South Australia’s electricity grid will be effectively “islanded” for up to two weeks, following the dramatic weather events on Friday that resulted in a tornado knocking down at six large transmission towers on one of the main 500kV lines in Victoria.

The loss of the towers north of Colac, on the Moorabool to Mortlake and Moorabool to Tarrone transmission lines, has effectively closed the main electricity highway between Victoria and South Australia (the Heywood Interconnector).

And while the smaller MurrayLink in the north of the state remains open, and will allow some limited transfers to and from South Australia, the Australian Energy Market Operator is effectively operating the South Australia grid as an island.

It presents itself with a situation almost unique in the world – a state grid that is normally powered more than 50 per cent by renewables operating without any major links to another grid.

South Australia should have sufficient resources to cope, and fortunately the forecast for the coming week is for mild temperatures. But to deal with this unique situation, AEMO is implementing a series of constraints – including limiting and shutting down the output of four wind farm operations – and will brief industry on Monday about other measures to be introduced.

The main Australian grid faced enormous challenges on Friday, and into Saturday, due to the heat wave that struck south east Australia, with temperatures soaring above 45°C in Victoria and NSW (above the levels where coal and gas plants can be relied upon), along with bushfires in NSW and Victoria, and storms in South Australia and Victoria, including the tornadoes that tore down the main transmission lines.

The grid got through, however, with no widespread outages, and no scheduled load shedding, even though the situation got very tight in Victoria and in NSW, and AEMO called on its “reserve trader” mechanism to try and ensure sufficient supply.

In NSW, the situation got very tight. State energy minister Matt Kean cited three coal units that caused issues, and there are questions as to why one of the main gas generators – Snowy Hydro’s Colongra gas station – withdrew all its 667MW capacity without explanation for nearly half an hour at the height of peak demand.

This move by Snowy Hydro helped push the NSW grid into a “lack of reserve level 2” situation, where the operator declares it has insufficient capacity to deal with any further unexpected outages.

See this story on Watt Clarity, the providers of RenewEconomy’s popular NEM-Watch widget, for a detailed look at what happened there.

Watt Clarity’s Paul McArdle says there are major questions about the bidding for the gas-fired generator, including the level of market power that will be injected into Snowy Hydro when it also operates the planned Snowy 2.0 pumped hydro scheme, which will dominate the storage market on the grid and push out potentially competing battery storage installations.

” I … can imagine that others would use a few different adjectives in relating their own perceptions of this sort of process, and participant behaviour,” McArdle wrote.

“What’s perhaps worth thinking about later is what the implications might be once Snowy 2.0 is up and running – with a single portfolio controlling a large volume of storage-based peaking capacity, particularly where it is located in the grid. A challenge for the ‘effective competition’ boffins.”

The relief at AEMO in dealing with what its spokesmen described as “unique challenges” was reflected by CEO Audrey Zibelman’s tweet late on Friday, thanking the efforts of her staff after the biggest dangers had passed.

“A rough day in the NEM but this girl is how I feel,” Zibelman declared, tweeting a photo and a video of a you girl banging away on the drums to a Nirvana song.

Zibelman has overseen a dramatic turnaround in the culture and the focus of AEMO since taking up her role in early 2017, around six months after the disastrous “system black” in South Australia where the actions of AEMO were called into questions.

Zibelman has sought to build a 20-year blueprint to ensure the systems and infrastructure are in place to deal with the transition to renewables, and ensure a tighter and more conservative operating regime to minimise the risk of outages, even though she has made clear the market operator may be powerless to stop some “tail risk” events.

Her team’s efforts were applauded by many, including Clare Savage, the new chair of the Australian Energy Regulator. “They kept the power system running in the face of extreme weather, topping tx towers and a lack of reserves. True grit and ingenuity,” Savage wrote.

AEMO says there are no reserve shortfalls forecast for the week ahead in Victoria, or South Australia, with mild weather expected. However, it said the restoration of the transmission towers that were damaged around 2.30pm on Friday may take a “week or two” and will require the available transmission network to be reconfigured.

One of these changes has enabled electricity supply to the Alcoa Aluminium Smelter in Portland, Victoria to resume, while the impacts on the wind farms – Macarthur and Portland in Victoria, and Canunda and Lake Bonney 1, 2 and 3 in South Australia – will continue in order to manage system security.

“As a result of the unusual transmission network configuration which limits transmission capacity, four windfarms in South Australia and Victoria have been directed by AEMO to constrain their output,” it said.

“With South Australia also islanded from the National Electricity Market, AEMO may need to either limit or direct generation at times to manage system security.

“AEMO has no forecast reserve issues in the coming week in South Australia, but we will continue to monitor and work with generators and the government.”

In a separate statement, Ausnet – which owns and operates the affected transmission lines – confirmed six towers were knocked to the ground and another tower suffered damage, separating the Victoria and South Australia grids and interrupting supply to Portland.

“We’re moving ahead with urgency due to the importance of the reconnection of the Portland aluminium smelter to the 500kV lines. We’ve taken immediate steps to commence design and installation of temporary towers to enable their reconnection,” it said.

“Preliminary design works for the temporary reconstruction of the transmission towers has been completed, materials are expected to start arriving onsite Monday, February 3, with construction works commencing Tuesday subject to weather conditions.

“We will work to repair and reconstruct these lines as soon as possible, given the extent of the damage it will take some time. Subject to weather conditions, we expect the construction of the temporary towers and restoration of both lines to be completed over the next two weeks. We’re aiming to have at least one line restored within a week.”

Ausnet did not provide pictures of the fallen towers, but included this one pictured during works conducted a few years to “indicate the same scale of work that will be required for the temporary towers we will construct next week.”