Transgrid Project Assessment Conclusions Report: Managing the risk of circuit breaker failure

Market Network Service Provider
StageProject Assessment Conclusions Report
ConvenorAEMO NSP
Accepting submissions?No

Transgrid has published a Project Assessment Conclusions Report (PACR) for Managing the risk of circuit breaker failure. Publication of this PACR represents the final step in the Regulatory Test for Transmission (RIT-T) process.

Circuit breakers are essential for the control and protection of the high voltage network. We have identified 122 circuit breakers on our network that will have reached or be approaching the end of their technical life by 2027/28. The probability of failure for these assets is high and is expected to increase as the assets age. If left unaddressed, this will result in greater unserved energy for consumers, greater safety and environment risk, and greater financial costs associated with emergency repair and replacements.

Given the high population of circuit breakers that have been identified for replacement, we consider it prudent and cost effective to manage this risk through a single asset replacement program. This replacement will help limit the amount of in-service failures that occur (along with the associated interruptions to customer load, and safety and environmental consequences).

Transgrid published a Project Specification Consultation Report (PSCR) for managing the risk of circuit breaker failure in May 2023.
In the PSCR Transgrid presented two credible network options that would meet the identified need from a technical, commercial, and project delivery perspective. This PSCR found that implementation of Option 2 is the preferred option. Under Option 2:

  • 55 of the 122 identified circuit breakers will be replaced with a DTCB. For these circuit breakers, the associated current transformers are approaching the end of their technical life.
  • 67 of the 122 identified circuit breakers will be replaced with a LHCB. For these circuit breakers, either replacement with a DTCB is not technically feasible, there is no associated current transformers, or the current transformers have substantial remaining life.

No submissions were received in response to the PSCR during the consultation period which closed in August 2023 and no additional credible options have been identified.

Option 2 remains the preferred option at this stage of the RIT-T process. The estimated capital cost of this option is approximately $41.50 million +/- 25 per cent. Transgrid is the proponent of the proposed network project.

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

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