A smart roadmap for transmission line relocation

Image: Zinfra Mandalong
Image: Zinfra Mandalong

When Centennial Coal announced plans to extend the underground operations of its Mandalong Mine, the impact on existing above-ground power infrastructure had to be considered. Relocation of a section of transmission line offered the best solution, with Zinfra utilising its strong capabilities in the power sector to deliver an excellent outcome on a complex and challenging project.

Earlier this year, Zinfra was engaged by TransGrid to relocate a 2.4km section of its 330kV transmission line (TL24), including the removal of 12 existing steel towers and the installation of eight new steel towers situated on a new alignment, to enable the extension plans for the mine.

This section of transmission line represented a significant constraint to the plan to extend the southern area of Centennial Coal’s Mandalong Mine in New South Wales.

A feasibility study carried out by TransGrid had confirmed that the best way to manage subsidence-related impacts on its infrastructure within the mine’s Southern Extension Area was to relocate the relevant section of TL24.

The complex project involved the following key stages: establishment of access tracks and clearing of the required 60m wide easement; construction of the tower foundations and establishment of towers for the new section of TL24; stringing and cutting-in of lines on the new section of TL24; the removal of redundant TL24 structures, and the remediation of existing easements.

“The main focus in a lot of our work, especially in transmission lines, is outage dates. With a line deviation, the major outage date is the cut-in, where the new section of the line is connected to the existing line and energised, and we successfully completed our works on the original cut-in dates,” Zinfra Project Manager, Rebecca Hampson, said.

Minimal community impact through strong stakeholder management

Zinfra gained possession of the site on 9 October 2017 and achieved practical completion mid-September 2018, ahead of the expected 12 month construction period.

Ms Hampson said that proactive and effective stakeholder management was essential throughout the project, as the works were impacting on a number of the neighbouring properties.“It was a combined effort between Zinfra, TransGrid and Centennial Coal to ensure that our works had minimal impact on the surrounding land owners, both in regards to noise and also the traffic going in and out.”

An outstanding example of safety and quality

Helicopters were used during the stringing process due to the hilly terrain which posed additional challenges when installing the new line.

“There was a section of the line that wasn’t cleared underneath, so we were pulling conductors over trees. The line was also on quite a sharp angle for a couple of the towers which is challenging when you’re trying to feed the conductors through,” Ms Hampson said.

The project underwent rigorous safety and quality checks, passing both with flying colours.

“The site was well managed by an experienced Construction Manager and highly skilled subcontractors. There was ongoing safety monitoring – we provided monthly safety and quality audit documentation to TransGrid, and Centennial also conducted weekly site inspections,” Ms Hampson said.

“During this project, we had three quality audits. There was an external auditor employed by TransGrid, an internal audit carried out by Zinfra’s safety team, and an additional corporate audit that was undertaken by the Zinfra head office.

“The report detailing the outcome of the corporate audit was well received by all, and circulated within Zinfra as a leading example of what other projects should be aiming for in terms of overall safety reviews.

“Furthermore, the project achieved a runner-up place in an internal competition run by TransGrid based on customer satisfaction. The result was really pleasing, considering it was another Zinfra project that took first place.”

We acknowledge the Traditional Owners of the lands upon which we operate and recognise their continuing connection to land, waters, and culture. We pay our respects to their Elders past and present.

Pictured: Artwork by Aboriginal artist Chern’ee Sutton from Mount Isa for our Group’s Reconciliation Action Plan.