ABB Drives cut £100,000 from Severn Trent Water's pumping bill
Severn Trent Water (STW) is saving around £100,000 per year on energy costs thanks to the installation of ABB variable speed drives at its Wanlip Sewage Treatment Works.
STW was suffering low flow rates on its dry well flow pumps, with typical rates being less than 400 litres per second against a design of 550 litres per second. This meant that under storm conditions the works was unable to achieve the rates specified under the Environment Agency's consents, without the need for supplementary temporary pumping; further adding to the company's operating costs.
Sentridge Control, a member of the ABB Drives Alliance, had cured a similar problem at an-other of STW's treatment works and was asked to get involved in providing a solution at Wanlip. Sentridge's Glen Hickman says: "We suspected the problem was due to ragging of the pumps and reversed the flow of selected pumps to prove this. Ragging is where rags foul the pump inlet and prevent the pump from operating normally."
The original installation had four direct on-line pumps and two pumps controlled by variable speed drives (VSDs). One of the VSD driven pumps was a duty pump while the other was used to assist as pumping requirements demanded.
Historically, reversing the pumps had allowed them to achieve higher flow rates for short pe-riods of time. One of the direct on line pumps achieved 550 litres per second compared to 325 litres a second previously, while one of the VSD powered pumps achieved 575 litres a second, compared to 390 litres a second.
To solve the problem permanently, Sentridge suggested installing 75kW ABB industrial drives on all the pumps, each equipped with ABB Anti-Jam software, part of its Intelligent Pump Control (IPC) software. An add-on to ABB industrial drives, IPC contains all the com-mon functions needed by water and waste utilities, industrial plants and other pump users.
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