Patent GB-390200-A (GB)
Title: Improvements in and relating to electric converting apparatus
IPC: H02M7/51
Filed: 1931-09-29
Abstract: 390,200. Converting. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Bedford, B. D. ; 329, Germania Avenue, Schenectady, New York, U.S.A.) Sept. 29, 1931, No. 27128. Convention date, Sept. 29, 1930. [Class 38 (ii).] Current from a D.C. supply 10 is converted into polyphase A.C. by means of impulses of short duration applied simultaneously to the grids, of two or more valves. In a simple twophase circuit, Fig. 1 (not shown), two paralleltype inverter circuits are connected in parallel and the grids connected to a divided secondary winding of a transformer delivering a peaked waveform. Positive impulses are applied simultaneously to the valve grids of one inverter, the valves conducting alternately owing to the increased anode voltage applied to the inoperative valve by the divided primary winding of the output transformer and the discharge of the commutating condenser connected across the winding, the period of discharge being longer than the duration of the positive grid impulses. The output of each inverter is therefore single phase current of half the frequency of the grid impulses. The two inverters being controlled by the impulses of opposite sign thus deliver two phase current. In another two-phase circuit, Fig. 3, the grids of all four valves 19 .. 22 receive the same impulses from the transformer 30, the actual applied potential being modified by transformers 35, 36 each connected to the output of the other inverter. The 'divided secondary windings 37, 38 cause the valves of each pair to conduct alternately delivering half-frequency single phase current, and the sequence of valve conduction in the inverters is governed by the energization of each of the transformers 35, 36 by the flow of current in the other inverter. Specifications 386, 371 and 390,184 are referred to. The Specification as open to inspection under Sect. 91 comprises also the use of one half of the circuit described, to deliver single-phase current. It comprises also a three-phase system employing a similar principle, all the valves 65, 66, 67, Fig. 4 (Cancelled), receiving grid potential from a common transformer, 30 in series with which are transformer secondaries 71, 72, 73 each feeding the grid of one valve and being energized from a primary connected between the anode of that valve and the anode of the next succeeding valve in the order of phase rotation. As the anode potential is low on the valve that is conducting, say 65, and is raised above the D.C. potential on the other two valves, on the valve 66 by the winding 63 in the circuit of the valve 65 inducing positive voltage in the primary 54 of the transformer 57, and on the valve. 67 by the winding 62 coupled with the transformer 56, both transformers 74, 76 receive current, but the transformer 76 applies negative potential to the valve 67. At the next impulse delivered by the transformer 30 the valve 66 is thus rendered conductive. In view of the interconnection of the 'primary windings of the transformers 56, 57, 58 in star zigzag, full wave current is generated in the secondary windings 59, 60, 61 that are star connected and supply three-phase lines 50, 51, 52. This subjectmatter does not appear in the Specification as accepted.