Recent improvements in large induction motors

Like that of many other rotating electrical machines, the development of the large induction motor has been a steady and an interesting progression. From the first induction motor to the present product has been a long step, marked by the analytical ability of many capable engineers, and accompanied by continual improvements in construction, some of which are reviewed in this paper. To describe the advancement in this type of motor to its present state, it has been necessary to follow some trends in development from their beginning; thus not all of the improvements mentioned in this paper can be called recent, as time in the rapidly advancing electrical industry is measured. The paper, taking up briefly the subjects of ventilation, insulation, coil design and bracing, collectors, bearings, and manufacturing improvements, should be of interest to the many users of the large induction motor.