Patent GB-190624582-A (GB)
Title: Improvements in Phase Transformers, specially applicable for Transforming Single Phase Electric Currents to Polyphase Electric Currents, or vice versa.
Filed: 1906-11-03
Granted: 1908-01-03
Abstract: 24,582. Bruce, Peebles, & Co., and La Cour, J. L. Nov. 3. Converting alternating currents; distributing. - Consists of a compounded transformer especially suitable for supplying polyphase currents to railway motors from a singlephase supply, a high power-factor being obtained. In the form shown in Fig. 1, a single-phase current is supplied from the trolly t to the windings I, II of a phase transformer of the Ferraris type, consisting of an induction motor, the squirrel-cage rotor Q of which reacts to produce three-phase currents in the three windings I, II, III for supplying the train motors through the leads 1, 2, 3. The machine is so excited as to take no wattless current from the line by means of a motor winding W, which is brought out to a commutator and receives current tapped off from the stator at points x, y, z. The polyphase exciting-current may be made proportional to the load by feeding it through windings s<1>, s<2>, s<3> of a transformer T which carries the motor current. The exciting - winding W may be replaced by a magnetizing- winding concentrated in a few large slots in a squirrel-cage rotor. This winding W<1>, Fig. 6, is energized by direct current taken from a rotary converter M, or a converter of the type described in Specification No. 4871, A.D. 1906, [Abridgment Class Dynamoelectric generators &c.], to which the leads l<1>, l<2>, l<3> supply current from the compound transformer T, Fig. 1, so that the current in the winding W<1> is dependent on the current passing through the phase transformer. According to the Provisional Specification, a low-frequency alternating-current may be used instead of a direct current for exciting. Fig. 3 shows connexions suitable for single-phase high voltage, the rotor being excited by windings x<1>, y<1>, z<1>, which are separate from the stator windings I, II, III. In this case, the singlephase supply is introduced between the motors and the transformer coils C', C<11>. To obtain a polyphase voltage different from that of the single-phase supply, static transformers or two stator windings may be used or, a single winding may hav autotransformer tappings. To equalize the watt current in the phases at various loads, the transformer windings may be unsymmetric in time rotation, and the numbers of-turns may be varied to give unsymmetric polypbase voltages. Similar effects may be produced by asymmetric time or magnitude relations of the motor windings, and the copper sections of the different parts of the windings may be varied to suit the currents in them. Fig. 4 shows an arrangement for supplying two-phase current. to the motor leads 1, 2 and 3, 4, which are respectively tapped off from and connected to the stator windings A, B, D, E of the phase transformer. The rotor is excited through leads a, b, and c, d, which are connected to transformer windings p, q and m, s. The primary winding B, C consists of two opposed parts such that the rotor phase a, b is excited by wattless currents, while the phase c, d receives both watt and wattless components. Fig. 5 shows the adaptaton to a " Scott " system in which H, G and A, B, C, D are the two-phase stator coils, supplying the motors through leads 1, 2, 3, 4. The motoring coils A, B and C, D are connected together and to -the generating coils H, G bywindings B, K, K, C, which are so wound with regard to each other and the transformer coil K, G that watt currents cannot induce voltage in the winding a of the rotor exciting-circuit c, d. The second rotor phase is supplied through leads a, b from transformers p, q and p<1>, q<1>, the portions q, ql, together with the windings A, F and D, E, being wound in two parts similarly to the windings B, C and q in Fig. 4.