The accident, on February 9, wiped 600MW of power from the national grid when one of the turbine units that was undergoing routine tests malfunctioned, causing it to fly apart and sparking a fire.
In its bland and under-reported statement last month Eskom said publicly that the repair time at Duvha would be more than a year. However, a technical expert told the Mail & Guardian that it would take a minimum of two years to replace the damaged equipment.
The incident is likely to have a severe impact on the reliability of Eskom’s operations, as the scheduled maintenance of other stations will have to be delayed to make up for the lost capacity.
In addition, sources inside the industry pointed out that when the first 700MW unit of the new Medupi power station comes on stream — expected in 2012 — the extra capacity it was meant to add to the system would do little more than plug the gap created by the Duvha accident.
Real risk of rolling blackouts
As South Africa heads into winter, a period of peak demand, the strain on ageing plants and equipment could pose a major threat to the security of the county’s power supply.
The government has already warned that one of the most important factors in preventing load-shedding is the health of Eskom’s generator fleet.
In the medium-term risk mitigation plan, published in September last year alongside the draft integrated resource plan (IRP 2010), the government warned that South Africa faced “a real risk of rolling blackouts, similar to those experienced in 2008”, from 2011 through to 2016.
The years 2011 and 2012, before the Medupi and, later the Kusile power plant come on stream, were expected to be particularly fraught. At the time, the government warned that Eskom would be hard pressed to sustain its fleet performance at required standards, because of “the lack of time available to undertake adequate maintenance and to improve the quality of coal supplied to certain stations”.
The declines in the energy available from existing plants — the energy availability factor (EAF) — was a “major risk”, it said. In addition, less planning in the maintenance programme meant more unplanned outages in a “vicious downward spiral”.
This week Eskom representatives told Parliament during a joint sitting of the portfolio committees on energy and public enterprises that in 2012 the country will hit a peak power gap of nine terawatt-hours. This is the equivalent of about 1 000MW, or the energy needed to power a city the size of Cape Town.
Maintenance schedules to be affected
But Kannan Lakmeeharan, managing director for systems operation and planning at Eskom, told the M&G that the system was designed to withstand 2 500MW of unplanned outages and could therefore cope with the failure at Duvha. However, he said the maintenance schedule for other stations would be affected, putting strain on an already pressured system.
During the briefing Lakmeeharan said Eskom was working to improve its supply capacity by upgrading plant performance and targeting more than a billion kWh of savings internally.
It aimed to sign up more than 400MW in co-generation and own generation projects by April. In addition, he said, Eskom has begun to sign short-term contracts with municipal power stations such as the Kelvin station in Johannesburg to try to bring in additional capacity.
The industry has waited with bated breath for the final IRP, which the Cabinet approved for promulgation this week. It forms the basis of the South African power generation programme for the next 20 years.
The Cabinet also approved the tabling of the Independent System and Market Operator (ISMO) Bill in Parliament. The establishment of an ISMO is a key requirement for bringing independent power producers (IPPs) onto the grid.
“IPPs will minimise the financial burden on the state in relation to the building of new generation capacity and they will spread the burden and risk relating to providing power capacity,” the Cabinet said in a statement this week.
Pictures of generator tell a thousand words
Photographs that appear to be of the aftermath of the accident at the Duvha power station in Mpumalanga on February 9 have found their way onto the internet, fuelling speculation that the accident was the result of operator error.
The pictures, posted on the Facebook page of Chris Yelland, the managing director of EE Publishers, show the extent of the destruction inflicted on one of six generator units, which malfunctioned during a test of the turbine’s overspeed-protection system.
Eskom released a statement after the incident saying that it was conducting a technical investigation into the matter. In response to media queries Eskom spokesperson Hilary Joffe said the damage would take year or more to repair.
However, a turbine expert told the Mail & Guardian this week that the damage appeared to be so severe, it could take two if not three years to repair, as the unit would probably have to be replaced in its entirety.
Joffe said Eskom had made “no secret” of the fact that the damage at Duhva was “extensive”. She said Eskom had acknowledged that the supply situation was tight and the utility was “on the alert”.
“But we are determined to avoid load-shedding, as we have said, and we are managing the risks carefully. We simply cannot speculate on the outcome of the investigation that is being conducted,” she said. “We will make a statement on the findings once the investigation is complete.”
A failure of safety mechanisms
The expert, who asked to remain anonymous, said the damage depicted in the photographs suggested that every safety mechanism on the turbine unit had failed, including the manual override system. The unit appeared to have sped up to such an extent its component materials had failed under the massive centrifugal force created.
Portions of the turbo-generator’s shafts sheared off the unit’s central line, while blades, bolts and other bits of debris punched holes in the roof of the turbine hall.
One very large hole in the roof suggested that large pieces of machinery were hurled into the air and out of the building. One of the photographs appears to indicate that a large portion of the turbine shaft embedded itself in the concrete.
“It is a miracle that no one was killed,” the expert said.
For a material failure of this magnitude, the turbo-generator would have had to be spinning at more than 4 000 revolutions per minute — well above the test rate.
The source estimated that the damage could cost billions, especially if the entire turbo-generator train had to be replaced.
The M&G received an email from someone claiming to have internal Eskom information and alleging that in a situation in which three independent protection systems on the turbine system failed, the manual override system had been left unmanned.
The M&G understands that a roll-call, required before the test was meant to take place, was not carried out, suggesting that basic procedure was not followed. Eskom did not answer questions directly relating to these claims.
[Editor: A similar incident happenned at this same power station in 2003. See http://www.massengineers.com/generator_accident_in_africa.htm