There are three types of the wireless power transmission ; inductive coupling, radio wave, and resonance coupling. These are the same technologies based on Maxwell equations, however, method of the power transmission is different and characteristics are different. In this paper, we show the wireless power transmission technologies, mainly wireless power transmission via microwave.

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This paper presents an impact study of pre-specified PV installation and network configuration on the maximum PV potential in distribution networks. Although there is an optimal solution for installing PV systems to achieve the maximum potential of PV installation under a bus voltage constraint in a distribution network, the practical installation of PV systems may not exactly equal to the optimal solution. A sensitivity analysis of maximum PV installation by varying a pre-specified PV installation capacity at a particular bus is performed to investigate the impact on the change of PV installation capacities at other buses and on the degradation of the maximum potential of PV installation of a distribution network. The impact of pre-specified PV installation is also considered in different configurations of the distribution network. Finally, decisions for the PV installation in a distribution network are discussed.

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An automatic fault-recorder installed in a substation of Chubu Electric Power Company detected a peculiar phenomenon that bus-bar voltage fell to around 20-30% of the nominal value for a short time (about 8-10 cycles) though electric current didn't change during the period. The phenominon was recorded several times.
In this paper, we analyzed the origin of this phenomenon and conducted simulations by EMTP. As a result, we estimated that this phenomenon occurred by the saturation of VT (voltage transformer), and this saturation caused by lightning strokes to the transmission line with line arresters, which have been increasingly installed in recent years. Moreover, we evaluated the influence of the phenomenon to protection relays.

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A new Autonomous Stabilizing Controller (ASC) has been developed, which is based on the concept of using only locall information measured at the substation where ASC is installed. ASC prevents the power system from wide-area blackout by shedding generators optimally when a serious fault occurs in 154kV-or-below-voltage power system and is cleared by backup relay. ASC consists of three functions, a function of detecting faults and judging of starting stability calculations (The first function), a function of calculating power system stability (The second function), and a function of selecting optimal generators to be shed (The third function). The first function composes a signal for starting stability calculations when a fault cleared by backup relay is detected. According to the starting signal composed by the first function, the second function executes stability calculations based on equal area criterion. If the result of stability calculations is instable, the third function selects a generator to be shed by considering not only the stabilizing effect but also the quickly restoration after shedding.
This paper presents total algorithms applied in ASC.

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At a transformer's steady-state condition, whereby a transformer and its load are constantly supplied by a sinusoidal source, the current-flux pair within the transformer core and its windings will cycle along a hysteresis loop. This nonlinear current-flux characteristic becomes important while at transformer gets reenergized. A remaining residual flux and the fact that a transformer is typically used up to its saturation level can lead to high-amplitude magnetizing inrush currents and associated voltage disturbances. These disturbances can be reduced by controlled transformer switching. In order to pre-evaluate the effect of a specific controlled transformer energization, pre-simulations can be applied. In that case the hysteresis loop and its saturation characteristic will become the most important model parameter. If the corresponding manufacturer specifications are not available a standard hysteresis loops can be used, but might come up with an inaccurate simulation result. Therefore, this paper analyses the measured 3-phase currents from two delta-connected power transformers by “Fourier Series” in order to deduce a single-phase hysteresis loop, which can be implemented into a typical 3-phase transformer model. Additionally, the saturation behavior of a power-transformer will be estimated and a comparison of ATP/EMTP simulations will conclude this paper.

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A hydrogen co-production solid oxide fuel cell power generation system that uses methane (natural gas) as fuel and can supply both electrical power and hydrogen is newly proposed. It is made clear that the system with the electrical power generation efficiency of over 35% and the overall system efficiency of over 70% can be realized by optimally selecting the gas flow configuration and the operating conditions. The decrease in the electrical power generation efficiency by the reduction of the air outlet temperature is compensated by the increase in the hydrogen production efficiency. This indicates that the operating mode changes depending upon the air outlet temperature without deteriorating the total system performance. The system performance under the part-load operation is also investigated, and it is made clear that the sufficiently high performance operation can be expected even under the part-load condition.

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This paper describes the wrong detection preventive method, which is useful to the inter-harmonics injection type islanding detector that detects a ground fault of primary distribution line within 0.1 seconds indirectly. The results are as follows. Injection of single-phase inter-harmonics current equals to injection of inter-harmonics current which consists of the same quantity of positive-phase-sequence and negative-phase-sequence components. Therefore, the quantity of inter-harmonics positive-phase-sequence admittance, which is calculated by inter-harmonics positive-phase-sequence current and voltage, equals to the quantity of inter-harmonics negative-phase-sequence admittance. Islanding phenomena which is three-phase-circuit breaking phenomena causes to the same change between the inter-harmonics positive-phase-sequence admittance and the negative-phase-sequence admittance. But the transient phenomena causes to the different change between the inter-harmonics positive-phase-sequence admittance and the negative-phase-sequence admittance. This paper proposes the wrong detection preventive method using this relation (the different change or the same change) between the inter-harmonics positive-phase-sequence admittance and the negative-phase-sequence admittance. This paper shows that this method is appropriate for the wrong detection prevention through simulation and experiment.

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Higher contamination flashover voltage of a semi-conducting glaze (SG) insulator owes primarily to the drying effect by leakage current flowing in the glaze. Significant reduction in contamination flashover voltage was confirmed on a cylindrical SG insulator when fog density was increased from 0.5g/m³ to 13g/m³ in clean fog test. The effect of de-energized duration between trip-out and re-energization on the contamination flashover voltage of a cylindrical SG insulator under cold-wet switch-on conditions was investigated. As the de-energized duration becomes shorter, the flashover voltage of a cylindrical SG insulator becomes higher. Higher contamination design voltages may be adopted even under cold-wet switch-on conditions.

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There are lots of global warming countermeasures. In the power sector, nuclear power plants play an important role because they do not produce CO₂ emissions during production of electricity. However, if the generation share of nuclear is too high at nighttime, it becomes difficult to keep enough capacity of Load Frequency Control (LFC) because nuclear power plants do not change the output (i.e., without load following operation) in Japan.
On the other hand, in the transport sector, Plug-in Hybrid Electric Vehicle (PHEV) is being developed as an environmentally friendly vehicle. The electric energy of PHEV is charged mainly during nighttime when the electricity price is low. Therefore, we have proposed a charging power control of PHEVs to compensate LFC capacity in nighttime. In this study, we evaluated the economic value of charging power control by using an optimal generation planning model, and obtained the following results. Charging power control is effective in reduction of CO₂ emissions and enhancement of economic efficiency of power system. Particularly, even in the low market share of PHEVs, the charge control has a high economic value because it substitutes nuclear power plant, base-load provider with low fuel cost, for LNG-CC, LEC provider with high fuel cost.

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The fluctuation of the total power output of clustered PV systems would be smaller than that of single PV system because of the time difference in the power output fluctuation among PV systems at different locations. This effect, so called smoothing-effect, must be taken into account properly when the impact of clustered PV systems on electric power system is assessed. If the average power output of clustered PV systems can be estimated from the power output of single PV system, it is very useful and helpful for the impact assessment. In this study, we propose a simple method to estimate the total power output fluctuation of clustered PV systems. In the proposed method, a smoothing effect is assumed to be caused as a result of two factors, i.e. time difference of overhead clouds passing among PV systems and the random change in the size and/or shape of clouds. The first one is formulated as a low-pass filter, assuming that output fluctuation is transmitted to the same direction as the wind direction at the constant speed. The second one is taken into account by using a Fourier transform surrogate data. The parameters in the proposed method were selected, so that the estimated fluctuation can be similar with that of ensemble average fluctuation of data observed at 5 points used as a training data set. Then, by using the selected parameters, the fluctuation property was estimated for other data set. The results show that the proposed method is useful for estimating the total power output fluctuation of clustered PV systems.

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The large-scaled photovoltaic generation (PV) system that called “mega-solar” is expected to spread for penetrating PV system. But penetration of mega-solar may impact to stable operation of power system such as the load frequency control. As the one of solution for this problem, energy storage system (ESS) is tentatively installed to absorb short-term fluctuation of PV output. However, since the ESS is still expensive, it is favorable to reduce its required capacity of ESS for saving installation cost. In Wakkanai PV power station, sodium-sulfur (NAS) battery system is adopted as ESS and is operated to achieve suppression of short-term fluctuation and scheduled operation. In this paper, authors propose a control method of NAS battery system for reducing its MW capacity required for fluctuation suppressing based on characteristic of solar radiation.

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When a fault arc occurs in electrical power equipment, the pressure in the latter increases due to the high temperature of the arc. To clarify the phenomenon of internal pressure-rise in the electrical power equipment, this paper shows the influence of the arc current on the energy balance when the former occurs in a closed chamber. Internal pressure-rises in the closed chamber were measured within an arc current of 4 to 12.5kA. Copper, iron and aluminum electrodes were used in the experiments with rod shapes of 20mm in diameter. The main results with the dependence of the arc current are as follows. When using an aluminum electrode, the energy due to the oxidation of the electrode vapor exceeded that obtained from the use of other electrodes. However the ratio of the energy due to the oxidation of electrode vapor to the arc energy was nearly independent of the arc current. When using an iron electrode, the ratio of radiation loss energy relative to total consumption energy was significant, particularly in the low current domain, while when using a copper electrode, since the oxidation energy was smaller than the evaporation energy, the ratio of the energy due to the evaporation of the electrode relative to the consumption energy increased in line with the arc current.

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The integrated grounding system which bundles up all various grounding electrodes has been introduced as a new grounding system from the movement toward the formation of standard international adjustment in recent years, and the example adopted also in high voltage receipt equipment is increasing. However, there are very many differences between TN system in the West and TT system in our country and points to be checked since the grounding purpose is crossing variably as the account of the upper stated, when adopting an integrated grounding system, and there are few examples checked experimentally until now. In this research, the viewpoint was extracted to lightning protection in such a background, the grounding system and integrated grounding system which were used with high voltage receipt equipment until now were compared, and real experiment and EMTP analysis were carried out for the purpose of grasping the characteristic in an integrated grounding system. From the experiment result in high voltage receipt equipment, and an analysis result, the result verified about the usefulness of integrated grounding to lightning protection is reported.

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As the information society progresses, a variety of electronic appliances have come into wide use in common houses. If a lightning stroke causes faults or incorrect operations of these electronic appliances, a social economic loss is considered to be large. For this reason, the focus of lightning protection measures for distribution lines in Japan has expanded to include the low-voltage side of the distribution line in addition to the high-voltage side. In order to calculate lightning overvoltages at the low-voltage side, the surge characteristics of service-drop wires and interior-wiring cables have to be modeled accurately.
First, this paper describes test results of the surge characteristics of service-drop wires and interior-wiring cables. The modal surge impedances and the propagation velocities of various service-drop wires and interior-wiring cables are obtained by the test. Based on the test results obtained, this paper proposes a modeling methodology of these wires and cables for accurate EMTP (Electro-Magnetic Transients Program) lightning overvoltage simulations. The proposed model is validated by comparing EMTP simulation results with field test results.

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In this letter, it proposed the device that detect the short-circuit fault of the photovoltaic generation system, and this propose device examined about the effectiveness. As a result, this device can confirm the short-circuit protection in photovoltaic generation system. The proposed device is effectiveness to operate within the range of design value.

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