Show accretion on transmission lines in heavy snowfall areas may cause critical accidents such as tower collapses, sleet jumps, etc.. To assist power system operators in making plan of deicing countermeasures against these accidents, a prototype expert system had been developed. The system forecasts snow accretion on transmission lines and lists all the feasible and effective deicing countermeasures. This paper presents a technique to choose the optimal deicing countermeasure, which will help power system operators to make a decision. This optimization is done by fuzzy multiattribute decisionmaking approach which is expected as an effective tool in the presence of uncertain evaluation data. The proposed algorithm generates evaluation functions for all alternatives in terms of fuzzy sets, compares them to choose the alternative with the least evaluation function, and presents the decision result in the form of a statement describing the strength of preference in natural language. Fast calculation algorithms for extended algebraic operation of fuzzy numbers is presented too.

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Recently, voltage instability has been becoming one of major problems of power systems, and therefore, a lot of researchers have been studying this problem. A recent major topic arising as the results of these studies is associated with the mechanism leading to voltage collapse, especially the contribution of load dynamics to this phenomena. In fact, different assumptions as to load representations, that is static or dynamic, have given different analysis results in many previous studies. Further, the theoretical interpretation about the difference has not yet been given completely up to now.
This paper provides a resolution of the above problems by extending the authors' previous study⁽⁹⁾, in which possible voltage instability patterns have been classified into four types. In the first half of this paper, the relationships among the classified instabilities are theoretically derived using a general expression of load dynamics. The theoretical meaning of general analysis results under static and dynamic load representations is also examined here. Then, taking Nagao's simulation method as an example⁽¹⁰⁾, the effectiveness of this method is studied from the view point of its inherent characteristics as well as analysis errors caused by its assumption of static loads. In the latter half, these theoretical results are verified through numerical simulations in IEEE 14 test system, with taking into account dynamic characteristics of generators, controllers, tap changers, induction motor loads, etc.

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Load factors of power systems are decreasing in these days. Under the circumstances, it is considered that “load management” is an effective method to cut down the production cost of electricity. On the other hand, the introduction of energy storage equipments increases the load factor. It can be said that “load management” has almost similar effect as “energy storage”. When “load management” and/or “energy storage” is considered to be introduced, it is very important to estimate the effect of each method on the production cost. Since each area has its own load profile, the effect of “load management” or “energy storage” on the area is different from that on the other area. In this paper, the relationship between the improvement of the production cost and the load profile is discussed. It is found that “load management” is more effective on the area which has small load factor and large kWh operation factor and “energy storage” is more effective on the area which has small skewness of load profile.

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Lightning-induced voltage waveforms at the end of an overhead wire over lossy ground are calculated with respect to the conductivity of the ground and lightning striking points. By numerical calculation, it is pointed out that the crest value of the lightning-induced voltage waveforms is greatly affected by the lightning striking points. It is confirmed that the disagreement of the polarity of the induced voltage at both ends does occur at an incident of a lightning stroke within about 3km. Accuracy of these results is evidenced by the experimental results.

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By using the developed 6, 600V/210V, 100kVA hybrid-type superconducting transformer, a short-circuit test is carried out. Excessive ohmic heating gave damage in the superconducting low-voltage winding after a superconducting-normal transition (quenching) was induced and resulted in wire ruptures at three points. The superconducting wire was partially colored in brown in 1.3 turns including those ruptured points. The metallic composition in the cross-section of the superconducting wire is observed by a SEM and an X-ray microanalyzer. The critical quenching currents of the short samples picked out of the superconducting winding are also measured. The following results are derived: (1) The arrangements of metallic composition in the superconducting wire are distorted around the ruptured point, at which the wire temperature is estimated to have reached higher than 900°C, (2) The critical quenching current of the short sample taken out of the colored portion is degraded into 70% of that in the other uncolored portion, (3) No distortion of the metallic composition or no degradation of the critical quenching current is recognized in the uncolored portion of the winding.
These results suggest that the partial and steep temperature gradient was developed around the ruptured point along the superconducting winding after the quenching was induced.

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Lightning surge and switching surge can be suppressed with an arrester. Generally, it is effective to install the arrester at the open end of the bus or the transmission line, and the overvoltage value can be calculated by using a digital computer or a TNA. But we can not know the value before the computation is done.
This paper gives a simple formula with which we can know easily the overvoltage value on the line with the arrester installed at the open end.
By the way, lightning surge in a substation becomes lower by using the arrester with more reduced residual voltage. But it must deal with more energy of switching surges. So, reducing the residual voltage has its limits. Also, even if the arrester is used, it happens to exceed the desired overvoltage value when the bus circuit is long.
This paper also shows that the lightning surge can be suppressed well by installing a supplemental arrester at the open end of the bus, even if it is a light-duty arrester. The overvoltage value is shown by using the formula developed in the paper.

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As same as in other type cells, the electromotive force in a tubular type cell is relatively high at the fuel inlet and the oxidizer inlet, therefore the current tends to concentrate there. And also the current distribution is greatly influenced by the resistivities, thickness and the dimensions of the electrolyte and the electrodes.
To investigate the current concentration, a simulation model has been made in which the effects of resistivity, thickness and dimension are simulated by the ladder circuit and the effect of the gas flow is simulated by the 2 dimensional flow taking into consideration of the gas diffusion. The current concentrations are predicted to be alleviated by the effect of gas diffusion, and the efficiencies are decreased by the gas concentration polarizations. And the appropriate segmentation of the power generating area is also effective in alleviating the current concentration to increase the power generating efficiency both in the ETL type cells and the WH type cells, especially in the ETL type cells.

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