In recent years, the wind energy has been reconsidered because it is clean and the many studies for the effective use of the wind energy have been done. The generation of electric power using wind turbine generators is distinguished from conventional methods of generation by the variability of the prime source of power. A matter of concern is the effect of the varing wind on the generated power of wind turbine generators. This problem is very important to the power systems with small capacity in remote areas or islands.
The purpose of this paper is to keep the generated power of wind turbine generators at a rated value under the varing wind, by changing the blade pitch angle. Here the backstepping algorithm is used to design the pitch angle controller in order to consider the non-linearity for wind turbine generator systems. The proposed controller not only locally asymptotically stabilizes the plants, but also effectively keep the gererated power of wind turbine generators at a rated value under the varing wind. Digital computer simulations using parameters of the actual windmill generator system also give good results.

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The maximum power peak has sharpened in recent years in accordance with the widespread use of air conditioners and other such equipment. Additionally, the gap between power demand during the day and night, as well as that among the seasons, is widening, while the annual load factor is on the decline. These factors prevent the effective use of generating facilities and are driving costs up. Countermeasures in the form of the promotion of load leveling from the demand side have become a national priority.
It was in these circumstances that the New Energy and Industrial Technology Development Organization (NEDO) officially requested that Kyushu Electric Power Co., Inc. (KEPCO) develop load leveling technology for the future. For eight years starting in 1986, KEPCO conducted a demonstration test in which it directly controlled customer water heaters and air conditioners in a district in the city of Kagoshima. In addition, the company started a test in 1994 to demonstrate load leveling effects through indirect load control in a district in the city of Fukuoka. This load control involved providing customers on the demand side with their own load curves, electricity charge data, and other information so that they would themselves experiment with electricity use.
This paper will outline the Centralized Load Control System demonstration test and discuss system configuration and the 1996 test results of indirect load control that generated effects such as a peak reduction of 0.1kW per household.

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Overhead transmission lines are usually equipped with suspension insulators for keeping insulation. The suspension insulators are subjected to harsh environments in service for a long time. Long-term reliability of the insulators is required for both mechanical and electrical performances. We studied long-term reliability of mechanical strength on the suspension insulators. S P T (Strength, Probability & Time) characteristics, were obtained by testing the suspension insulators loaded at considerably high tensile stress for a long time. Based on these characteristics, we studied the method predicting failure risk at normal loads in service. Change in cement properties with time affected mechanical strength of the suspension insulators. Predicted failure risk was unrealistically low when using the S P T characteristics on the insulators with not aged cement. Increase in failure risk was estimated from the data on the cement-aged insulators. It was also verified that quality suspension insulators showed very low calculated failure rate under normal loading conditions in the field, which can ensure the long-term reliability of the insulators.

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Water trees are the most hazardous factor in the life of XLPE distribution cables and the major cause of insulation failure. It is well known that insulation failure causes stoppages in electrical service and requires extensive repair work. Therefore, deterioration of cable insulation has been diagnosed mainly by DC leakage current method. It is difficult, however to interrupt electrical service for diagnostic measurement. Several types of hot-line diagnostic methods (including the DC component current and DC superposition methods) are used to detect water tree deterioration. However, these methods have some problems, e. g., the effect of stray current, and the accuracy of measureent etc. On this account, we have been developing a new hot-line diagnostic method. We investigated whether the superposition of the voltage of various frequencies from the cover layer of energized cable and deterioration by water tree and the signal were correlated. As a result, we found that a deterioration signal of 1Hz was observed when we superposed the AC voltage (commercial frequency × 2+1Hz) on to the cover layer of cable where water tree had occurred in the insulation.

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For wide-use of a power plant utilizing solar energy, the improvement of its economics is important. Both economics and characteristics of a CO₂-capturing solar thermal hybrid power generation system have been evaluated in this paper. Since relatively low temperature steam of 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine, the solar collector can attain high heat collecting efficiency. The net fuel-to-electricity conversion efficiency of the hybrid system was estimated to be higher than 60% on lower heating value basis. It has been estimated that the gross income and the period of depreciation of the proposed system are 34.8×10⁵ yen/year and 8.89 years, respectively, and that the system is economically feasible, when the system is assumed to have the solar collector area of 10 ha, the maximum net power output of 4 MW and the heat storage capacity of 2000m³. The amount of the fuel saving and the reduction of CO₂ emission of this system, compared to a conventional natural gas firing plant, have also been estimated in the paper.

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The development of feeding cables is being advanced for use in supplying power to propulsion coils with a view of realizing the Yamanashi experimental lines of superconducting magnetic levitation railway (Maglev). To the XLPE insulation of feeding cables, a step voltage waveform is applied by an inverter in which high frequencies are superimposed on the basic commercial frequency. The authors deviced electrical testing equipment that can output such specific waveforms, and they investigated the effect of such waveforms on the insulation properties of XLPE cable, the breakdown characteristics of the model cables and their long-term characteristics. As a result, it was learned that the insulation breakdown depends on the voltage waveform peak value, and that the long- term characteristics are determined by the basic frequency. This knowledge will be usuful for the insulation design of feeding cable system of Yamanashi experimantal line.

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We observed winter lightning on 500kV transmission lines from 1984 to 1993. The observation was lightning course by camera and lightning current at the lower part of transmission tower on 31 towers, in 12.7 kilo-meter transmission lines. And we also observed lightning on isolated tower in nuclear power station.
Through the ten-years lightning observations, we have confirmed lightning protection design on transmission line. The distribution of lightning incidence angle (θ) was m=2 (cos^m θ) for the 3 dimensional case, and m=3.5 for the 2 dimensional. We had no case of shield missing on 500kV transmission lines. The ratio of lightning current at the top of isolated tower to the lower part was about 11 to 1. And the lightning current waveform at the top of isolated tower was similar to the one at the lower part.

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High-frequency current interruption caused by chattering of electrodes in a vacuum switch is calculated by a Mayr type macroscopic arc equation. Measured and calculated arc voltage and current are in good agreement, except for spike voltage escalations at current zero, under conditions of 75k, 100k, 120k and 200kHz resonance frequency of a L-C circuit parallel to the vacuum switch. Similar result is obtained in a case of 171kHz resonance frequency of a L-C circuit with a 1.0Ω dumping resistance. It is concluded that the use of the macroscopic arc equation is effective for calculation of arc voltage and current in vacuum switches.

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This paper describes the results of tests and discussions carried out to develop a system for partial discharge monitoring in GIS. They include the propagation characteristics of partial discharge pulses in each GIS component, the test results obtained using actual 300kV GIS. This paper also includes the results of verification test of the GIS partial discharge monitoring and location system which authors have developed.

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Magneto-acoustic Instability of nonequilibrium plasma in a disk MHD generator was investigated experimentally and analytically. At a low load resistance, a striated discharge structure was observed and it was found that the resonance line spectrum of cesium and recombination radiation fluctuated simultaneously under the conditions of some seed fractions. Furthermore, it was found that the fluctuation of recombination radiation became smaller when a high enthalpy extraction was obtained. On the other hand, at a high load resistance, a large fluctuation of static pressure with frequency of 2[kHz] which was thought of a magneto-acoustic wave was observed and it seemed that the pressure wave propagated upstream against the flow. Optical measurements suggested that the fluctuation of electron density did not depend on the fluctuation of electron temperature in the case of existence of the pressure wave. In addition, growth rates of magneto-acoustic wave were calculated by a liner perturbation theory, and the growth rate was found to get smaller with increase of seed fraction because the Hall parameter becomes lower at higher seed fraction. This analytical prediction agreed well with the experimental result. The analysis also indicated that the wave was amplified by a spatial gradient of the collision force between electrons and heavy particles which was caused by an increase in local collision frequency.

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