Three-speed single-winding single-phase induction motor

Abstract

SynopsisThe 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.List of principal symbols n = magnetising turns, due to a phase winding acting at an angular position 6, measured mechanically around the perimeter n m = magnetising turns acting at the centre of each pole p = pole pairs k = modulation cycles in the complete machine perimeter k w = winding factor X = pole pitch x = slot pitch N = turns in seriesThe suffixes 1 and 2 refer to the 2-phase windings. A is used as a constant and also in referring to phase A, as explained in the text. Similarly, B is used for flux density and also in referring to phase B.