Very Fast FCAS Market Transition

In the NEM, there are eight Contingency FCAS markets, designed to ensure there is enough frequency response in the system to deal with a single credible contingency, which is typically the loss of a large generating unit or major industrial load.

The Very Fast Raise and Very Fast Lower Contingency services were introduced on 9th October 2023.
The amount of Very Fast Contingency FCAS (VF FCAS) procured will be dependent on the size of the largest credible contingency, assumed load relief, and operating inertia levels.


The VF FCAS raise and lower markets each commenced operation on 9 October 2023 with a global NEM, system normal requirement that was limited at 50 MW. A market transition approach is intended to support the start of these markets by progressively increasing the allowed requirement volumes, while ensuring that sufficient capacity is registered and committed for VF FCAS market participation. This is being done with the objective of avoiding extended periods of supply shortage.

Market transition arrangements

AEMO will review levels of registered capacity that is committed for VF FCAS market participation on a monthly basis and decide whether the allowed requirement volumes can be incremented.
The size of increments and length of transition period will be dependent on the level of registered capacity and participation in the VF FCAS services.

Increments to the amounts required for islanded NEM regions will be made separately, recognising that the volume of VF FCAS registered to support local versus global requirements may differ.

AEMO will regularly monitor Contingency FCAS performance throughout the transition and may revise allowed requirement volumes if any unexpected outcomes are noted.

Current allowed requirement volumes

 Participants will be notified of upcoming increments via Market Notices.

Date & time of implementation Very fast requirement type
 Requirement limit
15/04/2024 13:05
Global, lower
 200 MW
15/04/2024 13:05
 Global, raise 325 MW

Understanding underlying requirement volumes

Once sufficient supply is registered and participating in the VF FCAS markets, the requirement volumetric limits will be removed, and VF FCAS procurement will be equivalent to the underlying VF FCAS requirements.

For transparency reasons, AEMO provides the underlying VF FCAS requirements via ‘data snap’ constraints. These can be identified via constraint equations IDs starting with D_XXXXXX, with the constraint ID otherwise identical to the corresponding VF FCAS constraint.

These 'data snap' constraints calculate an uncapped VF FCAS requirement, with a RHS offset of -10,000 then applied to prevent them binding.

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