South Africa's Eskom said on Friday it had suspended managers at two of its power stations after breakdowns which forced the utility to ramp up rolling blackouts earlier this week to avoid tripping the national grid.

Eskom, which has implemented rotational powercuts on and off for more than a decade due to infrastructure failures largely blamed on years of inadequate maintenance, said its group chief executive André de Ruyter suspended the managers at the Tutuka and Kendal stations on Thursday morning pending disciplinary inquiries. 

Further interventions were ongoing at the Kriel and Duvha power stations, said the state-owned company, which supplies around 95 percent of South Africa's electricity.

On Tuesday Eskom said it would be forced to resume stage 2 load-shedding -- which entails suppressing 2 000 megawatts of electricity demand at a given time -- to avoid overwhelming the grid after ten generation units at seven power stations broke down.

It ramped this up to stage 4 on Wednesday, taking 4 000 MW of demand off the load, citing additional pressure from cold weather.

On Friday, the utility said its board was working closely with the executive management to speedily resolve the crisis.

"Engagements have been held with other power station managers to ensure that the previous culture of weak consequence management will no longer be the norm and will no longer be tolerated at Eskom," it said.

"The executive has, in the meantime, deployed three senior generation managers to the sites in question (Duvha, Kriel, Tutuka and Kendal power stations) to provide leadership and oversight in person."

Some 5 000 megawatts of capacity were currently on planned maintenance and 10 950 MW on unplanned breakdowns, the company said, adding this had culminated in an approximately 3 000 MW energy demand deficit, aggravated by very high demand during the cold front.

"The board is pleased that some units have since returned to service, but is aware that the level of failures is unacceptably high," it said.

"Whilst it is true that the aging fleet is plagued by legacy issues of neglect and omitted maintenance and is therefore susceptible to unpredictable breakdowns, it is also true that the situation is exacerbated by serious issues of apathetic behaviour by some management staff."

It said the board and executives were fully cognisant of the substantial strain that load shedding exerted on the wellbeing of citizens and on an already depressed economy, and were fully committed to attaining the sustainability and reliability of Eskom's plants.

The executives had met Public Enterprises Minister Pravin Gordhan twice in the past two days to interrogate the systemic causes of load shedding and the measures being taken to repair breakdowns.

Participants of the meetings agreed that an urgent culture change and the enhancement of competence across all 44 000 Eskom workers should be accelerated.

Eskom has struggled with financial constraints for years, largely blamed on years of mismanagement by former senior executives, many of whom left the company under the cloud of corruption allegations.