High-speed permanent magnet synchronous motors(PMSMs)have recently been widely applied in various applications.However,due to the increased rotor speed and operating frequency increase,the winding AC losses rise subst...High-speed permanent magnet synchronous motors(PMSMs)have recently been widely applied in various applications.However,due to the increased rotor speed and operating frequency increase,the winding AC losses rise substantially,posing risks to the safety operation.Accurate modeling of the AC losses has therefore become critical at the motor initial design stage.This paper reviews the main modeling methods for AC copper losses in PMSMs,including analytical methods,finite element methods,and hybrid modeling methods.The advantages and disadvantages of each method are analyzed in detail,and key issues in the modeling process are discussed.Finally,future research directions in AC copper loss modeling are explored,providing new insights for motor design and performance optimization.展开更多
This paper is devoted to predict AC loss of cable in conduit conductor （CICC） which is of importance in the design of conductors. The consideration for the conductor＇s design and main parameters for the magnets are...This paper is devoted to predict AC loss of cable in conduit conductor （CICC） which is of importance in the design of conductors. The consideration for the conductor＇s design and main parameters for the magnets are introduced. In order to attain a good accuracy in the calculation of AC losses, the field distribution within superconducting outsert should be considered. Calculation of the AC losses, including hysteresis losses and coupling losses, is conducted. An emphasis is put on the hysteresis loss during the ramp up of the current to the operational current （15.3 kA） and the coupling loss of the conductor in a power-down condition for insert. The results are obtained to be 74.9 kJ and 950 J for 40 T hybrid magnets, respectively. Based on the calculation, a brief analysis of losses effect on the conductor design and the operation of magnet is given for the purpose that the capacity of the cryogenertor can be evaluated and the stability regime can be improved in our future work on the hybrid magnets.展开更多
The poloidal field model coil （PFMC） of EAST was a large NbTi superconducting coil. The PFMC was designed and constructed by Institute of Plasma Physics, CAS, and it was tested during 2003 at our institute. One of t...The poloidal field model coil （PFMC） of EAST was a large NbTi superconducting coil. The PFMC was designed and constructed by Institute of Plasma Physics, CAS, and it was tested during 2003 at our institute. One of the most important performance testing items was the AC （Alternating Current） loss. It was able to measure the AC losses by the calorimetric method. The results will be useful for the evaluation of the AC losses of the poloidal coil and provide meaningful data for future operation of the EAST device.展开更多
The central solenoid(CS) is an important component of China Fusion Engineering Test Reactor, for producing, forming and stabilizing plasma in the superconducting tokamak. It is a complicated work to design and manufac...The central solenoid(CS) is an important component of China Fusion Engineering Test Reactor, for producing, forming and stabilizing plasma in the superconducting tokamak. It is a complicated work to design and manufacture the large superconducting CS magnet, so it is meaningful to design a central solenoid model coil(CSMC) and analyze its electromagnetic properties in advance. In this paper, the structure, design parameters and magnetic field distribution of the CS model coil are discussed. The peak power of radial and axial turn conductors and time bucket loss are analyzed by using piecewise-linear method. The CSMC AC loss with different Nb3 Sn CICCs and AC loss of ITER CS coil are compared. The special electrometric method to measure AC loss of the CS model coil for future reference is presented.展开更多
A reliable prediction of AC loss is essential for the application of International Thermonuclear Experimental Reactor(ITER) cable-in-conduit conductors(CICCs);however,the calculation of AC loss of ITER CICCs is a cumb...A reliable prediction of AC loss is essential for the application of International Thermonuclear Experimental Reactor(ITER) cable-in-conduit conductors(CICCs);however,the calculation of AC loss of ITER CICCs is a cumbersome task due to the complicated geometry of the multistage cables and the extreme operating conditions in ITER.In this paper,we described the models developed for hysteresis and coupling loss calculation,which can be suitable for the construction of ITER magnetic system.Meanwhile,we compared the results of theoretical analysis with the SULTAN test result to evaluate the numerical model we used.In addition,we introduced the n-value and AC loss with transport current for CICCs based on the DC measurement results at SULTAN,which lays the foundation for the further study.展开更多
High-temperature superconductors in superconductor apparatuses are subjected to mechanical strains under operating conditions.These strains cause the degradation of the critical current densities and influence AC loss...High-temperature superconductors in superconductor apparatuses are subjected to mechanical strains under operating conditions.These strains cause the degradation of the critical current densities and influence AC losses in the superconductors.Based on the dynamic process of thermomagnetic interaction,we report the results of numerical analysis of AC losses in an infinite high-temperature superconducting slab subjected to a uniform in-plane strain in an alternating external magnetic field parallel to the sample surface.The numerical analysis shows the details of electromagnetic phenomena in the slab and the dependences of AC loss on various external parameters including the uniform strain in the slab and the amplitude and frequency of the external magnetic field.In this paper,we find that whether the magnetic field fully penetrates the superconductor is the key factor that influences the features of AC loss.When the magnetic field cannot fully penetrate the superconductor,the loss rises with increasing strain or decreasing frequency.When the magnetic field can fully penetrate the superconductor,the feature is just opposite.We also analyze the effects of periodic strain on AC loss.It is interesting to find that when the periodic strain frequency equals the external magnetic field frequency,the AC loss reaches the maximum,regardless if the magnetic field fully penetrates the superconductor or not.展开更多
The CICC (cable-in-conduit conductor) in ITER (International Thermal-nuclear Experimental Reactor) will run in high-current, fast transient magnet field and complex environment. In response to the impact of magnet fie...The CICC (cable-in-conduit conductor) in ITER (International Thermal-nuclear Experimental Reactor) will run in high-current, fast transient magnet field and complex environment. In response to the impact of magnet fields above 10 T, the Nb3Sn conductor has been introduced. However, the AC (alternating current) loss mechanism of Nb3Sn conductor on strain has not been explored. So, it is necessary to study the AC loss calculation method with transient electromagnetic field and wide range of strain, the coupling current in complex field and current signal of field is simplified to the spectrum effects of coil excitation, and calculation technology of AC loss, which contains the frequency, magnet field, coil characteristics and other parameters, is constructed to meet the discrete Fourier transform (DFT). By comparative analysis of simulation, it is found that the AC loss calculation of the conductor with spectrum algorithm is closer to the actual project value than the traditional algorithm. For the rapid excitation, in particular plasma discharge and burst, spectrum algorithm and the traditional algorithm are consistent. For the relative error calculation of hysteresis loss and coupling loss, it is found that the coupling loss is cumulative linearly, where the hysteresis loss is not so. As a function of the amplitude, frequency and phase angle, the relative error is less than 40%. The results showed that the method of Fourier restructuring is satisfactory.展开更多
High Temperature Superconductor(HTS)materials can operate at higher magnetic fields up to 20 T with high critical current and higher operating temperature,compared to low temperature superconductors(LTS).A Highly Flex...High Temperature Superconductor(HTS)materials can operate at higher magnetic fields up to 20 T with high critical current and higher operating temperature,compared to low temperature superconductors(LTS).A Highly Flexible REBCO Cable(HFRC)is introduced at the Institute of Plasma Physics,Chinese Academy of Sciences(ASIPP);a cabling method that is suitable for REBCO HTS tape having anisotropic material properties in its thin REBCO layer.This type of HTS superconducting cable shows high potential for applications in nuclear fusion.The alternating currents and magnetic fields in tokamak type of fusion magnets,cause AC power losses in such cables,which can provoke instability of the conductor by induced currents and increase the temperature.As a first step in characterizing the electromagnetic(EM)performance of an HFRC cable,the AC loss and contact resistance of the HFRC prototype cable were measured at the University of Twente.The measurements were done in liquid helium(4.2 K)with AC magnetic fields,applied perpendicular to the cable's long axis.The AC loss was measured simultaneously by a calibrated gas flow calorimeter utilizing the helium boil-off method,and by the magnetization method using pick-up coils.For the applied test conditions,no coupling loss could be distinguished as a part of the overall AC loss.It is suggested that this might be explained by the shielding of the conductor interior from the applied magnetic field by the outer tape layer due to the high critical current density of the REBCO tape,leading to a high penetration field.展开更多
We present a new calorimetric method for measuring alternative current(AC)losses of high-temperature superconducting(HTS)tapes by optical fiber Bragg grating(FBG),which is particularly well suited for the AC loss meas...We present a new calorimetric method for measuring alternative current(AC)losses of high-temperature superconducting(HTS)tapes by optical fiber Bragg grating(FBG),which is particularly well suited for the AC loss measurement of Re BCO wires,so-called the second generation(2G)HTS wires.Compared with conventional calorimetric methods,the suggested method is both free of electromagnetic disturbance,magnetic field,and fast as well as simple.Self-field AC losses are measured by the optical FBG method and the conventional lock-in-amplifier(LIA)technique,respectively.The results show that the measured AC loss is in good agreement with those measured by the electric method,thus the presented calorimetric method would be available for measuring the AC loss of 2G wire and is expected to be generalized for the measurement of AC loss or thermal performances of HTS bulk.展开更多
High-temperature superconducting(HTS)technology provides an alternative approach to achieve compact transformers.Addressing AC loss in the HTS winding is crucial for HTS transformer applications.Most numerical AC loss...High-temperature superconducting(HTS)technology provides an alternative approach to achieve compact transformers.Addressing AC loss in the HTS winding is crucial for HTS transformer applications.Most numerical AC loss studies on HTS transformers have neglected the influence of iron cores.This work carries out an AC loss study to explore the impact of an iron core on the HTS windings in a 3-phase HTS 1 MVA transformer coupled with it.AC loss simulations for the transformer winding both with and without the iron core are conducted by adopting the three-dimensional(3D)T-A homogenization method.When the iron core is incorporated,the saturation magnetic fields of iron materials,flux diverters(FDs)with different geometries,and variations in turn spacings in the LV winding composed of Roebel cables are considered to investigate their influence on the AC loss of the transformer winding.The inclusion of the iron core leads to a 1.2%increase in AC loss for the transformer winding while simulating at the rated current.We attribute this slight difference to the non-inductive winding structure of the transformer winding,where a strong magnetic field generated in the space between the LV and HV windings effectively shields the influence of the iron core.展开更多
As an elegant and fast numerical tool for solving time‐dependent electromagnetic field problems in hard superconductors,Brandt’s method has played an important role in understading the magnetic behavior of supercond...As an elegant and fast numerical tool for solving time‐dependent electromagnetic field problems in hard superconductors,Brandt’s method has played an important role in understading the magnetic behavior of superconducting strips,discs,bars and cylinders in various aspect ratios.However,the application of this convenient method was mainly in magnetization processes.Traditionally,the solution of current transport problem needs to introduce a driving electric field E_(a),which requires a low efficiency iterative process and E_(a) itself was not clearly explained.In this work,three integral algorithms based on the Brandt’s method are developed to deal with current transport problems,which directly adopt the applied current as a boundary condition.Namely the current(I)‐driven version and two current‐field‐driven versions A and B.Moreover,the arbitrary applied magnetic field can also be included in the I‐driven version.The derivation with all necessary formulas for the methods are given in this work.As an example,the new methods,as well as the traditional method are used for calculating transport ac loss Q of a superconducting cylinder or strip obeying a power‐law relation of E∝J^(n)as a function of a given I(t).Derived from the Ampère law and the differential rather than the integral expression of the Faraday law,the current‐driven version can be used for more accurate and much quicker computation.Being an intermediate quantity,E_(a)(t) in the two current‐field‐driven versions is accurately calculated under the given I(t),but version B is much quicker than A.Problems relating to E_(a)(t) and Q stabilization process are discussed.展开更多
AC loss presents a significant challenge for high-temperature superconducting (HTS) rotating machines. To date, the behaviour of total AC loss (Qtol) (with current) and magnetization loss (Qm) (without current) in a s...AC loss presents a significant challenge for high-temperature superconducting (HTS) rotating machines. To date, the behaviour of total AC loss (Qtol) (with current) and magnetization loss (Qm) (without current) in a single HTS tape under rotating magnetic fields (RF) have been explored. However, a research gap remains in understanding how these findings translate to the more complex HTS windings of rotating machines. Further exploration is needed to understand the loss behaviour of more complex HTS structures, such as HTS stacks. In this work, Qtol and Qm, in the HTS stacks under RF and a perpendicular AC standing wave magnetic field are numerically investigated. Two different RF models are considered: one is the Uni-RF model, characterized by a uniform field with equal field amplitudes and phases at each position, and the other is a non-uniform field created by a rotating Halbach array, referred to as the Hal-RF model. The dependence of AC loss on parameters such as the number of tapes in the stacks, tape width (2a), and the inclination angle (α) of tapes, which refers to the angle between the normal direction of the stack and the vertical direction, have been explored. The number of tapes in the stacks ranges from 1 to 16, α ranges from 0° to 90°, and the tape width includes 4 mm and 40 mm. Additionally, different rotating field directions are also considered. Interestingly, the analytical values from Brandt and Indenbom equation for Q_(m) of a superconducting strip (BI-strip) are close to Q_(m) results of the stacks under the standing wave at high fields, while they are over twice as high as those in the Hal-RF model at 1 T. This suggests the BI-strip equation is not reliable for predicting Q_(m) under RF at high fields. We also show in the Hal-RF model that different rotation directions of the field lead to varying Q_(m) and Qtol when asymmetric Jc (B, θ) data are applied. Moreover, it has been observed that the inclination angle has no impact on Q_(m) under uniform RF while significantly impacts both Q_(m) and Qtol in the Hal-RF model.展开更多
AC loss is one of the greatest obstacles for high‐temperature superconducting(HTS)applications.In some HTS applications,coated conductors carry non‐sinusoidal currents.Thus,it is important to investigate the effect ...AC loss is one of the greatest obstacles for high‐temperature superconducting(HTS)applications.In some HTS applications,coated conductors carry non‐sinusoidal currents.Thus,it is important to investigate the effect of various waveforms on AC loss in coated conductors.In this work,transport AC loss in a 4 mm‐wide REBCO coated conductor carrying sinusoidal and non‐sinusoidal currents,is numerically investigated.The current amplitudes,the frequency of the transport current,and n‐value are varied.Non‐sinusoidal transport current waveforms studied include square,five types of trapezoidal,and triangular waveforms.Simulated results show that,for a given current amplitude,AC loss for the square current waveform is the greatest,that for the triangular waveform is the smallest.The sequence of AC loss in the conductor for different current waveforms coincides with the penetration depth,which implies the penetration depth determines the AC loss of the coated conductor.Furthermore,the transport AC loss in the conductor was found to decrease with frequency as f2=n for non‐sinusoidal transport current.展开更多
For an accurate estimation of the AC losses of superconducting triaxial cables,in this paper we present a two‐dimensional model capable to provide a global assessment of multi‐layer triaxial cables,validated against...For an accurate estimation of the AC losses of superconducting triaxial cables,in this paper we present a two‐dimensional model capable to provide a global assessment of multi‐layer triaxial cables,validated against the reported AC‐losses measurements on single‐phase cables provided by the Russian Scientific and Research Institute of the Cable Industry(VNIIKP).Four models are presented,the first being a single‐phase cable of 50 tapes and the others being three triaxial cables made of up to 135 coated conductors distributed in up to 9 layers.A systematic study is devised,where the number of layers per phase increases from 1 to 3,with at least 14 tapes distributed across each layer of the first(innermost)phase,15 in the secondary(middle)phase,and 16 in the third(outermost)phase,respectively.Remarkably,our results reveal that the simple strategy of considering an unbalanced distribution for the amplitudes of the applied current,can generally balance the magnetic field between the three phases even for the bilayer and trilayer cables,resulting in negligible magnetic leaks in all situations.Besides,our high‐resolution simulations allow to see for the first time how the transport and magnetization currents distribute across the thickness of all the superconducting tapes,from which we have found that the AC‐losses of the 2nd phase is generally higher than at the other phases at low to moderate transport currents,I_(tr)<0:8I c,being I_(c) the critical current of the corresponding tapes.Nevertheless,depending on whether the I_(c) of the SC tapes at the 3rd phase layers is lower than the one at the 2nd phase,the layers at the third phase can exhibit a considerable increment on the AC losses.This is result of the considered magneto angular anisotropy of the superconducting tapes,which lead to intriguing electromagnetic features that suggest a practical threshold for the applied transport current,being it 0:8I_(c).Likewise,the relative change in the AC‐losses per adding layers,per phase,and as a function of the entire range of applied transport current is disclosed.展开更多
AC loss is one of the critical issues for designing REBCO fast‐ramping magnets operating at cryogenic temperatures.There are many ways to reduce AC loss for coil windings.However,it is not clear which method is the m...AC loss is one of the critical issues for designing REBCO fast‐ramping magnets operating at cryogenic temperatures.There are many ways to reduce AC loss for coil windings.However,it is not clear which method is the most effective way to minimize AC loss in the coil windings for a given Ampere‐turns.In this work,we numerically studied coil configurations of several small superconducting magnets constructed from 12 mm SuperPower REBCO coated conductors,for fast‐ramping application with the same Ampere‐turns to identify the lowest AC loss among them.The HTS magnets have a total turn number of 50 and inner diameter of 30 cm,carrying AC current operating in the temperature range of 20–40 K at 25 Hz.We incorporated several existing loss reduction strategies including spacing between the turns for single pancake coils,grading Ic values for the solenoid configuration,and applying flux diverters to shape the magnetic field around the coil windings.The simulation was implemented using a homogenized H‐formulation.Across all studied loss reduction methods,the use of flux diverters has the largest impact in AC loss reduction.The AC loss values in the solenoid winding comprising a stack of five single pancake coils with 0.1 mm turn‐to‐turn gap with the flux diverters agree well with those in the single pancake coil for 2 mm turn‐to‐turn gap with the flux diverters.Solenoid type coil configurations with flux diverters generate much smaller AC loss than the single pancake type with flux diverters when they generate the same center magnetic field.展开更多
High‐temperature superconducting(HTS)AC electrical devices generally carry AC transport currents and are exposed to AC external magnetic fields with arbitrary orientations.Realistic HTS coated conductors(CCs)show div...High‐temperature superconducting(HTS)AC electrical devices generally carry AC transport currents and are exposed to AC external magnetic fields with arbitrary orientations.Realistic HTS coated conductors(CCs)show diverse critical current anisotropy and field dependence(I_(c)(B,θ),which directly affect the superconducting behavior.However,under complex electromagnetic(EM)conditions,the discrepancies in AC loss characteristics caused by different(I_(c)(B,θ),features are still unclear.Moreover,the selection of CCs with desirable(I_(c)(B,θ),features to further reduce AC loss under various EM conditions remains overlooked.In this work,the transport AC loss(Q_(t))(without field),magnetization loss(Q_(m)),and total AC loss(Q_(tot))of the nearly isotropic Shanghai Creative(SCST)CC and the strongly anisotropic Fujikura(FYSC)CC,along with their stacks,are investigated in the range of 90°and 90°(parallel to the CC wide surface)field angles based on the H‐formulation.The results show that,due to the opposite angular dependence of I_(c),the effective penetration fields of these two CCs or stacks exhibit distinct trends with the field angle,and the Q_(m)in the nearly isotropic CC is less dominated by the perpendicular field component compared to that in the strongly anisotropic CC.Furthermore,due to the different field dependence of Ic at various field angles,the two CCs or stacks exhibit opposite flux flow loss behaviors with the field angle.Overall,the SCST CC and its stack show lower Q_(tot)within the angle range around 0°,and this range expands as the external field increases,while the FYSC CC and its stack show lower Q_(tot)at the remaining angles.This is further explained by analyzing the field distribution and Q_(tot)of each tape in the stacks.This paper clarifies the discrepancies in AC loss caused by different(I_(c)(B,θ),and identifies the applicable EM conditions for different REBCO materials to reduce AC loss,providing valuable references for material selection to minimize loss in HTS AC devices across different scenarios.展开更多
单级式双有源桥(dual active bridge,DAB)DC/AC变换器控制自由度多,变压器匝比、漏感、开关频率等参数相互耦合,导致变换器效率优化面临多重制约。该文分析变压器匝比、漏感与软开关范围、漏感电流有效值、漏感电流峰值之间的约束关系,...单级式双有源桥(dual active bridge,DAB)DC/AC变换器控制自由度多,变压器匝比、漏感、开关频率等参数相互耦合,导致变换器效率优化面临多重制约。该文分析变压器匝比、漏感与软开关范围、漏感电流有效值、漏感电流峰值之间的约束关系,提出直接表征DAB-DC/AC变换器效率的物理量:效率敏感因子。通过研究效率敏感因子对系统损耗的影响机理,实现变换器效率最优的硬件参数设计,为多参数耦合的单级式DAB-DC/AC变换器效率优化提供理论指导。最后通过一台450 W样机验证所提理论的正确性。展开更多
The electromagnetic properties of high temperature superconductors(HTS)are characterized with the explicit intent to improve their integration in electric power systems.A tape and a coil made of Bismuth Strontium Calc...The electromagnetic properties of high temperature superconductors(HTS)are characterized with the explicit intent to improve their integration in electric power systems.A tape and a coil made of Bismuth Strontium Calcium Copper Oxide(BSCCO)are considered in the presence of electromagnetically active materials in order to mimic properly the electromagnetic environment typical of electrical machines.The characterization consists of the determining the critical current and the AC losses at different values of the frequency and the transport current.The effects induced by the proximity of the active materials are studied and some related experimental issues are analyzedc.展开更多
基金supported in part by the National Natural Science Foundation of China under Grants 52025073 and 52377055。
文摘High-speed permanent magnet synchronous motors(PMSMs)have recently been widely applied in various applications.However,due to the increased rotor speed and operating frequency increase,the winding AC losses rise substantially,posing risks to the safety operation.Accurate modeling of the AC losses has therefore become critical at the motor initial design stage.This paper reviews the main modeling methods for AC copper losses in PMSMs,including analytical methods,finite element methods,and hybrid modeling methods.The advantages and disadvantages of each method are analyzed in detail,and key issues in the modeling process are discussed.Finally,future research directions in AC copper loss modeling are explored,providing new insights for motor design and performance optimization.
文摘This paper is devoted to predict AC loss of cable in conduit conductor （CICC） which is of importance in the design of conductors. The consideration for the conductor＇s design and main parameters for the magnets are introduced. In order to attain a good accuracy in the calculation of AC losses, the field distribution within superconducting outsert should be considered. Calculation of the AC losses, including hysteresis losses and coupling losses, is conducted. An emphasis is put on the hysteresis loss during the ramp up of the current to the operational current （15.3 kA） and the coupling loss of the conductor in a power-down condition for insert. The results are obtained to be 74.9 kJ and 950 J for 40 T hybrid magnets, respectively. Based on the calculation, a brief analysis of losses effect on the conductor design and the operation of magnet is given for the purpose that the capacity of the cryogenertor can be evaluated and the stability regime can be improved in our future work on the hybrid magnets.
基金supported by National Meg-science Engineering Project of the Chinese Government
文摘The poloidal field model coil （PFMC） of EAST was a large NbTi superconducting coil. The PFMC was designed and constructed by Institute of Plasma Physics, CAS, and it was tested during 2003 at our institute. One of the most important performance testing items was the AC （Alternating Current） loss. It was able to measure the AC losses by the calorimetric method. The results will be useful for the evaluation of the AC losses of the poloidal coil and provide meaningful data for future operation of the EAST device.
文摘The central solenoid(CS) is an important component of China Fusion Engineering Test Reactor, for producing, forming and stabilizing plasma in the superconducting tokamak. It is a complicated work to design and manufacture the large superconducting CS magnet, so it is meaningful to design a central solenoid model coil(CSMC) and analyze its electromagnetic properties in advance. In this paper, the structure, design parameters and magnetic field distribution of the CS model coil are discussed. The peak power of radial and axial turn conductors and time bucket loss are analyzed by using piecewise-linear method. The CSMC AC loss with different Nb3 Sn CICCs and AC loss of ITER CS coil are compared. The special electrometric method to measure AC loss of the CS model coil for future reference is presented.
基金supported in part by Ministry of Science and Technology of China under Grant 2014GB105001
文摘A reliable prediction of AC loss is essential for the application of International Thermonuclear Experimental Reactor(ITER) cable-in-conduit conductors(CICCs);however,the calculation of AC loss of ITER CICCs is a cumbersome task due to the complicated geometry of the multistage cables and the extreme operating conditions in ITER.In this paper,we described the models developed for hysteresis and coupling loss calculation,which can be suitable for the construction of ITER magnetic system.Meanwhile,we compared the results of theoretical analysis with the SULTAN test result to evaluate the numerical model we used.In addition,we introduced the n-value and AC loss with transport current for CICCs based on the DC measurement results at SULTAN,which lays the foundation for the further study.
基金supported by the National Natural Science Foundation of China(Grant Nos.11032006,11121202 and 11202087)National Key Project of Magneto-Constrained Fusion Energy Development Program(Grant No.2013GB110002)
文摘High-temperature superconductors in superconductor apparatuses are subjected to mechanical strains under operating conditions.These strains cause the degradation of the critical current densities and influence AC losses in the superconductors.Based on the dynamic process of thermomagnetic interaction,we report the results of numerical analysis of AC losses in an infinite high-temperature superconducting slab subjected to a uniform in-plane strain in an alternating external magnetic field parallel to the sample surface.The numerical analysis shows the details of electromagnetic phenomena in the slab and the dependences of AC loss on various external parameters including the uniform strain in the slab and the amplitude and frequency of the external magnetic field.In this paper,we find that whether the magnetic field fully penetrates the superconductor is the key factor that influences the features of AC loss.When the magnetic field cannot fully penetrate the superconductor,the loss rises with increasing strain or decreasing frequency.When the magnetic field can fully penetrate the superconductor,the feature is just opposite.We also analyze the effects of periodic strain on AC loss.It is interesting to find that when the periodic strain frequency equals the external magnetic field frequency,the AC loss reaches the maximum,regardless if the magnetic field fully penetrates the superconductor or not.
基金supported by the Major International (Regional) Joint Research Program of China (Grant No. 2004CB720704) the Excellent Young Teachers Program for Higher Education of Henan Province (Grant No. 2010GGJS-088)
文摘The CICC (cable-in-conduit conductor) in ITER (International Thermal-nuclear Experimental Reactor) will run in high-current, fast transient magnet field and complex environment. In response to the impact of magnet fields above 10 T, the Nb3Sn conductor has been introduced. However, the AC (alternating current) loss mechanism of Nb3Sn conductor on strain has not been explored. So, it is necessary to study the AC loss calculation method with transient electromagnetic field and wide range of strain, the coupling current in complex field and current signal of field is simplified to the spectrum effects of coil excitation, and calculation technology of AC loss, which contains the frequency, magnet field, coil characteristics and other parameters, is constructed to meet the discrete Fourier transform (DFT). By comparative analysis of simulation, it is found that the AC loss calculation of the conductor with spectrum algorithm is closer to the actual project value than the traditional algorithm. For the rapid excitation, in particular plasma discharge and burst, spectrum algorithm and the traditional algorithm are consistent. For the relative error calculation of hysteresis loss and coupling loss, it is found that the coupling loss is cumulative linearly, where the hysteresis loss is not so. As a function of the amplitude, frequency and phase angle, the relative error is less than 40%. The results showed that the method of Fourier restructuring is satisfactory.
基金supported by the Strategic Priority Research Program of Chinese Academy of Science under Grant No.XDB25000000Comprehensive Research Facility for Fusion Technology Program of China under Contract No.2018-000052-73-01-001228+2 种基金the National Nature Science Foundation of China(No.52077212)the Youth Innovation Promotion Association,Chinese Academy of ScienceChina Scholarship Council.
文摘High Temperature Superconductor(HTS)materials can operate at higher magnetic fields up to 20 T with high critical current and higher operating temperature,compared to low temperature superconductors(LTS).A Highly Flexible REBCO Cable(HFRC)is introduced at the Institute of Plasma Physics,Chinese Academy of Sciences(ASIPP);a cabling method that is suitable for REBCO HTS tape having anisotropic material properties in its thin REBCO layer.This type of HTS superconducting cable shows high potential for applications in nuclear fusion.The alternating currents and magnetic fields in tokamak type of fusion magnets,cause AC power losses in such cables,which can provoke instability of the conductor by induced currents and increase the temperature.As a first step in characterizing the electromagnetic(EM)performance of an HFRC cable,the AC loss and contact resistance of the HFRC prototype cable were measured at the University of Twente.The measurements were done in liquid helium(4.2 K)with AC magnetic fields,applied perpendicular to the cable's long axis.The AC loss was measured simultaneously by a calibrated gas flow calorimeter utilizing the helium boil-off method,and by the magnetization method using pick-up coils.For the applied test conditions,no coupling loss could be distinguished as a part of the overall AC loss.It is suggested that this might be explained by the shielding of the conductor interior from the applied magnetic field by the outer tape layer due to the high critical current density of the REBCO tape,leading to a high penetration field.
基金supported by the National Natural Science Foundation of China(Grant No.51477053)the Beijing Education Commissions(Grant No.GJ2013009)
文摘We present a new calorimetric method for measuring alternative current(AC)losses of high-temperature superconducting(HTS)tapes by optical fiber Bragg grating(FBG),which is particularly well suited for the AC loss measurement of Re BCO wires,so-called the second generation(2G)HTS wires.Compared with conventional calorimetric methods,the suggested method is both free of electromagnetic disturbance,magnetic field,and fast as well as simple.Self-field AC losses are measured by the optical FBG method and the conventional lock-in-amplifier(LIA)technique,respectively.The results show that the measured AC loss is in good agreement with those measured by the electric method,thus the presented calorimetric method would be available for measuring the AC loss of 2G wire and is expected to be generalized for the measurement of AC loss or thermal performances of HTS bulk.
基金New Zealand Ministry of Business,Innovation and Employment(MBIE)Strategic Science Investment Fund“Advanced Energy Technology Platforms”under contract No.RTVU2004.
文摘High-temperature superconducting(HTS)technology provides an alternative approach to achieve compact transformers.Addressing AC loss in the HTS winding is crucial for HTS transformer applications.Most numerical AC loss studies on HTS transformers have neglected the influence of iron cores.This work carries out an AC loss study to explore the impact of an iron core on the HTS windings in a 3-phase HTS 1 MVA transformer coupled with it.AC loss simulations for the transformer winding both with and without the iron core are conducted by adopting the three-dimensional(3D)T-A homogenization method.When the iron core is incorporated,the saturation magnetic fields of iron materials,flux diverters(FDs)with different geometries,and variations in turn spacings in the LV winding composed of Roebel cables are considered to investigate their influence on the AC loss of the transformer winding.The inclusion of the iron core leads to a 1.2%increase in AC loss for the transformer winding while simulating at the rated current.We attribute this slight difference to the non-inductive winding structure of the transformer winding,where a strong magnetic field generated in the space between the LV and HV windings effectively shields the influence of the iron core.
文摘As an elegant and fast numerical tool for solving time‐dependent electromagnetic field problems in hard superconductors,Brandt’s method has played an important role in understading the magnetic behavior of superconducting strips,discs,bars and cylinders in various aspect ratios.However,the application of this convenient method was mainly in magnetization processes.Traditionally,the solution of current transport problem needs to introduce a driving electric field E_(a),which requires a low efficiency iterative process and E_(a) itself was not clearly explained.In this work,three integral algorithms based on the Brandt’s method are developed to deal with current transport problems,which directly adopt the applied current as a boundary condition.Namely the current(I)‐driven version and two current‐field‐driven versions A and B.Moreover,the arbitrary applied magnetic field can also be included in the I‐driven version.The derivation with all necessary formulas for the methods are given in this work.As an example,the new methods,as well as the traditional method are used for calculating transport ac loss Q of a superconducting cylinder or strip obeying a power‐law relation of E∝J^(n)as a function of a given I(t).Derived from the Ampère law and the differential rather than the integral expression of the Faraday law,the current‐driven version can be used for more accurate and much quicker computation.Being an intermediate quantity,E_(a)(t) in the two current‐field‐driven versions is accurately calculated under the given I(t),but version B is much quicker than A.Problems relating to E_(a)(t) and Q stabilization process are discussed.
基金New Zealand Ministry of Business,Innovation and Employment under the Advanced Energy Technology Platform program“High power electric motors for large scale transport”contract number RTVU2004in part supported by the Air Force Office of Scientific Research under award number FA2386-22-1-4054Yuan Wang acknowledges financial supports from the Chinese Scholarship Council(CSC)and the CSC/Victoria University of Wellington Scholarship.
文摘AC loss presents a significant challenge for high-temperature superconducting (HTS) rotating machines. To date, the behaviour of total AC loss (Qtol) (with current) and magnetization loss (Qm) (without current) in a single HTS tape under rotating magnetic fields (RF) have been explored. However, a research gap remains in understanding how these findings translate to the more complex HTS windings of rotating machines. Further exploration is needed to understand the loss behaviour of more complex HTS structures, such as HTS stacks. In this work, Qtol and Qm, in the HTS stacks under RF and a perpendicular AC standing wave magnetic field are numerically investigated. Two different RF models are considered: one is the Uni-RF model, characterized by a uniform field with equal field amplitudes and phases at each position, and the other is a non-uniform field created by a rotating Halbach array, referred to as the Hal-RF model. The dependence of AC loss on parameters such as the number of tapes in the stacks, tape width (2a), and the inclination angle (α) of tapes, which refers to the angle between the normal direction of the stack and the vertical direction, have been explored. The number of tapes in the stacks ranges from 1 to 16, α ranges from 0° to 90°, and the tape width includes 4 mm and 40 mm. Additionally, different rotating field directions are also considered. Interestingly, the analytical values from Brandt and Indenbom equation for Q_(m) of a superconducting strip (BI-strip) are close to Q_(m) results of the stacks under the standing wave at high fields, while they are over twice as high as those in the Hal-RF model at 1 T. This suggests the BI-strip equation is not reliable for predicting Q_(m) under RF at high fields. We also show in the Hal-RF model that different rotation directions of the field lead to varying Q_(m) and Qtol when asymmetric Jc (B, θ) data are applied. Moreover, it has been observed that the inclination angle has no impact on Q_(m) under uniform RF while significantly impacts both Q_(m) and Qtol in the Hal-RF model.
基金supported by the New Zealand Ministry of Business,Innovation and Employment under Catalyst Space and Fusion project“International Science Co‐operation on Superconductor Technologies”contract number RTVU1916supported by the New Zealand Ministry of Business,Innovation and Employment under the Advanced Energy Technology Platform program“High power electric motors for large scale transport”contract number RTVU2004.
文摘AC loss is one of the greatest obstacles for high‐temperature superconducting(HTS)applications.In some HTS applications,coated conductors carry non‐sinusoidal currents.Thus,it is important to investigate the effect of various waveforms on AC loss in coated conductors.In this work,transport AC loss in a 4 mm‐wide REBCO coated conductor carrying sinusoidal and non‐sinusoidal currents,is numerically investigated.The current amplitudes,the frequency of the transport current,and n‐value are varied.Non‐sinusoidal transport current waveforms studied include square,five types of trapezoidal,and triangular waveforms.Simulated results show that,for a given current amplitude,AC loss for the square current waveform is the greatest,that for the triangular waveform is the smallest.The sequence of AC loss in the conductor for different current waveforms coincides with the penetration depth,which implies the penetration depth determines the AC loss of the coated conductor.Furthermore,the transport AC loss in the conductor was found to decrease with frequency as f2=n for non‐sinusoidal transport current.
基金supported by the UK Research and Innovation,Engineering and Physical Sciences Research Council(EPSRC),grant Ref.EP/S025707/1,led by H.S.R.
文摘For an accurate estimation of the AC losses of superconducting triaxial cables,in this paper we present a two‐dimensional model capable to provide a global assessment of multi‐layer triaxial cables,validated against the reported AC‐losses measurements on single‐phase cables provided by the Russian Scientific and Research Institute of the Cable Industry(VNIIKP).Four models are presented,the first being a single‐phase cable of 50 tapes and the others being three triaxial cables made of up to 135 coated conductors distributed in up to 9 layers.A systematic study is devised,where the number of layers per phase increases from 1 to 3,with at least 14 tapes distributed across each layer of the first(innermost)phase,15 in the secondary(middle)phase,and 16 in the third(outermost)phase,respectively.Remarkably,our results reveal that the simple strategy of considering an unbalanced distribution for the amplitudes of the applied current,can generally balance the magnetic field between the three phases even for the bilayer and trilayer cables,resulting in negligible magnetic leaks in all situations.Besides,our high‐resolution simulations allow to see for the first time how the transport and magnetization currents distribute across the thickness of all the superconducting tapes,from which we have found that the AC‐losses of the 2nd phase is generally higher than at the other phases at low to moderate transport currents,I_(tr)<0:8I c,being I_(c) the critical current of the corresponding tapes.Nevertheless,depending on whether the I_(c) of the SC tapes at the 3rd phase layers is lower than the one at the 2nd phase,the layers at the third phase can exhibit a considerable increment on the AC losses.This is result of the considered magneto angular anisotropy of the superconducting tapes,which lead to intriguing electromagnetic features that suggest a practical threshold for the applied transport current,being it 0:8I_(c).Likewise,the relative change in the AC‐losses per adding layers,per phase,and as a function of the entire range of applied transport current is disclosed.
基金supported in part by New Zealand Ministry of Business,Innovation and Employment(MBIE)by the Strategic Science Investment Fund“Advanced Energy Technology Platforms”under Contract RTVU20042020 Google Excellence Research University ProgramUS DOE Ernst Courant Traineeship in Accelerator Sciences and Engineering,the educational program of next generation of accelerator physicists and engineer,US Department of Energy,HEP office.
文摘AC loss is one of the critical issues for designing REBCO fast‐ramping magnets operating at cryogenic temperatures.There are many ways to reduce AC loss for coil windings.However,it is not clear which method is the most effective way to minimize AC loss in the coil windings for a given Ampere‐turns.In this work,we numerically studied coil configurations of several small superconducting magnets constructed from 12 mm SuperPower REBCO coated conductors,for fast‐ramping application with the same Ampere‐turns to identify the lowest AC loss among them.The HTS magnets have a total turn number of 50 and inner diameter of 30 cm,carrying AC current operating in the temperature range of 20–40 K at 25 Hz.We incorporated several existing loss reduction strategies including spacing between the turns for single pancake coils,grading Ic values for the solenoid configuration,and applying flux diverters to shape the magnetic field around the coil windings.The simulation was implemented using a homogenized H‐formulation.Across all studied loss reduction methods,the use of flux diverters has the largest impact in AC loss reduction.The AC loss values in the solenoid winding comprising a stack of five single pancake coils with 0.1 mm turn‐to‐turn gap with the flux diverters agree well with those in the single pancake coil for 2 mm turn‐to‐turn gap with the flux diverters.Solenoid type coil configurations with flux diverters generate much smaller AC loss than the single pancake type with flux diverters when they generate the same center magnetic field.
基金supported by National Natural Science Foundation of China(Grant Nos.52172271,12374378,52307026)the National Key R&D Program of China(Grant No.2022YFE03150200)Shanghai Science and Technology Innovation Program(Grant Nos.22511100200,23511101600).
文摘High‐temperature superconducting(HTS)AC electrical devices generally carry AC transport currents and are exposed to AC external magnetic fields with arbitrary orientations.Realistic HTS coated conductors(CCs)show diverse critical current anisotropy and field dependence(I_(c)(B,θ),which directly affect the superconducting behavior.However,under complex electromagnetic(EM)conditions,the discrepancies in AC loss characteristics caused by different(I_(c)(B,θ),features are still unclear.Moreover,the selection of CCs with desirable(I_(c)(B,θ),features to further reduce AC loss under various EM conditions remains overlooked.In this work,the transport AC loss(Q_(t))(without field),magnetization loss(Q_(m)),and total AC loss(Q_(tot))of the nearly isotropic Shanghai Creative(SCST)CC and the strongly anisotropic Fujikura(FYSC)CC,along with their stacks,are investigated in the range of 90°and 90°(parallel to the CC wide surface)field angles based on the H‐formulation.The results show that,due to the opposite angular dependence of I_(c),the effective penetration fields of these two CCs or stacks exhibit distinct trends with the field angle,and the Q_(m)in the nearly isotropic CC is less dominated by the perpendicular field component compared to that in the strongly anisotropic CC.Furthermore,due to the different field dependence of Ic at various field angles,the two CCs or stacks exhibit opposite flux flow loss behaviors with the field angle.Overall,the SCST CC and its stack show lower Q_(tot)within the angle range around 0°,and this range expands as the external field increases,while the FYSC CC and its stack show lower Q_(tot)at the remaining angles.This is further explained by analyzing the field distribution and Q_(tot)of each tape in the stacks.This paper clarifies the discrepancies in AC loss caused by different(I_(c)(B,θ),and identifies the applicable EM conditions for different REBCO materials to reduce AC loss,providing valuable references for material selection to minimize loss in HTS AC devices across different scenarios.
文摘单级式双有源桥(dual active bridge,DAB)DC/AC变换器控制自由度多,变压器匝比、漏感、开关频率等参数相互耦合,导致变换器效率优化面临多重制约。该文分析变压器匝比、漏感与软开关范围、漏感电流有效值、漏感电流峰值之间的约束关系,提出直接表征DAB-DC/AC变换器效率的物理量:效率敏感因子。通过研究效率敏感因子对系统损耗的影响机理,实现变换器效率最优的硬件参数设计,为多参数耦合的单级式DAB-DC/AC变换器效率优化提供理论指导。最后通过一台450 W样机验证所提理论的正确性。
文摘The electromagnetic properties of high temperature superconductors(HTS)are characterized with the explicit intent to improve their integration in electric power systems.A tape and a coil made of Bismuth Strontium Calcium Copper Oxide(BSCCO)are considered in the presence of electromagnetically active materials in order to mimic properly the electromagnetic environment typical of electrical machines.The characterization consists of the determining the critical current and the AC losses at different values of the frequency and the transport current.The effects induced by the proximity of the active materials are studied and some related experimental issues are analyzedc.
