Experimental Research On AC Losses Of HTS Tapes By Optical Fiber Bragg Grating

With the development of superconducting and low temperature technology as well as the increasing capacity demand of electric power system, superconducting technology is expected to have potential application in power system. High temperature superconducting (HTS) applications in power system has many advantages such as low AC (alternative current) loss and high stability, the reduction of AC loss has been become one of the most important aspects of the research in superconducting applications. The study on AC loss of HTS tape will found the theoretical and experimental basis for HTS power applications and has important practical significance to promote superconducting electrical technology.This thesis presents a new calorimetric method by using FBG for measuring AC losses of high temperature superconductor which is different from the conventional calorimetric method. Comparing with conventional electric and calorimetric methods, FBG temperature sensor has many advantages of rapid response and free from electromagnetic interference due to its thin geometrical sizes and optical characteristics, it is thus very suitable to AC loss measurement of HTS applications in much more complicated electromagnetic circumstance.The principle of FBG temperature sensing is experimentally studied. The characteristics of temperature response of FBG at low temperature is studied by experiment, the experimental results indicated that FBG has good enough repeatability of dependence of wavelength shift on temperature around liquid nitrogen temperature of77K. Calibration of the relationship between FBG wavelength and loss was performed under DC (direct current) magnetic field in order to promote the quench of HTS tape, which provides the foundation for subsequent measurements of AC loss. In this thesis, AC loss of HTS tape in self-field was measured by calorimetric method in liquid nitrogen temperature based on FBG and conventional electric method using lock-in amplifier (LIA). It is shown that the AC loss measured by calorimetric method is agreement with the results measured by electric method and those based on Norris theory, so that the presented calorimetric method is available for measuring the AC loss of superconductors. Then AC losses of HTS tape in parallel and perpendicular DC field as well as the AC losses generated with carrying AC and DC current is also measured by the two methods. The measurement results by the two methods are in agreement and consistent with theory, which further illustrates that the calorimetric method based on FBG is available for measuring the AC loss of superconductors and expected to be generalized to AC loss or thermal measurements of other bulk superconductors. The experimental results have also some important reference values for the research of AC loss in superconductor.