Experimental Tests on a Superconducting Fault Current Limiter Using Three-Strand $\hbox {MgB}_{2}$ Wire

Magnesium diboride (MgB₂) in simple round wire form has shown significant potential to be a low-cost resistive superconducting fault current limiter (SFCL). The commercial exploitation of MgB₂ SFCLs for typical distribution network voltages requires a considerable scale-up of the current-carrying capability of MgB₂ wire. The two obvious options to achieve this are to increase the wire size and use multifilament wire and/or use multiple wire strands. This paper assesses the current capacity for multi-strand wire and presents results of initial tests on a three-strand MgB₂ demonstrator SFCL coil. Three strands of monofilament MgB₂ wire were braided together to form a single multi- strand wire. The wire was fabricated, wound on a ceramic former and heat treated by Hyper Tech Research, Inc. One of the key performance aspects of this type of wire arrangement is ensuring each strand of wire carries the same current. This paper demonstrates the potential for increasing the current capacity of SFCL using multi-strand MgB₂ wire to that required for distribution network levels. The paper includes a detailed analysis of the results and the implications for the practical design of commercial SFCLs.