The polyphase shunt motor

There exists a demand for a reliable, adjustable-speed, alternating-current motor, suitable for operation at a large number of speeds. The neutralized motor with shunt field control is analyzed and it is shown that it is not practical for commercial frequencies on account of the expensive control equipment required. The induction motor with commutator on the secondary side is discussed. It may find some application for the larger outputs; the control is, however, still too complicated to make this type of motor suitable for the smaller machine-tool drives. The induction motor with commutator on the primary side offers the best solution for machine-tool motors. Its theory is discussed in detail, and a complete description is given of the mechanism required to shift the brushes and the new type of armature winding used.