A power system is configured from generating plants, substations, consumers and the transmission lines that tie them together. In order to perform inspection, maintenance and expansion of these facilities, regular and systematic outage of this system must be conducted.
Moreover, the organization that manages this power system is hierarchy that comprises various levels of section. In order to prepare a comprehensive schedule from the various outage requests submitted by the many sections, it is necessary for the engineer to investigate thousands of outage requests based on reliability of the power system, economical supply of power, and safety of personnel.
This paper presents a computerized support system that has been developed to support a coordinating engineer in power system outage scheduling. The user interface expressed as fuzzy expressions “Fuzzy User Interface” that comprises an operator model of the coordinating engineer based on analysis of such work performed at a dispatching center is discussed.

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This paper describes a diagnostic method based on models of discrete event driven systems. Diagonosis is performed with generate-and-test strategy. The method has the following three advantages. (1) Diagnosis systems can be made by only inputting system models. (2) Verification is easy, because only a model is necessary to be checked. (3) Performance of diagnosis system depends entirely on the minuteness of models.
We showed that the proposed method had generality beyond one domain by applying the proposed method to two different domains, one network fault diagnosis and the other fault diagnosis of numeric calculation circuits. But two problems remained unsolved: The modeling method was not defined completely, and the speed of diagnosis was slow.
In this paper, a modeling method and improvement of calculation speed are reported. As for a modeling method, the structure is modeled with object-oriented technique, and the function is modeled with transition networks that explain state transition of components. Transition networks are generated by combining structure data with rules that describe causal relations of state transitions. Creating transition networks in advance improves calculation speed, because interpretation of causal rules is not needed during diagnosis.
Application to network fault diagnosis is also explained. Two models whose description levels are different are created, and it is shown that diagnosis results depend only on the model.

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System structure of expert system on the insulation diagnosis of high voltage rotating machines was investigated. We proposed the system which was composed of two systems for inspection site and for works. Both systems made it possible to judge obtained data rapidly and residual life of the machine precisely. We also made the prototype expert system of insulation diagnosis. The features of prototype system are followings:
(1) The prototype has the function of supporting the non-destructive measurement which helps the correct judgement on expert system.
(2) The residual life is judged by considering two methods. One is the method which is evaluated from the residual rate of the breakdown voltage obtained from results of non-destructive measurements and another is the method which is evaluated from the residual rate of the breakdown voltage obtained from operating records of the machine.
(3) Classified structures of knowledge bases and dividing into inference modules of knowledge bases made it easy to add and renew the knowledge base of the system.
Inference results of the prototype system by using acutual machines showed good agreement with the expert judgement and acutual breakdown voltages.

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With increasing recent power demand in urban areas, the ways of power supply have been changing, and many power cables are being used. Among those cables, XLPE cables (which are also called CV cables) have been rapidly taken places of conventional cables such as OF cables or SL cables since 1960's because of the relatively easy construction and maintenablity. However initial cables or cables used in severe environment become deteriorated (the reason is mainly due to water treeing), and some of those cables are having insulation breakdown. So far many diagnosing methods have been developed, but there have been no decisive method for diagnosing diteriorations and forecasting lifes of XLPE cables. This paper develops an expert system which can solve the problem.

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Application of an expert system is expected to be effective for solving problems in power system restoration. In fact, many papers have been published on expert systems for power system restoration. However, most of these papers consider constraints only at a time section during the restoration process; they do not consider dynamic changes in conditions of generators and other dynamic constraints, which will be crucially important for a practical restoration.
Considering this, the authors have developed a practical expert system for restoration of power systems from blackout. This expert system targets restoration of trunk networks and gives priority to thermal power plants in restoration sequence, considering the existing power systems in Japan, where thermal power generation normally prevails over hydro power generation. The system proposed in this paper has three features; Firstly, to increase restoring source, thermal power plants should be started up earlier than other kind of plants. Secondly, in planning of power system restoration strategy, it is examined by reasoning whether seven general constraints are satisfied. This permits to establish restoration strategy without backtracking. Finally, The knowledge of the automatic restoration system is represented by object, knowledge representation based on objectoriented paradigm. This makes the expert system well maintainable.

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Power system operation should be carried out by taking into account both economy and security that are contradictory to each other. Optimal power flow (OPF) can be used as a powerful tool for making operation plans to compromise these objectives. Newton type OPF is very fast in its execution due to the adoption of sparse techniques and hence it is the most promising algorithm as on-line applications. In energy control centers, the OPF algorithm would be used interactively by system operators. If the OPF does not yield a converged solution in such on-line environment, it must be extremely difficult to correctly identify the causes of nonconvergence and take necessary measures.
This paper is to propose an expert system for assisting the on-line OPF algorithm whose knowledge base is extracted from acquired know-how through the development research of the Newton OPF in our research group. The main objective of this expert system is to assist operators to obtain a converged OPF solution when the first OPF run fails to give a satisfactory solution. That is, the system first tries to obtain a solution by taking several countermeasures based on the knowledge base. In case a solution still cannot be obtained, the system then displays possible cause for nonconvergence, thus making it possible for the operator to change or relax some of constraints listed. Therefore, this expert system works not only as an automatic trouble-shooter, but also as a consultation system. This expert system will enhance the credibility and reliability of the OPF algorithm as an on-line tool.

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Power generation scheduling is a planning problem to determine an operation schedule of generation units corresponding to the estimated power demand considering constraints and evaluation factors. This paper presents an expert system which assists planners in making power generation scheduling.
The system takes advantage of knowledge engineering to overcome some drawbacks of conventional methods. Since the scheduling problem is too large to solve, it is divided into several sub-problems. In order to find a better solution, planners have to try various planning strategies. They also have to change the mathematical problem itself according to the changes in scheduling conditions. To cope with these requirements, the architecture of the system allows easy changes and additions of constraints, planning strategies and solution methods at planners' intention by describing them not in the algorithms but in the knowledge base. In order to solve sub-problems efficiently, the system adopts heuristic solution methods in addition to the mathematical programming methods.
The system effectiveness for practical use is verified using several sets of full-scale model data.

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Voltage/Reactive power planning is very tremendous process which requires a planner to have intellectual expertise. This paper presents the large knowledge based system that can make the voltage/reactive power planning. The knowledge acquisition has been completed on the basis of interview and protocol analysis methods. The result shows that the voltage/reactive power planning is composed of three phases.
The first is reactive power adjustment where overall reactive power balance is investigated. The second is voltage adjustment where all bus voltages are tuned within permissible operational range. The third is voltage adjustment with a single fault of all major lines. The knowledge base is coded by about 700 production rules. It can succeed in making a voltage/reactive power plan for a real large power system.

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A sudden loss in the amount of generation that is available to a power system can result in a very rapid decline of frequency. Shedding selected portions of load can equalize the imbalance between load and available generation to avoid a possible system collapse. The aim of this paper is to develop an expert system to support system operators in identifying the optimal shedding points among multiple load shedding candidates when a large amount of generation loss is encountered. The load shedding is assumed to be executed immediately after generation outages within 5s. The time elapsed for the system frequency recovery is determined by off-line computation and stored in a data base in the expert system. Then in the proposed expert system, a criterion of the relative transient stability obtained from the second method of Lyapunov has been used to determine the power system stabilizing control. This stability criterion provides a means of defining a stability index which gives a rapid and good picture of the system stability behavior and therefore constitutes a substantial practical advantage. The proposed load shedding scheme supported by the knowledge based system is implemented on a 9-bus, 5-machine power system for demonstrating its validity and effectiveness.

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This paper presents a new approximate model for analysis of steam turbine synchronous generators. This new model is a set of fourth-order differential equations. Its variables are an internal phase angle, a rotation slip, a field flux linkage and a flux linkage of q axis damper circuit with large time constant. This model is an extended version of the third-order model for salient-pole type machines derived previously by the authors. The model has three important aspects as follows: 1) It includes two dynamic equations for rotor flux linkages in addition to a second-order equation of mechanical motion. 2) The output torque equation is derived by analyzing an asynchronous condition. 3) It is a non-linear model applicable to transient problems for large disturbances.
The accuracy of the new model is discussed for two conditions in this paper; that is, steady state and transient. At first, eigenvalues obtained from the linearized version of the new model are compared with the dominant eigenvalues obtained from the complete model (8th order model). As a result, it is shown that the new model is sufficiently accurate as a steady state model for small disturbances. Next, dynamic responses for several large disturbances calculated from the new model are compared with those obtained from the complete model. As a result, it is concluded that the new model is also very effective as a transient model for large disturbances.

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In a reversed field pinch (RFP), a thick metal shell has to be closely fitted to a plasma for stability requirement. In optimizing the design of an equilibrium control system, the shell causes several problems, such as the production of the error magnetic field (B_g-err) at insulating gaps of the shell and shielding of the fast varying vertical field which actively controls the plasma position. To solve these problems, the equilibrium control system in the nuclear fusion experimental machine TPE-1RM15 (major radius 0.7m, minor radius 0.135m) is designed to have a thick copper shell with 25mm thickness, fast varying vertical field of 110mT (B_cv), quasi-stationary vertical field of 20mT (B_dcv), pulsed vertical field produced inside the shell (B_pv) and local compensating field at shell gaps (B_sdc). The shell provides main equlibrium vertical field, B_cv compensates B_g-err, B_dcv controls the plasma position, B_pv cancels the B_dcv at initial plasma breakdown and B_sdc provides additional compensating field for B_g-err. Experimental results with the system show that the compensation of B_g-err is essential for setting up and maintenace of RFP configuration and that plasma resistance decreases from 470 to 280μΩ with the equilibrium position control in the order of mm.

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We have studied breakdown characteristics using hemi-spherical tip rod (10_??_60mm) molded with epoxy resin to plate gap in SF₆ gas up to 0.20MPa.
The result shows that breakdown characteristics are classified into three regions (A, B and C region) depending on gap length. In A-region breakdown voltage is lowered compared with bare hemi-spherical tip rod to plate gap. In B-region breakdown voltage is raised sharply with gap length. In C-region it saturates. The maximum increase ratio of breakdown voltage in B- and C-region are 1.95 times (AC) and 1.68 times (Impulse) compared with bare hemi-spherical tip rod to plate gap characteristic.
The ratios depend on the diameter of hemi-spherical tip rod and thickness of epoxy resin.
We have concluded that the increase of breakdown voltage is attributed to synergism effect of decrease of maximum electric field strength by epoxy resin and the suppretion of field emission.
The use of composite insulation we have studied reduces gap length drastically in the gas insulated switchgear for instance OGIS (Cubicle type Gas Insulated Switchgear).

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Voltage stability problem has long been studied by many researchers mainly by means of two approaches. One is static approach where voltage stability is considered as a load flow problem, while the other is dynamic approach in which it is dealt with as a stability problem in dynamic systems. However, these separate approaches have not clarified sufficiently the whole aspect of voltage problem up to now; in fact, there are no proper criteria to determine which approach is suited to analyze voltage stability. Thus, a basic study seems to be needed under such situation.
This paper investigates voltage stability problem from the viewpoint of mechanism causing voltage instability. Various dynamic factors which affect voltages are studied as much as possible. In the first place, possible voltage instability patterns are classified based on singular perturbation theory. That is, four categories of instabilities are defined mathematically. Secondly, a method of stability assessment for each instability is presented. It is clarified that the determinant of the load flow Jacobian is an effective index to approximately assess two types of the instabilities. On the other hand, the remaining instabilities require eigenvalue analyses or direct nonlinear analyses. The validity of these results is verified through numerical simulations and eigenvalue analyses, in which dynamic characteristics of generating units, loads and tap-changing transformers are taken into account.

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