Essential System Services

As part of the Wholesale Electricity Market’s (WEM) transition to Security-Constrained Economic Dispatch (SCED), the Essential System Services (ESS) will replace the existing suite of Ancillary Services.

As is the case currently, ESS will be used by AEMO to manage ongoing power system security.

Frequency Co-optimised Essential System Services

In the future, AEMO will 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 a FCESS will be able to seek accreditation and subsequently participate in any FCESS market for which their Facility is accredited.

Under the WEM Rules, those Facilities which are currently certified for Ancillary Services will be obligated to seek accreditation for the corresponding FCESS.


Existing Ancillary Service



Load Following Ancillary Services (LFAS)

Regulation Raise 

Regulation Lower 


Spinning Reserve Ancillary Services (SR)

Load Rejection Reserve Ancillary Services (LRR)

Contingency Reserve Raise 


Contingency Reserve Lower 



Rate of Change of Frequency Control Service

Non-Co-optimised Essential System Services

The Non-Co-optimised Essential System Services (NCESS) framework will replace the current frameworks for Network Control Services (NCS) and Dispatch Support Services (DSS) in the WEM Rules, and provide 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 Service, are procured on a case-by-case basis:

  • System Restart Service (SRS)
    • SRS will allow parts of the power system to be re-energised by black start equipped generation capacity following a full (or partial) black out.
  • Non-Co-optimised Essential System Services (NCESS)

Please contact AEMO via email 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:

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