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. Prior to the commencement of the Very Fast FCAS markets on 9 October 2023, a review of the assumed load relief for the mainland and Tasmania region was completed in November 2019 and November 2020 respectively.
The amount of Contingency FCAS procured is equal to the size of the largest credible contingency minus assumed load relief. Load relief is an assumed change in load that occurs when power system frequency changes. It relates to how particular types of load (particularly traditional motors, pumps, and fans) draw less power when frequency is low, and more power when frequency is high.
Since the NEM commenced, mainland load relief has been assumed to be 1.5%; this means that for a 1% change in frequency (0.5 Hertz), the total mainland demand is assumed to change by 1.5%.
AEMO is acting on a recent review of load relief in the National Electricity Market (NEM). Accordingly, from September 2019, AEMO slowly reduced assumed mainland load relief from 1.5% to its current value of 0.5%, with a review point at 1%. Subsequently, AEMO’s analysis of power system events in the mainland during 2020 confirmed that a load relief value of 0.5% remains appropriate at this stage for the mainland NEM.
A further review in June 2023 based on a “bottom-up” analysis of load composition supports a load relief value of 0.5% as remaining appropriate at this stage for the mainland NEM.
Since the Tasmania Region joined the NEM, the Tasmania Region load relief has been assumed to be 1%; this means that for a 1% change in frequency (0.5 Hertz), the total Tasmania Region demand is assumed to change by 1%. AEMO is acting on a recent review of load relief in the Tasmania Region of the National Electricity Market (NEM). Accordingly, on 9 December 2020 AEMO will start reducing the assumed Tasmania Region load relief from 1% to 0%, at the rate of 0.1% per fortnight. The reduction is scheduled to be fully implemented before winter 2021.