TasNetworks has published the Project Specification Consultation Report (PSCR) for Managing safe and reliable operation of St Marys substation. Publication of this PSCR represents the first step in the Regulatory Investment Test for Transmission (RIT-T) process.
St Marys substation is located on the east coast of Tasmania, south of the township of St Marys. The substation supplies approximately 6,636 customers along almost 130km of the north-east coast of Tasmania, stretching from Coles Bay in the south to Binalong Bay in the north.
St Marys substation currently operates with two 10 MVA transformers – T1 and T2 – that were commissioned in 1966. However, peak loading of the St Marys substation exceeds 10 MVA. As such, the load supplied from St Marys substation is non-firm.
TasNetworks has identified that the transformers at St Marys are approaching their end of life based on condition assessment. In the event of a failure in one transformer, the remaining unit would be forced to operate above its 100% nameplate rating during peak demand periods, jeopardizing its operational limits. During peak demand periods, this scenario would force load shedding until a system spare is commissioned. In addition, these transformers do not align with current standard fire mitigation requirements and a fire incident could lead to the simultaneous loss of both transformer assets, increasing unserved load.
More broadly, the bushings of T2 are original and in the case of catastrophic failure the porcelain may shatter sending sharp projectiles across the switchyard. This is a safety concern to operators or adjacent in-service equipment. Finally, the transformer’s aged oil containment systems have deficiencies, which pose environmental risks in the event of oil leakages.
Addressing the condition issues of the transformers will enable us to manage reliability, financial, safety and environmental risks at St Marys substation. TasNetworks expects that addressing these issues will result in significant market benefits and, as such, we consider the identified need for this investment to be market benefits under the RIT-T.
We consider that there are four credible options from a technical, commercial, and project delivery perspective that can be implemented in sufficient time to meet the identified need. This PSCR has found that Option 1 is the preferred option at this stage of the RIT-T.
Option 1 involves completely replacing both St Marys transformers, along with associated oil containment systems. Specifically, both T1 and T2 transformers would be replaced in the 2024-2029 regulatory control period (R24).
The estimated capital expenditure associated with Option 1 is $7 million (in 2023/24 dollars). The works are estimated to take place between financial years 2023/24 and 2025/26, with practical completion and commissioning in the first half of financial year 2025/2026.
TasNetworks welcomes written submissions on materials contained in this PSCR. Submissions are due by 18th October 2024.
In accordance with the requirements of the Rules, a summary of the Project Specification Consultation Report is made available on the AEMO website. A copy of the PSCR can be obtained from TasNetworks’ website at Our current projects - TasNetworks or by emailing regulation@tasnetworks.com.au.