We were unable to post about this yesterday, but a belated article today as something we might expand on later (and reference in GenInsights Quarterly Update for 2024 Q2 , when we come to compile that).
At 11:22 on Friday 12th April, the AEMO noted MN116095 as follows:
‘——————————————————————-
MARKET NOTICE
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From : AEMO
To : NEMITWEB1
Creation Date : 12/04/2024 11:22:09
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Notice ID : 116095
Notice Type ID : POWER SYSTEM EVENTS
Notice Type Description : Emergency events/conditions
Issue Date : 12/04/2024
External Reference : Non-credible contingency event – TAS region – 12/04/2024
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Reason :
AEMO ELECTRICITY MARKET NOTICE.
Non-credible contingency event – TAS region – 12/04/2024
At 1048 hrs the Sheffield – Farrell No.2 220 kV line tripped during restoration due to fault on the line.
AEMO did not instruct load shedding.
AEMO has been advised of disconnection of major industrial load approximately 550 MW.
The cause of this non credible contingency event is not known at this stage.
Manager NEM Real Time Operations
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END OF REPORT
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By our calculations, a 550MW tripping of major industrial load represents at least three large energy users in Tasmania (some of them our clients for reasons such as these), and potentially four or more.
This was followed at 13:39 with MN116098 noting the following:
‘——————————————————————-
MARKET NOTICE
——————————————————————-
From : AEMO
To : NEMITWEB1
Creation Date : 12/04/2024 13:39:23
——————————————————————-
Notice ID : 116098
Notice Type ID : POWER SYSTEM EVENTS
Notice Type Description : Emergency events/conditions
Issue Date : 12/04/2024
External Reference : Update – Non-credible contingency event – TAS region – 12/04/2024
——————————————————————-
Reason :
AEMO ELECTRICITY MARKET NOTICE.
Update – Non-credible contingency event – TAS region – 12/04/2024
Refer AEMO Electricity Market Notice 116095
At 1304 hrs the Sheffield – Farrell No.2 220 kV line was returned to service.
The cause of this non-credible contingency event has been identified and AEMO is satisfied that another occurrence of this event is unlikely under the current circumstances.
AEMO will not reclassify this event as a credible contingency event.
Manager NEM Real Time Operations
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END OF REPORT
——————————————————————-‘
We can see the significance of the event in this snapshot from NEMwatch this morning, looking back 24 hours, so incorporating the effect of this trip:
Uhh? Does anyone have a frequency plot for Tassie for event 1? A near 50% system load rejection is pretty huge. I assume the load was shaken off due to a severe voltage depression from switching onto a fault? Generation did not run back by 500MW so assume Basslink imports stopped. Dare I say a zone two distance protection operation from the opposite end so a slow clearance? What happened at 1.39pm? Generation went down so did this imply Basslink started to import again? Would be interesting to pull this one apart a bit more if someone has the operational data.