The Reliability Panel has made a final determination to revise the energy sector’s frequency operating standard (FOS) for a more secure and resilient power system for customers in the future.

As lower cost, variable inverter-based generation technologies such as batteries, wind and solar come online and thermal generators gradually leave the system, maintaining stable frequency and operation in the power system is becoming increasingly important.

Power system equipment, including generators, may disconnect from the power system if system frequency becomes unstable and changes too quickly, or varies too far from 50Hz, which can in the worst case, lead to the collapse of all or part of the power system.

Reliability Panel Chair Charles Popple said the improved FOS provides a solid foundation to help manage risks to system security going forward.

“Defining the operating range for the power system is fundamental to maintaining secure operation, which, in turn, means a reliable supply of electricity for customers and delivers reduced costs for customers in the longer-term,” Mr Popple said.

"The release of a revised FOS is also an important step towards defining the secure operating parameters for our low carbon energy system of the future.” 

The revised FOS features additions and amendments including:

  • introduction of system limits for rate of change of frequency (RoCoF) following contingency events that would likely involve the failure or sudden and unexpected removal of a generating unit or transmission element from the power system
  • changes to the limits and thresholds for contingency events, including the extension of the 144MW Tasmanian generation event limit to also include network and load events and aligning the thresholds for a generation and events in Tasmania
  • renaming of “supply scarcity” operating conditions to “system restoration” and revising the operational frequency tolerance band (OFTB) during system restoration
  • confirmation of the allowable ranges for frequency during normal operation, confirmation of the primary frequency control band (PFCB) consistent with the current setting in the Rules and clarification that the target frequency in the national electricity market (NEM) is 50Hz
  • removal of the limit for accumulated time error, while maintaining an obligation on the Australian Energy Market Operator (AEMO) to monitor and report on time error accumulation.

The proposed RoCoF limits in the revised FOS will formalise AEMO’s existing operational practices in light of reducing levels of system inertia, helping to manage the risks of contingency events, such as the failure of network infrastructure.

These arrangements will have flow-on benefits, promoting the timely investment of the services, such as synchronous and synthetic inertia, needed to help manage RoCoF after a contingency event. 

They will also support the implementation of new fast frequency response market ancillary services that can be provided by inverter-based technologies such as wind, solar PV, battery and demand-side resources.

The Panel’s determination to confirm the current PFCB settings in the FOS reflects advice from AEMO and GHD that controlling frequency closer to 50Hz delivers value to customers by reducing costs and increasing power system security and resilience. 

The proposed PFCB settings build on the AEMC’s recent rule change to establish a framework to incentivise market participants with frequency performance payments, which comes into full effect on 8 June 2025.

As part of its process, the Panel is recommending a follow-up review of the FOS to be completed by no later than the end of 2027, and that the review takes in the consideration of the normal operation settings and RoCoF settings.  

The revised FOS will come into effect on 9 October 2023. This date aligns with the commencement of the new market ancillary service arrangements for very-fast contingency FCAS, which provide fast frequency response.

Visit the project page for more information, contact details, and details on making a submission. 

Media:  Jessica Rich, 0459 918 964,