Fuel cell is a provisional energy source in 21st century to handle the construction of hydrogen-based sustainable-energy societies. This report focus on variety types of fuel cells and their practical applications as dispersed energy source systems. Their contribution for power system will be expected regarding efficiency and exploitation of renewable energy. Especially, SOFC (Solid Oxide Fuel Cell) system is a prospective energy system to serve electric and thermal energy for its highest operation temperature so that the environmental issue would be handled.

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Di-methyl-ether (DME), an oxygenated hydrocarbon, can facilitate hydrogen manufacture by steam reforming reaction at low temperature. Methanol and DME steam reforming at 250-300°C, reforming DME into hydrogen, can be performed easily with small-scale and simple equipment.
Whether the hydrogen output from the reformer for supply to the fuel cell includes DME, and how this affects the generation performance has yet to be confirmed. The purpose of this paper is to investigate the supply of a fuel cell with mixtures of DME and H₂ in varying proportions and to clarify the effect on generation performance. Conclusions are as follows: (1) For a supply of DME and H₂ mixed gas, DME is consumed after the H₂ is consumed. By comparing the experimental values with theoretical values of consumption of pure H₂, a mixture of DME and H₂, and pure DME, it proved to be possible to roughly predict the experimental values by calculation. (2) The voltage value moved to near the DME voltage after the H₂ was consumed, the current density increased after the H₂ was consumed. (3) During continuous running the voltage load was observed to fluctuate.

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This paper presents an empirical formula for preliminary loss allocation to each generator in a network. From the relationship of Incremental Transmission Loss (ITL) and the power outputs of generators, we have derived a preliminary loss allocation formula for each generator. To get the allocated losses to generators, the preliminary losses have been adjusted according to the correction factors calculated from them. Preliminary losses are adjusted so that the sum of allocated losses equals the total loss calculated by DC Optimal Power Flow (DC-OPF). Using DC-OPF the procedure for loss allocation including the preliminary loss calculation formula has been tested for 6-bus-3-generator and IEEE 118-bus-36-generator model power systems. Allocated losses calculated by our procedure have been compared with those of incremental method for the both model power systems and the features of the proposed method have been discussed.

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This paper proposes a new stand-alone hybrid power system with a wind turbine generator and photovoltaic modules for a small-scale radio base station. We studied the system characteristics by simulation of operation on Yonaguni Island, where wind speed exceeds 4.0m/s throughout the year, and average annual wind speed is about 7.0m/s. The results of simulation show that, to attain a system operation rate of 100%, the base station equipment requires a wind turbine generator output power of 8kW, a photovoltaic output power of 7.6kW, and 3-day backup storage batteries.

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The authors have been studying a new approach for modal analysis of large power systems that utilizes GPS-based synchronous measurement technology. The approach is based on the identification of a linearized Multi-Input Multi-Output model of power system. Since the identified model expresses approximately the electromechanical dynamics of actual power system, modal frequencies, dampings and mode shapes corresponding to electromechanical modes can be estimated as eigenvalues and eigenvectors of the identified model. In the paper, in order to advance our approach to a practical technique, it is mainly discussed how to select a small number of machines suitable for measurement locations to estimate eigenvalues associated with dominant slow modes. Such machines can be detected by identifying coherent groups related to the slow modes. The reference generators that behave representatively in each coherent group are the optimal ones to be measured. Therefore, the slow modes can be obtained by observing one generator from each group. The verification of the new modal analysis and coherency-based machine selection is done through simulation studies using IEEJ EAST 10-machine system model.

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We have proposed a method which can smooth a short-term change in PV system's output by suppressing a response of MPPT against a rapid insolation change. Because our proposed method does not convert insolation to electricity when insolation changes rapidly, it might increase energy conversion loss and decrease economy of a PV system. Comparative assessment on economics was made for two PV systems equipped with an output smoothing function, i.e. our proposed system adjusting MPPT and a battery system. By using the data on insolation for a year, we evaluated the energy conversion loss of PV system, which utilizes the proposed MPPT for smoothing the output. Then, taking into account the required capacity of battery, we compared the annual cost for smoothing PV system's output. The result suggests that the proposed method could be more economical relative to the smoothing method using a battery with future target cost.

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The breakdown voltage of high temperature CO₂ was measured at temperatures around 4000K and in the temperature from 300 to 700K at an absolute pressure of 0.1MPa. A voltage was applied to the high temperature CO₂ through a set of two rod electrodes made of stainless steel with a diameter of 2mm. The gap length between the electrodes was adjusted to be of 1mm. The breakdown voltage of the hot CO₂ proved to decrease in inverse proportion to the increase in temperature, in the range from 300 to 700K. Further increase in temperature of the CO₂ reduced the breakdown voltage more markedly. For example, at 4000 K the breakdown voltage was measured to be of 55V. This breakdown voltage is only 1.1% of that at room temperature.

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In the purpose to find an alternative gas to SF₆, this paper describes the results of current-interruption experiment for a rotary-arc type of load-break switch filled with CO₂, H₂, He and SF₆ at an absolute pressure of 0.1MPa in case of ring electrode made of stainless steel. In addition, in case of the switch filled with CO₂, current-interruption experiments were also performed for the ring electrode made of copper. The interrupting capability was found to be higher in order of SF₆, H₂, CO₂ and He. Moreover, the switch proved to have the higher current-interrupting capability for the copper than for the stainless steel. The phenomenon was found to arise from change in magnetic flux in an inner space of a ring electrode, depending the electrode material. This change in the magnetic flux also proved to result from variation of a resistance of the ring electrode.

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Influence of POM (polyoxymethylene), PE (polyethylene) and PMMA (polymethylmethacrylate) polymer solid powder injections on thermal plasmas was experimentally investigated for the fundamental study of ablation phenomena in a circuit breaker. For this purpose, the inductively coupled thermal plasma (ICTP) technique was used to sustain Ar thermal plasmas at atmospheric pressure at a high-power of 80kW. Spectroscopic observation was carried out to measure the radiation intensity of Ar I, H I and C I lines emitted from the thermal plasma. The excitation temperature of Ar atom was estimated from the relative ratio of the Ar spectral line intensities. The temperature around the center axis was found to decrease by the injection of polymer solid powders. The estimation method of polymer vapor concentrations in thermal plasmas was developed using the calculated emission coefficient ratios of the specified spectral lines. The radial distribution of polymer vapor concentrations was evaluated on the assumption of local thermal equilibrium. From the results, it was found that the polymer vapor was about 0.5-1.0% in the experiments, and that PMMA vapor seemed to have a higher plasma cooling efficiency than PE and POM.

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The repainting cycle depends on removal of rust in maintenance of outdoor steel-frame structural facilities. However existing stripping process, which is usually made by hands with brushes, cannot strip the rust completely in maintenance of power transmission towers, for example. To solve this problem, we investigated laser fluence and pulse width for removal of rust using DPSSL (Diode Pumped Solid State Laser), and selected optimum laser supply. Then we checked the effect of laser stripping on prolongation of the repainting cycle compared with the conventional stripping process. Utilizing results of the research, we developed rust stripping system using DPSSL. From the results of field trial of rust removal operation using this system at high places of a power transmission tower, possibility of practical use of the system for the maintenance was confirmed.

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When the lightning occurs at the neighborhood of outdoor high voltage distribution lines, the creeping discharges propagate along the wire surface from the binding wire tip just after the flashover of insulator. These discharges give rise to the various disasters at distribution lines, for instance, disconnection and melting of wire, punch-through breakdown etc. We must clarify the creeping discharge characteristics under various inductive lightning surges from a viewpoint of a safety in high voltage distribution systems. In our previous paper, it was reported that the lengths and aspects of the negative creeping discharges were influenced by the duration of wave front of impulse voltage applied to the central line under the grounded binding wire. The present study was accomplished in order to obtain more information on such creeping discharges.
This paper describes the distinctive characteristics of creeping discharge along the insulated wire surface when the impulse voltages with various durations of wave front are applied to the binding wire.

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