GB871843A - Improvements in electrical servo-systems - Google Patents

Abstract

871,843. Automatic arc furnace control systems. SQUIRE, L. E. March 18, 1959, No. 9340/59. Class 38 (4). [Also in Group XXXVII] In a system for automatically-adjusting the position of the electrodes of an arc furnace in accordance with arc current and arc voltage, the A.C. or D.C. motor for driving the arcadjusting mechanism (not shown) has two opposing windings the currents through which are controlled respectively in accordance with arc current and arc voltage, together with a saturable reactor controlled by both control signals so as to limit the current drawn by the motor when stationary due to balance between the opposing windings. It is stated that the reactors may be replaced by electronic amplifiers. In one embodiment, Fig. 1, using a splitfield A.C. series motor 1, the fields 2, 3 are in series with saturable reactors 5, 6, controlled in accordance with arc voltage and arc current, so that when these quantities are in balance, the fields exactly oppose and the motor remains stationary, any unbalance causing rotation in the appropriate direction to restore balance. A third reactor 9 in series with the motor has opposed control windings also energized in accordance with arc voltage and current so that its impedance is a maximum when the motor is stationary. In a modification, Fig. 2 (not shown), the three reactors are similarly connected to two stator windings of a repulsion motor. In another modification, Fig. 3, the two reactors 5, 6 control the currents through two sets of brushes 13, 14 of a repulsion motor, with the current limiting reactor 9 in series with a single stator winding. In another modification, Fig. 4, a split field D.C. series motor 1c is supplied from rectifiers 18, 22, the supplies to which are controlled by the two reactors 5, 6, with the current limiting reactor 9 in the common supply lead. In another modification, Fig. 5 (not shown), the armature of a separately-excited D.C. motor is supplied through a rectifier controlled by the current limiting reactor 9 and the two field windings are supplied by rectifiers controlled by the two reactors 5, 6. In another modification, Fig. 6 (not shown), the fields of a separately-excited D.C. motor are directly energized by the arc current and arc voltage signals without the interposition of saturable reactors.