| 摘要 |
Fractional horsepower induction motors having a fixed number of poles (and, accordingly, a single no load synchronous speed) that are particularly adapted for multi-speed operation when driving a fan load by changing the field strength of the main winding. Induction motors of N fundamental poles have squirrel cage rotor having a plurality of interrelated conductor bars and end rings that are arranged so that multiple sets of the rotor bars establish a predetermined number of separately identifiable cage sets such that the fundamental pole structure of the stator field is coupled with the rotor and such that the third harmonic of the stator field is not coupled with the rotor. The rotor slot number and total number of separately identifiable cage sets are selected so that a cage set pattern is provided that has two-thirds of a fundamental pole pitch. In addition, the number of rotor cage end rings at one end times the number of rotor cage end rings at the other end is greater than or equal to the number of different cage types.
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