Stage 4 load shedding is set to continue until 23:00 on Tuesday night, but will be dropped to stage 2 for a brief period on Wednesday morning, Eskom has said.
After 09:00, Stage 4 will resume again.
The power utility announced stage 4 load shedding on Tuesday afternoon after Unit 1 tripped at Koeberg power station near Cape Town. It emphasised that there was no risk to safety.
Repairs were expected to take some days, Eskom warned in a statement.
"The seawater circulating water pump was damaged, and it is expected that repairs will take a number of days before the unit can be brought back into operation."
Unplanned breakdowns were at 12 046MW at 17:50 and planned maintenance was at 6 155MW, it added.
Additionally, said the power utility, demand has increased since January.