Analysis and Modeling of Rotor Slot Enclosure Effects in High-Speed Induction Motors

In this paper, the effects due to the presence of closed or open rotor slots in high-speed induction motors are presented. In particular, the problem linked to electromagnetic effects on the motor current is analyzed in detail. Two 32 000-r/min induction motor prototypes, the former with open rotor slots and the latter with closed ones, have been built and tested in order to verify the theoretical analysis. A modified steady-state equivalent circuit to take into account the electromagnetic effects of rotor closed slots is proposed, and experimental tests have been performed to validate the proposed model. The presented study is focused on high-speed induction motors for turbomolecular vacuum pumps.