Patent GB-190916170-A (GB)
Title: Improvements in Alternating Current Dynamo-electric Machines.
IPC: H02K17/14
Filed: 1909-07-10
Granted: 1910-02-03
Abstract: 16,170. Hunt, L. J., and Sandycroft Foundry Co. July 10. Alternating - current induction machines; windings.-Relates to alternating - current induction motors in which the rotor and stator are both provided with windings giving two different numbers of poles and interconnected in such a way that they will work in cascade, and in which the rotor bars that neutralize the effect of each other are omitted as described in Specification 15,711/06. The present invention consists in arranging in the slots from which bars have been omitted additional windings connected between the rotor windings and slip-rings, which slip-rings can be 'interconnected directly or through resistances to give speeds corresponding to the numbers 'of poles of the basal windings: One end of each of the threephase windings a, b, c shown in Fig. 3 of Specification 15,711/06, is brought to a star connexion 10, Fig. 1, and the other end to a slip-ring 11, and from the slip-rings 11 the additional windings are taken through the blank slots to slip-rings 12. The cascade speed is obtained by arranging the connexions as shown in Fig. 2, while the four-pole speed is obtained by disconnecting the slip-rings 11 and connecting together the slip-rings 12, and the two-pole speed by short-circuiting the rings 12 and connecting together the rings 11. These rotor windings are used with suitable stator windings, as described for instance in Specification 6224/06. By arranging the rotor windings as shown in Fig. 7, the C<2> R losses and the magnetic leakage are lessened. This winding is obtained from two separate three-phase windings, Fig. 5, giving respectively four poles and two poles rotating in opposite directions. The pairs of bars neutralizing the action of each other are omitted and the bars carrying currents differing in phase by 60 degrees are replaced by a single bar, Fig. 6. The bars at the bottom of the slots are connected in mesh, and the other bars are joined to the points of the mesh and united in star-connexion 25. Two additional bars having each half the cross-section of the other bars and insulated from each other are inserted-in the slots from which bars have been omitted. By connecting together the slip-rings 15, the'four-pole speed is obtained. The winding is further simplified by the arrangement shown in Fig. 11, in which the half-width bars are replaced by a single bar and the end connexions modified, Fig. 11 showing the arrangement for the cascade speed, and Fig. 13 the arrangement for the fourpole speed. In the latter arrangement, the current in each bar is half as much again as the current in each bar in the arrangement in which the rings 15, Fig. 7, are short-circuited. Windings giving eight and four poles are obtained by repeating the above windings two or more times round the circumference and connecting them in parallel or series. The windings could be connected in cascade to give a speed corresponding to the difference of the numbers of poles of the basal windings. Other speeds may be obtained by opening-up the neutral points of the windings and connecting them up to slip-rings, between which resistances can be inserted as described in connexion with Fig. 1.