In recent years, squirrel-cage rotor induction generators are widely used as wind generators because of their cost, simple and robust rotor construction, and virtually reliable maintenance free operation. However, when they are injected to the utility grid, transient rush current, which amounts to several times as large as the rated machine current, and causes the voltage fluctuation in the power system. This transient voltage variation can not be disregarded especially in the case of large-scale wind machines from the view point of power system operation, because the electric power company has obligation to maintain the voltage within predetermined limit. Hence, it is necessary to estimate the value and duration of the voltage fluctuation for the company.
The voltage variation can be found by solving a set of simultaneous differential equations describing the dynamics of a wind turbine, a generator and power system. Since these equations usually contain linear and/or non-linear elements, it is difficult to solve them by using an analytical method, and so a numerical simulation is one of the most powerful method.
This paper proposes a new dynamic model to analyse electrical transient phenomena of a wind power generation system connected to the utility grid. And then, the over all system dynamics including linear and non-linear elements was simulated, and the voltage fluctuation was estimated. The simulation results showed that the voltage fluctuation in transient state was within the predetermined limit.

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Auto-parametric resonance (internal resonance) is regarded as a kind of nonlinear oscillation stemming from the nonlinearity of synchronizing power of generators. The resonance is closely related to power system stability, especially to unstable oscillation phenomena such as “negative damping” and “sustained oscillation”. The authors have already developed a quantitative analysis method and proposed a stability index to estimate power system's viability under resonance condition.
This paper studies a countermeasure to prevent auto-parametric resonance, taking two-mode resonance as a representative example of auto-parametric resonance. First, a control index, which is used as the control objective, is established based on the stability index which has been developed in our earlier works. Then, we examine system parameters governing the control index through sensitivity analysis, and propose an effective method of monitoring and control. The proposed control method can be integrated into the conventional ELD by adding another constraint relating to the resonance to conventional security constraints. The effectiveness of the proposed method is demonstrated using a longitudinal 4-machine system through numerical simulations.

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To determine the very small quantity of salt attaching on pilot insulator for watching insulation characteristics of practical insulator installed in various electric power equipments an energy dispersive X-ray fluorescence method using a particular X-ray tube of small size and low power output was applied. The X-rays from the low voltage X-ray tube, 37.2mm dia. and 85mm length, having the 8μm thick transmission type Ti target and the 0.5mm thick Be window are irradiated on the surface of contaminated insulator, and the Cl KX-rays produced from the salt (NaCl) attached on the insulator are spectrometrically observed by a proportional counter following a multichannel analyzer. To detect faint 2.62keV Cl KX-rays clearly, the elimination of 2.96keV Ar KX-rays generated in air of the X-ray path between the X-ray tube and the detecter was examined by the following two methods: (1) substitution of air by CH₄ gas after flowing through a CH₄ gas flow type proportional counter, and (2) use of an X-ray filter of 30μm polyvinylidene chloride set up in front of a Ne gas filled proportional counter. The latter method was applied for a 250mm dia. suspention insulator of crevice type, and the attaching salt quantity more than about 0.01mg/cm² was found to be detectable. The coexistence of dust resulted in decrease of apparent salt quantity because of self absorption of Cl KX-rays with the dust substances. The experimental results obtained by an insulator placed nearby seaside area showed directional distribution of the attaching salt on the insulator surface. The observation of time dependent soil accumulation on insulator surface is also easily practicable by this method.

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It becomes difficult and high in cost to construct new ducts and/or tunnels for power cables in dense underground region of urban area. In this paper, engineering evaluation of compact high-T_c superconducting (HTSC) cables which should be applied to existing ducts and/or tunnels and its assessment of application were conducted, and the following items became clear.
(1) The future model system with the merit for HTSC cables was developed.
(2) The necessity of flowing the current in the inner part of superconductor because of such low H_c1 as 100G was indicated, and it became clear by the measurement of hysteresis curve that the current flow in the superconductor roughly obeyed Bean model.
(3) The design procedure of compact HTSC cable by Bean model was developed, and the conceptual design of HTSC cables for the model system was conducted. As a result, it became clear that J_c as 1×10^5-6A/cm² at 0.1_??_0.2T was necessary for the 66kV, 1, 000 MVA HTSC cable which diameter was 130mm.
(4) There was no problem of the model system for the voltage stability, short circuit current, power stability, and so on by the system analysis.
(5) 21% cost reduction of the HTSC cable model system was estimated compared with the nomal-conducting cable model system.

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Demands for the the application of fuel cells to home appliances and industrial equipments have been increasing because of their long life and continuous electricity. A methanol fuel cell is so handy that it is profitable to portable use.
It is most important for fuel cells to operate them with higher efficiency. A fuel supplying system which could operate the methanol fuel cell with higher efficiency was studied in this paper.
Since the consumption ratio of water and methanol in the cell varied with operating conditions, the system which methanol and water, were supplied independently from tanks in the circulating system of anordic electrolyte was adopted firstly. Then, the amounts of methanol and water supply were controlled by methanol concentration and liquid level sensors. The methanol concentration sensor based on electrochemical reaction under constant voltage could accurately detect methanol concentration in the range of 0.4_??_1.5mol/ι.
On the other hand, the liquid level sensors were based on the principle that short circuit current flowed while they were immersed in anordic electrolyte, and were arranged at the upper, middle and bottom of the liquid level. As the result of operating the methanol fuel cell with this fuel supplying system, high efficient and stable characteristics of the cell within the variation of ±0.1mol/ι of specified of methanol concentration could be obtained.

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