An explosion at the 1,586MW Callide coal-fired power plant in Australia's Queensland state in May 2021 was the result of the simultaneous failure of key electrical equipment and system back-ups in a "complex series of events that could not have been anticipated", Queensland state-controlled utility CS Energy said.
A technical report on the causes of the incident released on 13 February has determined that the trigger was a collapse of voltage in the direct current (DC) system of the 420MW Callide C4 unit, just as a new battery charger was being connected to the facility. The unit turbine tripped because of the loss of supplies but remained connected to the grid. The turbine generator continued to spin with the loss of critical systems, directly leading to its explosion, CS Energy said.
The blast led to blackouts in large parts of the state, including some of its largest coal ports, and boosted gas-fired generation and electricity prices over the 2021 winter.
The report is based on CS Energy's assessment of the incident including contribution from third-party experts such as consultancy Aurecon and independent investigator Sean Brady, who is yet to complete a final assessment, the utility said.
CS Energy said it has modified the design of the Callide C plant, which also comprises the 466MW C3 unit, as the original design did not enable two batteries being connected to the same DC supply system. This will ensure a battery is always connected, backing critical protection circuits, the utility said. It has also made several other modifications to prevent a similar event from happening again.
The utility operates the Callide C joint venture on behalf of IG Power, formerly known as InterGen Australia. The C4 unit is scheduled to return partially on 30 June 2024, pushed back from previous schedules, while the C3 unit is expected to reconnect to the grid partially on 29 February, reaching full capacity on 31 March. The C3 unit went back on line already in winter 2021 but suffered a structural failure of the cooling plant in October 2022.
CS Energy also operates and fully owns the 700MW Callide B plant, which is currently operational.
