GB140452A - Improvements in and relating to three-phase alternating-current dynamo-electric machines - Google Patents

Abstract

140,452. Siemens - Schuckertwerke. April 23, 1918, [Convention date]. Motors, controlling.-The number of poles of a three-phase winding is changed in the ratio of 2 : 1 by reversing the direction of current flow through certain of the coil-groups and at the same time changing over the connexions of the phase windings from star to delta for the purpose of keeping constant the magnetic induction at the air-gap. Fig. 1 shows a two-layer winding with a coil-width s substantially equal to the smaller pole-pitch, the coil-groups of the different phases being indicated by different kinds of lines and marked a1, a2; b1, b2; c1, c2, respectively. To obtain the larger number of poles, all the coils of each phase are joined in series and the three phases are interlinked in star-connexion, as shown in Fig. 2. To change over to the smaller pole-number, the direction of current in every other coil-group is reversed, and the phase connexion is altered to delta, as shown in Fig. 3; in this figure, the positive direction of current flow is indicated by full lines and the reverse direction by double lines. Instead of series-connexion of the coil-groups, these may be connected in parallel.