Seto Ohashi Bridge comprises a four-lane highway and double-track railway, as well as an additional two tracks for a Shinkansen line to be incorporated in the future. This series of highway-railway combined spans has an upper deck for the highway and a lower deck for the railway. Salt pollution problems were investigated at this lower deck. The main results are summerlized as follows. The wind direction was East-West or West-East all through year, which was different from the seaside districts of Seto Inland Sea. The maximum instantaneous wind speed at the bridge was 55.5m/s caused by typhoon, and it was confirmed that the wind speed of this height was more rapid by far than the seaside districs. The salt pollutions on the insulator surfaces were heavy in case of typhoon and in winter dry season. The maximum salt deposit density of 250mm suspension insulator surface was 0.13mg/cm². It was concluded that the site severity of Honshu-Shikoku bridge is equivalent to the average pollution according to the classification by Society of Electrical Co-operative Research.

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A present-day power system is operated with high reliability, and it is rare that a blackout extends all over the system. However, considering its influence upon the society, it is prudent to prepare plans for restoring the system swiftly and securely. This paper deals with automatic power supply to loads after a complete blackout of the system. First, taking characteristics of generators, loads, and initial power sources into account, we propose a method of allocating several generators to each load, paralleling them to the system and supplying power to the load in sequence. Secondly, in order to remove imbalance between supply and demand of power, we propose a method of adjusting the amount of supply and generation according to a present imbalance and the sum of past ones. Thirdly, in order to automatically issue orders for start-up, parallel, follow-up, stand-by, and stop of generators, we set several rules for each power station, and make an expert system based on them. Lastly, we apply the expert system to a model power system, and verify that it can restore loads without any trouble for a complete blackout occured at any time of a day, and in any restoration pattern.

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This paper presents a sensitivity-based approach for structural control of electric power networks using FACTS (Flexible AC Transmission System) devices in order to improve transient stability margin. It is based on the sensitivity analysis of critical energy of TEF (Transient Energy Function). The control strategy problems are formulated as optimization problems. Also, techniques employing Neural Network to compute the sensitivity, and using Genetic Algorithms to sovle the optimization problems are presented. A related practical application to a 39-bus test system follows and shows that the structural control of power networks is effective for the enhancement of power system transient stability.

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Service restoration in distribution systems can be formulated as a combinatorial optimization problem. It is the problem to determine power sources for each load considering radial network constraints and power source limits. Up to now, the problem has been dealt with using conventional methods such as branch and bounds method, expert system, neural networks, and fuzzy reasoning.
Recently, Genetic Algorithms (GA) are noticed as one of the efficient methods for solving large combinator-ial optimization problems. The method can perform parallel search and can search optimal solution easier.
This paper presents an application of GA to service restoration in distribution systems. The feasibility of the proposed method is demonstrated on a typical distribution system model. The result shows that the method can solve the problem efficiently and this tendency becomes dominant by increasing of problem dimensions.

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This paper addresses a new effective method for the generator maintenance scheduling. As the scheduling is a 0-1 integer problem, no excellent approach to find optimal solution has been presented for a large scale problem because of the combination explosion. The proposed method combines a simulated evolu-tion and a branch and bound method. The idea of the simulated evolution is based on an analogy of the natural competition and selection process. The proposed method is not guaranteed to find an optimal solution. It has a capability to find sub-optimal ones with less CPU time by means of an effective search, however. It features (1) the high-speed search of a feasible solution by using depth priority search, (2) the effective improvement of the solution by the re-construction of the branching tree, and (3) requirement less memory size and CPU time. The proposed method was applied to a small scale 10 generator system and large scale 38 generator system. With comparing to branch and bound method, the ability of finding the optimum solution and of the effective search were verified.

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This paper proposes a method to compute voltages across insulator strings considering the effect of lightning strokes. Line voltages are handled as lightning-induced voltages on multiconductor systems with transition points caused by inclined lightning strokes. It is easy to solve line equations derived from Maxwell's equations using a difference method. However, it is difficult to obtain voltages and currents at the transition points consisting of various elements (lumped and distributed parameter circuits, arresters, gaps, and so on). Then, the proposed method uses Dommel method, which can easily and stably handle a large electric network, in order to solve the circuits of the transition points with equivalent sources and backward impedances. A program developed by the proposed method is based on the Electromagnetic Transients Program (EMTP), thus, input data is almost compatible with that of the EMTP. The calculated values by the program agree well with the experimental results using a scale model.

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Recently, cogeneration systems(CGS) are regarded as a main role of urban energy systems since they provide both electricity and thermal energy at the same time. However, the total energy efficiency depends on the energy demand pattern. Wheeling and thermal energy transportation systems are therefore expected to improve the total efficiency.
In this paper, the authors develop a model to evaluate the effects of cogeneration systems with wheeling and thermal energy transportation systems. This model consists of three steps. In the first step, this model minimizes the total cost under the given the electricity and thermal energy demand and generates the optimal capacity and operation patterns of CGS without wheeling and heat transportation system. In the second step, the minimized cost with them is calculated. Since the difference of the minimized cost between the above two steps represents their additional benefits, it is calculated among the cogenerator, consumer and electric power company by the tariff systems in the third step. Mixed integer programming model is also employed to see the partial load characterictics of CGS.
The simulation results show the followings: (1)The optimal capacity of CGS increases by wheeling and thermal energy transportation systems. (2)Office and retail building can be efficient cogenerators when wheeling and thermal energy transportation systems are available. (3)The charasteristics of tariff systems to distribute the total benefit of wheeling and thermal energy transportation are clarified.

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This paper resolves the generation mechanism of the singular transient response waveform of the ceramic transfomer by using a result of proposed equivalent circuit and its analysis. It is shown that it is impossible to explain the actual measurement by the computer simulation that considered the polarization of a difference direction and a higher harmonics in the conventional equivalent circuit analysis. The difference between this experimental value and calculated value is studied qualitatively by new equivalent circuite drawn from the structure of the element and its method of the analysis. As for the generation mechanism of the singular transient vibration, a conposite of the voltage that depends on the machine vibration and the electric circuit is made clear form the numerical value calculation of the proposed new equivalent circuit analysis. Consequently the difference of both analysis methods are clarified, and the propriety of this analysis method is ascertained in the inspection experiment.

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The present paper deals with a modeling method of electric equipments for a transient calculation. The model developed in the paper is expressed as an ARMA model which is suited for a discrete time domain simulation. Parameters of the ARMA model have been conventiaonally evaluated by a non-linear optimization method. The non-linear optimization method inherently involves numerical instabilities. For example, there is no assurance of convergence into an optimum value which minimizes the sum of square errors. In this paper, a linearized least-squares method (LLS) is proposed for improving the numerical stability. The LLS always gives the optimized parameters of the ARMA model without an iterative calculation, and a very small calculation time is required. The proposed modeling method is applied to an LCR series circuit, a transformer, and a frequency-dependent overhead line. Transient responses evaluated by the proposed model agree well with the measured results and the exact solution.

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The photovoltaic power system has a great future as clean energy instead of fossil fuel which has many environmental problems such as exhausted gas or air pollution. Sunlight, a source of energy for the system, is greatly influenced by the weather conditions, seasons and times of a day, therefore it can not supply constant electric power. The photovoltaic/fuel cell power hybrid system is assumed, it combines PV array, hydrogen generator, storage tank and fuel cells by using hydrogen. This system can supply constant electric power to the electric load in a solitary island separated from a commercial electric network. The possibility of this system is examined by the computer simulation. Input data includes the global irradiance on inclined plane and temperature of HASP data of Tokyo, ten kinds of electrical load forms with 400 MWh electric power a year and conversion efficiencies of each subsystem. As a result of simulation, it was revealed that the area of PV array with 8170m² and the volume of hydrogen tank from 22×103 to 30×10³ k^l are necessary.

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Human experts diagnose artifacts by generating fault trees, i. e., finding possible faulty components and their cause-effect relations from observations. Lately such task seems to be much harder, as artifacts become complex. Therefore computational methods, such as model-based reasoning, are expected to cope with the complexity. This paper presents a method of generating fault trees that uses qualitative reasoning. The proposed method deals with “model generation” which relates to the structural complexity and “inference on symptoms” which relates to the behavioral complexity. First, a target model is generated by using a model library that includes component models and structural data that are originally drawn on a design information. Second, states of components under an abnormal symptom are inferred by using two procedures ; constraint propagation and state transition. Third, possible faulty components are detected by using inferred states and fault models. Finally, each possible faulty component is managed by using fault trees. The result of applying this method to a protective relay is also discussed.

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Tohoku Electric Power Company constructed an LLP-system that covered Tohoku District with 9 magnetic direction finders (DFs). This system is capable of locating flashes with current exceeding 10 kA in good location accuracy, throughout the coverage area. The successful operation of this new system was achieved through the modification of waveform discrimination criteria to improve detection efficiency, and through the optimum arrangement of the DFs, together with the evaluation of site error at each DF.
Based on the analysis of the data obtained so far, operational characteristics of the system and some factors which affect the performance of the system have been revealed.

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