Retaining rings in a generator are used to constrain the centrifugal force of the field winding end turns. A conventional retaining ring may cause a high pressure drop at the stator-rotor gap entrance and thus result in a large windage loss. The present work relates to the design of a retaining ring with a spline profile near its inboard end to thereby improve the axial cooling flow fluidity and enhance generator cooling efficiency. By altering the outer profile of the retaining ring, it has been found that approximately 30–60% of the pressure drop across the stator-rotor gap entrance can be reduced. As a result, the overall generator efficiency may increase about 0.005–0.01%.

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