AC loss in high-temperature superconducting conductors, cables and windings for power devices

Abstract

High-temperature superconducting (HTS) transformers and reactor coils promise decreased weight and volume and higher efficiency. A critical design parameter for such devices is the AC loss in the conductor. The state of the art for AC-loss reduction in HTS power devices is described, starting from the loss in the single HTS tape. Improved tape manufacturing techniques have led to a significant decrease in the magnetization loss. Transport-current loss is decreased by choosing the right operating current and temperature. The role of tape dimensions, filament twist and resistive matrix is discussed and a comparison is made between state-of-the-art BSCCO and YBCO tapes. In transformer and reactor coils the AC loss in the tape is influenced by adjacent tapes in the coil, fields from other coils, overcurrents and higher harmonics. These factors are accounted for by a new AC-loss prediction model. Field components perpendicular to the tape are minimized by optimizing the coil design and by flux guidance pieces. High-current windings are made of Roebel conductors with transposed tapes. The model iteratively finds the temperature distribution in the winding and predicts the onset of thermal instability. We have fabricated and tested several AC windings and used them to validate the model. Now we can confidently use the model as an engineering tool for designing HTS windings and for determining the necessary tape properties.

Inductor design for cryogenic power electronics

“…In the design of an ambient temperature inductor the governing consideration is the rise in internal temperature caused by dissipation in the windings and core [10]. The former produce a specific heat generation (1) where J is the average current density and is the average resistivity. Within the core the loss generally has a power law dependence on induction B; for purposes of this simplified analysis we assume (2) which is close to the dependence observed in our measurements.…”

“…This would permit all the components in a power converter which handle large currents to be grouped in a common cryogenic envelope. Superconducting transformers and inductors operating at the line frequency are currently under development [1]- [3]. For the power converter application, the frequency of operation would be significantly higher, in the range 1-10 kHz.…”

Numerical calculations of the total ac loss of Cu-stabilized YBa2Cu3O7−δ coated conductor with a ferromagnetic substrate

“…1,2 ac losses, however, are a significant challenge for large-scale power applications and remain one of the most important issues in the development and commercialization of YBCO applications. [3][4][5] The coated conductor architecture consists of a substrate ͑with thickness of 50-100 m͒ which is often ferromagnetic, one or more buffer layers, the HTS layer, a thin Ag layer, and a Cu stabilizer layer. 1, [6][7][8] The buffer layers are typically thin insulating oxides and thus neither carry current nor generate heat.…”

Material Laws and numerical Methods in applied superconductivity

“…In fact, almost in all the conceived applications for superconducting wires, is well known that each one of the wires holds an AC transport current and experiences an additional AC magnetic field due to the neighboring wires. This situation is found, for example, in superconductor windings for AC magnets, generators, transformers and motors, where each turn feels the magnetic field of all the others [81][82][83][84][85][86].…”