An explosion at a central Queensland power station that left nearly half a million people without power could not have been anticipated, according to a report into the incident.

State-owned operator CS Energy released findings into the Callide Power Station's C4 unit today, which found the incident had been caused by failing electrical equipment and system back-ups.

"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," chief executive Darren Busine said.

Mr Busine said the event was not caused by a lack of maintenance.

'Unstoppable sequence'

There are two types of power used at power stations, including alternating current (AC), which is what the station produces and sends to the market, and a direct current (DC) system, which is used for protection systems such as emergency back-up power.

The report found that on May 25, 2021, a new DC system with a battery charger had been commissioned and was being connected to the C4 unit.

"Voltage unexpectedly dropped to zero, causing a trip in the AC system," Mr Busine said.

"The loss of the AC system then prevented the recovery of the DC system."

This meant the power station unit could not disconnect from the grid or shut down safely.

"Ultimately the turbine generator went from generating electricity to consuming electricity," Mr Busine said.

"It became an unstoppable sequence of events which led to the emergency evacuation of the site ahead of the destruction of the generator."

The turbine generator spun, and this, alongside the loss of other critical systems like lubrication oil pumps, caused the explosion.

Mr Busine thanked staff for their handling of the incident.

No-one was injured.

"All this happened within seconds — what's important to understand also is that the control room went black," Mr Busine said.

'Cannot happen again'

CS Energy said it had already implemented several design changes to prevent similar incidents from happening.

It will install an extra switchboard, battery and battery charger before the C4 unit returns to service.

The unit is expected to be online by the end of July.

"The improvements that we've now made into the system will mean that this incident cannot happen again," Mr Busine said.

CS Energy said it had made changes at other plants, including Kogan Creek and Callide B and C.

It has also hired more operators, a safety team and an engineering team to focus on standards and quality assurance.

Critics had been sceptical of the time it was taking CS Energy to release its report, but chair Adam Aspinall said information was shared with the public as soon as it was possible to do so.

He said the design of the unit was typical of recently built power stations, including Kogan Creek, Tarong North, and others built in New South Wales.

A report from forensic engineer Sean Brady is expected in the coming months.