Representation of rotor spiders in reduced finite-element models for cage rotors

The high degree of symmetry present in many induction motor cage rotors lends itself well to a reduction in model size from one that comprises one or more poles, to one spanning a single slot pitch. This use of a reduced model ensures that a fine finite element mesh of typically around 300 nodes may be used to model intricate rotor slot shapes. Such a fine mesh would be prohibitively expensive if a greater part of the machine had to be modelled. The single-slot symmetry of the cage rotor is disrupted, however, when the rotor core is supported using a spider. The purpose of this paper is to investigate means of accommodating rotor spiders in reduced rotor models in an averaged sense. Comparisons are made between models with modifications that allow for spiders and more extensive models in which these features are more realistically represented.