Airplane companies have required the improvement of fuel efficiency because of steep rise in oil prices; a lot of new technologies have been utilized for latest airplanes. Lately, composites such as CFRP (Carbon Fiber Reinforced Plastic) have been used as structural materials; lightness and long utilization of airplanes have been realized. An airplane often has lightning strikes when going through between thundercloud and the earth. With the utilization of CFRP instead of other metal materials such as aluminum, new lightning protection technologies have made remarkable progress. In this paper, specially, researches about lightning current distribution on CFRP structures, suppression methods of discharge around a fastener and damage mechanism of a lightning strike point have been discussed.
The propagation of lightning current underground was investigated by the remanent magnetization of materials. The study was conducted around a tower struck by lightning. (1) The remanent magnetization of the mortar layer of a transmission tower in the city of Hakusan, Ishikawa Prefecture, was studied. The distribution of magnetization showed a clockwise circular direction, indicating that a magnetic field was induced by the positive lightning current. The magnetic intensity of the mortar layer varied between the areas surrounding each of the four iron tower feet, which indicates that the shunting of the lightning current to the tower is anisotropic. (2) The behaviors of lightning current in the counterpoise and electrode were investigated through a rocket-triggered lightning experiment. The samples near the counterpoise placed at 1.3m from the tower foot had two magnetic components of different polarities, whereas the samples at 8.8m had only one component. This implies that the lightning currents of both polarities propagated in the counterpoise up to a distance of 1.8m; however, only the positive lightning current reached the electrode at a distance of 8.8m from the tower foot. The method using remanent magnetization is found to be effective for investigating the propagation of current after a lightning strike.
Recently, renewable energy have been attracting attention from the global warming and the depletion of fossil fuel. The photovoltaic (PV) systems spread rapidly in the world because the PV systems generate electric power quietly and they can be installed in many places. The output power generated in the PV system fluctuates according to the changes in solar irradiance and panel temperature. The reverse flow of steep surplus power may have bad influences on electric power quality such as a frequency and a voltage in the power system. A residential distributed generation (DG) system composed of the fuel cell (FC) unit, the electrolyzer (EL) unit and the PV system has been proposed for solving these problems. In order to operate this system without interruption, the hydrogen storage volume needs to be managed. This paper proposes a novel hydrogen management method in the residential DG system with the PV cells and the hydrogen-storage type FC's. The hydrogen storage volume is managed to be the preset reference by operating the FC unit and the EL unit. The models of PV, FC and EL are constructed in the simulation. It is clarified by the simulation that the proposed management method is available for the residential DG systems with the PV cells and the hydrogen-storage type FC's.
The authors conduct a two-dimensional (r-z) MHD numerical simulation for examining the influence of asymmetric placement of radio-frequency (rf) induction coil on the generator performance of a commercial scale, large nonequilibrium disk-shaped MHD generator with an rf preionization technique. The MHD numerical simulation is carried out under two different placement conditions of rf induction coil: one is that an rf induction coil is placed on only one side disk wall and the other is that it is symmetrically placed on each of both disk walls. Numerical results show the performance of MHD generator with one-sided rf induction coil placement inducing an asymmetric rf electromagnetic (EM) field is comparable to that of the MHD generator with both-sided rf indction coil placement inducing a symmetric rf EM field, although the one-sided induction rf coil placement causes an asymmetric distribution in the z-direction of plasma properties such as electron temperature and ionization degree near the rf induction coil.
An experimental investigation was performed on a UHV gantry tower model for the EMTP calculation of lightning overvoltage at substation. The various lightning surge response characteristics were measured on a 1/10 scale UHV gantry tower. We present the comparison between measured and calculated voltage waveforms at various point of gantry tower. It showed that measured waveforms were not reproduced in the conventional EMTP model. It was estimated that it did not take horizontal element into consideration. Since then, the model was improved in new model, which had a horizontal element. Measured waveforms were reproduced by the improved EMTP model. Surge impedance of the improved model is as the next. Vertical element is 220-ohm, horizontal element is 140-ohm.
As many wind farms have been installed in power systems in the world, frequency fluctuations due to output power variations have become a serious problem. Various countermeasures for the problem such as battery systems have been investigated. It is very important to evaluate the magnitude of frequency fluctuation for designing compensating systems. This letter presents a simple method to evaluate expected value of the frequency deviation due to variations of wind farm output.
The insulation strength of a vacuum interrupter is investigated before and after dozens of large current interruptions. The breakdown voltage decreases from 119.5kV to 103.2kV by the current interruption test.