauna management plan was also developed specifically to protect native species that may have been present on site. All on-site personnel were trained to identify all threatened species likely to be encountered. We also had constrained tower sites, with one particular tower site (89A) located on a steep hillside where there was an existing tower in place. 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. This exercise ensured we could fit the new tower safely and identify foundation systems that suited its location.”
Mr Mayoh highlighted that the one other challenge throughout the project was the poor ground conditions encountered along the transmission line, which added extra pressure on an already complex project. “There were a number of sites where a high groundwater table was encountered and we had to change our foundation systems, including the addition of large piers to achieve bearing capacity. We also went with a micropile pole foundation, which offered some significant savings for the client over alternative foundations considered. It was a one-off, but we wanted to provide the best outcome for both the site and the client.” Mr Mayoh said.
COLLABORATION CRUCIAL TO A SUCCESSFUL PROJECT OUTCOME
Zinfra shared site offices with the TasNetworks project team, working closely together as part of its commitment to effective stakeholder management. “Another key stakeholder was Hydro Tasmania. We drew on our previous experience working with them, and the relationship we have built with Hydro Tasmania, to help overcome any challenges we faced,” Mr Mayoh said.
“We also had regular meetings and contact with the owners of the wind farm to inform them of our progress and to coordinate construction activities. From a safety and quality side of things, Zinfra has processes and procedures in place to ensure we’re delivering successful project outcomes. The team all had a really positive attitude which helped contribute to approximately 55,000 hours of work with no lost time injury.” Mr Mayoh stated that one of the things he has found working in the renewables space is that once a project gets approval, there are tight timeframes on construction schedules. “The way that Zinfra was able to react and make sure it could hit the required commissioning times reflects highly on our skills and capabilities. When we encountered issues with the ground conditions and tower foundations on this project, we were able to move quickly to resequence activities and resource up to ensure we still met those key project milestones.”
Zinfra achieved practical completion in November 2019, and the wind farm is expected to be fully operational by mid-2020.