Dynamic loss and magnetization loss of HTS coated conductors, stacks, and coils for high-speed synchronous machines

Abstract

Dynamic loss is an essential parameter to consider for the design of high temperature superconducting (HTS) synchronous machine windings. For aerospace electric propulsion systems, the fundamental frequency component and harmonics in electric machines can attain kHz level because of the high rotating speed. However, for HTS coated conductors (CC), the existing definition of dynamic loss only considers the HTS layer, the validity of which at high frequencies is questionable. Besides, the variation of dynamic loss and magnetization loss under skin effect due to high frequency is still unknown. Additionally, the influence of shielding effects among distinct turns on the dynamic loss of HTS stacks and coils remains unclear. In response to the above concerns, by use of the H -formulation based numerical multilayer modelling method which considers all layers of a CC, the frequency dependence of dynamic loss and magnetization loss of HTS CCs, stacks and coils over a wide range up to 20 kHz has been investigated. Results show that the existing definition of the dynamic region is no longer valid at kHz level, which shrinks rapidly with increasing frequency and magnetization loss plays a progressively important role due to skin effect. Meanwhile, the shielding effect in HTS stacks and coils can enhance the significance of dynamic loss. This paper clarifies the characteristics of dynamic loss and magnetization loss of HTS CCs, stacks, and coils over a wide frequency band, which can serve as a useful reference for accurate loss controlling of machine windings in future aerospace HTS propulsion systems.

Electromagnetic properties of curved HTS trapped field stacks under high-frequency cross fields for high-speed rotating machines

“…This paper is a follow-up work of our previous publications [25][26][27][28]. TFSs are a potential field source applied to highspeed HTS machines.…”

“…In addition, to avoid ambiguity, it should be clarified here that though the studied HTS stack is curved, the orthonormal field dependence has been well considered. As illustrated in Figure 19 in [28], the Jc(B) dependence is closely linked to the angle between the field vector and the wide surface normal of the CC. Then, the local parallel and perpendicular flux densities at the studied point can be expressed as…”

“…For now, the electromagnetic behaviour of HTS TFSs under high-frequency fields remains unclear. In addition, according to our previous research work [25][26][27][28], at frequencies higher than 100 Hz, it is necessary to consider the multilayer physical structure of HTS CCs to quantify magnetization loss due to the skin effect. The existence of the copper stabilizers, silver overlayer, and substrate can influence the loss distribution inside CCs [29].…”

“…This paper is a flow-up work of [28], in which we have built an H-formulation based 3D multilayer numerical model for HTS racetrack coils, and validated it with published experimental data. In response to the above-mentioned issues, here we adapt the 3D numerical model in [28] to a curved HTS TFS. Firstly, we have studied the electromagnetic characteristics of a single curved square CC under perpendicular field magnetization.…”

Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines

“…Aiming to illuminate the state of the art of AC-loss-related research work and determine its future research trends in superconducting machine domains, we have conducted a comprehensive overview of AC-loss-related topics, including superconducting materials adopted in electrical machines, loss mechanism, and analytical formulae, modelling methods, measurement approaches, as well as loss reduction techniques. It should be pointed out that, as reported by our previous research work [22][23][24], the superconductors employed in high-speed rotating machines have to experience high-frequency electromagnetic environments. In this case, the total loss inside electrical machines is not purely contributed by the superconducting parts, but also by the normal conducting parts, due to the skin effect, which poses great challenges to the existing loss quantification and reduction techniques.…”