The recent drastic increase in the number of air conditioners has caused sharp and narrow peaks in summer seasons due to the inherent temperature sensitive characteristics. The authors proposed to reduce the peak power demand by controlling air conditioner operations, verifying its effectiveness on peak demand clipping. However, the former study has shortcomings in that any qualitative treatment of room temperatures or pleasant feeling was not attempted and it did not provide a way of assessing peak demand clipping in a power system as a whole.
In this paper, we shall first propose a new control method that can compromise pleasant feeling and reduction in power demand. Although air conditioners are used to pursue “pleasant feeling”, this contradicts to reduce power consumption and further more the concept of “pleasant feeling” is very vague. Hence, “Weber-Fechner's law” is utilized to quantify the pleasant feeling which is treated as fuzzy quantity. Fuzzy co-ordination method is used to compromise power demand curtailment and pleasantness.
In the second part of this paper, we shall propose an approach of assessing the amount of peak load clipping when the newly proposed control strategy is adopted in a real size power system: A decrease in the required generation capacity is estimated provided that the Loss of Load Probability ( LOLP ) is maintained at the same level before and after the application of the new control strategy. The reduction can be regarded as a dividend of load management.

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When electric power supply is interrupted due to a fault, it is imperative to promptly restore the power system to an optimal target configuration after the fault. A problem of obtaining a target system is referred to as power system restoration. Both mathematical programming (MP) and expert systems (ES) have been used to solve restoration problems. However, existing approaches based on either MP or ES alone have inherent limitations stemming from their own paradigms. MP can obtain an optimal configuration under specified operational constraints, but needs a relatively long solution time. Although ES is suitable to the problems in that it can utilize experts' knowledge, a large scale ES needs a prohibitive amount of efforts at maintenance.
This paper proposes a new approach for power system restoration that utilizes the both methodologies to exploit their advantages. That is, a system under study is decomposed into a set of subsystems based on the knowledge of restoration experts, which is realized as an expert system. Then, MP is applied to each decomposed subsystem to obtain an optimal target configuration. A feasible operation sequence leading to the target configuration is generated by ES. As a result of this approach, the computation time to obtain the target systems becomes far less compared with solving the total system as unity. Moreover, the number of rules in the knowledge-base has greatly decreased.

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With economic growth, municipal refuse as well as electric energy consumption of the refuse disposal plants are rapidly increasing. Therefore, the improvement of refuse disposal plants and the conservation of energy have become the most important issues in the refuse disposal sector in Japan. Recently, the refuse fired power plants have been constructed at many local municipalities. However, some plants can not help disposing of the refuse at a high cost.
In this paper, in order to minimize the total cost necessary for refuse disposal, a linear programming model of the wide-area operation is presented on the basis of the ten existing refuse disposal plants in Aichi prefecture. This operation cuts down the total cost by about 6 hundred million yen and increases the total electric energy by about 3 GWh compared with the actual values under the electricity sales price 10 yen/kWh and the unit price of transportation of refuse 43 yen/ton/km.

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This paper presents an application of parallel processing and pipeline processing in power system analysis. The system matrix is transformed to a BBDF (bordered block diagonal form) matrix for effective utilization of the processors. After LU factorization, subnetworks organize sparse matrices and boundary network organizes a full matrix. First, parallel processing technique is used to calculate subnetworks. Then, pipeline processing being applied, inverse matrix of boundary network is multiplied. The proposed method is made operational on parallel computing system including a pipeline processor. A consideration on the transient stability analysis using the proposed method is also presented at the end of this paper.

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This paper proposes graphical representation methods of static and dynamic characteristics of power systems. The methods use the computed results of load flow calculation and dynamic stability calculation. This work develops three kinds of representation methods using maps and animation which are sequential graphical representation of maps based on dynamic stability calculation. Conventionally the results of load flow calculation and dynamic stability calculation are represented and comprehended using load flow maps or dynamic swing curve. However, quick and effective comprehension of power system characteristics by such conventional representation methods is becoming more difficult as power system to be analyzed is becoming larger and more complicated, especially in power systems with many loops or grids. Graphical representation using the proposed methods makes it easy to understand the static and dynamic characteristics of power systems quickly and comprehensively.
In addition to these methods, this paper proposes a heuristic logic that makes it possible to draw maps automatically. It is very convenient to apply these methods to arbitrary power systems even if we do not know their constitutions or characteristics well.

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This paper presents a new switching control scheme for static var compensator (SVC) using fuzzy logic control rules to enhance the overall stability of electric power systems. In addition, the coordination with power system stabilizers (PSS) is also considered to achieve a wider stable region. An SVC is set on one of the busbars in the transmission system, where the real power flow signal is utilized at the location of the SVC to determine the firing-angle of the thyristor switch. The switching control scheme is simple so as not to require heavy computation on the micro-computer based switching controller. PSS's are also set on the generators in the study system. Simulation results show the effectiveness of the proposed fuzzy logic switching control scheme for the SVC. The coordination between SVC and PSS is also effective to enlarge the stable region.

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Variations with time of the utility-grid frequency, voltage, harmonics, and voltage phase were calculated from measured voltage waveforms and quantitatively determined. The experiment consisted of connecting approximately 100 PV systems of 2-kW capacity to a 10-km long simulated distribution line. As a result, it was made clear that PV systems did not have adverse effects on harmonics of voltage in ordinary operation. It was also found that the changes in frequency, voltage and voltage phase increased with the PV output immediately before the occurrence of islanding, while the increase in harmonics settled at certain levels regardless of the PV output in case PV systems incorporating current-controlled type inverters were involved. Changes in frequency and voltage and increases in harmonics were governed by the difference in the type of the electrical load.

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Storage batteries or pumped power stations have been used for storing the electric power. However, there are some problems on storage batteries, such as long charging time, limited cycle life, low coulomb efficiency and inaccurate residual power meter. Because of the facts, practical power applications are not yet prevailed.
To solve those problems, a complex system of capacitors and electronic circuits named ECS (energy capacitor system) is proposed. The capacitor part of the ECS is a group of electric double-layer capacitors of increased energy density. The circuits part is built around switching regulators. Though the capacitors alone are not capable of delivering stable output, the accompanied circuits compensate the various characteristics all through the charge- and discharge-cycle.
Combined together, the energy density is to be increased about 16 times from the conventional electric double-layer capacitors to almost the level of lead acid batteries, with low enough output resistance and better voltage stability. Other than the energy density, the ECS inherently features short charging time, very long cycle life, good coulomb efficiency. The cells are completely sealed, made from inexpensive materials that may not be harmful to the environment.

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The overhead ground wire is generally used on transmission lines as one of the lightning protection devices for the power conductors, In recent years, the ground wire with an optical fiber cable in it (OPGW) has been employed on the transmission systems. The strands of the ground wire are, however, frequently melted down because of lightning strokes to them not only in summer but also in winter, For this reason, it is necessary to devise the new lightning protection method for the ground wire. As the protection method, lightning rods installed on the transmission tower arms and projection rods wound around a ground wire are proposed by authors, lightning protection effects of these methods are shown by model experiments which simulate summer and winter lightning strokes, It has been made clear that these methods are useful as one of the lightning protection methods for transmission lines, and application conditions of them for practical use are also shown.

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In back flashover analysis of a transmission line by a circuit simulator like EMTP, we should use the adequate equivalent circuit of transmission line towers for reliable results. The tower surge impedance in many reports has been discussed by the electromagnetic field theory or loop voltage method that calculates the voltage by magnetic potential. However, the theoretical values are several tens ohms larger than the measured values. In this paper the several reasons of the discrepancy between the theory and measured values were discussed. From the results, it became clear that Maxwell's equations are not satisfied in the conventional loop voltage method, in which the tower current is assumed as a constant value and constant velocity current between the tower top and the ground base. The loop voltage method does not satisfy the boundary condition that the tangential electric field on the conductor of the tower is zero, and this incongruity makes the calculated tower surge impedance larger than measured one. Although the loop voltage method is convenient to calculate the tower surge impedance as function of the tower height and the radius, it should be examined in the application of the theory to the back flashover analysis.
A nonuniform transmission line model was applied to calculate the surge impedance of a rod vertical to ground. The surge impedance calculated numerically by inverse Laplace transformation showed good accordance with the average characteristic impedance. For the simple calculation of surge impedance, we obtained also an analytical equation by the approximation of the nonuniform transmission line, which is almost equal to the experimental equation.

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We proposed a transmission line tower model in frequency domain for the back flashover analysis, which has a uniform characteristic impedance and a uniform propagation constant. Most conventional tower models are constructed as a constant and uniform parameter transmission line that is independent of frequency, but our models have the frequency dependency of the characteristic impedance and the propagation constant to express the frequency characteristic of the transmission line tower. Two models, a cylinder model and a four-flames model were investigated to simulate the tower. Their surge responses were computed by the numerical electromagnetic field analysis based on the moment method. From the results, the twoport circuit constants were calculated in frequency domain, and the characteristic impedance and the propagation constant are derived from them. The complex artificial oscillations appeared in frequency dependency of the parameters because the parameters were calculated numerically. We obtained the equations with analytical form by approximating with a smooth curve to the oscillations. It is possible for the equations to represent the transmission line constants as a function of geometrical parameters such as the tower height and the radius. It was found close agreement between the surge response computed by the numerical electromagnetic field analysis and the result calculated by inverse Laplace transformation of the analytical equations. To prove the model, we compared the experimental results with the computed ones of the cylinder model that has arms, and it was shown that the new model agrees with the experiment closer than conventional transmission line models.

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The influence of NiO content and sintering temperature on several properties of Nickel-Zirconia Cermet that is usually applied to Solid Oxide Fuel Cell anode was investigated. The conductivity was mainly influenced by the NiO content, and approximately 100S/cm was attained by the addition of 60 wt% NiO. As for porosity, it was determined by the NiO content and was also influenced a little by the sintering temperature. Thermal expansion coefficient was also measured and results revealed that the coefficient was not affected by the sintering temperature but only by the NiO content. The thermal expansion coefficient increased almost linearly with increasing NiO content.

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In the field of protective relay, a dream which is unable to be realized by analogue technology has come true with the advance of computer technology. However, there is still room for the development of high functional protective system, which makes the most of a merit of digital processing because the present digital relay uses the same principle as analogue one. The points of proposed theory are that firstly it uses a lot of data of fault, secondly uses the First and Second Kirch-Hoffs laws at the same time which are the starting point of electric circuit theory, and thirdly calculates both fault lacation and resistance by solving non-linear simultaneous equations.
In this paper, high speed calculation for protective relays is achieved by solving a compact matrix using Newton-Raphson method.
The matrix consists of two sorts of variables (fault location, fault resistance), and the non-linear simultaneous equation is reduced by definition of new variables.
As a result of applying this theory to some real faults, we testified that the fault location error was within 0.1%, and the calculation time was less than 5 ms.
Therefore we think that this theory has been already on a practical stage.
The ultimate goal of this theory is the integration of various algorithms on protective relay, fault locater, and fault restoration operation.

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