Due to the limited transmission capability of transmission lines and the difficulty in finding new locations for generation, one method to overcome the additional load accommodation problem is the adequate utilization of the Reactive Power Supplier (RPS) which is installed in the system. However, calculating the amount of RPS is difficult, as it becomes a nonlinear combinatorial integer problem. This paper proposed the Pyramid genetic algorithm which improves the convergence characteristic of the genetic algorithm, and also proposed the successive iteration method between the pyramid genetic algorithm and Newton-Raphson load flow method to solve the reactive power supplier operation problem. Furthermore, we analytically determined the range of the mutation and crossover probability of the genetic algorithm which was chosen only by experience. The proposed method was applied to the IEEE 30 bus 6 generator system to prove its validity and effectiveness.

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Recently, there has been growing interest in utilizing DGS(Dispersed Generation System) to integrate various generation resources and to meet the changing electricity demand. In the long term, as much more introduction of both small and large capacity DGSs into the distribution system is expected, complete integration of this new technology into the utility system will bring about changes of design strategy and structural facility of the system. Thus a study is necessary to determine the introduction limit of DGS into the traditonal distribution system without any facility change. In this paper, the authors propose methods of determining the introduction limits of DGS from a viewpoint of voltage regulation in the distribution system using LRT(Load-Ratio control Transformer) and LDC (Line Drop Compensator) as the control scheme.

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In designing power system stabilizer (PSS), a major difficulty is to successfully treat the system's uncertainties. These uncertainties arise because of changes in operating conditions, approximations in modeling, parameter variations caused by faults, etc. It is known that in the presence of uncertainties, conventional methodologies such as linear optimal technique, adaptive controls, etc., may fail to guarantee the stability of the system. On the other hand, the H∞ control theory provides potential ability to overcome this problem. However, some limitations still exist in the treatment of uncertainty. That is, the existing standard H∞-PSSs cannot adequately treat the system uncertainties. Moreover, performance problems can arise in this approach due to the pole-zero cancellation phenomenon.
To deal with the above mentioned limitations, a new design methodology for H∞-PSS based on the 'numerator-denominator' uncertainty representation is proposed, where partial pole placement technique is used. Simulation results suggest that the proposed PSS is more robust and less sensitive to disturbances than both the conventional PSS and the standard H∞-PSS. The superiority of the proposed PSS has also been confirmed by computational results of stability margin as well as the Bode plots of the sensitivity functions.

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This paper presents an efficient technique for the S-matrix method that focuses on the most dominant eigenvalue in power system dynamic stability. In order to speed up the convergence characteristics of the S-matrix method, this paper makes use of a shifting technique with the generalizecdRayleigh quotient. Although the generalized Rayleigh quotient iteration method is quite attractive in terms of the efficiency of the shifted matrix, it does not have a theoretical guideline for updating the shift parameter. It is known that the method is very powerful under some good conditions. Indeed, the method follows heuristics on the matrix shift. As a result, the method is not reliable in obtaining solutions with any initial values. To overcome the problem, this paper proposes a modified generalized Rayleigh quotient iteration method with considerations of updating the shift parameter appropriately. The method is based on the recent results of the conditions of the parameter in the S-matrix transform. The effectiveness of the modified generalized Rayleigh quotient iteration method is demonstrated in examples.

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Generally, improving voltage stability against the power demand increase tends to increase short circuit capacity. In this paper, two methods are proposed in order to obtain the appropriate system separation points which minimize the short circuit capacity increase and the voltage stability decrease.
Considering the Q-ε network which expresses the relation of voltage and reactive power, the voltage sen-sitivity is equivalent to the element of the system impedance matrix. A fast calculation procedure for the change of the impedance matrix element due to bus connection changes has been proposed. It can be applied to the calculation of both the voltage sensitivities and the short circuit capacities. The results give the information on the most appropriate separation points among the designated candidates, against the short circuit capacity problem and voltage stability consideration.
The second method proposed uses a linear programming technique with variable line impedances and the objective function of minimizing the short circuit capacity subject to bus voltage dip constraints. This gives the information on the preferable separation points in large and complicated systems. Some practical procedures are also given.

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In a power system, maintenance works and updates of power system facilities are continually needed to secure stable power supply, which inevitably cause the outage of power facilities. The outage planning of electric power facilities (called “outage works”) should be done to realize a system configuration as similar to normal one as possible by utilizing flexibility in power system configurations. Since the amount of information necessary to handle the planning is prohibitively large, it has become too difficult to adjust outage works by planning engineers year by year. In addition, in traditional ways where requests for outage works are just rearranged, it is impossible to make up outage plans that secure power supply reliability in the true meaning.
This paper proposes a supporting system for drawing up outage work plans of electric power facilities. The proposed system is designed to keep a high power supply reliability during outage works. In attempting to develop an automated system of adjusting relevant outage works, the maintenance of a high supply reliability has been regarded as the primary objective. Hence, the proposed supporting system does not fundamentally require information on the time and date of outage works in the first stage and only needs to specify the weather and dates that can impede outage works. To realize this, the combination of outage works is determined by executing numerical calculations associated with power supply reliability.

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Thyristor controlled series capacitor (TCSC) can improve power system damping-This paper proposes a systematic design procedure based on modal analysis for tuning damping controllers of TCSC. The procedure makes it possible to improve damping in multi-machine power systems by using single input and single output TCSC. In this procedure, the influence to the control input signal caused by output of TCSC can be taken into account. This procedure is used to design TCSC controllers to improve power system damping in 3 machine system and its validity is demonstrated through digital simulations.

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The global warming caused by the increase of the atmospheric CO₂ concentration has been regarded as a serious environmental issue. Due to significant uncertainty as to mechanisms of terrestrial carbon cycle and climate system, the solution of this problem is considered to be extremely complicated. It is, therefore, quite uncertain whether or not political muscles will be used for tackling the CO₂ problem in the near future.
In such a context, to conduct a decision analysis under uncertain CO₂ concentration control policies, the authors developed a global energy model which minimizes the expected value of discounted total energy system costs up to the year 2055. The model developed here enables us to analyze a two-step decision making process, and is formulated as a dynamic linear programming problem with about ten thousand equations. Within the framework of the model, the whole world is divided into six regions. The model takes into account energy conservation in end-use and conversion sectors, utilization of various renewable energy resources, disposal and recycle of CO₂ recovered, and innovative system technologies.
In this paper we analyzed the optimal future global energy system particularly focusing on Japanese electric power sector, and presents the insight into the optimal strategy for energy system development under uncertain policies.

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In this paper, an algorithm is proposed to find a quasi-optimal schedule for the short-term thermal unit commitment problem considering LNG fuel constraints.
In recent years, LNG fuel is used increasingly. As a result, LNG fuel constraints should be considered in making a unit commitment schedule. Generally, unit commitment is a non-linear combinatorial problem including discrete variables. Adding LNG fuel constraints extensively increases the complexity of the problem. To solve the problem, a two-step algorithm is developed using mathematical programming methods. First a Linear Porgramming problem is solved to determine the amount of LNG fuel to be consumed by each LNG unit, then a Lagrangian Relaxation approach is used to obtain a unit commitment schedule. This two-step algorithm simplifies the problem and thus has good characteristics in convergence.
To test the effectiveness of the proposed algorithm, a numerical simulation is carried out on a 46-unit thermal system over a 24-hour period. The result is obtained with the dual-gap of 0.00546.

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A large-scale power system usually consists of several subsystems and the subsystems are connected weakly through tie lines or long distance transmission lines. As a result, there exist two types of oscillatory modes, one of which is local modes representing the dynamics of one subsystem and the other of which is global modes representing the dynamics of multiple subsystems. This property makes it advantageous to utilize decentralized and hierarchical control method for improving the stability of such a large-scale power system. In this paper, a novel control method called decentralized and hierarchical eigenvalue control, which aims at improving the steady-state stability of the large-scale power system, is proposed. Under this control scheme, first, stabilization of the local modes utilizing eigenvalue control is performed in each subsystem, and second, eigenvalue control of the whole system is performed to stabilize the global modes. Numerical examples make it clear that the proposed method can improve the steady-state stability of power system much more efficiently than the centralized eigenvalue control.

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In order to maintain the high reliability and security of electric power systems, the problem for stabilizing control is thought to be one of important subjects. Also, for the control of complex large scale nonlinear system like power system, decentralized control is preferable to centralized one. Therefore, the field of decentralized technology is much expected for the future power system.
In this paper, a three-machine power model system is treated as an example, and first a decentralized system is constructed on a basis of the swing datas by looking over the whole system at the largest generator bus. Next, the decentralized system is rewritten into a form of fuzzy system, and the stability theorem is applied to it. Then, feedback gains of the fuzzy control input can be determined under the guarantee of the stability, and the control input is given to the generator. Similarly, for the second generator, the decentralized system is obtained, and so on. Finally, it is shown that the decentralized control is constructed by using swing datas based on three different faults, and is also available for another fault in the simulation.

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In recent years, exploitation of natural energy by saving fossil energy is being reconsidered. One of the expected sources of natural energy for the future is wind energy, which has been actively studied as a substitute source of energy for the world. However, the wind energy is influenced by geographic and weather conditions, so that the generating power varies with time. Therefore, in order to make the windmill generator system to extract available maximum power from wind energy, this paper proposes a tracking control method of maximum power operating point using the recursively least square method with forgetting factor. The proposed method is simple since it identifies the system parameters and controls the actual rotor speed by means of a PI controller. The system parameters are identified by using the information for generating power and windmill speed. We verify the effectiveness of the proposed control method with numerical simulations and experiments.

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Solid oxide fuel cell(SOFC) using a magnecia stabilized zirconia(MSZ) is favoured for its properties of lower operating temperature and higher ionic conductivity than those of SOFC using the yittria stabilized zirconia(YSZ). In this paper, SOFC using MSZ is studied under the various conditions including the operating temperature and the quantity of the doped magnecium oxide(MgO). When SOFC using MSZ prepared by the sintering of mixture of 13mol%MgO and 87mol%ZrO₂ is operated at temperature regions of 880 to 1000°C, the cell efficiency drops with time in order to cause the phase transition in crystal structures of the solid oxide electrolyte. However, at operating temperatures from 800 to 860°C, the phase transition and the drop of the cell voltage were not observed. As a result, it was found that SOFC using MSZ is sufficient to operate at a temperature of 840_??_860°C.

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Ignition characteristics of a multi-stage Marx generator as a popular HV testing equipment was studied regarding the output voltage waveform distortion. The transient overvoltages across the ignition gaps and between stages were measured using a Pockels electric field sensing system.
These overvoltages showed internal high-frequency oscillations which varied with the gap distances. The detailed discussion on the characteristics of the superimposed oscillations revealed that the output waveform will vary in its very front part with different gap lengths and with different charging voltages. The change of the waveform would disappear in about three hundred nano-seconds.
As a result, the influence of the triggering behavior on a waveform parameter is small in general.

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Generally a model of Metal Oxide Surge Arrester (MOSA) for numerical analysis uses a non-linear resistance. But actual Voltage-Current (V-I) characteristics of MOSA have hysterisis loop in time domain like i-Φ characteristic of a transformer and frequency dependency.
The authors have investigated relation between the actual V-I hysterisis characteristics obtained by some current waveforms and static V-I characteristics. From the voltage difference between above two characteristics, an equation was derived and a new model of MOSA was developed. This model consists of a non-linear resistance representing fundamental V-I characteristic, a linear inductance and voltage source which depends on the absorbed energy.
The calculated results by the proposed model are compared with measurement results by using the waveform of standard impulse current, steep front current and oscillated current. And the accuracy of the model has been confirmed to be satisfactory. The model is expected to be useful to investigate insulation coordination of power systems.

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The barrier effect of the corona and surface discharge characteristics of SF₆ and mixture (SF₆+N₂), in high-field needle to plane gaps with short gap length, was examined under negative polarity pulse voltages with various wave fronts. At constant gap length in SF₆ gas, the discharge voltage increased with the barrier height. And also the discharge voltage increased with increasing the wave fronts in the μs region. On the other hand, under same barrier condition in N₂ gas the discharge voltage decreased with increasing the wave fronts. In order to make clear the mechanism of corona initiated surface discharge, the charge magnitude on the barrier induced with the corona was measured by a electrostatic voltmeter. The charge density was approximately 4×10^-4C/m² at 0.1Mpa and 15kV. The corona properties under various pulse wave fronts were observed with an optical technique such as an image intensifier tube. Anomalous V-t curves obtained in SF₆ gas are considered to arise from the relaxation of electric field resulting from the influence of charge accumulated on the barrier due to corona at wave front of applied pulse.

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Gas-Insulated Switchgear(GIS) has very high reliability compared to Air-Insulated Switchgear (AIS), But any fault in it may once occur, the impacts due to it for modern society is vast and serious. The needs of predictive maintenance for GIS is on the rise, especially development of partial discharge sensor is strongly requested.
We have been developed the GIS partial discharge locating system whose advantages are simple construction, the least number of sensors, easy maintenance, and high reliability.
This paper describes about the basic experiment to develop the system, the principle of location of partial discharge source, application to the actual switching stations, Chubu Electric Power Co., Inc. TOYONE SW/S and consideration about the field data. We used the external type par-tial discharge sensor. The location of partial discharge can be calculated from the travel time differences between the partial discharge source and sensors. The data obtained in the SW/S shows the suggested algorithm for partial discharge judgment and location of partial discharge source is useful and function of external noise reduction effectively acts as we expected.

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Internal reforming molten carbonate fuel cell realizes high power generating efficiency by utilizing its generated heats in the cell to convert fuels into hydrogen rich gases. One of the crucial problem is deactivation of catalysts loaded in the cell. Deactivation phenomena of catalysts have been investigated by analyzing various catalysts after operating several thousands hours. The analyzed data suggest that the deactivation of catalyst is caused by the sintering of catalyst and support material. A correlation equation has been derived relating between the surface area or the specific dameter of catalysts and modified operation time, which explains the effect of operating temperature. Decay characteristics of reforming rate of internal reforming fuel cells have been predicted using this equation. They have shown same trend with experimental decay characteristics of several cells and stacks, utilizing various fuel gas compositions under the different flow patterns and the different operation temperatures.

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A new statistical estimation method of the lifetime of the insulation which had been used for a long period by using the probabilistic mixture model of the Weibull-power-law is shown in this paper. The cross-linked polyethylene insulated cables which are used under the ground are considered to be deteriorate at various rates in accordance with their stress circumstances. Such a phenomenon leads us to propose the mixture model. This method can be applied to the residual lifetime estimation of the removed cables which had been used under the specified service voltage stress for a long period. For example, the parameters and the residual lifetime estimates are obtained for 22 kV and 33 kV cables which had been used for decades by classifying the whole samples into four groups. The estimated deterioration rates totally differ from those obtained by the conventional accelerated life tests.

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A difficult problem is encountered when the ground resistance of a large grounding system is measured by the fall-of-potential method. The problem is that a horizontal curve section does not exist with a fall-of-potential curve.
In this case it is difficult to estimate the ground resistanse from the fall-of potential curve. In this paper, a method for determination of potential probe position to estimate the ground resistance of a vertical electrode is proposed when the horizontal curve section does not exist. First the exact potential probe position is obtained in two-layers ground case. Next, in three-layers ground case, three- layers ground is replaced with two-layers ground by some procedures, and the potential probe position for the three-layers ground is taken as the position for the replaced two-layers ground. Error extent of the ground resistance from the replacement is estimated. Also in four-layers ground case, the procedures for replacement of four-layers ground with two-layers ground, and error extent of the ground resistance from the replacement are described. Last, for the case where the ground configuration is not clear, another method is proposed and error extent is described.

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