Essential System Services

As part of Security Constrained Economic Dispatch (SCED), Essential System Services (ESS) are used by AEMO to maintain security and reliability of supply, thereby supporting the energy market.

Frequency Co-optimised Essential System Services

AEMO operate five Frequency Co-optimised Essential System Services (FCESS):

  • Regulation Raise
  • Regulation Lower
  • Contingency Reserve Raise
  • Contingency Reserve Lower
  • Rate of Change of Frequency (RoCoF) Control Service

Market Participants with Facilities which meet the Performance Requirements for an FCESS can seek accreditation and subsequently participate in any FCESS market for which their Facility is accredited. If insufficient FCESS is projected to be available in the Real Time Market (RTM), AEMO can trigger longer-term procurement of FCESS through the Supplementary Essential System Service Mechanism (SESSM). The ERA can also trigger the SESSM where FCESS market outcomes are inconsistent with competitive provision.

Non-Co-optimised Essential System Services

The Non-Co-optimised Essential System Services (NCESS) framework has replaced the current frameworks for Network Control Services (NCS) and Dispatch Support Services (DSS) in the WEM Rules and provides a more efficient framework for transparently identifying the need, specifying the requirements, procuring, dispatching and recovering costs for new types of ESS not already catered for under FCESS.

NCESS, including System Restart Services (SRS), are procured on a case-by-case basis:

NCESS can be procured by AEMO or the Network Operator where an NCESS procurement process is triggered by the Coordinator. The NCESS framework is designed to support system and network needs which are not being met through the existing market mechanisms (clause 3.11A.2(e) of the WEM Rules) or can be more economically procured through contracting. Examples to date have included services to mitigate minimum demand events.

System Restart Services

AEMO procures System Restart Services (SRS) in the unlikely event that it will need to restart the system following a widespread blackout of the SWIS (a ‘system black’ event). AEMO procures these services contractually under the framework in the WEM Rules.

Please contact AEMO at for general enquiries or technical enquiries regarding the procurement of these Essential System Services.

For more information on the Essential System Services framework, please refer to the below resources:

Chapter 3.9 describes the details for each ESS.

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