​To ensure the safe and reliable supply of electricity to the ACT, and support the future growth of the region, TransGrid has undertaken a joint project with the ACT Government and Evoenergy called the ACT Second Electrical Supply Project.

The project includes the construction of a substation and will ensure TransGrid’s electricity supply meets the reliability
level prescribed by the ACT Government.

As transmission network service provider for the ACT, TransGrid must comply with licence conditions which require provision of two independent

The standard includes the provision of two geographically separate 330 kV supplies to the ACT by 2020. TransGrid currently supplies the ACT load via its Williamsdale and Canberra substations. However, the Williamsdale substation is dependent on the Canberra substation. The requirement for a second, fully independent supply point is being met by the construction of a new substation located at Stockdill Drive.

The project involves construction of a:

  • 330 kV substation at Stockdill Drive
  • New 330 kV transmission line that links the new substation to TransGrid’s existing Canberra and Williamsdale substation, including some line rearrangements at the Canberra substation
  • New Evoenergy 132 kV transmission line connecting the Stockdill drive substation to the existing A1 Woden to Canberra 132 kV transmission line

Site works for the project commenced late last year, and it is expected that the project will be completed by December 2019.

Selecting the site

A number of factors influenced the decision to proceed with the Stockdill Drive substation site. The site needed to meet a range of criteria, including:

  • Security of supply
  • Impact on urban development potential
  • Environmental and heritage values
  • Cost of infrastructure construction
  • Land use planning, amenity and co–location
  • Technical requirements

After a rigorous site selection process and collaborative working group with ACT Government agencies, the Stockdill Drive was identified, and then approved by the ACT Government in March 2015.

Historically the ACT and surrounding areas have been supplied by a 132 kV transmission network emanating from the Canberra 330/132 kV Substation. While there is adequate capacity to supply the area, its location presented some challenges in efficiently supplying urban growth areas to the south-east of Canberra.

In considering the need for a second supply point, TransGrid also determined that the infrastructure should be located at a reasonable distance from the existing Canberra Substation to ensure that no single “catastrophic event” could disable both sites. This would ensure that the supply into the ACT would be maintained in the event of any one site being damaged.

As the project has evolved, it has also become apparent that there will be an opportunity to address the need to replace the aging 330/132kV transformers at Canberra Substation that have reached the end of their serviceable life.

Bringing the plans to life

2019 has been a busy year for milestones for the project. The year commenced with TransGrid obtaining leasehold on the site and shortly after the Department of Environment and Energy approved the Environmental Impact Statement.

In April, TransGrid received approval of the Construction Environmental Management Plan allowing construction to commence. At the time of print, TransGrid was planning to commence works on the transmission line and substation in the very near future.

Planning and design of this project has taken into account a range of forward-looking energy demand forecasts for the ACT, and working in partnership with the ACT Government has allowed TransGrid to understand the energy needs in the area with a lot of detail.

There have also been some ancillary works identified to help support future energy growth in the ACT, including line modifications and switchbay installations to support Evoenergy’s planned Molonglo Zone Substation (planned for construction in 2021) and Strathnairn Zone Substation (planned for construction approximately 2026) which will play a big role in supply to growing areas of the ACT.

Innovation in the substation

TransGrid has plans to utilise a range of innovative design and construction techniques through the development of this project.

Across the board, TransGrid is transitioning towards digital substations, having completed the Avon 330kV Switching Station in early 2018 using IEC61850 technology.

This was achieved by digitising the control and protection signals from the yard with the use of outdoor merging units into the Secondary Systems Building.

The benefit of using this design is reduced auxiliary power load and cables, resulting in significant savings on civil works associated with trenching and secondary systems buildings.

Further, the use of redundant merging units and Ethernet infrastructure improves reliability through the use of virtual duplicated protection systems.

For example the loss of a merging unit doesn’t impair the capability of the network and triggers an alarm.

Stockdill Substation is also atypical of TransGrid substations, with the ‘rain garden’ system incorporated into the drainage design. The use of earthen swales lined with pebbles, and a variety of native grasses, filter nutrients out of the soil and release clean water off the site.

The rain gardens are a result of collaboration with the ACT Government, and TransGrid’s environmental consultant WSP, and reduces the construction impact on the site.

Working in partnership

The project is being jointly undertaken by TransGrid, the ACT Government and Evoenergy, which has provided a unique set of challenges to work within.

All three stakeholders have formed strong working relationships as they moved towards site work commencement.

The hurdles along the way have been well managed and continually followed up by TransGrid to minimise any critical milestone delays.

TransGrid has a greater level of understanding of ACT requirements from the lessons learnt in the preparation of site works for Stockdill Drive and the required approvals processes when working in the ACT.

With construction now imminent, and completion scheduled for the end of the year, the project will provide Canberrans with an enhanced security of supply, critically important as we move towards a future that is more reliant on clean electricity delivered through our networks.

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