Abridgment of A-C. elevator motors of the squirrelcage type

This paper sets forth the features of squirrelcage motor design which differentiate it from standard motors. Much of the paper is devoted to the two-speed motor with two separate stator windings having speed ratios of 2/1, 3/1, 4/1 and 6/1. The two-speed motor with a single winding is limited to the 2/1 ratio. Higher ratios are necessary for high elevator speed and low and accurate landing speed. The elevator motor is subjected to continual starting and stopping. The effects of inertia in such service are considered in connection with motor heating. The proper division of slot area between the two stator windings and the problem of building a rotor with proper characteristics on both speeds are explained. Noise elimination is necessary in elevator motors. The effect of this requirement in design is considered. The effect of rotor skew is compared to the effect of distributed winding in the stator. The quantitative effect of skew is embodied in a constant called “skew factor.” The possibility of transformer effects between the windings of a two-speed motor is explained and methods of correcting to eliminate circulating currents are indicated.