Optimal Design Of Premium Efficiency Cage Induction Motors With Non-Skewed Asymmetrical Rotor Bars

The induction motor with skewed rotor bars are widely used to weaken the adverse effect caused by slot harmonics field, in small and medium induction motors, however, skewed rotors may cause magnetic saturation, the higher iron losses, meanwhile, the additional loss caused by inter-bar currents between rotor bars and other adverse effects. In order to solve this problem, the motor with non-skewed asymmetrical rotor bars are used in premium efficiency cage induction motors. With the time stepping finite element method, the loss, starting performance, air-gap force of the induction motor with non-skewed asymmetrical rotor bars are systematically studied. The main works are as below:1. Taking 5.5kW induction motor and 55kW induction motor as examples, the thesis analyzes the air gap magnetic field distribution characteristics of rotor respectively with straight bars, skewed bars and non-skewed asymmetrical bars at the initial moment by using time stepping finite element method, and studies the influence of the straight rotor bars, skewed rotor bars with different angle and non-skewed asymmetrical bars on the starting torque, starting current and breakdown torque. The starting performance of the motor with non-skewed asymmetrical rotor bars are compared and analyzed2. Taking 5.5kW induction motor as an example, the thesis analyzes the variety law of the iron loss, the fundamental copper loss of the stator, the copper loss of the stator, rotor copper loss, the total loss and the air-gap force. From the point of reducing loss and vibration, the optimal slot-combination with non-skewed asymmetrical rotor bars is proposed.3. The combination scheme of asymmetrical distribution rotor slot with different modulate coefficient of spatial position is designed, and the characteristics of the corresponding loss and air gap force are compared and analyzed. According to the natural vibration frequency of the motor, the variety laws of loss and air gap force are summarized. Taking noise and vibration into consideration, the reasonable non-skewed asymmetrical bars is selected.