Patent GB-116724-A (GB)
Title: Improvements in or relating to Electric Motor Control Systems.
IPC: H02P7/34
Filed: 1918-06-13
Abstract: 116,724. British Westinghouse Electric Manufacturing Co., (Assignees of Lammers, E. S.). June 13, 1917, [Convention date]. Systems for continuous-current motors only; master control systems.-In a control system, resistances in the main or field circuits of the dynamo and motor are controlled by progressivelyoperated switches, each having' a pair of operating coils, one of each pair being controlled by the preceding contactor and by a manually operated controller, the other coil of each pair being controlled in accordance with the value of the motor current. In order to operate a switch both coils must be energized but one coil is sufficient to hold the switch closed. The armatures of the generator G and motor M. Fig. 1, are directly connected in a closed circuit, and the generator field coil 1 is connected to the exciting circuit by reversing switches 3, 4, 5, 6 and is controlled by the resistance switches 7, 8, 9, 10. The motor field coil 12 is connected with a resistance 13 controlled by switches 14, 15, 16, 17. Each resistance switch has actuating coils 18, 19, the former 18 of which are energized in succession according to the operation of the controller 20 and or the preceding contactor, while the latter 19 of each set are connected in parallel and are simultaneously energized. The coils 19 of the generator switches 7 - - 10 are connected in series with the contacts of a main current relay 22 and those of the motor switches 14 - - 17 are controlled by a main current relay 34. The effect of the relay 22 is controlled by a relay 27 with two coils 28, 29. The coil 28 is connected in series with the coils 18 of the switches 7 - - 10 and therefore carries a current proportional to the number of coils energized, and the coil 29 carries the generator voltage. The relay 36 controls the effect of the relay 34 and has a coil 38 which carries a current proportional to the motor field current, and a coil 37 connected in series with the coils 18 of the switches 14 - - 17. To start the motor, the switch 44 is closed to complete the circuits of the coils 19 for the two sets of switches through the relays 22, 27 and 34, 36. The switches 7 - - 10 remain open as the coils 18 are deenergized, but the switches 14 - - 17 are closed, as an interlock 47 on the open contactor 10 completes a circuit for the coil 18 on the switch 14. The circuits for the coils 18 on the switches 15, 16, 17 are completed through previous contactor interlocks. The major portion of the resistance 13 is thus short-circuited and the motor starts with a strong field. An interlock on switch 17 connects the coil 38 of the relay 36 across the section of resistance 13 not controlled by the switches 14 - - 17 and the coil is energized to a maximum extent at starting. This causes the relay 36 to move from the position shown in Fig. 2 and to de-energize the coils 19 of the switches 14 - - 17. When the controller is moved to its first position in either direction, the reversing switches 3, 5, or 4, 6 are closed, and interlocks on the switches 3, 4 ensure the operation of the correct pair. In the next position of the controller, the coil 18 of the switch 7 is energized and the switch closes to cut out a section of resistance from the generator field circuit. The switch 7 closes an interlock in the circuit of the coil 18 of the switch 8 and this switch closes when the controller is moved to the next position c. In positions d, e of the controller, the switches 9, 10 close and each switch closes a maintaining circuit for the preceding switch. In position f of the controller, the switch 14 opens to insert resistance into the motor field circuit and the further operation of the controller causes the switches 15, 16, 17 to open in succession. The controller may be operated in a continuous movement and the switches will operate automatically. The relay 27 will not operate in this case as the coil 28 is energized more strongly than the coil 29 and holds the relay in the position shown. With the switch 17 open, the coil 38 of relay 36 is de-energized, and the coil 37 is also de-energized; the relay is therefore held in its normal position by the spring 41, to complete the circuits of the coils 19. If the increase of the motor current exceeds a predetermined rate, the coil 23 operates the relay 22 to open the circuits of the coils 19 of the switches 7 - - 10. The switches that are closed are held by the coils 18, but the operation of the others is stopped until the current falls. The operation of the motor field circuit switches 14 - - 17 is controlled similarly by the relay 34. When the controller is moved from the position i to the position h as a first step for stopping, the switch 17 closes and the coil 38 is energized. The relay 36 is operated to break the circuit of the coils 19 of the motor field switches. In the controller position g, the coil 18 of switch 16 and the relay coil 37 are energized. The relay 36 is operated to complete the circuit of the coils 19 and the switch 16 then closes. The other switchs 15, 14 follow in order as the controller is moved, the relay 36 being operated between the closing of successive switches to prevent the switches from closing at a rate faster than that at which the field current increases. Tn position d of the controller, the switch 10 is de-energized and the pull of the coil 28 of the relay 27 is reduced. The coil 29 operates the relay to open the circuits of the coils 19 on the generator switches. This causes the switch 10 to open to insert resistance, and the motor may then run regeneratively. If the current exceeds the predetermined limit, the relay 22 is lifted to stop the operation of the switches 9, 8, 7 but otherwise they operate in succession. In a modification, a resistance in the motor armature circuit is controlled by contactors with two sets of coils operating as previously described, the circuit of one set of coils being completed by a shunt relay and the hand controller, the circuit of the other set being completed through the contacts of a relay when the motor current is below a predetermined value.