A comparative study of energy saving benefits in softstarters for three-phase induction motors

Modern soft-starters have both soft-starter capability and energy saving functions which are special useful when the motor runs at low load. This paper investigates modern soft-starters for induction motors at three different power levels (3 kW, 7.5 kW and 22 kW). The investigation includes efficiency measurements, start-up measurements and measurement of the grid current harmonics at different loads to investigate the soft-starters performance against new regulations. The measurements are compared with an induction motor without soft-starters. It is concluded soft-starters have energy saving capabilities at low load up to 4% of rated power for small motors, but it is also concluded the payback time will be long. Finally, it is concluded soft-starters have problems with new grid disturbance regulations at low load operation.