GB1126073A - Improvements in or relating to rotary electric machines - Google Patents

Abstract

1,126,073. Change-pole machines. NATIONAL RESEARCH DEVELOPMENT CORP. 30 Jan., 1967 [17 Feb., 1966], No. 7005/66. Heading H2A. A commutator machine is arranged for polechanging by reversing half of the stator field and lifting or disconnecting some of the brushes used in the lower pole-number. The machine may be of any sort, A.C. or D.C., and stator and rotor may be interchanged, and pole-changing may be by pole-amplitude modulation. In its simplest form, a 2/4 pole machine has an armature of 2/3 pitch for two poles and so 4/3 pitch for four poles, thus being inductive to both. In the 2-pole connection, only two of the four brushes are used, alternate brushes being lifted from the commutator, but the effective number of armature conductors in series in this connection is doubled so that the machine runs slower. For higher pole-numbers, brushes which are used in parallel but lifted for the lower pole-number, may be permanently shorted together (Fig. 3, not shown). The field windings may be wound on salient poles (Fig. 2, not shown) and interpoles may be used. Alternatively (Figs. 4 and 5, not shown) the field winding may be distributed in slots, and it is described (Figs. 4, 5 and 5a, not shown) how a single-phase winding derived from a threephase winding by the omission of one phase, may be connected to provide two or eight poles. Where salient poles are used, these may be graded as regards pole amplitudes and poll width, for the higher pole numbers. Alternate poles are narrower but more strongly excited (Fig. 7, not shown), and a similar effect may be produced in distributed windings by grading the pole-amplitudes by coil grouping.