A battery failure has been blamed for an explosion at a Queensland coal-fired power plant that left nearly half a million residents without electricity.
A report and video released by state-owned CS Energy on Tuesday revealed the simultaneous failure of key equipment and backups that led to the explosion in Callide Power Station's C4 unit near Biloela in Queensland in May 2021.
"This was an extraordinary chain of events which we could never have anticipated," CS Energy chief executive Darren Busine said.
The contributing factors could be traced back to the power station's design, he said.
The incident happened while a new battery charger was being connected to the plant.
Two types of power are used at the station - alternating (AC) and direct current (DC) systems.
The DC system lost voltage and tripped the AC supply, ensuring the turbine generator went from generating electricity to consuming it and ultimately led to an explosion leaving 470,000 homes and businesses without power.
No one was injured at the Callide C plant which can generate up to 1540MW of electricity, about 30 per cent of the state's overnight demand.
None of the backup systems worked to prevent the incident and systems in the control room went black, meaning staff could not understand or stop the incident.
The Callide C3 plant had undergone the process before the explosion without a hiccup but a drop in the voltage of a battery at the C4 plant led to the incident.
"In hindsight, we can look back and say what events led to this and therefore what additional predictions we could put in place," Mr Busine said.
He said the plant had undergone significant modifications and reassured the affected community that it would not happen again.
An independent report into the Callide Power Station explosion is yet to be released.
Shadow Energy Minister Deb Frecklington criticised Tuesday's technical report and the long wait for the independent report to be released.
"We have seen a highly made-up video of how the explosion happened but we certainly haven't heard why it happened," she said in parliament.
But Energy Minister Mick de Brenni hit back and implied the technical report was the first piece of information regarding what happened at Callide.
Mr De Brenni said the video highlighted complexities in identifying how the incident occurred.
He said when the independent report was finished, the government would consider how to respond.
The CS Energy report had been released just days after an announcement that the Australian Energy Regulator would begin Federal Court proceedings against Callide Power Trading (CPT), which trades the output of the plant.
The regulator alleges Callide's C4 unit failed to ensure its plant met performance standards and did not design its facilities to comply with those requirements.
The regulator is seeking pecuniary penalties, declarations, orders for remedying the breach or preventing the recurrence of the breach, and costs.
Mr Busine said the release of the findings was not a defence to the energy regulator and accepted its investigation into the plant's performance.