Optimal design of rotor slot geometry of squirrel-cage type induction motors

This paper deals with the optimal design of squirrel-cage rotor slots and copper bars of high power induction motors with respect to the values of starting torque, breakdown torque, rated values of efficiency and power factor as well as rotor heating. Three geometries of rotor slots and of bars cross-section, keeping the same cross-section area, are considered: rectangular shape, stepped shape and step-holed shape. This study is based on the finite element analysis of the induction motor where only the rotor slots and bars cross-section configurations change from an application to another. The comparison of simulation results proves that important increase of starting torque and high values of efficiency of copper squirrel-cage type induction motors can be obtained in case of step-holed shape of rotor bars cross-section, without significant decrease of the breakdown torque. Criteria for evaluation of optimal geometry of rotor bars and of optimal value of bars cross-section area are studied.