Eskom on Monday confirmed that the Medupi power station experienced an explosion on the Unit 4 generator.
The incident occurred at about 10.50pm on Sunday, and is suspected to have resulted in Unit 5 tripping, said the utility.
No injuries have been reported and all employees and contractors have been accounted for.
Emergency services attended to seven colleagues requiring treatment for shock.
Unit 4 had been on a short-term outage since August 6.
All work on the unit was suspended with immediate effect. This included the suspension of all permits to work on the plant until further notice.
“The area was secured and once it has been cleared by the fire chief and resident engineers; inspections and assessments will begin to determine the cause of the incident and extent of the damage caused,” said Eskom.
“Preparation for the return to service of Medupi Unit 5 is currently in progress.
“Investigations are under way into the cause of the incident and Eskom will update the public on developments, as well as to what extent this unfortunate incident will impact the national electricity grid.”