Study On The AC Loss Characteristics Of HTS YBCO Tapes,Coils And Magnets

AC loss is an unavoidable problem for a HTS SMES magnet during dynamic operations,which may cause a temperature raise and threaten the reliable operation of the magnet.Therefore,accurately estimating the AC loss and its distribution of the magnet as well as the reliable current operating range and current ramp rate is very important to the optimization of cryogenic configuration,reduction of heat losses during dynamic operation and reliable operation of the magnet.In order to study the AC losses of HTS magnets,the AC loss characteristics of HTS tapes and coils should be understood firstly.In this paper,the calculation method of AC loss of YBCO tapes,coils and magnets has been investigated and the simulation results have been validated by the experimental results.The AC loss and its distribution as well as the electromagnetic parameters which may affect the AC loss have been discussed in detail.In addition,the critical currents of YBCO coils and a SMES magnet were estimated.The details are as follows:(1)In terms of AC loss calculation,the numerical models based on H-formulation have been established.Then,these models were applied to studying the AC loss characteristics of YBCO tapes with and without a ferromagnetic substrate.What's more,a method to reduce the AC loss of YBCO tapes with a ferromagnetic substrate has been investigated and confirmed by experiments and FEM analyses.(2)The magnetic field distribution,current density distribution,AC loss distribution and critical current of a HTS coil wound by YBCO tapes with a ferromagnetic substrate have been studied based on modified H-formulation.Meanwhile,The FEM results were compared to the experimental results.In addition,a 3D electromagnetic model has been proposed to estimate the AC loss of a D-type double pancake coil.In order to reduce the solved degree of freedom and speed up the calculation,the homogenization strategy was employed to realize the 3D modeling.(3)The anisotropic homogenization method has been used to realize the modeling of a hybrid SMES magnet which has a maximum of approximately seven thousand turns based on H-formulation.Firstly,the homogenization method was validated that it could reasonably predict the AC losses of both YBCCO coils and BSCCO coils;Then,AC loss characteristics of the SMES magnet during dynamic operations were investigated.Besides,the AC loss dependence on steady-state current,dynamic current and current ramp rate was presented and discussed for different operation conductions.Finally,the critical current and inductance variation characteristics of the SMES magnet were discussed briefly.