Design study of a high-temperature superconducting transformer

Many research and development projects on high-temperature superconducting apparatus such as a transformer, fault current limiter, and cable are being actively pursued in the power field as a result of performance improvement of Bi silver sheath high-temperature superconducting (HTS) wire. HTS transformers are considered to be among the most promising applications in view of efficiency improvement, the interface with cryogenic cable and normal temperature devices, incombustibility, overload capability, the function as a reactor, and the possibility of use as a fault current limiter. The necessary technical development items of an HTS transformer in order to achieve performance superior to conventional devices are examined. For this purpose, three-phase 66-kV 100-MVA transformers were designed for the comparison of an HTS transformer and a conventional one with oil cooling. The desirable development items are an HTS wire current density of about 40 A/mm(2), an allowable winding strain of about 0.5%, a percent impedance of 7.5%, an Air gap flux density of about 0.3 T, and AC losses of about 0.3 W/km-A. (C) 2002 Wiley Periodicals, Inc.