Demarcation Currents and Corner Field for Dynamic Resistance of HTS-Coated Conductors

Dynamic resistance is essential to evaluate the performance of high-temperature superconducting (HTS) coated conductors, especially when applied in synchronous electric machines and HTS flux pumps. The analytical expression of dynamic resistance has been proposed and verified in many cases, and it appears that dynamic resistance Rdyn is in a linear correlation with transport current It and the amplitude of external ac magnetic field Bext. However, some experimental data have shown that the linearity of Rdyn(It) and Rdyn(Bext) curves only exists within a certain range. To quantitatively describe this interval, the lower demarcation current Idl, the upper demarcation current Idu, and the corner field Bcor have been defined in this article with explicit formulas. The proposed demarcation currents and the corner field, which is used to characterize the nonlinearity of dynamic resistance, have been validated by the simulation and experimental measurements. This article further adds upon the existing knowledge regarding the interaction of dynamic resistance with transport current and magnetic field, which is particularly significant for accurate loss controlling in HTS magnets, rotating machines, and flux pumps.