The engineering design of ITER was completed, based on the world-wide physics and engineering R & D's conducted in the 9 years international joint work. ITER has the main scientific missions such as; to achieve inductively driven or non-inductively sustained burning plasmas at a sufficiently high energy multiplication factor Q≥5_??_10; to integrate fusion technology; and to test the fusion nuclear components such as blankets. An acceleration plan of fusion energy development is investigated on the basis of the ITER program. The key subjects of future fusion development are the steady state sustainment of high beta plasmas, material development, and demonstration of electricity generation and tritium breeding blankets.
This study provides the theoretical basis for the use of wavelet packet transform (WPT) approach for root mean square (rms) and power/energy measurements. The proposed approach can simultaneously measure the distribution of the rms and power with respect to individual frequency bands directly from the wavelet transform coefficients (WTCs) associated with concurrent voltage current pair. Their dependent quantities such as power factor and total harmonic band distortion can be calculated as well. Uniform frequency bands are yielded from the WPT decomposition process of power system waveforms and can be used for identification of harmonic components. The frequency bands also retain both the time and frequency relationship of the original waveforms, which is one of the major benefits provided by this approach. The approach is evaluated by its application to both analytical and actual power system waveforms.
Electric double-layer capacitors showing a remarkably high energy density (compared with conventional electrolytic capacitors) are now under development. Capacitors of this type have significant advantage; namely high durability against repeated charge and discharge and no need for maintenance. Therefore we have studied feasible basic circuit configurations and control methods required to apply electric double-layer capacitors as an energy storage element in output-power leveling systems for solar cells or windmill power generators, and in uninterruptible power supply systems. This paper discussed on operating methods for a capacitor bank to improve the efficiency. High efficiency has been obtained resulting from the simulations and the experiments.
Demand for electrical energy has been increasing by the time as related to both technological developments and increase in population. It is necessary to enhance the quality of the electrical energy, especially supplied one. With considering voltage stability of power system, which includes nonlinear loads, during the planning, operating, and controlling of electrical power systems, more reliable and high quality energy is supplied. In this study, the effects of harmonic components on voltage stability, caused by nonlinear elements, have been demonstrated by a synthesis of harmonic power flow analysis and voltage stability one based on Newton-Raphson method. Harmonic modeling for power system and the models obtained from mathematical equations belonging to the steady-state voltage stability have been used together to realize this synthesis. Accordingly, the effects of non-sinusoidal quantities on the voltage stability, neglected so far, are considered and then the analysis is performed under this condition. Thus, the more realistic results were obtained by the harmonic power flow based upon the voltage stability analysis.
The field utilization factor η (the mean electric field/the maximum electric field) of the standard sphere gaps was calculated by the charge simulation method, taking into account the ground plane and shanks. Sparkover voltages were also calculated by integration of ionization index, except the sparkover for positive impulse. η and the sparkover voltage may change by the length and the diameter of shanks in the range permitted by the IEC standard 60052. Generally, the rate of the change of sparkover voltage is not larger than the one of η, because the sparkover voltage is averaged by integration of ionization index on the center axis between the sphere electrodes. In the range where the gap length is near the sphere radius, the change rate of η and the sparkover voltage is almost same. The reason is that the streamer criterion is satisfied near the crest point of the upper sphere electrode.
The electromagnetic waves emitted from partial discharge (PD) due to material defects in high-voltage electric power apparatus and facilities are broadband signals including VHF, UHF (Very High Frequency, Ultra High Frequency). A VHF-UHF radio interferometer system (VURIS) for locating PD source has been originally designed, constructed and tested. The system is based on the idea extracting the phase differences at different frequencies between a pair of the received signals by the Fourier transform and computing the direction of the electromagnetic waves emitted from PD source. It can be small-sized, more suitable for compact and portable system, because UHF half-wavelength dipole antennas are used to receive the electromagnetic waves and the baseline between the antennas is very short. And it requires fewer antennas to achieve equivalent angular resolution than a narrow band interferometer system, which requires multiple baselines corresponding to a few times of half-wavelength of the observation frequency. Therefore, it's able to reduce the operating time at the measurement site because it's not needed to arrange many antennas at the many points. The indoor test results indicate that the system is able to estimate the arrival angle of the electromagnetic waves emitted from PD source.
High-voltage Schottky barrier diodes (SBDs) are fabricated on 4H-SiC epitaxial layers obtained at a high growth rate (14_??_16μm/h). The epitaxial layers are grown in a vertical radiant-heating reactor, with pre-growth and growth conditions controlled to reduce morphological defects. A good morphology with a low density of growth pits is achieved by applying to substrates pre-growth hydrogen etching under reduced pressure down to 4000Pa. Two types of edge termination structures, B-implanted termination and junction termination extension (JTE), were tested for use in fabricating high-voltage 4H-SiC SBDs. A high blocking voltage of 1.2kV was achieved when using a 10μm-thick layer by applying B-implanted termination, despite the layer being grown in only 40 minutes. When using 27pm-thick epitaxial layers, a 2.4kV-9.1 mΩcm2 SBD with B-implanted termination and 3.4kV-16.0 mΩcm2 SBD with JTE were successfully fabricated. We also succeeded in obtaining a 4 mmφ diode with an allowable leakage current, and a high yield rate exceeding 90% for the 1 mmφ diodes.
A new fossil-fuel-utilized high-performance combined power generation system with liquefaction recovery of carbon dioxide is proposed. In the system, pure oxygen is used as the oxidant gas to prevent the mixture of nitrogen in the exhaust gas and to make the liquefaction recovery of carbon dioxide possible. Solid oxide fuel cell is selected as the topping cycle. The exhaust fuel gas of the solid oxide fuel cell is afterburned with its exhaust oxidant gas of pure oxygen and the heat of the combustion gas is utilized in the bottoming cycle. Nonequilibrium MHD/noble gas turbine cycle is selected as the bottoming cycle because the temperature of the combustion gas reaches about 2300 K. It is made clear through detailed examination of energy balance that the total thermal efficiency of the system using natural gas (methane) as the fuel reaches 63.24% (HHV) or 70.18% (LHV). This efficiency is very high as for the system with carbon dioxide recovery. The proposed system, therefore, has excellent performance and is worth carrying out further research and development.
To improve GIS insulation specifications, it is important to recognize the insulation characteristics under oscillatoryovervoltage waveforms occurring in the field. This paper describes investigations of insulation characteristics for single-frequency oscillatory waveforms with various frequencies and damping ratios. As a result, it was obtained that minimum breakdown voltages (Vmin) rose with frequency rising under same damping condition and Vmin rose with damping ratio rising under same frequency condition. From an analysis of actual breakdown voltage characteristics, a probability of breakdown at a valley of oscillation rose with damping increasing. It was found that the insulation characteristics were treated all-inclusively based on the characteristics of Vmin for rising time or damping time.
For the rationalization of insulation design of 11.4kV distribution line that consists of existing 6.6kV equipment in use, we had calculated transient overvoltages by EMTP. We investigated the references on the conditions of existing 6.6kV distribution lines, and selected some typical models for calculation. As a result of the parameter analysis by the typical model, we recognized the system condition of the distribution line that caused the largest transient overvoltage. The largest transient overvoltage occurred in the case of reclosing surge. In the case of the reclosing surge, the maximum per unit value of the transient overvoltage became 3.81pu. The maximum voltage is heavily affected by the closing phase and the neutral resistance. Moreover, from the result of calculations considering the effect of surge arrester attached to the current transformer, we found that the overvoltage was reduced to 3.3pu. According to the above result, the conventional test voltage for 11.4kV distribution equipment could be reduced by approximately 30%.
To increase the transmission capacity of 6.6kV distribution lines economically, 11.4kV distribution system that is constructed of existing 6.6kV equipment in use is being examined. For the application of the 11.4kV distribution system to the real field, we are trying to calculate transient over voltage by EMTP to decide the rational test voltage of 11.4kV equipment. So, to confirm the calculation precision of EMTP concerned with transient over voltage in 11.4kV distribution line, we had made an experiment measuring the characteristics of over voltages, which occur in 11.4kV distribution lines. We compared the calculated waveform with the measured waveform, and investigated the difference of the two. About some test data we compared the calculated waveform by EMTP with the measured waveform, and we found that the range of computing errors were from 1.8% to 10.8%.
This paper describes the result of measurement of residual dc charge decay in a 500kV transmission line, when the line is separated from power sources or other equipment by a circuit breaker. The measurement aims at obtaining data for calculating closing surges of circuit breaker, and appreciating the value and duration of dc voltage that affects the ac GIs insulation performances including inter-pole insulation of the circuit breaker. Since the measurement was performed in fine and dry days of winter season, the measured time constants are considered to be the largest among those of whole seasons. The measured decay curves indicate two parts; the rapid decrease part appears in the beginning stage of the phenomena and the following slowly decrease part. The time constant of the residual charge decay, which is defined as the time until the residual voltage decreases to l/e of the initial value, shows large scattering, but there appears clear polarity difference. Positive polarity gives 56-387 sec. from 38 measurements, and the average is 211 sec. Negative polarity gives 26-301 sec. from 24 measurements, and the average is 98sec.
A novel brushless variable-speed induction generator system is proposed for small-scale hydroelectricity. The stator of the second induction generator has six-phase windings connected with a twelve-pulse rectifier system to reduce adverse effects of lower-harmonic currents. The simulation results show that the first induction generator can produce nearly sinusoidal currents.