The risk of a total blackout is lower than it was a decade ago, according to the man behind Eskom’s load shedding operations.
Eskom’s general manager of the national electricity system operator, Robbie van Heerden, said the transmission network has been strengthened, and there is heightened awareness and contingency plans in place to avoid a blackout scenario.
He was speaking at a South African Institute of Electrical Engineers (SAIEE) seminar last week about the future of South Africa’ power network.
Antonio Ruffini, who wrote a story for the June edition of the institute’s wattnow magazine, said a blackout would be a “black swan” event.
The black swan theory is a metaphor that describes an event that comes as a surprise, has a major effect, and is often inappropriately rationalised after the fact with the benefit of hindsight, according to Wikipedia.
Total blackout would have catastrophic effect
Unlike load shedding, which is the controlled rotational shedding of electricity supply to prevent the chances of a complete blackout, a total blackout of the national power system would be a catastrophic event, according to Van Heerden.
“It is an extremely low probability, very high impact event, likely to occur once every 50 or a 100 years, coming about due to an unforeseen sequence of occurrences that results in the cascading collapse of the integrated transmission or generation system,” Ruffini wrote.
“In the event of a complete blackout, a cold start of the national power system would be required and it could take up to two weeks before electricity supply is restored in certain areas,” he wrote.
Similar to civil war breaking out
Van Heerden told the seminar that it would be a “disaster akin to civil war breaking out in the country. Darkness, no or minimal telecoms, water reticulation schemes running dry within days, social unrest, looting…
“In order to sustain South Africa’s grid at its 50 Hz frequency level and avoid the risks of a total blackout, taking into account the ongoing tight state of the national electricity system, frequent load shedding occurs, even with the use of emergency diesel fired generation units, interruptible loads, and the country’s pumped storage facilities.
“However, in spite of the lack of spinning reserve, something mitigated in part due to the interruptible supply agreement Eskom has with BHP Billiton’s aluminium smelters, the risks of a total blackout today could be lower than they were a decade ago.”
What could cause a blackout
“It would require the system frequency to drop to about 47 Hz for the various turbines in the grid to trip and create the blackout event, and the lowest under-frequency occurrence thus far in the present era has been above 49.1 Hz.
“Typically an event that brings the frequency to about or below 49.2 Hz occurs once a year, the last being an incident on the 6th of March 2014 when the majority of units at Kendal power station tripped out. Frequency stability was restored within 45 seconds.
“South Africa experiences demand in summer of about 32 GW, going up to 36 GW or 37 GW during winter peaks. The system can withstand load on the grid being down to about 7 000 to 10 000 MW before the network becomes unstable and islanding starts happening in an attempt to avoid a total black start.
“The SAIEE is confident that the monitoring and operational management of the power constraint to the demand in the national grid is in good hands and that the residual technical skills capacity responsible for this critical activity is doing an excellent job in preventing a national grid failure or blackout event,” wrote Ruffini.
* The complete story will be published in the June 2015 issue of the wattnow magazine.
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