‘Unstoppable’: Catastrophic explosion at Callide Power Station unpredictable

The series of equipment failures which led to the catastrophic explosion at Callide Power Station could not have been predicted according to state-owned CS Energy.

The series of equipment failures which led to the catastrophic explosion at Callide Power Station could not have been predicted according to state-owned CS Energy.

And the government corporation is adamant a lack of maintenance did not lead to the May 2021 incident which plunged nearly 500,000 homes and businesses into darkness.

But the original design of the station was a factor according to chief executive Darren Busine.

Callide C is Queensland’s fifth largest coal fired power station. It is run by state-owned CS Energy which owns half the station in a joint venture with IG Power.

Workers from the Callide Power Station outside the facility.

Technical findings into what caused the explosion of C4 were released by CS Energy for the first time — 19 months after the incident occurred and days after the Australian Energy Regulator confirmed it would be taking legal action against Callide C’s trading arm.

The reports take in expert advice including from Dr Sean Brady, but the forensic engineer’s full investigation into what caused Unit C4’s failure is still being written.

“This was an extraordinary chain of events which we could never have anticipated. And once in train, none of the backup systems were able to avert it,” Mr Busine said.

“It became an unstoppable sequence of events, which led to emergency evacuation of the site ahead of the eventual destruction of the generator.”

Under CS Energy’s findings Unit C4’s downfall was the result of key electrical equipment failing simultaneously, with backups systems also failing to kick in as part of a series of complex events that could not have been anticipated.

The day C4 exploded the unit was set to have a battery charger critical to the flow of DC power replaced — a planned upgrade that had been successfully completed on sibling generator Unit C3 and Callide C’s back up power supply unit.

But unlike the two other upgrades, when engineers reached step four of five the voltage of the battery charger unexpectedly dropped, triggering a series of events which led to a loss of DC and AC power supply.

CS Energy Chairman Adam Aspinall (right) and CEO Darren Busine speak during a press conference to provide the technical findings and learnings into the Unit C4 incident at Callide Power Station in May 2021. Picture: Dan Peled / NCA NewsWire

Consequently protection systems were not triggered and it took the nearby Powerlink-controlled substation connected to Callide C4 to detect an electrical fault before the generator was disconnected from the grid.

The disconnection severely destabilised the electricity grid, tripping nine other power stations across the state.

“Some of the contributing factors can be traced back to the original design of the power station, which while tested and compliant with connection standards we now realise, could have been more robust,” Mr Busine said.

“I’d also like to reinforce that our investigation has shown that the full contributing factors to this event will not the result of a lack of maintenance.”

Mr Busine, who was installed as CS Energy chief executive in July last year, said he never wanted to see “this event or anything like it happen again”.

“That’s why I’m totally committed to ensuring that we have got safe operations that we’ve got the controls in place that we learn from this, and then we make improvements into our business,” he said.

There are no other instances similar to what happened at C4 across Australia.

Opposition Energy spokeswoman Deb Frecklington blasted the government for the long delay in the release of the full Brady report.

She also took aim at a 21 minute-long sleek animation released by CS Energy to visually explain what occurred at Unit C4.

Callide Power Station Unit C4 pictured – A 300-kilogram chunk of shrapnel was found lodged in the roof of the Callide Power Station following the major explosion. Picture Supplied

Ms Frecklington questioned how long Energy Minister Mick de Brenni had been aware of the information contained within the reports released on Tuesday.

Mr Busine affirmed a lot of the information released by CS Energy on Tuesday had “come together at the back end of last year” and into early 2024.

“The board has been considering the information and understanding the best way to communicate that and so that’s what we’ve decided,” he said.

Meanwhile, the partial return of service date for Callide C3 — which has been offline since November 2022 after its cooling towers collapsed — has been cancelled.

Unit C3 was due to partially come back online on February 29, but CS Energy and joint venture partner IG Power revealed on Tuesday this scheduled event had been removed.

Instead the unit will come online, in full, at the end of March as previously scheduled.

“Unit C3 has been in ‘preservation mode’ while the C3 cooling tower is being rebuilt,” a CS Energy spokeswoman said in a statement.

“Throughout this time a regular inspection and maintenance program has been occurring to ensure the power station’s plant and equipment remain in good working condition to enable return to service.

“This inspection program has detected carbon dust in the C3 generator which has arisen during the preservation process.

“To ensure safety in the return to service of the unit, the JV has made the prudent decision to fully inspect and clean the generator which will impact the return to service for partial load.”

This change in return to service for C3 is unrelated to the rebuild of the cooling towers, which remains on schedule according to the state-owned corporation.