Many studies have been investigated about the generator controller which aims at coordinated control of AVR and Governor with multivariable control scheme. The most of these studies cnsidered one-machine infinite-bus model system and calculated the effect of controller. So there are few papers to deal with the interaction among the generators in multi-machine power system.
This paper presents a novel control scheme for decentralized generator controller in multi-machine power system. We consider the interaction among the generators as the equivalent disturbance from the external system. In this sence, the proposed cntrol scheme can be realized for the noninteractive generator control in multi-machine power system. The simulations by the three-machine loop system and five-machine radial system demonstrate the effectiveness of this control scheme.

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The research on decentralized control of electric power system, which has become more complex, is a.nimportant subject for the stabilizing control. In particular, since electric power system is a. large scalenonlinear control one, decentralized (not divided) systems with cooperation should be constructed.
The purpose of this paper is to present a.n a.pproach for constructing decentralized systems of electricpower system. In Chapter 2, swing da.tas of a. three-machine model system are obtained, and in Chapter 3, coefficient pa.ra.meters of the model equation based ou one-machine infinite-bus system with AVR said GOVa.re estimated liy the least square method. In Chapter 4, the equivalence calculated by using the estiuia.tedvalues is discussed, and also the effect of conditions for the fault is considered. Finally, Chapter 5 is devotedto summarizing the result for the decentralized system identification.

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Load flow calculation is a basic tool for power system planning and control which include load flow analysis, voltage control, service restoration, network reconfiguration, and etc. In these applications, it is very important to solve the load flow problem as efficiently as possible.
This paper presents a fast load flow using parallel processing for radial power systems. The method can be applied to secondary systems and distribution systems. Since it uses only active and reactive power injection to main lines and laterals as state variables, reduction of number of state variables can be realized. Radial networks are mapped to the tree structure of parallel processor systems in the proposed method. The forward/backward sweep approach is realized by communication from a root processor to leaf processors and vice versa. Using the mapping scheme of the proposed method, each processor has to communicate with only neighboring processors. The proposed method is evaluated on various radial systems with promising results.

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Islanding phenomenon of the utility interconnected photovoltaic(PV) power generating systems mainly installed in residential houses is a most serious problem for the safety of utility distribution lines. The 3rd harmonic voltage detecting method is one of the recommended measures in the Japanese guidelines on utility interconnection. However, detailed conditions of the method when detecting have not been clarified yet. This has prevented establishing the optimum islanding prevention method including combinations with other prevention measures. In this study, detailed detecting conditions of the 3rd harmonic voltage detecting method were analyzed by a simulation developed based on demonstration tests in Rokko Island. The simulation showed the following:
• 3rd harmonic voltage increases remarkably and can be detected clearly when the imbalance of load currents of each phase is more than about 15%.
• There are conditions of PV power output and relationships between PV power outputs and loads at which islanding detection fails, when the imbalance of load currents of each phase is less than about 15%. The ratio of PV power output and load in the case of failed detection tends to be less than 1.0.
• The 3rd harmonic voltage detecting method is a useful supplement when other islanding prevention measures fails in combined methods.

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In general, it is impossible to analyze power system by experiment, because it is very complex and large. Therefore power system is analyzed by computer simulation now. To make it easy to understand analysis results intuitively, network diagram with these results must be create . But it needs very considerable labor and time to make network diagram, because it is made by hand from a data that contains its connection. To save these time and labor, automatic display system for power system diagram has been developed. The number of intersections of lines must be minimized to make it easy to see. Concerning this subject, there are planar graph, hierarchical graph, routing problem on VLSI, printed writing board, and so on.
This paper presents a method for creating power system diagram of minimum line intersections by means of a shortest paths search method. This method is usually used in VLSI layouts. Still more, to make it easy to see the displayed network diagram by the above method, route of branches is reformed remaining layout topology by algorithm of rubber-band and spoke.

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This paper proposes a new control method based on the power demand estimation and fuzzy control considering effects of the self-regulation to improve the load frequency control(LFC) characteristics of power system. The proposed control first, to satisfy LFC requirements, estimates power demand variations of the control areas and uses them as the output set-point values of power plants, in-stead of using an integral-type controller. However, when a remarkable change of load occurs, tielines and frequency can not immediately reach the steady state value due to undesirable oscillations appeared in the process. Next, to solve the problem of LFC system using the fore-mentioned output set-point control method, the self-regulation of generators in each area have set an optimal point within the actual range, and to improve stability and robustness in this system, the fuzzy control is implemented.
The fuzzy controller is designed by using the frequency deviation and its change represented in the phase plane, and membership functions of the phase angle and magnitude are determined. The con-trol signal is calculated by means of defuzzification using center of gravity method.
To study the effectiveness of the proposed control, a 3-area longitudinal system which is com-posed of reheat and non-reheat steam power plants is considered as a model system for the computer simulation.

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This paper describes deterioration characteristics of 266kV magnetic blow out type surge arrester with series gaps having actual about 30 years operation, and metal oxide surge arrester as its improvement. Main deteriorated components of surge arresters are extinguished chambers closed in series gaps, grading resistors for series gaps and covers for sealing. In case of deterioration of covers, water contents immerse into porcelain containers. Power frequency sparkover voltage decreases gradually. Finally, surge arresters are possible to fail down at normal operating voltage. It is important to seal covers with gaskets between porcelain fittings and ceramics porcelains.

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This paper discussed an optical current transducer which had a bulk Faraday sensor inserted into a gapped iron core and porcelain insulator with built-in optical fibers.The Faraday sensor had Bi₁₂SiO₂₀ single crystals with right and left optical rotatory power to cancel out temperture dependency. And a 66 kV to 275 kV class insulator with built-in optical fibers was also confirmed to have the required optical transmission performance. A prototype 161 kV optical current transducer demonstrated 0.3 % class accurracy for metering.

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Demands on power supply equipment, especially reliability and serviceability have been increasing year by year as social conditions have become increasingly complex. With these demands, the approach to equipment maintenance has changed from the time-based (scheduled) maintenance of the past to the condition-based (predictive) maintenance of the day. The condition-based maintenance system monitors power supply equipment in substations using sensors, both online and real-time. In this system, insulation capability is monitored by partial discharge detectors using acoustic emission sensors. We developed micro computer based detector and tested these detectors to the basic switchgear models and to real field switchgears which past for more than ten years.
And we report the results of these tests.
(1) Test results of the basic model and switchgear are very similar.
(2) Magnetic base sensor is very. useful to locate the abnormal insulation device in switchgear.

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This paper presents a number of flow visualization tests conducted on a 300kW WTGS rotor blades under evaluation now.
Aerodynamic phenomenon including flow separation, which is essential for the evaluation and improvement of rotor performance, has not been fully understood so far-Therefore a two way approach was made in this visualization study, one is oil flow method on the existing blades and the other is smoke wind tunnel test with two-dimentional blade section models.
These experiments show that the aerodynamic properties of blade between 75% and 95% radius position were excellent and various suggestions were obtained for the aerodynamic design of WTGS rotor blades.

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Optical voltage and current measurement generally necessitates the compensation of light beam intensity variation which occurs in the optical measuring system, because it is possible the light beam intensity variation may give rise to a measuring error. Therefore, such compensation methods as dividing the A C component by the D C component of the light beam intensity are usefully introduced in optical A C voltage and current measurement, but these methods are not useful exactly for the optical measurement of the quantities including D C components.
This paper deals with a new useful compensation method for light beam intensity variation in the optical D C current measurement. Linearly polarized light beam passes through two kinds of Faraday sensors, in which one detects D C magnetic field caused by D C current and the other detects externally applied constant A C magnetic field. Then, the compensation of the light beam intensity variation is carried out by measuring the D C and A C components of the beam. The principle of the compensation method using the A C component is described in the paper. Experimental results of this method using flint glass as the Faraday effect cells are reported and it is clarified that this method can decrease the measuring error of the modulation depth for D C current and compensate light beam intensity variation validly.

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The switching time and the minimum firing voltage of a triggered vacuum gap employing a trigger electrode in the cathode and anode( double triggered vacuum gap ) were measured. The double triggered vacuum gap was operating below 100V independent of the high voltage main electrode polarity ( positive or negative). This minimum firing voltage is lower than that of the conventional triggered vacuum gap. The switching time is about 0.5 μs in the range 3 to 18kV.
The conventional triggered vacuum gap has a trigger electrode which is placed at the center of the grounded main electrode. The polarity of the main electrode affected the switching time characteristics. We added a trigger electrode to the high voltage main electrode. The double triggered vacuum gap was scarcely influenced by the polarity of the high voltage main electrode when both main electrodes were triggered at the same time.

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For application to current monitoring in electric power facilities, the authors have been developing a current sensor utilizing the Faraday effect of an optical fiber manufactured from flint glass having very small photo-elastic constant. This paper describes the result of study on constitution of the sensing system, which is composed of a sensor head, a light source, fibers for light transmission and a signal processing circuit.
Firstly, results from investigation are reported with respect to causes affecting performance and durability of the sensor. Examinations of countermeasures to them are also described. As a result of the research, it was confirmed experimentally that several means are effective to improve characteristics of the sensor. Then, design and test results of a sensor model constructed with application of the means are described. From the test results, it was proved that the model shows excellent characteristics satisfying basic requirements of the standard for conventional current transformers.

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It is an important problem to keep dynamic stability of a power system of large scale. In this paper, a method stabilizing a power system of large scale is proposed by using a dynamic compensator for each generator to realize the cooperative excitation control system. The model reduction method of internally balanced type is extented such that it is applicable to unstable power systems. Using the proposed design algorithm with dynamic compensators, practical parameters of the dynamic compensator are determined and a decentralized excitation control system is designed. Also, it is suggested that pole placement for the dynamic compensators is solved by the homotopy method which is preferable to global convergence.

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In the DC component method, one of the typical method for insulation diagnosis of 6.6kV live cables, the mechanism for evolution of DC component current is closely associated with the detecting sensitivity to water trees. However, the mechanism is not yet fully understood. So that, we studied on the mechanism and the effectiveness of the DC component method by XLPE cable model. The experimental results indicate that the origin of DC component current is the apparent electromotive force, nearly 0.1V, and arises from the weak rectifying effect on the interface of moisture in semiconducting layer and Cu₂O on corroded shielding tape. The dependence of DC component current on AC electric field seems to be explained on Poole-Frenkel mechanism. The DC component current which arises from the electromotive force is nearly 10pA per one water tree under AC electric field of 1.1kV/mm.

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