Power quality has become a common concern of customers and utilities in improving respective profits in the context of an open electricity market. Power electronics is the essential technology to control power quality in accordance with customer requirements and utility standards. This paper first summarizes power quality definitions and indices used in IEEE and IEC standards. It clarifies the problem to be solved and the role of power electronics devices. Then the overview of power quality control methods and equipments employing power electronics devices is explained. The control methodology discussed in this paper includes various schemes of future distribution and power supply system now under development.

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In order to analyze the system dynamics of a large integrated power system, it is required to analyze the system composed with detail models of power system components such as generators, loads and transmission networks. As it is time consuming and laborious task to analyze the total detail power system, the aggregation method is efficient. This paper proposes the engineering-based aggregation method using modal analysis, to improve the analytical accuracy that is fatal defect of engineering-based aggregation method. Furthermore, the proposed method is verified by using two types of systems in which it is difficult to apply the existing engineering-based aggregation method; one is the system with different control constants and the other is the system with weak coherency. The proposed method is to adjust the constants of control system of the aggregated system using modal analysis based on typical engineering-based aggregation method such as “the short- circuit current method".

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A time scale separation (TSS) method is proposed for the coordination of voltage controls of different time scales. The method is applied to a design of voltage regulator for static var compensator (SVC) which will be used with a step voltage regulator (SVR) in a distribution system. A simple filter, an input filter to the conventional SVC, is developed for the coordination with SVR controllers. The proposed filter can also be used as an input filter to AVR of the dispersed generators for the coordination controls with the conventional tap control devices. Effectiveness of the proposed method is demonstrated through numerical simulations in a distribution system having a large disturbance source of a wind power generator.

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This paper presents the mixed H₂/H_∞ controller design with regional pole constraints for damping power system oscillations. The state feedback gain can be obtained by solving a linear matrix inequality (LMI) feasibility problem that robustly assigns the closed-loop poles in a prescribed LMI region. The proposed technique is illustrated with applications to the design of stabilizer for a typical single-machine infinite-bus (SMIB) and a multimachine power system. The LMI-based control ensures adequate damping for widely varying system operating conditions. The simulation results illustrate the effectiveness and robustness of the proposed stabilizer.

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We have developed the Reliability Analysis System for Protective Relays (RASPR), which is composed of a database for protective relay equipment and its failures, and reliability analysis part. The data for relay systems and their failures have been collected since fiscal 1997.
In this paper, the following suggestion was made from the analysis of the reliability for protective relays; 1) Omission of interruption of automatic checking at fault doesn’t have an influence on the reliability such as the availability, 2) Improvement of the availability was cleared from the analysis of effect of shortening of the testing time required, 3) The extension of the periodic testing period could be possible if 70% of failures discovered in a periodic testing were detected by continuous monitoring.

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The rapid spread of CHP systems will put pressure on the regional power system to requiring an examination of the power and heat output of CHP systems. When considering the country-wide potential of the CHP system one should examine such system in coordination with the grid power system. It is essential to calculate the heat and power demand at end-use level. In the paper, annual heat and power demands of end-use sectors are forecast to the year 2025 based on 20 year data. Regression analysis is used. Estimated annual demands are divided into the seasonal hourly demands considering demand characteristics. Daily load curves of heat and power demands are determined for the Japanese end-use sectors, and the annual changes of such demands are shown by duration curves of heat to power ratios. Moreover, the grid power daily load curves are computed numerically from the estimated heat and power demands at manufacturing, residential and commercial sectors. Such load curves also consider self-generated power at manufacturing industry and own consumption of the grid power. Estimating heat and power demands allow for a joint analysis between the power system and the future phasing in of CHP systems.

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Power system small signal stability studies have been carried out using a synchronous machine model with field mutual-leakage reactance called Canay reactance in the d-axis equivalent circuit. The influence of Canay reactance on effects of power system stabilizer (PSS) was checked with eigenvalue calculation method. The values of Canay reactance reported in the literatures were also investigated statistically, and an approximated expression possible to be adopted in stability studies was also proposed.

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For the rationalization of lightning protection design of distribution lines, it is important to clarify the behavior of distribution line when direct or nearby lightning occurs. Because of the lower insulation level than is for transmission line, in study on lightning protection design of distribution line, not only direct lightning strokes but also induced voltages caused by nearby strokes must be taken into account. So it is necessary to grasp the frequency of occurrence on lightning phenomena around distribution lines. For this aim, lightning phenomena on TEPCO’s distribution lines in use had been continuously observed for 6 years (1996-2001). The observation was carried out in composite way, using still-cameras and sensors for acquisition of lightning surge waveform data. Through the observation, new interesting phenomena about lightning performance on distribution lines in fields became apparent. In some case, in spite of direct striking to the line, flashover did not occur. This fact means that distribution line has a certain level of lightning resistance. Moreover, it was confirmed that AC following current generated between both ends of insulator disappeared naturally. These results are the interesting discoveries that can be useful to estimate the fault ratio precisely.

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For the purpose of following electricity demand change and improving the efficiency of generation for fuel cells, a new system, which is called metal hydride intermediate buffer method, is developing. The system uses the selective reacting function of hydrogen on metal hydride materials. It is said that metal hydride could be easy to be poisoned by impurities except for hydrogen. Therefore a surface treatment has been adopted with the material to avoid it. We have found that the treatment is effective against H₂O and CO₂, which exist mainly in the reformed gas. One of general concerns about poisoning by CO included slightly in the reformed gas must be confirmed. In order to verify the treatment effect against CO, hydrogen absorption and desorption experiment were repeated with the simulated reformed gas (SRG) including 100ppm or 1% of CO concentration. In the result, it has been clarified that the metal hydride keeps the absorption property in spite of CO existence. In the CO 100ppm condition, functional deterioration due to CO-poisoning is not recognized at all. The hydrogen absorption rate is significantly reduced in the CO 1% experiment compared with the fuel gas without CO, but the absorption property has not been lost entirely. On the other hand, it has been found that the absorption property is gradually degraded, even if pure hydrogen without any impurities is used.

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The performance of a liquid metal MHD generator is investigated with a two-dimensional numerical simulation. The effects of the electrode length, the position of current lead connection and the insertion of insulator on the performance are examined taking account of the current flow in the electrode. There exists an optimal electrode length for a given distribution of applied magnetic flux density. For a short electrode, the efficiency decreases because the power output becomes small. For a long electrode, on the other hand, the efficiency also decreases owing to the leakage current from the upstream and downstream edges of the electrode. An optimal current lead position was revealed. This fact is ascribed to the distributions of induced magnetic field and the current flow in the electrode. It was found that the insertion of insulator is effective for improving the performance, by which the eddy current can be reduced.

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The present standards of AC insulation tests for high voltage power equipment in Japan are based on the reliability evaluation according to the Weibull statistical distribution as fault (breakdown or partial discharge) occurrence probability of the equipment. This paper analyzes various issues in the process, such as how to apply Weibull distributions as well as their experimentally determined parameters for transformers and GIS’s (gas insulated switchgears). The present evaluation is not considered proper as it does not take into account non-accidental change of the equipment with time. The paper gives the proper expression of the fault probability when two different levels of voltage are applied to equipment. It also discusses the issues of an n-value (slope of V-t characteristics in a logarithmic scale) separated in two time regions as well as experimental data for GIS’s.

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