Patent GB-227118-A (GB)
Title: Improvements in and relating to electromagnetic devices
IPC: H01F7/13
Filed: 1924-12-31
Abstract: 227,118. British Thomson-Houston Co., Ltd., (Assignees of McNairy, J. TV., and Tritle, J. F.). Dec. 31, 1923, [Convention date]. Automatic circuit-breakers. - An electromagnetioally actuated device, which is movable from one position to another, has electromagnetic means for automatically retarding the movement of the device at a definite immediate position to reduce the momentum of the moving parts. The invention is particularly applicable to the interrupter described in Specification 187,993. In Figs. 1 and 2, the movable switch arm 1 is pivoted to a movable magnetic member 3, itself pivoted at 4, and both are biassed by a spring 5, connected to a setting screw 6, to open position, whilst in the attracted position of member 3 the arm 1 is biassed against contact 2. The electromagnet 7 for holding the switch closed has a shunt coil 8 and poles 9, 10, and a series coil 11 is disposed on a magnetic coil 12 in the air-gap and releases the switch on overload. Electromagnetic closing mechanism 13 comprises an energizing coil 15, a short-circuited coil 16 and a magnetic operating member 17 pivoted to a bell-crank lever carrying a roller 20. The adjustable core 21, Fig. 3, is bored to slidably receive a magnetic stop 22. The interrupter has the usual blow-out coil 23, arcing contacts 24, and shoot 25, and is supported on insulating rods 26 on a base 27. The circuit is shown in Fig. 4 and comprises a line 28, disconnecting and low-voltage switches 29, 30, interrupter and earth. The coil 8 is in series with a normally closed switch 32 and resistance 33, and the coil 15 is controlled by a. relay 34, the coil 35 of which is shorted by a switch 37 when the member 3 moves to the attracted position. Magnetic plugs 38, 39, Fig. 5, are adjustably secured. in the magnet 7 for varying the value of the release current. In operation, the switches 29, 30 are closed to energize the coil 8 and switch 36 is closed to energize coil 35 and close the relay 34, thereby energizing the coil 15 of the closing mechanism which attracts the member 17 and rotates the switch arm 1 and member 3. Prior to the latter reaching its attracted position, the member 17 reaches the stop 22 causing an increase of flux and closing force, which increase is, however, limited by the action of the shortcircuited coil 16. At the same time, the attraction between member 17 and core 21 decreases, thereby retarding movement of the member 3, until the stop 22 becomes saturated. The closing force then increases till the member 3 reaches its attracted position without a jar, and closes. the switch 37 to de-energize coil 15. From Fig. 4, it will be seen that by shorting the resistance 33 through the coil 35, the current in the coil 8 increases and over-exites the magnet 7. This over-excitation further increases when the coil 35 is shorted by the switch 37, which feature is an advantage as the power circuit can be successfully closed when the resulting current in the series winding is only slightly below the releasing valve. When the coil 15 is de-energized the decay of the flux is retarded by the coil 16, till the spring 5 is strong enough to move the member 17. The member 22 slides down till its collar engages the core 21 when the movement is temporarily retarded. When the flux has decayed sufficiently the member 17 leaves the stop 22' and the spring 5 finally closes the switch without a jar which might move the member 3 from its attracted position. Should the load become excessive, the current in the series coil 11 increases the flux in the part 12 and decreases that in the member 3 so that the spring 5 opens the switch. To avoid delay in, or prevention of, the opening due to a reversal of flux in the member 3 on heavy overload, the tips of poles 9, 10 are separated by only a small air-gap to provide a. path of relatively low reluctance after the member 3 has opened a short way, and the part 12 is adapted to be saturated at a value slightly above maximum releasing value.