Search

An extremely large amount of volcanic gas has been released since mid-August 2000 from the volcanic island of Miyakejima, Japan, after formation of a summit caldera of 1.6 km diameter. The volcanic gas emission was continuous with very little extrusive magma activity. Variation of the S[O.sub.2] emission rate was monitored by repeated measurements with an airborne correlation spectrometer. In December 2000, the S[O.sub.2] emission rate averaged for the month peaked at 54 kt/d, which is twice the global S[O.sub.2] emission rate from nonerupting volcanoes evaluated before this activity. The S[O.sub.2] emission rate gradually decreased, almost linearly when plotted on a log scale, to 7 kt/d by the end of 2002, and then remained constant until at least December 2003. The total S[O.sub.2] emission amounts to 18 Mt, comparable to the emission of a large explosive eruption such as Pinatubo in 1991. A theoretical evaluation, based on the model of magma convection in a conduit, suggests that extremely large volcanic gas emissions can be caused by formation of a magma pathway with a slightly larger diameter than exists in common systems, because the magma-transport rate is proportional to the fourth power of the conduit radius. Because volcanic gas emissions were initiated by formation of a summit collapse caldera of 1.6 km diameter, the creation of a large magma-conduit system through fractures formed during caldera collapse is likely the underlying cause of the extremely large volcanic gas emissions from the volcano. Keywords: S[O.sub.2] flux, volcano, degassing process, magma convection, conduit.

Technologies for the after-laying test of a long-distance gas insulated transmission line (GLL) have been developed for the detection of partial discharge (PD) and contact defects. We constructed long (168 m) test line in a deep tunnel and clarified the propagation characteristics of PD signals through the GIL as well as the spatial sensitivity and S/N characteristics of PD sensors for locating metallic particles. We have also proposed the application of a fiber-optic temperature distribution sensor for locating contact defects and confirmed the validity of this sensor for the GlL test line. Keywords - Gas insulated transmission line, GIL, In-tunnel, After-laying test, Partial discharge, Metallic particle, Metallic foil electrode, External antenna, Contact defects, Fiber-optic temperature distribution sensor

This study provides comparisons of aerosol representation methods incorporated into a regional-scale nonhydrostatic meteorology–chemistry model (NHM-Chem). Three options for aerosol representations are currently available: the five-category non-equilibrium (Aitken, soot-free accumulation, soot-containing accumulation, dust, and sea salt), three-category non-equilibrium (Aitken, accumulation, and coarse), and bulk equilibrium (submicron, dust, and sea salt) methods. The three-category method is widely used in three-dimensional air quality models. The five-category method, the standard method of NHM-Chem, is an extensional development of the three-category method and provides improved predictions of variables relating to aerosol–cloud–radiation interaction processes by implementing separate treatments of light absorber and ice nuclei particles, namely, soot and dust, from the accumulation- and coarse-mode categories (implementation of aerosol feedback processes to NHM-Chem is still ongoing, though). The bulk equilibrium method was developed for operational air quality forecasting with simple aerosol dynamics representations. The total CPU times of the five-category and three-category methods were 91 % and 44 % greater than that of the bulk method, respectively. The bulk equilibrium method was shown to be eligible for operational forecast purposes, namely, the surface mass concentrations of air pollutants such as O3 , mineral dust, and PM2.5. The simulated surface concentrations and depositions of bulk chemical species of the three-category method were not significantly different from those of the five-category method. However, the internal mixture assumption of soot/soot-free and dust/sea salt particles in the three-category method resulted in significant differences in the size distribution and hygroscopicity of the particles. The unrealistic dust/sea salt complete mixture of the three-category method induced significant errors in the prediction of the mineral dust-containing cloud condensation nuclei (CCN), which alters heterogeneous ice nucleation in cold rain processes. The overestimation of soot hygroscopicity by the three-category method induced errors in the BC-containing CCN, BC deposition, and light-absorbing aerosol optical thickness (AAOT). Nevertheless, the difference in AAOT was less pronounced with the three-category method because the overestimation of the absorption enhancement was compensated by the overestimation of hygroscopic growth and the consequent loss due to in-cloud scavenging. In terms of total properties, such as aerosol optical thickness (AOT) and CCN, the results of the three-category method were acceptable. [ABSTRACT FROM AUTHOR]

Generally, insulating spacers of gas insulated switchgear (GIS) have outstanding durability and are not considered prone to insulation failure within a design life of about 30 years, provided the products conform and have passed the partial discharge (PD) test. However, to assume operation over 30 years, degradation characteristics are important in cases where an extremely microscopic defect below the detection level in the PD test is present or produced inside the insulator. Accordingly, to date, the authors have obtained the breakdown voltagetime (V-t) characteristics using epoxy insulators provided with three types of micro-defect (crack, void, and delamination); the apparent PD of which is equivalent to 1 pC for an actual 550 kV-GIS spacer. It emerged based on these V-t characteristics that the breakdown risk peaked for a crack defect among those three types of shape and that it was essential to obtain data on long-term breakdown characteristics at the actual operating electric field level to rigorously evaluate the breakdown risk under long-term operation. Therefore, this paper includes a study on the equivalence of accelerated degradation by frequency acceleration as a means of determining the long-term breakdown characteristics. In the study, the dependency of various PD characteristics on frequency was initially examined by changing the frequency of the applied voltage within the range 60 to 3000 Hz. Consequently, the increase in the number of PDs per unit time proportional to frequency could be confirmed without any abnormal phenomena, such as suspended discharge, observed within the frequency range this time. In other words, it was clarified that the degradation due to PD could be accelerated by increasing the frequency. Subsequently, breakdown tests were conducted with frequency as a parameter to evaluate the frequency up to which the equivalence of accelerated degradation could be maintained based on breakdown times. As a result, it was found that the equivalence of acceleration degradation by frequency acceleration was valid in acceleration at up to 1500 Hz because the breakdown time was shortened in reverse proportion to the frequency. [ABSTRACT FROM AUTHOR]

The degradation characteristic of solid insulators is considered to be one of the key factors to perform a risk assessment of highly aged gas insulated switchgear (GIS). The present study experimentally obtained the insulation characteristics of epoxy insulator mainly with an internal microscopic delamination-shaped defect. In the experiment, a short-time breakdown electric field (EF) was initially obtained and comparison was made with the breakdown EF for the void and crack defects to evaluate the breakdown risk with respect to the defect shape. These defect models (delamination, void, and crack) were designed and produced so that an apparent partial (PD) might be 1 pC in an actual 550 kV-GIS spacer. Consequently, it emerged that the area where the EF was concentrated influenced the breakdown. Of the three types of defect, the degree of EF concentration was the lowest for delamination defects, meaning the lowest breakdown risk for the same. Subsequently, the V-t characteristics were obtained through an EF acceleration test. The V-t characteristics obtained were extrapolated to estimate the breakdown risk in 30 to 50 years operation, which is considered the design life of GIS. As a result, it was determined that the potential for eventual breakdown was extremely low under the normal operating EF, even if a delamination defect equivalent to an apparent PD of 1 pC was present in an actual 550 kV-GIS spacer. Hence, controlling a defect using 1 pC for actual GIS is considered to ensure reliability under long-term operation. [ABSTRACT FROM AUTHOR]

Presently, an increasing number of gas insulated switchgear (GIS) has been operated for longer than 30 years, which is generally considered their service life. The degradation in solid insulators is considered to be one of the key factors determining the service life of such highly aged GIS in terms of insulation. Under normal circumstances, GIS insulators have outstanding electrical performance and insulation failure is considered unlikely within the design life of 30 years or so, provided the units conform and have passed the partial discharge (PD) test. However, assuming operation beyond 30 years, the insulation characteristics must be clarified in case ultra-microscopic defects undetectable via the PD test are present inside insulators. Accordingly, in the preceding study, micro-defect models in three types of shape (void, crack, and delamination) with an apparent PD of 1 pC in an actual 550 kV-GIS spacer, were designed and produced. Of those three, the present study covered void-shaped defects and obtained breakdown voltage-time (V-t) characteristics through an electric field (EF) acceleration test. These V-t characteristics were extrapolated to evaluate the breakdown risk in 30 to 50 years operation, which is considered the design life of GIS. As a result, void-shaped defects of about 1 pC were evaluated as highly unlikely to cause any problem according to the 50% value of the V-t characteristics. Given the relatively large dispersion among the breakdown times in the EF acceleration test results, a study was subsequently conducted with this dispersion taken into account. The probability of breakdown within 50 years was evaluated at less than 0.1%, assuming an operating EF of 4 kVrms/mm. Furthermore, when considering the location parameter that does not result in breakdown within a certain period, the probability of breakdown was considered to be much smaller. In fact, since the declining gradient of the V-t characteristics is considered smaller in the long time region, evaluation by extrapolating the V-t characteristics in the present study is considered sufficiently safe. The Vt characteristics obtained have made it possible to evaluate the period to breakdown and the breakdown risk where ultra-microscopic voids are present. [ABSTRACT FROM PUBLISHER]

The degradation characteristic of solid insulators is considered to be one of the key factors to perform a risk assessment of highly aged gas insulated switchgear (GIS). The present study experimentally obtained the breakdown voltage-time (V-t) characteristics of epoxy insulator with an internal microscopic crack-shaped defect. This defect model was designed and produced so that an apparent partial discharge (PD) might be 1 pC in an actual 550 kV-GIS spacer. During the experiment, the change in the PD magnitude over time and the PD waveform were measured to clarify the PD characteristics until breakdown occurred. Consequently, in terms of the change in the PD magnitude over time, it was likely that the lower the applied electric field (EF), the larger the ratio of the time until the PD magnitude drastically increased (tree induction time) to the total time until breakdown occurred. When 6 kVrms/mm, or the lowest EF in the present test, was applied, two distinctively different trends were observed; one where the PD stably continued and breakdown occurred within several to several tens of hours, and the other where the PD was suspended in mid-course and it was longer than 100 hours until breakdown occurred. Subsequently, the breakdown EF under long-term operation was estimated by extrapolating the V-t characteristics, whereupon a risk under long-term operation was recognized when a micro-defect of 1 pC was present in actual GIS; even though such defect was extremely unlikely. According to the observation results of the PD magnitude, however, the tree induction time was longer at a low EF of the operating EF level and the declining gradient of the V-t characteristics was considered lower. For a rigorous evaluation of breakdown risk under long-term operation, therefore, it was considered that evaluation via simple extrapolation of the V-t characteristics by straight line was not sufficient and the insulation characteristics under a low EF must be obtained. [ABSTRACT FROM AUTHOR]

Gas insulated switchgear (GIS) has been widely applied in power equipment since the late 1960s due to its reliability and compactness. Because epoxy insulators in GIS are important insulation components that affect the dielectric withstand level and the equipment lifetime, high voltage tests and sensitive partial discharge (PD) tests have been carried out on them in the factory. If a latent defect occurs inside an actual epoxy insulator, its size is predicted to be small, such as a micro-defect, because it will have passed rigorous tests and multiple inspections at the factory. Although many studies have clarified the fundamental phenomena of deterioration caused by PD occurring due to defects in inner epoxy, little is known about the actual size of such defects and their effect on insulation properties. Therefore, to assess the risks associated with aging GIS equipment, it is essential to understand the actual size of latent defects in inner epoxy insulators of GIS and the impact the defects have on the insulation performance. The puncture properties and PD characteristics of artificial micro-defects of cracks, voids, and delaminations produced using an accurate estimation technique and precise production control were investigated and are described. The results suggest that an estimation method using electric field analysis is useful for designing the defect shape and that the breakdown voltage depends on the three-dimensional shape of the defect. Techniques for accurate estimation of small defects in epoxy resin and stable production of micro-defects have thus been achieved. [ABSTRACT FROM PUBLISHER]

The lightning impulse withstand voltage test waveform for electric power equipment is specified in IEC 60060-1 "High-voltage test techniques" as revised in 2010. At present, test standards for UHV-class equipment are under study. Increasing equipment capacity and the digitization of measuring equipment are mentioned as these backgrounds. Withstand voltage test by the standard waveform specified in the previous standard had been difficult (it eventually becomes an overshoot waveform) with increasing equipment capacitance. In response, an evaluation method using the kfactor function (test voltage function) was introduced, whereby the overshoot waveform was converted to the test voltage waveform. To date, concerning these kfactor values, measurement results based on experiments have been reported, but most were from small-scale insulation models with breakdown voltage levels mainly around 100 kV. The present study reports the experimental results of the insulation breakdown characteristics for the lightning impulse withstand voltage test waveform in the largest SF6 gas insulation model possible assuming actual UHV-class gas insulated switchgear. Breakdown voltage and breakdown time were measured with the superimposed oscillation frequency, overshoot rate, and front time as parameters. Following evaluation of the k-factor value based on these experimental results, the k-factor value with the overshoot rate of 10% was almost identical to that of the existing k-factor function. Consequently, evaluation using the existing k-factor function is considered appropriate. Subsequently, the existing k-factor function is most likely to be effective also for UHV-class equipment. In addition, it emerged that changes in the insulation breakdown characteristics due to the extension of the front time were small. It was considered that extending the front time, rather than allowing an excessive overshoot rate, would enable proper verification of the insulation performance as part of standard assuming UHV-class equipment. [ABSTRACT FROM AUTHOR]

Abstract: The current material design of the International fusion materials irradiation facility (IFMIF) back-plate in Japan consists of an austenitic stainless steel type-316L and a RAF/M steel type-F82H. The 316L and F82H are welded together. The 316L region of the back-plate is also welded to the target assembly made of 316L. The back-plate operates under a severe neutron irradiation condition (50dpa/year). Therefore, it is important to perform metallurgical and mechanical tests for these welds in engineering design of the IFMIF. The F82H/316L weld joint with a filler metal type-Y309 was fabricated using TIG-welding method, followed by PWHT at 1013K for 1h. The 316L/316L weld joint was fabricated using YAG-laser welding method. The F82H/316L TIG-weld was found to be satisfactory. However, although the 316L/316L YAG-weld showed no harmful defect, the hardness was somewhat lower in the weld metal. Rupture occurred in the weld metal, and strength and elongation decreased somewhat. Furthermore, small dimples with several large voids were also visible in the fracture surface. [Copyright &y& Elsevier]

An extremely large amount of volcanic gas has been released since mid-August 2000 from the volcanic island of Miyakejima, Japan, after formation of a summit caldera of 1.6 km diameter. The volcanic gas emission was continuous with very little extrusive magma activity. Variation of the SO2 emission rate was monitored by repeated measurements with an airborne correlation spectrometer. In December 2000, the SO2 emission rate averaged for the month peaked at 54 kt/d, which is twice the global SO2 emission rate from nonerupting volcanoes evaluated before this activity. The SO2 emission rate gradually decreased, almost linearly when plotted on a log scale, to 7 kt/d by the end of 2002, and then remained constant until at least December 2003. The total SO2 emission amounts to 18 Mt, comparable to the emission of a large explosive eruption such as Pinatubo in 1991. A theoretical evaluation, based on the model of magma convection in a conduit, suggests that extremely large volcanic gas emissions can be caused by formation of a magma pathway with a slightly larger diameter than exists in common systems, because the magma-transport rate is proportional to the fourth power of the conduit radius. Because volcanic gas emissions were initiated by formation of a summit collapse caldera of 1.6 km diameter, the creation of a large magma-conduit system through fractures formed during caldera collapse is likely the underlying cause of the extremely large volcanic gas emissions from the volcano. [ABSTRACT FROM AUTHOR]

Changing into slippers when entering the nuclear medicine management district prevented pollution expansion. Accidents involving patients falling occurred in university facilities. It was thought that changing slippers was the cause. The pollution situation was measured in three facilities by using the smear method and the direct technique to examine the effect of changing slippers. The current state was measured. After pollution prevention guidance was continuously done, pollution expansion was measured; three weeks of measurements were compared. Pollution was detected in the first period of weeks at a frequency of 19 times. For the latter period, it was detected 6 times. Half the pollution was in the restroom. Pollution was reduced by doing pollution prevention guidance for the restroom. Patients' falls occur even if they change slippers. Falling accidents can be decreased.