Ancillary services causer pays contribution factors

One of the features of the ancillary service market is that only the costs for frequency control regulation services are to be allocated in accordance with the contribution factors, as set out in clause 3.15.6A of the National Electricity Rules and detailed in the following causer pays procedure.


Under the Rules, AEMO must update these contribution factors every four weeks, and publish the factors at least 10 business days prior to them being applied in the market.

The Rules also require AEMO to publish the historical data used to calculate these factors. This historical data is available here on the AEMO web site.

Final factors used in settlements may vary slightly from previously published values due to minor error corrections.

AEMO calculates contribution factors normalised according to region demand. 

Ancillary Service Market Causer Pays factors - application period 8 August 2021 to 4 September 2021.

The dispatch intervals were discarded in the contribution factor calculation process for the sampling period 20 June 2021 to 18 July 2021 for reasons other than the effect of contingencies and the data samples where FI and system frequency were mismatched, are listed in Exclusions List (pdf).

The number of dispatch intervals that were discarded in the contribution factor calculation process for the sampling period 20 June 2021 to 18 July 2021 due to contingencies that caused the power system frequency to leave the normal operating frequency band are:

Tasmania – 285 dispatch intervals

Dispatch intervals are automatically excluded if a significant proportion of the 4-second data has been excluded due to a mismatch of frequency and Frequency Indicator (refer to clause 4.4.2(c) of the Regulation FCAS Contribution Factors procedure). Previously a threshold of 50% has been used, however based on operational experience following the implementation of AGC changes for Primary Frequency Control in December 2020, AEMO has increased the threshold to 66%. This means that for factors published from 25 June 2021 onwards, a dispatch interval will be excluded if more than 66% (or 50 of the 75 values) of 4-second data is mismatched.

Documentation 2021

Documentation 2020

Documentation archive

Older archived files

For older documentation please contact the AEMO Information and Support Hub.

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