Kei Shiohara

Noncontact Characterization of In-Plane Distribution of Critical Current Desity in Multifilamentary Coated Conductor

Using a scanning Hall-probe microscopy, we have developed a noncontact characterization method for multifilamentary coated conductors. In-plane distributions of sheet current density in a multifilamentary coated conductor were visualized at different conditions of external magnetic field. From these results, we could extract local critical current and equivalent width of each filament as a function of longitudinal position. These items will be indispensable for quality control of multifilamentary coated conductors and for the precise estimation of their AC losses. This means that this characterization method will be a key technology for the establishment of multifilamentary coated conductors which promise electric power applications with low AC losses.

Lateral Distribution of Critical Current Density in Coated Conductors Slit by Different Cutting Methods

We have investigated the lateral distributions of critical current densities in narrow coated conductors slit by different cutting methods. The objective was to find an optimal slitting process to make a narrow conductor that should be effective for ac loss reduction of assembled conductors such as power transmission cables. In-plane 2-D distribution of critical current density was characterized by means of scanning Hall-probe microscopy. From an analysis along the width direction, we could estimate the degradation in critical current density by a slitting process at both tape edges. We determined an equivalent width for the slit tapes in order to discuss such degradation with a high spatial resolution. Furthermore, the 2-D scanning allows us to evaluate the effective tape width as a function of longitudinal coordinate. In other words, we could evaluate the equivalent width of a slit conductor together with its statistics along the longitudinal direction. As a result, it was found that coated conductors slit by laser cutting processes were clearly better than those by mechanical ones from the viewpoint of less degradation at their edges. In addition, an optimal condition among laser slitting processes was also presented.

Design of 22-kV 10-kA HTS Triaxial Superconducting Bus

A 22-kV 10-kA HTS superconducting bus was designed and manufactured with YBCO superconducting tapes. A triaxial configuration was adopted to minimize the ac loss of the cable without shielding layer. The YBCO tapes were prepared by a TFA-MOD (trifluoroacetic acid-metal organic deposition) method on the substrate manufactured by a sputter-IBAD technique. First, bath-cooling the completed cable down to 77 K with liquid nitrogen in atmospheric pressure, we observed the current-versus-voltage characteristics. The critical current Ic of each phase exceeded 3 kA. The dielectric breakdown test between the phases and against the earth was also carried out at 77 K in atmospheric pressure. The lightning impulse withstand level of ±125 kV and the withstand level of AC excess voltage of 50 kV for 1 min were verified. The partial discharge was not also observed for AC excess voltage. Liquid nitrogen flow was simulated. The pressure loss was only 60 kPa, which was small enough compared with the pumping power of 0.6 MPa for circulating liquid nitrogen.