Optimized Manufacturing Process and Modelling of Squirrel-Cage Induction Machines with Copper Cage and Axially Segmented End Rings for High-Speed Applications

In this paper, calculation models and measurement results of squirrel-cage induction machines with copper cage and axially segmented end rings produced by an optimized manufacturing process are presented. The design of the copper-bar rotor winding is based on an analytical calculation approach that takes into account the technologically and electrically interconnection between rotor bars and segmented short-circuit rings according to the applied laser and electron beam welding process. Rotors with aluminum and copper short-circuit cages manufactured by die-casting serve as a basis for comparison. Based on the separation of losses as well as no-load, load and short-circuit measurements, the influences of the optimized production process using laser welding and the cage material on the efficiency and the operating behavior are discussed. In addition, aspects of mechanical high-speed performance for application in electric mobility are considered by means of overspeed tests of prototype rotors. Moreover, numerical models are derived to describe the electromagnetic behavior of segmented rotor cages. Using numerical 3D field calculation, the current and loss densities, which are particularly important in the interconnection between rotor bars and short-circuit end rings, are determined. With the aim of increasing the accuracy of the design process, analytical calculation approaches for the most accurate consideration of the welded joint in the short circuit ring are presented.