Hydrogen is considered as the energy source of the next generation. This paper proposes a system which consists of FlyWheel Generator (FWG), Wind Energy Conversionr System (WECS), and Hydrogen Electrolyzer (HE), for the purpose of hydrogen generation and grid output power smoothing. The cooperative control among flywheel generator, hydrogen electrolyzer, and wind generator is performed by controlling the flywheel generator. Simulations have been done by PSCAD/EMTDC.

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The spread of wind power generation is progressed hugely in recent years from a viewpoint of environmental problems including global warming. Though wind power is considered as a very prospective energy source, wind power fluctuation due to the random fluctuation of wind speed has still created some problems. Therefore, research has been performed how to smooth the wind power fluctuation. This paper proposes Energy Capacitor System (ECS) for the smoothing of wind power which consists of Electric Double-Layer Capacitor (EDLC) and power electronics devices and works as an electric power storage system. Moreover, hydrogen has received much attention in recent years from a viewpoint of exhaustion problem of fossil fuel. Therefore it is also proposed that a hydrogen generator is installed at the wind farm to generate hydrogen. In this paper, the effectiveness of the proposed system is verified by the simulation analyses using PSCAD/EMTDC.

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This paper proposed an approximate calculation method to analyze the voltage in distribution system with distributed generation systems. The dependency of loads, distributed generation system, static var compensator (SVC) and energy storage system (ESS) on the voltage is represented by the exponential model. Applying the Taylor series approximation to the exponential model, we have found the linear relationship between the voltage and the current injection which is summation of currents flowing into the load, distributed generation system, SVC and ESS. In the electric transmission system, the imaginary part of the voltage drop between sending end and receiving end was ignored. It was found that these approximations enable us to make a linear equation of node voltage and obtain the approximate value of the receiving end voltage. It was shown that the error ratio of approximate value increases with the magnitude of line impedance. However, it was found that the application of the proposed method to the general distribution system enable us to analyze the voltage which is in error by up to 1%.

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In recent years, there have been focus on environmental pollution issue resulting from consumption of fuel, e.g., coal and oil. Thus, introduction of an alternative energy source such as solar energy is expected. However, insolation is not constant and output of photovoltaic (PV) system is influenced by meteorological conditions. In order to predict the power output for PV system as accurate as possible, it requires method of insolation estimation. In this paper, the authors take the insolation of each month into consideration, and confirm the validity of using neural network to predict insolation by computer simulations. The proposed method in this paper does not require complicated calculation and mathematical model with only meteorological data.

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Recently, doubly fed induction generator (DFIG) and synchronous generator are mostly applied for wind power generation due to high efficiently for wind energy capture. An inverter system is required to control wind turbine speed and power factor in those generators. The inverter rating of the synchronous generator equals to generator rating. However, DFIG has the advantage that the inverter rating is about 25% to the generator rating. The paper describes a vector control of DFIG inter-connected to power line.
The performance of proposed vector control is examined using power system simulation software PSCAD/EMTDC for the DFIG inter-connected to 6.6kv distribution line. The results show good dynamic responses and high accuracy to the stator active power control and the stator reactive power control.

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With recent development of power electronics technology, power system stability enhancement and optimal power flow control by using Flexible AC Transmission System (FACTS) devices have so far been studied. The FACTS devices to relieve multiple constraints can also make it possible to enhance Available Transfer Capability (ATC) without construction of new transmission lines. The previous research revealed that ATC is expanded by avoiding multiple constraints in OPF using Unified Power Flow Controller (UPFC). For long-term operation of such ATC-expanded power system, it is necessary to evaluate power system reliability. In this paper, the evaluation method of supply reliability for UPFC-installed power system is proposed. Both thermal capacity and transient stability constraints are considered. The effectiveness of the proposed method is shown by numerical examples for IEEJ East10-machine test system.

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Time series models are popular in attempts to model and forecast price dynamics in various markets. In this paper, we have formulated two state space models and tested them for its applicability to power price modeling and forecasting using JEPX (Japan Electric Power eXchange) data. The state space models generally have a high degree of flexibility with its time-dependent state transition matrix and system equation configurations. Based on empirical data analysis and past literatures, we used calculation assumptions to a) extract stochastic trend component to capture non-stationarity, and b) detect structural changes underlying in the market. The stepwise calculation algorithm followed that of Kalman Filter. We then evaluated the two models' forecasting capabilities, in comparison with ordinary AR (autoregressive) and ARCH (autoregressive conditional heteroskedasticity) models. By choosing proper explanatory variables, the latter state space model yielded as good a forecasting capability as that of the AR and the ARCH models for a short forecasting horizon.

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A methodology was developed to design the number and capacity for each piece of equipment (e.g. gas engines, batteries, thermal storage tanks) in microgrids with combined heat and power systems. We analyzed three types of microgrids; the first one consists of an office building and an apartment, the second one consists of a hospital and an apartment, the third one consists of a hotel, office and retails. In the methodology, annual cost is minimized by considering the partial load efficiency of a gas engine and its scale economy, and the optimal number and capacity of each piece of equipment and the annual operational schedule are determined by using the optimal planning method. Based on calculations using this design methodology, it is found that the optimal number of gas engines is determined by the ratio of bottom to peak of the electricity demand and the ratio of heat to electricity demand. The optimal capacity of a battery required to supply electricity for a limited time during a peak demand period is auxiliary. The thermal storage tank for space cooling and space heating is selected to minimize the use of auxiliary equipment such as a gas absorption chiller.

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Electric utility deregulation made possible for PPSs (Power Producer and Supplier) to entry the electricity market. PPSs are supposed to achieve 30-minute balancing control for stable supply of electric power. Meanwhile, load rejection and instantaneous voltage drop greatly affect turbine shafting, that is torsional torque oscillation. Therefore, PPSs have to consider reduction of torsional torque to prevent generator shaft damage. This paper propose the control system which enables to achieve both 30-minute balancing control and reduction of torsional torque by using H_∞ controller. The effectiveness of proposed controller will be verified by using MATLAB.

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This paper presents a method for monitoring the power system stability based on wide area phasor measurements. The authors have developed a method for detecting inter-area low-frequency modes from measured small oscillations associated with the load fluctuation by approximating filtered oscillations as a simplified oscillation model. The advantage of this method is that steady state phasor fluctuations are available to evaluate the stability of the power system. In this paper, another type of the filter based on the FFT analysis is developed for improving the accuracy of identified eigenvalues with observation sites changed. The method based on the FFT-based filtering is also applied to extract low-frequency oscillations from phasor data of one observation site. Some numerical analyses demonstrate the effectiveness of the method by using phasor dynamical data obtained by a power system simulation package and the phasor measurement system developed in Japan.

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The secondary system is expressed by reduced model in trunk transmission system analysis. So, many distributed generators that exist in secondary system are expressed by reduced model. But, by representing distributed generators by reduced model, a partial dropout of distributed generators cannot be expressed. Therefore there is a possibility that we cannot analyze accurately. Then, we studied the modeling method of dropout characteristic which distributed generators are expressed by reduced model. To obtain the dropout characteristic, we ran the parameter study by the detailed model and the reduced model in secondary system on same conditions. By the parameter study, in the dropout characteristic, we obtained the result that there is the correlation of the remaining rate of voltage in the primary system with the containing rate of induction machine in the secondary system. As a result, we contrived the dropout characteristic in which two above-mentioned were assumed to be a parameter. And, to confirm the validity of the contrived dropout characteristic, we calculated the amounts of dropout of distributed generator are two or more conditions by both the detailed model and the reduced model.

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The on-line TSC (Transient Stability Control) system is the world's first online-type stabilization system for electric power systems, which realizes optimum stabilized control of moment-by-moment power system conditions by obtaining power system information online and carrying out stability calculations at certain intervals.
This paper discusses the new transient stability ranking method for severity of each contingency, which will be introduced to the new on-line TSC system of Chubu Electric Power Company. The ranking method is based on system parameter estimation and the Extended Equal Area Criterion. The method can be applied to unbalanced fault.

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Distribution generation using new energy resources have been expected in the future power system. However, the interconnection cost and equipment cost of distributed generation (DG) are still expensive and stunt the growth of installed DG capacity. From the economic and environmental points of view, promotion of DG installation is indispensable in the future. This paper proposes a DG installation promotion program based on the load curtailment contract. In the proposed program, the load curtailment contract saves investments required for future power system reinforcement and induces the customers to install DG. Economical and environmental feasibility of the proposed program are discussed through numerical studies.

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In recent years, as the deregulation in electric power industry has advanced in many countries, a spot market trading of electricity has been done. Generation companies are allowed to purchase the electricity through the electric power market and supply electric power for their bilateral customers. Under this circumstance, it is important for the generation companies to procure the required electricity with cheaper cost to increase their profit.
The market price is volatile since it is determined by bidding between buyer and seller. The pumped storage power plant, one of the storage facilities is promising against such volatile market price since it can produce a profit by purchasing electricity with lower-price and selling it with higher-price. This paper discusses the optimal operation of the pumped storage power plants considering bidding strategy to an uncertain spot market. The volatilities in market price and demand are represented by the Vasicek model in our estimation. This paper also discusses the allocation of operational reserve to the pumped storage power plant.

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This paper discusses the influence of mass installation of a home co-generation system (H-CGS) using a polymer electrolyte fuel cell (PEFC) on the voltage profile of power distribution system in residential area. The influence of H-CGS is compared with that of photovoltaic power generation systems (PV systems). The operation pattern of H-CGS is assumed based on the electricity and hot-water demand observed in 10 households for a year. The main results are as follows. With the clustered H-CGS, the voltage of each bus is higher by about 1-3% compared with the conventional system without any distributed generators. Because H-CGS tends to increase the output during the early evening, H-CGS contributes to recover the voltage drop during the early evening, resulting in smaller voltage variation of distribution system throughout a day. Because of small rated power output about 1kW, the influence on voltage profile by the clustered H-CGS is smaller than that by the clustered PV systems. The highest voltage during the day time is not so high as compared with the distribution system with the clustered PV systems, even if the reverse power flow from H-CGS is allowed.

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The supply reliability of the power system strongly depends on the system planning and operation. Under the competitive environment, system planning and operation become more complicated and difficult due to the new uncertainties that have not been considered so far. Which may also results in the enlargement of difficulties in forecast in the planning stage, and causes the deterioration of supply reliability. In the competitive environment, the transmission network must be planned and operated with the economical rationality and fairness. However, it is difficult to realize the system planning and operation considering the economical rationality and fairness because of the uncertainties. Then, the high flexibility and robustness against the uncertainties are required for the system planning and operation. This paper evaluates the performance of system expansion planning from two points of views: the probabilistic supply reliability and transmission margin in power system. As indices, the Expected Energy Not Supplied (EENS) and Available Transmission Capability (ATC) are used in this study.

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We report the operational results of distributed generators (DGs) in a microgrid and present the effects after incorporating photovoltaic power generation (PV) systems into the microgrid for electric power system. The microgrid was constructed at the EXPO 2005 Aichi site as part of a demonstration promoted by NEDO. A solution is needed to problems where instability in the DGs that utilize natural energy such as solar light and wind force negatively influence existing electric power systems. So, we developed energy control system and controlled DGs output to reduce the fluctuation at the grid connected point caused by PV system's instability output. Our microgrid consists of DGs such as PV systems, fuel cells, and NaS batteries, and these DGs are controlled by an energy control system. We verified practical effectiveness of the installing the microgrid as follows. (1) 99.5% of the power imbalance in the supply and demand over 30 minutes was within a range of ±3% under normal operating conditions, (2) the microgrid contributes to the load leveling, (3) energy control system smoothes the power flow fluctuation of PV system output at the grid connected point, (4) in the future, installing a microgrid will help reduce the additional LFC (Load Frequency Control) capacity.

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Forecast of daily-solar-irradiance curve with higher precision is required for more efficient operation of energy supply system utilizing solar energy. We had developed ERDI method which calculates the daily-solar-irradiance curve from daily-total-insolation forecasted by feed-forward neural network. If the daily-solar-irradiance curve would have been forecasted by “Forecast method for Individual Site (FIS method)”, fiddly procedures such as selection of available data, training of the neural network, and generation of correction curve in ERDI method should be required for every forecast sites. The present paper presents the simpler method, in which a representative model was individually applied for 10 climatic districts, named the method of “Climatic-District Representative modeling in Japan (CDR method)”. CDR method obviously makes it possible that the daily-solar-irradiance curve can be forecasted in the site where the weather data is not available. Forecast errors between CDR and FIS methods were almost similar, which were in the range of 110 to 130Wh/(m²·h) nationwide.

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In this paper, the authors propose the mathematical model which derives the optimal operation strategies of an on-site power storage system through the use of stochastic dynamic programming technique. The model takes account of the variations and uncertainties of electricity market prices as well as the outage costs of power grid failures. The market price fluctuation is modeled with stochastic differential equation. The stochastic state transitions between normal and failed systems are modeled with exponential density functions. The derived optimal operation indicates that the economic value of the storage system may be increased substantially, if the avoided outage costs are explicitly taken into account. The results of the sensitivity analysis indicate that the most influential parameters are the magnitude of outage cost and the mean time to failure of power grid.

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A new method is proposed for credit risk evaluation in a power market. The credit risk evaluation is to measure the bankruptcy risk of the company. The power system liberalization results in new environment that puts emphasis on the profit maximization and the risk minimization. There is a high probability that the electricity transaction causes a risk between companies. So, power market players are concerned with the risk minimization. As a management strategy, a risk index is requested to evaluate the worth of the business partner. This paper proposes a new method for evaluating the credit risk with Random Forest (RF) that makes ensemble learning for the decision tree. RF is one of efficient data mining technique in clustering data and extracting relationship between input and output data. In addition, the method of generating pseudo-measurements is proposed to improve the performance of RF. The proposed method is successfully applied to real financial data of energy utilities in the power market. A comparison is made between the proposed and the conventional methods.

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In a future distribution network, it is difficult to maintain voltage because a large number of distributed generators are introduced to the system. The authors have proposed an autonomous decentralized voltage control method using multi-agent technology in the previous work. However, the control method does not include the function which saves the excessive decrease of power factor of distributed generators. In this paper, we propose a new control method which is improved to save the reactive power output. Generally, an autonomous decentralized control method is inferior to a centralized control method in efficiency. However, the efficiency of this proposed method is greatly improved using local information exchange about reactive power output. The proposed method is tested in 4-node simple model and 24-node complicated model. The relationship between control performance and information exchange area is also discussed.

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In the small-scale heat and power system like the micro grid, customers request the optimal equipment composition and optimal driving plan that can reduce the cost for introducing and driving generators and carbon-dioxide emissions, in consideration of the heat and power load in the area and the candidate of equipment. In this paper, the optimal equipment planning is modeled as a mixed integer linear programming. With this model we can calculate the equipment composition that put out the optimal output pattern according to the load pattern of given heat and power, and the list of the prepared equipment. To express the lower bound of the operating power of the generator, our model has a lot of integer variables, but we adjusted division of time to drive the generator by the load pattern, so we can solve that by a branch-and-bound approach in effective time.

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This study presents thermal diffusion distribution of the electric wires when overcurrent is supplied to copper wires. And then, this study intends to provide a basis of knowledge for analyzing the causes of electric accidents through hybrid technology. In the thermal image distribution analysis of the electric wire to which fusing current was supplied, it was found that less heat was accumulated in the thin wires because of easier heat dispersion, while more heat was accumulated in the thicker wires. The 3-dimensional thermal image analysis showed that heat distribution was concentrated at the center of the wire and the inclination of heat distribution was steep in the thicker wires. When 81A was supplied to 1.6mm copper wire for 500 seconds, the surface temperature of wire was maximum 46.68°C and minimum 30.87°C. It revealed the initial characteristics of insulation deterioration that generates white smoke without external deformation. In the analysis with stereoscopic microscope, the surface turned dark brown and rough with the increase of fusing current. Also, it was known that exfoliation occurred when wire melted down with 2 times the fusing current. With the increase of current, we found the number of primary arms of the dendrite structure to be increased and those of the secondary and tertiary arms to be decreased. Also, when the overcurrent reached twice the fusing current, it was found that columnar composition, observed in the cross sectional structure of molten wire, appeared and formed regular directivity.
As described above, we could present the burning pattern and change in characteristics of insulation and conductor quantitatively. And we could not only minimize the analysis error by combining the information but also present the scientific basis in the analysis of causes of electric accidents, mediation of disputes on product liability concerning the electric products.

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This paper proposes the pole change generator for windmill. Since the micro windmill system generates power from natural energy, power generation characteristics of a wide band are necessary. However, the conventional generator, where the open voltage is simply proportional to rotational velocity, encounters difficulty in generating power across a wide range of rotational velocity from low to high, in view of power generation characteristics.
To develop a generator of a wide power band suitable for micro windmill, this paper proposes a technique of switching the status of generator coil connection. To prove the effectiveness of pole changing, we assumed a pole-changing generator with 16 coils as an example. The coils can be connected by four patterns: 16-pole series, 8-pole 2-parallel, 4-pole 4-parallel, and 2-pole 8-parallel.
Then, theoretical and experimental studies from this point of view demonstrate that this technique is effective.

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This paper presents a study on the power system transient stability improvement by means of interline power flow controller (IPFC). The power injection model of IPFC in transient analysis is proposed and can be easily incorporated into existing power systems. Based on the energy function analysis, the operation of IPFC should guarantee that the time derivative of the global energy of the system is not greater than zero in order to damp the electromechanical oscillations. Accordingly, control laws of IPFC are proposed for its application to the single-machine infinite-bus (SMIB) system and the multimachine systems, respectively. Numerical simulations on the corresponding model power systems are presented to demonstrate their effectiveness in improving power system transient stability.

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Distributed Generation (DG) provides many advantages to distribution systems. However, the presence of DG units usually causes voltage fluctuation in the systems, and even causes voltage violation. A number of researches have paid attention to this issue that is widely known for years. The other fact that is revealed in this paper is momentary electricity interruptions due to the voltage violation. To prevent damages resulting from voltage violation, sensitive loads are normally equipped with over/under-voltage relays. As a result, the more frequent bus voltages violate their limits, the more momentary electricity interruption tends to occur. In this paper, Momentary Average Interruption Event Frequency Index (MAIFI_E) is evaluated to study this influence. In addition, uncertainty from renewable resources is integrated into the proposed voltage regulation method by using Probabilistic Load Flow (PLF). For IEEE-34 Bus test system, the numerical examples show that the uncertainty from renewable energy resources causes considerable MAIFI_E, and the proposed method for voltage regulation can serve as an effective prevention for this problem.

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Lightning-related overvoltages on 6.6-kV overhead distribution lines can roughly be classified into the two types: overvoltages induced by a nearby lightning stroke and overvoltages due to a direct lightning stroke to the distribution line. Protection measures against the former, which is commonly called lightning-induced overvoltages, have been taken and can be considered as completed. Regarding the latter, recent experimental studies have revealed that protection against a direct lightning hit is possible by applying appropriate countermeasures. Studies of such countermeasures are now carried out by digital simulations using the EMTP (Electro-Magnetic Transients Program), and thus components of a distribution line must be modeled appropriately in the EMTP for accurate simulations.
This paper presents surge characteristics of a distribution line obtained by experiments using a reduced-scale distribution line model. The reduced-scale model includes a reinforced concrete pole, a ground wire, phase wires, a grounding lead conductor installed along the pole, and a lightning channel. Unlike preceding studies, the surge impedance of a reinforced concrete pole is measured considering the effects of a ground wire and phase wires. Voltages at various positions of the distribution line model have been measured with varying the wavefront time of the injected current simulating a lightning stroke and also varying the grounding resistance of the pole, and their effects are examined.

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Electric power industry faces circumstances where advances in system automation technologies and enhancement of operational reliability make on-the-job training (OJT) opportunities less frequent and consequently it becomes difficult to rely simply on a traditional method based on OJT for successfully passing experimental knowledge and skills from one generation of technicians to another. In addition, the “year 2007 issue” puts companies concerned at risk of losing sophisticated skills or know-how which veterans in their employment have accumulated over many years of service.
This paper discusses, in light of the usefulness of “guided experience” under an apprentice system, a training/education scheme designed to realize an inheritance of experienced personnel's know-how, in particular tacit knowledge, and a new educational system which is based on this notion. A system is proposed which involves: 1) making use of a work simulator, 2) accumulating tacit knowledge which experienced personnel use as the way or process to identify, analyze and solve complex problems in specific challenging situations, and 3) realizing “learning by doing” which is supported by the database of tacit knowledge. Trial on a prototype has proved the feasibility of this system.

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Focusing on control that can be used to efficiently regulate SMES, unique control logics for power system stabilization were devised by combining the popularly used power deviation (ΔP) of a generator with the angular velocity deviation (Δω) of a generator or the phase correction. In the previous paper, we analyzed the performance and characteristics of the new control logics (ΔP + Δω control logic, ΔP + Δω + phase correction control logic) on both one-and multi-machine infinite-bus systems using the Y-method power system dynamics analysis program, and suggested that the new logics could improve the stability of power systems in comparison to the conventional ΔP control logic.
For the next phase of research, we have evaluated the performance and characteristics of the control logics mentioned above based on analogue simulation. As a result, the logics have showed the same tendency as the case of the digital simulation and it have been confirmed that the logics, especially ΔP + Δω+ phase correction control logic, have the superior effect on the improvement of the stability of power system.

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This paper describes an improvement of a conductor-subdivision-based method for calculating the frequency-dependent series impedance matrix of arbitrary cross-section conductors considering both skin and proximity effects. Analytical skin-effect formulas are available, but they are only for some simple conductor shapes and the proximity effect is ignored. Conductor-subdivision-based approaches can take into account both skin and proximity effects and are applicable to arbitrary cross-section conductors. However, at high frequencies where skin depth becomes very small, the subdivision-based approaches require an unrealistic number of subdivision. The proposed improvement assumes a current distribution obtained by an analytical skin-effect formula at surface subconductors for accurately representing the skin effect at high frequencies. Numerical examples show that the proposed improvement accurately reproduces the skin and proximity effects with a small number of subdivision even at high frequencies.

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In this paper, the equivalent radius of a thin wire represented using the FDTD method in the two-dimensional (2D) cylindrical coordinate system is identified as 0.135Δr, where Δr is the lateral side length of the rectangular cells, while that of a thin wire represented in the 3D Cartesian coordinate system is known to be 0.230Δr. Furthermore, it is shown that the technique proposed by Noda and Yokoyama to represent a thin wire having an arbitrary radius in the 3D Cartesian coordinate system can be applied successfully to representing such a thin wire in the 2D cylindrical coordinate system if 0.135Δr is used for the equivalent radius instead of 0.230Δr.

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A pole-mounted transformer on a power distribution line is vulnerable to lightning overvoltages, and is one of the most frequently damaged instruments in Japan. Therefore, the response of transformers to the overvoltage draws great concern. By incorporating the modeling for the secondary windings proposed by Mr. Honda et al., the authors develop equivalent circuits of distribution transformers of 10kVA, 20kVA and 30kVA rated capacity based on modal analysis of measured admittance whereby one can evaluate its response to overvoltages on a low-voltage line as well as on a medium-voltage line. The validity of calculated results obtained by using the developed circuits is demonstrated by comparison with experimental results. The response of transformers made by the same manufacturer to the lightning impulse voltage waveforms is influenced by the rated capacity, and the phase and the degree of such influence is demonstrated.

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The eddy current is induced in silicon steel sheets of core block of power reactor due to the fringing flux, and this causes a local overheating. If a bevel edge core is used in the reactor composed of laminated core, the eddy current loss may be reduced. In order to investigate the behavior of flux and eddy current in the reactor, a modeling technique of laminated core for exact and quick practical nonlinear analysis is investigated. It is shown that the practical analysis under distorted flux waveform is possible by subdividing only the region near the surface of lamination, and the inner part is subdivided as a bulk core having anisotropic conductivity. The flux and eddy current distribution of the bevel edge core reactor is investigated using the modeling technique of laminated core. It is illustrated that the maximum eddy current loss is reduced to about 20%, and the total eddy current loss is decreased to about 50% by introducing the bevel edge core.

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In this paper, a new absorbing boundary condition based on the advection equation has been proposed, which considers the attenuation of electromagnetic waves propagating towards the absorbing boundaries. The validity of the proposed condition has been tested by comparing the results, calculated using the FDTD method with the proposed absorbing boundary condition, with those calculated with other representative absorbing boundary conditions such as Liao's first- and second-order conditions. It has become clear that the proposed absorbing boundary condition is more effective than the other representative advection-equation-based absorbing boundary conditions.

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Lightning electric-field waveforms related to power line faults in winter have been identified. Most of those waveforms are inferred to be associated with upward lightning discharges with absolute peak currents over 100kA. They are quite different from common return-stroke waveforms, and lightning discharges which produce these characteristic waveforms are named GC (Ground to Cloud) flashes. These high-current lightning discharges distribute around the coastline in different ways depending on their polarities. Also, spatial distributions of high-current lightning discharges around Japan are investigated. As a result, it is revealed that the region on Honshu Island along the coastline of the Sea of Japan belongs to the area, where the density of high-current lightning flashes is the highest in Japan through the year.

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The lightning detection network has widely spread, and the research has actively been done by using the location of the lightning striking point and/or the peak current obtained by the network. Recently, Cummins et al. have clarified that the maritime return-stroke current on southern and eastern sea of the USA is higher than the inland return-stroke current by using the results obtained by NLDN. In this paper we compare the inland and the maritime return-stroke current in southeastern part of Kyushu by using the data obtained by JLDN. In case of negative first strokes, the maritime return-stroke current is higher than the inland stroke current in contrast to the cases of negative subsequent and positive first strokes. The authors investigate characteristics of the electric field waveforms associated with maritime negative and positive strokes in summer. As a result, it is pointed out that high frequency of occurrence of time-derivative of E-field waveforms having multiple pulses close to the dominant peak might be one of causes of the observed difference between the maritime and inland stroke currents in case of negative first strokes.

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Due to deregulation of electric power market, the several power transactions and the distributed generators will increase year by year. The power flow in power system will vary increasingly more complex and more uncertain by them. So it is difficult for Voltage and reactive power(Q) Control (VQC) to sustain the adequate voltages in the power system. On the other hand, the economy and security are requested for power system operation and control under the competitive environment. The optimization algorithm is effective to satisfy these trade-off problem. The optimization of VQC traces the combinational optimization problem with shunt devices, transformer tap and generator terminal voltage. Tabu Search (TS), which is one of meta-heuristic approaches, is suitable for the optimization problem of VQC. Because it is able to deal with the discrete variables such as shunt devices easily and it needs few tuning parameters.
In this paper, in order to realize flexible VQC which responds to the uncertain power flow with competitive environment, we propose the optimization of VQC with TS algorithm taking into account of both economy and security. The security is considered as the minimization of generator reactive outputs and transformer tap positions difference from the neutral. Moreover, the novel neighborhood condition setting focused on the control interference between voltage control equipments is applied to minimizing the objective function. It is confirmed by several numerical simulations using IEEE 14 and 57 bus system that the proposed scheme is able to ensure the security and to find the useful optimal solution efficiently.

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Over ten years have passed since the start of operation of on-line TSC (Transient Stability Control) system, which is the world's first online-type stabilization system for electric power systems. This paper discusses the challenges this on-line TSC system has so far faced in its actual operations and our development of new technologies and functions to overcome these challenges. Using transient stability ranking technique based on simplified transient stability calculation, new TSC system expect two advantages; (1) Accurate response to changes in power system conditions. (2) Using differentiation of severity of stability for each contingency contribute cost reduction.

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Generally, the battery is built with wind power generator to level the output power fluctuation of wind power generator, since output power fluctuation of wind power generator is large. However, if large battery is installed in power system, the capital cost for wind power system will increase. Hence, the smallest size of battery should be determined to save the capital cost.
This paper evaluates the effect of the output power leveling by introducing battery, and optimal size of battery is determined. A generated power output of a wind generator is easily calculated by real wind speed data only. However, battery charge/discharge actions are changed by control parameters for battery, it is difficult to decided the optimum battery system capacity. In this paper, output power fluctuation of wind power generator with battery system is calculated and estimated, so that the power output deviation is less than specific value, then minimum capital cost is decided by optimum battery capacity. The proposed technique determines the optimum size and control parameters for installed battery.

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The slowdown in power demand increase and facility replacement causes the aging and lower reliability in power facility. And the aging is followed by the rapid increase of repair and replacement when many facilities reach their lifetime in future. This paper describes a method to estimate the repair and replacement costs in future by applying the life-cycle cost model and renewal theory to the historical data. This paper also describes a method to decide the optimum investment plan, which replaces facilities in the order of cost-effectiveness by setting replacement priority formula, and the minimum investment level to keep the reliability. Estimation examples applied to substation facilities show that the reasonable and leveled future cash-out can keep the reliability by lowering the percentage of replacements caused by fatal failures.

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Development of decision support tools for maintenance strategy of electric power equipment based on the asset management technique becomes very intensive in order to reduce maintenance cost due to the liberalization of power business. In these years many theses have been presented about asset management in this area, but there are not yet so many concrete researches. This article introduces two approaches of decision support tool development for power equipment in CRIEPI. One is to support evaluation of dissolved gas analysis for oil-immersed transformers. It provides comparison to data obtained from the same kind of transformers, and criteria among them. The other is to evaluate average annual maintenance cost by considering an overhaul effect and failure risk. It provides an optimum overhaul strategy with suitable parameters.

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We have been studying the diagnostics ^{(5)(7)(9)(11)} and the degradation^(3)(8)(10) of ZnO elements which were installed in 275kV surge arresters operated for 20 years. I have examined the leakage currents of ZnO elements as I have accomplished ageing tests. As the results of examinations, I found that migrated oxygen ions are evaporated by supplied voltages⁽²⁾⁽⁶⁾, and again this oxygen gas evaporated is absorbed into ZnO elements in no voltage period⁽¹⁾⁽⁴⁾. The evaporation and the absorption are concerned with the Gibbs free energy and the diffusion energy of oxygen. When the Schottky barriers of ZnO elements are higher than 0.5RT; R is the gas constant and T is the absolute temperature, the evaporation and the absorption are stopped earlier. This reason is that the diffusion energy of oxygen becomes zero before the Gibbs free energy is reached to the balance.

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This paper studies the technique using neural network in order to estimate recession characteristics of river flow rate into a dam after rainfall. The rainfall is classified by similarity such as accumulation amount of rainfall, rainfall intensity, and base flow to the peak rainfall by using the cluster analysis. The training of the neural network is carried out by using the one out of the rainfalls of the similar group. The one data of remainder is used to asses the performance of the neural network on the accuracy of the estimated RTC of the river flow rate. The estimated error by cluster analysis becomes small.

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