Slide rule reveals the energy-saving potential of variable-speed drives for motors
The savings that can be achieved by converting a direct-on-line motor to variable-speed control can be assessed using a free slide rule from ABB. The first stage is to select the power of the direct-on-line motor, and its typical running costs and energy consumption are revealed in a window. Turning the slide rule over shows the effect of applying a variable speed drive under a wide range of conditions.
The worst case is a motor running at full speed, with no damper or throttle. The comparison is with a variable-speed drive at 20% lower speed for anything from 8 h a day over a 5-day week to continuous operation over a whole year.
For example, a 110 kW motor without any form of speed control uses 771 MWh a year when run for 8760 h. Adding variable-speed control more than halves the annual energy consumption to 376 MWh.
That saving is equivalent to the energy used by 3422 high-efficiency light bulbs.
