The purpose of the study was to practice teaching electric theory to first graders using a hands-on approach in a technology teacher training course at a teacher's education university, and to verify the effect. Hands-on activities included simple electrical experiments and simulations in a lecture room. To allow time for hands-on activities, flipped classrooms were used as a teaching method. In the flipped classroom, students were required to watch the video lectures in advance and then engaged in hands-on activities. Fifteen lessons were taught, and the effect was examined based on test and questionnaire results of the group using the hands-on activities (experimental group) and a group without the activity (control group). The results showed that the average score of the short tests and regular examinations was significantly higher than that in the control group, except in the case of the AC circuit field. Thus, the experiments and simulations contributed to improved interest and comprehension, therefore, demonstrating the educational effect of the hands-on approach.

In magnetic field coupling type contactless power transfer, there is a problem that stable power transfer is not possible to changes in the position, angle, and distance of the transmission and receiving coils. In the case of mobile devices charging the battery using the contactless power transfer, the angle between the power transmission and receiving coils is not constant. Therefore, the power transmission efficiency is influenced by changing the position between the power transmission and receiving coils. In this study, the shape of the power transmission coils was investigated with stably supply power in all directions to mobile devices. We studied three coils consisting of cubic coil with 4 squares connected in parallel(4 squares cubic coil), cubic coil with 4 L-shapes connected in parallel(L4 cubic coil) and octagonal star prism coil with 8 square coils connected in parallel(octagonal star prism coil) . The S-parameters between the transmission and receiving coils were measured using a Vector Network Analyzer and after converting S-Parameters to Z-parameters. The theoretical maximum efficiency was obtained from the kQ product and compared with different coil shapes.

This paper presents a new plasma treatment system for decomposition of organic compounds in polluted water with high conductivity. The polluted water is normally set between two metal electrodes as a dielectric layer, but it is used as a grounded column electrode in the new treatment system. When the water column coming out of a grounded nozzle is close to an aluminum rod electrode covered by a glass tube subjected to an ac high voltage, a dielectric-barrier-discharge (DBD) occurs at the air gap between the water column and the glass. Since the DBD current flows along the water column electrode, the discharge current increase with increasing the conductivity of water. The decomposition of a blue dye in a high-conductive solution including with NaCl or MgSO₄ is carried out. Experimental results show that the DBD occurs steadily and can decolorize indigo-carmine even when the conductivity of the solution was varied in the range of 0.1 mS/cm to 30 mS/cm. Simulation of power consumption in an equivalent circuit model also show that the higher-conductive solution over 30 mS/cm is also decolorized by DBD with the water column electrode.

The gas circuit breakers have the problem of re-ignition after current zero. The instantaneous voltage drop causes enormous damage in the case of current interruption failure. Therefore, it is the responsibility of circuit breaker to interrupt the current quickly and reliably. Efficient cooling of the arc temperature is important in order to prevent the re-ignition caused by the transient recovery voltage. In this paper, the arc temperature as a function of opening electrodes timing was analyzed. As a result, the three-dimensional transition of arc temperature to current zero for each current interruption timing at each sine wave time was obtained. In addition, the opening electrodes timing that decreases the arc conductance at current zero was elucidated.

The pulsed electroacoustic method determines the distribution of space charge in an insulation system by applying a pulse voltage and detecting the acoustic response. It estimates the location and magnitude of charges from time-domain signals. For quantitative analysis, a bias voltage is applied to a specimen with no space charge, and the acoustic signal generated from the electrodes only is used as a reference waveform for calibration. However, a full-scale, extra-high voltage insulation system often already contains space charges in it. Therefore, a method of acquiring a reference signal under such a condition was studied. We studied methods to compare voltage variations and response signal variations. We proposed a method that measures the signal difference at different voltages. In addition, we proposed a method of correlating voltage and signal variations that may allow for more rapid signal acquisition. The feasibility was proved using an 11 mm-thick mimic polyethylene specimen.

It is concerned that the recent expansion of the application environment of power electronics to high-altitude and/or high-radiation environments will cause deteriorations of insulation materials used in power electronics due to charging caused by cosmic ray irradiation. With respect to the high-radiation environments, the exposure of high-energy charged particles such as protons, electrons, etc. to the insulation materials gives rise to the charge accumulations, which dielectric BD (breakdown) of the materials and make the power electronics equipment inoperable, in the materials due to changes in the insulation characteristics of the materials. Therefore, in this paper, we report the feasibility study on the deteriorations of BD characteristics of three insulation materials (Alicyclic EP, OCN, PPS) due to proton or electron irradiation. As a result, it was found that BDE (BD electric field) of some insulation materials (Alicyclic EP, OCN) decreases due to proton or electron irradiation. The oxidation and the change in the electric field distribution in the materials caused by proton or electron irradiation may be one of the reasons for the decreases in BDE of the materials.

Quantitative analysis of iron loss taking magnetic hysteresis behavior into account is essential to loss reduction in electric machines. In the previous research, a novel magnetic circuit model, which incorporates a play model and a Cauer circuit, was proposed. Besides, the play model can be derived from dc hysteresis loops calculated by a simplified Landau-Lifshitz-Gilbert (LLG) equation. However, this method cannot necessarily calculate dc hysteresis loops with high accuracy in all cases so that there is potential for further improvement in its calculation accuracy. Therefore, in this paper, the calculation accuracy of the simplified LLG equation is examined in detail under various conditions.

A stress relief cone plays an essential role in a prefabricated termination for the XLPE cable system. It has been pointed out that precipitates occur on certain parts of the stress relief cone surface under long-term operation, which could lead to a dielectric breakdown. This paper describes the development of two-step numerical calculation programs to understand the appearance process of precipitate on the surface of the stress relief cone. The first step is to estimate the distribution of precipitation occurrence over time, considering several ten-year operations. The second step is to estimate the detailed formation process of precipitates based on the molecular dynamics method. As a result, it is confirmed that the occurrence condition of precipitate led by the developed numerical calculation methods is similar to that obtained at the dismantled stress relief cone.

Silicone gel is widely used to encapsulate power modules, and improvement of its dielectric strength has been required. So, the purpose of our research is to improve dielectric strength of silicone gel encapsulant, and we focus on crosslinking degree of silicone gel. Previous studies have shown that growth mechanism of electrical tree changes with crosslinking degree of silicone gel. This suggests the possibility that the presence of the interface by different crosslinking degrees inhibits the tree growth. In this paper, we have investigated the tree growth and breakdown characteristics in silicone gel - crosslinking degrees graded layer materials. The interfaces in our study are arrange as being vertical to the line of electric force. Consequently, it was clarified that barrier effect of interface by different crosslinking degrees and the relaxation of electric field in low crosslinking degree region retards on tree growth, which improves the dielectric strength.

In recent years, the shift to electric vehicles (EVs) has become more prominent in many countries around the world. In line with this trend, research on systems that provide wireless power to running EVs is also underway in many countries. In order to realize this system, it is important to make the infrastructure easy and inexpensive, and one of the most important issues to be solved is to reduce the number of power sources used. We have proposed a repeater coil system as a power transmission method that can be expected to extend the power supply section per power source. In this paper, we discuss the usefulness of a series of repeater coils in a running wireless power transfer system, as well as their coil geometry and power supply characteristics.