A “once in 50 years” storm causes a complete grid failure in South Australia leaving 1.7 million residents without electricity.
On Wednesday 28 September 2016, two tornadoes ripped through South Australia. Winds of up to 160 mph battered the state, along with at least 80,000 lightning strikes.
The storm knocked out 22 high-voltage pylons that carry electricity from Port Augusta to the rest of the state.
The first power line to trip was a 66 kV line near Adelaide, followed by a major fault on the 275 kV line between Brinkworth and Templers.
A third 275 kV transmission line, Davenport-Mount Lock, tripped seconds later. This led to a succession of six voltage dips on the South Australia grid in two minutes.
This voltage drop triggered automatic protection mechanisms at nine wind farms, causing a generation loss of 456 MW.
The Heywood Interconnector, which links South Australia and Victoria, tried to respond to the loss of load by increasing flow.
But as it was already close to full capacity at 613 MW, the increased strain caused the interconnector to trip as well.
Although load shedding kicked in, the drop in frequency was so dramatic that it wasn’t enough. This led to South Australia disconnecting from the National Electricity Market to protect the network infrastructure from further damage.
Virtually everyone in the state lost their electricity supply at approximately 4:20 pm.
The only exception was Kangaroo Island, where the power station had a built-in contingency in case of a failure with the rest of the network.
The First Black Start In Australia
The incident triggered what’s known as a “system black”, a Black Start of the network from scratch. It was the first time any Australian state had to use this measure of last resort.
Jay Weatherill, South Australia Premier at the time, explained: “What happens is the system protects itself by tripping all the generators in the system and also by severing the interconnector with Victoria.
“It then triggers a protocol about how we bring it back up. There are a series of back-up generators which gradually re-power the system.
“Once the system is balanced then power is restored. This would happen to any system anywhere in the world if they had a similar circumstance.”
The Victorian interconnectors initiated the Black Start. Once there was a stable frequency on the network, South Australia power generators gradually came back online to restore power as quickly as possible.
The Adelaide metropolitan area was the immediate priority. Some suburbs regained power within about three hours, with much of the city following suit by 10 pm.
By the Friday morning, there were still around 30,000 properties across the state without power, with the continued stormy weather continuing to cause problems.
Why Was The South Australia Grid Vulnerable?
Simple geography. In the United States or western Europe, when transmission lines get knocked out or malfunction, they tend to be part of a dense network where nearby lines can usually pick up the slack without the risk of overloading.
This isn’t the case in Australia. Its National Electricity Market is acknowledged as being amongst the world’s most spread-out interconnected electricity grids.
So when there’s a major failure on one line, there are far fewer alternative routes for the electricity to flow. This means power lines are more prone to overloading and tripping out.
This scenario is particularly true with states such as Queensland and South Australia. The network infrastructure there is far more widespread than more densely populated areas such as Victoria or New South Wales.
Installing more transmission lines could, in theory, have avoided the South Australia blackout. But adding in such redundancy would inevitably come at great expense.
Jumping To Conclusions
As the gravity of the incident became clear, some incorrectly pointed the finger at wind farms and the growing dependence on renewable energy.
Wind power was providing around 70% of the indigenous generation at the time of the incident.
Among those was then Deputy Prime Minister Barnaby Joyce, who claimed: “Obviously we know that South Australia has had a strong desire to become basically all renewable energy and the question has to be asked does this make them more vulnerable to an issue such as what happened last night.
“If you turn power into just a complete social policy and say well we are going to save the planet one state at a time and in so doing you create vulnerability to your state, so that if it comes under stress with a severe lightning storm, as they did, that this makes it more likely that you will have a total blackout.”
ElectraNet, the owner of the stricken high-voltage transmission lines, refuted such claims. It stated storm damage to the network was the main cause.
The Official Verdict
In March 2017, the Australian Energy Market Operator (AEMO) published its fourth and final technical report into the September system failure.
It admitted there were challenges posed by the changing energy generation mix. The network would need to adapt to an increasing reliance on renewable energy.
This wasn’t the first time there had been a complete loss of the Heywood Interconnector. However, it was the first occasion that required a Black Start reboot of the system.
According to the document: “The key difference between the 28 September 2016 event and the other three events is that there was significantly lower inertia in South Australia, due to a lower number of online synchronous generators.
“This resulted in a substantially faster rate of change of frequency compared to the other events, exceeding the ability of the under-frequency load shedding scheme to arrest the frequency fall before it dropped below 47 Hz.”
The report reveals that overly sensitive protection mechanisms in some wind farms caused the grid collapse and subsequent Black Start. The feature automatically reduced output after a certain number of voltage dips.
Nine of the state’s 13 wind farms switched off because they couldn’t withstand the storm’s voltage disturbances.
Output dropped by 456 MW and when the Heywood Interconnector from Victoria tried to overcome the shortfall, it experienced a power surge that tripped it offline and sent the grid frequency plummeting.
This over-sensitive defence mechanism issue was flagged up in AEMO’s third incident report. Changes were already made to turbine settings to ensure the same problem wouldn’t happen again.
According to the report: “Had the generation deficit [from the wind farms going offline] not occurred, AEMO’s modelling indicates South Australia would have remained connected to Victoria and the Black Start would have been avoided”.
The investigation also warned that it wasn’t viable to solely rely on traditional sources of electricity generation such as coal and gas to keep the network balanced.
It advises authorities to consider adding capacity to help improve inertia, frequency and voltage control.
All 19 of the major recommendations in the report were due for completion by December 2017.
What Happened Next?
On 27 December, severe storms caused damage to more than 300 power lines, leading to blackouts lasting 12 hours. At the peak of the storm, 150,000 properties were without electricity.
Then 90,000 homes lost power for 45 minutes during a heatwave on 8 February 2017.
AMEO ordered 100 MW of load shedding, but 300 MW was mistakenly cut instead.
