GB761071A - Improvements in and relating to arc furnace control systems - Google Patents

Abstract

761,071. Automatic control systems for arc furnaces. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 1, 1954 [Sept. 1, 1953], No. 24161/53. Class 38 (4). In an A.C. arc furnace the ratio of arc voltage to current is maintained constant by automatically controlling, through saturable reactors, an A.C. motor adjusting electrode position. In Fig. 1 direct voltages respectively proportional to arc voltage and current of a furnace electrode are produced across resistors VR1 and R3 through rectifiers W2 and W1. The two voltages are opposed and when the ratio of arc voltage to arc current has the desired value, zero voltage is applied to a D.C. amplifier E. If, however, the ratio deviates from the desired value amplifier E produces an output, of polarity corresponding to the sense of the deviation, which, through a rectifier W4 or W3, energizes the control windings of saturable reactors A1 and A2 or B1 and B2, thereby selectively reducing impedances in the supply lines to a three-phase motor M so that it runs in the appropriate direction to correct the deviation by adjustment of the electrode position. A similar arrangement in which electrode position is controlled by a single phase reversible capacitor motor is described. The saturable reactors and hence motor M may be controlled manually by a controller C. Amplifier E may be dispensed with and the difference voltage utilized directly to energize the saturable reactor control windings.