Transition frequency of transport ac losses in high temperature superconducting coated conductors

What is it about?

We explore the behavior of high-temperature superconducting coated conductors (HTS CCs) when carrying electrical currents at different frequencies. Typically, these conductors are used in various applications such as transmission cables, transformers, and power devices. The focus is on understanding transport alternating current (ac) losses in HTS CCs, which can affect cryogenic stability and overall efficiency. The traditional understanding of these losses suggests that the losses per cycle should increase proportionally with the frequency of the current. However, the experimental data in this study reveal an unexpected behavior: above a certain "transition frequency," the losses per cycle start to decrease. To investigate this phenomenon, we used a finite element model to separate different types of losses and proposed a circuit model to explain our observations. We found that at high frequencies, losses in the metallic components become predominant, increasing with frequency up to the transition frequency, beyond which they start to decrease. Additionally, ferromagnetic and hysteresis losses per cycle remain nearly independent of the frequency below the transition frequency but decrease rapidly beyond it. The study suggests several factors contributing to this behavior, including the migration of supercurrent into the metallic path at higher frequencies and the realization that the current in the metallic material is not a conventional eddy current but a transport current inductively coupled to the superconducting current.

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Photo by Tobias Carlsson on Unsplash

Photo by Tobias Carlsson on Unsplash

Why is it important?

This research provides valuable insights into the frequency-dependent transport ac losses of HTS CCs. Understanding these behaviors is crucial for designing and optimizing power devices using superconducting materials. The findings challenge previous theoretical descriptions and offer new perspectives for future applications of high-temperature superconductors in electrical systems.

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