GB1110916A - Automatic voltage compensator for three phase - Google Patents

Abstract

1,110,916. Supply arrangements for welding systems. WELDING RESEARCH Inc. 12 Aug., 1966, No. 36205/66. Heading H2H. [Also in Division G3] In a welding system the supply of welding current is automatically regulated, in a manner to compensate for variations in the threephase supply voltage, by control of the firing angle of ignitrons connected in the primary circuit of the welding transformer. To effect the desired regulation the three-phase voltages of the A.C. supply are rectified to produce a direct voltage which varies in amplitude as the phase voltages vary; alternating voltages are also derived from each phase of the supply and these voltages are applied to a circuit, including valves connected for push-pull cathode follower operation; the said direct voltage and the outputs from the cathode follower circuit are applied to the grid/cathode circuits of further valves which are also associated with an adjustable voltage reference source, the arrangement being such that the further valves conduct to produce firing pulses when the grid/ cathode voltage exceeds the reference voltage. As the said grid/cathode voltage varies in dependence upon supply voltage variations the firing pulses are phase-shifted in accordance with these variations, whereby the firing angle of the ignitrons is controlled in the desired manner. A suitable control circuit arrangement incorporating dual-triode valves is described with reference to Figs. 2 and 3 (not shown).