Recent progress in induction-motor construction

The paper describes the principal developments in inductionmotor construction which have taken place during the past few years. A full description is given of a number of welded-steel yokes or stator frames made by different manufacturers together with a discussion of the advantages and disadvantages of this type of frame. The welded-steel rotor centre or spider is similarly described in detail and discussed. The general trend of mechanical construction is outlined, together with considerations affecting enclosure and ventilation, while the construction of end-shields, pedestal-onbracket machines, and bedplates, is discussed. The magnetic forces between stator and rotor are explained and an improved expression for the calculation of unbalanced magnetic pull is developed, and extended by means of examples to show the characteristics of this type of loading. The sources of the various types of noise in an induction motor are classified and discussed.