Patent GB-159598-A (GB)
Title: Improvements in and relating to time element switch devices for controlling electric circuits
IPC: G04F1/04
Filed: 1919-11-29
Abstract: 159,598. British Thomson-Houston Co., Ltd., (General Electric Co.). Nov. 29, 1919. Automatic circuit-breakers; electromagnetic switches; time-limit devices; cases.-Relates to time-element switches in which an unbalanced fly-wheel disc is revolubly mounted and held in an unstable position, the time element consisting in the time taken by the fly-wheel on release to pass from the unstable position to a final stable position, in which position a contact carried by the fly-wheel co-operates with a fixed contact to open or close a circuit. The means for releasing the fly-wheel from and restoring it to its unstable position may consist of a spring-controlled catch which is released by an electromagnet, the operation of which may be dependent upon conditions in an electric circuit, and means for varying the time-element of the device may be provided, consisting of an electromagnet energized upon pre. determined conditions in an electric circuit, the action of the electromagnet being to retard or temporarily stop the motion of the released flywheel disc. The time-element device is mounted within a casing 4, a lug 3 carrying a spindle 2 on which is rotatably mounted the fly-wheel disc 1, the balance of which is upset by a hole 5 bored near the periphery, or by other suitable means. A spring-controlled hook-shaped arm 19 is mounted on a spindle 18 passing through the casing 4, as shown in Fig. 3, an L-shaped lever 17 being secured on the projecting end of the spindle. The fly-wheel disc 1 carries pins 9, 20. 22 in the positions shown, and a lug 10 is provided on the casing 4 to limit the motion of the fly-wheel disc. The fly-wheel releasing- mechanism consists of an electromagnet 11, which attracts an armature 13 secured on a shaft 14, the shaft also carrying a lower arm 15, one end of which carries a roller 16. On the shaft 14 may also be secured one or more resilientlymounted switch, contacts 12, which, on attraction of the armature, engage fixed contacts 12 secured to the switch base. Fig. 1 shows the disposition of parts when the electromagnet 11 is not energized, the spring-pressed arm 19 forcing the disc to an unstable position by abutting against the pin 20, in which position the pin 22 rests against the lug 10. On excitation of electromagnet 11, the armature 13 is attracted and moves to the position shown in Fig. 2, forcing the roller 16 against the lever 17, thereby releasing the catch 19, and allowing the fly-wheel disc to move according to its bias in an anticlockwise direction. This motion is limited by the pin 9 engaging the stop 10, the fly-wheel disc moving to the position shown in Fig. 2. In this position, a contact 6 on the fly-wheel is forced against a fixed contact 7, which is carried by a flat spring 8 mounted on, but insulated from, a projection of the casing 4. When the electromagnet 11 is de-energized, the spring 23 restores the arm 19 to its former position, at the same time moving the fly-wheel disc to its previous unstable position, the arm 19 in its motion first engaging the pin 9 near the periphery of the disc with force sufficient to overcome the pressure between the contacts 6, 7; and, finally, the hook-shaped end of the lever 19 engages the pin 20, the restarting motion being checked by the abutment of the pin 22 against the lug 10. The time period taken by the rotation of the fly-wheel may be varied by varying the amount of angular rotation of the fly-wheel disc, for instance, by the provision of a series of holes 23, 24, in which the pin 22 may be placed. Further means of varying the time period consists in the provision of an electromagnet 25 and core 25d, the magnetic circuit of which is completed through the fly-wheel disc, the energization of the magnet causing a retardation or temporary stoppage of the disc. Fig. 4 illustrates the use of switches of this type in the control of an alternating- current induction motor with a wound rotor. A pilot switch 27 is closed, energizing the electromagnet 11<1> and closing the double-pole switch 12<1>, thus allowing current to pass from the threephase mains 26 to the starter of the motor M, at the same time releasing the fly-wheel disc 1<1>. If the starter current exceeds a predetermined value, the core of the overload relay 28 is attracted, and the relay contacts close a circuit through the electromagnet 25<1>, thus retarding or stopping the motion of the disc 1<1>. until the current falls and the core of the relay 28 is released. When the fly-wheel disc 1<1> has completed its motion, its contact 6 touches the fixed contact 7', thus completing a circuit through the electromagnet 11<11>, closing the switch 12<11>, and short-circuiting resistances R' in the rotor circuit, at the same time releasing the fly-wheel disc 1<11>. If the current again exceeds the predetermined value, the overload relay again operates, energizing the retarding-magnet 25". Finally the contacts 6<11> and 7<11> are brought together by the fly-wheel disc 1<11>, thus energizing the electromagnet of the switch 29, and by cutting out resistances R<2>, the rotor of the motor M is short-circuited for normal running. A modified form of switch is shown in Fig. 5; in this form, the contacts 12, 12, on the base and shaft 14 respectively, and the retarding-magnet 25 are omitted. Fig. 6 shows a switch for controlling the tripping-circuit of a normally-open oil switch 30 so that the circuit controlled by the oil switch shall not be opened until a predetermined overload has existed for a predetermined time. The supply mains 31 are connected to the load through the double-pole oil switch 30, an overload relay 32 being included in the circuit. An auxiliary tripping supply 33 is also provided. If the current in the main circuit exceeds a predetermined value, the core of the overload relay 32 is raised, exciting the electromagnet 11 and thus releasing the fly-wheel disc 1. When the fly-wheel disc has completed its motion, contacts 6, 7 complete a circuit through the circuitbreaker tripping-coil 34, thereby releasing a catch 35 and permitting a spring 36 to open the oii switch 30. If the overload ceases before the contacts 6, 7 come together, the dropping of the core 32 de-energizes the electromagnet 11, and the spring-controlled catch restores the fly-wheel disc 1 to its former unstable position, without affecting the main circuit controlled by the oil switch.