Patent GB-190606224-A (GB)
Title: Improvements in Alternating Current Dynamo Electric Machines.
Filed: 1906-03-14
Granted: 1907-03-14
Abstract: 6224. Hunt, L. J., and Sandycroft Foundry Co. March 14. Armatures field magnets; motors, controlling.- Relates to improvements upon the alternating- current induction machines described in Specification No. 14,401, A.D. 1905, both the stator and rotor of which are provided with two independent windings of different pole-numbers, one stator winding being connected to the mains and the other shortcircuited, while the two rotor windings are in conductive connexion. According to this invention, each pair of windings on the same core may be replaced by a single winding or group of windings having the same effect, and further speed variation is obtained by connecting together the rotor windings through slip-rings and resistances. In the arrangement shown in Fig. 1, one winding or group of windings is arranged to have the same effect as two stator windings of different polenumbers by splitting up each winding into a number of parallel paths, e.g. 17, 18, &c. Equipotential points in the parallel windings with reference to the conductively-applied current are connected together either directly or through resistances 25, producing a number of local circuits, the currents induced in which by the field of the second rotor winding give rise to the second stator field. In the case of rotor windings, the latter are preferably divided into two or more groups, each group being so interconnected that, when acted upon by either stator field, the sum of the electromotive forces generated in the windings taken in order is nil. The two-phase windings of Fig. 9 are connected in parallel groups 2, 4 and the mid point of each generating-conductor, or set of conductors in series, of the one group is connected to the junction of a pair of conductors or sets of conductors in the other group. In Fig. 3, a compound stator winding corresponding to two windings of different pole numbers is shown used in conjunction with two separate rotor windings. The points of junction r, s, t of the rotor windings 2, 4 are connected by slip-rings to a rheostat 11, and each phase of the compound stator winding has on it four tappings A, B, C, D joined to corresponding switch contacts, the connexions being omitted in the diagram. In the starting position shown, the tappings A are joined to the mains, the tappings B are joined to the tappings C, and the tappings D are joined together, the connexions resembling those shown in Fig. 1 and the operation of the motor being similar to that described in the Specification referred to above. A second speed corresponding to one of the polenumbers is obtained by cutting out the resistance 11 and opening the switch controlling the shortcircuits B, C. A third speed corresponding to the other pole-number is obtained by opening the switch that short-circuits the tappings D, reversing the middle switch so that it short-circuits the tappings C, and reversing the remaining switch to join the tappings B to the mains. A fourth speed may be obtained by reversing the connexions of the rotor windings with one another so that the field due to the second rotor winding rotates in the same direction as the first instead of in the opposite direction. In this case, the rotor terminals are connected to the rheostat 11 by means of five slip-rings and two reversing-switches. The Provisional Specification describes the application of the speed-control arrangements to machines having two or more separate windings on the stator, and states also that such machines may be operated as synchronous motors or generators by supplying one of the stator windings with continuous current, being started asynchronously either as above described or by means of a separate winding.