Planning for operability

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 years as part of its obligations to assess system strength, inertia and Network Support and Control Ancillary Services (NSCAS) requirements and shortfalls. Any shortfall declarations must be addressed by the transmission network service providers (or by AEMO in some cases for NSCAS).

This page provides AEMO’s system strength, inertia and NSCAS assessments, collectively known as the System Security Reports under the National Electricity Rules (5.20). Further information on AEMO’s other planning and coordination for power system security can be found on the Integrated System Plan (ISP)  and Renewable Integration Study (RIS) and Power System Frequency Risk Review (PSFRR) pages.

Current assessments

On 17 December 2021 AEMO published the 2021 System Security Reports providing system strength, inertia and NSCAS assessments for the next five years.

Methodologies, procedures and position statements

System strength

AEMO sees system strength as the ability of the power system to maintain and control the voltage waveform at any given location in the power system, both during steady state operation and following a disturbance. More information about system strength can be found in AEMO’s System strength explained, and AEMO’s Power System Requirements reference papers.

To meet its obligation to consider system strength requirements in the NEM, AEMO:

• Publishes a system strength requirements methodology (provided below).

• Determines system strength requirements, including fault level nodes in each region and a minimum three phase fault level at each node, using fault level as a proxy for system strength.

• Assesses whether there is or is likely to be fault level shortfall in the region for the upcoming five-year period. 

Inertia

Inertial responses provide a rapid and automatic injection of energy to suppress rapid frequency deviations, slowing the rate of change of frequency in the power system. A lack of inertial response can present risks to system security in the event that affected regions become separated from the rest of the NEM. More information about inertia can be found in AEMO’s Power System Requirements reference paper.

To meet its obligation to consider inertia requirements in the NEM, AEMO:

• Publishes an inertia requirements methodology (provided below).

• Determines the minimum threshold level of inertia for when a region is either islanded from the rest of the NEM or at credible risk of separation.

• Determines the secure operating level of inertia for when a region is electrically islanded.

• Assesses whether there is or is likely to be an inertia shortfall in the region for the upcoming five-year period.

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

To meet its obligation to consider NSCAS needs in the NEM, AEMO:

• Develops and publishes a NSCAS description and quantity procedure (provided below).

• Assesses NSCAS needs for the upcoming five-year period.

• Publishes NSCAS tender guidelines, for cases where AEMO tenders for NSCAS rather than the transmission network service provider.

AEMO has now completed consultation on amendments to the NSCAS description and quantity procedure, with details available on the 2021 Network Support and Control Ancillary Services Description and Quantity Procedure Consultation page.

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

Previous version of the NSCAS description and quantity procedure:

The consultation materials on version 2.1 can be found on the 2020 NSCAS Description and Quantity Procedure Amendments consultation page.

Historical assessments

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