Abstract: A cooling system for a superconducting power apparatus including a reservoir tank for reserving a liquefied gas, a circulating pump, a heat exchanger for cooling the liquefied gas, and a circulation loop through which the liquefied gas is circulated, the superconducting power apparatus being cooled by circulating the liquefied gas in a subcooled state using the circulating pump. The cooling system further includes a pressurizing mechanism for pressurizing the liquefied gas in the reservoir tank with the same type of gas as the liquefied gas, wherein a liquid level in the reservoir tank for reserving the liquefied gas in a pressurized state is located above an outlet of a return piping of a circulating liquefied gas at least by a dissolving depth of the pressurizing gas+(plus) a liquid level movement correction amount.

Abstract: There is provided a superconducting strand for alternating current which is formed by stranding 13 or more superconducting wires having a diameter smaller than that of a non-magnetic core member in a single-layered form on the outer peripheral surface of the core member and which can efficiently remove heat caused by AC loss, avoid a quenching phenomenon and stably maintain the superconducting state. Preferably, an electrically insulataive braided layer formed of polyester fiber is interposed between the core member and the stranded superconducting wires and stable insulation can be maintained therebetween, thereby preventing flow of coupling current caused by defective insulation and suppressing partial heat generation. The superconducting wire contains a large number of NbTi superconducting filaments and a non-magnetic stainless steel wire can be preferably used for the core member.