Induction motor efficiency improvements with low additional production costs

In order to verify the efficiency class limits imposed by the American and European standards, a redesign of the induction motors now in production is generally requested. If the stator core diameters or the slot geometries have to be changed, the investment costs for producing high efficiency induction motors can be prohibitive for small and medium companies. For these reasons, it is interesting to analyze low cost solutions can lead to an efficiency improvements. A simple method consists in the axial length increase of the motor core. In order to quantify the effects of an axial motor increase onto machine efficiency, two induction motor prototype have been realized. These prototypes have been obtained from standard motors with an increment of the magnetic core axial length and with optimized stator rewinding. The complete design procedure together with the motor test experimental results are reported. The energetic performance of the prototype have been performed in accordance with the IEEE std.112-96 method B. The obtained results confirm the validity of the proposed solution and the obtained efficiency improvements can be considered very interesting.