A Design Study of High Temperature Superconducting Transformer

Abstract

Many researches and developments of the high temperature superconducting apparatus such as a transformer, a fault current limiter, a cable, etc. are being made actively in the power field in accordance with the performance advancement of the Bi silver sheath high temperature superconducting (HTS) wire. In these, an HTS transformer is considered to be one of the most promising applications in view of efficiency improvement, the interface with the cryogenic cable and the normal temperature device, incombustibility, over load capability, the function as a reactor and the possibility of a fault current limiter. The necessary technical development items of an HTS transformer in order to achieve superior performances to the conventional one are examined. For this purpose, the 3-phase 66kV-100MVA transformers are designed for the comparison of an HTS transformer and a conventional one with the oil cooling. The desirable development items are an HTS wire current density of, about 40A/mm², allowable winding strain of about 0.5%, a percent impedance of 7.5%, the air gap flux density of about 0.3T and ac losses of about 0.3W/km•A.