GB590892A - Improvements in or relating to the control of a.c. circuits subject to line voltage variation - Google Patents

Abstract

590,892. Automatic voltage regulation. BUDD MANUFACTURING CO., E. G. May 12, 1944, No. 9126. Convention date, April 19, 1943. [Class 38 (iv)] Constant power in a system, such as a resistance welding system, subject to line voltage variations is obtained by the phase shift of the voltage applied to the grids of valves 20, 21 arranged to trigger ignitrons 15, 16 under the control of a peaking transformer 45 supplied across a phase shifter, which includes a bridge system 49 having a resistance 54 and a reactor 52 arranged to function as a resistance, and has also a voltage bridge 89 controlling means for varying the effective resistance of reactor 52 to compensate for line voltage changes, the normal effective resistance of the reactor 52 being greater than that of resistance 54, whereby the degree of compensation of line voltage change varies directly with changes in load. The reactor 52 comprises the primary winding of a transformer 53 which has'its secondary winding 70 connected across the anodes of a pair of triode valves 71, 72 with strapped control grids connected to a potentiometer 102 across the bridge 89, so that the reactor 52 is variably loaded (inductively) in accordance with changes in the grid voltage, which is the difference between a constant voltage and the load circuit voltage. The bridge 89 comprises a gas-filled diode 94 and resistance 95 in series parallel with a resistance 96 and diode 97, these being connected across a filtrated full-wave rectifier circuit supplied by a transformer connected across the supply lines 28. At normal line voltage the bridge 89 is balanced, and when the line voltage varies a constant voltage obtains across the diodes, the difference appearing across the resistances. The triggering valves 20, 21 associated with the ignitrons 15, 16 are provided with shield grids 24 whereby additional control is exercised by a biassing transformer 35 with a primary winding 36 connected across the lines 28, and two pairs of associated secondary windings 37, 39 and 38, 40 forming units of opposite polarity, one end of each unit being connected to a shield grid 24 and the other end to a control grid 25 or 26. Timing of the welds is controlled by a control device which has a coil 46 arranged as a primary winding associated with the secondary windings 39, 40 of the biassing transformer 35. Specification 551,775 is referred to.