The Research On Direct Current Carrying Characteristics Of High Temperature Superconductor With Multi-Coupled Fields

Superconducting electric power technology is important high technology storage for the electric power industry in the 21th century. The high performace and the low cost of the high temperature superconductor (HTS) make it possible to apply superconductor in the electric power industry on a large scale. The direct current carrying characteristics of the HTS is the basic application. Most of the research works were carried out by the experimental method and mathematic equation deduction before. With the development of the theory of the HTS electric property and the computer technology, people begin to pay attention to the simulation of the HTS. Based on the validation of the experiment, simulation is an effective method to study the HTS electric property. The direct current carrying characteristics of HTS in various applicable fields is studied in this paper. The multi-coupled fields'simulation combined with the experimental validation is adopted during the research. The work could provide the theoretic support and practical guide for the HTS application scientifically and reasonably.Aiming at the HTS current lead and HTS electrical contact, two kinds of models are constructed respectively, in which the affection of self magnetic field on the local electric property is introduced based on the Kim modle and the thermal-electromagnetic coupling is considered. Firstly, a 2D axial symmetrical microscopic flux flow resistance model is constructed based on the magnetic flux dynamics, and a simulation method is realized based on the Matlab software. Then, a prospect of the thermal-electromagnetic coupling is described, then an advanced power law model is presented, and a realizition method with the Gambit/Fluent for the advanced power low is designed. The typical HTS direct current carrying characteristics are calculated with above two models and the validity of the two models is verified through comparing the simulation results with the experimental ones respectively.With the flux flow resistance model, numerical simulation is carried out to analysis the direct current carrying characteristics of HTS current lead and the simulation results are compared with the experimental results. By investigating the direct current carrying characteristics of the rod current lead and the tube current lead, it is found that the current carrying efficiency of tube current lead is higher than the rod current lead. Aiming at the quenching process of current lead, a modified Ansys program is carried out with APDL languge. A non-linear transient thermal analysis is carried out for a tube current lead with this program, and the variational characteristics of temperature and resistivity along the axial direction are obtained. It is noted that the quenching process of the current lead can be divided into two stages. The operating time for protecting the quenching current lead should be smaller than the first stage time. The study provides a theoretical support for the design current lead safely and reasonablely. With the application background of mechanical persistant current switch (MPCS) in the superconducting magnetic energy storage (SMES) system, the electrical contact characteristics of YBCO bulk with and without deposition metal film are investigated systemically based on the advanced power law model. The detailed field distributions nearby the contact spot are obtained. The transition from the low-impedance state to the high-impedance state is explained from the viewpoint of multi-coupled fields. The deposited Ag film plays an important role on reducing the current density in the YBCO bulk nearby the contact spot by shunting most of the carrying current, which reduces the contact resistance and improves the transfer current. The work provides a theoretical instruction for the MPCS design.For various layouts of the magnetic material and Bi-2223 tape, simulations are carried out to analyse magnetic field distribution and its effect on the critical current of the tape from viewpoint of magnetic filed affection on the carrying current capacity of the tape. With the instruction of the simulations, six groups of experiments are designed to test the critical current of the tape. After analysing the experimental results and the simulation results, it is found that placeing magnetic material vertically at the side of the tape can enhance the critical current remarkably. This conclusion is significant for improving the carrying current capacity and economizing the HTS tape.