Electromagnetic loss is a crucial factor to evaluate the performance of high temperature superconducting (HTS) coated conductors (CCs). Although the loss characteristics around power frequency have been well studied, it is still unclear how loss varies towards high frequencies above kHz level, which is important to a wide range of applications, such as wireless power transfer. This paper is to investigate the frequency dependence of both magnetization and transport current loss in HTS CCs and therefore, to provide comprehensive analyses through a detailed multilayer model reflecting their actual structures. In this paper, a T-formulation based multilayer numerical model for HTS CCs, consisting of HTS layer, substrate, silver overlayer, and copper stabilizers, has been developed. Both magnetization loss and transport current loss over a wide frequency range, from 50 Hz to 1 MHz, have been simulated and discussed. The results obtained by the existing thin film model based on T-formulation, multilayer model and homogenization model by H-formulation are also presented and compared. The proposed multilayer model has been validated by experimental measurements, which has proven the widely adopted HTS thin film model to be inapplicable for frequencies above 100 Hz. In addition, most magnetization losses occur in the copper stabilizers above 1.2 kHz due to skin effect. Results can be used to study the performance of HTS devices towards high frequencies at kHz or even MHz level.
Dynamic loss is significant for evaluating the performance of type-II high-temperature superconductor (HTS) coated conductors (CC), especially when used in electric machines. Although analytical expressions of dynamic loss have been proposed and verified for HTS CCs exposed to low external magnetic fields with a low current load rate, the non-linearity of dynamic loss at high current load ratios and simultaneous high magnetic fields is still unclear and cannot be predicted by the existing analytical equations. This paper proposes a completely new formulation to characterize the non-linearity of dynamic loss taking into account the J
c(B) dependence of CCs, which can be used for full ranges of both magnetic fields and current load ratios. The proposed analytical formulas have been verified by a
T
-formulation based numerical model and experiments. This paper comprehensively demonstrates the variation of dynamic loss and provides a meaningful reference of loss controlling for HTS CCs, which is vital for HTS machine windings to avoid quench.
Properties of superconductors, such as critical current and n-value, have a significant impact on their loss characteristics. This impact is essential for the design of superconducting devices and their loss reduction, and therefore need to be thoroughly understood. The dependence of AC loss in high temperature superconductors (HTS) on these properties has been well studied. However, it is still unknown how dynamic loss is affected. This paper is to address this unsolved problem and provide comprehensive analyses through both numerical simulation and experimental measurements. In this paper, HTS coated conductors with a wide range of critical currents and n-values have been extensively studied. Their dynamic losses and resistance under various conditions have been modelled and compared to available experiment measurements. Results clearly show the dependence of dynamic loss and resistance on critical current and n-value. The cases with high current load under strong external magnetic field have been studied as well. All these results show a rapid change of dynamic loss around certain magnetic fields, which we defined to be the "corner field", B cor. This paper clearly demonstrates the dependence of dynamic loss and resistance on critical current and n-value, which can be used as a reference for material selection and design optimization.
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