GB781639A - Improvements in and relating to electric arc furnaces - Google Patents

Abstract

781,639. Automatic control systems for arc furnaces. BRITISH THOMSON-HOUSTON CO., Ltd, Oct. 31, 1955, No. 31099/55. Class 38 (4). In an arrangement for automatically maintaining constant the current in an electric A.C. arc furnace by obtaining control voltages responsive to the current in and voltage across the arc and utilizing said voltages to control a reversible D.C. electric motor to adjust electrode position, compensation is introduced for the reactance of the lead between the electrode and the point at which the voltage is measured. As shown, a direct voltage V1 representative of the current to an electrode 1 of a three-phase arc furnace 2 is derived from a current transformer 8 through a rectifier 10. A second direct voltage V representative of the voltage across the arc is derived through a rectifier 3 and is compensated for the effect of the volt drop in lead 12 by introducing an inductance 6 of appropriate impedance in series with the input to rectifier 3 and developing across it, through a transformer 12, an opposing voltage dependent on arc current. A capacitance 5 compensates for the effect of the reactance of inductance 6 on current flowing in the voltage responsive circuit. The difference between voltages V and V1 controls, in a manner not shown, an amplidyne exciter supplying a D.C. motor adjusting electrode position to maintain operating voltage at a value determined by the setting of a rheostat 7.