Arc plasma generated by arc discharge is used in various fields due to its extraordinary characteristics as in its very high temperature and high energy density etc. On the other hand, a principle of current interruption by extinguishing the arc discharge between electrical contacts is practical and useful in many kinds of circuit breakers. The arc discharge and the electrical contacts have been well investigated, and numerous procedures have been developed. In this review paper we introduce the recent technical trend regarding arc plasma treating wastes, synthesizing new materials, and the latest circuit breakers equipped with arc plasma and electrical contacts techniques.

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Influence of polymer plates, made from Al₂O₃, PE (polyethylene), POM (polyoxymethylene), PBS (polybutylenesuccinate), PA66 (polyamide 66) installed in the vicinity of arc column, on arc properties was investigated experimentally. Arc voltage initiated between the parallel polymer plates were measured in the range of several kA. In addition, composition of gas ablated from the polymer plates during the current interruption was analyzed. Current interruption experiment for gas analysis was carried out in the sampling bag backfilled with N₂ to distinguish the ablated gas from the gas included in the air. It was found that the major composition of ablated gas was H₂ and CO.

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The arc power-loss and the arc time-constant of a CO₂ arc before the current zero during a current-interruption process were measured in a CO₂-blast quenching chamber. The CO₂ arc at a pressure of 0.1MPa showed decrease in the arc power loss from about 5 to 1.4kW with the passage of a time from -20 to -2μs and revealed decline in the arc time constant from about 5 to 1.5μs with the same elapse of the time. The increase in the pressure to 0.2MPa caused growth in the arc power loss, but resulting in no significant variation in the time constant. These dependences of the arc parameters on the pressure were explained on the basis of theoretical calculation on an extinguishing arc.

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An asymmetrical structure GCB that employed resister closing method equips an interrupter and a closing resister contact in one shield, and so the shield diameter becomes large. In this study, we investigated the optimum tank diameter and major radius of shield electrode of asymmetrical structure GCB by three-dimensional electric field calculation. We also investigated these optimum structures of symmetrical structure GCB and compared the result with that of the asymmetrical structure GCB. In conclusion, the tank diameter of asymmetrical structure GCB becomes larger than the tank diameter of symmetrical structure GCB by 24%.

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Firstly, current interrupting experiments were performed for a rotary-arc type of load-break switch filled with pure CO₂ at a total pressure of 0.1MPa. Augment in the coil turns for generating magnetic field from 1 to 1.8, 2.5 and 3.6 (arbitrary unit) proved to raise the current interrupting capability from 2.6kA to 3.2, 3.5 and 4.1kA. Secondly, experiments were performed for CO₂ gas mixture under the condition of the coil turns of 3.6. Gases of He, O₂, N₂, and air were admixted to CO₂. Adding either He or O₂ to CO₂ at the concentration of 30% allows the switch to have the higher interrupting capability than using of pure CO₂.

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To investigate the trolley breaking phenomena by the arc between the trolley and the pantograph, the phenomena have been replicated through the experiments. The element analysis of the contact strip is performed in detail and the influence of the arc on the contact strip elements and hardness of the material is investigated. As one of the hypotheses, it is expected that the decrease of the metal elements in the contact strip caused by the heat from the arc results in the decrease of the hardness of the material and finally leads to the local abrasion of the contact strip. It is confirmed through the electron probe microanalysis (EPMA), in this paper, that the copper element decrease near the arc spot. The decrease of the material hardness is also confirmed through the micro Vickers hardness analysis.

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We investigated by numerical analysis the dependence of vaporization behavior of aluminum particle injected into transferred type arc plasma on injection conditions in synthesis of aluminum nitride ultra fine particle. On the basis of calculation results, we chose one proper injection condition where aluminum particle vaporized more.

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Current zero measurements are performed for 245kV-50kA-60Hz short line fault (L90) interruption tests with a self-blast interrupting chamber (double volume system) which has the interrupting capability up to 245kV-50kA-50Hz L90. Lower L90 interruption capability is observed for longer arcing time although very high pressure rise is obtained. It may be caused by higher blowing temperature and lower blowing density for longer arcing time. Interruption criteria and a optimization method of the chamber design are discussed to improve L90 interruption capability with it. The new chambers are designed at 245kV-50kA-60Hz to improve gas density in thermal volume for long arcing time. 245kV-50kA-60Hz L90 interruptions are performed with the new chamber. The suggested optimization method is an efficient tool for the self-blast interrupting chamber design although study of computing methods is required to calculate arc conductance around current zero as a direct criterion for L90 interruption capability with higher accuracy.

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Influence of polymer powder injection into Ar thermal plasmas was investigated by numerical approaches. Thermal plasma-polymer solid coupling phenomena such as melting and evaporation were considered to study plasma-quenching effect of polymer injection. Dominant process for decay of plasma temperature was examined by changing thermodynamic parameters such as melting, boiling temperatures and their latent heats of solid and liquid polymers. As a result, thermodynamic properties of evaporated polymer vapor directly affect plasma-quenching phenomena more markedly than the properties of liquid and solid which influence plasma quenching efficiency through the amount of evaporation.

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Phenomena in power systems tend to exhibit higher nonlinearity, because efficient operation accompanies severer power transfer. In such cases, there might exist some limitation to the use of conventional linear control design scheme due to the nonlinearity. As for consideration to the nonlinearity, we have developed a nonlinear analysis method based on normal form theory. In this paper, we develop a new control design scheme based on the nonlinear analysis method.
The developed method is effective in a case when oscillatory instability occurs. In the developed method, the parameters of control devices are adjusted so as to enlarge the stability limit against the oscillatory instability, unless each eigenvalue exceed its allowable threshold. We verify the effectiveness of the developed method in the IEEJ 10-machine System Model by applying to PSS (Power System Stabilizer). We show that the power transfer limit increases by a few percent.

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