Patent GB-191214236-A (GB)
Title: Improvements in Commutating Devices for Dynamo Electric Machines.
Inventor: DERI MAX
IPC: H02K13/14
Filed: 1912-06-18
Granted: 1913-06-12
Abstract: 14,236. DÚri, M. June 18. Commutation, improving by auxiliary voltage introduced between brushes; brushes; commutators. - For sparkless commutation, dynamos are provided with pairs of brushes so placed with respect to one or more commutators as not to shortcircuit the armature coils, and these brushes are supplied, from external circuits, with alternating voltages of the frequency and phase value requisite to compensate the reactance voltage of communication. Several methods of producing the compensating - voltage are shown. In the form shown in Fig. 1, the main armature 1 is connected to two commutators 2, 3, the brush pairs 4, 5, 9, 10 of which never short - circuit the armature coils and are connected to windings 6, 11, the mid-points 7, 12 of which are connected to the main circuit. The coils 6, 11 form the armature windings of an auxiliary machine, the field coils 14 of which receive the main current, at 15, 16, and therefore cause the coils 6, 11 to annul the reactance voltage at the brushes 4, 5 and 9, 10. The windings 6, 11 may form the secondary coils of transformers, the primary coils of which are supplied by an auxiliary machine operating under similar conditions to the main machine. The windings 6, 11 belonging to different poles may be linked together electrically or magnetically. In place of using two commutators, a single one may be used, as shown with a drum winding in Fig. 3, the brushes 4, 5 and 9, 10 of each pair being correspondingly separated on the commutator surface, and the armature 6, 11 of the auxiliary machine being wound in a corresponding number of phases, namely two in the four - pole case shown. The magnet 14 is geared up at 17, 18 to give the required frequency, the gear ratio depending upon the numbers of poles in the auxiliary machine and segments in the main commutator. The auxiliary machine may be an induction machine driven at hypersynchronous speed and having its stator connected to the brushes of the main machine, and it may have a wound rotor with regulating resistances for varying the voltage impressed on the commutating circuit. In place of using a separate machine of a non-commutating type, the auxiliary windings may be placed on the stator and rotor of the main machine itself, the existing armature slots being optionally employed. The wave shape of the compensating voltage may be adapted to that of the commutation voltage by using condensers, in combination with the auxiliary machine, connected, for example, between the windings 6, 11, Fig. 1, and the brushes 4, 5 and 9, 10. In the form shown in Fig. 6, the armature coils 1 and brushes 2, 3 are stationary and the windings 6, 11 of the auxiliary source are connected to two pairs of rotating commutator segments 4, 5 and 9, 10. In this case, condensers 20 are included in the brush leads. The capacity is preferably such as to cause resonance and may be combined with inductance to take up the wattless load. The coils which provide the compensating voltage may alternatively be connected between the armature windings and the brushes. In order to obtain the proper wave form of commutation current, the brushes or segments have a diamond-shaped or curvilinear tapering section, as shown in Fig. 9, or a rhomboidal section as in Fig. 10, so that the contact resistance decreases rapidly from the pointed edges 1<1>, 3<1> to the central region 2<1>, 4<1>. Alternatively, brushes may be employed with an increasing conductivity towards the central part. With such brushes or segments, the auxiliary machine 6, 11 may be omitted from the arrangement shown in Fig. 6. the pairs of segments 4, 5 and 9, 10 being directly connected together and to the rings 11, 12.