Patent GB-190526281-A (GB)
Title: Improvements in Electro-magnetic Devices for use on Alternating Current Circuits.
Filed: 1905-12-16
Granted: 1906-12-15
Abstract: 26,281. Field, M. B., and Ferranti, Ltd. Dec. 16. Electro - magnets.- Chattering of the armature against the pole-piece of an alternating-current electro-magnet used in switches, arc lamps, signal devices, &c. is prevented by producing a lag in the magnetic flux through a portion of the divided horseshoe polar surface, by constructing the magnet casing so that it forms a closed conducting-circuit surrounding a portion of the poles, or by constructing the polepiece of laminµ of different thicknesses or partly of laminated iron and partly of solid iron. The application of the electromagnet to a no-voltage release circuit-breaker, to which may be added an overload solenoid, is described. The angle-shaped laminµ a, Fig. 3, slotted at one extremity b, are held together by the brass casing c with a piece of non-magnetic material d between their other extremities. The casing, together with the securmgbolts e and rivets f, forms a closed conducting- circuit, Fig. 1, round a portion of each of the poles, the magnetization of this portion being caused to lag behind that of the other when an alternating current is passed through the magnet coils g. The laminations on one side of the magnet pole may be thicker than those upon the other, or the laminations may be cut away on one side of the pole and a solid piece of dovetailed iron substituted, in which case the armature is shaped so that the gap under the laminated portion of the magnet is greater than that under the other portion. Two or more magnets with windings traversed by currents of different phases may be used. The application of the electromagnet to a no-load circuit-breaker is shown in Fig. 4, the electro-magnet being connected across two of the circuit-breaker contacts i, so that the coil is energized only when the circuit-breaker is closed. The movable contact j is carried by the rod l attached to the armature m, consisting of a number of magnetic stampings. The circuitbreaker is held without chattering, while the main circuit is complete, by the armature m engaging the poles of the electro-magnet, and is opened when the voltage in the main circuit ceases. The no-voltage release may be combined with an overload release as shown in Fig. 7 for a three-phase circuit. In this case, the armature m is hinged to the pivoted arm p carrying a pin r, which, in falling, owing to the release of the armature, releases the catch s and allows the spring-pressed switch arm to break contact. A set of three small solenoids 3, placed in series with the respective poles of the circuitbreaker, are adapted to attract plungers 4 raising a weighted disk 5 from the rounded contacts 6 when the current reaches a predetermined limit, breaking the current in the magnet coil and releasing the switch arm. Insulated knobs attached to the disks project through the casing containing the solenoids, so that they may be rotated by hand to clean the contact-pins and disks. The electro-magnet and its amature may be arranged horizontally, and may be employed in connexion with arc lamps, signalling, and the like. The Provisional Specification states that a portion of the poles may be surrounded by a closed winding to produce the desired lag.