Research On AC Loss Of The Superconducting Strand In AC Magnetic Fields

The preparation process and research on electromagnetic and mechanical properties of the second generation of high temperature superconducting(HTS)tapes,so called REBCO coated conductors(CCs),have made great progress with the development of superconducting technique.Compared with HTS tapes,HTS strands have the advantage of good current-carrying capacity,which can be applied in power transmission cable,superconducting fault current limiter,large magnet,etc.AC loss is an important factor for the reasonable design of superconducting power devices,which has a direct impact on the operation cost and stability of the superconducting devices,superconductors with lower AC loss have broader prospects for development in the engineering field.In this paper,we study a kind of quasi-isotropic HTS strand stacked by HTS tapes,which has a center symmetric structure.The HTS strand is mainly composed of the HTS tapes and metal sheath.The resistive wire located in the center of HTS strand and adiabatic treatment of the HTS strand provide the basis for AC loss measurement of the HTS strand.The 2D model of HTS strand is established through the finite element simulation software Comsol Multiphysics,from which the distribution of magnetic field is obtained.AC losses of the HTS strand including hysteresis losses,coupling losses and eddy-current losses are calculated using analytical and numerical method,the calculated results of two methods are compared with each other.The experimental results of sensing characteristics of the optical fiber Bragg grating(FBG)at low temperature show that FBG temperature measurement can be applied to liquid nitrogen environment,which provides the foundation for AC loss experiment of the HTS strand.The resistive wire is used to calibrate the relationship between FBG wavelength and energy loss.AC loss of the HTS strand in AC magnetic field is measured by FBG based on the background AC magnetic field produced by AC magnetic field generator.Theoretical calculations are in accordance with measured results,which shows the correctness of calculated model and experimental method.The temperature distribution and temperature variation with time of the HTS strand after energization of the resistive wire are simulated using Comsol Multiphysics 3D simplified model,and transverse resistivity of the HTS tapes is measured,which indicate the rationality of experiment and calculation from the side.