Increase of static electrification was experienced in aged transformers of both shell-form and core-form. The investigation disclosed increase of accumulated charge by aging of insulator (pressboard). For assessment of static electrification (SE) in aged transformers, accumulated charge evaluation by potential measurement becomes necessary instead of conventional electro-static charging tendency (ECT) of oil. As for the increase of SE, recent research disclosed that oxidation of sulfuric contents in oil, such as sulfide and sulfoxide, caused increase of high ECT of oil. Sulfoxide in pressboard also showed good correlation with accumulated charge on the pressboard. Sulfoxide in oil and pressboard can be a good indicator for the increase of SE. Further accumulation of the field data is important for development of diagnostic technology for SE in transformers.

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Metal Oxide Surge Arrester (MOSA) technology was first developed in Japan and improved. Original discovery was made by Matsushita Electric Industry Co., Ltd by a finding of some diode phenomenon. Meidensha Corporation applied it to high voltage grid system in Japan in 1975 as a reliable lightning protection device. Japanese MOSA manufactures played a leading role in world MOSA innovations and developments. The BIL has been standardized based on arrester protective characteristics. Due to MOSA, the product shift to MOSA occurred from the gapped type arresters (GTA) 35 years ago as GTA had many gap-related problems. The MOSA became a complete IEC standard (IEC60099-4-1991) taking 20 years from starting development. The MOSA now has a solid footprint in the world lightning protection space.

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Residential cogeneration system with PEFC is expected to become a promising technology as distributed resources of power systems in order to improve energy system efficiency. However, it is important to develop efficient algorithm for operation because the energy demand at each house is largely different every day. In this paper, we propose the operational algorithm and evaluate algorithm from view point of energy conservation and economic index based on the energy demand characteristics. In this algorithm, hot water and electrical demand on the next day is estimated based on the average of the past data. By using actually monitored energy demand data, the simulation results indicate that 1) the larger electrical demand a household has, the more efficient this algorithm become at the point of energy conservation 2) the larger hot water demand a household has, the more efficient this algorithm become at the point of economic index.

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The purpose of this paper is to propose a comprehensive congestion management scheme by generator and FACTS device operations. To relieve congestion effectively and quickly, we use two indices based on the DC method. However, calculation errors using the DC method may become large due to its approximations. Thus, we also propose an improved DC method, which is a DC method considering transmission losses and transformer tap ratios, and carry out simulations to confirm the validity of the improved DC method. Finally, we carry out simulations using the proposed congestion management scheme by means of the IEEJ EAST 30 machine system. With the simulation results, we can relieve congestion effectively and quickly.

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As known well, two of the fundamental processes which give rise to voltage collapse in power systems are the on load tap changers of transformers and dynamic characteristics of loads such as induction machines. It has been well established that, comparing among these two, the former makes slower collapse while the latter makes faster. However, in realistic situations, the load level of each induction machine is not uniform and it is well expected that only a part of loads collapses first, followed by collapse process of each load which did not go into instability during the preceding collapses. In such situations the over all equivalent collapse behavior viewed from bulk transmission level becomes somewhat different from the simple collapse driven by one aggregated induction machine.
This paper studies the process of cascaded voltage collapse among many induction machines by time simulation, where load distribution on a feeder line is modeled by several hundreds of induction machines and static impedance loads. It is shown that in some cases voltage collapse really cascades among induction machines, where the macroscopic load dynamics viewed from upper voltage level makes slower collapse than expected by the aggregated load model. Also shown is the effects of machine protection of induction machines, which also makes slower collapse.

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Nonlinear phenomena such as saturation in magnetic flux give considerable effects in power system analysis. It is reported that a failure in a real 500kV system triggered islanding operation, where resultant even harmonics caused malfunctions in protective relays. It is also reported that the major origin of this wave distortion is nothing but unidirectional magnetization of the transformer iron core. Time simulation is widely used today to analyze this type of phenomena, but it has basically two shortcomings. One is that the time simulation takes two much computing time in the vicinity of inflection points in the saturation characteristic curve because certain iterative procedure such as N-R (Newton-Raphson) should be used and such methods tend to be caught in an ill conditioned numerical hunting. The other is that such simulation methods sometimes do not help intuitive understanding of the studied phenomenon because the whole nonlinear equations are treated in a matrix form and not properly divided into understandable parts as done in linear systems.
This paper proposes a new computation scheme which is based on so called perturbation method. Magnetic saturation in iron cores in a generator and a transformer are taken into account. The proposed method has a special feature against the first shortcoming of the N-R based time simulation method stated above. In the proposed method no iterative process is used to reduce the equation residue but uses perturbation series, which means free from the ill condition problem. Users have only to calculate each perturbation terms one by one until he reaches necessary accuracy. In a numerical example treated in the present paper the first order perturbation can make reasonably high accuracy, which means very fast computing.
In numerical study three nonlinear elements are considered. Calculated results are almost identical to the conventional Newton-Raphson based time simulation, which shows the validity of the method. The proposed method would be effectively used in a screening where many case studies are needed.

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Partial discharge detection using a UHF band signal is a well known advanced insulation diagnosis method in gas insulated switchgear (GIS), and has been well studied. In contrast to conventional diagnosis with lower frequencies in the kHz range, UHF band signal above the cutoff frequency has been detected with higher-order modes that only appear in electromagnetic signal propagating inside the GIS tank. This is because the wavelength of UHF band signals is comparable to the GIS tank size. The authors had observed the characteristics of such higher-order electromagnetic waves with a focus on the resonance characteristics of the TE11 mode, using a disk-shaped UHF sensor with the sensor extending into the inside of the tank. The purpose of this paper is to investigate the propagation characteristics of higher-order mode waves in a coaxial GIS model. Considering application to actual equipment, it was investigated that the output of a sensor with an arch-shape not extending into the inside of the tank, which has less influence on the propagation mode of the inner electromagnetic wave. In the frequency domain below the cutoff frequency of the TE11 mode, the output characteristics were almost independent of the installation position of the UHF sensor, but in the higher frequency domain the output power displayed discontinuous increases at some frequencies. It was also studied that the circumferential dependence of sensor output. For higher-order modes resonant characteristics appeared that depended on the tank length, and it was recognized that the electric field distribution inside the tank influenced the output of the UHF sensor at resonant frequencies. Further, it was found that installing a spacer inside the tank shifted resonant frequencies and the influence of the spacer consistent with the relationship between the spacer position and the electric field distribution inside the tank.

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The power generation using natural energy contains electric power fluctuation. Therefore, in order to put such power generation system to practical use, compensation for system power fluctuation is needed. In this paper, we propose a power compensation method using biomass gas turbine generator and flywheel energy storage equipment. The gas turbine generator is used for compensation of low frequency power fluctuation in order to decrease capacity of flywheel. Usefulness of the proposed system is confirmed by experiment using a test plant.

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Water management factors such as diffusion coefficient and electro-osmotic coefficient of water vapor through MEA have been measured in our previous report, since these factors have important effects on performance of PEMFC. For unsteady analysis, more factors such as water content of MEA and mass transfer coefficients at both side of GDL boundary must be known. Then we have measured the water content of MEA and unsteady mass transfer coefficient between MEA and GDL. Since the local water transfer inside the PEMFC is quite difficult to be measured, so that the three dimensional analysis of PEMFC has been performed to estimate the mass transfer coefficient between channel and GDL. Then, unsteady power generation analysis with those measured mass (water) transport factors has been conducted. The computed results such as cell voltage transient response, current distributions, and membrane resistivity distributions are compared and agreed well with the measured results.

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In low-voltage distribution line of the three-phase four-wire system, the neutral conductor current increases by the current mainly on third harmonic wave which does not have the phase rotation under the condition in which a balance of the load was removed, when the harmonic generation equipment is contained for the load. The increase of such neutral conductor current is made to increase the waveform distortion of receiving end voltage, and various waveform interferences are arising. In order to reduce the neutral conductor current, the method for inserting the active filter for third harmonic wave near the load is proposed, and the protective effect of waveform interference is also reported.
In this paper, the method for drastically reducing the neutral conductor current by the method using resonance phenomena of the LC which is simpler than active filter is proposed.

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As for gas insulated switchgear (GIS), small space requirement and economical efficiency have been demanded. Circuit breakers (CB), disconnecting switches (DS) and earthing switches (ES) have been designed toward compactness. Compact & light bushings have been also required. As for bushings of GIS, there are roughly three types; capacitor, gas-filled and molding bushings. Since gas-filled bushings have the feature which is both of the lightness and the economical efficiency, it is important to develop compact and light gas-filled bushings by improvement of insulation technology. The main subject for compact design is reduction of electric field strength on the outside hollow insulator around the inside grounded electrode tip. We devised a new inner grounded electrode structure which consists of some column electrodes. This paper describes the effect of reduction of maximum value of electric field strength on the outside hollow insulator by a new inner grounded electrode. Then, improvement of insulation performance for electrodes with insulation coating in SF₆ gas is described as composite insulation technology. Finally, the efficacy of these insulation technologies is described by fundamental insulation test results of prototype compact 800kV SF₆ gas-filled bushing.

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Regarding a polymer electrolyte fuel cell (PEFC), the influence of degradations of a catalyst layer and a gas diffusion layer which are parts of membrane electrode assembly (MEA) on electrode flooding was investigated. On a PEFC, high humidity operation is desired for high performance because it is necessary to contain much water in proton exchange membrane and ionomer at catalyst layer. Additionally, high gas utilization is required for high system efficiency. However, under these conditions, significant degradation in a cell performance is caused by water-flooding of electrodes. The purpose of this study is to investigate how the degradation of a catalyst layer and a gas diffusion layer give the influence to occur flooding on electrode. The single cell was generated at 0.3A/cm² under high humidity operation for 10000 hours. And the cell performance was evaluated as cell voltage, cell resistance, IV curves, gas crossover rate, electrochemical surface area and Oxygen gain in order to find which part of the cell dominates such cell degradation. Consequently, it is found that the gas diffusivity degradation finally dominates the decay of the cell performance and it is mainly caused not in the gas diffusion layer but in the catalyst layer.

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Two estimation methods for a backward impedance of a power distribution system are proposed in this paper. A frequency response of a transient current flowing into a capacitor, which connected to a distribution line, has information of the backward impedance. The impedance is obtained from an attenuation constant and a resonance frequency determined by the capacitance and the impedance of power distribution system. These parameters are stably obtained from a frequency response of the transient current using a least square method. The accuracy of the method heavily depends on the origin on the time-axis for Fourier transform. Additional time-origin estimation is required for an accurate estimation of the backward impedance. The second method estimates the backward impedance using two transient current waveforms obtained by connecting alternately different capacitors to a distribution line. The backward impedance can be represented as a function of the frequency responses of these current. This method is suitable for an automatic measurement of the backward impedance because the method is independent from the time-origin. The proposed methods are applicable to an estimation of a harmonic current of the distribution system. In this paper, a harmonic current flowing through a distribution wire is estimated from the estimated backward impedance and the measured results of harmonic voltages obtained by an instrument developed by the authors.

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