One of Queensland's biggest power stations was operating without required regulatory approval when it was taken out by a catastrophic explosion.
Operators of the troubled Callide C coal power station in central Queensland have been fined almost $70,000 for breaching National Electricity Law, the Australian Energy Regulator (AER) said.
The Callide plant still has two generators offline since a May 2021 fire was started by a turbine hall explosion, ensuring blackouts for almost half a million customers.
In a joint venture, state-owned CS Energy runs and maintains the plant with the two generators expected to be up and running again from January 2024.
The AER fined CS Energy $67,800 for not being a registered participant with the Australian Energy Market Operator (AEMO) or holding a valid exemption at the time of the explosion.
CS Energy has operated the Callide plant for a number of years but did not submit an exemption application until after the AER uncovered the law breach.
It obtained an exemption last month.
The breach was uncovered during the AER's ongoing investigation into events that led to the May 2021 "power system event".
The Mining and Energy Union said the fine was inadequate for what was a very serious event.
"It's remarkable that no-one was killed," the union's Queensland District vice-president Shane Brunker said.
"To discover that Callide was operating without the required approval at the time is extremely alarming.
"It is inadequate to have this brushed off with a fine that will barely be noticed in CS Energy's accounts."
CS Energy told Renew Economy that an "historical oversight" was to blame for its failure to obtain an exemption as required.
Mr Brunker said the breach would further shake the confidence of employees at the plant.
"Failing to comply with AEMO registration requirements means there is less oversight of control and operation of a power generator," he said.
"Workers are still rattled from the 2021 explosion and subsequent safety and operational failures - this will shake their confidence in site management even further.
"We encourage AEMO to be fully transparent with information regarding this breach and ...(the) investigation into the serious events of 2021. Someone needs to be held accountable."
Comment has been sought from Energy Minister Mick de Brenni.
Built in 2001, Callide C is one of the state's newest electricity generators.
However, the power station near Biloela has been plagued with issues since the 2021 explosion.
Part of a cooling tower collapsed in October 2022.
In November 2022, units were knocked out following a series of accidents and equipment failures at the plant which supplies almost 20 per cent of the state's electricity.
