GB715428A - Improvements in apparatus for converting direct current into alternating current - Google Patents

Abstract

715,428. Converting. HEWITTTC SOC, AR.L. July 21, 1952 [Oct. 29, 1951], No. 18388/52. Class 38(2) The output frequency of a single-phase mercury arc inverter having main anodes 30, 31 is determined by a self-exciting parallel-type pilot inverter, comprising subsidiary anodes 2, 3, the common cathode 1 and self-energized grids, which energizes the grids associated with the main anodes. All the electrodes may be enclosed in one envelope. Closing switch 15 initiates operation by energizing and moving starting electrode 16 whereby a cathode hot spot is created and maintained by exciter anode 17. Consequent opening of switch p, q, r cuts out the starting electrode 16 and develops a voltage pulse in transformer winding 6 which, transmitted to winding 5 and through capacitor 12 and resistor 24 to the grid associated with anode 3, causes this to fire. Subsequently anode 2 fires and anode 3 is quenched by commutating condenser 8, and these two anodes continue to fire alternately in the known manner of an inverter at a frequency determined by the values of inductor 10, winding 4, resistors 9, 13, 14 and capacitors 8, 11, 12. The load on this inverter comprises the pulses developed in transformer 25, 26 and transmitted to the grids associated with the main anodes 30, 31, modified by the biasing direct voltage developed by rectifier 27, When switch 36 is closed a load connected to transformer 39 which is energized through capacitor 37, 38 from auto-transformers 34 to which anodes 30, 31 are connected, is therefore supplied with A.C. at the frequency of operation of the pilot inverter. The frequency is not altered by a change in the load, for the loading of the pilot inverter remain constant. In a modification, frequency varations due to changes in inductance of winding 4 with variations of the input direct voltage, are offset by changes in the resistance of lamps or other voltage variable resistors connected in series with resistor 9. Frequency stability is improved by provision of an intermediate pair of converter anodes with associated grids connected through high valve resistors to the grids of the pilot inverter, pulses for the main anode grids being derived from transformers with primary windings connected to the intermediate anodes. The main anodes may be housed in a separate envelope from that enclosing the pilot and intermediate anodes, Fig. 3 (not shown).