This paper proposes a new efficient formulation and its solution method for a maximum loading point or saddle node bifurcation point in electric power systems. This point, corresponding to a tip of the P (Q)-V curve, is characterized by singularity of the load flow Jacobian. The proposed formulation is of dimension n+1, instead of 2n+1 in the standard formulation, for n-dimensional load flow equations. The proposed method uses 1-dimensional singularity condition, obtained from a reduction of the standard n+1-dimensional singularity conditions. For this reduction, one of the diagonal elements of the load flow Jacobian is selected. We also propose an index for this selection to make the proposed method reliable. The solution for the proposed formulation can effectively be obtained based on the Newton-Raphson method with sparse matrix techniques. The computational performance of the proposed method is demonstrated on 6, 14, and 118 bus test systems.

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This paper deals with optimal voltage regulation methods in power distribution systems including Dispersed Energy Storage and Generation (DSG) systems. In order to deliver suitable voltages to as many customers as possible, the optimal sending voltage should be decided by the effective operation of voltage regulators at the distribution substations. In this paper, a modified voltage regulation method based on the existing method is presented and an optimal coordination method of multiple voltage regulators is extended. An on-line real time voltage regulation method by using neural networks is also proposed. In addition, the introduction impacts of DSG systems such as optimal location sites and introduction capacity are evaluated. The results from a case study show that the proposed methods can be a practical tool for the voltage regulation in distribution systems.

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It is necessary to detect sources of harmonic currents in order to reduce harmonic voltage distortion in an electric power distribution system. For this purpose, it is very important to judge the direction of a harmonic current flow, so far, there is no method to judge the direction of flows precisely, This report presents a method to separate transformer currents at a distribution substation into two elements quantitatively; one that flows into a distribution system due to harmonic voltages in a higher voltage system, and the other that flows to a higher voltage system due to sources of harmonic currents in a distribution system. The conventional method to judge the direction of flows using phase angles between harmonic voltages and harmonic currents may not be accurate. By using the newly developed method, the direction of harmonic current flows can be analyzed quantitatively and more accurately than the results by the conventional method. Measured values in both a business area and a residential area are analyzed to verify the new method and the results clearly show the difference of the characteristics of the two areas.

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In an actual power system, there are various types of controllers such as AVR, PSS and GOV which influence the stability of power system remarkably. It is necessary to properly tune the parameters of such controllers to stabilize a power system; eigenvalue sensitivity is a useful tool for this purpose. This paper presents an efficient algorithm for evaluating eigenvalue sensitivities in large power systems. In the proposed method, the sparsity of the system state matrix is fully exploited so that the sensitivity can be obtained with far less computational effort compared with the existing methods. Furthermore, we propose a useful technique to automatically calculate a derivative coefficient matrix which is necessary to evaluate the sensitivities. By using this technique, the eigenvalue sensitivities with respect to any parameters of various controllers can be evaluated easily. The efficiency of the proposed method is illustrated by applying it to a very large power system which has 220 generating units and 3000 state variables.

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Power system analysis is the basis of operation and planning. Since power system is very large and complex, however, it takes long computation time for the analysis. It is desired to develop a fast calculation method for stability analysis.
Recently, the method using multiple time scale numerical integration algorithm was developed for analizing long-term dynamics. This method has the problem of calculation time since the coefficient matrix is very large. It is expected that the calculation time can be shortened using parallel processing. In order to increase the efficiency of parallel processing, the coefficient matrix must be divided since solution of a.set of linear equations is the main part of stability analysis.
In this paper, coefficient matrix is converted into BBDF matrix for effective calculation of parallel processing. Each sub network block can be divided again since it is sparse. The algorithm discussed in this paper was implemented on the nCUBE2S parallel processing computer system. The computing time is measured so that it can be compared to the computing time of a single processor system.

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The frequency response analysis method are widely used in the parameters design of excitation system of generator. However, it can not be applied to a nonlinear excitation system, because it is difficult to calculate the synchronizing and damping torque of a generator with nonlinear excitation system precisely.
For extending the frequency response method to nonlinear systems, this paper proposes an approximation method to calculate the synchronizing and damping torque for nonlinear excitation systems, and using the frequency characteristics of damping torque to the parameters design of excitation systems.
As an example, the proposed method is applied in a generator control system with the power system stabilizer FUZZY-PSS. The power system stabilizer FUZZY-PSS consists of a fuzzy controller and a ΔP type PSS, which is a typical nonlinear control system. The application results show that the proposed method is very useful to aid the parameters design of such nonlinear systems, as well as the power system stabilizer FUZZY-PSS.

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Recently, diagnostic techniques have been investigated to detect a partial discharge (PD) associated with a dielectric material defect in a high-voltage electrical apparatus. However, the properties of PD aren't completely understood because the physical process of PD is complicated. For improvement of detection techniques of PD, it is important to make clear the fundamental physical process of PD.
Therefore, this paper analyzes the process of PD using Wavelet transform. Wavelet transform provides a direct quantitative measure of spectral content ( Dynamic spectrum ) in the time-frequency domain. As it is important to develop a non-contact method for detecting the insulation fault, this paper analyzes the electromagnetic waves emitted from PD using Wavelet transform.
This paper experimentally shows the process of PD as a two-dimensional distribution “Dynamic spectrum” in the time-frequency domain. This method is shown to be useful for detecting prediction of insulation fault.

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In heavy-current high-voltage engineering applications need employing many gap switches in parallel operation to decrease a circuit inductance and increase a life time of gap switches
. The switching characteristics of two parallel-connected triggered vacuum gaps have, therefore, been studied experimentally.
In order to obtain good characteristics of parallel operation, both triggered vacuum gaps must be operated in connection, which the polarity of respective nonholed main electrodes is positive.
It was found that, small time delay about 24 ns could be obtained by main inductance 91μH with the equal inductance of branch circuit 3.9μH. The efficiency of parallel ignition showed nearly 100% because no dependence of interelectrode gap spacing and main inductance on main voltage was observed.
It was found that, the switching time of parallel-connected triggered vacuum gaps was independent and nearly constant approximately 0.16μs to the varieties of main voltage at the instant of chopping in the range 6.8 to 17.3 kV. This switching time was 27.5% longer than that of a single TVG under the same condition.

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In this paper, the possibility of optical current transducers applying the optical heterodyning method is investigated. From results of experiments, the following advantages were confirmed regarding the characteristics of the current detection system using the method. [A]: Stability to signal level changes. [B]: Wide dynamic range of measurement.
However, in the experiments, it was also found that measurement errors appear due to cross-talk between the polarization components of the dual frequency light used. Study was conducted on countermeasures in case of generation of cross-talk at light insertion to polarization maintaining fiber for transmission. From the study, it became known that it is effective to make the state of incident light linearly and orthogonally polarized.
It was also observed that modulation depths of the beat signals change as time elapses. By experiments and analysis, it became clear that the undesirable phenomenon is related to the coherence of light. As a countermeasure, compensating the optical path length difference between normal polarization modes of the polarization maintaining fiber was proposed. Effect of the method was confirmed experimentally.

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This paper presents the surge responses of the grounding system using the scaled electrode models experimentally. To examine how the construction of the electrode elements affects the surge impedance, we selected the following electrode element models, a linear one, a straight one with linear branches, curved branches, and the complex electrode made by these elements. It was investigated into their surge responses from the condition of very high soil resistivity to low one simulated by the immersion of the model into the electrolyte medium. The experimental results showed that the impulse impedance decreases if the appropriate length of the electrode is connected to the end conductor of the mesh to divide current. It is also displayed the remarkable effect of the impedance reduction in the combination of the electrode elements simulated to the grounding mat. Besides the evaluation of the impulse impedance in time domain, we also calculated the frequency characteristic of the electrode model by Discrete Fourier Transform. In frequency domain, we obtained the similar relationships in order of the magnitude of the impedance with time domain.

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The role of an overhead ground wire on the generation mechanism of the lightning-induced voltage on a multiconductor line, associated with a vertical return-stroke channel, is studied based on numerical calculation. The induced voltage is calculated by the method where the tangential component of the electric field to the wire is looked upon as inducing sources. The analyzed multiconductor line consists of three phase wires and an overhead ground wire having one or two earthing points. The influence of the overhead ground wire on the induced voltage is dependent on the direction of a return stroke, as well as the ground conductivity. When a return stroke is on the side of a power distribution line, the induced voltage decreases with the decrease of the earthing resistance of the overhead ground wire, irrespective of the ground conductivity. When a return stroke is close to an end of a distribution line, the influence of the overhead ground wire is dependent on the ground conductivity. In this case, the induced voltage on overhead wires over lossy ground sometimes increases with the presence of an overhead ground wire having only one earthing point. This effect can be avoided by adding earthing points to the overhead ground wire.

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Insulating characteristics of small SF₆ gas gaps have been investigated for lightning impulse voltages. Electrodes, that radius is 20mm, are covered with 20μm thick PET films. At the region of gas gap less than 1mm, under 0.4MPa, the breakdown voltages are at least twice higher than Paschen's curve. And when gas gap is become longer than 1mm, the breakdown voltage of gas gap is getting near Paschen's curve. These phenomena can be explained well by assuming the lack of an initial electron. When gas gap is less than 1mm, the initial electron seems to be emitted from PET films at about 70kV/mm. When gas gap is over 1mm, the initial electron seems to be emitted from ions in gas gap. When the gas gap is Omm and the gas wedge gap is constructed, the flashover of gas occurs at about 3.5kV. With this voltage, the electric fields of covering PET films surface less than 35μm gap region are higher than 70kV/mm. Initial electrons are generated enough in this region, but flashover does not occur. This may be due to the secondary ionization effect (γ effect). PET film has the tendency to catch electrons, and avalanches are stopped effectively on covering PET films.

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The health effect of the weak current induced in the human body as a result of the interaction between human body and power line electric fields has been investigated. A human model (cylinder+semisphere) filled with tissues having different conductivities was used to analyze the internal current densities. In this analysis, only the magnitudes of the induced current densities were analyzed.
In this paper, the finite element method is applied to the analysis of the distributions of the horizontal and vertical currents induced in the cylindrical model. The calculation method is verified by comparing the calculated results with the experimental ones obtained elsewhere. The basic characteristics of the induced current distributions in the cylindrical model with the two tissues having different conductivities have been made clear.

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This paper investigates the insulator surface flashover characteristics in SF6 gas by applying lightning impulse. It especially discusses on the surface flashover characteristics of discharge patterns originating from an insulating surface as compared with the discharge pattern originating from one electrode attached to the insulator.
The origins of both patterns of discharge are points with a maximum electric field strength over an insulator surface and an electrode surface. The flashover electric field strength over the insulator surface is lower than that on electrode surface coated with insulation material, and, the dispertion of flashover voltages of insulator surface discharge is greater than that of electrode discharge. Thus there is a difference between the flashover characteristics of insulator surface discharge and electrode discharge and it seems that the variations of the surface conditions of insulators have some effect on them.
Therefore, in the insulation design for insulator surfaces in gas insulated switchgear (GIS), it is necessary to ensure reliability with some tolerance added over the electric field strength of the gas gaps.

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Constructing the hydrogen energy system in a global scale as an energy system which have not affected a global environment is assumed. One of the hydrogen energy system is a photovoltaic/fuel cell power hybrid system which is a combination of the photovoltaic power generation system and fuel cell. This system is composed of photovoltaic arrays, hydrogen generators, hydrogen storage system and fuel cell power generation system. The hydrogen storage system is composed of three hydrogen storage tanks. Each hydrogen storage tank has hydrogen absorbing alloys (LaNi5) and a shell and tube heat exchanger. This system can supply constant electric power to the electric loads in a solitary island separated from a commercial electric network.
The possibility of each of hydrogen storage tank in this system is examined by the computer simulation. Input data used in this simulation are as follows ; the global irradiance on inclined plane and the ambient temperature of HASP data of Tokyo, residential load data which have ten kinds of electrical load forms (annual electric load energy of 400 MWh), conversion efficiencies of each subsystem and so on.
As a result of the computer simulation, it was reveled that 745 kW in rated capacity of photovoltaic power generation system, 259.2 tons in total weight of hydrogen absorbing alloys, 150 kW in rated capacity of fuel cell power generation system are needed for the annual electric load of 400 MWh. And then a number of hydrogen absorption and desorption of hydrogen storage tanks per year are 1039 and 1749 times respectively.

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Adiabatic efficiency of aa supersonic Faraday MHD (magnetohydrodynamic) generator and its relation to Joule dissipation in the MHD channel were studied in a shock tube experiment. The adiabatic efficiency of 39.7% was obtained at the enthalpy extraction of 8.3%. A dissipation process, which reduces the adiabatic efficiency, is examined by evaluating loading parameters and entropy productions caused by the Joule dissipation. At low load resistances, large Faraday currents in the channel upstream cause extremely large Joule dissipation in both the main flow and the region near the electrodes. It is confirmed experimentally that a high loading parameter yields a high adiabatic efficiency because Joule dissipation is small throughout the MHD channel.

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If there is a local thermal insulation on the superconductor surface, the thermal equilibrium transport current can be measured. A simple graphical scheme is presented incorporating heat transfer and heat generation characteristics into the calculation of the stability of superconductors with local thermal insulation, modifying the equal area method presented by Maddock, et al. Minimum thermal equilibrium transport currents were calculated and compared with the experimental results.

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