Dielectric polymer composites with high thermal conductivity and high breakdown strength have wide applications in electronic devices and electrical equipment. In this study, poly(phenylene sulfide) [PPS] and boron nitride (BN) were selected for preparing high thermal conductivity composites for high temperature insulation application. The composites were prepared by melt compounding to contain 0-40.0wt% BN. Laser flash method was used to measure the thermal conductivity. As a result, the composites exhibit significantly enhanced thermal conductivity when compared with the pure polymer. For instance, the composite sample shows an increase of thermal conductivity from 0.28W/(m·K) (the pure PPS) to 1.21W/(m·K) when it contains 40.0wt% BN. Weibull statistical distribution was used to analyze the breakdown data and the characteristic breakdown strength was used to compare the breakdown strength of various samples. It was found that, except the sample containing the low concentration of BN filler, the composites show enhanced breakdown strength when compared with the pure PPS. Scanning electron microcopy (SEM) results show that the BN flakes are homogeneously distributed in the PPS matrix. Thermogravimetric analysis shows that the composites have increased thermal stability when compared with the pure PPS.

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The need of energy storage devices with higher rating for wider application range has led to a great interest among engineers and researchers in proposing better materials and preparation methods for the devices' electrodes. The paper reports our current research progress in developing a new higher rating energy storage device like an electric double-layer capacitor. New carbon materials were systematically prepared by a quick and low cost method of chemical reaction between insulating oil and high concentration sulphuric acid. The graphitic nature of the produced carbon materials were characterised by X-ray diffraction (XRD) measurement. Essential electrical properties of the carbon materials for energy storage application, such as their capacitive behavior, were investigated by cyclic voltammetry (CV) measurement. In order to observe the frequency characteristics of the carbon materials, one of the most important analytical tools known as electrochemical impedance spectroscopy (EIS) was used. The experimental results of the XRD, CV and EIS measurements are presented in forms of graphical plot.

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In this research, the partial discharge resistance was examined for eight kinds of polymer samples, namely, low-density polyethylene, polypropylene, poly-methyl-pentene, atactic polystyrene, syndiotactic polystyrene, polyethylene terephthalate, polyethylene naphthalate, and polyimide. An ac 500-Hz voltage with a designated value was applied to a sample sheet sandwiched between a pair of IEC (b) electrodes at 353 K (80°C) and 30% relative humidity for a designated period. The sheet surface degraded by partial discharges was then observed by a mechanical surface profilometer to measure the shape, from which the whole eroded volume was estimated. As a result, it has been clarified that polymers can exhibit superior partial discharge resistance when their melting point, molecular weight of chain repeating unit, density, weight ratio of benzene rings, and crystallinity are high.

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Mechanical strength simulation techniques for nanocomposite resins have been developed. Coarse grained molecular dynamics are used to calculate the nanofiller distribution in resin and the stress-strain curve (S-S curve) of nanocomposite resin. A molecular orbital method based on density functional theory in which the electrical fields from a large region (μm-mm) of surrounding resin are taken into consideration to obtain the inter-molecular forces for molecular dynamics. In addition, present simulations were applied to silica/epoxy nanocomposite resins and the following results were obtained. (1) While hydrophilic silica is uniformly distributed, hydrophobic silica forms a network in epoxy. These results agree with an experimental observation using scanning electron microscope. (2) The maximum level of stress of the calculated S-S curves of resin with hydrophobic silica is greater than that with hydrophilic silica. This result qualitatively agrees with the fracture-toughness measured by using a three-point bending test.

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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 with the integral equation and are compared with those obtained experimentally with an IEC(b) electrode system at various applied voltage frequency (25-1000 Hz). This paper is the revised version of that presented in ISEIM2011, in Kyoto.

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Since polyimide (PI) film shows a good performance as a polymeric insulating material even at high temperatures, it is used for a flexible print-circuit board (PCB). Recently, the PCB is required to be reduced in its thickness for downsizing of the electronic devices. When the thickness of insulating layer becomes much thinner, however, the applied electric field to the layer becomes much higher, and then the possibility of electrical breakdown in the layer becomes higher. Therefore we need to investigate the breakdown characteristics of thin PI film. To investigate the breakdown mechanism in polyimide film under dc stress, we have focused on space charge accumulation. It is well-known that the space charge accumulation in some polymeric materials strongly affects the breakdown characteristics under dc stress. Especially in this study, we focused on the relationship between the moisture of the sample and the breakdown strength. Through some experimental results, it was found that a certain kind of space charge always accumulates in the bulk of the sample before the electric breakdown under dc high electric field. Furthermore, it was also found that the breakdown strength and the time-to-breakdown are strongly affected by the moisture in the sample.

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To clarify the deterioration mechanism of cables installed in nuclear power plants, three kinds of XLPE sheets with differing antioxidant content were aged by 100Gy/h γ-ray irradiation at room temperature, 60°C, and 100°C. The remaining antioxidant content was estimated from the oxidation induction time using differential scanning calorimetry. The elongation at break decreases faster as the initial antioxidant content decreases. On the other hand, the evaluation parameter called oxidation degree, which is defined as the ratio of the absorbance due to carbonyl groups to that due to methylene groups obtained with infrared spectroscopy, increases with aging time. The elongation at break decreases as the oxidation degree increases, and the relationship between these two quantities can be expressed with a sigmoid master curve. Furthermore, both the elongation at break and oxidation degree show reasonably stable transitions until the antioxidant content decreases to a certain value. After this period, the elongation at break changes drastically and reaches a sufficiently low value. The experimental results reveal that there exists a threshold for antioxidant content that is needed to effectively inhibit oxidation.

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Space charge distribution and external current in low density polyethylene (LDPE) under dc high electric field were measured simultaneously using an improved pulsed electro-acoustic (PEA) measurement system. They were usually measured independently using different devices. However, to investigate the relationship between the space charge behavior and the conduction current, it is necessary to measure them simultaneously in the same sample. Therefore, we developed an improved PEA system to measure them simultaneously. In this improved system, the space charge distribution and the external current measurements are carried out by alternate switching the current measurement circuit to the PEA measurement. As the result of simultaneous measurements, it is found when the external current increases during the injection and the traveling of the positive charge from the anode towards the cathode. To explain the phenomenon, we estimated a displacement current, a conduction current and a conductivity distributions in the sample from the results of the measurements. Moreover, we examined the relationship between those distributions and the charge behavior in LDPE.

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This paper presents an attempt to derive the dc dielectric breakdown characteristic of epoxy composite containing alumina particles with mesoporous structure (Mesoporous-alumina/epoxy composite). By compounding epoxy resin and mesoporous-alumina particles which had the micrometric particle-diameter and the nanometric pore-size, mesoporous-alumina/epoxy composite was fabricated. The measurement of the specific gravity of mesoporous-alumina/epoxy composites revealed that the porosity of mesoporous-alumina particle even in the epoxy matrix was higher than that of nonporous-alumina particle. Furthermore, the measurement of the dielectric permittivity of the mesoporous-alumina/epoxy composites verified the existence of pore inside the mesoporous-alumina particle from the view point of electrical characteristics. From the breakdown test with using Mckeown electrode system, DC breakdown strength of mesoporous-alumina/epoxy composites was obtained, which was compared with that of the nonporous-alumina/epoxy composites. These results suggested that the nanometric pore with wormhole structure inside mesoporous particle could not be the critical defect for DC dielectric breakdown characteristic.

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The electric properties of hybrid organic-inorganic nanostructured coated XLPE are investigated in this paper with the purpose to understand if this class of nanostructured insulating material could have applications in the field of high voltage electrical insulation. Space charge measurements and aging tests under partial discharge activity were performed on different kinds of nanocoated specimens and the results compared to the base XLPE. The paper shows that space charge accumulation can be reduced significantly by some coatings which could increase the injection barrier. Moreover, surface erosion caused by partial discharges can be slowed down even by a thin coating of about 1μm, which creates a ‘barrier effect’ to partial discharge propagation in the insulation bulk.

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In HVDC transmission lines, hydrophobicity losing could occur even on well designed insulators, which causes the essential concern on the electrical accidents induced by the ageing of silicone rubber (SiR) insulators. Much attention has been paid on the accurate evaluation on the insulator hydrophobicity for the long-term performance of outdoor insulators in service. In this paper, based on dynamic dropping test (DDT), the acoustic characteristic of surface discharges was investigated to evaluate the hydrophobic properties of SiR insulator at different ageing degrees under dc voltage stress. The obtained results indicate that the acoustic characteristic of discharge is sensitive to the hydrophobic properties, which can be applied as a non-contact method for the hydrophobicity evaluation of HVDC insulators.

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Paper-liquid nitrogen (LN₂) composite system has been used as one of the insulating systems of the high-temperature superconducting cable. In this system, partial discharge may occur inside the N₂ gas bubbles due to the gasification of LN₂ in the insulation paper. We have been suggesting the paper-ice composite material as one of the candidates for the insulating system with LN₂ in high-temperature superconducting cables. The paper-ice composite material is an insulating paper filled with ice and it could inhibit the partial discharge inside the microscopic N₂ gas bubbles remained in the paper. This research investigated relative permittivity and dielectric loss tangent of the paper-ice composite material.

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The conduction modification is an effective method to raise the releasing ability of deposited charge in polymers under space environments. The inorganic semi-conductive filler was here chosen to modify the polytetrafluoroethylene. With this particular filler, the volume conduction of the composites varying with the temperature and electrostatic field were measured. The experimental results indicated, with different contents of filler, the temperature-dependent conduction shown a regular variation and the threshold field of nonlinear conduction property under different temperatures declined but nonlinear tendency significantly increased in particular. The modified polymer is considered to limit the level of deep charging to a safe level.

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The photoacoustic signal from the depletion layer beneath the metal electrode in a metal/semiconductor (M/S) structure was detected using the photoacoustic method. To measure the reverse-bias voltage dependence of distribution of the photoacoustic signal from the depletion layer, the surface of the electrode was illuminated and scanned by an intensity-modulated optical-beam. It was obtained that the photoacoustic signal phase differences between depletion layer generating and non-depletion layer were dependent on the depletion layer spreading. One dimensional scanning on the electrode has also revealed that spreading of a depletion layer extends from the each edges of an electrode.

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We have been designing and developing a 3-D lightning location system based on the broadband digital interferometry technique in LF bands. The LF broadband digital interferometer (LF DITF) consists of four or more LF receivers which detect electromagnetic (EM) waves in a wide frequency range from 400 Hz to 1 MHz associated with lightning discharges. Since each receiver detects EM waves in LF, the LF DITF is able to locate lightning discharges in several hundred kilometers. During the winter season in 2010-2011, a simultaneous observation of a LF DITF, a VHF DITF, and Rogowski coils was conducted in Hokuriku, Japan, which borders the Sea of Japan, for evaluation of the LF DITF for locating upward leaders and further understanding of winter lightning in Japan. We show the time series variation of the cases of a bipolar lightning flash and of an upward negative flash.

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Measurements are carried out on the breakdown voltage across a micro gap between a pair of spherical electrodes in atmosphere. The values are compared with two experimental formulas of the breakdown voltages. These data are important to discuss the dynamic characteristics of an electrostatic checker, electrical contacts and the field emission of electrons from surfaces.

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The activity of Ag supported zeolite was studied using NO oxidation after atmospheric pressure plasma treatment. The activity of bare zeolite was quite low after O₂ plasma treatment. On the other hand, the Ag supported zeolite had high oxidative activity after treatment. This activity could even be observed a day after treatment. These results indicate the active oxygen fixed on Ag surface by O₂ plasma plays a significant role in the oxidative removal of air pollutants using the plasma-catalyst hybrid system.

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