Patent GB-496745-A (GB)
Title: Improvements in or relating to electric driving arrangements for machines having heavy fly-wheel masses, in which direct current driving motors are supplied through controllable current converters
IPC: H02M7/00
Filed: 1937-03-01
Abstract: 496,745. Control of D.C. motors; converting. SIEMENS - SCHUCKERTWERKE AKT.-GES. March 1, 1937, No. 6123. Void. Convention date, Feb. 29, 1936. [Class 38 (iii)] [Also in Group XXXV] In a control system in which a D.C. motor M for driving machines having heavy flywheel masses, in particular pilger rolling mills is driven from A.C. mains through a gridcontrolled rectifier V which is adapted to act as an inverter for regenerative braking of the motor, two separate control devices Ra, Rb one serving for rectifier operation and the other for inverter operation, are provided and are arranged to be selectively switched over on the D.C. side, both control devices being arranged to be simultaneously actuated by a control lever H provided for adjusting the speed of the motor, the arrangement being such that one only of the control devices is in effective operation in accordance with the intended method of operation of the motor. The control devices are adjusted through a servomotor Th, which may be an oil pressure regulator having an adjusting coil ES and a working coil BS connected in a Wheatstone bridge formed by resistances W, Z. The resistance W is adjusted by the control lever H and the resistance Z by the servomotor, movement of the latter ceasing when the position of the arm of the resistance Z corresponds to that of the control lever and no current flows through the coil BS. The grid control regulators are adjusted in common until the maximum voltage is applied to the motor ; a toothed segment then comes out of engagement with a toothed wheel operating on the grid control regulators and, on further adjustment of the lever H, engages a second toothed wheel and adjusts a field regulator ER to increase further the speed of the motor by weakening its field excitation. When it is desired to brake the motor, the lever H is drawn back, and its hinged handle engages contacts b and energizes a switching over device B. This applies a blocking potential to the grid through the grid control device G. and at the same time, through the relay GR switches out the regulator Ra and switches in the regulator Rb in readiness for inverter operation. As soon as current ceases to flow through the converter, a relay UR1 releases and a change-over switch U is operated, a supplementary contact on the latter cutting out the switching device B and removing the blocking potential on the grid. On further movement of the lever H in the backward direction, the field regulator ER is first rotated backwards to strengthen the field, and when maximum field strength has been restored, further braking is obtained by adjusting the regulator Rb. A relay TR is provided which temporarily short-circuits the working coil BS of the servomotor whenever the current through the converter V exceeds an adjustable maximum. If it is desired to return from the braking to forward operation of the motor, the lever H is moved forwards, and contacts a are closed to energize the switching-over device A. A relay UR2 prevents this energization until the position of the adjusting arm on the resistance Z coincides with that of the lever H.