Remote escarpment ranges is the latest challenge overcome by Powerlink Queensland as it builds a high voltage transmission network in the North West Surat Basin to support the state’s natural gas industry.
Powerlink executive manager infrastructure delivery and technical services Greg Rice said work in the Surat included constructing more than 200km of transmission line and seven connecting substations across a broad area bounded by Wandoan, Roma and Injune.
“This sizable network extension supports Queensland’s multi-billion dollar gas industry, which has generated thousands of jobs and boosted the local economy in the region,” Mr Rice said.
“A key component of the project was the continued input from the local community, industry and government stakeholders.
“Valued feedback from a range of stakeholders, particularly landholders, has led to Powerlink improving our engagement practices. Improvements to date have included the launch of our land access protocol, project participation and access allowance, and new route selection engagement models.”
In June, the Powerlink project team reached another key milestone in its Surat project work: it completed construction of the Eurombah to Fairview transmission line. This section of the extension is 55km in length and, when energised, will supply power to Santos GLNG facilities in the region.
“This means 80 per cent of the overall network extension is now complete – a testament to the ongoing hard work and agile thinking demonstrated by our teams on the ground,” Mr Rice said.
Powerlink project manager Aaron McGrath said constructing the Eurombah to Fairview transmission line required technical innovation to overcome several challenges.
“The area we needed to construct the transmission line through was incredibly hilly. This was further complicated by the presence of four escarpment ranges that were about 200m in height,” Mr McGrath said.
“Due to these landscape restrictions we had to use larger spans – some more than 850m between transmission towers. These factors added a level of complexity to numerous activities.”
Tension stringing was used for most of the transmission line due to the topography and other local constraints such as environmental and cultural heritage considerations.
“The tension stringing process uses a smaller 13mm diameter draw-wire, which is considerably lighter in weight compared to the standard 22mm draw-wire,” Mr McGrath said.
“The wire is flown into the alignment by helicopter and is skilfully dropped onto specially designed pulleys or rollers installed on the end of the tower cross-arms and earthwire peaks.”
To ensure this work was undertaken safely a number of factors had to be considered. Not only did the team have to allow for the extra draw-wire wind and weight loadings due to the large spans, the helicopter also had to adjust to unpredictable wind elements caused from varying wind flows around the top of the escarpments.
“An Airbus AS350 B2 helicopter was used to safely lift 1000kg of draw wire up the escarpments while under tension,” Mr McGrath said.
While the smaller draw wire is not capable of directly pulling through the larger twin phosphorus conductor, Mr McGrath said there were environmental advantages to having a second 22mm draw-wire pulled through via a brake and winch.
“This approach avoided broad scale clearing on the ground. This enabled us to conserve sensitive vegetation and other areas of significance such as cultural heritage areas,” he said.
Powerlink projects under way in the North West Surat
Powerlink has completed more than 30 transmission connection services for loads and generators in the past 15 years.
In 2012, Powerlink was engaged by Santos GLNG and Australia Pacific LNG (APLNG) to establish direct connections into the high voltage transmission network to supply power to future gas facilities in the North West Surat Basin.
Delivering the direct connections required by Santos GLNG and APLNG involves constructing seven substations and six transmission lines to provide the power needed for six gas facilities.
As part of the project planning phase, Powerlink worked with Santos GLNG and APLNG to reduce the impact to landholders and the community by making sure, where possible, a shared infrastructure arrangement was in place to minimise the overall footprint of the electricity infrastructure.
Challenges in building the Eurombah to Fairview transmission line: Operating alongside gas infrastructure
Construction of the transmission line involved detailed planning to take account of strict safety procedures in place when working alongside gas infrastructure.
An essential part of this included transparent co-ordination between all parties operating onsite to ensure open, two-way communication. One of the key mechanisms used during the construction phase was weekly Simultaneous Operations (SIMOPS) meetings with Powerlink, contractors and Santos GLNG representatives. The SIMOPS meeting process allowed all working parties to present their forecasted activities to ensure opportunities for concurrent activities were realised – thereby limiting impacts to landholders– and that other required activities took place in a sequential and safe manner.
The SIMOPS also ensured specific safety procedures were followed when working near gas infrastructure. This part of the project encountered 55 water and gas pipelines traversing Powerlink’s easement with another 14 overhead distribution powerlines.
To ensure the safety of all personnel, a stringent permit to works procedure was administered, particularly when working around buried pipelines.
The topography the transmission line had to cross was strongly undulating through to rugged country, with steep escarpments and sandstone outcrops. Given the terrain, the three main areas of focus were the preservation of biodiversity values (flora and fauna), pest/weed management, and erosion and sediment control.
To help protect the biodiversity values, comprehensive flora, fauna, weed and geological surveys were undertaken. Based on these surveys, during the construction phase Powerlink was able to avoid clearing in crucial areas such as semi-evergreen vine thicket (SEVT), melaleuca irbyana, and significant riparian areas. In the other areas, Powerlink adopted specific clearing techniques such as mega-mulching, selected hand clearing and general clearing. Overall, the objective was to avoid or limit broad scale full easement clearing and to promote a mosaic type clearing effect, which conserves valued vegetation.
Clearing techniques were also adapted to help protect the fauna. During the fauna surveys, brigalow scaly-foot lizard and the golden tail gecko were identified as being present. The onsite ecologists were able to provide strategies to protect the individual fauna and their wider habitat area.
In the valleys there were numerous river and creek crossings surrounded by predominantly sandy soils, which are moderate- to highly-erodible. To better manage the erosion of soils in this hilly terrain topsoil and mulch was applied to exposed cuttings. This method not only returned the nutrient-filled topsoil back to the exposed areas, the mulch also provided physical protection from rainfall run-off. As the mulch eventually breaks down, the seedbank within the topsoil will strike, allowing vegetation to grow on the cuttings for long-term stability.
To achieve the quantities required, the mulch was produced by a semi-trailer-mounted Diamond Z DZH700 horizontal grinder. Within a week this 1000hp machine was able to grind approximately 1000 cubic metres of mulch. This approach made valuable use of otherwise unusable timber piles from pre-cleared tower-sites and access tracks.
As part of its construction activities, Powerlink understood the local community would be sharing the road with construction vehicles as workers accessed substation and transmission line construction sites and temporary accommodation camps.
To manage the impact of construction-related vehicles, Powerlink produced a comprehensive whole-of-region Traffic Management Plan (TMP) in consultation with the Department of Transport and Main Roads and regional councils.
The plan took account of many factors, such as school bus routes, stock routes and road conditions. As part of the plan, control measures were implemented to protect the safety of all road users and reduce impacts associated with vehicle movements around landholder properties.
Specific actions implemented include:
• Decrease interruption to school bus routes by ensuring oversized vehicles travelled outside school times.
• Limited vehicle speed to 80km/h on high-impact roads and 40km/h on unsealed access tracks.
• Where possible reduced traffic by using mini-buses to transport workers to the construction sites from nearby accommodation camps.
• Used portable batching plants close to construction sites to reduce the movement of concrete trucks.
• Practice proactive dust management and water unsealed roads where possible.
• Reduced speeds when passing homes and other vehicles on unsealed roads.