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Fault current limiters (FCLs) are expected to reduce fault current and improve stability of power systems. A flat type fault current limiter consisting of the pancake primary winding and a high‐Tc superconducting (HTS) disk was proposed as a modified version of a conventional magnetic shield type of the FCL with the superconducting cylinder. The flat type FCL has the advantage of being manufactured smaller than the cylinder type FCL. It is pointed out, from a magnetic field analysis, that the volume of the flat type FCL is smaller than that of the cylinder type FCL with same magnitude of the limiting inductance. Further, the magnetic field analysis suggests that a high inductance ratio can be realized by radially enlarging both the primary winding and the HTS disk, stacking the FCL modules in layers and sandwiching the primary winding with superconducting disks. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

We have proposed a flat type of the superconducting fault current limiter, which is a modified version of a magnetic shielding type FCL. The flat type FCL has a simple construction and basically consists of a spiral coil and a doughnut-like form high Tc superconductor (HTS) plate, each of which works as a primary winding and a secondary one-turn winding, respectively. The FCL modules can be easily built up to make a large scale FCL for a practical use.In the case of normal condition in power system, impedance of FCL is a very minute value, since the HTS has no resistance and a magnetic flux induced by the spiral coil and the HTS plate cancels out each other. Under fault condition, when an over-current flows to primary winding, the induced current in the HTS plate increases. If the current which flows the HTS plate exceeds the critical current value of the HTS plate, the HTS plate will generate resistance R sc . Consequently, the magnetic coupling between the spiral coil and the HTS plate is destroyed, and FCL generates the limiting impedance Z FCL and reduce the fault current.Current carrying tests were performed for the air-core-type module and iron-core type one as shown in Fig. 1(a) and (b). We supplied a.c. current of 60 Hz to the FCL and measured the current and the voltage across the FCL. The whole module of the FCL with the iron core was cooled by liquid nitrogen. Figure 2 illustrates the dependence of the impedance of FCL Z FCL (i.e. Z 0 and Z limit ) on the peak value of the primary current I p obtained by current carrying tests for the air-core-type module and iron-core-type one. In case of the air-core-type module (triangle in Fig. 2), the FCL impedance shows the saturating tend at about 5.5 mΩ, which corresponds to the 1.5 times of the impedance of 3.7 for I p < 20 A. In case of the iron-core-type module (circle in Fig. 2), The impedance ratio Z limit /Z 0 is 4.8, which is larger than that in th eair-core-type module.In order to clarify the static current-limiting performance of the flat-type FCL, magnetic field analyses were carried out for the small modules, which were slightly modified from the test small modules described in Fig. 1. The inductance of the FCL module can be estimated by calculating the magnetic energy. The derived magunitudes of the inductance for superconducting and normal-conducting state of the HTS plate, L 0 and L limit , are summerized together with their ratio L limit /L 0 in Table 1. The complete-iron-core-type module has very large inductance ratio of 10 3 order because whole the FCL is enveloped by the iron. This suggests that the flat-type FCL has a significant potential to suppress the fault current in the electric power system because the impedance ratio can be increased up to the order of 10 3 by decreasing the resistance of the primary winding and improving the iron core assembly. Hiroyuki Kado * * * MemberWe have proposed a flat type of the superconducting fault current limiter (FCL) which is a modified version of a magnetic shielding type of the fault current limit...

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We have proposed a current limiting element using the flux flow resistance in a high temperature superconductor (HTS) for a pulse over-current such as a magnetizing inrush current in a transformer. We experimentally investigated the generation process of flux flow resistance in a Bi2223 bulk with an inrush current. The voltage-current density characteristics and their dependence on the joule heat generated in the Bi2223 bulk were measured. Comparing the results with the characteristics for the ac over-current, we made it clear that the both have almost the same characteristics.