High-temperature Superconducting Dc Transmission Technology Is Discussed

In our modern industrialized society, electric power is the most important supports of the production and lives. Power systems from smallness to greatness, has passed through low voltage transmission to high voltage transmission, from DC transmission to AC transmission, which experienced some technique transforms, and became a more complexity system with high capacity, AC transmission associated with DC transmission system, which bring some new difficulties. Firstly, as the voltage that transmitted become higher and higher, and the transmitted lines becomes more and more longer ,the stability problems of the transmission system becomes more and more grimness; secondly, in big cities, the consumed electric power density rising year by year on the one hand, but the passage right can be used for power transmission decreasing on the other hand, so it is impossible to use the normal ways to resolve the high capacity power transmission in big cities; further more the copper or aluminum with resistance as the most important conductor, so the loss consumed on the transmitted lines is enormous. It is emergent to take huge technology reform in power system. Superconducting technology is an effective way to resolve the difficulties put forward above because of it's zero resistance and some other superiorities. High-temperature superconducting (HTS) cables, characterized by its ultra-high current density and super-low transmission loss, is a promising compact power cable with high transmission capacity, and has a variety of environmental advantages such as energy saving, resource conservation, zero EMI, nonexplosiveness, nonflammability, and nontoxicity.HTS cables have come into reality engineering project follow with the progress of HTS materials and technologies, most of the HTS cable projects were for AC transmission. But the characteristics of zero resistance only occur at DC condition, AC losses will always happen under AC condition unavoidably. In this paper, we will discusss a few key problems about HTS DC transmission, which combine with the advantages of DC transimission and HTS technology.We have tested the I-V characteristic of BSCCO and YBCO HTS tape under different magnitude and oriention magnetic fields respectively, which based on the HTS cable I-V testing system and provide some value datas for HTS DC cable design and using.Based on the analysis of spiral current magnetic and theory of current distribution, we established the theory model of HTS cable to calculate the magnetic fields and electromagnetic parameters for the priority design, manufacture of HTS cable. The magnetic field distribution of two conceptual superconducting DC cable models which based on the mechanical performance of the HTS tapes were presented with Ansoft/Maxwell in this paper, and the parameters such as inductance and capacitance of a coaxial cable were calculated from the basic equations of electromagnetism.At the end of this paper, we bring forward a project of HTS DC transmission system based on the cable model designed before, the power transmission performance such as energy loss, DC and AC faults of the DC system with HTS DC line been studied by numerical simulations using the demo "Thyristor-Based HVDC Link" in MATLAB, the impedance of frequency at AC and DC system being discussed too. The simulation results have shown that applications of HTS technology to power systems have a number of possible advantages in economy, and also reliability and stability, especially for the low-voltage high-current DC transmission.