GB505583A - Improvements in and relating to electric motors - Google Patents

Abstract

505,583. Induction motors. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 12, 1937, No. 31173. Convention date, Nov. 13, 1936. [Class 35] A split-phase motor has a laminated stator 10 provided with inwardly projecting main polepieces 16 increasing in width from a narrow neck portion to a wide pole-face portion, concentrated main winding coils 18 .. 21 being wound about the narrow neck portions, each pole having a slot 17 to receive the sides of adjacent coils 22 .. 25 of a starting winding, and the effective pitch P of the main winding coils being approximately 135 electrical degrees. It is explained in the Specification that the selected coil pitch results in a reduction in harmonie torques. The width of the pole face portion of each pole is approximately twice that of the neck portion and the slot 17 is triangular so that the pole is of substantially uniform crosssection. The main coils may be wound by an apparatus comprising arms 28, Fig. 3, slidable on and rotatable about a shaft 27, the arms having eyes 29 through which the wires 30 are fed to the coils. The slope of the poles tends to concentrate the coils on the narrow portions. During the winding operation, the slots 17 are plugged with sticks of wood 31 which extend from either end of the stator. Auxiliary poles 32 are provided to permit a satisfactory distribution of the starting winding flux and additional turns on these poles may be included in the starting winding circuit. The starting winding is of high resistance so that no phasemodifying impedance need be included, and the circuit is opened as the motor comes up to speed by a centrifugally or otherwise operated switch 27. In. a modification, the stator core laminations are nearly square in shape so as to economize material.