They say lightning strikes never hit twice. But on August 25 last year, a single lightning strike succeeded in extracting two major circuits on the main transmission line connecting NSW and Queensland.
The effect was almost instantaneous and felt over Australia's main grid. It caused a burden on a scale that made it much talked about in Victoria in January's heat wave seeing relatively small beers.
We reported the events at the time and noted the irony of the Tesla Big Battery, which held the network together on the very first full working day of the new Prime Minister, Scott Morrison, the man who had spent so much time promoting coal and ridicule new technologies like the big battery.
Our initial reports have now been highlighted by a detailed study by the Australian energy market operator who looked at why more than 1,190 MW of cargo was shed in three states, so Queensland worked for nearly an hour and a half in an uncertain state that could have been pear-shaped much quickly, and why South Australia's renewable domination had the most secure network during the events.
The report highlights a few important points.
One is that the large battery from Tesla again proved to be an unusually valuable asset in the face of such events.
It was the fastest to respond and showed a versatility that was not matched by any other asset and its efforts ensured that South Australia was the only state network that should not suffer major losses or operate in an uncertain state despite the great share of renewable energy sources.
Two, Australia's aging and slowly fleeting heritages responded poorly, and it is increasingly clear that they will create headaches for the market operator as it controls the energy transit, and seeks to perform the energy equivalent of the shift from analog to digital.
Three new technologies such as wind farms and roof sunroofs also key in curve balls with unexpected reactions to different situations;
And four, the market operator and the regulator must act quickly and decisively to introduce rules that are useful for the latest technology and not for the last centuries.
So what happened on August 25th?
It was a Saturday and right after. 11.00 hit the lightning and took the two circuits of the main connection between NSW and Queensland, and within two seconds the Queensland network was practiced.
The frequency dropped in the rest of the grid and almost immediately above 900 MW of melt load (two pan lines at Alcoa and one on Tomago) lost in Victoria and NSW as well as another 93 MW consumer load in both states.
Another 80 MW industrial load was lost in Tasmania. Within a few seconds, South Australia interrupted as a result of the events but had no negative effects.
According to AEMO, South Australia has virtually Tesla Big Battery – owned and operated by Neoen at Hornsdale – thank you for that – yet another validation for the technology that causes greater concern about how to manage the network.
"The large battery storage in SA was valuable in this regard, which helps to contain the initial drop in system frequency and then rapidly switch production from generation back to load to limit the frequency condition in SA after separation from (Victoria)," notes the report.
The AEMO's assessment of other technologies is not so glowing, and its report underlines the serious concerns about the state of thermal production (coal and gas), which it says did not respond to events as hoped.
- "Many (coal and gas) generators no longer adapt automatically outputs in response to local changes in frequency or respond only when the frequency is beyond a wider band (dead band) than historically stated", notes it.
- "This lack of response resulted in significant technical challenges that controlled the frequency system frequency during this event, which delayed the resynchronization of QLD with NSW."
The report noted two trips by generators in Queensland, one a "baseload" gas plant and another a small hydro facility and dangerous and disturbing fluctuations at both Liddell and Bayswater coal generators in NSW, which responded poorly to the frequency excursions.
Even more worryingly, the report notes that the Queensland network for all its gigawatters of coal and gas plants operated in uncertain condition for almost 90 minutes because none of the coal and gas units could provide primary frequency control, which meant that it had none Protection in the case of one of its large units falls over.
The report also removes problems with wind and sun. Another software problem was discovered in four wind farms in South Australia, although on this occasion it worked in the network because their 80 MW output was hurt to zero, which helped solve the over frequency. That problem has now been solved.
More confusing, AEMO also uncovered ongoing problems with some sun shades on the roof despite new standards introduced in 2016. In fact, in South Australia, the failure rate for the new converters was twice as large as those installed before the standards changed in 2016. This problem has not yet been solved.
But it is the speed and accuracy of the answer to the Tesla battery that is the highlight of the AEMO report.
Within hours of South Australia's state-wide blackout in September 2016, promoters and developers stated that a number of small batteries, or even a large battery or two, could have kept the network together and minimized the outbreaks.
The estimate was repeated several months later by Tesla chief technologies JB Straubel, which in turn led to the so-called "billonaire tweets" between musk and Australia's Mike Cannon Brookes and eventually the construction of the large Tesla battery next to the Hornsdale wind farm. – in less than 100 days
We will never know if the battery or other technology would have been enough to withstand the catastrophic order of events in South Australia in September 2016, but the event last August put the battery to its worst test yet.
What we now know seems to be capable of delivering exactly what the battery leaders say it would – the lights of South Australia maintained, while other states that depended on older fossil fuel technologies had major outbreaks.
It is ironic that this should be the case because most of the net was on litter and gas – (96 percent according to AEMO, plus about 10 percent from the sun roof on the roof). South Australia was split about 50-50 – with only her 800 MW gas, 210 MW large wind and sun, and another 600 MW roof on PV.
As the AEMO notes, the Tesla battery in Hornsdale did exactly what it was supposed to do.
It charged at -38 MW just before the event before immediately switching to discharge (up to 44 MW) as the frequency dropped over the net after the Queensland line was separated and then a few seconds later switched back (in the blink of an eye) ) for charging (down to -62MW) to help take into account the frequency overrun after the South Australia link failed.
"This response is in line with the design," notes AEMO. "It helped both stop the initial decline of the system frequency and then by rapidly switching generation from generation to load to halt the frequency state in SA after separation from VIC.
"Only active power response delivered prior to the minimum or maximum frequency condition in an event such as this helps to stop the change in frequency.
"The very fast rate response frequency response from the Hornsdale battery was valuable in this case and ensured the response that helped limit the under and over frequency conditions."
In contrast, the response to the frequency excursions from the gas plants in the state was poor, with "little equivalent short-lived movement in the output of synchronous generation to the correct frequency" and only a "slow and limited response to the system frequency".
Overall, AEMO is particularly concerned that the breakdown of frequency response from the large thermal generators over the last decade means the system is now dependent on industrial and consumer loads being turned off when such incidents occur. That was not always the case.
- "The first frequency response from some generation was delayed to the point where it was not beneficial to include the rapid rate changes that immediately follow a major power system event such as regional separation," it notes.
- "The frequency response response from these generators must be improved wherever possible so that it can effectively contain the critical offset."
This lack of response resulted in significant technical challenges that controlled the power system frequency during this event, which delayed the resynchronization of QLD with NSW.
AEMO is particularly concerned that the breakdown of frequency response from the large thermal generators over the last decade means that the system is now dependent on industrial and consumer loads being turned off when such events occur.
This event indicates that the resulting drop in primary frequency control has reduced the power system's ability to stop the effect of unreliable unforeseen events in time to avoid the risk of cascade failure. caused by extension of deadband setting.
It has a long list of things to do. This involves looking at whether some of the coal and gas plants in Queensland could supply FCAS, examining the control settings for interconnectors that it fears is no longer appropriate, and getting to the bottom of the solar converters on the roof and making sure they can be an asset instead of an obligation under such circumstances.