GB713235A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

713,235. Automatic speed control systems. GENERAL ELECTRIC CO. July 9, 1952 [July 11, 19511, No. 17315/52. Class 38(4) In a system for automatically controlling the speed of an electric motor, a voltage derived from the motor armature circuit controls the grids of a pair of electric valves reversely connected in parallel with each other and arranged in series with the motor armature across an A.C. source. In Fig. 2 the armature 1a of a separately-excited D.C. motor 1 is supplied from an A.C. source 4, 5 through reversely' connected grid-controlled thyratron valves 6 and 7, and the direction and speed of rotation of the motor is determined by the sense and magnitude of adjustment of the slider 3a of a potentiometer 3 from a central position. When the slider is in a central position the two sections of a double-triode valve 10, which are directly coupled to thyratrons 6 and 7 respectively, are arranged to conduct equally by the setting of a cathode potentiometer 11a, and neither of the equal potentials of anodes 10a, 10d is sufficiently high to cause conduction of either thyratron to a degree necessary to cause motor rotation. Adjustment of potentiometer 3 in one sense or the other from this position, however, raises the potential of one or other of the anodes of double-triode 10 so that one or other of thyratrons 6, 7 conducts sufficiently to accelerate the motor in the corresponding direction. The motor accelerates until it reaches a speed at which the thyratron ceases to conduct due to the opposing voltage applied from the motor armature to the thyratron grid-cathode circuit through a potential divider 29, 30 and connection 31. The motor speed is thus dependent on the extent of unbalance of the double-triode and hence on the setting of potentiometer 3. A voltage equal to the A.C. supply is injected into the grid-cathode circuit of thyratron 7 in such a sense as to cancel the supply voltage which would otherwise appear in this circuit due to reverse connection of this valve. Quadrature A.C. bias voltages for thryratrons 6 and 7 are developed in a condenser-resistance network 18 and D.C: bias voltage is controlled by a potentiometer 22. In a modification, Fig. 1 (not shown), involving additional rectifiers, the opposing voltage dependent on motor speed is obtained from a potential divider in parallel with the thyratrons.