Patent GB-191111349-A (GB)
Title: Improvements in and relating to Electro-magnetically Operated Devices for Controlling Electric Circuits.
IPC: H02P1/20
Filed: 1911-05-10
Granted: 1912-05-10
Abstract: 11,349. British Thomson-Houston Co., [General Electric Co.]. May 10. E l e c t r o - magnetic switches. -A switch is operated by an electromagnet which produces two fluxes in parallel paths; one flux predominates and holds the switch open when the actuating current is high, while the other causes the switch to close when the current falls to a predetermined value. The core 14, Fig. 1, of an electro-magnet 13 passes through a non-magnetic plate 14<1> preferably of brass or copper. A movable member 15 of magnetic material is pivoted on an iron support 17 secured to the plate 14<1>, and the switch arm 18 is pivoted to the member 15. A compression spring 20 permits the contact 12 to move sufficiently when forced against the contact 11 to furnisha wiping contact. A bar 22 of magnetic material secured to the member 15 passes close to the pole-piece 23, the parts resting normally in the position shown. The air-gap 25 may be varied by means of the brass nut 24 on the screw 26. A magnetic element 28 of limited capacity connects the plate 14<1> and pole-piece 23, and therefore shunts the air-gap 25. When the current in the winding 13 is relatively low, the element 28 shunts a relatively large portion of the flux round the gap 25, and the flux across the gap 15<11> closes the switch. When the current is relatively high, the air-gap 25 carries a greater proportion of the flux than before, and this is sufficient to hold the switch open. The shunt magnetic element 28 may have a band of copper &c. to carry induction currents that act as a time-lag on variations in flux. The switches may be provided with additional means under the control of an operator which will prevent the closing even when the current in the main coil is of the proper value. One such switch is shown in Fig. 5, in which an additional winding 29 is placed on the shunt member 28 in such a way that the shunt 28 is magnetized and holds the switch open as long as the coil 29 is energized. In this form the air-gap 25 is varied by means of an iron nut 24<1> on a stationary brass screw. In another modification, Fig. 7, the switch is held open by means of a coil 30 which acts on a pivoted armature 31 linked to the armature 22, or a shunt coil may be arranged below the coil 13 to increase the flux across the air-gap 25. The holding coil may be mounted on the pole 23 or may be placed parallel to the shunt 28. In the further modification shown in Fig. 11, the arm 40 is pivoted to the central part of the core 42, which is provided with two pole-pieces 41, 43, the latter of which is separated from its yoke by a brass block 44. The shunt magnetic path is arranged as shown and when the current is large the flux across the air-gap 47 keeps the switch open. The range of operation of the apparatus may be increased by diminishing the cross-section of the iron in series with the polepiece 41. In another modification, the core of a solenoid carries at its lower end a U-shaped member extending outside the winding. An iron ring and a copper ring are mounted beneath the winding. In the modification shown in Fig. 13, the movable core 59 carries a brass rod 62 with a disk 86 to hold the switch open when the core is down. The switch arm is pivoted in iron lugs 61 on an iron plate 60, the ends of which are separated from the magnet frame by brass spacers 71, 73 and by air-gaps. Another modification is shown in Fig. 15 in which the core is fixed and the switch arm is held open by a pin on a lever 109. The pin rests in a slot 112 in the switch arm.