| The superconducting magnet is one of the main components of most superconducting power equipment.Its AC loss is directly related to the efficiency of the entire system.The heat generated by the loss will cause the temperature of the magnet to rise,and even cause the magnet to quench,affecting the safety of the system.For the safety problem of superconducting magnet operation,accurate calculation and measurement of the magnet AC loss,evaluation of the temperature rise inside the magnet,obtaining a safe and reliable current running interval,and structure optimization of superconducting magnet by combining safety theory and electrical technology,starting from the superconducting coil to prevent quenching and achieving intrinsic safety are of great significance to the safe and efficient operation of the entire system.In this paper,the method of electromagnetic thermal coupling is used to model and analyze the single pancake coil wound by ReBCO,with considering the electromagnetic field and temperature field of the coil.The AC loss and temperature of the coil for wireless power transmission system,electromagnetic energy storage control system and cryogenic DC chopper system are studied respectively.The safe operation of the coil is analyzed,and the range of safe current for different applications is obtained.The details are as follows:(1)The mechanism of quenching is elaborated,and the safe operation criterion of superconducting coil is given.The calculation and measurement method of AC loss and analysis method of thermal stability of superconducting coil are introduced.(2)A two-dimensional axisymmetric simulation model of the ReBCO superconducting coil is established in Comsol Multiphysics using H formulation,and the AC losses of superconducting coil for three different applications are calculated.Based on the distribution of magnetic field and current density inside the coil,the effects of different currents on the loss of coil are discussed.In addition,the loss-reducing performance of the diverters with different structure is evaluated and optimized.The lock-in amplifier method is used to measure the loss of the coil in each application,and compared with the integral calculation results and simulation results.The three results have good consistency,and the availability of the simulation model is verified from experiments.(3)Using the electromagnetic thermal coupling method,the temperature of the coil during operation is calculated by simulation,the thermal stability of the coil is analyzed,and the area where the coil is prone to quench is identified.The range of current that the coil can operate safely is given: For the coils in wireless power transmission system,the 8th turn is easier to quench,and the upper limit of the safe current is 148.1 A;For the coils in electromagnetic energy storage control system,the area that is more likely to be quenched is around the 11 th turn,and the upper limit of the safe current is 176.2 A;For the coils in low-temperature DC chopper,the region that is easy to quench is the 6th turn,and the upper limit of the safe current is 184 A.The paper analyzed the electromagnetic and thermal characteristics for three different applications,and obtained reliable range of safe current,which provides a certain reference for effective protection measures. |
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