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Inductance is a very commonly used electrical parameter in transient progress analysis, as well as in energy storage evaluations. It was normally considered as constant when the geometrical configuration of a coil is determined. However, experiments on Bi-2223 (Bi 2 Sr 2 Ca 2 Cu 3 O 10+x ) and YBCO (YBa 2 Cu 4 O 7-x ) coils, both show 10% rise inductance while increasing the applied current. The inductance grows approximately a linear relationship from its minimum to maximum. We used both theoretical and experimental analysis to deeply understand the mechanism of the variation in terms of current distribution in high-temperature superconducting (HTS) coils. Taking this inductance change into account would benefit the accuracy in energy storage applications and in transient analysis occasions. Besides, inductance controllable devices could be achieved by manipulating the bias current applied on HTS coils.

Until recently, a new type of open magnetic shielding system was realized by the combination of a series of closed high temperature superconductor coils. We experimentally confirmed that the shielding factor (SF) of the new shielding system can reach more than 40 dB in the frequency spectrum of 0.1–16 000 Hz. Because of its superior ability to resist alternating magnetic field, we named, the system Tesla-shielding (TS), to commemorate the father of alternating current, Nikola Tesla. In this paper, we will report the design and realization of a Helmholtz coil-based TS. The Helmholtz TS has many advantages over the previous planar TS. Especially, the Helmholtz TS has an engineering way of regulating the device for a better SF. We will introduce the design of the Helmholtz TS with the help of numerical simulation. The main electromagnetic properties of the TS, such as SF in the frequency spectrum and its shielding ability in the long duration measurement, are given in this paper.

In this paper, the I c degradation of bent YBCO tapes has been experimentally studied. The I c characteristics in length direction was measured through a non-contact, continuous I c measurement equipment (Mcorder), which is suitable for all kinds of high temperature superconducting (HTS) tapes. The detailed J c mapping of bent tapes was investigated by a Hall microscopy equipment (Mcorder 2-D), which scans the fields distribution on the surface of the films or bulks. A 4.1-m-long YBCO tape was wound on a 4.5-mm-diameter core with YBCO face outside or inside. The critical current of the YBCO tape before and after winding was measured lengthwise. And the 2-D J c map of the samples of degraded sections was measured. The result shows that the smallest safe bending diameter is larger than 14 mm and smaller than 4.5 mm, for YBCO face outside and inside, respectively, which indicates that the YBCO face is recommended to be inside in bending cases. The relation between critical current of YBCO face outside bent tapes and diameters was fitted to a sigmoid-like function, to help further development where YBCO face outside bending is unavoidable.

Since there is no iron core and the energy is only coupled through the primary and secondary windings, air-core transformers have advantages of no iron loss, no magnetic saturation, and compact in size, which make them attractive to be studied for practical applications. Due to its high current density and low loss, high temperature superconductor (HTS) brings additional advantages for this type of transformer. The HTS wires are highly magnetic field dependent and their characteristics are required for the HTS implementation and the design of the air-core transformers. As a result, magnetic field distribution of the HTS windings is researched, and its influence on the HTS critical currents, ac loss, and the transforming efficiency of the HTS air-core are analyzed.

Most HTS (high-temperature superconductor) coils will quench due to defects in the winding. Some of these defects come from tape manufacturing, but more commonly are generated in the process of making a coil, especially for the YBCO racetrack coils that use epoxy resin to solidify the winding. In order to find out defects, chemical solutions are used to dissolve epoxy resin of three damaged YBCO racetrack coils. YBCO tapes reclaimed from these coils are scanned by MCorder, a continuous critical current measurement device that can tell amplitude of defects and distribution of defects in a high speed and high resolution. The scan result shows severe defects everywhere in the winding. However, during the solidification process, outer turns are more vulnerable to the defects than the inner turns. We believe that the delamination of YBCO tape caused by contraction of the epoxy resin contributes to the defects.