A performance comparison of different rotor types for high-speed induction motors

In recent years, improvements in the manufacturing, transport and process industries have brought about an increase in the optimum operating speed for drive systems. In this respect, the recently developed, high-speed, gearless or direct electrical drives are currently very popular, because of the reduction in the total structural volume of the drive system. In this study, the performances of four high-speed induction motors with different types of rotor, i.e., cage, smooth solid, slitted solid and coated solid, were examined in cases where the geometrical size is kept constant. All the motors with different rotor types have a particular number of turns per phase in their slots, which is arranged to obtain the same rated current value when compared with the reference, conventional cage-induction machine. In order to compare the performance characteristics brought about by the change in the rotor's structure for different numbers of turns, all the induction motors were analyzed with the finite-element method (FEM). Using a coating with a high electrical resistivity was shown to increase the torque output. It was also clear that cutting the rotor in the axial direction increases both the flux penetration and the efficiency.