GB544832A - Improvements in and relating to dynamo electric machines - Google Patents

Abstract

544,832. Inductor alternators. WOODS, Ltd., M. W., and DALY, B. B. Feb. 4, 1941, No. 1447. [Class 35] An inductor-alternator has 2p n evenly distributed wound poles and (2pΠ1) n evenly distributed inductor poles, where p, n are positive integers and n is even if p=1. In the three-phase machine shown p=3 and n=2 so that twelve stator windings a ... l are opposed to ten rotor poles in n (=2) electrically identical sections. To enable exciting D.C. and generated A.C. to flow through the same windings, two sets of windings per section, a, c, e and b, d, f for one section and g, i, k and h, j, I for the other, which intersect fluxes in phase-opposition, are connected in parallel star so that corresponding windings, a, d for example, deliver A.C. in the same phase to the output circuit, while excitation D.C. is fed in at the star points and passes through corresponding windings in series. In Fig. 2 each section is in parallel with the D.C. source, while in Fig. 4 the sections are in series, isolating condensers Cr being necessary to stop D.C. circulating in the A.C. connections. It is not necessary for p to equal the number of phases as in a two phase machine, Fig. 5 (not shown), p=4 giving a four-wire system and avoiding the connection of an A.C. supply line to the star point which is necessary if p=2 ; if a three-wire system is required an isolating transformer may be interposed. In a single-phase system, Fig. 6 (not shown) either p=1, n=2, when the voltages in each set of windings are in phase, or p=2, when the voltages are 90 degrees out of phase, giving a resultant at 45 degrees to either. The successive poles are preferably wound so as to give opposite polarities, and n is chosen greater than 1 so as to avoid unbalanced magnetic attraction between rotor and stator. The n sections need not occupy geometrically similar portions of the stator, as electrically equivalent windings may be selected from any positions to form a section. The pole-width is preferably 35-40 per cent. of the pole pitch to avoid excessive induction.