High Phase Order Induction Motors - Part I-Description and Theoretical Considerations

The characteristics of induction motors having more than three phases are presented. The sequence sets of the symmetrical component method are used to determine the inductances with time harmonics in the source waveform such as for inverter sources. The effect of stator coil pitch on these inductances is explained. It is shown that some of these harmonics cannot induce rotor currents in motors having many phases, thereby reducing the torque pulsations and rotor I2R loss below the values for three-phase motors. Other advantages are lower current per phase and the ability of the motor to start and run with one phase open. Six and nine-phase motors are found to be especially attractive.