Influence of the air-gap length to the performance of an axial-flux induction motor

The influence of the air-gap length on the performance of a 45 kW / 6000 min^-1 axial-flux aluminium-cage solid-rotor-core induction motor is studied. The length of the air-gap has a significant influence on the characteristics of an electric machine. In the machines that are designed for speeds above 3000 min^-1 (which can be reached with the 50 Hz network), the air-gap length has to be increased considerably from the value obtained for a standard electric motor. Especially, if the motor is equipped with a solid rotor core, the air-gap length has to be designed with special care. It is shown that the efficiency of the studied motor is highly dependent on the rotor eddy current losses. The determination of the losses is done by using numerical 2D FEM calculations and measurements for the prototype machine. In this paper, it is shown that by changing the air-gap length the loss minimum can be found between the rising stator copper losses and the diminishing rotor harmonic eddy current losses.