GB329517A - Improvements relating to alternating-current electric motors - Google Patents

Abstract

329,517. Jacoby, H. C. E., and Gilbert, N. W.. May 29, 1929. Alternating-current commutator and induction machines. - The rotor of an induction motor having a squirrel-cage and another winding, either of squirrel-cage or commutating type, is made by assembling laminae of two types one of which has deep open slots adapted to contain both windings and the other of which has shallower outer slots for one winding and inner piercings which form tunnels for the other winding. By apportioning the ratio of the two kinds of laminae in the core. the requisite reactance properties may be conferred upon the windings to give the motor a desired characteristic. Figs. 1 and 2 show one combination of laminµ comprising plates 0 with open-topped slots o having wide and narrow outer and inner portions o', o<2> respectively and plates B having wide outer slots b' and narrow inner tunnels b<2> which register with the slots of the plates 0. The complete rotor comprises a central portion of plates 0 and end-portions of plates B, a squirrel-cage being placed in the tunnels b<2> and slots o<2> and a commutator winding in the outer slots b<1>, o<1>. The cage winding has a high leakage inductance in the end-portions and a low inductance in the central part of the core. The inner tun. nels may be placed radially below some only of the slots in plates B and narrow air-slits may connect the slots and tunnels. Figs. 4 and 5 show a double squirrel-cage rotor with bars of circular section comprising end-packets of plates B with slots b<1> and tunnels b<2> and a central portion of plates 0 having outer slots similar to the slots b' alternating with wide slots o terminating in enlargements coincident with the tunnels b<2>. All the slots have narrow peripheral openings o<3>. The winding g has a high leakage inductance and the winding h a low inductance, the values of which depend upon the numbers of plates of each type employed. The Specification describes how a repulsion motor may be given a shunt motor speed characteristic and an improved power factor by employing a peripheral commutator winding and an inner squirrel-cage winding in a composite core as above described, the cage bars being arranged so as to produce no torque or only a slight torque at all speeds in core-sections such as B and full torque in sections such as 0.