Induction motor downsizing as a low-cost strategy to save energy

Most three-phase, squirrel-cage, induction motors (SCIMs) are oversized. In the European Union (EU), the average load factor of SCIMs is slightly lower than 60%. In fact, in some industrial sectors, a large part of SCIMs operates with a load factor as low as 25%. Therefore, since the motor load factor is an average of its load over the operating cycle, it can be said that a large quantity of IMs operates with a load under 60%. In oversized IMs, if the actual load cycle is known, it is possible to properly redesign the original stator winding in order to match the peak efficiency with the maximum or dominant load, by means of a magnetizing flux reduction, ultimately leading to the motor power decrease (i.e., downsizing). Moreover, since the original motor active material quantity is maintained, the iron and copper losses and the magnetic saturation level will be reduced, improving the motor efficiency and power factor. In some cases, it is possible to convert an oversized standard motor into a well-sized high-efficiency motor, particularly if best practice is applied during motor repair/rewinding. Even considering the typical 1% efficiency drop due to poor-quality motor repair/rewinding, the motor efficiency gain after downsizing can still be significant. The motor lifetime can also be extended, which is an environmentally advantageous aspect. In this paper, a short review on optimized redesign of oversized SCIM stator windings is presented. Additionally, a large-scale rewinding-based motor downsizing strategy is proposed and the associated savings potential in the EU is estimated.