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Analytical Calculation Model of an Induction Machine with Combined Star-Delta Windings and Analysis of Possible Connections

An analytical calculation model of an induction machine with combined star-delta windings and squirrel cage rotors taking into account multiple armature reaction, slot openings and saturation is presented. The model bases on the harmonic field theory and makes it possible to calculate the steady-state behaviour including harmonic currents in stator and rotor as well as parasitic torque components. Furthermore, every phase is considered seperately which permits to analyse different connections in detail. It is to mention that the model is also valid for regular six-phase machines. The derivation of the model with all its simplifications and assumptions as well as the consideration of saturation are discussed. The analytical calculation model is compared to the results of a transient FEM considering iron saturation as well as measurements to verify its validity. Moreover, the paper presents another method to substitute integral slot windings of three-phase machines with an uneven number of slots per pole per phase with combined star delta windings. Also, the paper compares the performance characteristics of the combined star-delta winding in series and parallel connection with a three-phase and a true six-phase winding.