Patent GB-430683-A (GB)
Title: Improvements in regenerative direct current electric traction systems
IPC: H02P3/08
Filed: 1934-03-12
Abstract: 430,683. Master control of D.C. motors. FERGUSON, A. D., Ardriac, Ashton Lane, Ashton-on-Mersey, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. March 12, 1934, No. 7828. [Class 38 (iii)] Regenerative braking.-A regenerative system for traction motors M1-M4 comprises switching means R1, R2, RR1, RR2, for gradually cutting out series resistance r, rr for accelerating, switching means S3-S7 for varying the field excitation for further acceleration and regenerative braking, manual control means MD for alternatively establishing initial connections for motoring and regeneration from a deenergized condition of the motors, and control means SMD operable in accordance with the electrical conditions in the motor circuit automatically to effect respective complete sequences of switching operations giving acceleration to full speed and maximum increase of regenerative current during regeneration, which control means is arranged automatically to condition the several switching means to produce appropriate series resistance connections and field excitation adjustment, either for motoring or regenerating as selected by the manual control means, corresponding to the speed of the motors at any moment after a period of de-energization. With the master controller MD operated to its first power position, reversing switches FR are operated, and a change-over switch operated to close interlocks M. This change-over switch controls the series fields SF1-SF4 and makes appropriate connections between duplicate energizing circuits for the controlling contactors, and the contact fingers of the sequence drum SMD for motoring operation. Prior to the closing of a line contactor LS1, a coil C of an entry relay is energized to bias its moving contact to a position in which a switch EG is closed. When the switch LS1 closes the entry relay is influenced only by two opposing coils A and B, one connected across the armature of the motors M3 and M4, and the other across the supply so that after the motor voltages have had time to build up to a total value less than the supply voltage, the entry relay closes a switch EM to close a contactor 10 and complete the motor connections to the supply. The master controller MD may be operated to further power positions corresponding to series, parallel, and weakened field operation of the motors, the sequence drum SMD effecting complete sequential series resistance and shunt field control switching stages corresponding to the position of the master controller MD under the control of a current limit relay and an interruption relay which ensures step-by-step movement. If at any time during motoring the master controller is returned to its " off " position, the driving motors coast and the sequence drum moves to its " off " position, and if it is desired then to reinstate motoring conditions the master controller is operated to one of its power positions. The entry relay will then remain in a position in which the switch EM is open until such time as the sequence drum has automatically advanced sufficiently to cause the shunt fields of the motors to be weakened and the series or parallel connections to be made whereby the motor voltage becomes lower than the line voltage. When this voltage condition obtains, the entry relay closes its switch EM to cause the motors to be connected to the supply. For regenerative operation after a period of coasting the master controller MD is operated to one of its brake positions, the change-over switch is operated to make appropriate connections between the duplicate energizing circuits for the controlling contactors and the sequence drum to connect the motors in parallel with armature resistance excluded and shunt fields weakened, even though the sequence drum is in the off position. The sequence drum advances progressively under the control of the limit relay to strengthen the shunt fields and if necessary change from parallel to series connection, until the motor voltage is greater than the line voltage whereupon the entry relay closes its contact EG and completes the regenerative connections to the supply. The sequence drum then completes the switching sequence to the limit of series connections with strengthened shunt fields under the control of the limit relay, the operating limit of which is adjusted by resistance lr in the circuit of a shunt coil to a degree depending upon the movement of the master controller to its second or third braking positions. The adjustment of the coil A of the entry relay to suit the series or parallel connection of the motors is effected by an interlock JR-in of the contactor JR.