GB163444A - Improvements in and relating to controlling devices for alternating electric currentof variable frequency - Google Patents

Abstract

163,444. British Thomson - Houston Co., Ltd., and Taylor, H. W. Feb. 13,. 1920. Alternating - current induction machines. - The magnetic cores of apparatus for controlling alternating currents of variable frequency by the reaction of eddy currents, such for instance as used in the rotor circuits of induction motors for starting, are provided with a large surface exposed to the magnetizing action of the coils. This may be effected by radially slitting a solid core, Fig. 1<a>, or by forming the core with a stellate cross-section either solid or hollow, as in Fig. 1<c>, in which case a cut may be made at one place as shown. Longitudinal holes may be made through the core, these communicating with its outer surface by radial slits and assisting the ventilation in addition to providing an increased surface for eddy current action. The end members of a magnetic circuit containing such cores have an exposed surface area which is not less than that of the cores. Thus, the radially slit cores A of a three-limb inductance shown in cross-section in Fig. 2 are joined by end-members C of channel section having an exposed area per unit length not less than that of the limbs.