Calorimetric Measurements Of AC Losses In High Temperature Superconducting Cables

AC losses of high temperature superconducting (HTS) cable are an important parameter for the characterization of HTS material properties. It will increase the burden of cooling system and has the direct affects on the efficiency of HTS apparatus and economic benefit. The measurement of AC losses has great significance to the application of HTS. The calorimetric measurement is one of the main methods to measure the AC losses of HTS cables. It is mainly concerned about the temperature and pressure change of liquid nitrogen (LN2) in system. As the cooling medium, the stable circulation of sub-cooled LN2is the important factor that superconducting cable cryogenic system can operate stably. In cryogenic system, if the temperature of LN2is more than77K, it would appear vaporization. Vaporization can destroy the insulation of superconducting cable, even result in the overpressure and breakdown.In the HTS cable system, temperature is affected by heat load. The heat load mainly comes from terminal heat leak, cryogen heat leak, valve heat leak. Sub-cooled LN2is forced to flow and cool the superconducting cable and take the heat away. In order to analyze the temperature field of LN2in the cable, a30m long model is established that the sub-cooled LN2was forced to flow and cool the superconducting cable. The flow, terminal heat leak, AC losses and cryogen heat leak are chosen to be variables and the effect of which on the temperature field has been studied by using FLUENT. In30m cable, the voltage drop of LN2is very small, so the pressure in the cryogen is uniform and stable. In order to study the pressure field in the cable, a1km long model is established. The LN2temperature field of1km long single-phase and three-phase superconducting cable is simulated as the above four variables are gave. Also, the pressure difference between inlet and outlet is simulated and the simulation results and the theoretical calculations are compared.In order to achieve a quick and accurate measurement of AC losses for HTS cables, an experimental platform that measure AC losses of HTS cable is established. Electrometric method is used to measure the AC losses of3m HTS cable. And the experimental results are analyzed. The calorimetric measurement of AC losses is systematically investigated in this thesis based on the analysis of public published research achievements about HTS. An experimental method of calorimetric measurement is proposed and the equipments are selected.