発電所から需要家に電力・エネルギーを安全に送り届けるためには，ガス絶縁開閉装置，スイッチギヤ，遮断器，避雷器などの開閉保護装置・機器が必要であり，これまでに産・学の多くの技術者や研究者の努力によりそのコンパクト化や高信頼度化などが図られてきた。例えば，遮断器に

The high-voltage switchgear is installed in the electric power system to realize a stable electric supply. SF₆ gas insulation enabled the switchgear to be compact, and its economics and reliability have been improved. Recently, as actions to prevent climate change and realize the sustainable society, reduction of environmental burdens and increase of renewable energy resources are major issue even on the high-voltage switchgear. For prevention of climate change, Alternative technology for SF₆ which is one of the global warming gases is vigorously being developed. Vacuum circuit breaker is one of the solutions and technology of vacuum insulation and interruption for high voltage level are introduced. However, extra-high-voltage level, still some breakthroughs are desired and seven requirements for SF₆ alternative technology are proposed from a working group in Japan. Moreover, for large penetration of renewable energy, the high-voltage direct-current circuit breakers are developing globally. Verification tests are in progress for proposed pure mechanical type dc circuit breaker with vacuum interrupting technology and hybrid type one with solid-state and mechanical switches.

Carbon dioxide (CO₂) is considered as one of the sulfur hexa-fluoride (SF₆) alternatives for arc-quenching gas. In this paper, polytetrafluoroethylen (PTFE) was assumed as the nozzle material of the gas circuit breaker. The dielectric properties in the hot CO₂ gas contaminated by PTFE vapor were calculated in the temperature range of 300K to 4,000K at a pressure of 0.8MPa. In this calculation, not only 48 gaseous phase species but also the carbon in solid phase one (graphite) were adopted as component species. It is derived that at temperatures below 2,000K, the critical reduced electric field strength of the hot CO₂ gas contaminated with PTFE vapor becomes higher than that of pure CO₂ as the PTFE vapor concentration increases. By contrast, in the high temperature region exceeding 2,000K, the critical reduced electric field strength is less than that of pure CO₂ when PTFE contamination is 20% or 40%. The dominant reactions governing the critical reduced electric field strength are discussed and listed in the Tables. It is concluded that the dominant reactions are brought about by the dominant particles or particles having large electron collision cross sections.

A highly accurate analysis method for compressible fluid that considers arc behavior was developed to understand physical phenomena and evaluate the interruption performance in high-voltage gas circuit breakers. Compressible fluid equations are solved with the constrained of interpolation profile method. The applications of this analysis program as a design tool for gas circuit breakers are reviewed in this paper. The following characteristics are related to interruption specifications: (i) small current interruption, (ii) hot-gas exhaustion in high current interruption, (iii) pressure build-up considering nozzle ablation, and (iv) spatial distribution of breakdown voltage just after a clearing current.

Strands of an optical fiber composite overhead ground wire (OPGW) can be broken by lightning strikes if the energy of the lightning is high. Especially, winter lightning around Japanese sea coast tends to have huge energy because of its long current duration time, therefore numbers of literatures report results of DC arc tests on OPGWs simulating winter lightning strike on them. On the other hands, short duration high current arc tests have not been conducted enough. This paper reports the results of arc tests on OPGWs using impulse current generator whose output current peak is 50kA and wave front/tail duration of 8/20μs. The arc shape was observed by high speed cameras and observation of the OPGW strand after the test was also conducted. The results seemed that the main cause of melting of the OPGW strand in the test was electric heating due to the voltage and the high current at the boundary between the strand and the arc. Taking the voltage, time variation of current density, characteristics of the material of the OPGW strand into account, simple calculation was done to estimate the melting depth and the evaporated amount of the material due to the arc. According to the results, a strand of the OPGW struck by a short-duration lightning may not be damaged seriously.

Characteristics of ignition process of polymer-ablated arc with different current values were investigated with electromagnetic thermofluid analysis. This thermofluid simulation is based on calculated particle composition, thermodynamic and transport properties of evaporated vapor of polymer material and electrode material. Polymer ablation was assumed to occur by heat flux from the arc plasma. The initiation of polymer ablation was studied for different polymer materials because polymer ablation can affect arc behavior and then arc interruption ability. Results showed that it took time of milli- to tens milliseconds to initiate polymer ablation, and that its initiation time decreases with increasing current.

In astronomy, a method to obtain spectroscopic data of two-dimensional image is used. This method is referred to as Integral Field Spectroscopy (IFS). By combining a high-speed camera system with an IFS system, it is possible to record the time evolution of a two-dimensional arc image and its spectral data. We named this method “Time-Resolved Integral Field Spectroscopy”.

The gases used in high voltage electric power equipment are required to withstand against an externally applied electric field strength. It is therefore essential to find out the electrical insulation strength of the gas. However the high temperature gas formed after the current zero through the arc extinction process in a circuit breaker shows different insulation strengths from that at room temperature, because the high temperature gas consists of various molecular products different from the original gas at room temperature. The CF₃CFCH₂ (called as HFO-1234yf) at room temperature is known to have a remarkable electrical insulation property similar to SF₆. After describing the products generated in CO₂ gas mixture with O₂ and HFO-1234yf decompositions at temperatures below 3000K, this paper mentions dielectric breakdown properties of the mixtures in view of the molar fractions of the molecular products. Discussions are furthermore made to compare dielectric breakdown properties of CO₂ gas and CO₂/O₂ gas mixture at high temperatures.

In vacuum interrupters, an insulation ability is degraded immediately after high current interruption, because of thermal electrons, metal vapors, and residual plasma. Thermal electrons and metal vapors are produced from the electrode surface, which is heated by the arc between electrodes. Therefore the electrode temperature affects its insulation ability. It is important to measure the transient of temperature distribution at anode surface after current zero, for explication of interruption phenomenon in vacuum. Two color pyrometer method with a high-speed camera for temperature measurement of electrode in vacuum was applied. Temperature of Cu-Cr spiral test electrode was measured after current zero by its method and time change of temperature distribution at anode surface was obtained. Also, relationship between interruption current and time change of anode temperature was investigated.

High-voltage gas circuit breakers (GCBs) have been developing to reduce their size and further to use an alternative gas of SF₆ which is one of greenhouse gas. Therefore, optimization of interrupter design is so important as to improve interrupting performance with compact size and/or the alternative gas of less arc extinction capability. Recent progress of analysis can lead the optimization of GCB design for higher interrupting performance. To improve quantitative evaluation of interrupting performance, it is required to model a dielectric recovery in consideration of remaining hot gas just after current interruption. The dielectric recovery in arcing zone must be evaluated dynamically and under non-uniform condition of temperature and pressure. As the first step, development of electronic avalanche was analyzed with one-dimensional flow simulation considering 26 collisional reactions of electron, ions, and neutral particles for two regions of high-temperature and low-pressure, and low-temperature and high-pressure. In this paper, the effect of low-temperature and high-pressure gas on electronic avalanches was investigated. As a result, the higher the critical electric field is in low-temperature and high-pressure, the lower the possibility of electron avalanche development is. It is concluded that the effect of electron avalanche at a gas area with largely different regions of the critical electric fields.

DC arc interruptions were carried out under following two conditions: (1) silica sand filling without any cylinder arrangement (designation: Silica), and (2) The silica sand filling with a quartz cylinder arrangement (designation: SilicaQuartz). During these experiments, optical emission spectroscopy (OES) measurements were carried out to investigate an arc column resistance rise by the quartz cylinder arrangement. An arc temperature T and a Cu vapor concentration were evaluated from the OES results. As a result, T were measured to be around 24 kK for the Silica condition and 17kK for the SilicaQuartz condition at a current peak. The Cu vapor concentration under the Silica condition gradually decreased with T decaying. On the other hands, the quartz cylinder arrangement in the silica sand filling space drastically decreased the Cu vapor concentration during an arc-quenching process. This drastic decrease in the Cu vapor concentration is one of key factors to increase r_col under the cylinder arrangement in the silica sand filling space. This verification result can be useful to increase an interruption capacity of fuse.

Numerical simulation was conducted for dynamic behavior of copper vapor in arcs under reduced pressure condition using the developed model. The developed model uses MPS method for atoms and ions, while it uses finite volume method for electron energy and electro-magnetic fields. In this paper, the influence of shield wall inner radius for vapor dynamics was studied on the heavy particle temperature, electron temperature and ionization degree. The particle in MPS method was assumed to be neutralized and mirror-reflected on the shield wall. As a result, the shield wall with a larger radius causes lower density of metal vapor, lower ionization degree between the electrodes.