Repairs and restarting procedures will take three weeks at the Koeberg power station near Cape Town, Eskom said on Thursday.

Specialists from Alstom ? the original equipment manufacturer ? are at the site to assist with the inspection and diagnosis of the problem which resulted in the closure of station's second unit.

Meanwhile, the Majuba and Duvha power stations in Mpumalanga had technical failures on Wednesday.

The power utility's Managing Director for Corporation Services, Steven Lennon said, that at the Majuba power station, a submerged scraper conveyer which moved ash from the bottom of the boiler jammed.

"The unit was brought back onstream on Thursday morning," said Lennon.

The unit at Duvha power station had a boiler tube leak and was expected back onstream over the weekend.

"These incidents increased the risk of supply shortages, but we did have adequate reserves which enabled us to sustain power supply nationally," Lennon said.

Any loss of generation capacity placed strain on the national grid, he said.

"This was due to inadequate reserve margin between available generation and demand," he said.

Lennon said this would continue until benefits of the expansion programme became available or the demand for electricity was reduced.

Eskom appealed to consumers to reduce electricity demand by switching off all non-essential lights and electrical applications during peak hours, 5pm until 9pm.