Patent GB-235361-A (GB)
Title: Improvements in electric converting apparatus
IPC: H02M7/54
Filed: 1924-05-05
Abstract: 235,361. Calverley, J. E., and Highfield, W. E. May 5, 1924. Commutator switching-arrangements; phase, changing; polyphase transformers.-Relates to apparatus for conversion from alternating to direct current or vice versa of the kind in which a polyphase system of a relatively small number of phases, termed the primary system, is associated through the medium of a number of transformer cores with another system of a materially higher number of phases. termed the secondary system, which system is connected through commutating gear to a direct-current system. Apparatus of this kind is described in Specifications 140,853, 150,824, 150,825, and 184,259 and according to the invention there is applied to the transformer cores an arrangement whereby a definite wave form of flux is impressed on each core under the influence of an alternating e.m.f. produced by means external to the systems and having the same value for each core and appropriate phase relationships for the various cores. The impressing may be by separate or the secondary winding, the connections between the winding and the source being of low resistance and self-induction to reduce distortion. The e.m.f. may be supplied by a separate alternator or from tappings from the armature of the synchronous motor driving the brush gear of the commutator and the magnetizing current of the transformer cores may be supplied by third windings thereon, as described in Specifications 150,825 and 221,551. Fig. 4 shows the apparatus shown in Figs. 1-3, which correspond with the drawing of Specification 184,259, but with the arrangement of the synchronous machine impressing a definite wave form of flux applied to it. The secondary winding is a. closed ring or vector polygon S of thirtysix phases 1 - - 18, 1<A> - - 18A, Fig. 2, which numerals also designate in Fig. 1 the cores which corresponding secondary windings are located. In the latter Figure the eighteen cores are comprised in six three-phase transformers (repeated three times in the Figure for purposes of clearness) fed from three phases A - - C, the paths being to A<1> - - C<1>, respectively. The vector polygon P of the delta-connected primary has its outer sections grouped symmetrically and arranged parallel with the corresponding sections of the secondary system S. The synchronous machine has a field F and armature G, while the system of delta-connected compensating windings H has a vector in phase with corresponding side, of S, P. The windings H may be omitted and, instead, eighteen of the secondary sections may be connected at their ends to tappings of the armature G. Further, there may be two, instead of one, compensating windings for each core where there are two secondary phases on each core, the windings being oppositelyconnected on the armature G may be definitely connected to the secondary system or to the primary system so as to draw energy thereform to rotate the brush gear. Where the cores are built up into three-phase groups, closed circuit windings, as described in Specification 184,259, and shown in Fig. 3, may be employed.