System Strength Withstand SCR Methodology Review
AEMO is currently investigating an issue with the application of Withstand Short Circuit Ratio (SCR) test methodology in the System Strength Impact Assessment Guidelines (SSIAG). As defined in the SSIAG, the tests do not contemplate active power absorption by connecting plant and can result in power transfer limits being breached. This represents a gap in the current test methodology which results in plant being incapable of simultaneously satisfying the requirements of the acceptance criteria in the SSIAG for maximum active power absorption in weak grid conditions. The absence of clear guidance on the appropriate methodology to be applied to plant that absorbs active power is impacting some projects in the connections process, and has resulted in a variety of approaches being adopted to overcome the issue.
A technical note has been prepared setting out the theory, analysis, and proposed clarifications and adjustments to the test methodology. AEMO has undertaken early engagement with NSPs to seek input and feedback on the proposed methodology. In addition, AEMO is engaging directly with industry stakeholders that have experienced the issue in the past. Any other interested parties are welcome to make contact to discuss the technical note.
To enable transparency with industry the technical note has been published. The note provides an update on progress, the proposed way forward, and assists industry to prepare for future consultations. Following early engagement, an updated technical note that provides detailed guidance on specific tests is expected to be published in November 2024. Formal consultation in accordance with the Rules consultation procedures will be undertaken prior to any amendment to the SSIAG being implemented.
Application of the adjusted methodology
AEMO considers the approach proposed in the technical note best gives effect to the intent of the current SSIAG methodology. In the absence of clear guidance in the SSIAG on the appropriate methodology to apply to plant that absorbs active power, AEMO encourages NSPs to consider adopting the principles of the methodology proposed in the technical note. This will assist in developing a consistent methodology across the NEM as compared with the variety of approaches which have been employed to date. It will also inform ongoing work to review and refine the SSIAG methodology in advance of future amendments to the SSIAG.
AEMO recognises that resolution of this issue is occurring in parallel with projects already progressing through the connections process. Impacted stakeholders are encouraged to raise questions or concerns with the connecting NSP and the respective Onboarding and Connections Engineering lead. Onboarding and Connections can also be reached by emailing contact.connections@aemo.com.au.
SSIAG amendment
AEMO is committed to working with industry to resolve known issues with the system strength framework, as set out in the System Strength Status Report prepared by the System Strength Market Body Working Group. AEMO is intending to carry out two tranches of consultation on amendments to the SSIAG in 2025 and 2026 to balance timely resolution of issues, while minimising the number of changes that may impact investment certainty.
The Withstand SCR test methodology adjustments are planned for inclusion in the first tranche of amendments to the SSIAG with consultation commencing in Q1 2025.