| 摘要 |
<p>PURPOSE:To prevent AC and DC external magnetic fields from entering a secondary winding by a method wherein a ring-shape shield composed of a superconductor is provided along at least one circumferential direction of a primary conductor and the secondary winding is provided inside the shield. CONSTITUTION:A shield 6 composed of a superconductor surrounding both side ends and circumferential parts of a core 2 and a secondary winding 3 is provided and the temperature of the shield 6 is kept below the critical temperature by a heat insulating container 7. The heat insulating container 7 contains coolant and has a structure holding the core 2 and the secondary winding 3. With this constitution, the secondary winding 3 is shielded from all external magnetic fields regardless to AC components or DC components by the Meissner effect of the superconductor of which the shield 6 is composed so that misoperation can be avoided and the sectional area of the core 2 which is enlarged in order to avoid misoperation in the conventional constitution can be reduced and the weight can be reduced.</p> |
