GB293508A - Improvements in dynamo electric machines - Google Patents

Abstract

293,508. MacFarlane, J. C., and Macfarlane, W. A. April 25, 1927. Pole-pieces. - Each pole of a constant current dynamo is divided into two parts, one part having a high magnetic reluctance and the other a low reluctance, and the parts are so proportioned that under short-circuit conditions, the cross flux due to armature reaction saturates the high reluctance part to such an extent that the total flux passing through the armature from pole to pole is reduced to an amount which is just sufficient to keep the short-circuit current circulating in the armature winding. The operation of the invention is explained in the Specification with reference to a diagram showing the magnetomotive forces produced by the field and armature windings. The trailing horn T of the pole is given a high reluctance by providing an apertune O as shown in Figs. 2 and 3 extending parallel to the axis of the armature; the gap between the inner pole-tips Tg, Lg may be open or may be closed by a thin bridge C of iron. In order to vary the characteristics of the machine, the air gaps under the leading and trailing horns may be of different lengths or may have different areas. The pole horns may be separate members bolted to the yoke. Fig. 6 shows the invention applied to a two-pole machine provided with a series winding D<1>, D<2> and a shunt winding S<1>, S<2>. Control may be effected by moving the brushes and the effect may be increased by providing series-wound interpoles I which in addition to improving the commutation can be made to add or subtract part of their flux to the main field. The interpoles also assist in stabilizing the machine by eliminating the currents in the coils shortcircuited by the brushes. The invention is particularly applicable to welding generators.