Study On Electromagnetic Characteristics Of High Temperature Superconductors Based On T-A Formulation

In recent years,the numerical models based on the H-formulation have been widely used to calculate the electromagnetic characteristic of high temperature superconductors(HTS).The homogeneous model and multi-scaling model based on H-formulation can greatly improve the calculation speed.Unfortunately,for largescale HTS magnets,a great degree of freedom is still to be solved,and the calculation is difficult.The development of the T-A model can further improve the calculation speed,and the calculation accuracy is higher.Based on the COMSOL Multiphysics software,this paper will establish the Hformulation model and T-A formulation model,study the electromagnetic characteristic of HTS,and analyze the calculation speed and accuracy of different models.The effect of mesh quality and element order on the calculation efficiency of different models is to be studied,and T-A formulation model is optimized to improve the calculation efficiency.And then,this paper would study the homogeneous model based on the T-A formulation.By simplifying the structure of the superconducting coil,the homogeneous model is optimized to further improve the calculation accuracy of the model.The optimized model is applied to study the electromagnetic characteristics and AC loss characteristics of large-scale HTS magnets.The details are as follows:(1)The H-formulation model and T-A formulation model are established to study the AC loss characteristics and electromagnetic characteristics of the HTS pancake coils,respectively.The high accuracy and high efficiency of the T-A formulation model has been verified.The influence of different element orders and mesh quality on the calculation efficiency of the models has been studied.(2)Homogeneous model based on the T-A formulation is established.The T-A homogeneous model is optimized,and Semi-homogeneous model is proposed.By studying the magnetic field distribution and AC loss of the YBCO coils,the Semihomogeneous model which can maintain a relatively high calculation accuracy has been verified.(3)The Semi-homogeneous model is used to study the electromagnetic characteristics of superconducting magnetic energy storage(SMES)magnet with different structures,under different operations.The Semi-homogeneous model is used to establish a two-dimensional axisymmetric model of the SMES magnet.Critical current of the pancake coils and SMES magnet has been calculated.The calculated results have been compared with the experimental date,which verified the high accuracy and high efficiency of the optimized model.When the SMES applied in DC Microgrid is under charge and discharge operation,the AC loss characteristics of SMES magnet has been studied.