Pretoria - Workers who deviated from the rules earlier this year knocked unit four at Eskom’s Duvha power station - and thus 600MW of critical generation capacity - out of the generation system.
The power giant this week disclosed the findings of a comprehensive investigation into an event that on February 9 resulted in massive damage to the steam turbine, electricity generator and components supporting the unit.
The loss of 600MW could topple the balance of South Africa's extremely fragile electricity supply, again causing power cuts to ravage the country, particularly over the coming three months.
The mechanical damage at Duvha at the time caused a fire leading to structural damage to the adjacent walls and steel support structures.
The good news is that Eskom’s insurer will cover the claim for the damage. Eskom spokesperson Hilary Joffe declined to disclose the amount, but said that it was considerably less than the R3bn previously mentioned to Sake24. As in the case of any other insurance claim, an excess payment is required, said Joffe.
Last week Eskom chief executive Brian Dames said that Eskom itself, two groups of independent consultants from the insurer as well as Eskom’s engineering consultants had come to the conclusion that deficient and ineffective management in several areas had led to the incident.
The underlying cause was modifications to the control system in 2004. The direct cause was that the operator had deviated from the prescribed procedure for the overspeed test.
Joffe previously explained to Sake24 that the turbine generator unit normally rotated at 3 000 revolutions a minute.
Eskom is statutorily obliged to perform an overspeed test once a year. During this test the unit is uncoupled from the national grid.
A valve that controls an enormous burst of steam to drive the turbine is then gradually opened to increase the steam’s pressure on the turbine. The speed at which the turbine rotates increases as the steam pressure rises.
Joffe said that the system has a bolt that starts to retard the rotational speed of the turbine as soon as it exceeds the design speed of 3 000 revolutions a minute by more than 10%. This time, for some other reason, the safety mechanism failed.
The result was that the turbine rotated faster and faster. The rotational speed increased too rapidly for anything to be done before the massive machine exploded into pieces with tremendous impact.
Eskom said the modifications have since been replaced by modifications approved by the manufacturer. All other units at Duvha have been inspected and, where necessary, the same modifications have been replaced. New rules have been introduced to prevent a repetition.
Where staff members had deviated from prescribed procedures Eskom would take disciplinary action, if necessary, said Joffe. Monitoring requirements for similar testing and training materials have also been improved
Dames said the current focus was on repairing the unit.
Eskom’s teams have already dismantled the damaged equipment, determined the precise extent of the damage and started to buy new components.
The turbine and the foundations of the generator will be repaired early next year, after which the system will be assembled by mid-year.
The unit is expected to return to operation by the third quarter of 2012.
Switch off for electricity
On Wednesday Eskom warned that the amount of electricity that it is able to generate in the next three months will be too little to meet demand. South Africa therefore faces power cuts.
According to the power giant’s forecast there will virtually continually be a shortage of up to 1 000MW. From December 12 to 25, and again in the February 6 week, the shortage could run to 2 000MW.
The situation can improve considerably if electricity consumers switch off appliances, especially during peak periods.
