Design And Analysis Stress-cone For Cold Dielectric High Temperature Superconducting Cable Termination

With the advantages of high current density, small size and light weight, high temperature superconducting (HTS) cable becomes a hotspot in recent research. HTS cable should keep superconducting state staying in the liquid nitrogen, so it needs extra superconducting cooling cycle device. Thus at present, the HTS cable cannot be applied in the electric power transmission in large-scale and long distance with the limitation of refrigeration and it has to unite with conventional power equipments in the power grid. In connection between conventional grid and HTS cable, it involves the temperature transition of liquid nitrogen temperature to room temperature and the electrical connection of HTS cables to the conventional power grid. In this case, HTS cable terminal is necessary to realize the above two processes. Stress-cone, as an important part of the HTS cable terminal, has the effect of homogenization of the electric field distribution, effectively preventing the occurrence of insulation breakdown resulted from terminal electric field concentration.Firstly, the HTS cable terminal without electric field shield layer was analyzed, then electric field distribution analytic expression of HTS cable terminal was deduced, finally the factors influencing the electric field distribution of the HTS cable terminal were found. based on summarizing all kinds of control modes for improving HTS cable terminal, the circuit model of HTS cable stress-cone terminal was established. Then the HTS cable terminal design formula of stress-cone was deduced, eventually the theoretical calculation results of stress-Cone were obtained. According to the theoretical calculation results, the different structure parameters were analyzed by ANSYS, such as stress-cone length, insulation thickness, stress-cone radius and uplift stress-cone length. The optimized structure size and parameters of stress-cone was determined after comprehensive analysis.Secondly, with the requirements of HTS cable terminal insulation material on insulation stability and mechanical properties in the liquid nitrogen, the epoxy resin was determined as the HTS cable terminal insulation material. Different ratio of epoxy resins were made up to take breakdown test. The best allocation of epoxy resin was determined. The partial discharge test of the epoxy resin was done in order to get the epoxy resin O-Q discharge spectrogram under liquid nitrogen. Conclusion and analysis of partial discharge stages were made, including discharge starting stage, development stage, serious stage and dangerous stage.Finally, according to the scheme of the design of the HTS cable stress-cone terminal, the prototype model of HTS cable terminal was fabricated, the lightning impulse test and partial discharge test were carried out. The experiment proved that structure design of HTS cable terminal is reasonable, it can satisfy all performance requirements of the HTS cable termination, and validates the correctness of the theoretical results and simulation design. This work for the further research of HTS cable terminal stress-cone lays a solid foundation.