Analysis And Study On The Structural Design And Performance Of Superconducting Cable Under Liquid Hydrogen Condition

In the future development of the global energy internet,large-scale power transmission with low loss is a major challenge facing our transmission grid.Superconducting cable transmission technology has become one of the most hot research direction since the discovery of the high temperature superconductors in 1986,the superconducting cable has the advantage of light weight,small size,large capacity,low losses,etc.compared with the normal cable.Hydrogen and electricity hybrid transfer cable relatively liquid nitrogen cooled superconducting cable has a huge advantage in the transport capacity which make it becomes the most promising solution of the problem of large capacity,low loss power transmission.Various superconducting power cables based on high temperature superconductors have been already developed with liquid nitrogen as a coolant,using the liquid hydrogen as a coolant is seldom reported.This thesis carried out a feasibility study for the design of superconducting cable structure on liquid hydrogen temperature,which aims to provide an optional way for future energy development of the internet.Firstly,MgB2 is chosen as the preferable choice for the superconducting cable system with LH2 by comparing the basic characteristics of the commonly used high temperature superconductors.The structure of HTS cable is briefly introduced in this thesis,and the matrix equation of electromagnetic parameters of HTS cable is calculated according to the mathematical model which is established based on the structure of HTS cable,the effects of the change of the winding angle on the current carrying capacity are studied.The thesis focuses on the former,insulation layer,conductor layer design principle of HTS cable under LH2 temperature,the minimum cross-sectional area of former is given according to physical properties of copper at liquid hydrogen temperature and the heat-steady-state principle.Simultaneously,the characteristics of the commonly used low temperature insulation materials are compared,and we adopt polypropylene laminated thesis(PPLP)as the insulation material and main insulation layers,the simulation results verify the feasibility of the insulation layer thickness,which is calculated by adopting partial-discharge-free under AC stress.Finally,according to the goal of the project 110kV/4kA,we designed a HTS cable with two layers of conductor.Secondly,the 2-D simulation model of MgB2 superconducting tape and superconducting cable is established based on PDE interface of COMSOL finite element analysis software,the current density and AC loss of MgB2 tape were simulated and compared with theoretical calculated results,which verified the correctness and effectiveness of the 2-D model,the current distribution in each conductor layer of superconducting cable is simulated too.Finally,the experimental platform for the current carrying capacity of superconducting cable has been set up,a demo superconducting cable with length of 50cm has been fabricated and the current-carrying capacity test at 20K has been taken to the model cable at last.The critical current of the demo cable can not be measured due to the limitation of the maximum current output of the DC power supply,but the results of test w:ith a DC 1000A show that demo cable has good operating stability.