Patent GB-251301-A (GB)
Title: Improvements in and relating to the control of electric power systems
IPC: H02M7/15
Filed: 1926-04-26
Abstract: 251,301. British Thomson-Houston Co., Ltd., (Assignees of Alexanderson, E. F. W., and Mittag, A. H.). April 25, 1925, [Convention date]. Vapour apparatus, arrangements of.-In systems in which power is interchanged between alternating and direct current systems by means of electron discharge devices, the relative characteristics of the two systems are varied by controlling the phase of an alternating potential applied to the grids of the devices. In the system shown in Fig. 1, power is supplied from one phase of a three phase system 3, through a transformer 4, anodes 18, 19 and cathode 14 of a vapour rectifier 5 and through a smoothing choke 6 to a load such .as the armature 2 of a direct current motor. The field 8 of the motor is similarly supplied by a rectifier 9 thus giving shunt characteristics. Series characteristics can be obtained by supplying the rectifier 9 from a current transformer connected in series with the primary of the transformer 4. Grids 20, 21 surrounding the anodes 18, 19 are supplied through a transformer 26 from a phase displacing device comprising a stator 31 supplied with three phases and a single phase rotor 29 which can be set in any desired angular position. When the rotor 29 is set so that the potentials of the grids 18, 19 are exactly 180‹ out of phase with the respective anodes 20, 21, no current flows through the rectifier 5 and thus there is no potential across the armature 2. As the rotor is gradually turned the potential across the armature 2 increases up to a maximum when the potentials of the grids are exactly in phase with their respective anodes. Regenerative braking of the motor is effected by throwing a reversing switch 7 and suitably adjusting the rotor 29. Sparking at switch 7 can be prevented by interlocking it with the rotor so that it can only be thrown when the rotor is placed so that no current can flow through the rectifier 5. Such an interlocking arrangement is shown in Fig. 2, where the wires 42, 43 correspond to the direct current output, and the switch 7 is connected by a flexible member 44 to the rotor 29. Modifications are described in which the alternating current is a single phase supply and the winding 31 is then supplied by distorting the single phase into three phase in the usual manner. Also the two rectifiers 5, 9 may be combined into a single apparatus. The Specification as open to inspection under Sect. 91 (3) (a), comprises also the system shown in Fig. 9 (Cancelled). A polyphase supply 70 is connected through a rectifier 74, reversing switch 76, and polarized relay 78 to a traction system 71. The grid phase control device 80 is operated by a pilot motor 88 the armature of which is connected through a reversing switch 89 and a battery 91 to the system 71. Thus the direction of current through the pilot motor 88 depends on whether the voltage of the system 71 is greater or less than that of the battery 91, and therefore the system 71 is kept at constant voltage. Switches 76. 89 are shown in the position for regenerative braking of the locomotive 103. When braking ceases, current from the battery 91 flows through the field of the motor 88, the relay 78 and armature of the motor 88 in such a direction as to close the relay onto contacts 93, 94 and turn the pilot motor to close contacts 101, whereupon a coil 100 is energized to throw the switches 76, 89 to the left hand position for supply of power from the system 70 to the system 71 and to give correct operation of the pilot motor. When braking is initiated the relay 78 closes on to contacts 95, 96 and the pilot motor again closes its contacts whereupon a coil 99 is energized to throw the switches to the right hand position as shown. Also, in any of the modifications, a variable magnitude direct potential may be impressed upon the grids in place of the variable phase alternating potential. This subject-matter does not appear in the Specification as accepted.