Surge arresters which installed at customer's facilities and distribution linesare often damaged by winter lightning in mountainous areas facing the Sea of Japan. Therefore we have observed the lightning performance at a mountainous area, since 1998, in order to verify the effective lightning protection methods for customer's facilities and distribution lines. Based on the observation data and analysis results using the EMTP, we propose the effective lightning protection methods for customer's facilities.
(1) When grounding resistance of a customer'sfacility is less than 10 Ω, lowering the grounding resistance is one of the effective lightning protection methods for preventing a customer's arrester failure.
(2) It is effective for preventing a customer's arrester failure that grounding of a customer's facility is connected with an overhead ground wire of a distribution line through an earth wire, and it dose not increase a failure probability of a distribution arrester.

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According to the phenomenal process of electrical conductance in metals and alloys, a 3-dimensional unit net model for calculating the electrical conductivity of shammed alloys is presented in this paper. By this model, the influence of the components and their distribution upon conductivity of CuCr serial alloys are simulated, as well as the gas content in the phase structure. The comparison of the simulation results with typical experimental values is carried out. The precision of the model is analyzed. The results approved the availability and effectiveness of this model.

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Lightning outages on high-voltage power distribution lines have been decreased steadily for lightning protection with surge arresters and overhead ground wires for high-voltage power distribution lines in Japan. However the number of lightning outages on low-voltage distribution lines is on the increase for the information-oriented and computerized society. We have examined lightning overvoltages in low-voltage distribution lines with service drop lines for customers. The peak value of the line conductor voltage in a low-voltage line is reduced and the waveform of it resembles that of the neutral conductor voltage due to installing a DV wire and a grounding at the neutral conductor. The service drop line should be taken into account when lightning overvoltages in low-voltage distribution lines is examined. We have studied protection of low-voltage distribution lines against lightning induced overvoltages with the model of low-voltage distribution line using the Electro-Magnetic Transients Program (EMTP) on the basis of the experimental results. Nevertheless the grounding resistance value is higher, separate groundings on the closest pole to a pole transformer and the termination of low-voltage line is as effective as a single low grounding on the middle of low-voltage line.

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This paper describes an improved surface charge method (SCM) that analyzes the electric field in composite dielectrics in a three-dimensional (3D) arrangement. In this SCM, curved boundary surfaces are represented by thirdorder shape representation functions, and surface charge density distributions on the surfaces are expressed by non-conforming first-order charge representation functions. This type of SCM realizes natural treatment of curved surfaces, and also numerically stable treatment of edge parts of the shapes and triple junctions of different materials without any additional modifications. Two benchmark-test calculations are carried out to confirm the validity of the proposed method. It has also been applied to field analysis for a real 3D dielectric support of a high voltage feed line.

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This paper presents the results of the surge voltage distribution test at Kihokuconverter station to verify the EMTP simulation modeling. The test voltage applied at the DC or AC transmission line entrance of the station. We calculated the voltage distribution of the converter station by EMTP taking the test conditionsinto consideration in addition to that of prior analyses. The simulated voltage distributions of either side of voltage application case agree very well withthose of test results. The accordance shows that the EMTP modeling used in the study was appropriate.

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Sensing techniques with a Pockels crystal have been applied to directly measure the potential and electric field distribution of surface discharge creeping on adielectric material. The transient change of potential distribution with a surface discharge, which propagates on a 780 μm thickness BOO crystal in SF₆ at 160_??_760 Torr pressure, is measured with high time and spatio resolution by using Pockels sensor, a CCD camera and a streak camera.
Little significant differenceis recognized between the potential distribution along a negative discharge and thatalong a positive one. The distribution of E_x along a streamer has a triangular profile and E_x has its maximum near the head of it. The value of E_x around the streamer head keeps around the critical value for the gas ionization. During subsequent stepwise propagation of the streamer, a leader, whose electrical conductivity is relatively high, is being inside previous discharges.

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We have studied interrupting phenomena with alternative gasses to SF₆, especially N₂-SF₆ gas mixture. This paper describes capacitive current switching phenomena and performance of the gas mixture. Capacitive current switching tests were performed with N₂-SF₆ gas mixture, N₂ and SF₆ in a 300kV class gas circuit breaker. Dielectric recovery characteristics have been calculated by combining breakdown field strength data with gas flow calculations and electric field calculations. Comparing both results, the influence of dielectric synergism and gas flow of the gas mixture on the performance is discussed. As a result it is found that capacitive current switching performance of N₂(85%)-SF₆(15%) gas mixture is almost80% of that of pure SF₆. Consequently it will be possible to realize full performance with gas mixture by improvement of GCB design.

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The purpose of the present paper is to show the dielectric characteristics of inhomogeneous hot SF₆ gas in a dead-tank-type gas circuit breaker (GCB) experimentally. High-temperature and low-density SF₆ gas generated during a heavy current interruption is distributed inhomogeneously in the grounded tank, and can strongly threaten the dielectric capability of the GCB. Few studies, however, have been carried out on the dielectric characteristics of the inhomogeneous hot gas. Using small gap discharges, the hot gas behavior of a GCB model, having breakdown or no breakdown occurring, was investigated. As a result, it was found that there was little or no effect on breakdown voltages of the cool gas in the breakdown paths. This suggests that the breakdown voltage of inhomogeneous hot gas could be obtained as the applied voltage at which the electrical field strength equals E_crit of local hot gas at the concerned location.

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This paper addresses the issue of the computation techniques for assessing the steady state power flows controlled by Flexible AC transmission Systems (FACTS), which contain variable series compensators (VSC), phase shifters (PS), interphase power controllers (IPC), unified power flow controllers (UPFC). An improved Newton-Raphson load flow program has been developed based on an analysis of convergence characteristic of the conventional method. It is shown that the conventional method tends to suffer from ill-conditioning problem, resulting in the shrink of the convergence region. Based on examinations of the condition number of the Jacobian, a penalty function method is adopted in order to avoid the ill-conditioning problem and to guarantee a successful convergence. Although the computational burden is increased about twice to three times, the proposed method much extends the region of convergence. The effectiveness of the proposed method is demonstrated through numerical examinations using IEEE 57 and 118 bus systems.

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In recent years, introduction of micro co-generation system (μCGS) is expected to be a promising measure for improving energy efficiency in house. This paper discusses an operation pattern and heat-storage capacity of μCGS introduced in house use by using hot water load pattern expressed in minute. The simulation results reveal that (i)the introduction of μCGS drastically contributes to energy saving, (ii)the required heat-storage capacity turned out to be in feasible volume range, (iii)the calculation based on hourly averaged hot water load patterns underestimates the heat-storage capacity, (iv) when reverse power flow is No.accepted, value of μCGS as a hot water supply is diminished because operation of μCGS is considerably restricted and μCGS canNo. supply sufficient hot water.

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Recently customers who need electricity of higher quality have been installing co-generation facilities. They can avoid voltage sags and other distribution system related disturbances by supplying electricity to important load from their generators. For another example, FRIENDS, highly reliable distribution system using semiconductor switches or storage devices based on power electronics technology, is proposed. These examples illustrates that the request for high reliability in distribution system is increasing. In order to realize these systems, fast relaying algorithms are indispensable. The authors propose the necessity of pro-tection devices that implements the fast relaying algorithms for distribution system. In designing higy speed protection system, fast discrimination of magnetizing inrush current is also indispensable. Conventional method of inrush current detection for transformer protection uses the ratio of second order components of differential current. The authors propose a new method of detecting inrush current based on transformer magnetizing characteristics. Inrush current occurs when transformer core becomes saturated. The proposed method estimates transformer core saturation by the linear relation between differential current and the integral of voltage. The propose method can be applied for single-phase transformer and also for three-phase transformer by considering subsidy effect. The proposed method is verified using experimental data using single-phase transformer and three-phase transformer and the proposed method is proved to be effective.

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This paper proposed an optimization method for the equipment planning problem of District Heating and Cooling energy supply system (DHC), and verified the method through a simulation against a conventional design case. The DHC problem above-mentioned is to determine the optimal combination (best-mix) of heating and cooling equipment and the required units of equipment, which minimize the total cost while satisfying the heating and cooling demands simultaneously. The algorithm employed for the method is the extended dynamic programming (ExDP) already reported by the authors, which solves the DHC problem exactly and effectively by relaxing the combinatorial explosion.
Simulation result showed that the configuration of heating and cooling equipment by its solution was better than that by conventional design in view of the total cost and thermal output ratios. Furthermore it was assured that an effective analysis was done in computation due to the reduction of states size by using the ExDP algorithm. This experimental verification can lead to the practical applicability of the proposed method to the DHC problem. Consequently, an optimal DHC planning system has been developed, which helps providing better designs of heating and cooling equipment than the conventional ones.

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Though the power supply to airplane warning light installed in transmission line tower is generally carried out by low voltage distribution line, in especially basic transmission line over 500kV with many mountainous area the inside of transmission line, there are many cases in which there is no a distribution line near, and considerable labor and cost for the power supply are needed. Then, authors developed electromagnetic induction type power source equipment which took out the electric power by using current transformer from induced current which flows in overhead earth wire.
First, the power source equipment which used the penetration type for CT for the power: was developed, and the demonstration experiment for about 10 months was carried out in Tokyo Electric Power Co., Inc. Minami Niigata trunk line. As the result it was able to be verified that operating characteristic and environment-resistant characteristics of the power source equipment were good. For the purpose of applying to Tokyo Electric Power Co., Inc. Minami Iwaki trunk line in continueing, the power source equipment which used winding type for CT for the power was developed. This equipment finishes the installation construction in July, 1999, after the test in the factory is carried out, and it is carrying out the practical use in Minami Iwaki trunk line at present.
In this paper, the content is reported on power source equipment applied to Minami Iwaki trunk line on EMTP analysis of the overhead earth wire current and outline of developed power source equipment and means of application to the continuous line road and operation situation in the operation and comparison examination with analytic value.

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The influence of water contamination in the working gas on the performance of closed cycle disk MHD gen-erator was investigated experimentally. The experiment was carried out using the Fuji-1 blow-down facility. It was found that the enthalpy extraction ratio of the disk MHD generator decreased with the increase of water concentration when it was higher than about 500ppm. This concentration is remarkably higher than the permissible level predicted by previous numerical simulations. It is observed that higher seed fraction is required for higher water concentration in working gas. It is suggested that the water moleculars react with the Cs seeds in a generator.
The reduction of water concentration can be realized by the increase in the bottom temperature of heat exchanger under its careful heat-up operation.

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Thermoelectric devices have been investigated widely in order to transform a lowtemperature heat source to the electrical power. In this report, we proposed a knitted wire panel as a thermoelectric power generator. A thermocouple on the knitted wire panel was formed by knitting an alumel wire and a chromel wire(φ0.3mm).The knitted wire panel was set at a measurement system using a peltier coolingdevice, and electrical characteristics were measured. Additionally, we discuss here the characteristics of electrical power generation from the panel using a equivalent circuit model. As a result, electrical power from the panel increases linearly with increasing a number of thermocouple formed by wire knitting processonthe panel. It is considered that thermocouples can be formed easily by wires knitting process.

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A superconducting generator is expected to be a next-generation machine because of many advantages over a conventional generator. Super-GM has been promoting R&D of 70MW-class superconducting model generators to verify the basic technologies required for the design and manufacture of a 200MW-class superconducting pilotgenerator. Verification tests of the third model generator, quick response excitation type C generator, finished by Jun 1999. The excellent characteristics as asuperconducting generator were verified through the series of tests. We reportmain test results such as “Open and shortcircuit test, “Loaded test”, “Quick excitation test”, “Negative phase sequence overcurrent test” and “Sudden short circuit test”.

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MHD electrical power generation with frozen helium plasma (FHP) is examined numerically. The FHP can be initiated by pre-ionized helium without the alkali metalseed at the generator inlet. Since the three-body recombination coefficient of helium ions is low at the electron temperature above 5000K, the ionization degreecan be kept almost constant in the entire region of the generator channel. The r-θ two-dimensional numerical results show that the performance of the FHP MHD generator is comparable to that of the seeded plasma MHD generator, if the additional power consumed to pre-ionization is ignored. In the FHP MHD generator, the ionization degree at the inlet should be controlled precisely, as well as the seed fraction in the seeded plasma MHD generator. Under the adequate inlet ionization degree for sustaining the FHP plasma, the plasma maintains the uniform structure. On the other hand, a slightly excess ionization degree causes the strong Lorentz force in the upstream region of the generator, then the generator performance is deteriorated.

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Excessive ohmic heating may damage superconducting wires when a quench occurs in a superconducting coil and hence it is necessary to detect the quench as fast as possible in order to protect the superconducting coil. We have proposed a new quench detecting method, which can detect an active power after a quench with high precision.
In this paper, in order to investigate the usefulness of the proposed method for HTS (High Temperature Superconducting) coils, quench detection tests of a small HIS coil are carried out and the results are presented. In general, HTS coils are not necessarily self-protective because quench propagation velocities in high Tc superconductors are slower than those in low Tc superconductors. Therefore a quench detecting method with high precision and fast response is required for HIS coils. Through the quench detection tests of a small Ag/Bi-2223 HTS coil, the usefulness of the proposed method is investigated. In addition, through the off-line quench detection tests of AC LTS (Low Temperature Superconducting) coils by the numerical simulation, the usefulness of the proposed method for AC LTS coils is also discussed.

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A load demand following method has been proposed for polymer electrolyte fuel cell with reformer, which purifies hydrogen from reformed gas by using metal hydride. To investigate the basic performance, an exper-imental apparatus was fabricated, and absorption and release experiments of hydrogen from mimic reformed gas were carried out with LaNi metal hydride. In the results, neither poisoning nor deterioration of absorption property due to CO₂ and H₂O was verified, which are the main impurities of the steam reforming process. And approximately 100% purified hydrogen was obtained in the release process. Even if the utilization factor of the material was used over 90%, the recovery rate higher than 90% was certainly secured under a lower flow rate control condition. Therefore, satisfactory practical use performance has been demonstrated by the experiment. Also an appropriate system concept has been considered for the hydrogen release process with energy-saving, which effectively uses heat sources, such as low concentration hydrogen leak gas, heat radiation in the absorption process, and waste heat from the fuel cell system.

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The authors propose the following similarity law which is expected to hold for generation channel section of high-performance nonequilibrium disk MHD generator. From a generation channel with a certain thermal input, a generation channel with n times thermal input and almost same performance can be derived by similarly changing the size by a factor √n and also changing the seed fraction by a factor 1√n in comparison with their original ones. The proposed similarity law is, at first, theoretically verified using the two-dimensional basic equations of the working plasma and its approximate validity is successfully demonstrated. Next, the law is verified numerically by two-dimensional time-dependent simulations. The already designed generation channel with 100 MW thermal input is adopted as the original channel and two generation channels with 25 and 400MW thermal input are derived from the original one according to the similarity law. The numerically obtained distributions are similar and performance is almost same for these three channels, indicating that the similarity law holds in high accuracy.

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UHV designed transmission lines have already been in operation at 500kV since 1992. UHV substation equipments have also been energized in the test yard since 1996. For rationalization in insulation design and cost reduction, it is important to evaluate the phenomena of lightning for the UHV designed transmission lines.
Some studies to observe current waveshapes have been conducted before, but they were ones conducted on independent towers and do not provide many data in a large-current region. So, we have been observing lightning currents on 60 transmission towers (mainly 500kV lines) since 1994. On UHV-class transmission lines with sections of 500kV-class insulation, lightning observations have been made to study the generation and the propagation of overvoltages into substations. Voltages and currents were recorded at the substations and at junction-tower footings on the UHV system. This paper describes the study of lightning phenomena and EMTP calculations on the UHV transmission lines.

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