Development of Extruded Polymer Insulated DC Superconducting 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 layrs. The purposes of this study are two fold. One is to evaluate the conductors behavior in the relevant cable design. The other is to evaluate the performance of the EPR insulation design on the rough surface of high temperature superconducting wires. 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). The ac loss of superconductors was measured before and after the wrapping of EPR insulation layr and there were no difference i … More n its magnitude. This reveals that the radial, circumferential and lengthwise 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 which are generally considered to be vulnerable to the mechanical stress. The dccritical current and quench current measurements also showed that they are only slightly affected by the mechanical stresses of the wrapped EPR insulation. The furthermore the DC short circuit treeing test of EPR sample clearly gave extremely high tree resistance which is very favorable results for designing DC.These results are indicating the surmounting of obstacles set against the DC cable by extruded polymer insulation at RT and the realization of high temperature superconducting DC cable design by extruded 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. Less