Patent GB-481761-A (GB)
Title: Improvements in and relating to electric motor control equipments
IPC: B60L15/04
Filed: 1936-10-31
Abstract: 481,761. Master control of D.C. motors. GRAY, W. T., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Oct. 31, 1936, No. 29659. [Class 38 (iii)] Non-regenerative braking.-Two or more series motors or groups of motors M1, M2, are accelerated first in series and then in parallel by respective armature resistances 3, 5, the transition being effected by a bridge system, and for rheostatic braking the motors are connected in closed circuits with cross-connected fields, the closed circuits being completed by a common connection including the resistances 3, 5, connected in series through the switch JR by which they are connected in series during the series accelerating stage. Switches LS1, LS4, and JR are first closed to complete a series connection of the motors with resistances 3, 5, in series. The resistances 3, 5, are then progressively removed by switches 4, 6 and the switch J then closed to make a direct connection of the series connected motors across the supply. The switches 4, 6, are then opened and switches LS2, LS3, closed, and this transition stage is followed by the opening of the switch J whereby the motors are connected in parallel, each in series with its respective resistance 3, 5. The resistances 3, 5, are then again progressively removed. For braking, change-over switches 7, 8, are operated to their braking positions, and each motor armature is connected in a closed circuit with the field of the other motor, the resistances 3, 5, connected in series by the switch JR, forming a common connection which completes .the closed circuits. The braking circuits may include the eddy-current brakes 20, 21, which in a traction system may act on axles of the vehicle which are not motor driven. The removal of the resistances 3, 5, during braking may be under the control of a current limit relay 19, or a retardation governor may be provided to control the deceleration. The system is described with reference to Figs. 4 and 5 (not shown) as applied to the control equipment described in Specification 470,065 in which the control is exerted by a drum controller operated by a servo-motor as described in Specification 451,514. The change-over switch for altering the connections from motoring to braking is electromagnetically operated and interlocked with the switch JR. The braking operation is controlled'by an additional master controller mechanically interlocked with the accelerating controller. The braking controller has an application position in which the braking is applied under the control of a retardation governor, and the servo-motor operated controller moves to its full series position. The braking controller also has a holding position to which it is moved to arrest movement of the controller and maintain the value of braking resistance at any particular value, and a resetting position in which the line switches are reset when the controller moves to its off position. Where, in the equipment described in Specification 470,065, a testing relay is provided to permit operation of the sevo-motor operated controller with the line switches open, the same relay may be used to open the line switches for braking when the braking controller is operated. Instead of a separate braking controller this may be combined with the accelerating controller so that the braking operation is controlled by operating the accelerating controller to further positions, or a separate handle may be provided for the braking controller interlocked with the accelerating controller.