GB629284A - Improvements in alternating current control apparatus particularly for arc welding - Google Patents

Abstract

629,284. Automatic voltage regulation. BRITISH THOMSON-HOUSTON CO., Ltd. Aug. 28, 1944, No. 16258. Convention date, Aug. 28, 1943. [Class 38 (iv)] In an arc - welding arrangement, the voltage across the arcing electrodes 10, 12 is kept to a safe value both during welding and during idling. In the arrangement shown, the A.C: supply 16 is adapted to be applied through contacts 29 to the primary 20 of the welding transformer 15 by energization of a relay 19, a power-factor improving condenser 32 being simultaneously connected in a parallel circuit. The relay 19 and a second relay 18 are adapted to be energized from tappings on the secondary of a transformer 17 also fed from the supply 16. To provide the above-mentioned protection, a switch 47 is moved into its lower position. A voltage of 55 between tappings 38, 39 then energizes relay 18 through resistance 52, causing the closing of contacts 50. A small current passes through relay 19, but is insufficient to operate it, and a safe voltage of 35 between tappings 37, 38 is applied through lines 43, 45 to the open electrodes 10, 12. To start welding, the electrodes 10, 12 are shortcircuited, whereupon the 35 volts operate relay 19 to cause the energization of the welding transformer, and the relay 18 is held operated by the 90 volts between tappings 37, 39, which energize a circuit including the relay 18, the lines 45, 43 and the electrodes 10, 12. The welding transformer, which on open circuit would have a voltage of 75 (the applied volts), has normally a safe welding voltage of from 25 to 40 volts. Should this voltage rise unduly, then since it is vectorially in series with the voltage across relay 18, the voltage across the latter will drop, causing the relay 18 to move to the " off " position, thereby de-energizing relay 19 and the welding transformer. The relay 18 will also open when the electrodes 10, 12 are open-circuited at the end of a welding operation and, in both cases, after de-energizing the welding transformer, it will reclose under the influence of the 55 volts between tappings 38, 39 and re-establish the voltage of 35 across the open electrodes, as already explained. In a modification, Fig. 3 (not shown), the welding transformer is dispensed with and a reactance takes its place for stabilizing the arc.