Online calculator highlights the huge savings potential of variable-speed drives

The effectiveness of variable-speed drives in reduce carbon emissions associated with electric motors can be assessed with ABB’s online calculator.
ABB has launched an online calculator that shows how much energy and carbon emissions can be reduced by controlling electric motors using variable-speed drives. Steve Ruddell, general manager for drives and motors, explains, ‘The possible savings can be very substantial. Reducing the speed of motors with variable-speed drives can frequently save over 50% of the energy used and, in extreme cases, by as much as 90% — without any detriment to the application. Motors are used in a wide variety of applications, dominated by pumps (32% of the energy consumption of industrial motors) and fans (22%). Both applications are capable of achieving large energy savings with variable-speed control. Many other applications can benefit from improved efficiency with variable-speed drives. Despite this, only about 3% of motors are equipped with efficient speed control. Considerable energy waste occurs when the flow of air or water is reduced by dampers or valves. On-off control results in poor control, irregular flow and considerable start-up current. The variable-speed drive is the only method of directly control flow at source by varying the speed of the electric motor. Steve Ruddell says, ‘Drives are easy to install and can be added to existing plant. Because they save energy, there is no long-term cost. On the contrary, they make a positive contribution to the bottom line. It will be difficult to achieve equally impressive saving with any other method.’ One recent ABB project involved replacing fixed-speed starters on two pumps with 30 kW motors. Once under drive control, these motors used only 6.7 kW. Electricity costs of £18 000 a year were reduced by 75%, or £13 600. The drives cost £9000 to buy, so the payback was only 33 weeks. This installation reduced carbon-dioxide emissions by 80 t a year.
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