| 摘要 |
<p>A current-switching device comprises a contact switch (1), a varistor (2) and a variable-resistance element (3) connected in parallel. The element is made from an electrically conductive soft magnetic powder, e.g. steel, coated with boride, carbide or nitride and immersed in a liquid, such as oil or perfluorinated polyether. the resistance of the element (3) is controlled by the magnetic field of an electromagnet (4). When the current in the main circuit is switched on or off, the electromagnet (4) is energised by a current pulse, which causes the element (3) to become conductive. During the current pulse, the contact switch (1) is either closed or opened, and this arrangement therefore prevents arcing occurring during switching. Alternatively, the element (3) can be connected in series with the contact switch. In this case, the magnet (4) is a combination of an electromagnet and a permanent magnet arranged to provide opposing magnetic fields within the element (3), such that, when the electromagnet is energised, the element (3) is non-conducting.</p> |
