Patent GB-659903-A (GB)
Title: Alternating current commutator machines
IPC: H02K13/14
Filed: 1949-02-04
Abstract: 659,903. Improving commutation. FORGES & ATELIERS DE CONSTRUCTIONS ELECTRIQUES DE JEUMONT. Feb. 4, 1949, Nos. 3089, 3090 and 3091. Convention dates, Feb. 5, 1948, Feb. 26, 1948, and Sept. 20, 1948. [Class 35] Commutation is improved in a single or poly-phase A.C. commutator machine by means of split-brushes connecting the coils being commutated to a stationary coil in which there is generated another E.M.F. approximately equal to that in the commutated coil, sparking being further suppressed by means of condensers and impedances in the outside circuit. In its simplest form, Fig. 1, the segments 1, 2, 3 connected to a lap winding G are spaced by gaps equal to two segments' width. The split brush B A , B B  is of sufficient width to span two segments at most and the brush parts are connected to the stationary coil S enbracing a magnetic circuit D<SP>1</SP> in which a flux is produced which may be equal to and synchronous with the flux of the main field pole D. The magnetic circuit D<SP>1</SP> may actually be the field magnet pole D. The coil S includes a resistance R and the load circuit is connected to A or A<SP>1</SP> by a switch (not shown) depending on the direction of rotation of the machine. Diagrams are given showing various commutating positions and it is described how damping resistances r1, r2 and condenser C serve to improve the commutation further. A further magnetic circuit M which may be excited in dependence on the armature current may be used to induce an E.M.F. to offset any harmful effects of these resistances. It is stated that the machine may also employ commutating poles. If desired, the gaps between these segments may be filled, as shown in Fig. 3, by two additional segments 1<SP>2</SP>, 1<SP>3</SP> connected to additional armature coils G2, G3, the conducting parts of the segments being axially spaced to allow commutation by separate brushes. This is achieved, as shown in Fig. 4, by providing the commutator segments with cut-out portions or insulating inserts as I, so that only one set of brushes, e.g. B1, makes contact with the coil G1. To provide smooth running, the double brush B A , B B , connected by leads N1, N2, is secured as shown in Fig. 7, between dummy brushes P so as to span the segments 1, 2, 3, 4, &c. In a modification, Fig. 8, in which the effect which the damping resistances have on the charging of the condenser C is eliminated, the charging of the condenser is done directly from the commutator segments, thus effectively suppressing sparking at the breaking contact, but the discharge takes place through the damping resistance to reduce the sparking at closure. The brushes B A , B B  have smaller auxiliary brushes ba, bb joined by the discharge damping resistance r and making contact with the same commutator segments. Switches M<SP>1</SP>, N and O are provided to connect the condenser C and resistance R correctly for the direction of rotation of the machine. In a further modification, the condenser is discharged through a discharge tube fired by an impulse from a small pilot brush between the brushes B A  and BB.