It is nearly two years since the Callide power station C4 unit caught fire and blew up. Callide power station is still not up and running. State owned CS Energy’s private sector partner Igen Group is insolvent. This graph shows when the Queensland electricity grid fell off a cliff. Below is a blow by blow description of what happened published in an ABC report one year after the event. It leaves the main cause of the fire and explosion unexplained.
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If you look at the graph below you can see nearly half of the electricity supplied at the time of the blackout was by renewable energy sources: wind – solar – hydro. It was the coal fired power stations that tripped after the explosion of C4 unit at Callide. 5000 MW of power was lost just before 2 pm on 25 May 2021. At this time there is plenty of solar energy available to the grid and you can see that a mixture of solar, wind and pumped hydro provided about 2000 MW after the collapse of the coal fired power stations at Biloela, Stanwell, and Gladstone. Traffic lights in Brisbane went out. The operators imported power from interstate whereas ,just before the explosion, Queensland was exporting electricity to the national grid.
Ian Curr, 31 March 2023.
What happened at the power station?
According to a report into the incident from the Australian Energy Market Operator (AEMO), at 1.33pm on May 25, 2021, the Callide C4 unit stopped generating power.
“Post-incident investigation confirmed that the generating unit lost excitation, steam supply, to the turbine and all AC auxiliary supplies but the generator circuit breaker did not open,” the report said.
“The C4 unit boiler, turbine and field switch had tripped but not its generator circuit breaker, leaving the generator motoring asynchronously on the power system.”
This meant the generator was drawing in power from the energy network, up to 90 megawatts at one point, turning it effectively into a very large motor.
The generator had a protection system in place, but it did not operate “most likely because of the loss of all DC power supplies to the unit”.
“At [1.40pm], CS Energy informed AEMO of a possible fire at Callide C4,” the report said.
“Around four minutes later, at [1.44pm], Callide C3 tripped from 417 MW and CS Energy contacted AEMO to confirm there was a fire in the Callide C turbine hall.”
In the first 30 minutes after the incident began, operators at the power plant were responding to 150,000 alarms.
Between 1.49pm and 2.04pm the control room and power station were evacuated.
“There is evidence that the associated loss of supply-to-oil circulation pumps and cooling systems may have led to overheating of the bearing oil,” the AEMO report said.
“This may be an initiating cause of a fire at generating unit C4, although there would have likely been other issues with the generator.”
The report highlighted that immediately prior to the incident “CS Energy personnel were undertaking maintenance activities on generating unit C4 battery charging systems”, a system connected to the C4 DC supplies.
Blackouts across the state
About 20 minutes after the incident began, power stations across Queensland, including in Gladstone and Stanwell tripped, as did the Queensland-New South Wales interconnector.
Some 470,000 homes and businesses across Queensland, from north of Cairns down to the Gold Coast, were left without power.
Towns in northern New South Wales, such as Tweed Heads, Kingscliff and Pottsville, were also impacted.
Police had to guide traffic in Brisbane after traffic lights went out as part of the statewide blackout.(ABC News: Lily Nothling)
Traffic lights in Brisbane stopped working and emergency generators had to be turned on at the Gold Coast University Hospital.
Remarkably, no one at the power station was injured because of the fire.
“You have a last line of defence, which is evacuation,” Mr Bills said.
“It was the training and professionalism of our people which is why no one was injured.
“I think it’s tremendous credit to those people.”
What’s the future of C4?
While most of the Callide Power Station came back online in the weeks following the incident, the C4 unit remains offline.
CS Energy, a Queensland Government-owned company, had originally forecast the rebuild would be completed by February 2023, but Mr Bills confirmed to the ABC that had been pushed back to April.
“You’ll be well aware of the supply chain issues that are affecting things globally, it’s not unique to CS Energy and this particular generator,” he said.
“So we’re sort of a little bit caught by how those supply chain constraints play out over the next eight to nine months.
“But at this stage, we’re still targeting April when it will be reconnecting.”
He said the focus now was removing the damaged equipment.
“It’s quite complicated and very thought through as there are some very tight areas to cut into, some very large bits of equipment and heavy bits of equipment,” he said.
“That’s been an ongoing process.
“We expect to see the [new] equipment turn up in the third quarter of this year and then we’ll start to install it.
“But up until now, it’s all been about removal, making sure the plant is in a safe condition ready for the installation of the new equipment.”
One year on, Mr Bills said the anniversary of the incident marked a time to acknowledge what workers went through that day.
“It’s about respecting and honouring some tough calls and showing that care and concern that everyone deserves in a situation like that,” he said.
“It’s a day that you never expect to have happen.
“For a lot of people, it’ll bring back those memories and we need be very cognisant of that and aware of how people are travelling.”
Reference
ABC report refers to AEMO report of sequence of events at Callide C: https://www.abc.net.au/news/2022-05-26/one-year-on-from-callide-power-station-fire/101098852https://reneweconomy.com.au/baseload-5gw-of-coal-capacity-missing-before-callide-coal-explosion/amp/