Evaluation of a Re-rated induction machine

Motor re-rating presents an alternative to field weakening for electrical machines used in traction applications. A re-rated motor is capable of providing its nominal torque at higher speeds, increasing its shaft power while keeping the motor mass constant. In this paper, a discussion of the impact of re-rating on the efficiency and various losses of an induction machine is presented. When a re-rated motor operates at higher speeds, the total loss of the machine increases more gradually than the shaft output power. Thus, the efficiency of this machine increases at higher speeds. Measured results from a re-rated 12.4 N-m induction machine support the discussion and show that re-rated induction machines can compete with permanent-magnet machines in terms of efficiency in traction applications.