Water, Sewage & Effluent January-February 2017 - Page 21

The pumped storage scheme consists of an upper and a lower dam , each capable of holding more than 20-million cubic metres of water .
generated by conventional coal and nuclear plants , is used to pump water to the upper reservoir .
The upper Bedford Dam , on Bedford stream — a tributary of the Wilge River — was completed in April 2011 . It is a 39m tall concrete-face rock-fill dam . It has a 22.4-million cubic metre water storage capacity , of which 19.2-million cubic metres can be used for power generation .
The lower Braamhoek Dam , on Braamhoek stream — a tributary of the Klip River — was completed in November 2011 . It is a 41m tall rollercompacted concrete gravity dam . It has a 26.3-million cubic metre water storage capacity , of which 21.9-million cubic metres can be pumped up to the upper reservoir .
A 2km long headrace tunnel connects the upper reservoir to the underground power station , which will house 4 × 333 megawatts ( 447 000hp ) reversible Francis pump-turbines . The elevation between the two reservoirs affords a hydraulic head ( water drop ) of 480m ( 0.30mi ). Water from the power station is discharged down a 2.5km ( 1.6mi ) long tailrace tunnel to the lower reservoir
To generate electricity during times of peak demand , water is released from the upper dam , passing through the pump / turbines , into the lower dam . During times of low energy demand , the pump / turbines are used to pump the water from the lower dam , back to the upper dam .
“ Water flows at high speed down to the turbines at around 60km / h , with enough water passing through each turbine to fill an Olympic-sized swimming pool in six seconds . Rotating at 428 revolutions per minute , each unit will produce 333MW , giving a total of 1 332MW for the station ,” Eskom explains .
“ On completion of all four units , Ingula will be part of Eskom ’ s peaking fleet of power stations . It can respond to demand increases on the national grid within two-and-a-half minutes . Upon completion , Ingula will be Africa ’ s newest and largest pumped storage scheme and the nineteenth largest in the world .” u networking tech news environment industry infrastructure municipalities
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