State-owned power utility Eskom on Thursday said Unit 4 at the Medupi coal-fired power station project, in Limpopo, had been synchronised to the national power grid this week.
This was the third of six units to come on stream and marked a key milestone towards the full commercial operation of the unit ahead of its scheduled commercial operation in 2018.
Unit 5 achieved successful synchronisation on September 8, 2016, and had reached commercial operation in April.
Medupi Unit 6 became commercially operational in 2015.