Squirrel Cage Induction Motor: a design-based comparison between aluminium and copper cages

In many industrial applications the self-starting capability of electric motors is still an important requirement enabling to simplify the drive architecture and increase the system's reliability. The efficiency improvement of this motor topology has been targeted by various national and international regulatory authorities with ad-hoc policies. Indeed, a lower energy consumption leads to the twofold benefits of reducing the operational costs and the CO 2 emissions. The adoption of a copper cage has been successfully proven to reduce the motor losses. However, this could affect other performance indexes, such as the starting torque. In this paper, the advantages and drawbacks of adopting a copper cage are analysed in depth by comparing the motors performance at different operating conditions, with respect to the more common aluminium cage. Starting from a set of induction machines optimized with an aluminium cage, the effect of the direct material cage substitution is analysed both in terms of electromagnetic and thermal aspects. The overall performance are also compared against machines specifically optimized with a copper cage. With the presented performance comparison exercise, general design guidelines are outlined aimed at improving the efficiency without deteriorating other performance metrics.