The phenomena in the electromagnetic field intrinsically spread over the infinite space. The purpose of this paper is to provide a useful method for numerical calculation of the electromagnetic field with open boundary.
The finite element method (FEM) and the boundary element method (BEM), which have entirely different features from each other, are useful for numerical analysis. This paper describes the hybrid finite element and boundary element method for the three-dimensional eddy current problems. The physical quantities we want to obtain finally are the eddy current density in the conductive region and the magnetic flux density in the free space. Therefore, in the hybrid method we adopt the electric field intensity E and the magnetic field intensity H directly as unknowns. The conductive region is analyzed by the FEM adopting E, on the other hand, the free space with a supply current by BEM using H. In this paper we also describe the appropriate boundary element discretization using edge elements, which is suitable for combining the FE region with the BE region.
To verify this approach some numerical results obtained by the proposed method are compared with measured ones.

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The finite element method (FEM) and the boundary element method (BEM), which have entirely different features from each other, are useful for numerical analysis. The FEM suits for the analysis of such a complicated region which includes non-linear materials. However, it has some disadvantages in dealing with the infinitely extending fields. On the other hand, the BEM is useful for analyzing very large linear fields.
Taking account of the advantages in these methods, this paper describes the hybrid utilization of both methods (the hybrid FE-BE method) for the electromagnetic problems with two semi-infinite regions. Each region, which is regarded as a semi-sphere with the radius of infinite length, is onstituted of a homogeneous material. The region near the center of two semi-spheres is complicated one, which may include conductive or non-linear materials. In the hybrid FE-BE method for such problems, the BEM is applied to the semi-infinite region and the FEM to the complicated region near the center. In applying the BEM to the semi-infinite region, the boundary element integration over the interface between two homogeneous materials has to be carried out as far as infinity. This paper concerns with the elimination of the infinite boundary integration.

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It has been reported that the flashover voltage of gaseous dielectrics may greatly increase when they are mixed with carbon-halide mist. However, the factors which bring about the increase of the flashover voltage are not fully clarified yet. Based on our study on the basic flashover characteristics of vapor-mist dielectrics, we have suggested the scarcity of initial electrons as the predominant factor.
In the present work, we have furthermore investigated the effect of ultraviolet light irradiation, flashover characteristics under forced supply of initial electrons and for lightning impulse superimposed on DC voltage. These results have verified that the scarcity of initial electrons is the decisive factor of increasing the lightning impulse flashover voltage of vapor-mist dielectrics. We have also made clear that the scarcity is principally attributed to: (1) the reduction of effective period (lifetime) of initial electrons, (2)the suppression of photoelectric emission from electrodes.

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Transmission power cables are heated by the conductor current. Morphology of the XLPE insulation may be changed through the thermal aging. Disk shaped insulating materials with semiconductive electrodes were used in order to understand this thermal effect against the dielectric breakdown strengths. The disk specimens were aged at 80°C and 100°C before the breakdown strength measurements.
These results showed that their dielectric breakdown strengths were improved with aging time. Analytical investigation of the insulating materials indicated that there were morphological changes such as increases of the lamella thickness and the spherulite diameter and decrease of the averaged lamella angle through heating. Cable specimens aged thermally with the same condition as the disk specimens were also observed the similar morphological changes in the insulation. Therefore the promotion of the crystallization by thermal aging is concluded to be effective in improving the breakdown strength of the XLPE insulation, unless it causes extreme deterioration.

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This paper proposes a compact expert system with fuzzy inference on insulation diagnoses of rotating machines for elevators by means of a personal computer. The hypotheses used in this system for backward reasoning are derived from the results of the fuzzy inference, which specifies the deterioration grades from the automatically measured data for some diagnosis factors. The hypotheses are verified by human visual inspection, and the system synthetically diagnoses the objective system by the results of the verified hypotheses. The results of the diagnosis are shown as the messages how to treat the machines on the display. This system has the advantage as follows: breakdown voltages can be estimated with the regression line which means the correlation between deterioration grades obtained through the fuzzy inference and breakdown voltages. It is finally shown that the resultant diagnosis of the system agrees well with that of the experts. Then, It is concluded that the system is promising for assising insulation diagnosis of the rotating machines.

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We developed a new measurement method for surface charge distribution on an insulating film by Pockels effect of BSO single-crystal cell. The cell has only one transparent metal plate electrode which is located at the rear surface of the cell and is grounded. The insulating film of PET is placed on the other surface. Electrical surface charges are placed on the film by a high-voltage discharge between the rear plate electrode and a point electrode. The applied AC voltage (50Hz) on a 36μm-thick film had a peak of approximately 4kV. Positive and negative discharge figures were alternately obtained using a reflection light from the BSO crystal cell. Using circular polarized incident light, the polarity of the surface charge was determined. These results are closely related to the charge densities obtained by other methods.

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