GB618365A - Improvements in or relating to electronic control circuits, for use in supplying a single phase load from a polyphase alternating voltage source - Google Patents

Abstract

618,365. Converting ; supply systems for resistance welding. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Oct. 28, 1946, No. 31888. Convention date, Oct. 31, 1945. [Classes 38 (ii) and 38 (iv)] A welding transformer 11, or other singlephase load, is supplied from a multiphase source 3-5 through a transformer 6 having pairs of reversely connected ignitrons, or other arc discharge devices, 101, 102, 201, 202, 301, 302 in each of the secondary phase windings, the grids of the discharge devices being so controlled that one of each pair is rendered conducting during a predetermined first time interval to pass current through the load in one direction, whilst during a following predetermined interval the other discharge devices are rendered conducting to reverse the direction of load current. A condenser 41 shunting the primary winding of the welding transformer ensures extinction of the devices associated with one interval prior to conduction of the devices associated with the second interval. The sum of the two intervals determines the frequency of the load current and is governed by a squarewave voltage generator 19, this voltage being superposed on alternating voltages provided by the three phase secondary windings 20, 22 of the transformer 21 and controlling the conduction of fixing valves 121, 122, 221, 222, 321 and 322 for the ignitrons, the ignition circuits of the last being energized upon conduction of the corresponding fixing values by the discharge of condensers, such as 319, previously charged over rectifiers, such as 327, from the appropriate phase of a six-phase transformer 14. In a modified arrangement the condenser 41 is omitted and extinction of one set of discharge prior to conduction of the other set is ensured by the connection of the load transformer to the discharge devices through the centre tap of a paralleling reactor connecting anodes of discharge devices 102, 202, 302 to the cathodes of the other three devices. A modified control circuit for the fixing valves is also described.