Western Australia: South West Interconnected System.
Status: operational.
Wholesale design: Bilateral-contract market with a real-time security-constrained dispatch market. Since 1 October 2023, the Real-Time Market co-optimises energy and Frequency Co-optimised Essential System Services (FCESS).
Operator
Australian Energy Market Operator (AEMO)
Nominal frequency
50 Hz
Where energy trades
Where does energy trade in Wholesale Electricity Market (WEM)?
Energy in Wholesale Electricity Market (WEM) trades in 3 layers: real-time energy, short-term energy market and bilateral contracts.
What a battery can sell
What ancillary services can a battery sell in Wholesale Electricity Market (WEM)?
Wholesale Electricity Market (WEM) has 5 ancillary-service products, across 4 families — regulation, contingency reserve, inertia & system strength and emergency control: Contingency Reserve Lower, Contingency Reserve Raise, Regulation Lower, Regulation Raise, Rate of Change of Frequency Control Service. Response timing, direction and eligibility for each are in the cards below, as the official sources state them.
Facts below are stated as the official sources state them. A missing line means the
source does not state that value — never that the value is zero.
Regulation
Regulation Lower REG_LOWER
operational
Frequently adjust injection or withdrawal under central control to lower SWIS frequency toward the Frequency Operating Standard.
Direction
lower generation; raise load
Expected within
5 seconds
Trigger / range
AEMO AGC desired-MW signal; no fixed public frequency threshold.
Eligibility
AEMO-accredited facilities meeting AGC, SCADA, communication and performance requirements.
Typical procurement
AEMO calculates interval-specific requirements.
Five seconds is maximum communication/control response lag, not full activation. Full activation and hold depend on accredited capability and dispatch.
Regulation Raise REG_RAISE
operational
Frequently adjust injection or withdrawal under central control to raise SWIS frequency toward the Frequency Operating Standard.
Direction
raise generation; lower load
Expected within
5 seconds
Trigger / range
AEMO AGC desired-MW signal; no fixed public frequency threshold.
Eligibility
AEMO-accredited facilities meeting AGC, SCADA, communication and performance requirements.
Typical procurement
AEMO calculates interval-specific requirements under the ESS Quantities Procedure.
Five seconds is the maximum communication/control response lag from receipt of the AEMO signal, not a universal full-ramp deadline. Full activation and hold depend on accredited ramp capability and dispatch.
Contingency reserve
Contingency Reserve Lower CR_LOWER
operational
Hold rapid downward response to contain frequency after a credible over-frequency contingency.
Direction
lower generation; raise load
Sustain
at least 15 min
Trigger / range
Automatic frequency-sensitive response after a contingency; facility-specific settings are accredited.
Dynamic requirement under the ESS Quantities Procedure.
No single market-wide full-activation deadline; accredited response capability applies. Sustain requirement is at least 15 minutes.
Inertia & system strength
Rate of Change of Frequency Control Service ROCOF
operational
Provide inertia or inertia-equivalent capability that limits the initial rate of change of SWIS frequency after a contingency.
Direction
symmetric
Full activation
0 s
Trigger / range
Inherent instantaneous response to RoCoF following a disturbance; no dispatch trigger threshold.
Eligibility
Facilities accredited for synchronous inertia or qualifying equivalent response under ESM Rules and procedures.
Typical procurement
Requirement is expressed through system inertia/RoCoF constraints, not a stable MW volume.
The service is procured as inertia contribution rather than an activated MW step, so there is no sustain duration to state.
Emergency control
Contingency Reserve Raise CR_RAISE
operational
Hold rapid upward response to contain frequency after a credible contingency and avoid under-frequency load shedding.
Direction
raise generation; lower load
Sustain
at least 15 min
Trigger / range
Automatic frequency-sensitive response after a contingency; facility-specific droop/block settings are accredited.
Eligibility
Accredited generation, storage or interruptible load; minimum certified response and technical tests apply.
Typical procurement
Dynamic Frequency Control Model quantity based on credible contingency size, inertia and facility performance.
No single market-wide full-activation deadline. Accreditation assigns a Facility Speed Factor from accepted bands 0.2, 0.5, 1, 3, 6, 10 or 15 seconds; the response must be sustainable for at least 15 minutes.
Getting paid to exist
Does Wholesale Electricity Market (WEM) have a capacity mechanism?
Yes — Reserve Capacity Mechanism is a central capacity market.
Reserve Capacity Mechanism
operational
AEMO determines Peak and Flexible Reserve Capacity Requirements, certifies facilities, assigns Capacity Credits and pays formula/administratively determined Reserve Capacity Prices for a future Capacity Year. Bilateral trade declarations and security obligations apply.
Auction held in 2025
No — No capacity auction for this market was found to have been held during 2025 in the sources reviewed.
The 2025 Reserve Capacity Cycle produced capacity-credit and price outcomes but was not a competitive clearing auction, so it is not counted as one here.
Caveats
Technical notes
Five FCESS products are co-optimised in real time; supplementary procurement may be triggered where market supply is insufficient.
Current as of · from the
Global Electricity Market Catalogue v1.2.0 (compiled to , CC BY 4.0). Facts belong to the linked official authorities;
verify the current rules before design or bidding decisions.
Questions
Common questions about Wholesale Electricity Market (WEM)
Who operates Wholesale Electricity Market (WEM)?
Australian Energy Market Operator (AEMO) operates Wholesale Electricity Market (WEM), covering Western Australia: South West Interconnected System.
Was a qualifying capacity event held in Wholesale Electricity Market (WEM) in 2025?
No. Reserve Capacity Mechanism: no qualifying 2025 event is recorded. No capacity auction for this market was found to have been held during 2025 in the sources reviewed.
How is energy traded, priced and settled in Wholesale Electricity Market (WEM)?
Wholesale Electricity Market (WEM): Bilateral-contract market with a real-time security-constrained dispatch market. Since 1 October 2023, the Real-Time Market co-optimises energy and Frequency Co-optimised Essential System Services (FCESS).