GB508789A - Improvements in and relating to electric control systems - Google Patents

Abstract

508,789. Control systems for consumption apparatus. BRITISH THOMSONHOUSTON CO., Ltd. Jan. 3, 1938, No. 116. Convention date, Jan. 2, 1937. [Class 38 (iv)] Switching control.-In a system for supplying an inductive load from a source of A.C. comprising an are discharge device, in order to prevent a reversal of voltage due to the inductance in circuit to occur when current flow is stopped, means including an auxiliary arc discharge device are provided which temporarily connects the load to an auxiliary source of A.C. to permit sufficient current to flow to prevent a reversal of voltage. Relates to a resistance spot welding system in which the welding electrodes 10 are supplied through a transformer 15, the circuit of which is controlled by a pair of reversely connected valves 17, 18 and is concerned with overcoming the inductive surge resulting from the decay of flux in the core of the transformer 13 when energization (e.g.) for only a half cycle takes place. This is effected by means of an auxiliary pair of reversely connected valves 19, 20 which are connected across the primary 14 of the transformer 13 through an auxiliary source of supply comprising a transformer 21 and are controlled from a phaseshifting network 53, 54 so that when the supply through the main valves ceases and auxiliary supply is furnished through the valves 19, 20 to prevent temporarily the decay of flux to allow (e.g.) the electrodes time to separate. The control of the main valves is effected by means of auxiliary valves 22, 23 the grid potentials of which are supplied from a transformer 43. Closure of the switch 59 enables peaked impulses from the rectifier 24 to become effective to control the valve 26 which conducts and discharges the condenser 41 thus giving an impulse in the transformer 43. The switch 59 may be linked with the mechanism operating the electrodes 10 so that current is supplied only when the electrodes are in engagement with the work. Specification 489,702 is referred to.