GB812055A - Improvements in and relating to electric carbon arc supply circuits - Google Patents

Abstract

812,055. Lighting arcs; protective arrangements; rectifying. BRITISH THOMSONHOUSTON CO. Ltd. Oct. 19, 1955 [Oct. 29, 1954], No. 31353/54. Classes 38 (2) and 38 (4). An electric carbon arc supply circuit connecting an A.C. source through a rectifier 2 to two carbon electrodes 1 between which may pass a D.C. arc embodies in series circuit relationship between the source and electrodes a ballast impedance comprising at least one capacitor 5 which provides a short-circuit current limiting impedance to reduce to a predetermined safe value the circuit current when the electrodes contact each other to start the arc; this value is that which while sufficient to strike the arc is small enough to obviate damage to the circuit components, particularly the rectifier. As shown, the source comprises a three-phase mains 4 which is connected through three capacitors 5 and a three-phase transformer 3 to three full-wave rectifiers 2 which can be of the dry-plate, preferably germanium kind. The capacitors 5 alternatively may be connected in the transformer secondary circuit, may have variable capacitance by using banks of fixed capacitors connected by individual switches, and may be prevented from resonating by series-connected resistors, not shown, shortcircuited when the circuit is on load by switches preferably automatically controlled by a contactor having its coil controlled by the arc circuit. A choke 6 may be connected in the arc circuit. Specifications 473,368 and 612,192 are referred to.