Automatic Change of the Stator-Winding Connection of Variable-Load Three-Phase Induction Motors to Improve the Efficiency and Power Factor

摘要

Most oversized three-phase induction motors operate with low efficiency and power factor, which is by far the most important cause of poor power factor in industrial installations. In the low-load operating periods, motor performance can be improved both in terms of efficiency and power factor through stator-winding connection change from delta to star. In this paper, a new low-cost electronic device for automatic change of the stator-winding connection for efficiency and power factor improvement in variable-load three-phase induction motors is proposed and experimental results are presented. Some technical and economical considerations related to the final application of the device are discussed. The proposed device is particularly suitable for low-medium power three-phase induction motors, with significant load variation during their duty-cycle, including long, low-load operating periods. The application of the proposed device in such motors can lead to significant energy savings and to the power factor improvement, largely compensating the additional modest investment in the device. The importance of this work is highlighted by the recent concerns about the need to achieve energy savings in the industrial and in the tertiary sectors.