Measurements of stray losses in induction machines with die-cast aluminium rotors

The rotor bars in induction machines are usually skewed in order to reduce parasitic effects created by the stator and the rotor slotting. In skewed rotors having uninsulated rotor bars, inter-bar currents can create large losses, reducing the efficiency of the machine. This paper presents results from calorimetric measurements of the total losses in an 11 kW induction machine, equipped with either a skewed or an unskewed die-cast rotor. The losses are segregated for a comparative study of the different loss components. It was found that, for the studied machine designs, the stray-load losses are redistributed rather than reduced when the rotor skew was removed.