System Security Planning

AEMO is responsible for maintaining and improving power system security in the National Electricity Market (NEM) and for providing a national, strategic perspective for electricity transmission planning and coordination.

AEMO considers the need for any power system security and reliability services in the NEM over the coming five to ten years as part of its obligations to assess system strength requirements, inertia shortfalls, and Network Support and Control Ancillary Services (NSCAS) needs. Transmission network service providers must consider any declared gaps or shortfalls, and provide AEMO with details of their proposed remediation activities. In some cases, AEMO may intervene directly to resolve an NSCAS gap using its last-resort planning powers.

On 1 December 2023, AEMO published the latest System Strength, Inertia, and NSCAS reports which are presented alongside their relevant methodologies on this page. Together these reports assess what is needed to ensure power system security as the NEM transitions to a greater reliance on firmed renewables. A summary infographic is also provided below.

System strength

System strength is defined as the ability of the power system to maintain and control the voltage waveform at any given location, both during steady state operation and following a disturbance. More information about system strength can be found in
AEMO’s  System strength explained document. AEMO conducts an annual assessment of system strength requirements over a ten-year horizon and, assesses shortfalls out to until 1 December 2025.

These reports implement the AEMC’s final determination on the Efficient management of system strength. Further information on the impact of this framework on connecting parties can be found in AEMO’s System Strength Impact Assessment Guidelines.


An inertial response is a fast and automatic injection of energy to suppress rapid frequency deviations in the power system and slow the rate of change of frequency. A lack of inertial response can present risks to system security if affected regions become separated from the rest of the NEM. More information about power system inertia can be found in AEMO’s Inertia in the NEM explained document. AEMO conducts an annual assessment of inertia requirements and shortfalls over a five-year horizon.


Network Support and Control Ancillary Services (NSCAS) are non-market ancillary services that may be delivered to maintain power system security and reliability of supply of the transmission network, or to maintain or increase the power transfer capability of the transmission network. AEMO conducts an annual assessment of NSCAS needs and gaps over a five-year horizon.

Additional information on NSCAS, including the NSCAS tender guidelines and other historical documents, can be found on the Network support and control ancillary services procedures and guidelines page.

Reference Material

Information on AEMO’s other planning and power system security coordination activities can be found on the Integrated System Plan (ISP), Engineering Framework, and General Power System Risk Review pages.

More information about the technical and operational needs of the power system can be found in AEMO’s Power System Requirements reference paper.

The previous methodology documents for System Strength and NSCAS are presented below.

The 2018 Inertia Requirements Methodology is still in its first version.

Historical assessments

AEMO’s historical system strength, inertia and NSCAS assessments are presented below.

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