Recently the electric double-layer capacitor (EDLC) which is rapidly charged and discharged and offers long life, maintenance-free, has been developed as a new energy storage element. Therefore, we developed the uninterruptible power supply as voltage sag compensator utilizing EDLC. This paper describes an abstract of EDLC and applying to voltage sag compensation.

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Recently many such distributed generating systems as co-generation, photovoltaic, wind, fuel cells etc. are introduced into power distribution system, and the power system must cope with the situation with distributed generators. Moreover, such industries as IT request reliable and high quality power to preserve their businesses, and some other electric energy based industries request less reliable but cheaper electricity. From these backgrounds, several new type power delivery systems are emerging where lots of distributed generators (DGs) can be connected and many benefits offered by DGs can be realized without affecting the existing power system. They are referred to various names. In U.S.A., Microgrid, Power Park and Virtual Utilities, etc. are proposed. In Europe, DISPOWER or Smart Grid is under developing. In Japan, FRIENDS and Demand Area Network System etc. are proposed and tested in real sites. In this paper, first, general concepts of such new type power delivery systems and new businesses expected to be created by using DGs are introduced. Then, recent research activities in this area in Japan are introduced so as to stimulate new business opportunities. In the later part of this paper, related NEDO's demonstrative projects are introduced. NEDO is the largest public R&D management organization and promoting several projects regarding grid connecting issues on the power system. Those projects were planned to solve several problems on the power system where distributed renewable energy resources are installed.

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This paper evaluates two proposed repowering systems together with a conventional repowering system. A power generation system utilizing waste heat produced by a garbage incineration plant (GIP), which treats 45 t/d of garbage, was taken as an objective power generation system to be repowered. As the conventional repowering system (Sys-C), a gas turbine system with waste heat boiler was adopted. In the proposed system 1 (Sys-P1), temperature of the low temperature steam generated at the GIP is raised in the gas combustor by burning fuel, and used to drive a gas turbine generator. Hence, required power for compressing the air becomes remarkably small and expected to be high efficient compared with Sys-C. In the proposed system 2 (Sys-P2), the low temperature steam generated at the GIP is superheated by using regenerative burner and used to drive a steam turbine generator, and hence making steam condition optimal becomes easy. Various basic characteristics of the three repowering systems were estimated through computer simulation, such as repowering efficiency, energy saving characteristics, and amount of CO₂ reduction. It was shown that Sys-P1 and Sys-P2 were both superior to the conventional repowering system Sys-C in the all characteristics, and Sys-P1 to Sys-P2 in repowering efficiency, and that Sys-P2 to Sys-P1 in energy saving characteristics and CO₂ reduction effect. It has also been estimated that all the repowering systems are economically feasible, and that the proposed systems Sys-P1 and Sys-P2 are both superior to the Sys-C in the three economical indices of unit cost of power, annual gross profit and depreciation year.

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The microgrid concept is being seriously considered as a solution to growing electricity demand. And to increase renewable energy near the demand side, a microgrid that utilizes controllable prime movers such as gas engines to compensate fluctuating demand and output of renewable energy is proposed here. We model the optimal operation planning of a microgrid system for the day ahead based on 30-minute demand data, and we conduct the sensitivity analysis of the battery capacity, contracted electric power demand from a utility grid, and PV capacity on costs. It is effective for annual cost reduction to make the contracted demand as small as possible. And the benefit of combination of PV and gas engine can be gained the most in the case that PV capacity is between 20% and 30% of the peak demand of the microgrid.

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The need for economical, reliable and effective delivery of electric power leads to the search for new, efficient and effective methods for diagnosing the high voltage equipments in the industries all over the world. As the average usage period of transformers increases, the necessity to know the internal condition of transformers is increasing. It is therefore critically important to establish monitoring and diagnostic techniques that can perform transformer condition assessment. Frequency response analysis, generally known as FRA, is one of the technologies to diagnose transformers.
Using case studies, this paper presents the effectiveness of FRA as measurements for detecting transformer faults. This paper introduces the fact that FRA waveforms have useful information about diagnosis of fault on winding shield and core earths, and that the condition outside transformers can affect frequency response characteristics. The FRA measurement results are further investigated through a simulation study using a computer model.

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Silicone liquid has the high performance in fire safety showing fire resistance by self-extinguishing, and that is less environmentally pollutant compared with mineral oil. Applicability of silicone liquid of 20cSt to transformers was investigated from the view point of the correlation of ignition time with critical radiant heat flux. The same tests were carried out using a mineral oil and synthetic ester oil. The basic properties of silicone liquid (20cSt) obtained from the series of the tests were verified in its application as a less-flammable transformer fluid.

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Induction heating has found a new feasibility in domestic appliances. Its application is known as an “induction range” or an “induction heating oven”. Conventional design schemes of them have depended on the experience and insight of designers. In the paper, the authors treat it as an electromagnetic device to investigate the mechanism of power dissipation using the Finite Element Method, where an impressed voltage supply is taken account of and the constant V/f condition is imposed for the constant impressed magnetic flux. Furthermore the authors will examine how to heat an aluminum pan and discuss the optimal frequency of a power supply.

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The service restoration problem in distribution power system has already been conducted with regard to this issue, for purposes such as the minimization of unrecovered load and power-supply loss, consideration of priority sections, and preparation of switching procedures. However, since this involves application of a number of methods, the related algorithms are complex. In this paper, in order to resolve this issues we first apply GA as an optimization method for investigation purposes, to simplify the algorithms used. Next, to confirm this proposed method's effects in reducing computing time, we consider the efficacy of the proposed method by using smaller numbers of generations and individual sizes than have been used in the past. The effectiveness of proposed method is shown by the system when failure occurs. It is clear that the proposed method, consisting of GA only, is superior in terms of average fitness values and ability to reduce computation times.

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This paper describes the new measuring method of the phase current for the high voltage three-phase cable. 24 pieces of independent coils wound around the coreless bobbins are used to compose the CT sensor. The primary phase current may be calculated from the output voltage of each coil. The certain correlation between the output voltage and primary phase current is observed by the experimental data. This new CT sensor enables the measurement of the phase current with whole conductors clamping method for three-phase cable.

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Following the examples of other countries, in April 2005 Japan launched wholesale electric power exchange operations as a primary item of system reform in line with electric liberalization. Only two years have passed since the initiation of these operations. However, in the summer of 2005, the surge in market prices was evident, which suggested that certain measures should be taken to confront potential market risks. Establishing a useful system for forecasting market prices through the modeling of price fluctuations in the wholesale electric market became essential. Currently, various price models are being proposed. Taking both the limited amount of data and the model's purpose into consideration, this study adopted the univariate time series model.
We conducted a time series analysis on the open price indexes in the JEPX spot market with the Box-Jenkins method. Since a seven-day cycle can be observed in the data, we adopted the seasonal ARIMA model. In accordance with the procedures of the Box-Jenkins method, we determined the degree of the model's polynomial using the autocorrelation and partial autocorrelation of the data and estimated the parameters of the model with the maximum likelihood method. We conducted a forecast on next day JEPX spot market prices with this time series model and examined its validity and utility as a forecasting tool.
Price forecasts made with this model require only a small amount of data and will save substantial analysis work. Consequently, this method is expected to be widely used by market participants as the reference data for their bid pricing.

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Lightning performance of grounding electrode is one of the most important lightning-protection features of power distribution lines. It is well known that ground resistance has current-dependent characteristic due to soil ionization. Moreover, it also has time-dependent characteristic. But especially transient behavior has not been represented by EMTP models well because its mechanism is not cleared.
In order to clarify the transient behaviors of the grounding electrode, experiments were conducted with full-scale grounding systems. In this study, the paper describes a grounding electrode model that can be easily used in the EMTP analysis. The proposed model considers both current-dependent and time-dependent characteristics. It is verified by comparing calculated results with the experimental results.

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This paper describes the measurement-based load current model of electric apparatus after a voltage sag occurrence. The terminal voltage and load current of a personal computer (PC), an inverter fluorescent light and an incandescent light were measured to find out the dependences of load characteristics on the voltage sag. The magnitude of the load current after voltage sag depends on both the magnitude of residual voltage and the time period of voltage sag. In order to make it possible to take account of these transient load characteristics in the power quality estimation, a load current model is proposed. The load current waveform is obtained using the database of harmonic component of load current and time variation in the parameters of load voltage characteristic. The proposed model enables us to estimate the load current within an error of about 5% when the voltage sag occur.

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Recently, there has been an increase in concern about the global environment. Interest is growing in developing an energy network by which new energy systems such as photovoltaic and fuel cells generate power locally and electric power and heat are controlled with a communications network. We developed the power generation forecast method for photovoltaic power systems in an energy network. The method makes use of weather information and regression analysis. We carried out forecasting power output of the photovoltaic power system installed in Expo 2005, Aichi Japan. As a result of comparing measurements with a prediction values, the average prediction error per day was about 26% of the measured power.

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Until recently, SF₆ gas has widely been used as the best insulating medium in substation equipment. However, SF₆ gas was specified to be a greenhouse gas at COP3 in 1997 because of its high global warming potential (GWP), alternative insulation gases to SF₆ have been looked for since long time in the past. Alternatives using the natural gases are considered to be suitable substitute but none of them show better properties for insulation as well as good environmental compatibility. Therefore, it is necessary to rationalize the equipment insulation level and reduce the test voltage of electric power apparatus as low as possible. The actual lightning surge waveform (so-called non-standard lightning impulse waveform) occurring in the actual field is different from the standard lightning impulse waveform (1.2/50μs). There are many cases what the actual lightning surge waveform has steeply rising and large decay of overvoltage, and the insulation requirements are not as severe as those of the standard lightning impulse waveform.
In this paper, we focused our research on N₂ gas as SF₆ substitute and investigated the insulation characteristics of N₂ gas for single-frequency oscillatory waveform with various frequencies from 2.7 to 20.0MHz and damping ratios. From experimental results, it might be possible to reduce the test voltage of N₂ gas insulation by evaluating the crest value of actual lightning surge waveform that was converted into an equivalent standard lightning impulse waveform.

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We have developed a remaining service life diagnostic technology for insulators, which are important parts involved in determining the service life of power distribution equipment. Application of chemical evaluation and the Mahalanobis-Taguchi method enabled us to diagnose the insulators' degree of deterioration with great accuracy and nondestructively on-site. The theory, which derives the threshold value of surface resistivity for electric discharge initiation calculated from rated voltage, the form of an insulator, etc., was established and a remaining service life was presumed from the diagnostic results by the MT method and the year in which the master curve of service life and the threshold value intersect. It was clarified that a remaining service life could be presumed by this technology because there was a good relationship between the check examination results of electric discharge initiation in the laboratory and the presumption results.

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