Study on Hot-Spot Temperature Limits of Epoxy-Impregnated Coil Wound With Bi/Ag Sheathed Wire to be Safe From Damage Caused by Quenches

Relations between quench protection conditions and hot-spot temperature of epoxy-impregnated Bi2223/Ag sheathed wire coils are experimentally investigated and limits of hot-spot temperature for the coils to be safe from damage caused by quenches are estimated using small-scale test coils. In the previous work using test coils wound with yttrium barium copper oxide (YBCO) wires, it was found that the hot-spot temperature limits are around 300 K, which is much lower than the temperature (500 K) where critical current of YBCO wire is degraded thermally. Structure and mechanical property together with superconducting property of Bi2223/Ag sheathed wire are different from those of YBCO wire. Therefore, relations between quench protection conditions and hot-spot temperature of epoxy-impregnated Bi/Ag sheathed wire coils together with hot-spot temperature limit are different from those of YBCO wire coil. The test coils used in the experiment are wound with Bi/Ag sheathed wire and epoxy impregnation, and their configurations are basically the same as those in the authors' previous work on YBCO coils, because both wires need to test in the same conditions. In this paper, it is found that the hot-spot temperature limits are also lower than temperature for Bi/Ag sheathed wires to degrade thermally. A reason for those results is discussed comparing with the case of YBCO coils.