Ancillary Services

One of AEMO's key roles is to determine, procure, and schedule Ancillary Services. The types of Ancillary Services in the WEM are listed below.

Load Following Ancillary Services (LFAS) is the primary mechanism in real time to ensure supply and demand are balanced. LFAS accounts for the difference between scheduled energy (what has been dispatched), actual load, and intermittent generation. Load following resources must have the ramping capability to pick up the load ramp between dispatch steps, as well as maintain the system frequency for other variations. Load following may be provided by units operating under automatic generation control (AGC). If a Facility is certified by AEMO as being capable of providing LFAS, it can then participate in the LFAS market.

Spinning Reserve Ancillary Services (SRAS) holds online capacity in reserve to respond rapidly should another unit experience a forced outage. The capacity can include online generation capacity, dispatchable loads, and interruptible loads (loads that respond automatically to frequency drops). There is currently no market for SRAS, however AEMO may contract with market participants individually to provide this service, with the costs involved set by the Regulator.

Load Rejection Reserve Ancillary Services (LRRAS) requires that generators be maintained in a state where they can rapidly decrease their output should a system fault result in the loss of load. This service is particularly important overnight, when most generating units in the system are operating at minimum loading and have limited capability to decrease their output in the timeframe required. There is currently no market for LRRAS, however AEMO may contract with market participants individually to provide this service, with the costs involved set by the Regulator.

Dispatch Support Service (DSS) ensures voltage levels around the power system are maintained, and includes other services required to support the security and reliability of the power system that are not covered by other balancing or Ancillary Services. There is currently no market for DSS, however AEMO may contract with market participants individually to provide this service. This process is overseen by the Regulator.

System Restart Service (SRS) allows parts of the power system to be re-energised by black start equipped generation capacity following a full (or partial) black out. Unlike other generators, black start equipped generators can be started up without requiring a supply of energy from the transmission network. There is currently no market for SRS as AEMO procures SRS services via an expression of interest (EOI) process. The details of this process are published when AEMO determines that new or replacement SRS services are required to:

  • assist AEMO in identifying Rule Participants who are interested in participating in a competitive tender process to provide SRS in the North Metropolitan and/or South Metropolitan subnetwork areas of the SWIS. 
  • conduct a preliminary assessment of those Rule Participants’ ability to meet the relevant technical criteria for the provision of SRS.

AEMO opened the SRS closed tender process on Monday, 31 August 2020. However, any additional Rule Participants who would like to submit a tender can email enquiries to  as soon as possible. AEMO will close this tender process on Wednesday, 30 September 2020.

AEMO has extended the SRS closed tender process, and will close this process on Friday, 23 October 2020, 5:00 PM WST.

Additional information on current dispatch system capability follows:

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