GB345709A - Improvements in electric motor control systems - Google Patents

Abstract

345,709. Control of D.C. motors. ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Bush House, Aldwych, London. -(Assignees of Claytor, E. M. ; 399, Castlegate Road, Wilkinsburg, Pennsylvania, U.S.A.) Jan. 10, 1930, No. 1021. Convention date, Jan. 10, 1929. [Class 38 (iii).] Field control.-A compound wound winch motor is controlled so that while hoisting it operates with a strong shunt excitation for accelerating the load, and automatically at high speed when the steady hoisting load is below a certain value. While lowering it operates as a compound wound machine for a predetermined time after lowering begins, and then as a shunt machine whose field is automatically strengthened if the reverse power generated by an overhauling load exceeds a certain amount. In addition the system provides dynamic braking by shunting the armature, first by a high resistance and then after a time interval by a low resistance. With a master switch 15 in the " off " position and switches 19 closed, a switch 18 closes and completes a maintaining circuit for itself. On moving the switch 15 to position a, the motor 10 is placed in circuit with sections of resistance 55, 56 and 57 in the shunt field circuit with a starting resistance 39 in the armature series circuit, and with resistance 63 across the armature. Also a relay 41 closes, energizing a coil 17, and releasing a brake 16. When a relay 80 becomes energized by the volt drop across two sections of the resistance 39, sections 56, 57 of the shunt field resistance are short-circuited. As the switch 15 moves to positions c, d or e the series resistance 39 is cut out in sections resulting in the de-energization of the coil 85 of relay 80 which, however, is kept closed by the series coil 31. If, when the motor is running with the switch 15 in the final position e, the steady load falls below a certain value, the relay 80 opens so that sections of resistance 56, 57 are inserted in the field circuit, and a byepass resistance 9 is placed round the shunt field. When the switch 15 is moved to the left for lowering operations, the motor circuit is completed as before, but at the positions c<1>, e<1>, d<1>, the coil 101 of a relay 99 is short-circuited, and within a predetermined time interval, due to inductive discharge, the relay operates shortcircuiting the series field 12. With the switch 15 in position e<1>, the motor runs with shunt excitation. If, owing to excess lowering load, the regenerated current attains a certain value, the coil 112 of a relay 111 is sufficiently energized to close the relay which completes the circuit of a relay 110. This relay, in closing, short-circuits sections 54, 55, and 56 of resistance in the shunt field circuit. In addition the relay 80 operates to still further reduce the shunt field resistance by placing the resistance section 56, in parallel with the remaining section 57. When the switch 15 is placed in the " off " position, the high resistance 118 is placed across the armature, and a coil 122 which is energized when the switch 15 is in positions a or b<1>, discharges through a resistance 136, so that, after a time interval, a relay 120 opens to place a low resistance 126 across the armature.