Eskom offers insight into Duvha, Kendal trips, amid more load shedding

12th June 2014

By: Terence Creamer

Creamer Media Editor

  

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A further power system emergency was declared on Thursday afternoon and a second night of load shedding was instituted, following the first load shedding of winter on Wednesday June 11. Eskom also indicated that conditions for the rest of the month and July could “be similar”, owing the “short sharp evening peak”, which made the system vulnerable to “short term” failures.

The utility said it would use all necessary emergency resources at its disposal, with load shedding being deployed as a “last resort to protect the national grid from a total shutdown”.

The two hours of load shedding on June 11 was precipitated by trips at Kendal Unit 1 and Duvha Unit 5, as well as lower-than-expected supply from Cahora Bassa, in Mozambique.

Both unit trips were the result of “unexpected equipment failures” and Eskom insisted that the latest Duvha incident was “totally unrelated” to prior events where Duvha contributed to load shedding during 2014. Eskom deployed load shedding for 14 hours on March 6, as a result of coal-related problems.

Kendal Unit 1 tripped at 16:50 as a result of a boiler ‘thermo-pyro’ protection signal. “The protection signal was due to boiler instability caused by a half-load condition following a trip on one of the feed pumps. The feed pump tripped due to an electronic control card failure, which was replaced. The unit was resynchronised to the grid at 19:13,” Eskom explained.

At Duvha Unit 5, the 400 kV breaker opened at 17:59, owing to the negative phase sequence protection operating.  “The Unit ‘islanded’, meaning that the protection system identified a problem with, and disconnected itself from, the national grid – the unit remained fully functional but was not generating and supplying electricity to the network,” Eskom explained, saying that the cause was currently under investigation, with a faulty protection relay suspected.

The unit is currently in the process of being returned to service and is expected to be resynchronised to the grid on Friday morning.

Both units had been on outage recently, with Kendal Unit 1 returned to service in May 2013 and Duvha Unit 5 during December 2013.

Eskom insisted that the quality of all maintenance had been carefully monitored, but that the fleet was being “run hard” and units were, thus, prone to “higher levels of wear and tear, which results in higher levels of breakdowns”.

“Management actions have been initiated to improve technical reliability, for example reducing partial load losses, unit trips and boiler tube leaks. The risks at each power station and actions to mitigate those risks have been identified.”

Eskom was also expecting supply from Cahora Bassa to recover to 1 500 MW by the end of July, as opposed to the 1 200 MW it is currently receiving.

It was also drawing on all of its other supply- and demand-side options, having interrupted load to the BHP Billiton aluminium smelters during the June 11 emergency.

It also had about 1 000 MW of demand-reduction contracts in place with other energy-intensive consumers and was purchasing about 450 MW of additional capacity from private and municipal suppliers. Those contracts would remain in place until the end of April.

Edited by Creamer Media Reporter

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