The advancement of power electronics technologies has significantly developed the power system stabilizing controllers. Quantitative as well as qualitative evaluation on their effectiveness in power systems is a matter of great importance for the feasibility investigation of these apparatus. In this paper, the possible control region of FACTS controllers with series and/or shunt configuration in a single machine to infinite bus system is formulated in the power-angle curve with a set of algebraic equations. The effectiveness of TCPST (Thyristor-Controlled Phase Shifting Transformer), SSSC (Static Synchronous Series Compensator) and TCSC (Thyristor-Controlled Series Compensator) for the improvement of the transient stability is evaluated quantitatively as a numerical example. The correctness of the proposed method has been confirmed by the analysis based on the EMTP simulation with a detailed system model.

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This paper presents new concept of BTB. The main feature of proposed BTB is “Massively Parallel”. This system consists of a number of small or medium-capacity inverter units and they are connected in parallel. The concept of transmission power control, when unit fault occurs and BTB losses are minimalized, are investigated using MATLAB. The method for EMTP model of the new BTB is investigated, too. After this research, the new BTB system turns out to be very promising for large power system application because loss of the system is very small rather than conventional BTB using VSC (Voltage Source Converter), it can keep operating even if a inverter unit fails and it can improve power transmission capabillity.

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The 500kW wind generator was developed as one of NEDO's projects, and several tests on its performance have been made so far. Based on the measurement data, we performed the modeling of the NEDO 500kW wind generator, and have investigated a method to reduce power variations under fluctuating wind conditions in complex terrain. This paper presents a control strategy based on probabilistic optimal control scheme, and then the comparison between power variations with the conventional PID controller and with the proposed controller. The result showed that the proposed controller could reduce the power variations successfully.

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There are some cases where a small-sized grounding electrode for communication or computer, is adjacent to a large-sized grounding electrode for power. In the cases, when fault current flows into the large-sized electrode, the small-sized electrode is affected with the transfer voltage V_s. For the design of the two adjacent grounding electrodes, V_s has to be well known. In this paper, V_s is computed by the method of images and the current source superposition method.
A grid electrode and a combination electrode of a grid and four rods, are taken as the large-sized grounding electrode. A grid, a counterpoise, a rod and a combination of a counterpoise and two rods, are taken as the small-sized grounding electrode. Homogeneous ground and two-layers ground of the first layer resistivity ρ₁ and the second layer resistivity ρ₂, are taken into consideration. From the obtained results, it is pointed out that V_s in the case of a combination electrode of a grid and four rods, as the large-sized electrode, is greater than V_s in the case of a grid electrode only. It is also pointed out that V_s in the case of ρ₁&ρ₂ is greater than V_s in the case of homogeneous ground, and V_s in the case of ρ₁>ρ₂ is smaller than V_s in the case of homogeneous ground.

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It is expected that the introduction of the competition policy would bring us cheaper electricity. The effective use of protective equipment and the rationalization of the maintenance procedure are needed. To realize them, a reliability analysis system for protective relays has been expected. Conventional systems or methods didn't enable us to analyze the annual change of the reliability nor the reliability when maintenance procedure would be changed.
The Reliability Analysis System for protective relays (RASPR) developed satisfies the above requirements and solves the problems. The RASPR consists of two databases and reliability analysis part. The RASPR realizes to analyze the annual change of the reliability in combination with two databases and to analyze the influence on the index of the reliability according to the change of transition parameters. The construction method of an arbitrary transition diagram enables us to analyze the reliability under any maintenance procedure or for any type of protective relays.
This paper describes the features of the RASPR, the construction method of an arbitrary transition diagram, and finally some examples of the reliability analysis. The RASPR is in operation at all electric power companies in Japan.

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A high-speed multi-reclosing system is adopted in most EHV trunk transmission overhead lines. The dead time after the clearance of an unbalanced fault is about 1 second in 500kV systems, which is generally decided from the extinction time for secondary arc and the transient stability.
The power flow of trunk transmission lines will be heavier in the future. It is quite possible that the power system goes to step-out during the dead time after the clearance of an unbalanced fault.
The impedance seen by a step-out relay whose inputs are introduced from sound phases is analyzed by the method of symmetrical coordinates. According to the results, the electrical center whose definition in this paper is that the real part of the impedance is zero can be classified using the condition of the same phases in the other circuit. The results are verified by use of the dynamic stability simulation program. (Y-Method).

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In order to perform instantaneous-value analysis of a power system, savings of computation time and memory can be achieved by reducing the complexity of external subsystems, of which the internal variables are not of interest. In this case, it is necessary to identify a reduced-order model of the external subsystem seen from its interconnection point with the main system. This paper proposes an identification method of the reduced-order model, in which a low-order linear model in the rational form of Laplace operator s is identified from frequency response data of the external subsystem using a least-squares method. The proposed method shows a good identification performance by linearization of the least-squares process combined with an iteration procedure that adaptively changes the weighting on the residue evaluation, and also by fix of gain at zero and infinite frequencies to assure the model behavior at time zero and infinity. In this paper, a five-machine radial system model is used to show the identification performance of the proposed method, and an application to control-system design is also presented.

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Leakage currents on various kinds of porcelain insulators were measured under DC voltage application in artificial contamination tests by using powerful DC power source which practically gives no voltage drop against leakage current during the test. Magnitude, duration and waveform of leakage currents were analyzed in relation to kinds of insulators and test procedures.

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To make the contribution for optimizing pollution test methods for porcelain-housed gapless metal-oxide surge arresters, artificial pollution tests have been conducted at a continuous operating voltage under various polluted conditions, using a two-unit type porcelain-housed gapless metal-oxide surge arrester for 154kV. In these tests, the leakage currents and quantities of electricity on the surfaces and through the elements of the arrester, the states of the dry band formation on the porcelain housing, the occurrences of partial arcs and the temperature rises of the elements are measured. This paper describes the test results and analyzed results of temperature rise of the elements under the artificial polluted conditions.

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SF₆ gas recovery is considered one of the most serious issues when we utilize a gas mixture at low SF₆ content as an insulating medium for electric power apparatus. Liquefaction recovery is difficult to apply due to the increased recovery loss when SF₆ content becomes low. We have examined a method using membrane separator, which utilizes the difference in permeation rate of component gases. This paper reports experimental results on concentration of SF₆ in the recovered gas, recovery loss, and so on, for gas mixtures composed of SF₆ and N₂. It describes the effect of various parameters, such as gas flow, temperature, mixing ratio and gas pressure. The paper also discusses limits of allowable recovery loss and recovery speed when the method is applied into practice. The experimental results show the effectiveness of this method for SF₆ gas separation and recovery from gas mixtures with low SF₆ contents.

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Many power transformers in Japan have been operated under the standard of JEC-2200(Power Transformer) and “Loading Guide for Oil immersed Transformers” (No. 143: Technical Report of The Institute of Electrical Engineers of Japan), when it is necessary to operate to load more than rated conditions. On the other hand, transformers in foreign countries may have been also operated under the standard of IEC-354(Loading guide for oil-immersed power transformers) as well as in the same way in Japan.
On operating oil-immersed transformers, Technical Report No. 143 in Japan above-mentioned and IEC-354 are almost equivalent in determining permissible duties and the corresponding loss of life.
To obtain hot-spot temperature of windings in constantly varying temperature and load current, primary, secondary, electromagnetic core, and cooling material (Oil or SF₆ Gas) temperature equations are developed and solve differentially in this thesis. Then Loading Guide for individual transformer is come to realize since it has been thought to be complicate to make individual loading guides for each transformer.

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The thermal puffer type gas circuit breaker uses arc energy as the energy source of pressure rise in current interrupting operation. We proposed a calculation model of puffer pressure rise of thermal puffer type gas circuit breaker taking both arc energy and ablation gas due to nozzle clogging into consideration. In this model, nozzle ablation gas and arc energy dealt with boundary conditions. It was found that the ablation gas during nozzle clogging assists the back flow of gas in the passage and also it transfers arc energy to puffer chamber very efficiently. Thus the puffer pressure rise is influenced by the amount of ablation gas very much.
This paper describes the detail of the new model and the results of simulation.

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This paper describes a new method of measuring partial discharge (PD) via coaxial bonding wire for direct-buried power cable of which the sheaths at an sheath-insulated joint can be bonded at a terminal box, so-called link box, usually installed beside the joint but on the ground. When cable joints are directly buried under ground, it is difficult to use the conventional measuring method to detect PD, since it is necessary to install a PD detection sensor directly at or on the joint. For direct-buried cable line, the formation of sheath bonding for each joint can be usually determined at a link box that is connected to joint via coaxial bonding wire. The terminals of coaxial bonding wire at a joint are connected with sheathes of both sides of the joint, and the terminals of the other end of the coaxial wire are fixed inside the link box. This paper deals with the possibilities of measuring PD from the terminals of the coaxial wire. Some problems have to be solved when connecting a detection circuit to terminals of the coaxial wire, a) how to detect the PD signals from the coaxial wires high sensitively and safely; b) how to evaluate of the propagation attenuation of coaxial wire; c) how to do the measuring calibration for PD measurement system before detection. Some results of experiments simulating the cable conditions on side will be discussed. A practical PD measurement for this kind of direct-buried power cable conducted on site will be also introduced.

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We have developed SiC composite conductors which have light weight, high specific strength and heat resistance, and low thermal expansion coefficient. A performance evaluation on the developed composite conductors has been conducted for the case of practical application in test line. The evaluation suggested that the conductors allow significant increase in capasity or decrease in sagging rate compared with conventional conductors.

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Characteristics of crosslinked polyethylene that is insulation of a XLPE cable change over 100°C and therefore the electrical characteristics of crosslinked polyethylene insulated cables and tape lapped joints under the high temperature were studied. AC, Impulse, V-t and V-n characteristics of a cable are little changed at about 105°C. On the other hand, at about 105°C, the trend of maximum length and number of water trees are increasing.

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Characteristics of crosslinked polyethylene used in XLPE cable change much over 100°C. Mechanical characteristics of crosslinked polyethylene insulated cables and tape lapped joints under high temperature condition were studied. A cleat doesn't change shape of a cable and short-circuit current and ground fault current don't damage a cable at about 105°C. On the other hand, at about 105°C, performance of water impervious layer degraded. Copper taps lapped shield are broken at an offset position with thermal expansion and contraction. Support force of a cleat decreases and lead tape lapped shield is broken.

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The transient phenomena in a nonequilibrium disk subsonic MHD generator at load changes were examined with time dependent quasi-one-dimensional numerical simulations. When load resistance is suddenly changed, fluid-dynamical disturbances are caused near the anode and cathode. When the steady discharge is sustained, the disturbances gradually disappear in the generator channel after propagating and being re-flected at the boundaries. Thus, it is confirmed that the generator works stably at load changes, although the over-shooting in Hall potential is induced transiently. If the load resistance is changed as lower as the unsteady plasma appears, the disturbances attributed to it remain in the generator.

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This paper describes two fundamental characteristics of gas mixtures with c-C₄F₈ (perfluorocyclobutane), which the authors have proposed as a possible candidate for substituting SF₆ in gas insulation. One is concerning the release rate of an electro-negative gas from a gas mixture at liquefied recovery. Gas mixtures with c-C₄F₈ have the advantage of much lower release rate over SF₆/N₂. The other is DC discharge characteristics for a hemispherically-capped rod-to-plane gaps. Discharge voltages have been compared between SF₆/N₂, c-C₄F₈/N₂, and c-C₄F₈/CO₂ for a mixing ratio of an electronegative gas up to 20%.

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The purpose of this study is to clarify the wetting property of conductors for the reduction of audible noise generated from transmission lines during rain. This report shows that the audible noise from a super-water-repellent-surface conductor is the lowest by comparative results of artifi-cial rainfall tests using four kinds of conductors with different wetting properties.

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