Configuration method of tri-axial ReBCO cable suitable for long distance power transmission

We have investigated the electromagnetic and thermal characteristics of tri-axial HTS cable to apply the tri-axial HTS cable to the ac transmission cable for an offshore wind power generation system. In order to clarify why the long distance tri-axial HTS cable cannot be realized and what kind of cable structure is suitable for the long distance power transmission, we investigated the ac losses and the temperature distribution within a tri-axial ReBCO cable by electromagnetic field analysis, heat transfer analysis, and fluid analysis. As a result, we found that the temperature in the vicinity of the inlet of the outer refrigerant flow path reached the maximum allowable temperature because the temperature of the LN₂ in the inner refrigerant flow path was increased by the ac losses and the intrusion heat from the outside of the cable. Therefore, we inserted a low thermal conductive layer between the inner and outer refrigerant flow paths to suppress the temperature rise of the LN₂ in the inner refrigerant flow path. Due to the insertion of the low thermal conductive layer, the maximum-temperature place shifted from the vicinity of the inlet to the outlet of the outer refrigerant flow path. As a result, the maximum length of the cable cooled by one cooling station was greatly improved. This means that the insertion of the low thermal conductive layer between the outer and inner refrigerant flow paths is effective for realizing a long distance tri-axial HTS cable.