Itaru Ishii

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

Running Performance of a Pinning-Type Superconducting Magnetic Levitation Guide

A pinning-type superconducting magnetic levitation guide with bulk high-Tc superconductors was studied for use as a goods transportation system, an energy storage system, etc. A superconducting magnetic levitation running test apparatus with a circular track of ca. 38 m length, 12 m diameter, which comprises the magnetic rail constituted by Nd-B-Fe rare-earth permanent magnets and steel plates, was manufactured to examine loss and high-speed performance of the magnetic levitation guide. Running tests were conducted in air. These tests clarify that a vehicle supported by a superconducting magnetic levitation guide runs stably at speeds greater than 42 km/h above the circular track.

Magnetic rail construction for a low loss superconducting magnetic levitation linear guide

A pinning-type superconducting magnetic levitation linear guide which consists of bulk high-T/sub c/superconductors and a magnetic linear rail with permanent magnets and steel plates was investigated for a goods transportation system, an energy storage system, and other uses. This paper describes the loss of this linear guide and a construction of the magnetic linear rail in which no inhomogeneous magnetic field is generated in a comparatively large gap in a long distance configuration. The loss is evaluated analytically by a newly developed electromagnetic analysis program. This proposed magnetic rail construction suppresses inhomogeneous magnetic fields generated by the existence of such spaces as temperature change countermeasures. We performed analyses and experiments on this construction. Results show that calculated and measured values concur well both quantitatively and qualitatively, proving that the proposed magnetic linear rail shows magnetic field distribution that is uniform in the running direction in the required gap.

Optical measurement of transient phenomenon of liquid helium boiling under very high centrifugal operation

Abstract Optical observation is one of the best ways of measuring the transient phenomenon of liquid helium boiling. Especially for very high centrifugal operation, as in superconducting generators, a high speed observation technique is required, since the transient time is very short compared to that for normal gravity operation. Photographic measurement is a suitable observation technique because of its high speed response. This paper shows that the transient time of convection is a function of centrifugal acceleration and is proportional to the − 1 3 power of it. Also, a remarkable phenomenon, which is referred to as a ‘bubble cluster bridge’ and which has not been observed in the stationary experiment, occurs at the beginning of heating. A new type of optical sensor is applied to measure the transient phenomenon of convection as an auxiliary observation. The result shows that the bubble departure time from the heater surface is also proportional to the − 1 3 power of centrifugal acceleration.

Stability tests against thermal disturbances on rotating superconducting field windings

Abstract A superconducting test rotor was constructed and the transient stabilities of the field windings were studied. They were evaluated at various centrifugal accelerations up to 2000 g and it was found that the field windings with bare strands were extremely stable against transient disturbances, and that the insulator coating on the strands might be very detrimental from the viewpoint of both steady state and transient stabilities. It was also clarified that both the minimum film boiling and maximum nucleate boiling heat fluxes were considerably increased, even inside a slot under large centrifugal acceleration, and that these increases contributed to the improvement of stability of the windings. It was shown that even a small cooling channel inside the windings could be effective for cooling.

Review of the electrical insulation of superconducting generators

Superconducting generators have been developed in several countries. Field windings of them are made of NbTi superconductors and cooled with liquid helium. Electrical insulation of the field winding has to withstand high voltage during normal and abnormal operation, and also has to support the conductor against large centrifugal force and Lorentz force. This paper reviews the electrical insulation designs of the field windings of superconducting generators, mainly those of the latest Japanese generators.

Characteristics of a Superconducting Magnetic Bearing.

Both repulsive and attractive forces caused by the pinning state where a magnetic field is trapped in a superconductor are capable of noncontact steady support of an object in all directions. This paper describes the characteristics of the levitation forces, the force relaxation caused by the flux creep and the bearing loss under high rotational speed on a disc-type superconducting bearing at 77K, as well as the rotational characteristics of the pinning-type superconducting radial bearings. The bearing consists of Y1Ba2Cu3Ox(YBCO) oxide superconductors fabricated by the QMG (quench-melt-growth) process and rare-earth permanent magnets. The rotor with permanent magnets supported by the pinning force in the superconductor can be safely operated under high rotational speed.

A network of residential fuel cells and operational strategies: evaluation with a PC simulator and an experimental system

Introduction of fuel cells into residential homes would be a realistic option of near future in present state in Japan. Research and development on polymer electrolyte fuel cell (PEFC) for residential use is at the final stage toward commercial market launch. This paper presents the concept of the interconnection of residential homes with energy networks, and a PC simulator and an experimental system for evaluation of the advantages and disadvantages of the networks, and the result of simulation and experimentation with those evaluation tools. The homes can share their energy equipment virtually by the networks. It provides flexible and efficient operation of the equipment, and reduces partial load operation and start-stop operation which damage the efficiency or the life time of fuel processors. Some operational strategies of the fuel cells were proposed and evaluated with both simulation and experimentation. The evaluation result also revealed that fuel cell systems should be installed to not all homes but some homes within residential areas to realize efficient operation.

Fault current limiting transformer with variable reactance

The objective of this work is to prove experimentally the ability of a transformer with variable reactance to limit the fault current and to adjust the secondary voltage. This transformer is able to change its leakage reactance by a shift of a movable iron-core block. It has three functions of voltage transformation, fault current limitation, and voltage regulation. A small trial apparatus was manufactured and these functions were demonstrated experimentally. Its characteristics and some points that should be improved are also clarified.

Studies on energy networks of electricity, heat and hydrogen for residential dwellings equipped fuel cells

Introduction of fuel cells into residential dwellings would be a realistic option of near future in present state in Japan. Research and development on polymer electrolyte fuel cell (PEFC) for residential use is at the final stage toward commercial market launch. This paper presents the concept of interconnection of residential dwellings with energy networks, and experimental systems and PC simulators for evaluation of the advantages and disadvantages of the networks. The dwellings can share their energy equipment virtually by the networks. It provides flexible and efficient operation of the equipment, and reduces partial load operation and start-stop operation which damage the efficiency or the life time of fuel processors. Authors construct experimental systems and PC simulators to evaluate the networks. The experimental systems consist of fuel cells, electronic load devices and instrument control systems. The data which is obtained by the experimentation is provided to the PC simulators. The simulators demonstrate the more complicated analyses beyond the experimental systems, as the simulators are easily expandable. Combining the experimental systems and the simulators would provide more valuable intelligence