Junji Kondoh

Real-World MicroGrids-An Overview

Microgrids are networks of small, distributed electrical power generators operated as a collective unit - a system of energy systems. The range of hardware and control options for Microgrid operation are reviewed. The paper summarizes and highlights the operating principles and key conclusions of research and field trials to-date. An overview is given on demonstration projects for Microgrids which have been, and are being, constructed.

Operational strategies of networked fuel cells in residential homes

Residential fuel cells (FCs) have been recently launched in the commercial markets in Japan. The introduction of FCs in residential homes has become a realistic option. We previously proposed energy networks that enabled the interconnection of homes via electricity, heat, and hydrogen networks in order to allow consumers to interchange energy. Further, we have developed a PC-based simulator and an experimental system to evaluate the proposed energy networks. In this paper, analyses on the strategies of the electricity dispatch of FCs and their load sharing in the interconnected homes equipped with the energy networks were performed. The analyses were conducted with the experimental system, PC-based simulator, and a newly constructed mathematical model that optimizes the operation of the FCs with the minimization of both annual energy cost and CO2 emission. The basic characteristics of FC stacks were obtained by experimentations, and these were stored in the PC-based simulator. Four different operational strategies were carried out for four FC stacks, and these strategies were compared. It was concluded from the results that the operational strategies, which have different advantages with regard to efficiency in electricity generation and heat recovery, should be applied depending on the seasonal demand variations

AC loss measurement of HTS coils with ferromagnetic disks

Manufacturing techniques for low AC loss high-T/sub c/ superconducting coils are necessary to realize high efficiency superconducting power equipments. High-T/sub c/ superconducting tape conductors have anisotropic magnetic field dependence on critical current and AC magnetization loss. A magnetic field component perpendicular to the tape surface degrades HTS coil performance. We numerically investigated a magnetic field adjusting method and AC loss reduction effects by attaching ferromagnetic materials to both ends of HTS coils. We also measured total AC loss of an HTS coil comprising 10 HTS double pancake coils by the boil-off method. Total AC loss of the coil was dominated by mechanical loss due to vibration and movement of conductors and pancake coils. In this paper, methods to reduce total AC loss of HTS coils are discussed.

Force-balanced coil for large scale SMES

In large scale SMES, huge electromagnetic force caused by high magnetic fields and coil currents is a serious problem. In order to solve this problem, we propose a concept of force-balanced coil (FBC) applied to the SMES. The FBC balances the centering force with the hoop force, both of which are exerted in the major radius direction. Moreover, for the optimization of large aspect ratio superconducting coils, we propose a stress-balanced coil (SEC) concept, improving the concept of FBC, which balances magnetic pressures at the coil nose part where the produced magnetic field reaches its maximum value. Comparing the toroidal magnetic field coil (TFC) and FBC with SEC, the last can reduce coil stresses and obtain large stored energy with shorter length conductors and/or lower magnetic fields.

Direct load control for wind power integration

Output power fluctuation of high penetration of wind power causes demand and supply imbalance in electric power systems and results in frequency deviation if the fluctuation is not fully compensated by other regulable power plants. In Japan, some electric utilities have started to accept only the wind farms which disconnect and give up generating power during light-load periods with less adjustable reserve. Otherwise, wind farms are required to employ battery energy storage systems to charge the generated power during the light-load periods. Instead of these uneconomical solutions, this paper proposes direct control of loads such as electric water heaters (EWHs) for power system balancing. In the paper, the increase of acceptable wind power generation by the proposed load control has been evaluated quantitatively in the power system of the Hokkaido Island in Japan. The result indicates that the acceptable wind power generation increases almost three times higher by implementing the direct control on seven-tenth of EWHs in Hokkaido. However, the control interval of the direct load control is required to be shorter than or almost equal to the inertia constant of the power system.

Experimental study on AC loss reduction of HTS coils by use of ferromagnetic disks

Manufacturing techniques suitable for fabricating low AC loss high-temperature superconductor (HTS) coils are necessary to realize high-efficiency power equipment. Usually, the AC magnetization loss of HTS tape conductors is anisotropically dependent on the magnetic field, with a magnetic field perpendicular to the tape surface degrading HTS coil performance. Therefore, decreasing the magnetic field perpendicular to the tape surface is an efficient method of reducing the total AC loss of HTS coils. In a previous study, the possibility of AC loss reduction through the use of ferromagnetic materials was shown numerically, and the total AC loss of HTS coils with and without attached ferromagnetic disks was measured. However, no obvious differences in AC loss were observed because the total AC loss was dominated by mechanical loss. In this study, a low mechanical loss, 30 A, 90 mH HTS coil is fabricated by winding with stainless-steel tape and employing epoxy impregnation. A clear reduction in AC loss is then observed by attaching the ferromagnetic disks.

Mechanical properties of a niobium-tin superconductor reinforced by tantalum cores

We have been developing fiber-reinforced type of niobium-tin superconductor for large scale high field magnets. In this conductor, each niobium-tin filament has a tantalum core. Tantalum is selected as material for the core since it has good ductility with mechanical strength and hence a conventional drawing method can be applied to fabricate a conductor. Stress-strain characteristics and the irreversible strain limits of the conductor with different heat-treatment conditions are measured. Combining these results, discussions about the mechanical properties of the conductor are presented.

Transmutation of fission products by high-field tokamak reactor with force-balanced coils

Abstract A DT sub-ignited tokamak reactor is investigated as a transmuter of fission products with an average neutron wall loading of 1 MW m−2 basing on a novel coil concept to generate strong magnetic fields. By the use of the force-balanced coils (FBC) which reduces the net centering force by a factor of ten from that exerted on toroidal magnetic coils of the same dimension, the steady-state tokamak reactor can be designed to achieve the fusion reaction of QDT≃3.7. To transmute the fission product 129I effectively, a blanket is designed which consists of the neutron multiplier Be, the tritium breeder Li2O and a neutron reflector C. Using the optimal blanket, the amount of 129I is effectively halved in 2 years with quasi-self-consistent condition, QNET≃5.3, local TBR>1.7 and nuclear heating rate in superconducting magnets

Experimental study of solenoid using Bi2223/Ag tape with ferromagnetic disks

We have studied a disk-set solenoid: a superconducting solenoid that uses Bi2223/Ag tape and has ferromagnetic disks set on both its ends. A magnetic field applied to the tape conductors at the edges turns so it is parallel to the tape surface. We manufactured a solenoid made of 10 double pancakes and investigated differences in its characteristics with and without the ferromagnetic disks. The results showed that setting the disks increased the critical current of a double pancake on the edge 1.3 times. And measurements using the Hall elements demonstrated that the magnetic field applied perpendicularly to the tape surface near the edge was reduced to the same degree as indicated by the numerical calculation.

Influence of Ta-reinforcement geometry in Nb/sub 3/Sn wires

We have been developing tantalum-fiber-reinforced bronze process niobium-tin wires for use in large-scale high field magnets. They are fabricated by conventional drawing. We manufactured two kinds of the wires with different geometries but similar volume ratios. We have investigated their characteristics and have clarified that there are some differences in their superconducting critical current, critical magnetic field, critical temperature, and the influence of their heat-treatment conditions.