Whilst some of those in South-East Queensland felt the ground shake this morning – Tasmanians felt their own tremors (of a different kind) in the afternoon of Saturday 16th August 2025 … as captured in an ez2view ‘Notifications’ widget alert as shown here at 14:11 (NEM time):
So we take a quick look…
In the ENERGY market
This 292MW drop in ‘Market Demand’ to the 14:15 dispatch interval can be seen in this snapshot from NEMwatch for the 14:15 dispatch interval:
That’s enormous, in relation to the size of the Tasmanian regional ‘Market Demand’!
Don’t forget about FCAS!
Reflecting the admonition from Allan O’Neil back in February 2020 with relation to another system event, here’s three consecutive dispatch intervals of the ‘NEM Prices’ widget in ez2view (i.e. 14:10, 14:15 and 14:20) showing some wild gyrations in FCAS prices as a result of the loss of ~30% of the ‘Market Demand’ in the Tasmanian region.
What’s the frequency, Kenneth?
Taking a quick look at our live frequency monitor (note – readings taken in Brisbane) suggests that there might have been a sharp spike to 50.10Hz around the time of the loss of load:
Assuming the demand drop was real (i.e. there’s been a few operational glitches in the AEMO data at times), you’d expect to be some spike in frequency until measures like PFR and FCAS took corrective action – but there’s the added vagaries of the Basslink frequency control scheme (i.e. for the DC link, for those not so familiar) to keep in mind in terms of how such would have transferred.
MN128546 … Basslink outage
Further, at 14:33 the AEMO published MN128546 as follows:
‘——————————————————————-
MARKET NOTICE
——————————————————————-
From : AEMO
To : NEMITWEB1
Creation Date : 16/08/2025 14:33:40
——————————————————————-
Notice ID : 128546
Notice Type ID : INTER-REGIONAL TRANSFER
Notice Type Description : Inter-Regional Transfer limit variation
Issue Date : 16/08/2025
External Reference : Inter-regional transfer limit variation – Basslink- VIC region – 16/08/2025
——————————————————————-
Reason :
AEMO ELECTRICITY MARKET NOTICE
Inter-regional transfer limit variation – Basslink – VIC region – 16/08/2025
At 1409 hrs 16/08/2025 there was an unplanned outage of Basslink.
The following constraint set(s) invoked at 1420 hrs 16/08/2025
I-BL_ZERO
This constraint set(s) contains equations with the following interconnectors on the LHS.
T-V-MNSP1
Refer to the AEMO Network Outage Scheduler for further information.
Manager NEM Real Time Operations
——————————————————————-
END OF REPORT
——————————————————————-‘
So it looks like the Basslink trip is the cause of the demand drop. Basslink was carrying ~330 MW southward at the time; there’s a Frequency Control Special Protection Scheme (FCSPS) set up in Tas to manage the risk of Basslink tripping. In this event the FCSPS immediately dumps an amount of Tasmanian load sufficient to offset the loss of imports.
The 292 MW scheduled demand drop is about the size of lost Basslink imports, indicating that it’s likely the result of operation of the FCSPS after Basslink tripped from 330 MW.
Thank you (both) for publicizing this event, which is potentially (pun intended !) Impactful on Tasmanian community activities.
Dead silence emanating from public media and Government.
Strengthens the case for a new cable link to mainland Australia?
I am still waiting for a public explanation (by a responsible authority) explaining intemperate cable overload protection adjustments, possibly in response to desire for increased revenue, directly related to previous BassLink cable failure.