Three-speed single-winding single-phase induction motor

The pole-amplitude-modulation method of obtaining economic and efficient 2-speed and 3-speed operation of a normal 3-phase squirrel-cage induction motor with a single winding, developed by Rawcliffe and Fong, has been applied to the single-phase induction motor. The paper describes the theory and design methods, and presents experimental results obtained with a 3-speed 8/6/4-pole single-phase test motor. Performance of the motor at 6 poles and 4 poles is comparable with that of normal single-phase motors, while at 8 poles it is somewhat inferior. The winding is of a perfectly standard type. Ten terminals only are required for two speeds, and 12 terminals for three speeds, the control gear therefore being extremely simple.