In 1989, the low-frequency superposition method was developed as an online diagnostic method for XLPE cables for 6 kV power distribution, and its application to the field has started. However, various problems became clear, and the authors developed the AC insulation resistance measurement method in 1993 with the aim of solving these problems.

Since then, the results of online diagnostics using AC insulation resistance measurement have been accumulated, and the ability to detect deterioration of water trees has been confirmed to be excellent. However, there are unclear points such as the measurement range and the validity of the measurement results. Therefore, the validity of the measurement range and measurement results was verified by numerical calculation using an equivalent circuit.

Electronic devices used in the vicinity of AC overhead transmission lines are often suffered from malfunctions due to high electric field. However, the mechanism of the malfunction has not been clarified. In this paper, a simple electric circuit which is composed of two parts was fabricated and exposed to high electric field to clarify the malfunction occurrence condition. Based on the experiments, the safe separation distance between the electronic circuit and the transmission line was derived as a function of the electric field around the overhead transmission line.

A current flowing through a smoothing inductor in power converter usually contains the DC component. Hence, an air gap is inserted to the magnetic core in order to prevent magnetic saturation. In this case, the magnetic flux which spreads out from the core causes eddy current loss at windings placed close to the air gap. The fringing loss calculation is valuable for the increase in the power density and power conversion efficiency of converter, but it is very complex due to the heavy simulation required for calculating the eddy current. In this paper, a simple method to calculate the fringing loss is introduced and is used for design of the gapped inductor used in DC/DC converter. Subsequently, the proposed method has been verified based on the experiments with three different cores. The experimental results clarify the relation between inductor structure and efficiency.

In our previous study, we developed a colorimetric indicator based on methylene blue (MB)-dyed pullulan thin films for detection of hydroxyl radicals as a novel indicator to detect active oxygen species with improved oxidative ability; however, information concerning intermolecular interactions between MB and pullulan remain insufficient. In this study, we identified MB-pullulan interactions using molecular orbital (MO) calculations for used a truncated pullulan model represented by five glucose units to investigate the large and complex pullulan structure. The results identified MB-pullulan interactions at the HF/6-31G(d) level, revealing 10 MB-pullulan complex structures with full geometry optimization. Moreover, structural and energy analyses predicted the existence of the hydrogen-bonding interactions between pullulan hydroxyl groups and MB nitrogen, carbon, or sulfur atoms. The results of MO analysis suggested the formation of hydrogen bonds between S, C, and N atoms in the MB benzene ring with a pullulan OH group groups, resulting in a lower electronic energy in the complex structure relative to that observed in the individual molecules.

We investigated and compared the dissolved nitrogen and oxygen gas amounts of mineral oils that had been treated to room air or nitrogen gas replacement, nitrogen fine bubbles (FBs) addition, and nitrogen bubbling addition respectively after degassing treatment. As a result, it was found that most of the nitrogen and oxygen dissolved in mineral oil can be removed according to the degassing treatment used in this experiment. Additionally, it was also found that the nitrogen bubbling addition treatment requires a long time of several hours or more to remove oxygen dissolved in mineral oil, and it is difficult to completely remove the oxygen. Furthermore, it was also found that the nitrogen FBs addition treatment can dissolve a large amount of nitrogen in mineral oil in a short time of than 1/60 compared with the nitrogen bubbling addition treatment.

The authors have been developed the electromagnetic wave absorbers blended with plant-carbon powders. In this study, the electromagnetic wave absorption properties of above absorbers were measured in free space. In addition, the relationship between manufacturing process and absorption characteristic was investigated in the microwave band.