Naoji Kashima

Study of 10 MW-Class Wind Turbine Synchronous Generators With HTS Field Windings

We study the electro-magnetic design of 10 MW-class wind turbine generator with high temperature superconducting field winding by using the FEM analysis. The design examples are presented and the generator characteristics are investigated. The 10 MW-class HTS wind turbine generator is considered to be feasible from the stand point of the electro-magnetic design. In this study, 8-pole and 12-pole generators are investigated. From the results, it is considered that the 8-pole design is preferable compared with the 12-pole design. The analysis also reveals the small synchronous reactance of the HTS wind turbine generator. Therefore, proper protection is necessary for the large short circuit current.

Study on high temperature superconducting magnetic bearing for 10 kWh flywheel energy storage system

Flywheel energy storage systems with high temperature superconducting magnetic bearings are expected for load leveling use. A 1 kWh flywheel of 600 mm diameter was developed and the maximum energy storage of 1.4 kWh at 20,000 RPM was attained. For the development of a large capacity flywheel system, it is necessary to sophisticate the cooling system and improve the performance of the HTS magnetic bearing. So, an advanced cooling system of the bearing with a cryogenic refrigerator has been developed, and also the bearing characteristics in several cooling conditions have been investigated. It has been confirmed that the repulsive force of the bearing at 50 K was 1.5 times of its value at 80 K, and the rotating loss of the bearing at 50 K was one third of its value at 80 K, but the lateral magnetic stiffness at 50 K became small in comparison to that of 80 K. On the basis of the above results, an HTS magnetic bearing for 12.5 kWh flywheel system is under development.

Fabrication of coated conductors by multiple-stage CVD

The multiple-stage Chemical Vapor Deposition technique was developed for making a long coated conductor with high deposition speed. In this paper, a multi-coating of YBCO layer using 6-stage CVD system was described. Substrates were PLD-CeO/sub 2//IBAD-Gd/sub 2/Zr/sub 2/O/sub 7//Hastelloy. Thickness of each layer was about 1.0 /spl mu/m, 1.0 /spl mu/m and 0.1 mm respectively. /spl Delta//spl phi/ of CeO/sub 2/ layer was about 9-10/spl deg/. Deposition rate of YBCO layer was 25 m/h and 5 m/h. Number of passing was 10 times and 2 times respectively. I/sub c/ of the tape which was prepared at a speed of 25 m/h /spl times/ 10 passes was 100 A/cm. Thickness of total YBCO layer was about 1 /spl mu/m and its J/sub c/ was 1 MA/cm/sup 2/. I/sub c/ of the tape which was prepared at a speed of 5 m/h /spl times/ 2 passes was 101 A/cm. Thickness of total YBCO layer was also 1 /spl mu/m and its J/sub c/ was 1 MA/cm/sup 2/.

Development of High Strength Pancake Coil With Stress Controlling Structure by REBCO Coated Conductor

High strength against electromagnetic force is required for high magnetic field and large capacity coil in order to develop large-capacity superconducting magnetic energy storage (SMES) systems for electric power system control. Also, suppression of delaminating of Yttrium (Y) based coated conductor in a coil is required to manufacture the highly reliable and durable superconducting coil. Insulating coating, using liquid resin of low-temperature-curable-polyamide, was developed and showed durability at very low temperature without deterioration of transport properties of superconducting wire in a coil. Combining paraffin molding, delaminating, and deterioration of transport properties of superconducting wire were not also observed in a coil. These insulating techniques were applied to the pancake coil, in which superconducting wire and the reinforcing outer plates of the coil withstand electromagnetic force. The double pancake coil of this coil structure, called “Yoroi-coil; Y-based oxide superconductor and reinforcing outer integrated coil” was prepared and the durability against electromagnetic force by hoop stress test was verified. The coil achieved 1.5 kA transporting at 4.2 K in 8 T back-up magnetic field without the degradation of transport properties. Maximum hoop stress at the hoop stress test reached 1.7 GPa, based on the calculations. This result confirmed that Yoroi-coil structure has a capability to withstand the large hoop stress, which exceeded the tensile strength of Y-based coated conductors, and bring out highly durable and reliable superconducting coils.

Electromagnetic Design Study of Transverse Flux Enhanced Type Superconducting Wind Turbine Generators

Transverse flux enhanced type superconducting synchronous machines have been studied for large-capacity wind power generation. The generators have multiple circular superconducting field coils in the rotor and copper armature windings in the stator. A parametric design study and electromagnetic characteristic analysis of the superconducting wind turbine generators (WTGs) have been carried out. The target output is 10 MW for a rotational speed of 10 rpm, and the diameter of the whole coil system is 5 m. Superconducting technology is quite effective for compact and lightweight design of large power capacity, low-speed and high torque generators. Armature and field coil dimensions and the number of poles are key parameters in the design study. FEM analysis was carried out to obtain magnetic flux density, magnetic flux linkage, induced voltage, fundamental generator characteristics, etc. Required superconducting wire length was also estimated.

Fabrication of YBa2Cu3O7 thin film on cube-textured Cu tape

We achieved a biaxially oriented YBa2Cu3O7 film on a {100} ⟨001⟩ textured Cu tape with Jc of 1.9×106 A cm−2 at 77 K. A Ni overlayer was deposited by electroplating technique on the {100} ⟨001⟩ textured Cu tape to improve oxidation resistance of Cu substrate, and then YBa2Cu3O7 was deposited on the CeO2/YSZ/CeO2 buffered Ni-electroplated Cu tape. We confirmed that the Ni-electroplated Cu tape lost its ferromagnetism after 700 °C at 1 h heat treatment. Our rolling assisted biaxially textured substrate (RABiTS) type coated conductor can be used for ac applications and is thought to be more cost feasible than the standard RABiTS architecture using Ni-alloy tapes.

Rapid Formation of 200 m-long YBCO Coated Conductor by Multi-Stage CVD

Toward the industrialization of YBa2Cu3O7-x (YBCO) coated conductors for practical applications, metal-organic chemical vapor deposition (MOCVD) has been investigated. We applied multi-stage MOCVD to achieve high-speed production of coated conductor because the increase of the number of depositing stages placed in a line could enlarge deposition area. Using 12-stage CVD, we succeeded in deposition of highly biaxially oriented YBCO layer at tape transfer speed of 50 m/h on the CeO2 capped ion-beam-assisted-deposition (IBAD) - Gd2Zr2O7 (GZO) buffered Hastelloy tape, and achieved high critical current density ( Jc) exceeding 2 MA/cm2 in a short sample. And it was found that lowering substrate temperature according to YBCO layer growth was effective to increase Ic. Using this method, high critical current (Ic) of 174 A was achieved by 1 mum thick YBCO layer which passed through 12-stage CVD, and 227 A by 1 mum thick YBCO layer deposited by 6-stage one. Based on these results, three 200 m-class YBCO layers were deposited by multiple depositions at tape speed of 50 m/h each, using the 12-stage CVD system. A 203 m-long YBCO layer was successfully deposited with end-to-end Ic of 92.8 A, so that the multiplication of Ic and length reached 18.8 kA ldr m. These results indicate that a multi-stage CVD technique is useful for a rapid fabrication of long YBCO coated conductor.

Conceptual Design of Next Generation HTS Cyclotron

In recent years, the quality of high-temperature superconducting (HTS) tapes has been improving rapidly, becoming available in sufficient quantity and length, and can be applied to devices for power systems and industrial applications. Therefore, we are carrying out a feasibility study on the application of HTS coil to a medical accelerator system for particle cancer therapy, and designing a new HTS cyclotron that is to be compact, highly efficient, is able to extract high-energy beam and consume less power. In this paper, we report our effort to develop a conceptual magnetic design of a “next generation HTS cyclotron” using high-temperature superconducting technology.

Experimental study on superconducting fault current limiting transformer for fault current suppression and system stability improvement

We have been developing a superconducting fault current limiting transformer (SFCLT) with 3-phase, 500/275 kV, 625 MVA and optimized the main parameters by EMTP simulation. In this paper, we designed and fabricated an experimental scale-down model of SFCLT with 3-phase, 275/105 V, 6.25 kVA, using NbTi superconducting wire. We introduced the experimental model SFCLT into a transient network analyzer consisted of synchronous generators, transformers, transmission lines, circuit breakers and an infinite bus. It was revealed that experimental model had effective function-parameters as was simulated and experimental results clarified the effectiveness of SFCLT having both functions of the fault current suppression and the system stability improvement in a future superconducting power system.

Over-Current Characteristics of a 20-m-Long YBCO Model Cable

To achieve large current capacity and mechanical flexibility, high-temperature superconductor (HTS) power transmission cables consist of a number of YBCO coated conductors, which are assembled and wound spirally on a Cu former. In practical applications, superconducting cables might be subjected to short-circuit fault currents that are 10 to 30 times the operating current. Therefore, in order to ensure the stability and feasibility of HTS power cables and protect them from fault currents, it is important to estimate the redistribution of the transport current and electromagnetic coupling among the conductor layer, shield layer, and Cu former. In this study, we carried out experiments on a 20-m-long YBCO model cable, which was composed of two jointed 10-m-long YBCO model cables. Over-current with a peak of 31.8 kArms and a duration of 2.02 s was applied to the model cable. We performed numerical simulations using a newly developed computer program based on the 3D finite element method (FEM) in order to clarify the electromagnetic and thermal behaviors of the YBCO model cable in the presence of an over-current.