This paper describes the experimental study on the damping effect of transient swings in a laboratory size 3 kVA generator connected to an infinite-bus power system using a phase shifter with tap-changes. The phase-shift injection is implemented by thyristor-associated fast tap-changing based on a simple control rule consisting of the speed and angle deviations during transient conditions of the generator. The digital simulation studies are also carried out to test and compare the control scheme and its dynamic performances. As a result, the numerical studies show good agreement with the experimantal results. The phase shifter control, as an efficient on-line controller utilizing the microcomputer, is verified to damp the transient swings caused by a fault in this system.

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This paper proposes a new concept of electric power network which makes it possible that many types of dispersed generation plants owned by non-utility organizations can participate in an electric power market without the disadvantages of existing power utility and customers. We call the power network “Open Electric Energy Network (OEEN)” because the network is opened to the many types of plants for the participation. For achieving such openness, electric power storage devices, load controller at each customer and data communication network are installed in OEEN, and the flow of excess electric power generated by each plant is controlled autonomously and in the distributed way. That is, the control is done by transmitting the data about excess electric power such as generation and demand point, power quality, price and so on from each dispersed generation plant to the power storage devices and the load controllers through the communication network. Since this data driven power flow control is similar to the mail system for a packet with the addresses of sender and receiver, we call it “Packet Electric Power Trasportation”.
In OEEN, the storage device plays the different role from load leveling. Therefore, the way of determining the storage capacity is different from the conventional approach. In this paper, the applicability of queuing theory for determning the capacity is also discussed.

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The Jacobian matrix of load flow equation becomes singular on the voltage stability limit of a power system network. This fact is generally used to solve the voltage stability problems in direct manners. It is assumed that the demand in each load node makes increase simultaneously as the total system load makes increase in order to search the stability limit.
This paper discusses the parametric bifurcation which is occurred in this direct computational approach. As an example, if the distribution factor of demand in each load node reaches its bifurcation point, a catastrophic change of the stability limit condition will be observed in the specially composed network. This paper proposes that such parametric bifurcation will be detected to utilize the normal plane vector of Jacobian matrix. Some example systems are used to demonstrate the selection of parameter and its bifurcation aspects. These examples show that the power system network will be separated into the tight part and the marginal part from the voltage stability viewpoints, when the parametric bifurcation exists. The feasibility study is included for applying the features of parametric bifurcation to the stability enhancing operation of the power system.

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This paper proposes the nonlinear excitation controller for synchronous generators in power systems. Equivalent constants in field circuit can be changed to desired values by the nonlinear controller. Because the proposed controller adopts the nonlinear controller, this controller is valid in whole operating points. The usefulness and validity of proposed excitation controller are confirmed by numerical simulations. The nonlinear excitation controller can improve the stability of synchronous generators.

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The measurement of insulation resistance by superimposing the DC voltage has a large possibility as a means of detecting insulation deterioration. Deterioration signal current in the insulation can be detected from the cable-shield grounding wire, but the earth-current from a cable sheath also flows into that grounding wire as a noise. To detect the deterioration signal current properly, therefore, it is necessary to separate the earth-current from the sheath. On the other hand, to improve detection sensitivity, it is desirable to super-impose the highest possible DC voltage. In this case, provision must be made so that no adverse effects are caused on GPT.
With attention paid to the method of measuring high insulation resistance by configuring the bridge, therefore, the authors conducted study on how to detect the insulation deterioration signal with a high accuracy and sensitivity without impairing the functions of GPT. As a result, the following points were identified and, in this paper, the results of these achievements are reported.
(1) It is possible to measure insulation resistance as high as 100, 000 MΩ by superimposing DC 50 V through GPT after canceling earth-current and by configuring a bridge for determining insulation resistance from voltage ratio.
(2) Even if DC 50 V is superimposed through GPT, it is possible to prevent the magnetic saturation of GPT if the injection current caused by such superimposition is limited (e. g. below max. 5 mA).
(3) Provision of a bridge in which variable DC voltage supply is employed in place of variable resistor consequently requires no mechanically driven part, thus making it possible to realize a fully automatic monitoring system.

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In order to clarify the MCFC shorting by NiO dissolution, the shorting model was developed under the assumption that shorting occurs when Ni concentration at anode-matrix interface is over the critical value. The shorting time (TTS) was predicted as follows:
TTS^0.5/l=A+B/k P_CO2(l: matrix thickness, k: NiO solubility, A, B: constant).
Single cells were operated under different conditions until the shorting. The results supported the model.

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A decentralized control system is studied for stabilizing multimachine power systems. A longitudinal power system with three areas, each having one machine, is considered in this study. A decentralized control design method is proposed, which is based on the optimal regulator theory. First a centralized control system is designed without any consideration on whether state variables are all available or not. Second a pseudo-decentralized control system is designed by omitting control gains corresponding to state variables which give hardly any effects on the power system stability. It is found that only one variable of phase angle of each machine is absolutely necessary for the pseudo-decentralized control system. This leads to an idea based on power system engineering, that is say, new variables of tieline power flow are introduced in the decentralized control system design to substitute for the phase angle of each machine. Thus a decentralized control system for power system stability can be designed using the new variables of tieline power flow. It is demonstrated from simulation studies that the decentralized control system improves even longitudinal power system stability as well as the centralized control system.

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A constant current controller is applied to the rectifier, and a constant voltage controller and a constant extinction angle controller are applied to the inverter in the HVDC system. When the output signal of the extinction angle controller is selected for the inverter firing angle control, unstable operation is expected under certain conditions. We have experienced a power swing during a performance test of the frequency converter station in which the extinction angle control signal was selected.
This paper describes the stability analysis of the power swing that was carried out for finding a countermeasure. The linearized model of ac and dc circuits is used, and the Bode calculation is applied for stability check. Useful results of parameter study are mentioned, which shows instability is affected by ac system impedances, operational points, and time constants of controllers. The analog simulator is used to verify the modeling and to confirm the countermeasure. Furthermore a simplified block diagram for stability check is proposed.

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After the oil shock, industrial sector made an effort and succeeded in energy conservation. However, in trans-portation sector, effective means for energy conservation was not sufficiently developed yet. Especially, the road traffic in urban areas is not still efficient because of its heavy traffic jam. Since fuels for automobiles are one of main sources of CO₂ emission, reducing fuel consumption in transportation sector is certainly effective to avoid global warming. To make remarkable improvement in energy conservation in transportation sector, not only improvement of the efficiency of engine but also arrangement of land use in urban areas to reduce trip length is effective. The purpose of this paper is to suggest an appropriate urban structure minimizing necessary transportation energy consumption. To simplify the problem, we concentrated on the city model with commuting and business trip by automobiles. We developed an optimization model in which the fuel consumption is minimized by adjusting the distribution of living area, business area, and street area. Simulation results demonstrate some features of optimal structure; Optimized urban structure changes depending on poulation density; it has the optimal point of the density to minimize fuel consumption per person. These results are compared with schematic distribution of population density in real cities.

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Currently fault analysis of a synchronous machine has been carried out by using two-reaction theory. However, this analytical method becomes complicated and it is very difficult to understand a physicall phenomena.
While Yamamura has proposed spiral vector method, which gets a result from AC circuit theory and anal-ysys of AC motor. Now it will be also applied to analysis of the synchronous machine. Theoretical an-alysis of synchronous machine by the spiral vector method is more useful than analytical method so far. However, this analytical method isn't clear to analysis of real machine.
This paper presents both analytic solution and numerical solution result of spiral vector model synch-ronous machine. Both solution results gets almost coincident result. Therefor the spiral vector method is also useful of real machine analysis.

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In power systems, periodical maintenance works of generating facilities are continually needed to secure stable power supply. Planning engineers must perform this scheduling by considering both power system security and economy. The maintenance scheduling problem is a complex combinatorial optimization problem. Many approaches have been proposed to solve this problem. Though the mathematical programming method can find an optimum solution, it has not been applied to the large-scale problems because of the combination explosion.
This paper proposes a first method for the maintenance scheduling problem of the thermal generating facilities by using the Integer Programming. The ideas of this approach are followings. (1) The 0-1 variables are allocated on the available earliest periods (weeks) that the maintenance on each unit can start. (2) The maintenance contribution factor is introduced to formulate the problem. The factor is operated as increasing the security of the power system during the optimization process. (3) The whole problem is described by linear combination of two objective functions ; the maximizing the security and the minimizing the economics. We can decide the appropriate scheduling by adjusting the weights of both functions in order to reflect the power system conditions. The new approach has been applied to the large-scale maintenance scheduling problem (60 units 52 periods), and the computation results show that the reliable and economic maintenance schedule is obtained in reasonable computation time.

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Power systems comprising an enormous number of components are monitored and controlled by SCADA systems, For efficient monitoring and control of organically linked power systems, it is necessary to connect the related SCADA systems through a communications network and to exchange needed information.
The RCN (Realtime Computer Network) protocol serves as a foundation in building a communications network for SCADA systems. The RCN protocol complies with OSI (Open Systems Interconnection), the international standard for communications protocols, and with the API/F (Application Interface) communications protocols, which covers provisions exclusively required for communication among SCADA systems. The RCN protocol supports both an inter-process information communication function and a file transfer function, and it can be extensively applied to control systems other than SCAR systems.
This paper presents a detailed explanation of the RCN protocol and the performance of the RCN protocol.

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We developed a vacuum circuit breaker (VCB) surge generation simulation method which takes into account the interrupter parameters: the chopping characteristics, the arc life time characteristics and the dielectric recovery characteristics. The applicability of the method was confirmed by the probability characteristics obtained from the actual motor switching off test. It was found that the contact material and the contact separation speeds, particularly the initial contact separation speeds, are the most influential factors.

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When water-trees occurred in the insulation of XLPE cables, and extended so that the insulation is penetrated to either the conductor shield or the insulation shield, DC component has been observed. This DC component has been applied to diagnose insulation deterioration, but for its generating mechanism there remain unknown points. Therefore, the authors made holes on XLPE sheets and cable insulation, and by simulating the penetrating water-tree, the characteristics of the DC component and electrode potential were investigated. Based on the results, it was found that electrolyte solution is required for the generation of the DC component. Furthermore, as electrodes, the combination of different kinds of materials or the combination of different electrode areas is also needed. It was mentioned that the above conditions are also satisfied in actual cables, and from the experimental results at this time, it was presumed that the main cause of generating the DC component is the electrochemical reaction at the electrode interfaces.

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When a fault occurs on transmission or distribution systems due to lightning or overvoltage, there is often an arc discharge at the fault point. The arc discharge, which is caused by a fault current, has a high current, high temperature, strong light emission etc., so it sometimes causes heavy damages to the electric power equipment.
The arc discharge is influenced by the conditions around the arcs: gas, insulation materials, gap length, weather etc. And the arc voltage along the arc column indicates the characteristics of the arc. If the voltage waveforms of the arcs caused by the fault on transmission or distribution systems are classified, it is possible to find the location and the equipment where the fault occured.
This time, the arc voltage data in 6kV class XLPE cables and 6kV class overhead lines were analyzed and an artificial neural network method is applied to classify the arc voltage waveforms. The results obtained from the six artificial neural networks developed show that the artificial neural network method is effective for classification of arc voltage waveforms if adequate input parameters are selected.

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A CO₂-recovering hybrid power generation system utilizing solar thermal energy was proposed. In the system, relatively low temperature saturated steam around 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine in which generated CO₂ is recovered based on the method of oxygen combustion. Hence solar thermal utilization efficiency becomes considerably high compared with that of conventional solar thermal power plants in which superheated steam near 400°C has to be produced for using as the working fluid of steam turbines, and the requirement for solar radiation in the location in which the system is constructed can be significantly relaxed. The proposed system is a hybrid energy system using both the fossil fuel and solar thermal energy, thus the capacity factor of the system becomes very high. The fuel can be used in a exergetically excellent way in the system, that is, can be utilized for raising the temperature of the steam heated by utilizing the turbine exhaust gas more than 1000°C. The generated CO₂ can be recovered by using oxygen combustion method, so that high CO₂ capturing ratio near 100% as well as no thermal NO_x emission characteristics can be attained. It has been shown through simulation study that the proposed system has net power generation efficiency of 63.4%, being higher than 45.7% compared with that of the conventional power plant with 43.5% efficiency, when the amount of utilized solar energy is neglected and when the temperature of the saturated steam is 220°C.

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