Patent GB-722672-A (GB)
Title: Improvements in or relating to dynamic braking control systems for electric driving motors
IPC: B60L7/04
Filed: 1953-02-03
Abstract: 722,672. Control of D.C. motors. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Feb. 3, 1953 [March 6, 1952], No. 2996/53. Class 38 (3) Relates to a control system for traction motors in which continuous circulation of a weak spotting current in the dynamic braking circuit is instituted during coasting operation before full braking is applied. During the spotting operation, the excitation of the motors is controlled by means responsive to the motor current whilst the maximum resistance is maintained in the braking circuit. As shown, the motors have armatures Al, A2, and series field windings SF1, SF2, and each car has a master controller MC which, when moved to its first operative position, connects the motors in series to the line with full resistance in circuit with the motors and with maximum field excitation. In the second position of the master controller, an accelerating resistor R1 is short-circuited and portions of resistors R2, R3 are removed in sequence under the control of a current-limit relay CR, having an actuating coil in series with the motors and a cumulatively operating rate coil RC which is energized through a weightresponsive rheostat 205 during the acceleration period. Closure of the resistance-shorting switch 9-10 effects the energization of a transition switch J to remove the last accelerating resistance R4 and to open the seriesconnection switch JR. When the master controller MC is moved to its third position, parallelconnection switches M, G are closed and the switch J opens to re-initiate the progressive removal of portions of the resistors R2, R3. When maximum armature voltage is obtained for the motors, a coil FC-SF is energized for progressive operation of a field controller FC towards its weak-field position, such operation being regulated by the limit relay CR. If the controller MC is now returned. to its "off" position, switches B1, M, G establish a weak coasting-operation dynamic braking circuit with resistors R5, R2, R3 included in that circuit, each motor armature being loaded by the field winding of the other motor. A spotting relay SR is responsive to the motor current and operates to increase the motor excitation by moving the controller FC to or towards the fullfield position as the spotting current decreases. Full braking is applied by moving handle 207 to energize relay BR so causing the field controller FC to progress towards the full-field position under the control of the relay CR. When full-field conditions have been restored, a part of the braking resistance RS is removed by closure of switch B2, switches B5 and B6 then being closed in sequence under the control of relay CR which now has its rate coil RC connected in series with a rheostat 206 which is automatically changed in response to the position of the brake handle so that the rate coil has its maximum excitation when a low-braking rate is called for. Closure of switch B6 closes again the switch B2 to re-initiate the progression of switches 1-2, 3-4, 9-10, so resistors R2, R3 are removed in a stepped manner and the dynamic braking operation completed. Specification 660,414 is referred to.