Partial discharge (PD) phenomena are the major factors of insulation degradation to determine the life of high voltage power apparatus, and have been investigated from various viewpoints. In this paper, authors proposed an integral equation in order to explain the complex characteristics of partial discharge using very simple three-capacitance model with several numerical solutions at various applied voltage conditions. The φ-n distribution patterns are calculated by the integral equation and are compared with those obtained by Mote-Carlo Simulation. PD characteristic for low voltage conditions, in which only one PD pulse occurs within a half cycle of applied AC voltage, was already analyzed analytically. In this paper, PD characteristics have been analyzed for more complicated conditions in which multiple PD pluses occur in a half cycle of applied AC voltage as well as asymmetric electrode conditions.

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This paper deals with the method of partial discharge (PD) detection with the sensor (antenna) put at the outside of the GIS tank. The flange of the spacer is paid attention as a leakage place of the UHF from the PD. Three kinds of antennas are proposed and made for trial purposes. And one commercial antenna is selected for this study. Comparative studies of the four antennas with the internal PD sensor (disk coupler) used worldwide so far are made from the viewpoint of the sensitivity characteristics. The difference between the sensitivity behavior of each antenna and the coupling mechanism with the electromagnetic radiation is discussed based on this result, and the sensitivity improvement plan of the antenna is considered. As a result, it has been concluded that making the feeding point of the antenna stick to the spacer flange contributes sensitivity improvement in a comparatively low bandwidth.

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Since electric cables play important roles such as power supply and information transmission, their degradation may cause a serious problem. We have been trying to monitor the degradation of cable insulation by measuring the magnitude and phase angle of impedance as a function of frequency in a very wide frequency range. The cables tested were insulated with flame-retardant ethylene propylene rubber or special heat-resistant polyvinyl chloride. They were damaged partially by peeling off their insulation layers, or aged partially by heat and γ-rays. Impedance and phase angle were measured from a terminal of the cable. The difference in impedance between the damaged and sound cables becomes clear by fast Fourier transform analyses, from which the damaged portion can be located. It can be clearly shown that this method has a potential ability to detect the degradation of cable insulation induced by physical damage, γ-ray irradiation, and thermal aging.

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This paper reports an examination of hetero-space charge trapping site in cross linked polyethylene (XLPE) using Molecular Orbital calculation. We chose a simple model for polyethylene (C₂₄H₅₀) with one molecular of acetophenone (one of cross linking byproducts), for the examination of XLPE sample. Molecular Orbital calculation can give the microscopic information of electron energy levels, electron density distributions and electro-static potential maps for the simple molecular mode of XLPE. It is presumed that the negative hetero-space charge (electron) and positive hetero-space charge (hole) were trapped at the permanent dipole of acetophenone, and the hole carrier could move in the polyethylene chain.

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Introduction of metal oxide nanoparticles to polymer composite material is known to have unique dielectric behavior and significant advantage in the electrical insulation performance of electrical power apparatus. This paper presents an attempt to derive the dielectric characteristics of polymer composite filled with the metal oxide particle which has mesoporous structure. Experiments were carried out in the epoxy composites filled with alumina microparticles which have the mesoporous structure (mesoporous-alumina/epoxy composites) with different particle content. Based on the measurement of the specific gravity of mesoporous-alumina/epoxy composites, the porosity of mesoporous-alumina particle in the epoxy matrix was found to be higher than that of nonporous-alumina particle. Furthermore, we evaluated relative permittivity of mesoporous-alumina/epoxy composites by measuring the capacitance of its specimens. As the results, we verified that the permittivity of mesoporous-alumina/epoxy composites was lower than that of nonporous-alumina/epoxy composites due to the particle porosity.

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The power module for the electrical vehicle needs electrical insulation material with high thermal conductivity. Recently, the epoxy insulating material filled with boron-nitride particles (epoxy/boron-nitride composite) is focused as an effective solution. However, the insulation performance of epoxy/boron-nitride composite was not investigated enough especially at the high temperature in which the power module was used, i.e. more than 100°C. In this paper, we investigated high temperature characteristics in electrical breakdown and conduction current of epoxy/boron-nitride composite. Breakdown test under the application of DC lamp voltage and impulse voltage clarified that the epoxy/boron-nitride composite had the constant breakdown strength even in the high temperature. Comparison of the epoxy/boron-nitride composite with previous material, which was epoxy/alumina composite, indicated that the breakdown voltage of the epoxy/boron-nitride composite in the high temperature was found to be higher than that of epoxy/alumina composite under the same thermal-transfer quantity among them. Furthermore, conduction current measurement of epoxy/boron-nitride composite in the high temperature suggested the possibility of the ionic conduction mechanism.

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Research was carried out whether it is possible to detect water trees in a low density polyethylene sheet by terahertz light. The attenuation of the reflected intensity of THz light was observed on several points in the sample under a polyvinylchloride sheet. The intensity distribution of the reflected light agrees with the distribution of water trees in the sample. Therefore, the distribution of water trees would be detectable even if the trees are invisible to naked eyes.

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Since electronic equipment is required to be smaller and lighter, an insulating material for such equipment is consequently required to be thinner. However, under a certain DC voltage, the electric field in it becomes relatively higher according to the insulating material becomes thinner. Therefore, the insulating performance under high electric field must be important in such thin films. On the other hand, it is said that a space charge accumulation in them under DC high electric field is important because sometimes an electrical breakdown occurs in them due to an enhancement of electric field induced by the accumulated space charge. To investigate the characteristics of the space charge accumulation in them, PEA (Pulsed Electroacoustic) method is usually used. However, a spatial resolution of ordinary PEA system is not enough to observe the space charge distribution in thin films with thickness of several tens μm. Therefore, a new measurement system with high positional resolution is developed by making a thin piezo-electric film that is used as a sensor for PEA system. The obtained resolution of the developed system is 4 μm, and it is used for a typical measurement in LDPE film with thickness of 40 μm.

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Real time space charge measurement systems are also required to observe the localized space charge distribution in insulating materials. Since the space charge behavior is generally transient, a real time measurement system will be also required in the two or three dimensional (2D or 3D) space charge measurement systems. A 2D sensor array PEA system has been developed. However, the number of sensors is limited by A/D converter channel, because the cost of A/D converter is expensive. So, an improved 2D space charge measurement system in lateral and thickness direction for transient space charge has been developed by using the sensor array and semiconductor analog switch unit in the PEA method.

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It is crucial for proper insulation design of cast resin transformer to consider voids and delamination which might exist in cast molding because of several surface boundaries between resin and conductor. Such defects in the insulator lead to reduction of the life of the apparatus. In this report, we calculate the relation between the void size and discharge time lag occurring in a model simulating the insulation system of cast resin transformer.

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Audible noise arising due to corona discharge on overhead transmission line conductors is one of the important factors in the design of the transmission line conductors. Therefore, the audible-noise characteristics of the conductors are often measured using a corona cage.
In the corona cage, an electric field distribution is generated around the conductors in much the same state as an actual situation except for in the vicinity of both ends of the conductors. Since the length of the conductors in the corona-cage test is only 30m, it is necessary to convert the measured corona-audible-noise levels to values independent of the length of the conductors and the position of the microphone to predict corona-audible-noise levels from conductors in an actual situation. In the conventional technique, the measured corona-audible-noise levels are converted assuming that the electric field distribution on the conductors is uniform, although this is not actually the case.
In this paper, we propose a new technique for converting the measured results considering the electric field distribution on transmission line conductors and confirm the validity of the assumption used in the conventional technique.

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The topcoat thickness of thermal barrier coating (TBC) samples was measured using terahertz (THz) waves. The index of refraction of yttria stabilized zirconia (YSZ), which is the topcoat material, is necessary to obtain the topcoat thickness from time domain reflectometry. Time domain THz spectroscopy was applied to YSZ samples, and the index of refraction was measured to be 4.8 in the frequency region 0.1-1.2 THz. The topcoat thickness of 6 different TBC samples, which varied from 300 to 600 μm, was measured using THz waves. The results were in agreement with microscope observation results to within measurement error. In addition, the topcoat thickness profile of a turbine blade sample was measured with 2.4 μm resolution. The profile showed a standard deviation of 4 μm, which reflects the actual variation in the topcoat thickness. The results showed that THz waves are effective for high resolution measurement of the topcoat thickness.

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Electromagnetic (EM) radiation from information hardware under normal operating conditions can compromise secret information (EM information leakage), for example, operations or processed data contained in the hardware. Methods for analyzing EM radiation with the intention of extracting secret information have been proposed, and EM side-channel attacks on cryptographic hardware are a major concern. This paper investigates how EM information leakage changes with the configuration of information hardware, focusing on the frequency characteristics of the hardware. We assume that frequency characteristics of the EM radiation correspond to physical aspects of the hardware configuration. To address the issue of information leakage, this paper presents a novel analysis of EM radiation from information hardware by using a model circuit board. Through this model we show that the intensity of EM emission can be related to the layout of the hardware.

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Absorbing characteristics and the thermal contact resistance between the stainless steel plate and the net through the electromagnetic wave absorbing composite rubber sheets were evaluated. The optimum absorbing frequency and the thermal contact resistance decreased by using rubber filled with much amount of thermally conductive magnetic spherical metal fillers. However, the maximum value of the decreasing rate of thermal contact resistance existed because higher content of fillers in the rubber sheet led to the larger hardness. Moreover, the maximum value shifted for higher content of fillers due to the decrease in the hole size of the stainless steel net. Therefore, it was found that the balance of thermal conductivity and hardness of the composite rubber was important and the optimum balance could be evaluated by the present method.

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The partial discharge (PD) generated by the surge voltage is an issue in inverter-fed motor for the reliability of the electrical insulation. The measurement of PD waveform with a wide frequency range is one way to investigate this PD. However, measurement of the PD waveform under inverter surge voltage is not easy, because of the rapid rising time of the applied voltage. In this paper, the detecting circuit and the analysis method were studied to construct a novel analysis system for the PD current waveform with wide frequency range under the application of rapid rising voltage. A detecting circuit containing a detecting resistance, a coupling capacitor and a resistance for suppressing the ringing brought appropriate current waveform under a surge voltage application. It is also recognized that the PD current waveform is only extracted from the detected current waveform using a transfer function calculated by a voltage and current waveforms without PD. Furthermore, this system on the PD analysis may further be useful to clarify the PD mechanism under a surge voltage application because the PD current waveform, which contains information on PD mechanism, was extracted without waveform change.

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In order to study the acoustic noise generated by transformer cores, the authors have made many 3-phase model transformers, and have measured the noise levels. A unique behavior was found in one result of the noise measurements. The clamping pressures of 0.15MPa and 0.30MPa were applied on the model transformers. In the case of 0.15MPa, the noise levels at the flux densities of 1.5T and 1.6T were unnaturally high in comparison with 0.30MPa. In addition, the harmonic components in high frequency range were higher in the noise spectra at those flux densities. Concerning about the cause of the noise increase, it was assumed that the irregular overlap made in the core joint by accident formed the gap between the core sheets, so that the impact at the end of the sheet was caused by the vibration generated by magnetic attractive force, consequently, impulse sound was generated. For more detailed study, the model core for the investigation on core joints was built. The irregular overlap was intentionally made in the joint, and the waveform of sound pressure was measured. The impulse sound appeared on the measured waveform.

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We developed the new power supply that is able to output various kinds of surge voltage waveform and investigated partial discharge resistance of the nano-composite enameled wires using colloid solution mixing method. Experimental results revealed the relationship between surge voltage waveform and failure time of voltage endurance, as well as the difference in the strength and frequency of the partial discharge under the various kinds of surge voltage waveform. In addition, the developed nano-composite enameled wires have been verified to contribute to the improvement of the motor quality until the present time because long lifetime was confirmed in voltage endurance test with the damaged enameled wire and actual motor.

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The principle of sound production in human whistling is not well-known. The purpose of this letter is to study on the principle of sound production in human whistling using physical models of the human vocal tract. This letter shows that the whistling resonant mode is not also Helmholtz resonance, but also air-column resonance.

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