| 摘要 |
1,262,024. Excessive current protection. SIEMENS A.G. 25 June, 1970 [26 June, 1969], No. 30974/70. Addition to 1,163,027. Heading H2H. [Also in Division H1] An electrical current limiting arrangement has two parallel connected windings arranged so the resultant of the magnetic field is substantially zero at normal operating currents. One of the windings 1 consist entirely or partially of a superconductive material and has a critical current strength higher than the normal operating current and a preferably adjustable choke coil 5 connected in series. With a current which is lower than or equal to the critical current substantially same voltage drop is set up across the choke as across the second winding but when the current in the one winding exceeds the critical current it changes to a normally conductive state whereupon the inductance of the arrangement is increased. The windings, which are preferably tightly coupled to reduce stray fields, are enclosed in a heat insulating housing which is partly filled with a coolant e.g. liquid helium or nitrogen circulated through connections 4. Above the critical current, winding 1 rises to a relatively high resistance value so that most of the current is diverted into winding 2 the inductance of which is increased thus limiting the current flowing in a main circuit 8 and hence reducing the current which is broken by a circuit breaker 9. Winding 2 may consist of aluminium or copper or may alternatively consist of superconductive material having a critical current higher than that of winding 1 and arranged so that it may remain superconducting above the critical value. The end portions of winding 1 may be made of normally conducting material., The choke 5 may be air cored with taps, or have an adjustable iron core with a large air gap. A three phase arrangement is envisaged in the Specification which is stated to be especially suitable for protecting superconducting A.C. cables fed directly from generators without the interposition of transformers. |
