Development of High Performance Extruded Polymer Insulated DC Superconducting Model Cable using High Temperature Superconductor

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The investigators have been developing extruded ethylene-propylene rubber (EPR) insulated superconducting power cables. The model cable developed in this study had very simple structure : the silver sheathed bismuth type high temperature superconducting wires laid in parallel on a stabilizing core brass pipe is electrically insulated by wrapped EPR together with semiconducting shielding layers. The optimization of the layout of the superconducting wires on the core pipe gave their satisfactory contact with EPR insulation after repeated thermal cycles between room temperature (RT) and liquid nitrogen temperature (77K). This reveals that the radial, circumferential and length-wise thermal contractions of EPR at cooling do not affect the current characteristics of the superconducting wires. Hence the EPR insulation can be applied to the high temperature superconductors who are generally considered to be vulnerable to the mechanical stress. The dc critical current and quench current measurements also showed that they are only slightly affected by the mechanical stresses of the wrapped EPR insulation. The epoch-making fact is that DC superconducting cables can wipe out all the losses and drawbacks associated with AC version : hysteresis loss, eddy current loss, dielectric loss of insulation and partial discharges. Therefore the results obtained in this study open an avenue to the DC high temperature superconducting cables which can possibly play dominating roles in the future underground power transmission.