Influence of Villari Effect on the magnetizing current of Induction Machines by shrink fitting of rotor cores

In this paper the influence of the Villari effect, also known as the magnetoelastic effect due to the shrink fitting of rotor cores, on the magnetizing current of electrical machines is investigated. Typically the assembly between the shaft and the rotor lamination stack is done by an interference fit. The resulting mechanical tensions in the rotor lamination range up to the elastic limits. The mechanical tensions influence the magnetizing behavior of the laminations. A method is presented which includes these effects in numerical and analytical calculations of the magnetizing current based on measurements of the magnetic properties of the used material. The measurements are done with ring samples and an Epstein frame, for both DC and AC excitations. The influence of compressive and tensile stress is measured by a Single Sheet Tester (SST) providing the option to set a compressive and tensile stress. The mechanical tensions in the rotor laminations caused by the interference fit are analytically and numerically calculated in order to apply the results of the measurements with the SST on the electromagnetic calculation model. The mechanical tensions cause an increase of the magnetizing current. A recommendation is published concerning the mechanical dimensioning of the shrink fitting relating to the influence on the magnetizing current of the machine.