Research

研究現況 / Current Research Projects (2015)
日高・熊田研究室では、計測手法の開発を武器に

  1. 高電界・放電現象の解明
  2. 高電圧・大電流機器の絶縁技術
  3. スマートパワー機器への新展開

等に取り組んでいます。
今年度の詳細な研究現況は以下のようになっています。

The research topic-area are:

  1. Clarification of high voltage and electrical discharge phenomena
  2. Insulation technology of high voltage and high current equipment.
  3. Application to advanced smart power appratus

The details of each topic are listed as follows:

レーザ波面計測による放電中の電子密度測定
Electron Density Measurement in Arc Discharge by Wave-front Sensor
稲田優貴・松岡成居・熊田亜紀子・池田久利・日高邦彦
Y. INADA, S. MATSUOKA, A. KUMADA, H. IKEDA and K. HIDAKA
雷放電の研究および耐雷技術の開発、ガス絶縁機器の開発や放電プラズマ応用機器の開発などには、過渡的な放電現象の機構解明が求められており、放電に関する基礎物理量の1つである電子密度計測は特に重要である。本年度はシャックハルトマン型レーザ波面測定装置を用いてSF6ガス吹付けアーク内の2次元電子密度分布を測定し、電流遮断の成否と電子密度分布の相関関係を検討した。これにより、局所的に電子密度を低下させた方がアークの遮断には有利であることを明らかにした。
It has been needed to clarify the discharge process for lightning protection, efficient plasma reactors, and designing power apparatuses such as gas insulated switchgears. The study on discharge mechanism is possible through the measurement of fundamental physical quantities such as electron density, ion density, and electric field. The Shack-Hartmann type laser wave-front sensors were used for measuring 2-dimensional electron density distributions over long-gap decaying arcs in a free-recovery condition confined by a gas -blast nozzle simulating an actual arc-quenching chamber in gas circuit breakers. The successful acquisition of spatiotemporal electron density behaviors in several kinds of gas atmosphere demonstrated the feasibility of this technology to achieve the development of a next-generation-type gas circuit breaker with high performance and reliability and the effective searching of SF6 alternative gas.
直流電界下における絶縁物の帯電現象
Charge Accumulation on an Insulator under DC Electric Field
須田涼介・岩渕大行・松岡成居・熊田亜紀子・日高邦彦
R. SUDA, S. MATSUOKA, A. KUMADA and K. HIDAKA
ガス絶縁開閉機器(GIS)は、交流に用いられる場合においても断路器開極時に最大で運転電圧分の直流電圧が残留し、スペーサ近傍の電界分布は、容量分布に基づいて決定される場から、抵抗分布に基づいて決定される場へと移行する。抵抗場への移行に伴いスペーサとガスの界面には帯電が生じ、逆極性の電圧が加わった場合の破壊電圧の低下が指摘されている。本研究では、電力機器のコンパクト化、高耐圧化を目指し、GIS絶縁スペーサを模擬した絶縁物に直流を印加した際の帯電現象について、実験とシミュレーションの両面から検証を行っている。本年度は、印加電圧を高圧化することで放電や電子放出が帯電に与える影響を調査し、またSF6圧力を変化させることで気中導電の影響を調査している。シミュレーションにおいては、表面抵抗率の電界依存性を計算に組み込むことで精度を高めることに成功し、また任意の電荷が蓄積している状態での帯電の変化や、表面抵抗率が温度と電界の両方に依存した場合の計算手法についても開発を進めた。そのほか、測定方法を工夫することで帯電測定の時間分解能を高めることにも成功している。
Gas insulated switchgears (GIS) are widely used as major substation equipment because of their excellent insulation performance. However, when a DC voltage is applied to an insulating spacer in GIS, charges are accumulated on the surface of the insulator, and the breakdown voltage of it may become low. The charge accumulation phenomenon is also a problem in AC-GIS, because the switching operations may leave the residual DC charges on the AC-GIS spacer. We are now investigating three topics about charge accumulation phenomena. First, we are researching the fillers of epoxy-resin spacer and its influence on charge accumulation on the surface. Furthermore, this experimental setup is developed in terms of guarding triple junction. Second, the numerical simulation of charge accumulation phenomena was also conducted taking the volume conductivities and relative permittivities of the spacer and SF6 gas into account. It is based on electrical conduction of charge/ and on advection-diffusion of ions in gas. Third, we are investigating temperature distribution on GIS spacer and its influence on charge accumulation phenomena under DC field. During normal operation where rated current goes thorough GIS as the load current, the temperature of the central conductor exceeds 80℃ due to the Joule heating besides the temperature of the outer conductor is kept to the ambient temperature, i.e., below 40℃
マイクロギャップにおける沿面放電現象
Surface Discharge in Micrometer-scale Gap
岩渕大行・岡野俊樹・松岡成居・熊田亜紀子・日高邦彦
H. IWABUCHI, T. MORIMOTO, S. MATSUOKA, A. KUMADA and K. HIDAKA
数μm以下の微小ギャップ(マイクロギャップ)における絶縁破壊現象の解明は、MEMS等の信頼性確保の観点から喫緊の課題である。絶縁物表面のマイクロギャップにおける絶縁破壊特性はこれまでも数多く報告されているが、その特性は報告者によって大きく異なっているのが現状である。そこで本研究では、SiO2ウェハ上に作成した金属電極対を用いて放電の解析を行い、マイクロギャップにおける沿面放電現象の支配要因の解明を目指す。本年度は金属電極対の材料をタングステン、及びチタンに変更し、前駆電流特性、絶縁破壊特性の測定を実施した。その結果、負極性インパルス印加時の絶縁破壊電圧はタングステン電極とチタン電極でほぼ同一の値を示した。これは、負極性インパルス印加時の絶縁破壊電圧は、陰極表面の電界値によって決定されることを示唆している。負極性インパルス印加時の陰極表面の電界は109 V/mを超えるオーダに達するため、陰極材料の仕事関数の影響が小さくなったものと考えられる。
With the miniaturization of MEMS (micro electro-mechanical systems) devices, the insulation width and the separation between electrodes in such devices have been accordingly reduced. Consequently, electrical breakdown phenomenon across micrometer-scale gap is of great practical interest for insulation designing of miniaturized devices. In this research, breakdown and pre-breakdown phenomena under impulse voltage application across micro-meter scale gaps fabricated on silicon dioxide wafers were investigated. In this year, we have conducted simulation on micro-discharge by using PIC-MCC method. As a result, considering the electron flow-in from the side of the cathode, electrons were concentrated between the side of the cathode and the insulator surface. Therefore electric discharge is not caused in this condition. However considering the electron flow-in from the top of the cathode, electrons emitted from the top of the cathode can collide to the insulator surface and secondary electron can be emitted. The simulated result is consistent to the experimental results.
CF3I混合ガスの絶縁特性
Discharge characteristics of CF3I gas mixture and its applicability to Gas insulated transmission lines
竪山 智博・松岡成居・熊田亜紀子・日高邦彦
C. Tateyama, S. Matsuoka, A. Kumada and K. Hidaka
過去の研究からCF3Iを電力機器に実用化する際には、ガス絶縁開閉装置のような複雑な機構を持つものよりも、管路気中送電のような単純な形状のものがふさわしいと考えられる。そのような電力機器の絶縁媒体に適用するには、絶縁性能、飽和蒸気圧、液化温度、そしてGWPという観点から、総合的にバランスがとれた性質のガスが望ましい。CF3I/N2、CF3I/CO2 、CF3I/SF6混合ガスを対象にこれらの観点からの数値化による簡易ランキング評価を試みた。その結果、検討した混合比においてはN2、CO2の単体と並んで、それらにCF3Iを20%混合したものが電力機器への適用性が高いバランスがとれたガスであるという結果を得た。
SF6 gas is commonly used for high-voltage apparatus due to its superior properties as an insulation medium. However SF6 has a considerably negative impact on the environment, so its use and emission are requested to be regulated. As an alternative insulation medium, CF3I came under the spotlight. In our study, we have obtained the insulation characteristics such as V-t characteristics, 50% breakdown voltage by using Steep-front square pulse generator. CF3I has a low environmental impact and shows great insulation performance in a uniform field, but the drawbacks of CF3I are that the saturated vapor pressure is so low that CF3I is liquefied under high pressure, that its performance degrades considerably in a non-uniform field, and that by-product generated by discharge is the cause of degradation of insulation strength. Taking these drawbacks into account, we concluded that it was promising practically to apply CF3I/CO2 and CF3I/N2 gas mixtures to gas insulated transmission lines (GIL). In addition, we investigated whether CF3I gas mixtures could be applied to existing GIL with considering not only insulation strength but also heat-transfer characteristics.
ポッケルス効果を用いた電圧回転機電界緩和システムの電位分布計測
Potential Distribution Measurement on Stress Grading System of High-Voltage Rotating Machines by Using Pockels Effect
中村隆央・松岡成居・熊田亜紀子・日高邦彦・池田久利
T. Nakamura, Y. Morita, S. Matsuoka, A. Kumada, H. Ikeda and K. Hidaka
近年,省エネルギー化や制御の容易さの観点からインバータ駆動モータの導入が増加している。それに伴いインバータサージがモータの絶縁に与える影響が懸念されている。高圧モータにおいては鉄心付近の電界緩和システムの劣化が指摘されており,インバータ駆動に対応した絶縁設計をするために,電界緩和システムの表面電位分布を実測して評価することが望まれる。本研究では、高電圧を印加時の電界緩和システム表面の電位分布測定を行うため,ポッケルス効果を用いた測定システムの開発を行った。本測定システムを用いて,250nsで立ち上がる繰り返しインパルス印加時の電位分布を測定した。同時に温度分布の測定,部分放電の観測も行った。その結果,繰り返しインパルス印加時には立ち上がり時には低抵抗層部に,立ち下がり時に半導電層部に強い電界ストレスがかかっていることが明らかになった。
The importance of inverter fed drives to control high voltage motors has been increasing for energy saving. However, these drives using pulse width modulation are known to have adverse effects on the insulation system for motors especially in which stress grading materials are used in the end-winding design. The experimental information on the potential distribution is essential for advanced designing of end-winding insulation system.  In this study, a surface potential measuring system is developed utilizing Pockels sensor in longitudinal mode and applied it to the potential distribution measurement on the stress grading system of a model bar-coil under repetitive impulses, PWM voltages, DC biased voltage. In addition, measurement of temperature distribution and observation of light emission have been conducted. As a result, it turns out that under the application of repetitive impulses electrical field is concentrated on the corona armor tape during the wave-front, and on the semi-conductive tape during the wave-tale. In addition, computed results which are consistent with measured result has been obtained by using FEM. We can propose a more reliable insulation system with this analysis.
超電導ケーブルの部分放電測定
Breakdown Characteristic in HTS Cable
湯朝 雅信・松岡成居・熊田亜紀子・日高邦彦
M. YuasaA, S. Matsuoka, A. Kumada and K. Hidaka
都心部へ給電する電力ケーブルは送電容量の向上が望まれている。高温超電導ケーブル(High Temperature Superconducting Cable = HTSケーブル)は、高温超電導線材を導体に使用することにより、送電ロスを大幅に減らすことができ、軽量かつコンパクトで大容量の送電が可能となる。HTSケーブルの電気絶縁システムは、絶縁紙PPLP(Poly-Propylene Laminated Paper)と液体窒素の複合絶縁となる。既存のOFケーブルとは放電機構が異なり、従って液体窒素含浸時のPPLPの絶縁破壊および部分放電の体系的解明が望まれている。本研究では、PPLPの絶縁特性の体系的把握を目的とし、気体窒素中および液体窒素含浸時の部分放電特性及び絶縁破壊特性の比較を行う。本年度は、1.0MPaの気体窒素中において、PPLPの厚みが異なる複数のサンプルを用いた絶縁破壊電圧の体積効果の検証と1.0MPaの気体窒素中における5枚厚シートモデルの長時間V-t特性の観測を行った。得られた結果から、気体窒素中での出荷試験の代替試験において安全に試験できる電圧のレベルの提案を行った。
Nowadays, electrical cables that provide power to urban regions are nearly in the full of their capacity, and it is wanted to expand transmission capacity. High Temperature Superconducting (HTS) Cables, whose conductor is made of HTS material, can lessen transmission loss exceedingly and enable more lightweight, compact and high-capacity transmission system. HTS cable electrical insulation system consists of insulation paper PPLP and liquid N2. The discharge structure is different from that of OF cable, so that it is need to solve the destruction and partial discharge structure of PPLP in the condition of liquid N2. In this research, on the purpose of understanding insulation characteristics of PPLP, we compare partial discharge characteristics in the condition of N2 gas and liquid N2. In this year, we measured the characteristics of Breakdown voltage and long time V-t characteristic , and investigated volume effect using PPLP sheets/cable models which has different volume. By comparing the long time V-t characteristic in 1.0 MPa-N2 gas with PD inception voltage in 1.0 MPa-N2 gas, we have proposed the safe level of test voltage for shipping inspection in 1.0 MPa-N2 gas.
IGBTモジュール絶縁用ゲルにおける部分放電現象
Partial Discharges in Gel for IGBTs
佐藤正寛・松岡成居・熊田亜紀子・日高邦彦
M. Sato, S. Matsuoka, A. Kumada and K. Hidaka
IGBTモジュールはGTOと比べて優れた点が多いが、耐圧不足から現在では両者が共存している。従ってIGBTの高耐圧化が期待されている。特にゲルを用いた絶縁においては基板上の沿面放電が課題の一つであるものの、バルクとしての自己修復特性が報告されている程度であり、沿面での現象は不明な点が多い。部分放電の起点とされるボイドの残留を定量的に考察し、これを消滅する方法を定量的に予測し、実験により確認したところ理論が測定結果をよく説明した。以上を踏まえボイドレス試料の作成手法を提唱した。また、提案手法により、基板上の電極端が粗いサンプルを用いたとき、部分放電開始電圧を上昇することがができた。ゲル基板界面の沿面放電現象を解明することを目的に、ゲル中の沿面放電進展に伴う電位分布を高い空間分解能で把握できる測定装置の開発及び測定系の分解能の評価を行った。さらに光学系素子の選定、データ処理手法の改善により倍率の上昇に伴い顕在化した回折の影響を抑制した。結果逆算を含めた空間分解能は現状の系では80μmまた程度であることが分かった。ゲル中の沿面放電時の電位分布の時間応答を取得した。ゲル中のキャビティーの挙動を観察し、粘弾性体の構成方程式を用いることでゲル中の放電現象を定量的に評価する手法を提案し、これをゲル中の沿面放電に適用し、解析した。この結果とポッケルス効果により得られた結果を合わせることでゲル中の放電現象の描像が明らかになった。
IGBTs are used for power modules and the sales are growing rapidly. Comparing it with GTOs, it has better electrical properties and it is easier to handle. However IGBTs has not yet ousted GTOs. This is because IGBT have lower operating voltages. Therefore it is essential to improve the operating voltage. The objective of this research is to improve the partial discharge inception voltage of IGBTs by studying how discharge initiates. To analyze PDs, three information; time, coordinates and electrical potential is acquired at once by using the Pockels effect. To reduce noise, Tickonov’s regularization theory is applied. This calculation imposes the spatial resolution, and it was about 80mm. The potential distribution of PDs was obtained. The metallization edges and the interfaces in silicone gel have been pointed out as the weakest points in insulation where partial discharge easily occurs. It has been, therefore, desired to develop a void-free encapsulating technique with silicone gel. The capability of degassing of defects is discussed quantitatively. It turned out that the gas in these defects cannot be completely removed by vacuum degasifying. Next, the infiltration of liquid gel into defects is discussed quantitatively. This theoretical analysis is also experimentally checked by monitoring the infiltration of liquid gel into a pierced PMMA plate. The measured results were in good agreement with the proposed model. From the results we have proposed an effective encapsulation technique. This reduced the amplitude and number of PDs. We have proposed an analysis procedure of discharges within cavities based on the motion observation in viscoelastic material. The proposed procedure was applied to surface discharges in silicone-gel. The results indicated that streamers propagates through the tree structure of the cavity and accumulate electrical charges at the void surface at the tip of the cavity. The temporal response of surface charges had a strong asymmetry according to the polarity of the applied field in contrast to the symmetry of the amplitude of partial discharges. The amount of charge accumulated in a void was calculated to be approximately 0.1-1pC. For voids near the electrode, the increase of surface conductivity was observed whereas voids at the tip of the cavity are non-conductive. The maximum stopping length of cavities on AlN substrate was more than twice than that on other substrates, due to the increase of the conductivity of cavity path. Energy dispersive X-ray spectroscopy analysis showed that the increase in conductivity was presumably due to the reduction of nitrogen component. We have experimentally shown that oxidation treatment of the AlN substrate significantly reduces the cavity stopping length. Surface oxidation of AlN substrate surface increases the resistivity to degradation by surface discharges while retaining most of its thermal properties
真空遮断器におけるNSDD現象
Effect of micro particle in vacuum interrupter
阿部 圭佑・松岡成居・熊田亜紀子・日髙邦彦
K. Abe, S. Matsuoka, A. Kumada and K. Hidaka
空遮断器特有の放電現象として、非持続性放電「Non Sustained Disruptive Discharge (NSDD)」が生じることが知られている。先行研究から電極間に存在する微小な金属粒子の運動がNSDDのトリガになっているという説が有力であることが分かっているが、実際に粒子の運動の様子を詳しく観測した例は少なく、そのメカニズムは未だ解明されたとは言えない。そこで、本研究では高速度カメラを用いて、高電圧印加中の真空ギャップ間の粒子の運動と電界放出電流とを同時に観測することのできる実験系を立ち上げ、粒子の運動が放電現象に与える影響を調査した。銅粒子をあらかじめギャップ間に注入した状態で電圧を印加し、粒子の位置、速度の時間変化と電界放出電流を測定した結果、電極に衝突した際、電極から跳ね返る粒子と電極に付着する粒子が存在していた。電極から跳ね返る粒子は交流電圧の瞬時値と同期して速くなったり遅くなったりしながら電極間を移動していたのに対し、電極に付着する粒子は一度電極に付着すると再び動き始めるのは電圧極性が反転する半周期後以降であり、電極に付着するタイプの粒子は電圧零点付近で高速で移動している事例が観測された。セラミック粒子を用いた試験行うことで、電極に付着するタイプの粒子は酸化被膜を持った銅粒子など何らかの要因で電極間に存在する絶縁物粒子であることを突き止めた。また、この絶縁物粒子の電極への衝突に起因すると思われる放電をいくつか観測した。
In the middle voltage class, vacuum circuit breakers (VCBs) are widely used due to merit such as life span and size. In order to improve its dielectric strength, vacuum discharge phenomena must be clarified. However, most of its inception process is unknown. It is known that micro metal particle is one of the causes of vacuum discharge. In the previous research, particle induced discharge was observed. However, the result is not explained clearly. In this study, the deformation length of electrode caused by particle collision was calculated using classical mechanics. After that, the critical velocity to generate metallic vapor was calculated. It was found out that the deformation length highly depends on particle size and velocity, and it was sub 10 micron meter in the calculation. The critical velocity was about 900m/s. Therefore, it is natural to say that temperature rise due to particle collision is not key factor. And the case that particle has protrusion and emits electron from the tip was also simulated. As a result, it was turned out that probable electric field around protrusion was needed to vaporize. As a future work, we would like to understand particle phenomena by comparing simulation with experimental result.
次世代航空機用燃料タンクにおける効果的徐電法の検討
Monitoring of Electrostatic Activity in Aeroplanes with Carbon Fiber Composite Fuel Tank Structure
福山 佳佑・松岡成居・熊田亜紀子・日高邦彦
K. Fukuyama, S. Matsuoka, A. Kumada and K. Hidaka
近年、CFRP材が航空機に構造体に用いられるようになってきた。CFRPは軽くて丈夫であり、航空機への適性が高い物質であるが、航空機の燃料タンクにおいてどの程度の電界が発生し、
それによる放電の可能性はあるのかを見極める技術を得ることが急務となっている。そこで燃料タンク内の航空機燃料の帯電現象について調査を行い,帯電によるスパーク現象の発生を推定する手法を開発することを目的として研究を開始した。具体的には、燃料タンクに帯電した液体を封入したときの電荷密度分布の経時変化を差分法により解析するとともに、燃料模擬液体(シリコンオイル)を用いた実験によるタンク内壁の表面電位測定結果との比較を行った。タンク内壁の導電率や、タンク内壁に配置する接地露出箇所の形状が与える影響を解析、実験の両面から検討した。今後は、解析モデルの精緻化をはかるとともに、荷電電荷量の正確な把握ができるよう装置の改良を行う予定である。4種類の航空機模擬燃料タンクを用意し、材質やプライマーの塗り方によって除電過程がどのように変化するかを検証した。プライマーは除電にあまり影響を与えないということがわかった。
In recent years, carbon-fiber-reinforced plastic (CFRP) has been adopted to aircraft’s main body material, owing to its high strength-to-weight ratio and very good rigidity. Generation and accumulation of electrostatic charge during this type of aeroplane refueling is recognized as a potential hazard capable of producing incendiary discharge. To figure out the discharging process, the potential distribution on the inner surface of model fuel tank with electrified silicone oil, which is used as an alternative of liquid fuel, was monitored. The influences of the surface conductivity and the discharging area of inner wall on the charge decaying characteristics were discussed. Using four kinds of simulated airplane fuel tank, we researched how removal of electricity changes by the material of tank or how to paint primer.
Kerr効果を利用した電界測定システムの広帯域化
Expansion of Response Bandwidth of Electro-optic Sensors by 200MHz-Modulation Technique
-Measurement of Poisson’s field-
佐藤 正寛・松岡成居・熊田亜紀子・日高邦彦
T. Kamiya, M. Sato, S. Matsuoka, A. Kumada and K. Hidaka
二次の電気光学効果である気体Kerr効果を用いた電界測定法は、媒質自体が持つKerr効果を利用するため、汎用性が高い測定法であると考えられるが、気体のKerr定数はきわめて微小な値であり、気体中の電界測定にKerr効果を利用するのは困難であるとされてきた。ところが近年、光学的変調手法を導入した高S/N比測定装置を用いることにより、気体Kerr効果を利用した電界測定が実現されつつある。この測定法は、光が有する電磁無誘導性、電気絶縁性、広帯域性などの特長を最大限に活用することができる。任意の気体を挿入できるKerr効果測定装置を用いて、従来の帯域では測定不可能とされていた雷インパルス電界の測定を実現した。
Electric field measurement method using Kerr effect in gas is considered to be a highly versatile measurement method, because all substances have Kerr effect. However, since the Kerr constant in gas is very small value, it has been difficult to utilize Kerr effect when measuring electric field in gas. In recent years, by using a high S/N ratio measuring apparatus which introduces an optical modulation scheme, the electric field measurement using Kerr effect in gas is being achieved. This measurement method can make the most of features of light: non-magnetic induction, electric non-conductance, and broadband performance. In this study 200MHz modulation technique is developed for expanding the response bandwidth of electro-optic sensor. With this technique, lightning impulse electric field, which has been considered hard to measure in a conventional method, is successfully measured by using Kerr effect in gas. In order to quantitatively examine the measurement capability of Poisson’s field using electro-optic Kerr-effect (EOKE), Kerr constants of neutral molecules and ions were examined. Kerr constants are determined by dipole moment, polarizability, and hyper polarizability of molecules. Since these values are fundamentally quantum mechanical, computations was done by means of first principle quantum chemistry methods. The computed Kerr constants for neutral molecules (N2, CO2, SF6 and CF3I) were within 50% error of the experimental values, comparable to the scattering between experimental values itself. The results showed that SF6 has smaller Kerr constants compared to those of N2 and CO2 due to its high molecular symmetry. In contrast, CF3I has higher Kerr constant due to its permanent dipole. The computed Kerr constants for anions were larger by two orders of magnitude than those of neutral molecules. The difference is probably due to the shielding effect; electrons of anions are less attracted to the nucleus and likely to polarize under external electric field. For cations, the opposite holds true. However Kerr constants contain the anisotropic polarizability term, which is strongly influenced by the anisotropy of electron density distribution, and thus can be larger for cations. As a result, the calculated Kerr constants of cations were comparable to or smaller than those of neutral molecules. The ratio of Kerr constants of ions to those of neutral molecules did not exceed 103. Thus it was shown that EOKE is valid for measuring electric field in weakly ionized gas whose ionization degree is smaller than 10-3. Poisson’s field in air at atmospheric pressure was measured by means of EOKE measurement. It was shown that we have to compensate the change in number density of neutral molecules when measuring unstable discharges.
エポキシ樹脂中の電気トリー作成と観察
X-ray visualization of the electrical tree in epoxy resin
松岡成居・熊田亜紀子・日高邦彦
H. Hirai, A.Kumada and K. Hidaka
電気トリーとは、固体材料中にできる微小な空孔であり、有機絶縁材料の内部または導体との界面にボイドやクラックなどの空隙が存在すると部分放電が生じ、トリーが発生、それが絶縁物中を進展していき最終的に全路破壊へ至ることが知られている。しかしながら、実機で使用されるエポキシ樹脂等は充填剤により不透明で、トリーの様子を観察するのは難しい。そこで本研究ではまずマイクロフォーカスX線を利用し、透明なエポキシ樹脂中にトリーを作成し光学顕微鏡とX線により観察を行った。結果として針電極先端部分に作成したトリーの観察に成功した。今後は充填剤入りエポキシ樹脂中にトリーを作成し観察を行っていく。
Electrical Tree is very small holes in organic polymer. We know that tree occurs when partial discharge arises in void or crack and tree extends, finally insulator breakdowns. But epoxy resin in electrical power equipments is opacity because it contains filler. So it is difficult to observe electrical tree in epoxy resin. In this research, by using µ-focus X-ray, we try to observe electrical tree in epoxy resin, and an other technique to know the existence of tree easily is developed. Inner wall of tree is conductive. So, according to the existence of tree, the surface voltage of epoxy samples change when applied AC50Hz to samples. In taking X-ray pictures, Firstly, we made tree in transparent epoxy and observe by optical microscope and X-ray. There are some differences between optical microscope images and X-ray images because there are differences of the tree density or composition. In the future, we are going to prepare tree in epoxy resin containing filler and observe.

マイクロ波照射PCB脱塩素化装置における水素プラズマ電子温度
PCBs Dechlorination Under Microwave Irradiation
~Quantum Chemical Approach and Experimental Consideration of Discharge Effect~
山口正太郎・松岡成居・熊田亜紀子・日高邦彦
S. Yamaguchi, S. Matsuoka, A. Kumada and K. Hidaka
当該年度はマイクロ波照射下のPd/C 触媒(IPA や絶縁油溶媒中) に見られる水素プラズマの電子温度測定を行った。まずPCB脱塩素化装置における発光はPd/C 触媒間の放電に起因するものと仮定し、Pd/C触媒間で放電可能な電界強度が形成される可能性をモーメント法に基づく電界計算により検証したところ、900W のマイクロ波照射下においてPd/C 触媒間で放電が十分起こり得る電界が形成されることがわかった。その上でPCB脱塩素化装置における電子温度の測定を行った。測定方法としては強度比法を用い、具体的にはバルマー系列の656nmと486nmの波長を利用した。まず、発光は微弱なものであるがPCB脱塩素化装置においても観測された。そして、その電子温度としてはおおまかに12000K程度であった。またマイクロ波出力と発光頻度には、正の相関関係があった。次に試験管とPCB脱塩素化装置の内部の電界が同程度になるように、低出力試験管試験をおこなった。その際の電子温度は溶液組成の影響を受けIPA:Oil = 50:50が最大であった。またその温度は10000K程度であった。そして、特徴はPCB脱塩素化装置と類似していた。10000Kという温度では水素ラジカルが発生し、PCB脱塩素化反応が促進されると推定される。
In this year, we examined reaction pathway of PCBs dechlorination using quantum chemical calculation and considered the relationship between the number of discharges and the reaction rate. As a result of consideration using the quantum chemical calculation, it was found that IPA is easily dissociated and adsorbed on Pd/C catalysts as a form of acetone, hydrogen atom, CO, or metyl group. And it seems that the adsorbed hydrogen atom is desorbed to generate hydrogen molecule only when KOH is mixed with the IPA. But its reaction mechanism is not known. On the other hand, it is revealed that PCBs are easily dechlorinated by hydrogen radical generated by the discharge. In experimental consideration, at first we calculated the minimum size of the hydrogen bubbles capable of high-frequency discharging. By this calculation, it was found that the lower environmental pressure is, the smaller bubbles can cause a discharge and there is appropriate electric field strength to discharge. This result was confirmed by experimental result that showed negative correlation between the pressure and the number of the emit. Furthermore, the presence of PCBs or a high reaction rate of the dechlorination decreased the number of the emit. It is considered that this result was caused because hydrogen atoms on Pd/C catalysts was consumed in the chemical reaction without release as hydrogen molecule to make bubbles. As a result, it was found that a cause of change in the number of discharge can divide into two patterns. One is the case that the number of hydrogen bubbles capable of discharging increase or decrease because of a change in environmental pressure or electric field. And the other is that a change in state of the reaction vary the number of hydrogen bubbles itself.
Quantitative evaluation of charge transfer in insulating material, based on first principles calculation
M. Sato, A. Kumada, K. Hidaka, T. Hirano and F. Sato
Polymeric insulators are extensively used in high voltage applications. In order to improve the reliability, durability, operating voltage, compactness, cost-efficiency and functionality of electric power equipment and transmission cables, it is necessary to understand the aging process of polymeric insulators. Although it is widely accepted that degradation of polymers are correlated with space charge which is formed in the material [1,2], there remains a lack of understanding of charge transfer (CT) phenomena, despite extensive experimental efforts. One of the most fundamental parameters required to understand CT is charge carrier mobility of the material. Unfortunately, we are still far from computing charge carrier mobility in polymeric insulators without any ad hoc assumptions or parameters; moreover we can hardly discuss qualitative characteristics of mobilities in most electrically insulating materials. This is partly due to the fact that although CT in solids is intrinsically quantum mechanical, we were unfamiliar with such treatment. Considering the above, in this research, hole mobility in polyethylene (PE) is calculated by means of standard density functional theory. It turns out that hole transfer in PE occurs in a “hopping regime”. In addition it was shown that hole mobility in PE is smaller by more than five orders of magnitude than that in naphthalene; both due to small electronic coupling between molecules and large activation energy. In addition, it is implied that the existence of carbonyl defect is likely to increase hole mobility which is consistent with experimental results at least for low density PE.