Dynamoelectric machine having shielded retaining rings

Abstract

Surface currents are induced in dynamoelectric machine rotor body portions by negative sequence currents during unbalanced load operation. The surface currents are shunted away from retaining rings which are respectively situated on opposite axial ends of the rotor and function to restrain radial movement of conductor end turn portions which extend axially beyond the rotor's body portion. The retaining rings are shrink fitted on both ends of the rotor's body portion so as to structurally extend that body portion in both axial directions. Shunting the rotor surface currents away from the retaining rings provides an operating temperature therein of sufficiently low level to maintain high electrical joint integrity between the retaining ring and rotor. A mantle of highly conductive material surrounds both retaining rings in intimate electrical contact therewith. The mantle thickness is at least one-half depth of electrical current penetration for the rotor surface current's frequencies. The mantle is electrically connected to the rotor body portion preferably through interference fits with radial extensions of slot wedges which are situated in longitudinal slots formed in the rotor body radially outside electrical conductors disposed in those slots. The wedges constitute electrically conductive material and provide longitudinal electrical conductor retention in the rotor slots during high speed rotor rotation. Components joined through the interference fit include the mantle and the wedges' radial extensions. A material softer and of higher electrical conductivity than either of those joined components is preferably interposed as a plating material on either or both components.