Electrical Engineering in Japan最新文献

Corrosion and breakages of shielding layers are one of the factors for degradation of extruded three-layer (E-E type) 6.6 kV cross-linked polyethylene (XLPE) cables. Tohoku Electric Power Network has been measuring electrical resistances of shielding layers in E-E type 6.6 kV XLPE cables, and recently has found breakages of shielding layers. The authors performed an accelerated degradation test for shielding layers of E-E type 6.6 kV XLPE cables by taking account of aqueous solution, temperature, heat cycles, bending stress, frequency of an applied voltage, and water-proof layer in the test conditions, and investigated factors affecting corrosion and breakages of shielding layers. Corrosion, cracks, and breakages were found on shielding layers in the cables without water-proof layer, but no crack was found in the cables with water-proof layer, when heat cycles were applied to the cables, and shielding layers were supplied with artificial sea water. We investigated the suppressive effect of the cables with water-proof layer on cracks and breakages of shielding layers by measuring tensile strengths of copper tapes obtained from the shielding layers of the cables with and without water-proof layers.

The service restoration to sound sections within a short period as much as possible, performed after the permanent fault occurs in a distribution system, is significant for maintaining power supply reliability. This paper proposes an efficient method to find service restoration procedures based on fault searching and the optimal work scheduling of crews, considering the power supply priorities of loads and the probability of occurrence of faults. The proposed method is composed of two-stage problems to reduce the outage sections efficiently: (i) the problem to find a series of searching procedures for unknown fault locations in the first stage and (ii) the optimization problem of work schedules of crews in the second stage. In the first stage, the order of operation of switches opened for searching for the fault direction is determined, constituting the searching tree. After that, the proposed optimization method can efficiently solve the work scheduling problem by formulating it as a mixed-integer linear programming problem in the second stage. The computational experiments using a large-scale distribution system model with many remote and manual switches show that the proposed method can provide efficient service restoration procedures within a reasonable computational time.

This paper addresses semiconductor piezoresistive materials selection in MEMS engineering design. From the practical engineering point of view, it is important to understand piezoresistance properties of semiconductors even if less accuracy under feasibility design phase. However, piezoresistance is frequently analyzed based on first principle electronic band structure simulations by sophisticate physicists. Practical engineers not familiar with this simulation cannot directly apply useful information derived from the result of simulation. This paper provides practical prediction method for piezoresistance based on electronic band parameters obtained from the state-of-the-art solid-state physics. It is demonstrated that the crucial parameters which control the p-type shear piezoresistance coefficient π₄₄ in diamond and zinc-blend single crystals are the inverse of square of bond length in unit cell atom, the square root of valence light hole mass, and the shear elastic compliance coefficient S₄₄.

We are developing a small and lightweight direct-drive system toward the realization of in-wheel electric vehicles (EVs). To increase the power density of the motor, we developed a direct-cooling motor that immersed the core, coils, and magnets in cooling oil and improved cooling efficiency. Moreover, we performed measurements of frictional loss, measurement of pressure drop, and a continuous heat-run test on the test bench. The results demonstrated that direct cooling is effective and continuous operation can be achieved. Additionally, it was found that the coil temperature can be controlled by the flow rate of the cooling oil. In this paper, we report on the concept of direct cooling and the measurement results.

Experiments on power generation were conducted under the open-circuit condition to validate theoretical analyses on the power generation characteristics of a co-axial MHD energy conversion device. Considering distribution of externally applied magnetic field and the electromotive force induced by the rotation of the conductive inner cylinder, the results show that the experimental open-circuit voltage was lower than the theoretical one for the wide channel width, whereas the experimental open-circuit voltage was higher than the theoretical one for the narrow channel width. The inclination of the inner cylinder might cause the decrease in effective radial ratio.

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.

An interior permanent magnet synchronous motor (IPMSM) is characterized by its high efficiency. However, torque ripple and loss occur because of the spatial harmonics generated by air-gap permeance fluctuations. This study clarified that slot harmonic components can be suppressed by inserting magnetic wedges made of magnetic composite material in the slot opening of an IPMSM. First, the authors examined the torque and loss characteristics by varying relative permeability and saturation magnetic flux density of magnetic wedges using finite element analysis (FEA). Results indicated that the torque ripple and loss could be suppressed when the relative permeability of the magnetic wedge was μ_r = 10 to 22 and the saturation magnetic flux density was B_s = 0.5 to 0.75 T. Furthermore, the authors produced magnetic composite materials made of various soft magnetic material powders and examined their magnetic properties and viscosities. Results showed that a magnetic composite material with optimal magnetic properties and injectable viscosity could be manufactured using Fe-Si-Al with a low volume fraction.

The paper is proposed approximate formulas of the ac resistance of lead wires and coils which made by using copper clad aluminum (CCA) wires. There are the frequency range that the ac resistance of CCA wires is lower than it of cupper solid wires for lead wires and coils of an electrical equipment. It is shown that the application of CCA wires is economical as comparing with copper solid wires, if the design is due to successful calculation in the electrical equipment. The measured resistance is compared with the formula. CCA wires is an example of multiple conductors which shall be expected to apply in future.

Photovoltaics (PV) output prediction, which is indispensable for power system operation, can affects demand and supply adjustment adversely when large prediction error occurs. Thus, the reduction of large error as well as average error is required in PV power prediction. In 2019, the operation of the Meso-scale Ensemble Prediction System (MEPS) of numerical weather prediction started from the JapanMeteorological Agency, and the amount of forecasting information would be potentially useful for the improvement of PV power prediction. However, very few studies on inputting multiple meteorological elements of the MEPS have been reported. In this paper, we newly develop the prediction model for an area day-ahead PV power output composed of Just-In-Time Modeling (JIT Modeling) with multiple elements of theMEPS. The developed method achieves precise forecasts with low computational load by both selecting meteorological elements valid for improving prediction accuracy and adequately devising the structure of JIT Modeling. Some numerical examples demonstrating the effectiveness of the developed method are also presented. In particular, the proposed method reduces large error significantly.

A short-term solar irradiance forecasting method has been developed to provide highly accurate prediction, using satellite image prediction model in combination with numerical weather prediction model. This method was applied and evaluated using the solar irradiance observational site at the CRIEPI Akagi Testing Center (Gunma Prefecture, Japan). Based on historical forecasting and observation datasets at JMA observation sites in the computational domain, the best blending ratio between the satellite image prediction model and the numerical weather prediction model was selected and used. The developed method has shown high accuracy. Compared to satellite image forecasting, accuracy results averaged between three and 6 h of lead-time showed improvements in the RMSE by 44% for the before-sunrise case, 20% for the after-sunrise case, and 8% for the noon to sunset case.