GB529973A - Improvements in and relating to electric control systems - Google Patents

Abstract

529,973. Supply systems for resistance welding. BRITISH THOMSON - HOUSTON CO., Ltd. March 29, 1939, No. 9825. Convention date, March 29, 1938. [Class 38 (iv)] A.C. is supplied to a welding circuit 1, 3 from an A.C. supply by means of two groups 4, 5 of valves, the valves in one group being arranged reversely to those in the other group. The valves in each group are controlled to operate sequentially by means of a switch 51 which determines the connection of the control electrodes of the valves in the excitation circuit, to permit the valves to be operated at a higher rating than the normal continuous load rating. The contacts 55, 56 and 61, 62 of the switch 51 are sprung so that during changeover a control electrode of one valve in each group remains connected in the excitation circuit. The switch 51 is operated by a coil 50 intermittently energized from a supply 66 by means of a relay 64 which is periodically energized and de energized by means of a further relay 65. Excitation circuits 12 13 are provided for the groups 4, 5 respectively ; an impulse from the control circuit 27 applied across the resistance 26 causing the valve 14 in the circuit 12 to conduct and initiate discharge in the particular valve of group 4 to which it is connected by the switch 51. The impulses for controlling the group 5 of valves by means of the circuit 13 are derived from across the transformer 3 in the load circuit The impulse generator circuit 27 is of the kind described in Specification 495,700, [Group XL], the phase of the impulses being adjustable by means of a phaseshifter 44. Condensers 25 are connected in the grid circuits o: the valves 14 to dissipate any transients which may occur Specification 486,349 also is referred to.