The three-phase induction motor with solid-iron rotor has advantages in case of manufacture, in high torque per ampere at standstill, and in withstanding high rotational stresses. Recently there has been wide interest in the possible use of such a solid-rotor induction motor for ultrahigh-speed inverter drives with suitable high stator frequency. However, the copper loss of the solid-rotor induction motor becomes large, because it is designed with a high resistance rotor. Accordingly, the efficiency and the power factor of the motor are lower than those of conventional induction motor.
In this paper, it is clarified experimentally that starting and running characteristics of the solid-rotor induction motor are improved considerably by providing narrow slits and end-rings on the rotor. Then, a new equivalent circuit for the solid-rotor induction motor is derived considering the behavior of the solid-iron rotor as that of the double-cage rotor, and a method of determining the circuit constants for the motor is proposed. The starting characteristics for the solid-rotor induction motor with narrow slits and end-rings on the rotor is calculated using the proposed equivalent circuit. The results calculated for starting characteristics from the equivalent circuit method agreed satisfactorily with results obtained. from the measurement.