Patent GB-112495-A (GB)
Title: Improvements in and relating to Alternating Current Dynamo- electric Machines.
IPC: H02K27/12
Filed: 1917-01-06
Abstract: 112,495. Lancashire Dynamo & Motor Co., and Stansfield, W. Jan 6, 1917. Alternating-current commutator machines; coils and conductors; windings.-Machines which may be operated as synchronous motors or as alternating-current generators without the use of a separate exciter are provided with an ordinary singlephase or polyphase stator winding and with a rotor winding c<1>, Fig. 2, of the ring or drum type, reversely connected to the segments of a commutator c, that is to say, points 1-6 of the winding c<1> considered clockwise are connected to commutators bars 1<1>-6<1> considered counter-clockwise. The commutator brushes b<1>, b<2>, b<3> are connected either directly, Fig. 4<A>, or by means of transformers, in series or in shunt, Fig. 10, with the stator windings s, or compound arrangements of shunt and series transformers, Fig. 12, may be adopted. The brushes may be connected to tappings on the stator windings. To start to a machine operating as a motor, the terminals s<1>, s<2>, s<3> of the stator windings may be connected together by a regulating switch to a star point, and the brushes b<1>, b<2>, b<3> may be connected together through resistances which are afterwards cut out; when synchronism is reached, the brushes are connected to the stator ends as shown in Fig. 4<a>, fur. ther movement of the regulating switch serving to insert other resistances between the brushes. Alternatively, the motor may be started up as an induction motor by the use of slip-rings and resistance, or by means of an additional squirrel-cage winding carried in the rotor slots. The bars of the squirrel-cage winding may be in the form of slot wedges c<4>, Fig. 4<b>, separated from the bars c<2>, c' of the main rotor winding by magnetic bridges c<5>; or, as shown in Fig. 4<c>, the squirrel-cage elements may be in the form of metallic slot-linings c<6>, the wedges c' being metallic or otherwise. The starting resistances may be carried by the rotor as a closed distributed winding w, Fig. 5, connected at equidistant points to the rotor winding c<1> or to the commutator bars; in starting up, the stator ends s<1>, s<2>, s<3> are first connected by a switch J to a star point 0 and afterwards by the contacts j to the brushes b<1>, b<2>, b<3>. In a further modification, the rotor may be provided with two windings c<2>, c<3>, Fig. 5<a>, in parallel, one having more turns than the other. To improve the power factor automati. cally as the load varies, each phase of the stator windings may be made up of a major part S<1>, Fig. 6, and a minor part S<2> with a resistance R connected between them; the commutator brushes are connected to points between the parts S' and the resistance R. The same result may be obtained by connecting the brushes to a star point 0, Fig. 6<c>, through a three-phase choking coil T, the iron of which becomes saturated at a low current value ; or a choking coil Z, Fig. 7, having two windings z<1>, z<2> connected respectively in the stator and rotor circuits may be employed. To vary the power factor, each stator winding may be connected to different taps on one of the windings of the choking coil. To obtain a two-speed motor, an additional line of brushes, displaced 180 electrical degrees from one of the three lines of brushes described for a three-phase motor, is adapted to be short-circuited after the motor has reached halfsynchronous speed, there being no conducting connexion between the stator and rotor. The motor may also be run at half-speed by connecting the commutator brushes to the mains and shortcircuiting the stator windings. The machines maybe mechanically driven and operated as generators. An arrangement for this purpose is shown in Fig. 8, in which a voltage regulator V similar to an induction motor with a wound secondary member and slip-rings is used. The primary windings VI, VII, and VIII of the regulator are connected across the stator windings S; its secondary windings v' (one only is shown) are connected at one end to the primary windings, the other ends being connected to the commutator brushes b' &c. of the alternator. Resistances, such as y, may be connected across the windings v<1> &c. The angular position of the secondary member of the regulator may be adjusted by hand or automatically to vary or keep constant the voltage of the alternator. For automatic regulation, the torque between the primary and secondary members of the regulator may be utilized in opposition to that of a weight or spring; to compensate for the varying torque, the spring 2, Fig. 8<d>, (or weight) may operate at varying leverages by means of a crank 3 or a cam secured to the secondary member.