Operating Characteristics and Magnetic Field in Starting Process of Squirrel-cage Asynchronous Motor

A two dimensional finite element model of 1.1kW three-phase squirrel-cage asynchronous motor is built by using a finite element analysis software. The operating characteristics, the distribution of magnetic field and rotor current density are calculated and analyzed in the starting process. The diagrams of stator current and output torque against rotor speed are obtained. Motor magnetic lines of force and current of rotor bars at different times in the starting process are also obtained. It is shown that magnetic lines of force are mainly concentrated in the thin layer close to the surface of rotor while starting and the density of current of rotor bars gradually increases along the radial direction and the skin effect is significant. However, the magnetic lines of force are distributed evenly in the core of stator and rotor when the motor is steadily operating and the current of rotor bars is also evenly distributed. This kind of studies can offer a reliable basis for the calculation of parameters, the improvement of structure, the design of the control system of the motor and the temperature field calculation of asynchronous motors.