At 15:06 the AEMO published Market Notice 114625 as follows:
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MARKET NOTICE
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From : AEMO
To : NEMITWEB1
Creation Date : 13/02/2024 15:06:04
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Notice ID : 114625
Notice Type ID : POWER SYSTEM EVENTS
Notice Type Description : Emergency events/conditions
Issue Date : 13/02/2024
External Reference : Significant power system event – Victoria region – 13/02/2024
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Reason :
AEMO ELECTRICITY MARKET NOTICE.
At 1308 hrs 13/02/2024 the Moorabool Sydenham No1 and No2 500 kV lines tripped.
There have been reports of towers on the ground.
In the Victorian region
1000 MW of customer load lost during the fault has been restored
2690 Generation tripped
The AEMO instructed loadshed of 300 MW is being progressively restored.
Updates will be provided as additional information becomes available.
This Market Notice is issued in accordance with NER clause 4.8.3.
Manager NEM Real Time Operations
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END OF REPORT
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As highlighted, there are two important developments here:
1) Load shed earlier is being restored; but
2) There are rumours of transmission towers (and lines) on the ground.
Using ez2view at the 15:45 dispatch interval, here’s a view of the ‘Constraint Sets’ widget filtered down to Constraint Equations containing either ‘Moorabool’ or ‘Sydenham’ in the description:
The two x Constraint Sets highlighted here were both invoked from the 13:30 dispatch interval this afternoon (i.e. in response to the trip), and are at this time currently scheduled to last only until 17:00 today.:
1) The ‘V-MLSY_R’ constraint set has a description:
‘Out = Moorabool to Sydenham 500kV line, Radial Mode, EMTT scheme armed or other credible VIC-SA separation risk’
2) The ‘F-V-X_ML_BUSTIE_500’ constraint set has a description:
‘Out = combination of 500kV CBs at Moorabool (MLTS) leading to a single bus tie at Moorabool – FCAS requirements’
3) Also on the filtered gantt chart is the ‘V-X_MLSY’ constraint set, which …
(a) has a description:
‘Out = Both Moorabool – Sydenham (MLTS – SYTS) 500kV lines’
(b) was invoked at 15:05 (i.e. later than the above) and is currently invoked until 17:00.
So according to this table in the AEMO’s EMMS, the current expectation is that the lines will be returned to service … suggesting AEMO has not (yet?) confirmed the rumours of transmission lines on the ground?
There are pictures going around, but unless it is from a reliable source, then we still have to wait. If it is the case then we have had multiple events causing multiple failures with those 500kV towers. In both situations the towers were rated to handled higher wind speeds than those that generally occur around the events. Meaning we would have to either have a fault in the material, design, construction or maintenance of the towers, or we have had two previously extremely rare weather events within a year or so of each other.
I can only recall one incident with collapse of 500 kV towers, namely the collapse of the group of towers near Cressy in Jan 2020 which islanded SA. The 500 kV lines west of Moorabool are on double circuit towers. The 500 kV lines east of Moorabool, which tripped today, are on single circuit towers of completely different design.
There was the collapse of one double circuit 275 kV tower near Tailem Bend in Nov 2022 in a freak storm. A 220 kV tower near Poatina in TAS collapsed due to a landslip in Oct 2022. Back in Sep 2016 a number of towers on different 275 kV lines in different locations in SA’s Mid North collapsed in the storm that led to the System Black.
When EMTT (emergency transformer tripping) scheme is armed then things could have definitely gone a lot worse!
On the mid afternoon of Tue. 13 Feb 2024 I saw both Sydenham T.S. to Moorabool T.S. lines down from several km
away.
The road which is over-crossed by the two lines was blocked by police; they showed me a phone photo of two
collapsed towers; but wouldn’t allow public in the area. The police said six towers were collapsed.
The photo that I saw showed the collapse of the section part way up where the tower bifurcates to make
space for the centre phase.
It appeared that three sequential towers and thus four spans of each 3 ph. lines were not visible
from a distance.
I saw evidence of a microburst in the area with many trees uprooted and others snapped or torn apart.
There were some wet patches of road in the area indicating very recent rain.
The 500 kV lines in that area were built between 22 kV / 12.7 kV distribution lines. There were no aerial crossings.
(There is an underground 22 kV undercrossing outside the MLTS fence in Anakie Rd. some km to the south west from the tower collapse area) I would be very surprised if there were any recent aerial crossings.
JDH Consulting are wind loading specialists and have been studying failure of high voltage transmission line towers in Australia, particularly in Victoria for about 25 years. Failures due to small but intense storms such as microbursts are common for a number of reasons, such the wind structure within the storms and the directional orientation of the line. The risk of failure along a line is also dependent upon its length. JDH has been in discussion with AusNet regarding a specific study of line risk for the Victorian network, similar to the extensive studies carried out for ElectraNet in South Australia, following the many failures that occurred there in September 2016.
Noted here with respect to ‘Some *initial* headline questions following the transmission damage, unit trips & loss of load, initiated on Tuesday 13th February 2024’, John