Patent GB-191207147-A (GB)
Title: Improvements relating to Electro-magnet Apparatus.
Inventor: HARRY ARLINGTON LEWIS
IPC: H01H71/68
Filed: 1912-03-23
Abstract: 7147. Lewis, H. A., May 22, 1911, [Convention date]. Void. [Published under Section 91 of the Act]. Systems for continuous-current motors only ; controllers, actuating- mechanism for. - Each armature of an electromagnet provides two paths for the flux due to the magnetizing-coil, the action of the flux in one path being to produce movement of the armature, and of the flux in the other path to oppose such movement. The electro-magnets are designed more particularly for actuating switches in motor-control systems, the switches being caused to occupy their open positions not only when the magnets are deenergized, but also when their energizing currents rise above a certain value. One construction of magnet, Fig. 1, comprises a central core 10 surrounded by two coils 8, 9 and by magnetic sidebranches 11, 12, which connect the ends of the core 10 and are recessed between the coils, as shown. One or more movable armatures 2, 3 are mounted on pivots 17, and comprise arms 15, 16 with projections 18, inwardly extending arms 21, 22, and contact-bearing arms 23, 24 coacting with fixed contacts 4, 5 respectively. The coils 8, 9 act in conjunction; they may be parts of a single series winding; or the coil 8 may be a highresistance shunt coil and the coil 9 a series coil. Assuming that only the coil 8 is energized, the arms 21, 22 are attracted by the core 10, thereby closing the switch contacts 4, 6 and 5, 7. If, however, the coil 9 is strongly excited, leakage magnetic fluxes traverse the air-gaps provided by the adjusting-screws 25, and the projections 18 and the arms 15, 16 are attracted, thus preventing the closing of the switches until the current in the coil 9 falls below the predetermined value. In a modification, Fig. 2, a single coil 26 is provided with a central core 10, with a U-shaped magnetizable member 27, and with transverse members 28, 29. The cross-sectional area of the member 29 is less than that of the member 27. The switches are caused to close in the desired sequence by adjusting the widths of the leakage air-gaps 42, 43 by means of screws 40 passing through the armatures 30. Fig. 4 shows a motor-control system in which two of these magnets 91, 92 are used for cutting out in sequence sections 51, 52, 53, 54 of the starting-resistance at the contacts 108; a master switch 57 controls a switch 90 for reversing the current through the motor armature 67. As each section of the resistance is cut out, the resulting increase in the current through the coils 104, 105 retards the closing of the next switch until the current falls to a certain value. Another control system is described, illustrating the use of two magnets of the kind shown in Fig. 1. The magnet shunt coils 8 are connected to different points on the starting-resistance so that a higher voltage is applied to the coil the switches of which are to close first. The coils 9 are arranged in series with the motor or motors. A relay switch is also provided to cut in the starting-resistance in the event of an overload. Four accelerating steps may be provided in a motor-controller, bv providing a magnet of the kind shown in Fig. 2, with four branches 27 actuating four armatures, each controlling a switch-step of the motor starting-resistance.