GB530238A - Improvements in or relating to the control of electric current by means of dischargeapparatus - Google Patents

Abstract

530,238. Control systems for resistance welding; rectifying alternate currents. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. March 1, 1939, Nos. 6698 and 6699. Convention dates, March 5, 1938, and June 16, 1938. [Classes 38 (ii) and 38 (iv)] In apparatus wherein an alternating current is controlled by " ignitrons " the potentials of the starting electrodes of the ignitrons are supplied from the source of the current to be controlled through circuits which do not include rectifying devices or other means for distorting the potential curve. Fig. 1 shows such an arrangement applied to a seam-welding machine. The ignitrons 41, 43 are connected back-to-back across the supply leads 35, 37 in series with the primary 33 of the welding transformer and their igniting electrodes 49 are connected by conductor 91, 93 and a switch 85. The switch 85 is operated by a relay controlled by a commutator 57 driven by a motor 55, so that its circuit is closed for definite periods, each of which comprises several periods of the current. The relation of these periods and the result of the switch being closed at different points of the current-cycle are discussed in the Specification. The igniting- electrode and cathode of each rectifier may be connected by auxiliary circuiting including rectifiers. In a modification the winding 33 may be supplied directly from the mains through a transformer in opposition to the current through the ignitron, and the igniting-electrodes supplied from the tapping secondary of the transformer. In another modification for spot welding the igniting electrodes are connected through a relay arranged to break the circuit after a definite adjustable interval. Fig. 22 shows an arrangement for rectifying and controlling the current. The ignitrons 301, 303 are connected to the secondary of a transformer 299 and the load 297 to a centre tapping on 'the transformer. The igniting- electrodes 309 are supplied from the secondaries 319, 317 of a transformer 321 through windings 323, 325 on the side limb of a reactor 315. The load is connected in series with a winding 313 on the centre limb of the reactor, which is presaturated from a source 329. By regulating the degree of the saturation the point of the cycle at which the ignitrons conduct can be adjusted.