Patent GB-108824-A (GB)
Title: Improvements in Electric Motor Control Systems.
IPC: B60L7/12
Filed: 1917-03-26
Abstract: 108,824. British Westinghouse Electric & Manufacturing Co., (Westinghouse Electric & Manufacturing Co.). March 26, 1917. Systems for continuous - current motors only.-A regenerative control system for direct-current motors includes automatic devices actuated in accordance with the voltage or speed of the motors to connect them to the supply circuit for regeneration either in series or in parallel. The motor circuits and relays are shown in Fig. 1 and are subject to an accelerating- controller 22 operated through a rack and pinion by pneumatic means controlled by electro-magnetically operated valves, and a controller 23 operated in a similar way during regenerative braking. The actuating- circuits with the necessary interlocks and the master controller 36 are shown in Fig. 2. A dynamotor or motorgenerator 27, 28 is provided, and the generator winding is connected across the motor field coils 5, 6 during braking. Two relays 32, 33 have windings supplied with the motor voltage and the former 32 acts to cause the motors to be connected in series for braking, while the latter 33 causes the motors to be connected in parallel. A limit switch 24 is provided for accelerating and a limit switch 25 for braking. The change-over switch 26 is shown in the running position but it can be thrown to the braking position by the electromagnet 54. The controller-actuating means comprises two cylinders 42, 43 with pistons 40, 41 joined by a rack. The valve 45 of the cylinder 40 is normally closed but is opened to apply pressure when the electro-magnet 47 is energized. The valve 46 of the cylinder 43 is normally open to apply pressure but is closed when the electromagnet 48 is energized. When both electro-magnets are energized, the pistons move to the right, while if the magnet 47 alone is energized, the movement stops, and if both are de-energized the pistons move to the left. When the master controller 36 is moved to position I, the motors 3, 4 are connected in series and resistances 8, 9, 10 are included in circuit. When it is moved to position II, the resistance 8 is cut out and the windings 47, 48 are energized, the circuit of the latter 48 including the contacts of the limit switch 24. The controller 22 then moves step by step under the limit-switch control to cut out the resistances 9, 10. In position III of the master controller, the windings 47, 48 are de-energized and the controller 22 is returned to its position I. Relays are operated to connect the motors in parallel and with resistances 9, 10 in circuit. The windings 47, 48 are again energized and the controller 22 cuts out the resistances 9, 10 and finally cuts out parts of the field coils 5, 6 leaving the motors running in parallel with weakened fields. The motors may be run regeneratively by throwing the master controller to one of its positions I<1>, II<1>, III<1> and thereby connecting the generator 28 across the field coils 5, 6. At a predetermined machine voltage, the relay 32 rises and causes the motors to be connected in series, and at a higher voltage, the relay 33 completes a battery circuit to the winding of an auxiliary relay 55 which causes the motors to be connected in parallel. This arrangement ensures the action of the series relay before that of the parallel relays. If the conditions are suitable for parallel regeneration, the master controller can be thrown to its extreme position III'. The electro-magnet 54 is energized and moves the switch 26 into the position for braking. The winding 47 on one of the valves of controller 23 is energized, and the windings 160, 161, 162 are energized to close the switches 31, 18, 17. The switch 31 includes the coil 30 in circuit thereby ensuring a strong field for the dynamotor, and the switches 17, 18 connect the generator winding 28 to the field coils 5, 6 through resistances 20, 21 respectively. The valve winding 48 on the controller 23 is next energized through the contacts of the limit switch 25 and the controller moves forward step by step to cut-out the resistances 20, 21 under control of the limit switch. To keep the regenerated current constant, the limit switch 25 has an additional coil 189 supplied with current from the battery in some positions of the controller. Preparatory to the change from parallel connexion to series connexion of the motors, the switch 15 is energized. and the resistance 19 is connected in series with it to avoid closing a relatively low-resistance path across the supply circuit. Relays are then operated to connect the motors in series and the series circuit includes parallel connected resistances 20, 21. Further movement of the limit switch 25 and the controller 23 cuts out the resistances. If the conditions at the commencement of braking are not suitable for parallel regeneration, the relay 33 will not lift and the motors will be connected in series. The windings of the relays 32, 33 may be connected across the brushes of an auxiliary generator driven from a truck axle instead of being connected across one of the main motors.