Comparison of losses in star- and delta-connected induction motors with saturated core

Motor market is moving to IE3/Premium and IE4/Super-Premium efficiency classes and a significant effort is being made by motor manufacturers to increase the rated efficiency without increasing significantly manufacturing and materials cost. Moreover, since line-operated squirrel-cage induction motors can be started with electronic soft starters, their stator windings may be designed to operate in star-connection mode. In this paper, the possibility of reducing the motor losses by designing the stator windings to operate at rated voltage and rated power in star-connection mode is discussed. An experimental comparison of a star- and delta-connected motor, with regard to phase current, input power, losses, and efficiency, considering the same fundamental phase voltage, under different core saturation levels, is presented. This study indicates that the star connection can lead to lower homopolar harmonic losses for the same saturation level. This fact can be used by motor manufacturers to increase the motor efficiency or, alternatively, to increase the core saturation level while maintaining the motor efficiency. The latter option may lead to a reduction of the core length, ultimately providing a way to reduce the motor weight and manufacturing cost.