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 requirements, 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. 

AEMO conducts an annual assessment of the following:

• 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.
• Inertia – 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. 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 over a ten-year horizon.
• NSCAS – 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 Additional information on NSCAS, including the NSCAS tender guidelines and other historical documents, can be found on the Network support and control ancillary services procedures and guidelines page.

Under the National Electricity Rules, AEMO is also required to publish the Transition Plan for System Security. This report focusses on maintaining power system security in the NEM through the transition to a low-emissions power system over the coming decade. As of 1 December 2025, the Transition Plan for System Security (TPSS) incorporates the previously separate reports for system strength, inertia and NSCAS gap declaration.

AEMO’s assessment of system strength and inertia requirements, and NSCAS needs and gaps, are now available in the TPSS report.

Current methodology documents

The current methodology documents for System Strength, Inertia and NSCAS are presented below.

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.

Historical methodology documents

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

Historical assessments

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

This document presents AEMO’s 2024 assessment of the system strength requirements for each region over the coming 10 years. AEMO formally declares all shortfalls in the 2024 NSCAS report but references them in this report for informational purposes. 

This report implements 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.

This document presents AEMO’s 2024 assessment of NSCAS needs for each region over the coming five years, and assesses any potential NSCAS gaps to be addressed. 

This document also incorporates the AEMC’s final determination on the Improving security frameworks for the energy transition rule change, which includes assessment of inertia and system strength shortfalls over a three-year horizon until 1 December 2027.