Superconducting fault current limiters (SC-FCL) are expected to be introduced in electric power systems to suppress a short-circuit fault current. In present paper, three line-to-ground fault and single line-to-ground fault are assumed to happen at the exit of bus in a 275kV electric power system . The SC-FCL is supposed to be a commutation type, which consists of a non-inductive superconducting coil and a current limiting element (resistor or reactor). The introduction merits of the SC-FCL were investigated quantitatively by EMTP (Electro-Magnetic Transients Program) from the viewpoint of the current limiting performance, the prevention of the voltage drop at a load bus, reduction of the overvoltage and the joule heat generated in the SC-FCL. Through the performance evaluation of the SC-FCL in the power system, desired specification of design and operation parameters of the SC-FCL were given qualitatively. The differences of introduction merits due to the FCL-types and introduction location were also pointed out.

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Superconducting generators have many advantages such as increasing generation efficiency, improving power system stability and reducing size and weight in comparison with conventional generators. 70 MW class superconducting generators are being developed in Japan to verify the basic technologies for a 200 MW class superconducting pilot generator. Manufacture of 70 MW slow response excitation type rotor has begun in 1992 and factory tests were conducted in 1996. Succeeding to the factory tests, the rotor was combined to the stator with air gap windings in the verification test facility in Osaka power station and verification tests were conducted in 1998. The advantages and the reliability of superconducting generators have been clarified in these tests.
In this paper, experimental results and analysis of the stability of the superconducting field windings at two kinds of severe tests; a continuous pulse excitation test and a sudden short circuit test are discussed. The main results are summarized as follows.
(1) Any quench has not occurred in the severe tests.
(2) A calculation method for the temperature rise of the conductor and the helium is developed in order to explain the experimental results. The calculated results agree well with the experimental ones.

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In this paper, a systematic approach to design controllers based on H-infinity theory for multi-machine power system is presented.
Generally, a centralized control scheme is difficult for a large-scale interconnected power system because of the obtaining of information of the whole system, computation times and so on. In order to cope with these problems, two decentralized control schemes are proposed.
One is based on the decomposition of information. The feedback gains for the whole system is obtained and after decomposing the gains into sub-blocks for each area, the diagonal block is used to design the controller for each generator.
The other is based on the area decompositions. Decomposing the original system into blocks for each area carries out the procedure and the local feedback gain is obtained using information for each decomposed system.
Furthermore, to improve robustness of the system, an effective weighting matrix design, which remarks the allocation of eigenvalues, is also proposed.
Several simulation tests show the effectiveness of the proposed methods.

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In order to keep the quality of power and voltage stability, and to minimize transmission losses, a power company maintains the voltage at every point in the power system within the adequate range. Up to now, some automatic Voltage/Reactive power (Q) Control (VQC) methods were proposed. They mostly belong to either local VQC methods, merely based on the information at each substation, or central VQC methods which are based on the information collected at the central dispatching center. Local VQC methods, however, need a cooperative control function to restrain hunting action of transformer taps, a dispersible function to limit the number of actions at some facilities, and so forth. On the other hand, central VQC methods are known to cause control lag when power demand changes suddenly, because of necessity to handle and transmit massive amount of data. They, moreover, need a highly accurate state estimation function.
In this paper, we propose a new VQC method, Q-TBC (Reactive Power (Q)Tie-line Bias Control), that is based on the balance of reactive power in the system. The proposed method was developed by the analogy with frequency Tie-line Bias Control. Q-TBC has the advanced characteristics of autonomous and cooperative distributed control. The computer simulation using the practical system data of Kansai Electric Power Co. shows the effectiveness of Q-TBC methods.

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A Capacitor Commutated Converter (CCC) has a simple circuit topology of a series capacitor placed between the valve and the converter transformer in each phase. The series capacitor mitigates the inverter operation of a CCC by assisting the commutation with the voltage charged in it. But, it does not guarantee the complete commutation in any conditions for a valve does not have self turn off ability. Therefore, precise analysis on commutation process of a CCC is required to secure its operation., At first, the formulation of the interrelation among the converter parameters, ac voltage, dc current, firing delay angle, overlap angle and effective commutation margin angle is presented. The firing delay angle to a given effective margin angle is calculated by using the obtained equations, which can be applied to the constant extinction angle control. Next, this paper assesses the ac voltage stability of an AC/DC link, when constant extinction angle control is applied to the inverter of CCC. The calculated Voltage Stability Factor (VSF) shows that the commutation capacitor improves the ac voltage stability of the constant extinction angle control at the inverter linked to an weak ac system, but it differs by the rectifier operation mode and compensation factor of the commutation capacitor.

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Three kinds of operation methods are proposed for a solar / electric power hybrid hot-water system. The operation method A is a conventional operation in which the storage tank is heated with the night-only electricity without forecasting insolation of a next day. In the operation method B, solar energy of the next day is forecasted, and if the energy is not enough for next day hot-water load, the storage tank is heated with the night-only electricity. In the operation method C, insolations until a few days later are forecasted. FIrst, assuming that the insolation forecast has no error, the simulation is conducted using hourly data of insolation and air temperature in Shizuoka city, 1996. The result shows that the electricity charge reduces to 64% in the operation method B and to 55% in the operation method C, compared with in the operation method A, and the insolation forecast is enough for until 2 days later. Next, assuming that the insolation forecast has some error, the simulation is conducted under the operation method B and C, and the electricity charge is calculated as a function of the error ratio (10_??_50%). The result shows that the electricity charge in the operation method C reduces to 71% compared with the operation method A, even if the error ratio is 50%.

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Three-dimensional imaging of lightning channels by means of UHF interferometers is performed. To realize this, a field campaign was conducted with two observation sites in Darwin Australia. The distance between two sites is about 14km, and the triangulation scheme is applied to estimate locations of UHF radiation sources. Since the UHF radiation during the leader progression is more expected than the return stroke phase, imaging of lightning channels is obtained mainly for the downward leaders. Velocities of downward leaders are estimated and statistics are shown for first and subsequent strokes. The result is consistent with those of former investigators obtained by optical observations. The statistics for the velocity of leader propagation inside thunderclouds is shown in this paper. By using optical measurement, velocity estimation of leader progressions inside thundercloud is impossible, and presented results is concluded to be the first results.

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We measured an electric field in transformer oil/pressboard composite insulation system under dc voltage application using Kerr electro-optic measurement system. When a pressboard was inserted between two parallel-plane electrodes, the electric field between the pressboard and the cathode decreased monotonously with time. On the other hand, the electric field between the pressboard and the anode increased with time, reached a maximum value and then fell down.
In this paper, we measured an electric field in transformer oil/pressboard composite insulation system at different time of dc polarity reversal. Firstly, we studied a peak Value of electric field at anode side. Max. 2.4 times higher electric field appeared under dc polarity reversal condition. Secondly, we discussed this phenomenon by charge accumulation and potential distribution model considering the difference in charge accumulation rate on the pressboard surface between positive and negative charges. Finally, we estimated the velocity of the charge accumulation rate using numerical simulation model.

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Nuclear fusion is expected as a main energy source in the future. D-³He nuclear fusion has some better characteristics such as low neutron emission and capability of direct energy conversion than D-T or D-D nuclear fusion. The present paper studies effects of secondary electrons produced at grids of TWDEC by the high-energy protons. It is found that the loss caused by the acceleration of electrons is about 1% of the input kinetic energy of protons, and effects of the electrical charge and the radiation are small. Therefore, all the effects are much smaller than the input power of protons.

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A fault current limiter (FCL) is extensively needed to suppress fault current, particularly required for trunk power systems heavily connected high-voltage transmission lines, such as 500 kV class power system which constitutes the nucleus of the electric power system.
In this paper, we have proposed a new FCL system, consisting of solid-state diodes, DC coil and bypass AC coil, and described the specification of trunk electric power system and 6.6 kV reduction model.
Also we have proposed a 6.6 kV trial model and carried out an efficiency test with a short circuit generator, which we have trial produced of the new FCL system.

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An experimental study on performance of a disk MHD generator was carried out using a shock-tube driven facility. Effects of nozzle load resistance and stagnation gas pressure on the enthalpy extraction, the total pressure ratio and the adiabatic efficiency were investigated for the disk MHD generator with a small area ratio. The enthalpy extraction and the adiabatic efficiency were found to be affected by the nozzle load resistance. The result has suggested that the nozzle load resistance should be kept high for high performances of the disk MHD generator with the small area ratio. Furthermore, an increase of stagnation pressure resulted in a slight increase of enthalpy extraction. However, the increase of stagnation pressure led to a remarkable increase of adiabatic efficiency. The increase of the adiabatic efficiency was due to an increase of total pressure ratio. Effects of the electrical efficiency, the Mach number and loss parameters for heat and friction on the total pressure ratio were discussed. The discussion has suggested that the increase of total pressure ratio is ascribed to a relative decrease of pressure loss due to wall friction. In addition, the highest adiabatic efficiency for cesium seeded argon was achieved in the present experiment without an introduction of inlet swirl.

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A novel non-destructive diagnosis for medium-sized power transformers have been developed measuring a reflective absorbance of the insulating paper. Generally, the insulating paper gradually turns darker in color during long term use. This coloring is caused by the thermal oxidation of the paper. In this paper, the relationship between the average degree of polymerization of the insulating paper and the reflective absorbance is derived from the accelerated heating experiments using model materials. The values of reflective absorbance at different wavelengths, 600 nm and 800 nm, are used as a diagnostic parameter. The average degree of polymerization is one of the most important parameter to evaluate the life of transformers. We found that the reflective absorbance correlates with the average degree of polymerization of the insulating paper, the correlation coefficient being over 0.70. In this diagnosis, the degree of deterioration of the insulating paper can be calculated quantitatively using the diagnostic master curve, which is obtained from accelerated heating experiments. Using the master curve, the residual lifetime of the insulating paper until breakdown can be estimated theoretically. Therefore, this optical technique is theoretically applicable to residual lifetime diagnosis of power transformers.

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A new type of electric field meter has been proposed to measure the electric field on the earth. The field meter utilizes the charge up phenomena of water drops in the electric field. The system is simple, highly reliable, low cost, and will not strongly be affected by rain or snowfall. The dependence of the charge of the water drops on the electric field was evaluated and we see the linearity between them. In addition, dependences are evaluated of the charge on the flow rate of the water and on the horizontal electric field, and we have confirmed that the system is applicable as a electric field meter. By using the system the electric field on the earth was successfully evaluated, the result of which were confirmed to have a good correspondence with those measured by a field mill.

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There are four types of fuel cells such as Polymer Electrolyte Fuel Cells (PEFC), Phosphoric Acid Fuel Cells (PAFC), Molten Carbonate Fuel Cells (MCFC), and Solid Oxide Fuel Cells (SOFC). Performances of these fuel cells have been not compared. Equations which are able to express accurately performances of these fuel cells were derived or modified from the latest published performance data. Cell voltages of the four fuel cells were estimated by these equations, resulting that high temperature fuel cells such as MCFC and SOFC have higher energy conversion efficiencies than low temperature fuel cells such as PEFC and PAFC. This difference is originated from low cathode polarization overcoming both decrease of open circuit voltage with increasing temperature and higher Nernst losses for high temperature fuel cells of approximately 85 mV than those for low temperature fuel cells due to steam generation in the anode chamber in the high temperature fuel cells. Moreover, generalized relationship between cell voltage and operating temperature was derived and giving that cell voltage is almost constant from 500°C to 1100°C. A fuel cell which has proton as migration specie in electrolyte and works from 250°C to 500°C, would give a performance comparable with high temperature fuel cells due to lower Nernst loss than those for high temperature fuel cells.

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Lightning-induced voltage is one of the important factors in the insulation design of a power distribution line. A method of analysis of the lightning-induced voltage has been presented where the voltage is calculated in the frequency domain in order to take account of frequency-dependent characteristics in relation to finite ground conductivity. In this paper, this method is modified to take account of non-linear characteristics of a surge arrester, and the accuracy of calculated results by the proposed method is discussed.

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Lightning-Induced voltage is an important factor for the insulation design of a power distribution line. In this paper, a method is presented for analysis of lightning-induced voltage taking account of finite ground conductivty by using EIvTTP. In the method, Rusck's model is adopted as a field-to-line coupling model, and the influence of ground conductivity on induced voltage waveforms is taken into account through that on inducing sources in Rusck's original model and that on impedance of ground-return circuit. The validity of voltage waveforms calculated by this method is ensured by comparison with experimental results obtained by using reduced-scale models, irrespective of ground conductivity. Furthermore, voltage waveforms calculated by this method are also compared with those calculated by the method where Agrawal's field-to-line coupling model is adopted.

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It has been reported by many papers that the occurrence and the phase of partial discharge depend on sources of the discharge in GIS. In this letter, the difference of the phases among three kinds of sources is well explained and agrees with the result of an EMTP simulation, by introducing an extended Whitehead model analogized on a basis of the experiments.

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The voltage stability index based on load equilibration force is proposed in (1). The calculation algorithm of the index is described in the body part of the paper. That is based upon the load flow calculation. Its advantage is the utilization of commonly used calculation. Another algorithm the paper introduces is the linear equations method described in the appendix. This letter reports comparison study results of above two algorithms and says that the latter algorithm is superior in theory and practice.

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