System Strength Impact Assessment Guidelines amendment consultation

Market National Electricity Market
StageFinal Report
ConvenorAEMO NEM
Accepting submissions?No


  • Draft report and draft SSIAG published
    22 April 2024
  • Submissions due on draft report and draft SSIAG
    21 May 2024
  • Final report and final SSIAG
    28 June 2024

Key contact

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AEMO has concluded consultation on amendments to the System Strength Impact Assessment Guidelines (SSIAG) following the Australian Energy Market Commission’s (AEMC) final determination on Calculation of System Strength Quantity rule change.


In April 2023, AEMO identified that applying the System Strength Quantity (SSQ) formula in the NER, without adjustment, could significantly overstate the quantity of system strength required to support each connection. AEMO published guidance on Calculating system strength quantities in the NEM in May 2023 outlining the issue and proposing an adjusted formula that incorporates a stability coefficient, the same value applied in the reduction in available fault level (AFL) calculation.

In September 2023, AEMO submitted a rule change proposal to the AEMC proposing amendments to relevant clauses of the NER. The AEMC completed industry consultation and made its final determination and final rule on 29 February 2024.

The final rule requires AEMO to update the SSIAG in consultation with stakeholders by 30 June 2024, with an effective date of 1 July 2024.

Key changes

The final amendments to the SSIAG are set out in detail in the final report, and summarised below:

  • Incorporates a methodology to calculate SSQ, including guidance on the inputs and assumptions
  • A number of minor and administrative changes, including:
    • The introduction of terminology and concepts that are consequential on amendments to the NER made by the Integrating Energy Storage Systems (IESS) Rule, for which full implementation occurred on 3 June 2024
    • Clarification of the way in which the existing concept of the stability coefficient is defined and described
    • Clarification of the number of decimals to be used in calculating the Withstand SCR
    • A requirement for AEMO to provide reasons if it forms the opinion that a proposed plant alteration will have a general system strength impact
    • A requirement for physical elements within the models used for Withstand SCR testing to be identical to the models used for negotiation of Performance Standards
    • Other minor corrections and clarifications

AEMO has also updated the System Strength Framework Frequently Asked Questions Factsheet to improve clarity and further reflect stakeholder feedback on broader SSIAG matters.

The updates include:

  • Information and timing requirements for classification of inverter based loads
  • PSS®E short-circuit calculation method for system strength locational factor calculation
  • Consideration of harmonic filters for Withstand SCR assessment
  • Type of simulation tools for Withstand SCR assessment

Further work on broader system strength issues

As the system strength framework is increasingly tested through practice, AEMO recognises that there are several broader issues that may arise, requiring investigation and subsequent consultation with industry. A market bodies working group (comprising the AEMC, AER and AEMO) has been established to monitor, prioritise and respond to these issues.

The market bodies working group is developing a system strength framework status report that summarises the issues identified to date and planned actions to address these issues. The report is expected to be published in July 2024 and will be updated as actions are progressed, or new issues are identified.

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