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Metal vapour plays an important role in many applications of atmospheric-pressure arcs. For example, in gas-metal arc welding, metal vapour, formed mainly by evaporation of the wire electrode, can reach a mole fraction of over 0.5, and strongly affects the arc temperature and the weld penetration. In low-voltage circuit breakers, metal vapour is formed by evaporation of the electrodes (runners) and the splitter plates, and can strongly influence the motion of the arc as it enters the splitter plates. Experimental and modelling results on the influence of metal vapour in gas-tungsten arc welding, gas-metal arc welding and low-voltage circuit breakers are reviewed. The effects of the metal vapour are explained in terms of its influence on the transport and radiative properties of the plasma.

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Surface charge decay on dielectric materials in atmospheric air was studied. A dielectric circular disc placed on a plane electrode in a rod-plane air gap was charged by positive or negative DC corona discharge. The dielectric discs with a thickness of 0.1cm made of acrylic and glass epoxy multilayer have 16.0cm in diameters. The surface potential induced from accumulated surface charge was measured by an electrostatic voltmeter which can be controlled automatically by a computer at 0.5 cm intervals in the direction of X and Y. In case of the acrylic disc, it was observed that a bell shaped initial surface potential distribution decayed into a crater like shaped with time. The simulation model based on a charge neutralization mechanism by gas ions reproduced the measured result well. In contrast, in case of the glass epoxy multilayer disc, a bell shaped initial surface potential distribution sunk overall. Furthermore, the decay rate of surface charge on glass epoxy multilayer disc was relatively fast in comparison to the acrylic case. Besides the charge neutralization, it can be considered that electric conduction through the volume of the glass epoxy multilayer occurred because of its low volume resistivity.

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In this paper, a numerical procedure for computing electromagnetic fields in a three-dimensional space using the constrained interpolation profile (CIP) method is presented. Then, this method is applied to computing electromagnetic fields, which are generated by an engineering lightning return-stroke model such as the transmission-line (TL) model, the modified TL model with exponential current decay (MTLE) or the traveling-current-source (TCS) model located on flat perfectly conducting ground, and the CIP-computed electric- and magnetic-field waveforms are compared with the corresponding waveforms computed theoretically and using the finite-difference time-domain (FDTD) method.

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At present, studies are promoted on the standard for high-voltage test techniques for UHV-class equipment. In the lightning impulse voltage test, discussions are made on the use of the relative overshoot magnitude evaluation method and waveform conversion method with k-factor which were adopted in the IEC 60060-1. However, since issues still remain in adopting these methods to UHV-class equipment, the present paper examined techniques which can evaluate the lightning impulse test waveforms reasonably. As a result, two techniques were newly established. The one is base curve extraction method and the other is new k-factor suitable for UHV-class equipment.

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To establish an optimal lightning protection method for power distribution lines, factors such as the mechanism behind lightning surges as well as power distribution network and insulation level of power distribution lines should be taken into consideration. This study experimentally clarifies the voltage-time (V-t) characteristics of currently used 6.6-kV power distribution insulators having higher lightning impulse withstand voltage (LIWV) by considering the differences in polarity and the presence or absence of slurry. Furthermore, in this paper we propose approximation formulas based on the sparkover model for calculating the flashover characteristics of 6.6-kV power distribution insulators, which can contribute to insulation coordination throughout the power distribution system.

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The paper has investigated switching and fault surges in a power system connected with dispered power sources. Based on EMTP simulation results, the effects of various parameters, such as the capacity of a main source and distributed sources, on switching overvoltage characteristics are investigated. It is found that considering the switching surge overvoltage is sufficient from the viewpoint of protection and insulation design of equipment. In a system with a large wind farm, a switching overvoltage becomes smaller. Also, EMTP simulations are carried out to investigate excessive switching overvoltages due to multiple circuit breakers and load switches operation in a distributed power station with station loads connected to a main network, and it is found that an overvoltage more than 10 times of the rated voltage appears due to inductive current interruption under a specific switching condition.

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Wind power output varies over time under the influence of meteorological conditions. Understanding these variations is indispensable to further wind power integration and effective operation of the power system in the near future. In this study, we developed time-series wind power output data of 9 power systems in Japan in the 2010 and the 2011 fiscal year for power supply-demand analysis. We analyzed the variations in time windows of 20 minutes or more. Furthermore, we evaluated the effects of output increasing rate restriction control. We found that the large variations can be absorbed by the small energy loss, and that this increasing rate restriction control is very effective against infrequent large variations.

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A circuit analysis method of a line-to-ground voltage of a solar panel when a structure for a solar panel is struck by a lightning is discussed in this paper. The transient voltage is influenced by the current distribution within the structure. A characteristic of a voltage of an output terminal of a solar panel to ground caused by a lightning is also investigated in this paper. The resonant frequency and the maximum voltage of the overvoltage are clarified. The resonant frequency is determined by inductances of the structure, a capacitance between a frame and an output terminal of a solar panel, and a stray capacitance of a solar panel. An oscillation determined by the length of the struck structure is superimposed in the case of an indirect lightning. The characteristic of the maximum induced voltage depends on the electromotive force generated by the magnetic flux which links with a frame of a solar panel. An overvoltage caused by an indirect lightning can be obtained by an equivalent circuit with mutual impedances between a struck structure and a structure for a solar panel. The calculation can be easily carried out by the Electro-Magnetic Transients Program.

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Tidal current is the flow of sea water due to the tidal phenomenon. Therefore it is possible to predict generated output of the tidal current power generation system, which is more advantageous than other renewable energy sources, when the system is connected to the power system and operated. In this paper, we propose the tidal current power generation system which can be controlled to variable speeds. The generator is a doubly fed induction generator which can reduce the inverter capacity in comparison with a synchronous generator. We examine the gear ratio and generator capacity which maximize generated energy, when the tidal current power generation system is operated using the maximum power point tracking, constant turbine output, constant stator active power, and constant rotor supply voltage control method. This paper shows that the constant rotor supply voltage control method increases generated energy and capacity factor more than other control methods.

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Azimuthal magnetic fields at a far distance (50km), generated by a lightning strike to the top of a mountain and to the top of an 80-m-high grounded object located on the top of a mountain, have been analyzed using the finite-difference time-domain (FDTD) method in the two-dimensional cylindrical coordinate system. Also, the influence of the presence of a mountain range located between the lightning strike point and field observation point on the remote azimuthal magnetic field has been studied. Azimuthal magnetic fields associated with a lightning strike to the top of a mountain are higher than those associated with the corresponding strike to a flat ground for both fast- and slow-front lightning currents. The presence of an 80-m-high strike object further increases magnetic field peaks for higher ground conductivity (≥ 1000mS/m) and shorter current risetime (≤ 1µs). The far-field enhancement due to the presence of a lightning-struck mountain decreases with decreasing the ground conductivity. The shielding effect due to a 1-km-high mountain range located between the strike point and observation point is insignificant except for relatively fast-front lightning currents.

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This letter proposes a new strategy for supply-demand control which coordinates Energy Management System (EMS) and Dynamic Pricing (DP) in distributed energy systems. Genetic Algorithm (GA) is used not only for optimizing EMS which consists of production system, but also for optimizing DP which provides optimal electricity tariffs over time of day. While the proposed strategy for supply-demand control was applied to typical daily operation of a distributed energy system, the improvement of the load factor of a distributed energy system was achieved.

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高機能な高温超電導体であるBi系高温超電導ウィスカーを電磁石に応用することができると，省スペース・低コストで且つ強力な電磁石を実現することができる。しかしながら，流すことのできる最大の電流密度が，印加される磁場の角度によって極端に変化してしまうという問題点（J_c - θ依存性）が存在し，この応用の妨げとなっている。
本研究では，この問題を解決するためにBi系高温超電導ウィスカーへMgを添加した。これにより，J_c - θ依存性を約1/7へ改善することに成功した。

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