Research On Cryogenic Insulation Characteristics Of GHe Cooled Dielectric Bipolar Coaxial DC High Temperature Superconducting Cable

With the increasing demand for electricity,the transmission capacity and transmission density of the power grid gradually increase.High-temperature superconducting(HTS)cable is expected to become one of the important technologies for large-capacity power transmission in the future due to its advantages of large transmission capacity,high power density,small size,light weight and low transmission loss.Compared with HTS AC cable systems,HTS DC cables have zero-resistance characteristics and lower losses as well as compact structures,so that they are widely studied worldwide.As an important part of superconducting cable,insulation has a great influence on the reliability and safety of cable transmission.Therefore,it is of great significance to study the insulation characteristics of HTS DC cable.The thesis mainly studies the main insulation design of 10 kV bipolar coaxial high temperature superconducting DC cable.DC and lightning impulse breakdown experiments under different medium conditions were developed on PPLP and Kraft paper,which are suitable for insulation of superconducting cables.The experimental data were fitted by three-parameter Weibull distribution based on the gray model GM(1,1),and the DC and lightning impulse withstand voltage dielectric strength of PPLP and Kraft Paper are obtained as the basis for cable insulation design.With reference to the insulation design method of the AC cable and the national standard requirements,the main insulation of the 10 kV bipolar coaxial HTS DC cable under liquid nitrogen(LN2)and helium gas(GHe)environment are designed.According to the design results,the 3D geometrical model of the cables under LN2 and GHe are established by Maxwell Ansoft software and the electric field intensity distribution of the radial and axial are analyzed.The electric field strength is compared with the withstand voltage strength of the insulation material,and the rationality of the cable insulation design is initially determined.Finally,according to the insulation design scheme of 10 kV bipolar coaxial cable and the insulation structure of the actual cable,the model cables under LN2 and GHe are fabricated,respectively.The DC and lightning impulse withstand voltage test are performed on the model cable based on the requirements of national standards to verify the rationality of the insulation design.