GB424980A - Improvements in and relating to electric motors - Google Patents

Abstract

424,980. Induction motors. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Morrill, W. J. ; 2317, South Wayne Avenue, Fort Wayne, Indiana, U.S.A.) Sept. 13, 1933, No. 25387. Convention date, Sept. 13, 1932. [Class 35] A split-phase induction motor is so designed that the speed-torque curve shows a marked dip of the torque at a speed well below the maximum, with the result that the motor has two stable speed ranges, one below the dip and one above, and means are provided for producing a torque corresponding to each of these ranges. Fig. 3 shows a machine with two windings 22, 23 and a phase-splitting resistance 13. A centrifugally operated switch 14 short-circuits the resistance 13 when the motor has speeded up and the switch 19 selects the winding to be left in circuit for running. Fig. 5 shows a machine with a starting winding 26, cut out by a centrifugally operated switch 28, and a running winding 25, on which either of two voltages can be impressed by an autotransformer 29 and switch 30. To give a speed-torque curve of the required character, the rotor of the machine shown in Fig. 5 is formed with deep slots 21. In the arrangement shown in Fig. 3, the winding 23 is a distributed winding, but the winding 22 is a concentrated full pitch winding producing a forward revolving-third harmonic of flux. The rotor 15<1> has four squirrel cage bars producing a harmonic locking with the harmonic of the stator flux and giving a curve of the type required. The rotor in this case is preferably secured to its shaft by a spring coupling.