We have been studying on measuring capacitance and potential using long distance electrode for estimating a permittivity distribution. The estimating method of permittivity distribution was proposed using Finite Element Method (FEM) and Genetic Algorithm (GA). However, the measurement accuracy was not reviewed. In this paper, we carried out numerical analysis using FEM in case of change of diameter, position and permittivity of a rod of dielectric and discussed the measurement accuracy of capacitance and potential.

For the development of a practical method to estimate the energy of electrostatic air discharge without electrical measurements, the dependence of spectral characteristics of light emission from the spark discharge on electrostatic energy was investigated. It was found that the relative light intensity emitted from a monovalent positive ion of nitrogen (N II) to a nitrogen atom (N I) increased with the electrostatic energy from 0.02 mJ to 20 mJ. In the same electrostatic energy, the intensity ratio, that is the intensity of N II divided by that of N I, increased with the decrease of applied voltage. This implied that the ratio becomes large when increasing the electrostatic energy divided by the breakdown gap length. Separating the measurements into similar voltage groups, the relation between the ratio and the electrostatic energy became clear.

SiC-based nonlinear resistive materials and carbon-based semi-conductive materials (corona armor tape or CAT) are used at end-turn stress grading systems of high voltage rotating machines. Recent studies show that local heating as well as electric field along the system become problematic under PWM and high frequency repetitive pulses waveforms. Potential distribution, power dissipation and resulting temperature rise under the repetitive pulses are calculated based on three dimensional transient electric field and thermal coupled FEM computation. Computational results of surface temperature as a function of CAT conductivity have shown reasonable agreement with the experimental ones and we have validated those computations. In addition, the appropriate CAT conductivity for suppressing both local heating and electric field are evaluated based on the above computational results.

Mechanical parts, plants and cross-linkages inspected with magnetic-particle testing (MT) are typically complex 3D shapes. In complex 3D shape portions, because a magnetizer often cannot be configured to inspection portions and the test object cannot be appropriately magnetized, there is a possibility of overlooking a crack in such an instance. Thus, MT system development that was successfully able to detect omnidirectional cracks in 3D shape portions was considered in this study's trials. Two multi-coil type magnetizers were hence arranged face-to-face, and the magnetization of omnidirectional scenarios for all surfaces of 3D shape test object was evaluated.

This paper reports an educational practice to ensure out-of-class study hours enough to be required for academic credit, by developing e-learning materials of a lecture on electromagnetics in a university. We analyze their effects on students' out-of-class studying style from various data collected from a learning management system, and compare their academic achievement from final exams. The analyses demonstrate that students ensure out-of-class studying hours sufficiently, that is, twice as much time as the corresponding lecture, and improve their achievement in comparison with students attending the past lecture without the e-learning developed in this study.

For the relaxation and optimization of electric field distribution around Gas insulated switchgear (GIS) spacers, the application of functionally graded materials (FGM) with spatial distribution of dielectric permittivity (ε) can be one of the effective solutions. In this paper, we fabricated the coaxial disk-type ε-FGM using SrTiO₃/SiO₂ particles by the centrifugal force method. We also proposed the coaxial cone-type ε-FGM by the flexible mixture casting method and evaluated its electric field reduction effect and breakdown voltage in SF₆ gas by the volume-time theory.

Electron beam irradiated fluorinated materials, which are used for an OSR (Optical Solar Reflector) of spacecraft have been investigated using a space charge measurement system under DC high stress. It was found that a large amount of space charge accumulated in the electron beam irradiated ethylene-tetrafluoroethylene (ETFE) and fluorinated ethylene-propylene copolymer (FEP) under DC high stress, while it was not observed in non-irradiated them. In this report, a dependence of relaxation time after the irradiation on the space charge accumulation characteristics was also studied.

Silicone gel is widely used to encapsulate the power modules. In modules, partial discharges make the cavity and it propagates on the substrate. This article reports fundamental propagation characteristics of such cavity under repetitive voltage impulses, which will be applied to actual modules under the operation of pulse-width modulated voltage. The influence of frequency, rise time, pulse width of the repetitive surge voltage on the cavity length were investigated. The results show that the cavity length increases with the frequency. And also, the results show that the cavity length is especially long when the rise time is short.