Patent GB-219026-A (GB)
Title: Improvements in systems of electric distribution
IPC: H02M3/31
Filed: 1924-07-12
Abstract: 219,026. British Thomson-Houston Co., Ltd., (Assignees of Alexanderson, E. F. W., and Mittag, A. H.). July 13, 1923, [Convention date]. Thermionic generators; generating circuits employing vacuum or low-pressure apparatus.- Direct current is changed from one voltage to another by means of a transformer, the primary winding of which is supplied with current impulses of substantially rectangular form by connecting it to the source of direct-current through one or more controlled electric valves, while, the secondary winding is connected to the load through a rectifying device. In one arrangement, Fig. 1, the middle point of the primary winding 5 is connected to the positive main 1 through a reactance 27 and a switch 18, the ends of the winding being connected to the negative main 2 through thermionic valves 3, 4. The ends of the secondary winding 6 are connected to the anodes of a mercury-vapour rectfier 7, the cathode 14 of which is connected to the middle point of the winding through the load 13 and a reactance 28 inductively associated with the reactance 27. The grids of the valves are connected through resistances 10 to the ends of the secondary winding of a transformer 9, the primary winding of which is connected across the secondary side of the main transformer. In order to give a lead to the grid potentials, and thereby permit the current to start in one valve before it is completely interrupted in the other, a condenser 25 may be connected in the primary circuit of the transformer 9 through another transformer 26, the change in the wave form thus produced being corrected by inserting a reactance 11 in the connection between the middle point of the secondary winding of the transformer 9 and the cathodes of the valves. In a modified arrangement, the desired angle of lead is obtained by connecting the transformer 9 across a reactance connected 'in series with a resistance across the winding 6. The filaments of the valves may be heated during operation from the secondary side of the main transformer through a transformer 15, a battery 16 being used for starting. The circuit from the main 1 is first closed through a resistance 20, which is subsequently cut out by the switch 18. The frequency of the impulses in the main transformer is determined by connecting a condenser 24 across a part of the primary winding 5. The reactances 27, 28 are so arranged that the direct components of the currents flowing through them neutralize each other and have no saturating effect on the core. In a modification, a mercuryvapour valve, with two anodes and two auxiliary electrodes connected to the secondary terminals of the transformer 9, replaces the valves 3, 4. In a three-phase arrangement, Fig. 3, current from the mains 1, 2 is supplied through the thermionic valves 34 - - 36 to the primary winding 37 of a star-connected three-phase transformer, the secondary winding 38 of which is connected to the load through a three-phase rectifier 39. The secondary winding also supplies current to a synchronous condenser 40 which establishes the frequency of oscillation or commutation of the direct current supplied to the primary winding. The grid circuits are also excited from the synchronous condenser 40 through a phase shifter 41 and transformer 42. In another arrangement, Fig. 4, the valves 43, 44 are controlled by means of the magnetic field produced by the heating current, the cathodes being supplied with a constant direct current on which is superposed an alternating current which interrupts the current through the valves alternately. The direct current is obtained from a generator 45 driven by a directcurrent motor 46 supplied with current from the output side of the system through the lead 47. The controlling currents are obtained from the secondary winding 6 through a rectifier 48 and transformers 49, 50, the desired angle of lead being secured by means of a condenser 51. The system is started by supplying heating current to the cathodes of the valves 43, 44 from an auxiliary battery 52, which also drives the generator 45 as a motor and causes the machine 46 to start as a generator and supply current to the starting electrodes of the rectifier through a relay 54. A valve 55 may be included in the connection 47 to prevent the machine 46 from supplying current to the output side of the system. In a modification, the rectifier 48 is dispensed with, the potentials produced in the winding 6 being applied directly to the transformers 49, 50.