Load management projects at the Department of Water Affairs through an integrated systems approach

The Department of Water Affairs (DWA), is responsible for the sustainable supply of useable water in South Africa. This water is not only used for residential and agricultural purposes but also to provide water for industrial processes, the mining industries and cooling water for power stations. South Africa is divided into 19 water catchment areas. This case study focuses on the Usutu-Vaal Government Water Scheme (GWS). The Usutu-Vaal scheme in Mpumalanga close to Standerton supplies water to Sasol and four power stations - Tutuka, Matla, Kriel and Duvha. Water is also transferred from Matla to Kendal power station. Usutu-Vaal consists of six pump stations. For the purpose of this article only Grootdraai (GD), Grootfontein (GF) and Rietfontein (RF) pump stations are considered. Water is pumped from the Grootdraai dam, both to Tutuka power station and through a 40 km canal to GF which is a booster pump station. GF in turn pumps water to both Sasol and via Trichardt dam towards Rietfontein dam. New infrastructures were implemented to control the pumps and a new control philosophy was developed for the pump operational scheduling and for the management of the two pump stations in series. Due to the long distance of the canal, changes to the water flow at GD will take from 11 to 16 hours before being detectable at GF. The new control philosophy involves operating two pumps at both of these pump stations. The main objective of the DSM project is to ensure that water is not pumped during the ESKOM evening peak period at both GD and GF. Due to the lengthy delay in the actual water flow variation at GF, the GD pumps must be stopped between 07h00 and 09h00. Fortunately this coincides with the ESKOM morning peak period. The power-demand baseline, before project implementation, indicated that the average potential peak time power savings would be 10.15 MW. These savings were comfortably achieved by the new control philosophy.