Eskom: Warmer weather reduces demand

Johannesburg - Warmer weather this coming week will keep peak electricity demand below 35 000 Megawatts (MW), Eskom said in its 56th system status bulletin.

It forecast peak demand at 34 693 MW on Tuesday‚ 34 565 MW on Wednesday‚ 34 505 MW on Thursday‚ 33 693 MW on Friday‚ 32 379 MW on Saturday and 32 535 MW on Sunday.

The peak demand so far this year was supposed to be 36 258 MW on July 16, according to the 54th system status bulletin.

Demand side management‚ which involves asking large industrial users to temporarily stop some industrial processes‚ meant that the actual peak demand was only 35 443 MW or a saving of 815 MW on July 16.

Unplanned outages eased to 2 900 MW on July 23 from 4 500 MW on July 19 and 4 100 MW on July 16.

Eskom said in its planning for winter that planned maintenance would only be 600 MW last week instead of the actual planned maintenance of 2 250 MW.

Unplanned outages were 4 100 MW, even though the 900 MW Koeberg Unit 1 was returned to service after an electrical fault on the non-nuclear side of the unit shut down the unit on July 11.

The Koeberg shutdown meant that outages due to unplanned maintenance shot up to 4 717 MW on July 12 from 3 626 MW on July 9‚ but it should have returned to Eskom’s benchmark of not having more than 3 600 MW out in unplanned outages.

The peak unplanned outages so far this year were 5 776 MW on May 3.

The available capacity of 35 514 MW on July 12 was well down on the 37 105 MW available on July 9 and this year’s peak of 38 168 MW on June 25.

Planned maintenance and unplanned outages on July 23 were 2 266 MW and 2 900 MW from 4 240 MW and 4 011 MW respectively on May 21.

Unit 1 at the Koeberg nuclear power station only returned to service on May 31 after being taken out of service on March 12.

Each of the two units at Koeberg is shut down for refuelling‚ inspection and maintenance approximately every 16-18 months.

These routine shutdowns are scheduled so as to avoid having both units out of service at the same time, and to avoid the winter months in each year.

During these routine planned outages‚ one-third of the used nuclear fuel is replaced with new fuel‚ statutory inspections and maintenance are performed‚ and modifications that will improve safety or the plant performance are implemented.

The scheduled shutdown of Koeberg Unit 1 was part of Eskom's overall maintenance programme for its fleet of power stations.

The shutdown was therefore taken into account in Eskom's plans to keep the lights on‚ and did not result in a shortage of supply to the Western Cape or the rest of the country.

The return of all Koeberg’s units to service meant that available capacity rose to 36 558 MW on May 31 from only 34 884 MW on May 21‚ when peak demand was 34 390 MW.

This meant that spare capacity on May 21 was only 454 MW, or less than one 600 MW modern generator at a coal-fired power station. This was a margin of 1.3%.

The international norm is 15% as utilities need to provide for both planned maintenance and unplanned outages. On January 9 peak demand of 30 282 MW was met by available capacity of 30 742 MW.

The peak planned maintenance so far this year was 7 473 MW on April 5‚ while the peak unplanned outages were 5 776 MW on May 3‚ and the low was 2 200 MW on June 18.

On May 31‚ planned maintenance dropped to 3 185 MW‚ while unplanned outages were 3 460 MW.

On February 9 2011‚ the 600 MW unit 4 at Duvha power station was taken off-load for a statutory turbine test. The protection on the unit failed‚ causing severe mechanical damage to the turbo generator and the surrounding area and starting a fire.

The fire was rapidly brought under control by the power station’s fire team. This was the first time one of the Duvha units failed during such a test. The other five Duvha units were not affected and continued to supply electricity.

The root cause of the incident was a modification applied by Eskom in 2004 that‚ inadvertently‚ when installing a new programmable logic controller‚ removed a maximum speed limit during over-speed test conditions.

The modification error has been corrected on the remaining units‚ while corrective actions have been applied to eliminate contributory causes.

The Duvha recovery project is progressing in phases‚ with the unit due to come online in the second half of 2012.