Hironobu Kimura

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.

Test results of a HTS power transformer connected to a power grid

Abstract A 22 kV/6.9 kV–1 MVA high-Tc superconducting (HTS) power transformer has been developed as a prototype with single-phase part of a 3 MVA HTS power transformer. The prototype unit is cooled by a continuous subcooled liquid nitrogen (LN2) supply system with cryocoolers. During the field tests, the HTS transformer was connected to a distribution line at Imajuku substation (Kyushu Electric Power Co., Inc.) in Fukuoka, and inrush-current test and a long-term operation test were implemented. The test results demonstrated the HTS power transformers applicability to a power grid.

AC loss properties of a 4 kJ conduction-cooled pulse coil wound with a Bi2223 6-strand parallel conductor for SMES

We designed and fabricated a 4 kJ conduction-cooled superconducting pulse coil with a 6-strand interlayer-transposed parallel conductor composed of Bi2223 multifilamentary tapes. We adopted the helium gas forced-flow cooling system where the helium gas flowed inside a copper pipe soldered with the flanges of brass. We succeeded in the continuous pulse operation with an amplitude of 500 A-1.6 T at a sweep rate of 140 A/s at 30 K as designed. Even in the ac operation with an ac loss of 120 W, the difference in temperature inside the winding was only 5 K and it was possible to hold the coil temperature around 30 K. In this paper, we report the design and the test results of the coil system from the aspect of ac loss and thermal properties.

Thermal stability of a cryocooler-cooled HTS pancake coil wound with Bi2223 tape

Abstract We fabricated and tested a cryocooler-cooled high temperature superconducting (HTS) single pancake coil wound with a Bi2223 tape in order to investigate thermal stability of the HTS coil. The inner diameter of the coil is ∅100 mm and the outer diameter is ∅257 mm. The coil is impregnated with epoxy resin and a conduction plate made of aluminum is fixed on the surface of the coil through an AlN plate for insulation. We measured thermal runaway currents at several temperatures. In this paper the thermal stability of the coil is discussed.

Connecting tests of superconducting persistent-current-switch in a type of current transformer to 1 kWh SMES system

A full system of 1 kWh/1 MW module-type SMES (superconducting magnetic energy storage) has been completed at a substation in Fukuoka City. There is a need for a PCS (persistent-current-switch) with a quick response and large current capacity for use with a SMES system. We have investigated a superconducting PCS in a type of transformer which works according to the principle of a current transformer. A 900 A class PCS has already been manufactured. This paper describes experimental results with connecting tests of the PCS to a SMES which consists of two modules, each comprising a converter of 500 kVA and three superconducting pulse coils.

AC operating test results for a conduction-cooled HTS coil

We fabricated a conduction-cooled HTS coil wound with the conductors composed of four Ag-sheathed Bi2223 tapes, which have no insulator, and a CuNi tape coated with polyimide for reinforcement and insulation. Using the HTS coil we measured AC loss and investigated thermal stability of the conduction-cooled HTS coil. The coil is composed of 12 single-pancake coils and impregnated with epoxy resin. The inner diameter of the coil is /spl phi/100 mm, the outer diameter is /spl phi/190 mm and the height is 90 mm. The HTS coil carried 800 A at 20 K as designed and generated 2.9 T at the central point of the coil. Sinusoidal currents were supplied to the HTS coil at 20-50 K and AC losses were measured using the electrical method. The AC losses per cycle of the HTS coil increased with increasing the frequency of the current, which indicates the coupling losses would generate between Ag-sheathed Bi2223 tapes in addition to the hysteresis losses. Sinusoidal waveform current of 100 A and 1.32 Hz was continuously supplied to the coil in order to investigate the thermal stability of the coil in AC operations. Although the coil generated an AC loss of 125.6 W, the temperature of the coil became stable approximately 200 sec after starting operation, which indicates that Ag-sheathed Bi2223 coils have high thermal stability in AC operations and are suitable for AC applications.

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.

Test results of long-term and over-load operation for a 1 kWh/1 MW module-type SMES

Abstract The authors have developed a 1 kWh/1 MW module-type SMES system (ESK), linked to the actual power system, that was tested at Imajuku Substation in Fukuoka. The practical use of SMES at field sites requires ensuring its reliability, as well as reducing costs with minimum component set-ups. In order to quantitatively verify its reliability and performance limit, two kinds of tests were conducted on ESK: a long-term and over-load operation. In the long-term operation test, a DC500 triangle waveform up to 1000 A was applied to ESK 10,000 times. Further, the compensation ability for distribution line load fluctuation was observed for three days. The results revealed that ESK functioned adequately and in a stable manner. In the other test, a power output 1.2 times that of the rated output was attained, along with an energy storage capacity 1.44 times the rated value. This allowed us to confirm the over-load operation limit of ESK.