Patent GB-440031-A (GB)
Title: Improvements in and relating to gas or vapour filled electric discharge apparatus
IPC: H02M1/04
Filed: 1934-06-14
Abstract: 440,031. Converting; frequency-changing. SIEMENS - SCHUCKERTWERKE AKT.-GES., Siemensstadt, Berlin. June 14, 1934, Nos. 17649, 17650, 17651, and 17653. Convention dates, June 14, 1933, July 25, 1933, July 25, 1933, and Sept. 12, 1933. [Class 38 (ii)] [See also Group XL] A circuit arrangement comprises a gas. or vapour filled discharge device provided with a control grid and with an auxiliary grid, arranged between the control grid and the cathode, wherein to extinguish the arc at any moment a potential, negative with respect to the cathode, is applied to the auxiliary grid to create a space poor in ions, and a negative potential is subsequently applied to the control grid. The distance between the grid should be less than the mean free path of electrons and auxiliary grids may be arranged on both sides of the control grid and connected together preferably through a resistance, or to different sources of potential. To obtain the time lag between the application of the potential to the control grids 111, Fig. 1, and the auxiliary grids 115, resistances 112 and condensers 113, Fig. 1, or inductances 116 and condensers 117, Fig. 2, may be connected in circuit as shown. The circuit arrangement may be used for rectifying alternating current wherein during one halfcycle the arc is ignited a number of times when the anode potential falls in dependence upon the external circuit to a predetermined minimum u2, Fig. 3, and is extinguished a number of times when the anode potential rises to a maximum ul. A three-phase rectifier 205, Fig. 4, is provided with grids and means for effecting a time lag in the applications of the potentials to the control and auxiliary grids. Positive and negative potentials for starting and extinguishing the arc are applied to the grids through grid-controlled valves 203, 204 which are provided with thermionic cathodes, and through a rotary distributer 210 which rotates with the frequency of the alternating current and is adapted to supply the control potentials to the grids of the correct anode. The valves 203, 204 are ignited when the potential on the output side reaches the predetermined minimum and maximum values respectively. For this purpose, the line 220 of the output is connected to a variable tapping on a potentiometer 201, further tappings on which are connected to grid transformers 221, 222. The extinction of the valves 203, 204 is effected through condensers 207, 208. A negative bias from the battery 202 is maintained through the distributer 210 on those grids, the anodes of which are not working. The distributer 210 may be replaced by a threephase mercury-vapour discharge device. Upon a short-circuit in the external circuit, a valve 216, provided with a thermionic cathode, is ignited to reduce the control potentials to zero and extinguish the rectifier. When the shortcircuit occurs, the circuit of the valve 216 may be utilized to actuate signals or to operate a relay to regulate the position of the tappings on the potentiometer 201 so that when the rectifier is again ignited, the potential on the output side is, at first, below normal and is raised subsequently to its usual value. In another form, a discharge device 220, Fig. 5, is adapted to convert continuous current into single-phase alternating current and is connected to a choke 222 and an output transformer 226. By means of the apparatus, described with respect to Fig. 4, for providing grid-controlling impulses, the are is ignited and extinguished a number of times during each half-cycle at predetermined maximum and minimum values of anode potential. The wave form of the converted current is the same as that of an alternating current supplied. at 231 to the grid circuits of the valves 204, 203 and on which is superposed a continuous current through a resistance 230. A distributer 229, rotating synchronously with the desired frequency of the alternating-current, ensures that the correct anode is connected to the grid circuits associated with the valves 203, 204. Similarly, with the use of an uncontrolled rectifier, the converter may be used for phase conversion. In further forms, the ignition impulses to the grids follow the extinguishing impulses with a time lag instead of being dependent upon the magnitude of the anode potential. For example, the extinguishing impulses are supplied through a valve 241, Fig. 6, and the ignition impulses by an oscillatory circuit comprising members 240. The valve 241 may be dispensed with, the controlling potentials being fed through transformers to the grids. Adjustable continuous current from an alternating- or continuouscurrent source may be supplied to the consumer lines 30, Fig. 8, through a discharge device 260, the anode of which is connected to the negative line. The cathode is connected to the positive line through a choke 263 which is connected in parallel with an oscillatory circuit comprising a variable condenser 265. The control potentials for the control and auxiliary grids are supplied from the oscillatory circuit through an inductance 266. In a further form, a frequency converter is supplied through two three-phase secondary windings 302, Fig. 9, the star points of which are connected through ehokes 305 and windings of the output transformer 309 to the cathode. The rotary distributer 312, which rotates synchronously with the desired frequency, supplies the controlling impulses from the generator 315 through distributers 320, 321 to the grids. Adjustable segments 317 on the distributer 312 facilitates the flow of wattless current, and the distributers 320, 321 are provided with means whereby a negative potential is maintained on the grids which are not working. A distributer 323 which rotates synchronously with the desired frequency connects alternately the ends of the primary windings of the output transformer 309 to the controlling apparatus 315. Three such devices may be used for obtaining threephase current and may be so combined that the positive half-cycles of the output current are dealt with in one converter and the negative half-cycles in the other. The Specification as open to inspection under Sect. 91 describes circuit arrangements which are described in the Specification 439,957, [Group XL]. The subject-matter does not appear in the Specification as accepted.