Starting a single-phase induction motor using an asymmetrical rotor

An unconventional possibility of starting a single-phase induction motor using an asymmetrical squirrel-cage rotor is described. Several possibilities, such as the provision of an additional rotor bar or the removal of one of the bars of a symmetrical cage, can be used to give an instantaneous starting impulse to the rotor; but the magnitude and direction of the starting impulse depend upon the initial position of the rotor relative to the stator. Whether the rotor will or will not accelerate to a stable speed depends on many factors, such as moment of inertia, speed and transformer torques, and friction and other starting load. Theoretical prediction of the starting performance will be possible only after further study. Two motors using the above principles are found to have very odd starting characteristics, which cannot be explained by the simple approximation of sinusoidal flux distribution. Based on the flux distribution actually measured, the calculated value of the starting torque tallies very well with the measured value. Further work will be necessary to explore the possibilities completely, and to analyse fully the odd behaviour observed. The principle cannot at present be used commercially, and is of academic interest only, in its present form.