抄録
Some strands may carry large current in a multi-strand cable consisting of strands having a highly resistive layer, such as chrome plating, among the strands as a result of non-uniform current distribution. We analytically studied the characteristics of this current after normal transition using a distributed model circuit. The parameters used in this calculation are those of the US-DPC coil, which first exhibited instability due to current imbalance, so-called ramp-rate limitation. Thus, the conductance among strands and inductance of unit length loop and length of the conductor are assumed to be 1-100kS/m, 0.5μH/m and 150m, respectively. The calculation results show that the current of the strand reaching a normal state decays in order of 10-100ms. It was also found that the current transfer from the strand having normal resistance to the other superconducting strands does not take place at the end of the conductor within a few seconds after normal transition when normal resistance appears at the center of the conductor. In this case, the current is transferred among the strands without any effect from the boundary as well as the infinitely long conductor. Consequently, the current increases by return of the current which is transferred to the other strands if normal resistance decreases at the center of the conductor. These results indicate that there is a possibility of conductor quench due to the normal transition of several strands which carry the large current and initially transfer to normal state in a conductor consisting of strands that have highly resistive layers among them.
