Patent GB-754797-A (GB)
Title: Electromagnetic switch for direct or alternating current, particularly relay, contactor, overload switch, or the like
IPC: H01H47/22
Filed: 1954-08-09
Abstract: 754,797. Electrically-released switches; protective arrangements. SCHRACK ELEKTRIZITATS-AKT.-GES., E. Aug. 9, 1954 [Nov. 6, 1953], No. 23080/54. Class 38(5) An electromagnetic switch having a high remanence magnetic system and closed or opened by a direct current or rectified impulse magnetizing or demagnetizing the system, is opened when the supply voltage drops by a demagnetizing impulse which is taken exclusively from an energy-storage device which is independent of the supply at the moment of opening. The exciting circuit may be fed through a rectifier 1 (Fig. 1), and comprise a coil 2, having a permanent magnetic core in series with a capacitor 3, which are shunted by a resistance 4. When the exciting circuit is closed by switch 5 a magnetizing impulse flows through the coil 2, closing the main switch (not shown), and charging the capacitor 3. On failure of the supply voltage, or opening of switch 5, the capacitor 3 will discharge through the coil 2 and resistance 4, thus providing a demagnetizing impulse to open the main switch. The coil 2 may be arranged so that the closing circuit employs only part thereof whilst the opening circuit employs the whole coil. The closing switch may comprise a push-button bypassed by an auxiliary contact operating concurrently with the main switch (Fig. 3, not shown), two additional contacts, one manual and one voltage-responsive, being normally connected in the exciting circuit, but arranged so that the movement of either into the shunt circuit causes the main switch to open. In another arrangement (Fig. 5, not shown), a second capacitor is arranged in parallel with the exciting coil and permanently connected to the supply through the rectifier. On closure of the operating contact this capacitor delivers the magnetizing impulse and charges the first capacitor. Alternatively, a single capacitor may be used for opening and closing the main switch (Fig. 6, not shown). This has the supply voltage normally applied thereto and is connected by a voltage-responsive change-over switch to the exciting circuit or discharge circuit for opening or closing the main switch. The exciting circuit may be fed through a Gratz rectifier (Fig. 4). In a diagonal thereof the closing circuit comprising coil 2 and capacitor 3 is in parallel with the shunt path comprising resistance 4, auxiliary contact 12, operating concurrently with the main switch (not shown), and contact 9 operated by a voltage-drop relay 10. Normally contact 9 is open and contact 12 closed, but failure of the supply causes contact 9 to close the shunt path and thus open the main switch and contact 12. The storage device may comprise a transformer 18 (Fig. 7), having a soft iron core. The primary 18<SP>1</SP> is normally connected to the supply through a Gratz rectifier 11, and the secondary 18<SP>11</SP> in series with coil 2. On closing the main switch (not shown), the exciting circuit is interrupted by contact 19 and the secondary is connected with the coil 2 by contact 20. When the supply is disconnected the secondary 18<SP>11</SP> delivers a demagnetizing impulse to the coil 2.