Hidemi Hayashi

Development of a 1 T cryocooler-cooled pulse coil with a Bi2223 superconducting parallel conductor for SMES

The authors designed and fabricated a 1 T cryocooler-cooled pulse coil operating at 40 K. A 4-strand interlayer-transposed parallel conductor composed of Bi-2223 rectangular cross-sectional multifilamentary wires was adopted to realize a uniform current distribution and to reduce the AC loss density down to the level of that of a single strand. The pulse coil is a 16-layer solenoidal one with an inner diameter of 52 mm, an outer diameter of 111 mm and a height of 120 mm. The heat drains of AlN plates, which are insulators, are arranged between layers for the cooling of the heat due to the AC loss by heat conduction. They could continuously operate the coil in a triangular waveform mode with an amplitude of 1 T and a frequency of 1 Hz. The AC loss was 10.6 W and the other thermal load was 13 W.

Study on a mobile-type magnetic separator applying high-Tc bulk superconductors

Abstract We have developed a new water-treatment system that consists of a membrane separator and a magnetic separator that uses long high-Tc bulk superconductors (SCs) as permanent magnets. Basic tests were performed using a new prototype water-treatment system to verify the separator’s ability to remove water bloom. Based on the test results, we design the mobile-type magnetic separator system. The designed magnetic separator system consists of three components; a pre-process unit, a rotating membrane separator and a magnetic separator. The capacity of the magnetic separator is 100 ton/day. Removal rate is 90% or more. It is thought that the system is compact and high efficiency.

Results of tests on components and the system of 1 kWh/1 MW module-type SMES

A full system of 1 kWh/1 MW superconducting magnetic energy storage (SMES) has been completed early this year. This SMES is the first step to the realization of practical SMES system for power line stabilization. Main points in its design are two module type arrangement of six coils having three coils and one converter as one unit of module, modified-D-shaped coils with mechanical supports, liquid helium vessel type cooling of coils, and high-temperature superconducting current leads. The first test experiment was carried out on the site recently. The above design points were examined. A preliminary test for power line control was also made in the distribution line at the site. Satisfactory results were obtained.

Test Results of Power System Control by Experimental SMES

The authors have developed a solenoid model coil used for superconducting magnetic energy storage (SMES) for power system control, aimed at drastically reducing the costs of the SMES system. The single solenoid model coil of 2.9 MJ is designed with the rated current of 9.6 kA, a maximum magnetic field of 5.5 T and coil charge rates equivalent to those of the practical 100 MW/54 MJ class SMES. The coil is characterized by the use of an aluminum stabilized NbTi CIC (Cable-in-conduit) conductor. The experimental SMES consists mainly of a 2.9 MJ coil, the cooling system for the CIC conductor and the 1 MW class AC/DC converter. The SMES is connected to 6 kV distribution lines at a substation. In the field test, the SMESs 17 ms responses for the step input of active and reactive power were ascertained. Furthermore, its function of compensating for load fluctuation in the 6 kV distribution line was confirmed. The test results show the realization of a practical SMES system for power line control

Current distribution in superconducting parallel conductors wound into pancake coils

We made a preliminary investigation of the applicability of high-T/sub c/ superconducting parallel conductors to pancake coils. For the sake of a uniform current distribution and low AC loss, the constituent strands need to be transposed so as to be inductively equivalent with each other. We adopted an interdisk transposition where the strands are not transposed inside a single-pancake coil but only at the joint between the pancake coils. The fabrication process is simple. We have only to fabricate the same double-pancake coils and connect the strands individually with transposition outside the winding. We searched theoretically for the optimum transposition in the case of 3-strand and verified the theoretical result by using small test coils wound with NbTi 3-strand parallel conductors for convenience.

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.

Development of a 3 -66/6.9 kV-2 MVA REBCO Superconducting Transformer

We have designed and fabricated a 3Φ-66 kV/6.9 kV2 MVA transformer with RE1Ba2Cu3O7-δ(REBCO, RE:Rare Earth, Y, Gd etc.) superconducting tapes. It is a 1/10 model of a 3Φ-66 kV/6.9 kV-20 MVA one for a distribution power grid. The superconducting windings were reduced only in current capacity by reducing the number of tapes in parallel conductors. In the primary side, a single REBCO tape with a width of 5 mm was cylindrically wound into 8 layers. In the secondary one, an 8-strand parallel conductor was wound similarly into 2 layers, where each strand was transposed 15 times per one layer. The REBCO tapes for the secondary winding were also scribed by laser into a 3-filament structure to reduce the ac loss. The windings for 3 phases were installed into a GFRP cryostat which had an elliptic-cylinder-shape and three cylindroid bore for an iron core at room-temperature. A Ne turbo-Brayton refrigerator with a cooling capacity of 2 kW at 65 K was developed and located close to the transformer. The windings were cooled with subcooled liquid nitrogen at 65 to 70 K, which was forced-flowed by a pump unit between the transformer and the refrigerator. The completed transformer was first tested in liquid nitrogen at 77 K according to the domestic regulation for conventional transformers. The load loss, i.e., ac loss of the windings, was 26.9 W for the rated operation. The dielectric strength was also verified by applying 350 kV impulse voltage and 140 kV ac voltage for 1 minute.

Development of a REBCO Superconducting Transformer With Current Limiting Function

A single-phase 10 kVA transformer was designed and fabricated with RE1Ba2Cu30O7-δ (REBCO, RE: Rare Earth) superconducting tapes to quantitatively investigate the transition phenomenon of REBCO superconducting tapes to normal state due to a fault excess current. The voltage ratio was 1:1 and the rated voltage was 393 V. It had four windings. The primary and secondary windings had auxiliary windings in addition to main ones respectively. The main and auxiliary windings were connected in parallel in the both sides. The addition of the auxiliary windings made it possible to observe the induced normal resistances in the respective main ones individually. First usual performance tests were carried out and a stable operation as designed was confirmed. In steady state almost all of the current flowed in the main windings due to the small leakage reactance between them. At a sudden short-circuit test, the main windings quenched due to excess current over the critical current and the current was reduced to one fortieth as compared with the case of no current limiting function. It was clarified the whole of the main windings did not shift to normal state though the current exceeded the critical current all over the length and the induced normal zone was almost proportional to the primary voltage.

A Study of SMES Control Logic for Power System Stabilization

The authors have addressed developments of SMES system effective for power system stabilizing control. Focused on control logics that can be used to efficiently regulate SMES, a number of unique control logics were devised by combining the popularly used power deviation (DeltaP) of a generator with the angular velocity deviation (Deltaomega) of a generator or the phase correction. We practiced a digital simulation analysis for the created logics under both conditions of one- and multi-machine infinite-bus systems using the Y-method power system dynamics analysis program, which was compiled by the CRIEPI. As a result, it was revealed that the rated capacity and the amount stored energy of SMES necessary for power system stabilizing can be reduced by approximately 3 to 5% when compared to that obtained by employing the conventionally used DeltaP control method alone.

Development of a 1 kWh-class module-type SMES-design study

The authors are planning to build a 1 kWh/1 MW (maximum stored energy/maximum power capability) module-type SMES (named ESK; experimental SMES of Kyushu Electric Power) as a first step towards the realization of practical SMESs for power line control. The main points of the design are those of: module-type coils for the development of SMES capacity scale-up; the choice of low loss stranded cables for reducing pulse operating loss; the choices of modified D shape coils and the reduction of stresses in the conductor-which become more serious in scaling-up and high-T/sub c/ superconductor (HTSC) current leads for covering weak points due to thermal loss in a module-type SMES which need many current leads. Some other points are also studied such as the design of the cooling system in which a single coil quench does not induce that of others, and harmonics suppression in the SMES power converter system.