Research On AC Losses Of 35 KV/1kA Cold Dielectric HTS Cable

Due to its many advantages such as large capacity, low alternative current (AC) loss, high stability, compact structure, non-environmental pollution, cold dielectric (CD) high temperature superconducting (HTS) cable is expected to have broad application promises in the field of large capacity electric energy transmission in future. The AC losses are one of important parameters of HTS cable and has significant effect on its stability and operation cost. Therefore, the research on AC losses of HTS cable is particularly important, which will provide a solid theoretical and experimental basis for the power applications of superconducting technology.Combing with the structure of the CD HTS cable, the types of AC losses were summarized and the theoretical analysis for HTS cable AC losses calculation was established in this paper firstly. The calculation method was implemented and verified through the sample of 77 kV CD HTS cable in publication. Based on the Maxwell equations and the superconducting properties of HTS tape, a two-dimensional (2D) finite element model (FEM) to calculate the AC losses of HTS tape and HTS cable was established. The AC losses of the HTS tape and HTS cable were simulated by using numerical simulation software COMSOL Multiphysics and compared with the experimental results as well as theoretical calculated results, which verified the correctness and effectiveness of the 2D model for the calculation of HTS AC losses. The effect of magnetic substrate on the AC losses of HTS tape was theoretical analyzed and experimental researched. The 2D model is also modified to allow the inclusion of a magnetic substrate, combining with the magnetization properties of the magnetic substrate.The AC losses measurement of a 35 kV/1 kA CD HTS model cable has been carried out by electrical method. These experiments contain the cable termination joint resistance test, critical current test and AC losses test. The experimental results confirmed the influence of the cable termination joint resistance on the measurement and the termination loose effect on the AC losses of the HTS cable. After a 0.5 m CD HTS model cable is fabricated manually, the experiments on the critical current and AC losses of the model cable with different frequencies are performed in liquid nitrogen. The results proved the correctness of the calculation method and the reasonableness of experimental method as well as showed that the dominant AC losses of the CD HTS cable are the hysteresis loss duo to its linear relationship with the transport current frequency when the frequency is low.Finally, the influences of the cable termination on the performance of the HTS cable have been theoretically analyzed. The joint resistance of HTS cable termination enlarges the measured voltage, and the magnetic field results in magnetic field uneven distribution as well as reducing the critical current thus increasing the AC losses of the HTS cable. The effects of vibration caused by terminals welding loose on AC losses of HTS cable are qualitatively analyzed.