Patent GB-190722719-A (GB)
Title: Improved Method of and Apparatus for Controlling Electrical Circuits.
Inventor: BOULT ALFRED JULIUS
Filed: 1907-10-15
Granted: 1908-10-15
Abstract: 22,719. Boult, A. J., [Woodbridge, J. L.]. Oct. 15. Converting alternating and direct currents; regulating; distributing.-Relates to apparatus for the interconversion of alternating and continuous current, and to its use for controlling the field of a generator, such as a booster or rotary converter, in accordance with changes on the alternating-current circuit. The apparatus may also be used for controlling the transfer of energy between an alternating-current and a continuous-current circuit, and for controlling the power factor of the alternating-current circuit. Fig. 1 shows the apparatus used as a converter only. The secondaries of the transformers T', T<2>, T<3> in the three-phase system 1, 2, 3 are connected to the points 4, 6, 8 on the winding X on a magnetic core. The shaft H, driven by the motor S' or S<2>, carries two pairs of brushes 10, 11 and 12, 13 over the commutator 4, which is connected to the winding X in the usual manner. The brushes 10, 11 are short-circuited by the connexion O, and the brushes 12, 13 connected to the continuous-current circuit 21, 22. When the apparatus is used to convert alternating into continuous current, the switches Z<1>, Z<3> are opened and the switches Z, Z<2> closed, the shaft H being thus driven by the synchronous motor S<1>, and continuous current being supplied to the brushes 12, 13 and circuit 21, 22. In converting from continuous to alternating current, the switches Z, Z<2> are opened and the switches Z', Z<3> closed, thus connecting the continuous-current source N to the motor S<2> and the brushes 12, 13, the rotation of the latter producing a rotating magnetic field and, consequently, an alternating current in the leads 1, 2, 3. As shown in Fig. 2, the apparatus just described is arranged for controlling the field of a storage-battery booster B in response to variations of current on the alternating-current circuit 1, 2, 3. The synchronous motor S is shown as revolving the armature winding instead of the brushes, so that the rotating magnetic field is stationary in space. The field-coil F of the booster is in circuit with the brushes 12, 13, and the circuit 25, 26 of the battery C and booster B is connected through the switch I<1> to the brushes 10, 11. The circuit 25, 26 is also connected to the continuouscurrent terminals of the rotary converter R, the alternating-current terminals of which are connected to the circuit 1, 2, 3. With a normal current in the circuit 1, 2, 3, the potential-difference produced across the brushes 10, 11 is arranged to be equal to that across the leads 25, 26, so that no current flows through the wires 23, 24 or field-coil F. If the load on the circuit 1, 2, 3 increases, more current flows through the transformers T', T<2>, T3, and the potential across the brushes 10, 11 rises so that current flows through the booster armature, and the flow of this current through the winding X produces a second magnetic field causing current to flow through the brushes 12, 13 to the booster field-coil F. This flow of current is in such a direction as to excite the booster to cause the battery C to discharge through the converter R into the alternating-current circuit 1, 2, 3. Conversely, if the load on the circuit 1, 2, 3 decreases, current from the brushes 12, 13 flows in the reverse direction through the coil F, and the booster causes the battery to charge from the circuit 1, 2, 3. The booster is provided with a second field-winding F<1> and a rheostat Q<3> by which the point at which the battery begins to charge or discharge may be controlled. By means of the change-over switch I<1>, the brushes 10, 11 may be disconnected from the circuit 25, 26 and shortcircuited, and in this case the normal output in the circuit 1, 2, 3 produces a flow of current in the coil F, which must be neutralized for any given load by adjusting the current in the coil F<1>. In Fig. 3, two exciters E, E' are shown, driven by the synchronous motor S. The exciter E controls the field F of the booster B in the same manner as in Fig. 2, but in this case the armature D revolves in a magnetic field-structure provided with four polar projections P', P<2>, P<3>, P<4>. The points 4, 5, 6, 7, 8, 9 of the armature are connected in six-phase relation to the secondaries of the transformers T', T<2>, T3 in the main circuit 1, 2, 3. The rotating magnetic field produced in the armature is rendered stationary in space by the revolution of the armature in the reverse direction by the motor S, and a potential is produced across the brushes 10, 11 connected to the continuous-current circuit. A field-winding 60, 61, 62, 63, connected across the continuouscurrent system through a rheostat Q and reversing- switch I, is used to supplement or oppose the effect of the armature current so as to produce any desired voltage across the brushes 10, 11. The field-coil F is connected to the brushes. 12, 13 through a second field-winding 17, 18, 19, 20, which neutralizes the armature - reaction when current flows through this circuit. In order to control the power-factor of the circuit 1, 2, 3, the armature D<1> of the exciter E' is in six-phase connexion with the secondaries of the transformers T<4>, T<5>, T<6>, and is rotated by the motor S, thus producing a stationary magnetic field as before. The excitation due to this alternating current in the armature is normally balanced by a shunt fieldwinding 49, 50, 51, 52 connected by wires 42, 43 across the continuous-current terminals of the converter R. The brushes 45, 46 are short circuited, and the brushes 47, 48 are connected in a circuit passing from the brush 47 through the wire 42, continuous-current terminals of the converter, shunt field-winding U, wire 41, rheostat Q<2>, and field-winding 56, 55, 54, 53, to the brush 48. The latter field - winding neutralizes the armaturereaction when current flows through the above circuit. Normally, no voltage is produced across either pair of brushes, but, if the phase-relation of the current in the circuit 1, 2, 3 should change, the balance in the-voltage across the brushes 47, 48 is disturbed, and the current flowing through the field-winding U of the converter is increased or decreased according as the current in the circuit 1, 2, 3 lags or leads, whereby leading or lagging currents are introduced by the converter into the circuit 1, 2, 3. Continuous current translating- devices may be connected in the circuits 25, 26, Figs. 2 and 3.