Partial discharge (PD) resistance was evaluated for several kinds of nanocomposites. Following experimental results were obtained. Epoxy is stronger in PD resistance than polypropylene. But the enhancement of PD resistance by nano filler addition is higher for polypropylene that for epoxy. Silica and alumina nano fillers exhibit stronger PD resistance than layered silicate, when they are added into epoxy resins. Coupling agents or modifiers will help increase PD resistance. Similar level of the effect can be obtained for both cases of 5 wt% nano filler added epoxy and of 65 wt% micro filler loaded epoxy. Nano-micro composites are the strongest of all tested specimens as PD resistance. The above two experimental facts can be understood from the concept that the shortening of inter-particle distance is effective to reduce PD erosion.

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A sudden capacity increase in demand during the summer peak, or in contingencies such as malfunctioning transformers, may cause overload for normal transformers. In this paper, on the basis of examples of overloaded transformer operation in distributing substations, thermal aging testing in oil was carried out under various overload patterns, such as short time overload and long time overload, but with the winding insulation paper's life loss kept constant. From the results, various characteristics such as mean degree of polymerization and productions of furfural and (CO₂+CO), and their effects on the life loss of the insulation paper were obtained.

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We examined electrical properties of polylactic acid (PLA) with nucleating agent added. At that time, nucleating agent was added to PLA was then heat-treated at 100°C for 30 seconds. The crystallinity of the nucleating agent was added to PLA increased to more than 40%, and its crystallization speed also increased significantly. The temperature dependence of the conductivity (σ) was investigated, the σ of PLA to which nucleating agent had been added showed the tendency to become lower than the σ of PLA to which nucleating agent had not been added in σ at temperatures higher than 60°C. Furthermore, the temperature dependence of the dielectric breakdown strength (E_B) was investigated, E_B of nucleating agent was added to PLA was around 5.0 MV/cm at a temperature of 25°C. Of particular note was the fact that E_B of nucleating agent was added to PLA measured at 100°C was around 4.7 MV/cm, around 3 times greater than the E_B value for PLA to which nucleating agent had not been added. The temperature dependence of the relative dielectric constant (ε_r′) and the relative dielectric loss factor (ε_r″) was investigated, the peak dielectric absorption value of ε_r″ for the PLA to which nucleating agent had been added showed a tendency that lower than that of the PLA to which nucleating agent had not been added.

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By controlling electrochemical polymerization conditions conductive polymers have been fabricated not on the electrode but on the bottom of the electrochemical cell or in the electrolyte with needle-plane electrode structure. Poly(pyrrole), PPy with a fractal form has been successfully prepared by an electrochemical polymerization technique. The growth form of conductive polymer has been investigated as the effect of the composition of the electrolyte, that is, the kind of solvent, the kind of supporting electrolyte, and the monomer, and the difference in the concentrations, especially the effect of basic properties of the solvent such as the polarity (relative polarity measure), basicity (nucleophilic nature), that is, donor number, in addition, viscosity, relative permittivity, etc.

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Water treeing is a degradation mode of power cable with polymeric insulation. A water tree is composed of small droplets filled with water. As the conductivity in water tree is very high, it leads to dielectric breakdown when it grows up. As inside of the water tree is filled with trap sites, it is polarized with a certain distribution of relaxation time when a DC poling voltage is applied. Although its depolarization process after removing the poling voltage is determined by ambient temperature, applying a “depolarizing voltage” with the opposite polarity can accelerate the process. If a short pulse propagating through the cable is employed as a depolarization voltage, we may locate the water tree through looking at the time-resolved pulse response. This would lead to a diagnosing method with spatial resolution. In order to retain 100 m of spatial resolution, the response should be as sharp as 1 μs. As a preliminary study, a coaxial communication cable was aged to form water trees. A DC poling voltage was applied followed by a pulse voltage with opposite polarity. The rising time of the pulse was several hundreds of microseconds. A sharp pulse current response with 50 μs in width was observed, suggesting that a rapid depolarization took place. No such response was seen when the cable specimen was not aged. We concluded that the technique is quite feasible. As the response was found to be as quick as several microseconds, an experiment using 405 m-long cable, with 5 m of degraded length in the middle, was performed. It was shown that the degraded point was successfully located.

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Hydrophobicity of the polymer surface is one of the most valuable properties and it is also used as one of the deterioration indices of polymer insulator materials. This surface property has changed by many parameters, such as temperature, surface roughness, LMW fluid, etc. In this letter, the effect of parameters to the evaluation of hydrophobic condition is studied. From this research results, the deterioration condition of the polymer surface was quantitatively evaluated more accurately. By using the quantitative evaluation and diagnostic techniques, these parameters can improve the reliability of the evaluation of surface condition of the materials.

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The photoacoustic signal from the depletion layer was detected using the photoacoustic method formed within a planar metal-semiconductor-metal (MSM) structure. To measure the distribution of the photoacoustic signal from the depletion layer, the surface of the sample was illuminated and scanned by an intensity-modulated optical-beam. The amplitude and phase shifts of the observed signal increased with an increase in the reverse bias in the Schottky-barrier. The intensity distribution of the photoacoustic signal corresponded closely to the position of the photocurrent distribution showing the presence of the depletion layer measured by the photoelectric method. This demonstrates clearly that the photoacoustic signal reflects the presence of the depletion layer in semiconductor materials, and that the photoacoustic method can be used effectively for visualization of the depletion layer.

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This paper deals with the study on the possibility of an aerial flashover between a coil conductor and a casing in rotating machines under an application of lower voltage compared with Paschen's voltage even when enough insulation distance is secured. The time lag to aerial flashover originated from surface flashover was measured. To understand the aerial flashover influenced by the parameters of voltage application circuit, the aerial flashover distance was measured using cable which had a simulated pore to confirm the above consideration. A surface flashover characteristic was also measured using a photomultiplier tube (PMT). It became clear that the aerial flashover occurred at about a few milliseconds after the surface flashover generation. After showing the peak, the aerial flashover distance decreased with increasing time constant. The surface flashover time estimated by PMT output exhibited the different values with the change of a capacitance when the time constant is larger. On the other hand, the average surface flashover current was almost the same in spite of the change of a capacitance. Form these results, it was considered that the aerial flashover distance was influenced by time constant of circuit.

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Development of high efficient electrical rotating machines is an important issue in energy conservation. To realize this purpose, we have to consider details of magnetic phenomena in rotating machines. Therefore an accurate evaluation of the 2-D magnetic properties is indispensable. However, it is very difficult to measure these properties especially under high magnetic induction due to difficulty to measure rotating magnetic properties in the electrical steel sheets. In this paper, a new apparatus with 8-teeth-core, distributed windings, and inter-poles is proposed to measure the 2-D magnetic properties. We evaluate the uniformity of magnetic conditions in the specimen by using the finite element analysis.

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This paper discusses modeling of magnetization curves in non-oriented electrical steel sheet. Initial curve and hysteresis loop under 0.15 T are approximately modeled as Rayleigh model, and Rayleigh loop constants are nearly proportional to crystalline grain size. Hysteresis loops more than 0.15 T under magnetization rotation region are represented by Preisach model, grain size distribution and RD easy axis. Magnetization curves over 10 kA/m are calculated with magnetization rotation model. However, magnetization curves modeling is necessary between domain displacement model and magnetization rotation regions. Magnetization curves in this region are modeled considering field component B^N where B is flux density and N is the order of flux density and about 15.

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Computed tomography (CT) method has been used for industrial application as well as it has been mainly developed in a medical field. We have investigated the measurement of nonuniform electric field vector distributions in liquid dielectrics using an original method based on electrooptic Kerr effect and CT method. In applying CT method to the reconstruction of the electric field, a principle of CT method has been faithfully observed, which has been one of cause of the error. Specifically, region passing through of the light for measurements was not equal to the reconstructed region and the electric field was reconstructed without consideration of the value of cells outside of the region for reconstruction. So, to solve these problems, we suggested the improved algorithm for reconstruction using the concepts which we called “actual region projection data” and “extension of region for reconstruction”. By a simulation and an experiment, the usefulness of the improved method was studied.

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We conducted a first-principles examination to determine the most stable position of an icosahedral B₁₂ cluster near a Si(001) surface. We discovered that such a cluster is most stable when its center is located at the fourth layer position from the Si top surface where a Si dimer sits directly overhead. Scanning tunneling microscopy (STM) simulation revealed that Si dimers above the B₁₂ cluster are distinguishable from other dimers in STM images of low sample bias voltages.

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