Patent GB-190822500-A (GB)
Title: Improved Method of and Apparatus for, Controlling the Voltage of Dynamo Electric Machinery, especially applicable to Variable Speed Generators.
Inventor: STANSFIELD WILLIAM
Filed: 1908-10-23
Granted: 1909-10-21
Abstract: 22,500. Stansfield, W., and Hatt, J. J. Oct. 23. Dynamos, regulating; field magnets.-In the method of regulating the voltage of dynamo-electric generators, particularly variable-speed trainlighting generators, described in Specification No. 12,704, A.D. 1908, the main and auxiliary generators are combined into one machine, the armature conductors A, Fig. 1, and the field poles a corresponding to the main generator, and the armature conductors B and the field poles b corresponding to the auxiliary generator. Brushes P1, P2, P3 are arranged on the commutator as shown, and a fourth brush P2<1> may be placed opposite the brush P2. The mains M, N may be connected across the brushes P1, P3 or across the brushes P1, P2. The main field a is excited by two windings Ca, Ea connected across the brushes P1, P3 and P2, P3 respectively. The auxiliary field b is excited by two opposing windings Db, F connected across the brushes P1, P3, the winding Fb predominating over the winding Db at low speeds. The winding Db may be connected across the brushes P2, <p>2<1>. The resistance of the circuit Fb is adapted to increase with increase of current at a greater rate than that of the winding Db so that, when the armature speeds up, the winding Db predominates over Fb and reverses the auxiliary field. Any further increase of speed is accompanied by an increase of the reversed electromotive force in the conductors B. The greater increase of resistance of the circuit Fb may be effected by making the winding Fb or a resistance R, Fig. 4, in series therewith, of a material having a higher temperature coefficient than that of the winding Db, or by making the windings Db, Fb of the same material but having different cross - sectional areas. In place of, or together with, the resistance R a resistance having a negative temperature-coefficient may be connected in series with the winding Db. Similar results may be obtained by means of a resistance R, Fig. 5, controlled by an electro-magnet connected across the mains. The winding Db and resistance R may be connected across the brushes P2, P2<1> while the solenoid s may also be connected across the brushes P2, P2<1> or across the brushes P1, P2. The winding Ea may be divided into two parts, one part being connected across the brushes P2, P3 and wound around one pole a, and the other part being connected across the brushes P1, P2<1> and wound around the other pole a. Armature reaction is compensated for by windings Ga, Gb, Fig. 2. The coils Ga may be dispensed with by suitably proportioning the winding Ea and the armature conductors B. Where sudden variations of flux are likely to occur, closed coils Ha, Hb are wound around the poles. In a modification, one winding Ob, Fig. 6, only is used to excite the auxiliary field b, it being connected up to a Wheatstone net of resistances v<1>, v<2>, v<3>, v<4>, as shown, the resistances v<1>, v<2> and v<3>, v<4> being made to vary differently with variations of current through them. The bridge may be split, and the half v<1>, v<2> connected across the brushes P1, P2 and the other half v<3>, v<4> across the brushes P2<1>, P3 ; or the half v<1>, v<2> may be connected across the brushes P2<1>, P2 and the half v<3>, v<4> across the brushes P1, P3. In another modification, resistances are connected across the brushes P1, P2<1> and P2, P3 respectively, and the corners of the bridge which in Fig. 6 are connected across the mains are connected to their mid-points. These resistances may be used in connexion with any of the other windings. In a further modification, resistances are connected in series with the windings Fb, Db respectively, and a third resistance is connected between the junction of the winding Fb and the resistance in series therewith and an intermediate point in the resistance in series with the winding Db or in the winding Db itself. The machine may be constructed with as few as three poles but it may have any number of poles above three. With a four-pole machine, a two-pole ring or drum-wound armature is used.