Patent GB-190901705-A (GB)
Title: Improvements in and relating to Alternating Current Electric Machines of the Commutator Type.
IPC: H02K27/08
Filed: 1909-01-23
Granted: 1910-01-24
Abstract: 1705. Allgemeine Elektricitõts-Ges. Jan. 24,1908, [Convention date]. Alternating-current commutator machines. - Relates to alternating-current commutator machines of the kind described in Specification 23,288/02, in which outside potentials are impressed upon both the stator and rotor working windings and the field excitation is effected either wholly or in part through the rotor. Fig. 2 shows a machine of this kind having the stator working winding s and the working brushes b connected to points on the main transformer T, the exciting-brushes e being connected in series with either the stator or rotor working winding through a transformer t depending on which of the connexions X, X<1> is made. According to the present invention, the total working potential is distributed between the rotor and stator working windings so that the potential between the exciting-brushes e becomes a minimum. Assuming a winding ratio of 1 : 1 between the stator and rotor working windings, the total potential S is distributed between the windings in the proportion KS : (I-K) S, the value of K being given by the expression K=(n/N)<2>, where N is the speed of rotation and n is the frequency of the supply ; or generally with a winding-ratio of 1 : M, the distribution is-made in the proportion, K : M (I-K). Numerous arrangements for carrying out the invention are described. The machines may be started up with the exciting-brushes connected in series with the stator or rotor working windings, potentials derived from the main transformer T being afterwards impressed upon the exciting- brushes, for example as described in Specification 13,284/04. Part of the field excitation may be produced by a stator winding connected in series with the stator winding s or with the brushes b ; the exciting brushes e may be connected to another secondary winding on the transformer T ; or, as shown in Fig. 6, the. working brushes b may be supplied from a second transformer winding w<1> and the series exciting-current may pass through one-half of the armature and through the middle point of the winding w<1>, the constant-potential exciting-current passing through the other half of the armature. The stator and rotor windings may be supplied with fractional potentials of the transformer T independent of each other, as shown in Fig. 10. To improve the commutation at the working and exciting brushes, the strength of the field is influenced locally by commutating coils, slots, or the like. Several separate working-brush circuits may be employed, the brushes being arranged in parallel chords or in different pole-fields. The exciting-brushes may be arranged in a chord perpendicular to the short-circuit axis, or a chord winding may be used on the rotor, as described.in Specification 14,935/06. The Specification in the original form, as open to inspection under Section 91 (3) (a), comprises also the following matter: (1) two or more motors may be coupled together electrically so that the rotor working potential for one motor is supplied from the transformer winding feeding the other motor, and the working current of one motor may supply the exciting- current of the other motor ; (2) the commutating- coils may be short-circuited, they may be located in certain only of the pole fields, and may be arranged as described in Specification 11,633/08. This subject-matter does not appear in the Complete Specification as accepted.