Duhva Turbine Explosion Critical for Dark Days of South African Power Supply

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Written by Richard Finlayson, Senior International Editor for Industrial Info--In the second week of February, South Africa's state-owned power utility, Eskom, reported that a 600-megawatt (MW) unit at the 3,600-MW Duvha coal-fired power station in Emalahleni (also known as Witbank), in the Mpumalanga province, spun out of control and exploded while undergoing a statutory test. Replacing the turbine generator could cost more than $440 million and take 18 months, according to industry sources.

However long the process will take is of great concern to Eskom, which is involved in a power supply balancing act to prevent rolling power cuts during the next two years, before significant additional base load power is brought onto the grid.

During the test, the unit is disconnected from the grid and a steam control valve is eased open to raise pressure in the turbine. A bolt that activates a cut in the rotational speed of the turbine as it passes 10% above the design speed of 3,000 revolutions per minute (rpm) at normal operating voltage failed. Some reports said the turbine reached 4,250 rpm before the unit exploded, ripping steel plates of the turbine hall roof and scattering shrapnel-like shards through the hall.

Eskom has delayed maintenance at other power stations, which could compound the problems caused by the explosion by pushing power station turbines to operate near the limits of their design specifications, in order to maintain grid supplies. Eskom also might use diesel-powered standby generators, which would be an expensive gap filler, as their operation costs five times more per hour of operation than the conventional base load units. Eskom is conducting a technical review aimed at finding the cause of the unit failure to prevent similar accidents in the future. The other five units at Duvha are running normally. Duvha first started generating power to the grid in 1980, and the original six turbines were supplied by GEC (Rugby, England).The last unit started operations in 1984.

In March, the utility launched 49M, an energy-saving initiative backed by the government and business partners. "The simple truth is that Eskom cannot meet these challenges [of providing adequate power] alone," said Brian Dames, the chief executive officer of Eskom. "We need the active support of the entire population and a national commitment to developing practical energy-saving and energy-efficiency habits." He added that 49M would bring about a new way to grow and sustain South Africa as national energy consumption was reduced collectively, saving money in the process and contributing to a climate change solution.

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