TransGrid has recently published a Project Assessment Draft Report (PADR) for managing asset risks at Sydney South substation.
Sydney South substation:
- supplies most of the load in Sydney CBD, Eastern suburbs and South Sydney
- is the largest bulk supply point for Ausgrid’s distribution network with growing summer maximum demand at approximately 1,177 MW in 2019/20
- must meet redundancy category 3 reliability standards with only 0.6 minutes of expected unserved energy allowed each year across Inner Sydney.
Corrosion has been found on a large portion of gantries at Sydney South substation. The corrosion of holding down bolts and structural components, or ‘members’, ranges from initial development through to loss of steel thickness (cross-sectional area).
TransGrid’s analysis indicates that the holding down bolts and gantry members will reach the end of serviceable life by 2021. After this time, the loss of physical cross-sectional area from corrosion will decrease their capacity to provide structural support. This reduces structural integrity and significantly increases their probability of structural failure, especially during high wind events. Deterioration of holding down bolts has occurred across the site and action is required on the majority of structure footings.
If unaddressed, these issues may cause failure of gantries resulting in widespread outages and damage to other substation equipment.
TransGrid published a Project Specification Consultation Report (PSCR) for managing asset risks at Sydney South substation in September 2018. No submissions were received in response to the PSCR during the consultation period which closed in December 2018.
At the time of publication the cost estimate for refurbishing the Sydney South substation gantries was primarily based on a desktop assessment of the activity required to refurbish the gantries.
TransGrid has since undertaken additional investigations and onsite trials, in particular testing different blasting techniques. As the cost estimate of refurbishing the gantries outlined in the PSCR was much lower than the current estimates, more time has been spent developing better ways to address the need.
In this PADR, TransGrid has updated the cost estimates and developed a new option to replace the gantries, which would result in a 45-year life extension.
The PADR outlines two credible options that would meet the identified need from a technical and project delivery perspective:
- Option 1: in-situ renewal of the steelwork by removing corrosion, painting and replacement of components where required
- Option 2: replace the gantries
The preferred option, Option 2, involves the renewal of holding down bolts and replacing the gantries at Sydney South substation. In particular, this involves the remediation of substation gantries at Sydney South substation by, in a staged manner:
- Stage 1: treating corroded holding down bolts
- Stage 2: removing and replacing existing corroded gantry structures with new gantries
The resulting structures are expected to have a life of 45 years.
It is expected that the remediation works will be undertaken in various stages. The two broad stages to replacing all corroded elements are:
- Planning and procurement (including completion of the RIT-T) between 2018/19 and 2020/21
- Project delivery and construction between 2020/21 and 2023/24
The estimated capital cost for Option 2 is $42.5 million (-/+ 25%) in 2019/20 dollars. TransGrid is the proponent of the proposed network option.
In accordance with the requirements of the Rules, a summary of the Project Assessment Conclusions Report is made available on the AEMO website.
Submissions in response to this Project Assessment Draft Report are required by the closing date of 21 January 2020.