GB894583A - Improvements in and relating to electric motor equipments - Google Patents

Abstract

894,583. Control of motors. ENGLISH ELECTRIC CO. Ltd. March 23, 1959 [March 21, 1958], No. 9203/58. Class 38 (3). [Also in Group XXXV] In a motor control system a bi-stable amplifying device responsive to a control signal, dependent on a deviation of the motor speed from a reference value, energizes a change-over device in one sense so that the motor operates as a regenerative brake and in the other sense so that the motor drives a load. In an embodiment, Fig. 1, a control lever 18 positions a slider 17a of a speed reference potentiometer 17 and actuates change-over contacts 32, 33 to apply the correct polarity for the selected direction of rotation, to a control winding 16a of a bi-stable amplifying device 16. The voltage at the slider 17a is compared with the voltage of a tacho-generator 19, driven by an armature 10a of a direct-current winding motor 10, and the resultant voltage is fed to contacts 20a, 20b and to an error sensing device 28 which saturates at a predetermined resultant voltage. The amplitude-limited error signal is fed to a second control winding 16b and at a predetermined amplitude triggers the bi-stable amplifying device 16 to determine the energization of a field winding 14a of an exciter 14 through a magnetic amplifier 15. The exciter 14 supplies a field winding 10b of the motor 10. Polarized relays 29a, 29b are energized by the voltage drop across a resistor 30 in the supply to the field winding 10b and the appropriate relay closes changeover contacts 20a or 20b to apply the resultant voltage as an error signal to a negative error suppressing device 21 that passes positive amplitude error signals to an operating coil 22a of a grid control device 22 controlling a current converter 11. With increase in the positive error signal, the converter changes operation from an inverter, the motor then acting as a regenerative brake, to a rectifier, when the motor drives a load. In a modification, Fig. 2 (not shown), the magnetic amplifier 15 energizes polarized relays that reverse the connections to the armature 10a with respect to the current converter 11 and after a delay change-over contacts 20a, 20b. In another embodiment, Fig. 3, the error signal through the negative error suppressing device 21 operates an electrical transducer 108 to control the speed of a slip-ring induction motor 100 by varying the value of a resistor in the rotor circuit. At a predetermined amplitude and sense, the resultant voltage triggers the bi-stable device 16 and through the magnetic amplifier 15 operates a polarized relay 34 or 35. The polarized relay 34 closes a contactor 106 to apply a direct current or low-frequency alternating current to a stator of the motor 100 which then acts as a brake on the load. The polarized relay 35 closes a contactor 102 or a contactor 103, as selected by the control lever 18, to energize the stator of the motor 100 from a mains supply 104. Specification 892,231 is referred to.