Energy conservation with use of “soft-starter”

The authors describe how energy saving has been obtained by using the soft-starter to reduce the voltage applied to the motor. Iron losses are then reduced and energy saving is achieved. The use of an autotransformer instead of a soft-starter has enabled a high energy saving, because the additional losses due to the harmonic currents are not present in this case. Energy saving with no load motor has been about 11% by using the soft-starter and 25% when the autotransformer is used, for load torque proportional to speed and for constant torque loads. Energy saving is decreased when the load torque is increased. Energy saving has been obtained until a load torque of about 42% of the rated torque; for higher torques no energy conservation is achieved. So the results of this paper are useful only for low load conditions. When the autotransformer is used the power factor and efficiency are better than in the other cases