Patent GB-386675-A (GB)
Title: An improved method of, and means for, controlling electric currents by gaseous discharge tubes
IPC: B66B1/08
Filed: 1931-07-16
Abstract: 386,675. Controlling consuming devices ; converting electric currents ; automatic regulation. IGRANIC ELECTRIC CO., Ltd., 147, Queen Victoria Street, London.-(Cutler- Hammer Manufacturing Co. ; Milwaukee, Wisconsin, U.S.A.) July 16, 1931, No. 20422. [Classes 38 (ii) and 38 (iv).] A method of controlling current passing from a direct current source through a gaseous discharge tube, such as 3, Fig. 1, comprises impressing transient potentials on the anode and grid, for example by condensers 13, 12, connected with impedances 1, 2, 7 as shown, respectively to stop and to delay restarting of the discharge, and controlling the interval before restarting by allowing energy stored, during the preceding conducting period, in a capacitative device such as 12, to discharge therefrom at a given rate, for example through an impedance 14 and rectifier 8. The transient potential on the anode may be applied by a transformer 15, as shown in Fig. 2. An operating characteristic of a dynamo-electric machine may be automatically regulated by associating such a gaseous discharge tube with the machine. Fig. 3 shows the invention applied to an arrangement in which a motor armature 21 is subject to maximum strength of the field winding 22 during starting by reason of the heavy current through impedance 25 maintaining a considerable negative potential on the grid 38 of a tube 35, connected as shown, whilst a tube 30 is maintained fully conducting by positive potential on its grid. The field 22 thus receives current through impedances 28, 29 in parallel. When the armature current falls the potential of the grid 38 becomes less negative and permits current to start in the tube 35 whereupon transient potentials are applied to the anode and grid of the tube 30 and the field current is reduced to a minimum for a period depending on the adjustment of the impedance 40, or of the condenser 42, which has to discharge through it. When the tube 30 again conducts, the current in the tube 35 is stopped for a period depending on the adjustment of the impedance 41 and condenser 43, and the field winding 22 receives an average excitation depending on the ratio of the conducting periods of the two tubes. As current in the armature circuit varies the grid biassing potentials across the impedance 25 will vary and so also will the average field current. Any armature current transient, due, for example, to rapid alteration in controller adjustment, will be reduced by the operation of the tubes. An arrangement is also described in which the biassing impedance 25 is omitted and the grid condensers and resistances adjusted to give normally a high average field current and with which is associated the arrangement described in Specification 386,687 whereby the field may be progressively weakened in a definite time interval after opening a switch in shunt to a condenser inserted in series in the discharge circuit of the condenser 42. Such a switch may be operated by the last accelerating switch or be mounted in an elevator controller to be used at the will of the operator. In a further modification, Fig. 5, the strength of the motor field 222 is controlled in accordance with the speed of the armature 221, to which is coupled an auxiliary generator 246 the e.m.f. of which is included with a counter battery 245 in the circuit of the grid 233 to lengthen and shorten respectively the discharge time of the condenser 242. The control is modified in accordance with variations in armature current until the speed of the motor has caused the relay 247 to fall.