Shinichi Nose

Development of a 22 kV/6.9 kV single-phase model for a 3 MVA HTS power transformer

We have developed a 22 kV/6.9 kV HTS single-phase transformer cooled by liquid nitrogen for field test, which is a practical model for the single-phase part of a 3 MVA HTS power transformer. First, we numerically simulated electromagnetic, mechanical and thermal conditions of the windings in accidental cases of short-circuit and lightning impulse, and considered the winding structure withstanding the severe loads. We constructed a small-sized model coil of Bi-2223 Ag/Mn-sheathed tapes and confirmed applicability of the design concept for the overcurrent and high-withstand-voltage tests. We designed and constructed a single-phase HTS transformer on the basis of the model-coil-test results. The primary and secondary windings are transposed parallel conductors of two and six Bi-2223 Ag/Mn tapes, respectively. The same tests for the HTS transformer as for usual oil-filled ones indicated the reliable operation and high performance. The field test in a distribution grid of Kyushu Electric Power Co. included in-rush-current test and long-term operation of the transformer cooled by a continuous supply system of subcooled liquid nitrogen with cryocoolers.

AC loss properties of a 1 MVA single-phase HTS power transformer

We designed and built a single-phase 1 MVA-22/6.9 kV HTS transformer with the multi-layered cylindrical windings composed of Bi2223 parallel conductors. In advance of the design, the AC loss induced in the windings was estimated on the basis of the observed results in a strand. A subcooled liquid nitrogen cryogenic system with the corresponding cooling capacity was developed and attached to the transformer. The actual AC loss was measured by an electrical method. It was a great part of the total heat load and dominated the temperature rise of subcooled liquid nitrogen. We discussed the validity of the present estimation procedure of the AC loss in the windings as compared with the observed results.

Engineering research and development of magnetically levitated high-temperature superconducting coil system for mini-RT project

A magnetically levitated superconducting coil system is being developed using high temperature superconductors for examining a new magnetic confinement of high-beta plasmas. A miniature double-pancake coil was fabricated with a Bi-2223 Ag-sheathed tape for the purpose of developing a floating control using laser displacement gauges. The coil was inductively excited with liquid nitrogen cooling and successfully levitated in the air. A persistent current switch is also being developed with a Bi-2223 Ag-0.3wt%Mn-sheathed tape, and a prototype model was successfully tested.

Development of HTS current leads for 1 kWh/1 MW module type SMES system. I. Design study

We have been developing high-temperature superconducting (HTS) current leads for a 1 kWh/1 MW module-type SMEs. Each module of a module-type SMES requires a pair of current leads. Therefore, we employed bulk HTS in order to reduce the heat load of the current leads. It is important that HTS current leads for SMES be reliable. The HTS current leads described in this paper have been designed to minimize the heat load and to maintain a high level of reliability. The HTS current leads are designed to hold the heat load at the cold-end terminal to less than 0.1 W. They are also designed with safety leads to bypass current in the event the HTS is quenched and with metal superconductors to assure the continuation of SMES operation even if the HTS should fail or deteriorate in performance. This paper describes an optimal design and the results of a heat load evaluation of HTS current leads for SMES.

Ac Losses in Bi2223 Multifilamentary Wires Exposed to an Magnetic Field Perpendicular to the Wide Surface

We experimentally studied ac losses in Bi2223 superconducting wires exposed to an extemal ac magnetic field perpendicular to the wide surface. The ac losses were measured by use of a short sample of straight wires stacked to one or some layers and compared with the conventional theory based on the usual critical state model. As a result, it is shown that the ac losses of the stacking wires in the perpendicular field can be asymptotically estimated as those of superconducting slabs with the same thickness as the wire width and an overall J c in the stacked wires.

Fabrication and test of a 4 kJ Bi-2223 pulse coil for SMES

We designed and fabricated a 4 kJ conduction-cooled high-Tc superconducting (HTS) pulse coil. The coil is wound with an interlayer-transposed 6-strand parallel conductor which is composed of Bi-2223 silver alloy-sheathed multi-filamentary wires. We had developed a complete 3.6 MJ/1 MW low-Tc superconducting (LTS) SMES system for testing on a power line at Imajuku substation. Aiming at the feasible operation of SMES applying a HTS coil, we made a SMES system set-up in which HTS coils were serially connected to 3 LTS coils of the SMES. The SMES including the HTS coil was connected to Imajuku substations power system, to made operational tests of compensation for load fluctuation at the 6 kV power line. The test results lead to the feasibility of the HTS SMES for practical use in future power systems.

Losses in superconducting coils of 1 kWh/1 MW SMES

The in-situ measurements of pulse losses are carried out for the total system of ESK (Experimental SMES (superconducting magnetic energy storage) of Kyushu Electric Power Co.) with a capacity of 1 kWh/1 MW which was completed in 1998. ESK has six toroidal coils wound by Rutherford cables, each coil being contained in a fiber reinforced plastic (FRP) vessel set up in a Dewar. The loss was calculated by using a method of measuring the decrement of liquid helium (LHe) level in each vessel. The form of current variation for the measurement is a repeated triangular waveform. The charge-discharge rate was changed from 10 A/s to 140 A/s. Although there are considerable errors in the measurements, agreement between the measured results and theoretical calculations is satisfactory in view of the limited conditions of the in-situ measurement for the SMES coils of this scale. The origins of the loss are discussed in detail.

Test Results of the HTS Current Leads for 1kWh/1MW Module Type SMES System

We have developed two pairs of HTS current leads for 1kWh/1MW module type SMES system (which we call “ESK” for experimental SMES of Kyushu Electric Power Co., Inc.) in order to reduce the heat load from the current leads to the cryostat.

Development of HTS (high‐temperature‐superconductor) current leads for 1‐MW/1‐kWh modular SMES system

We are developing high-temperature-superconductor (HTS) current loads for a 1-MW/1-kWh modular SMES system. In the modular SMES system, a pair of current leads would be installed in each module so that the heat load to the low-temperature end through the leads is minimized. Design study of the lead configuration including the safety lead and its thermal characteristics is presented herein. The safety lead composed of stainless steel is placed in parallel to the bulk HTS. A test unit for verification of safe operation has been developed and the simulated bulk HTS quench test has been demonstrated. The maximum temperature of the safety lead reached 200 K and the terminal voltage of the safety lead was only 1.2 V in the case of a 1000-A quench test. This temperature rise was well below the designed value.