GB281250A - - Google Patents

Abstract

281,250. British Thomson-Houston Co., Ltd., (Assignees of kinnard, I. F.). Nov. 29, 1926, [Convention date], Alternating-current induction machines. - In an induction disc motor, the magnetic circuit is so proportioned as to operate with varying applied voltage over a selected flux-density range below saturation where its permeability changes in such a way that the ratio of applied voltage to operating flux varies in a predetermined manner. Fig. 2 shows the driving-magnet of an induction motor meter in which the damping action of the potential flux is corrected for by making the potential flux cutting the disc vary at a rate greater than the first power of the total potential flux. The inwardly projecting arms 17 of the potential magnet are so proportioned that they normally operate on the decreasing permeability part of the curve, such as the point C, Fig. 3, corresponding to a flux density of about 9 kilogausses. The other branch circuit of the potential flux, namely the arms 18, are proportioned so that they normaly operate on the increasing permeability part of the curve, such as the point C<1>, corresponding to a flux density of about 1 kilogauss. On an increase in voltage, the flux density through the parts 17 increases to the point D and that through the parts 18 to the point D', so that the path 17 decreases in permeability and the path 18 increases in permeability a greater proportion of the total flux therefore passing across the main airgap and a smaller proportion through the shunt path 17. The magnetic paths are so proportioned that this increase causes the increase in net torque to be proportional to the increase in voltage. In a modification the parts 18 are omitted and the parts 17 are operated at the point F on the permeability curve. The ratio of the potential flux to the current flux is made considerably greater than usual so as to minimize the damping effect of the current flux on overload.