Deregulation in power systems has created many technological challenges encouraging the intereconnection of dispersed generators (DG) and the changes of the operation in distribution power systems. Therfore more sophiscated analysis and operation of power systems will be expected regarding the impacts and power quality in association with such situations. This article discribes the new trend of simulation methods applied for distribtion power systems.

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A low-voltage molded-case circuit breaker using an auto-puffer technique is developed for the first time. This paper presents our research and development of this new-type circuit breaker.
In the research, arcing and quenching phenomenon in a simple chamber model is investigated experimentally and numerically. As the result, the quenching phenomenon is strongly influenced by the chamber, its material, dimension, shape and so on, and it is found that the gas flow and its component in the chamber are quite important for quenching phenomenon.
In the next stage, we developed a new commercial circuit breaker, based on the previous research. From the interruption tests of a 600V short circuit, the usefulness of this technique was verified. And it is found that this gas flow is also useful as an arc driving force as well as electromagnetic force.

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The electric power markets have been liberated partially and the liberation will be promoted continuously. On the other hand, refuse-fired generating systems (RGS) are constructed in many municipal corporations as on-sight power sources. This paper discussed the operation of a RGS which could transfer its excess energy to consumers through the electricity wheeling service of the electric utility. The RGS is operated by the dynamic programming method under the constraints of the RGS operation and the electricity wheeling service. In the DP method, the estimation function is the annual total electricity charge of both of the RGS and the consumers, and the control variable is the residual amount in the refuse pit. A university, a hospital, a welfare apartment house and their combinations are selected as consumers. The main results obtained are as follows: (1) the electricity wheeling service is more economical than the no electricity wheeling service when the annual demand of the consumer is higher than 70% of the excess energy of RGS, (2) it is more economical as the load factor increases if the annual demand is same, (3) the most economical consumer is the combination of four hospitals and five welfare apartment houses, and its total electricity charge can be reduced to 84% of with no wheeling service. It is concluded that the total electricity charge of the RGS with electricity wheeling service could be decreased considerably by selecting the consumer appropriately.

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A prototype 100kVA machine of adjustable speed generator with flywheel effect(FWM) and self-commutated converter was made. Experiments for power system stabilizing control were carried out in the 3.3kV mimic power system. The time responses of the machine were 20ms both for active power control and voltage control. It was certified that the synchronous generator does not step out when FWM is installed in the power system, even under the 3LG-O fault. To verify power system stability effects by FWM, the experiments were made for two control schemes, Braking control and damping control. By the experiments, the optimal parameters and conditions are studied. Theoretical analyses were also made and showed good agreement with experiments. Through these studies it was verified that FWM is very effective tool for improving power system stability.

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In recent years, by promotion of the deregulation of electricity markets, competition has been introduced in generation field. When planning for generation expansion, utilities must take into account independent power producers (IPPs). Utilities prefer introducing IPPs to building new generators if the participation of IPPs can maximize their profits. At the same time, IPPs want to maximize their own profits and therefore bid against each other to participate in the generation market. In the partially deregulated market where only generation sector has been liberalized, the relationship between utilities and IPPs is competitive, and also is cooperative, because they all want to maximize their own profits to obtain the share of generation in the same market. This paper discusses the bidding conditions for IPPs based on their scenario analyses, and proposes a solution for the utility to obtain the coordinative generation expansion planning from the viewpoint of a utility at the same time considering the profits of IPPs. Supply reliability and the environmental problem of emissions, such as of CO₂ emissions, are considered. Based on the extended Dynamic Programming (DP) approach, the feasibility of the proposed approach is demonstrated in a test power system, and the coordinative generation expansion plan for the utility, while the impact of IPPs is taken into account, is obtained.

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Because of low cost and maintenance free, inductron machines are widely used as the wind turbine generators. In order to get wind energy effectively, pole-change-type induction generators are adopted. Otherwise, the pole-change-type induction generator causes the voltage dips at starting and at pole changing time. To keep the power quality, it is important to know the state change of the generator operation.
In this paper a new state criterion of wind turbine generator in operation using the tower shadow effect, which is the oscillation of active power caused by a drop in rotation torque of the wind turbine when the tower of the wind turbine and the blade of the turbine overlap each other, is proposed. By using the developed method, the state of the wind turbine generator can be judged using the short period oscillation frequency of the active power of the wind turbine generator.The developed method is applied to measured data, and it is found that the developed method is effective in the state criterion of the wind turbine generator. It is also found that the moving average method is one of the efficient methods to suppress the fluctuations in the trend of error, namely, the deviation of the frequancy of the wind turbine generator.

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We have proposed a detection method of poor contact of the low voltage switch by an ultrasonic wave. In this paper, poor contact was artificially made putting dried grass, cherry tree, flour, and alumina, between two terminals of a model switch, and the ultrasonic wave was applied under the current flowing by the maximum 5A. From the change of magnitude and waveform of the terminal voltage, it was shown that the contact state of switch can be judged.

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A molded-case circuit breaker has deion plates to raise an arc voltage. To understand the phenomenon of a rise in an arc voltage due to deion plates, an arc current, arc voltage and voltages between the deion plates were measured for high-current air arc. The peak value of the arc voltage rose with a decrease in distance between the deion plates and electrodes. This rise resulted from the voltages between the deion plates. The voltage between the deion plates was found to consist of two voltages: (1) an arc-column voltage and (2) the voltage occuring between the arc column and the surface of the deion plates. These voltages (1) and (2) proved to be 2.3V/mm and 25V, respectively. On the basis of these results, the expression of the arc voltage affected by the arrangement of the deion plates was derived to be a function of current.

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Transient grounding impedance of a gas-insulated switchgear (GIS) substation were investigated through measurements on a commercial 300kV underground substation. From the results, the transient impedance of the grounding grid was clarified. The attenuation factor of the propagation line composed of the outer surface of the GIS tank and the concrete floor was also evaluated. Furthermore, the validity of EMTP analysis on the surge phenomena in the GIS grounding system was confirmed.

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SF₆ gas has been used for power apparatus as an insulation medium. Reduction of SF6 gas emission was discussed at COPS in 1997. It has been required to develop alternative gas apparatus as measures. This paper aims to acquire a sharp reduction in Global Warming Potential (GWP) of insulation gas without SF₆ gas. In this paper, C₃F₈ was selected as an alternative gas and insulation characteristics of C₃F₈/N₂, C₃F₈/CO₂ and C₃F₈/CF₄ gas mixtures were analyzed by Boltzmann equation. Furthermore, the experimental insulation characteristics of these gas mixtures for quasi-uniform electric field were obtained under ac voltage and were compared with analyses. As a result, analyses results corresponded to experimental results. All of insulation characteristics of tested gas mixtures had small synergism. Required gas pressures and GWP were discussed in comparison with those for SF₆ gas and C₃F₈/N₂ gas mixture had possibility of SF6 alternative gas in these gas mixtures.

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To improve GIS insulation specifications, it is important to recognize the insulation characteristics under oscillatory overvoltage waveforms occurring in the field. This paper describes investigations of insulation characteristics for single-frequency oscillatory waveforms with various conditions of gas pressure, gap length, surface roughness of electrode and bias voltage that is remained on electrode previously. As a result, it was obtained that minimum breakdown voltages (Vmin) were proportional to gas pressure (p) and gap length (d) in the range of experimental condition. Therefore Vmin were proportional to the product of gas pressure by gap length (pd). On the other hand, Vmin were independent on surface roughness of electrode and bias voltage in the range of experimental condition. Thus, it was verified that the experimental conditions, which had been treated in the series of research for the insulation characteristics under oscillatory waveforms, were appropriate to simulating the actual field conditions.

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