Transgrid has recently published a Project Assessment Conclusions Report (PACR) for managing risk of disconnector failure. Publication of this PACR represents the final step in the Regulatory Test for Transmission (RIT-T) process.
The identified need for this project is to ensure the safe and reliable operation of our transmission network by addressing the risk of failure of certain disconnectors that are approaching the end of their technical life.
There are 5,180 disconnectors installed in Transgrid’s network. Of this population, 30% will be over the nominal expected life of 40 years by 2027-28 and a strategic approach is required to plan investments over the coming years to manage these assets effectively and efficiently.
The disconnectors considered for replacement under this need are older disconnectors that have already reached their end of life. The failure of a disconnector is expected to result in additional equipment outages to isolate the failed disconnector for repair. In case of bus disconnectors this additional outage is significant due to the isolation of all other services from the affective bus bar. The potential outages are expected to disrupt customer and distributor supplies and increase corrective maintenance costs.
Addressing the condition of the identified assets provides the economic benefit of avoided involuntary load shedding to the NEM. We have classified this RIT-T as a ‘market benefits’ driven RIT-T as the economic assessment is not being progressed specifically to meet a mandated reliability standard but by the net benefits that are expected to be generated for end-customers. This means that options assessed within this RIT-T must provide net economic benefits compared to the base case if they are to be pursued.
In the PSCR Transgrid presented one credible network option that would meet the identified need from a technical, commercial, and project delivery perspective. The optimal commercially and technically feasible option presented in this PACR – Option 1 (disconnector replacement program) – is the preferred option to meet the identified need at this stage of the RIT-T.
No submissions were received in response to the PSCR during the consultation period which closed in November 2024 and no additional credible options have been identified.
Option 1 remains the preferred option at this stage of the RIT-T process. The estimated capital expenditure associated with this option is $21.46 million +/- 25 per cent in $2024/25 over the assessment period.
In accordance with the requirements of the Rules, a summary of the Project Assessment Conclusions Report is made available on the AEMO website. A copy of the PACR can be obtained from Transgrid’s website or by emailing regulatory.consultation@transgrid.com.au.