In the last few years, the increase of the electric power demand has been remarkable, especially in Asia district. In such trend, the electric power system of Japan has been supplied with high quality, high reliability and highly-stabilized electric power. This is supported by highly-sophisticated electric power system which prides oneself on high voltage and large capacity. In this paper, outlines of these technologies are described. And, newest technology trends such as electric power liberalization, innovation of dispersed power source, effective utilization of natural energy are also explained. In addition, the global standards are important to make the technological level of Japan to be the world one in future.

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Establishment of Condition Based Maintenance (CBM) for hydrogenerator is very important for monitoring the insulation of stator windings. The partial discharge (PD) testing is a promising method of stator winding insulation of hydrogenerator conditions monitoring. Therefore, the on-line PD testing has been used to provide useful information to diagnose and monitor the integrity of stator winding insulation of many hydrogenerators. In this paper, we estimated an occurrence position of on-line maximum PD on hydrogenerator stator winding using acoustic emission (AE) detection techniques. Additionally, the PD is dramatically influenced by elements of driving condition on hydrogenerator, which are coil temperature, humidity, output power and stator room temperature. Consequently, we investigated characteristics of PD for various driving condition by means of measuring AE produced by PD at the same time. Especially, we reported characteristics of partial discharge versus humidity that dramatically influenced characteristics of PD.

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To develop a propagation model of a local discharge on a wet polluted insulator, the authors have examined an electric field near a tip of the local discharge on an electrolytic solution simulating the wet polluted insulator surface. The local discharge was propagated on the solution under the impulse voltage. The local discharge is considered to propagate by ionization in the air near the tip of the local discharge. Therefore, to calculate the propagation of the local discharge, the electric field distribution near the tip of the local discharge must be previously known. In this paper, the authors measured the electric potential on the solution near the tip of the local discharge. Furthermore, the potential was obtained by calculation with the image method. It was found that the calculated values agree well with the measured values.

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This paper deals with the effect of the magnitude and polarity on the particle initiated breakdown characteristics around a simple shaped spacer in quasi-uniform field gap under lightning impulse voltage superimposed on pre-stressed DC voltage. The results are discussed on the dust figure technique and also on the breakdown voltage / delay time characteristics, while keeping in view the magnitude of the pre-stressed DC applied voltage. Consequently, it was found that the surface charges accumulated on the spacer in the vicinity of the particle tip under the pre-stressed DC voltage play an important role in the particle initiated breakdown phenomenon.

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We have studied the surface discharge initiation phenomena caused by attached charge itself. By using negative corona discharge, negative charge is attached to a film surface which covered a plane electrode in case of electrostatic probe method and to a BSO crystal surface in case of the Pockels effect. By lowering pressure, a ring-shaped discharge momentarily appears around the center of the attached negative charge. The relationship between the maximum tangential electric field strength and the critical pressure in the range of about 50 to 1000 hPa is obtained. It should be emphasized that the inception electric field is 6 to 8 kV/mm at atmospheric pressure and 0.5 kV/mm at 50 hPa. To clarify the mechanism of the surface discharge inception phenomena by electrificated charge, MC-PIC (Monte-Carlo Particle-in-Cell) simulation model, considering the gas photoinonization effect and the photoelectric effect on the electrified dielectric surface, is introduced. It was found that the photon produced in the active region plays an important role and especially the photoelectric emission from the electrified dielectric surface becomes the necessary condition for the surface discharge occurring.

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In order to prevent the accidents due to the contact of animals, trees and etc., prefab insulating covers are installed in overhead distribution lines. However, sufficient effect is not realized. To make their protection performance at high level, they should to be designed taking the combination with the lightning protection equipments into consideration. With arrestors, they are required to withstand the lightning and switching surges smaller than the operation voltage of the lightning arrestors. With high-speed circuit breakers, as the breakage by the lightning surge is permitted and the following current is intercepted, the covers should withstand the switching surge when the lines are re-closed. In this study, the impulse-withstand voltage of a gap between the conductor and the contact object was examined assuming that the conductor cover and the prefab insulating cover were damaged. And the authors proposed a design method of the prefab insulating cover by comparing the withstand voltage of the air gap with the operation voltage of the arrestor and the magnitude of the switching surge.

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Abstract - A new type of plasma system based on the Magnetic Neutral Loop Discharge (NLD) concept has been developed for sputter application. This system is characterized by plasma production around the magnetic null field on the target surface, where an RF electric field is applied. From the experimental results and numerical analysis of electron behavior in this system, we found that electrons around the magnetic null region on the target surface moved in meandering orbits like in the original NLD concept. Varying the magnetic flux density of magnets and their arrangement can control effective electron heating around the null region.

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The three dimensional optical technique has been applied to investigate the electromagnetic wave scattering phenomena. Recently, we have developed an ideal equation for analyzing the three dimensional transport character of light scattered due to many index-ellipsoids arranged directly along the light axis in series. The size of index-ellipsoid, the distance between two adjacent index-ellipsoids, the ellipsoid rate and others are considered. By using an analyzing equation devised by us, we succeeded to derive the condition the light can pass trough many spherical and transparent mediums connected in series with high efficiency.

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The nanosecond surface discharge phenomena have been studied by paying attention to the rise time of impulse voltage using a dust figure technique. From the experiment result, it is found that irrespective of the applied voltage holding a constant, the size of discharge patterns reduces with increasing the rise time form 0 to 120ns, and that irrespective of the applied voltage being increased from 6 to 12kV, the size of discharge patterns becomes a constant with an increase in rise time. Furthermore, it is found that the cease voltage of surface discharge development is 2.5kV. Finally, we succeeded in theoretically estimating the electric field distribution and also space charge distribution in the positive corona streamer based on the voltage distribution which is obtained experimentally.

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A diaphragm-type pressure sensor consisting of two optical fibers for SF₆ gas circuit breaker is described. The lights from two IR LEDs are mixed and put into a transmitting fiber. A receiving fiber receives the reflected light from the diaphragm and the reference light. The ratio of the reflected signal and the reference signal warrants precision of the measurement in even the presence of external fluctuations. The pressure measuring system has the measurement accuracy 3% of full scale over a pressure range of 0.1-3.0 MPa. The optical fiber pressure sensor is compared with a semiconductor pressure transducer by means of measuring the pressure in SF₆ gas circuit breaker.

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The step-up method is used to estimate the impulse breakdown voltageswhen the electrical insulation is not usable after it is broken. This paper analyses the reliability of the estimates of the underlying breakdown probability distribution inthe step-up method, when (1) the observed breakdown voltage itself is available and (2)it is not available. The former case has many advantages compared to the latter case such that (1) the confidence intervals of the estimates become smaller and (2) theestimates can be obtained in stable. This paper summarizes the results of the three cases that the underlying probability distribution for the breakdown voltage is assumedto be normal, Weibull, and gumbel types. The optimal test method is simply and clearlydescribed for various distribution models.

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To investigate effects of irradiation conditions of the laser beam on films prepared at the pulsed laser deposition (PLD) method, thin films of LaNiO₃ were prepared on quartz substrates under different irradiation conditions of the laser beam with the PLD method by using different lasers. The XeCl excimer laser or the Nd:YAG laser was used as a source of the laser beam. The spot size, the energy density and the energy of the laser beam at a target surface were changed as the irradiation conditions of the laser beam. The deposition rate and the surface morphologies of the films prepared on the substrates were estimated. As a result, it was found that the deposition rates of the prepared film with the XeCl excimer laser are determined by the spot size, and those with the Nd:YAG laser are determined by the energy of the laser beam. The surfaces of the films prepared by the XeCl excimer laser are smoother.

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Functionally graded materials that had gradient profiles of permittivity (i. e., ε-FGMs) were fabricated from an alumina/epoxy mixture by a centrifugal method. Gradient distribution of both the packing fraction and size of the dispersed alumina fillers was confirmed by SEM images. Furthermore, a new numerical method to simulate the fabrication process was proposed based on the movement of solid particles dispersed in the viscous liquid under the centrifugal operation. In the simulation, both the cumulative probability of the practical filler diameter and the existence and growth of the fully-packed layer were taken in account. Permittivity profiles in ε-FGM was calculated and compared with the experimental ones, resulting in reasonable agreement between them. Therefore, it is concluded that the simulation method proposed can be applied to model the similar process of fabricating FGMs by the centrifugal method. The gradient of the fillers is intentionally regulated not only by changing in both the velocity and/or duration of the centrifugal operation, but also by changing in the distribution of filler size. In particular, existence of fillers with various sizes is indispensable to attain and control the centrifugal process because the fillers, depending on their sizes, play different roles in determining the profiles of packing fraction and resultant permittivity.

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Repetitive pulsed power techniques have enormous potential for a wide range of applications, such as nano-particle and hydrogen production, gas and water processing and sterilization, and generation of X-ray, EUV, and high-power acoustics. This paper presents the state of the art of our activities on repetitive ultra-short and microsecond pulsed power sources, pulsed thermal and streamer corona plasmas. Critical circuit elements are heavy-duty thyristors, transmission line transformers, and triggered spark-gap switches.

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We developed a high-density magnet-optical disk system named “iD (intelligent or image Disk) PHOTO" for use in mobile storage devices such as digital still cameras. This system achieved a recording density as high as 4.6 Gb/in² by adopting technologies, such as CAD type MSR (Center Aperture Detection type Magnetically induced Super Resolution) readout method, LP-MFM (Laser Pumped Magnetic Field Modulation) recording method, etc. It was reported that using the pulsed laser instead of the continuous laser in the readout process improved the carrier level of the CAD type MSR media at the shorter mark length. The purpose of this study is to clarify the effect of the laser pumped readout method on the characteristics of the "iD PHOTO" system. Using the laser pumped readout method, we can get larger readout margin than the continuous irradiation. At lower duty ratio, the readout margin is larger, but the erased ratio is lower than that of higher duty ratio. At the optimum bottom power there is a large readout margin and a high erased ratio. The erased ratio at 1.2 mW of bottom power was up to 26 % higher than that of continuous irradiation. The influence of the laser pumped readout method on the characteristics of the erased ratio makes it a useful technique for the CAD type MSR disk.

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Polycrystalline samples of filled skutterudite phosphide La_xCe_1-xRu₄P₁₂(0 ≤ x ≤ 0.3) and La_xCe_1-xOs₄P₁₂(0 ≤ x ≤ 0.5) were synthesized using high temperature and high-pressure techniques. The samples were characterized by x-ray diffractometry. The thermoelectric properties were measured. These properties include electrical resistivity, the Seebeck coefficient and thermal conductivity. La doping Ce based filled skutterudite phosphides enhanced the high power factor value of 0.7×10^-3[W/K²m] due to a considerable decrease in the value of resistivity and thermal conductivity without much decrease in the Seebeck coefficient. It has been noticed that doping of more than one rare earth element caused a decrease in the thermal conductivity by increasing randomness and rattling effects.

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Photoluminescence (PL) spectra induced by irradiation of ultraviolet photons are compared among low-density polyethylene (LDPE), crosslinked polyethylene (XLPE), and polypropylene (PP). Three PL bands appear around 4.2, 3.6, and 3.1 eV in LDPE and XLPE, while similar three PL bands are observed at similar energies in PP. The PL spectra and their decay profiles are independent of the presence of additives and are also independent of whether the samples were crosslinked or not. These results indicate that neither the additives nor the crosslinking has any significant effects on the respective three PLs in PE and PP. When the sample was pre-irradiated by the ultraviolet photons under different atmospheres (air, O₂, and vacuum), all the PL intensities decrease with the progress of the pre-irradiation regardless of whether the sample is PE or PP. Therefore, all the PLs are considered to result from impurities. In all the pre-irradiated samples, a new PL band appears at 2.9 eV, of which intensity is stronger when the oxygen partial pressure during the pre-irradiation was lower. This PL is considered to be due to photo-induced conjugated double bonds. It has also been confirmed that water-tree degradation in LDPE or in XLPE does not contribute to PL.

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