GB803550A - Improvements in or relating to induction motor driving systems for adjusting the positions of movable objects - Google Patents

Abstract

803,550. Automatic control systems for induction motors. SIEMENS - SCHUCKERTWERKE A.G. May 24, 1955 [May 24, 1954], No. 15004/55. Class 38 (4). [Also in Group XXXVII] Relates to the use of a magnetic material having a substantially rectangular magnetization loop for the cores of a magnetic amplifier connected in the A.C. supply to, and controlling, an induction motor so as to provide a high starting torque. The motor may provide the drive for adjusting the position of a movable object, such as the electrode assembly of an arc furnace, by exerting large forces thereon for short periods. In one embodiment, the speed of a three-phase induction motor M, Fig. 2, is maintained constant, the phase-winding U being fed directly from phase R and the windings V, W, being fed from phases S, T, through a controlled bridge arrangement of self-saturating reactor pairs S1, S2, T 1, T2. The current in the D.C. control windings 1, 2, for the reactors is controlled in accordance with a speed error signal which is the difference between the voltage of the motor-driven tachogenerator 5 and a reference voltage from the potential divider 4. In a modification, the position, of a member moved by the motor is controlled by a position error signal which is the difference between a voltage derived from a potential divider 13, Fig. 2a, driven by the rotor 3 of the motor through shaft 11 and worm gearing 12, and a reference voltage from the potential divider 4. The application of the invention to two-phase motors fed from a three-phase supply or a single-phase supply is described, Figs. 6, 7, 8 and 10 (not shown). In an arc furnace in which the position of the electrodes 21, 22, 23, Fig. 5, is regulated by the three-phase motor M, the control windings of the reactor pairs S1, S2 T1, T2, associated with the field windings V, W, are fed from the D.C. outputs of magnetic amplifiers VI, V2. The ratio of arc voltage to arc current is maintained constant by opposed D.C. control signals representing these quantities, derived respectively from the potential divider 28 and transformer 29, and applied to windings a and b of the amplifiers VI, V2. A speed follow-up signal to prevent over-shooting is applied to windings c from the tachogenerator 5. In a further embodiment, the reactor pairs S1, S2, T1, T2, Fig. 9, are provided with D.C. control windings a, b, c, d and associated with a motor M regulating the position of a movable object. An error signal and a bias signal respectively are applied to windings a and b, follow-up signals being fed to windings c and d. To provide the latter, the A.C. voltage across the winding W of the delta-connected motor field windings U, V, W, is connected in series with two auxiliary voltages 180 degrees out of phase with one another and provided by the centretapped secondary of transformer 51, the resultant sum and difference voltages being rectified at 53, 54 to feed the windings d, c respectively. In a modification the follow-up quantity is derived from the voltage across the reactors T1, T2, Fig. 9a (not shown).