Patent GB-681825-A (GB)
Title: Improvements in or relating to the conversion of polyphase alternating current into unidirectional current impulses
IPC: B23K11/24
Filed: 1950-01-27
Abstract: 681,825. Frequency and phase changing. SOLOMON, J. L. Jan. 27, 1950 [Feb. 12, 1949], No. 2208/50. Class 38 (ii). A circuit for supplying series of pulses, in timed sequences, from a polyphase supply, comprises the combination of an inductive device having as many primary windings as there are phases in the polyphase supply, electric discharge valves for controlling the flow of current in the primary windings, the firing of each discharge valve being controlled by a further grid controlled valve, means for applying control potentials to the grid-controlled valve associated with one winding so to control the conductivity of the discharge valves and means to control the flow of current in the remaining windings in accordance with the flow of current through the first-mentioned winding. The prints A, B, C are connected to a timing mechanism which may be as that disclosed in Specification 681,819, A being a common cathode point, B and C being maintained normally negative thereto, but which may alternatively be rendered positive. When, say, point B is made positive, screen grid 32 of the thyratron 30 is also made positive so that when the control grid 40 thereof goes positive, the thyratron 30 fires, thus causing ignitron 25 to conduct and current will flow in the windings 14, 15 for as long as the anode of the ignitron 25 is positive. Flow of current through winding 15 energizes primary winding 46 of a transformer 47, thus inducing a voltage in the secondary windings 54, 71 of the transformer of such a polarity as to oppose the biasing voltage from the D.C. source 55, thus rendering the screen grids of thyratrons 52, 67 conducive to conduction. When therefore the control grid 60 of thyratron 52 is driven positive by the voltage induced in secondary winding 61 of a transformer 64, thyratron 52 fires, causing ignitron 50 to conduct to pass current in the windings 17, 18, the pulse being 120 degrees displaced from that in windings 14, 15. 120 degrees later, control grid 72 of thyratron 67 is made positive, thereby causing a current pulse to pass via ignitron 65 in the windings 19, 20. Windings 14, 15; 17, 18; 19, 20 form three primary windings of a transformer whose secondary supplies a load such as a welding circuit. These primary windings are, therefore, supplied with a succession of similarly-poled pulses displaced by 120 degrees until the magnetic flux in the transformer core reaches a pre-determined maximum. The point B is then made negative and the energization of the transformer ceases. Point C is now driven positive by the timing device, thereby causing the ignitrons 26, 51, 66 to conduct to pass a succession of pulses through windings 14, 15; 17, 18; 19, 20, as before, but reversely poled, thus producing in the load a single phase A.C. of low frequency. The firing of the thyratrons may be delayed up to 120 degrees by phase shifting the voltages supplied to the primaries of the transformers 44, 64, 74, thereby causing the ignitrons to conduct over part only of a half cycle. Specification 654,583 also is referred to.