In order to experimentally clarify the spark discharge that occurs when a grounded object moves toward a stationary charged object, spark length and the induced voltage in a magnetic probe that was 20 cm away from the spark discharge generation point were measured when a grounded metal sphere moved toward a stationary metal sphere whose charge potential was +10 kV. The moving speed of the grounded metal sphere ranged from 0.1 cm/s to 10 cm/s in this study. The experimental results showed that the average spark length decreased with an increase in the moving speed of the grounded metal sphere. On the other hand, the average value of the first peak of the induced voltage in the magnetic probe increased with an increase in the moving speed of the grounded metal sphere. The amplitudes in the amplitude spectra of the first peak of the induced voltage in the magnetic probe increased when the moving speed of the grounded metal sphere increased from 0.1 cm/s to 10 cm/s. The relation between the spark length and the induced voltage in the magnetic probe can be explained qualitatively by using an equation derived from the spark resistance formula proposed by Rompe and Weizel.

View full abstract

We discussed atmospheric DC corona microdischarge with the strong directionality using a miniature gas flow and a plate electrode having a circular opening with a diameter of 6 mm. The hollow electrode functioned as not only a grounded electrode but also a control one. The length and the repetitive current frequency of corona discharges changed when the position and the electric potential of the hollow electrode changed.

View full abstract

We have proposed and preproducted the voltage-current waveform sensor of resin molded type for measuring the power factor and harmonics in power distribution systems. We have executed numerical electromagnetic analyses using the finite element method to estimate the characteristics and behaviours of the sensor. Although the magnetic field analyses for the current sensor have involved the measurement circuit, the electric field analyses have not included the measurement circuit for measuring voltage waveforms of power lines. In this paper, we describe the electric field analyses with the measurement circuit and prove the insulating strength of the proposed sensor permissible to the use in 22kV power distribution systems.

View full abstract

A numerical method, which is newly developed here, is used in order to calculate internal body resistances in a voxelized biological model. By using this method, the internal resistances of an anatomical human model were calculated for the two current paths: 1400 Ω for a hand to foot, and 1500 Ω for a hand to hand. They are compared with experimental ones (500 ∼ 600 Ω for the hand to foot and 500 ∼ 700 Ω for the hand to hand), resulting in the conclusion that the numerical values of the internal resistance are twice or three times higher than the experimental ones. While there is the discrepancy between the calculated and measured results in the absolute values, the profiles of their relative values along the current paths showed good agreement. This implies that the factors such as the anisotropy of muscle conductivity and the difference between in vivo and in vitro conductivities need to be considered. In fact, in consideration of those factors, the calculated results approached the experimental ones.

View full abstract

A new dielectric relaxation measurement technique for analyses of polymer surface was developed. In this technique, in order to maintain the original surface, probing electrodes were placed away from the sample, and a liquid to stabilize the surface was filled in the space between the sample and the electrodes. From difference of dielectric relaxation between a bare polyimide and gold-coated polyimide, the surface of polyimide was characterized. The surface dielectric relaxation spectrum at room temperature depended on the liquid species: The Debye relaxation was obtained for ethanol, while multiple-relaxation was observed for ultrapure water. A thermal activation process of the polyimide surface was investigated using temperature-controlled ultrapure water, and it was found that the surface transited from the multiple-relaxation to the Debye relaxation at ∼95°C. In the Debye relaxation condition, the surface can be characterized with a capacitance independent of the liquid species. The capacitance estimated at 110 pF provided a characteristic curve of the polyimide surface. A surface model was proposed to explain the thermal activation process.

View full abstract

Collection of low resistive particulate matter (PM) generated from automobile and marine diesel engines or diesel generators have been known to be difficult by the conventional electrostatic precipitators (ESP). The collection efficiency for two types ESPs such as conventional DC energized ESP (DC ESP) and rectangular-AC-waveform energized ESP (AC ESP) were investigated. The low resistive PMs agglomerate like a pearl-chain on the collection plate in DC ESP, so that these are detached from the collection plate by electrostatic repulsion force and wind force. The pearl-chain particles are changed the shape, which is such a spherical, by AC ESP. Therefore, the particle re-entrainment is suppressed by AC ESP.

View full abstract

A generation and reduction of NOx on air-fed ozonizers using a ferroelectric packed bed reactor have been experimentally investigated. The reactors packed with CaTiO₃, SrTiO₃ and BaTiO₃ pellets are examined for ozone generation. An ac voltage is applied to the reactor to generate partial discharge. Ozone concentration and the different nitrogen oxides at downstream of the packed bed reactor were measured with UV absorption ozone monitor and a Fourier transform infrared spectroscope respectively. The dielectric constant of packed ferroelectric pellets influences the discharge characteristic, ozone and NOx generations are varied by the dielectric constant value. Focusing on a discharge pulse current and maximum discharge magnitude, the ferroelectric packed bed plasma reactors have been evaluated on nitrogen oxide and ozone generated concentrations.

View full abstract

AC atmospheric pressure multi-filament dielectric barrier discharge in oxygen has been simulated using two dimensional fluid model. In the discharge, three kinds of streamers have been obtained. They are primary streamers, small scale streamers and secondary streamers. The primary streamers are main streamers in the discharge and the small scale streamers are formed after the ceasing of the primary streamers. And the secondary streamers are formed on the trace of the primary streamers. In these streamers, the primary and the small scale streamers are very effective to generate O(³P) oxygen atoms which are precursor of ozone. And the ozone is generated mainly in the vicinity of the dielectrics. In high gas temperature region, ozone generation decreases in general. However, increase of the O(³P) oxygen atom density in high gas temperature region compensates decrease of ozone generation rate coefficient. As a result, amount of ozone generation has not changed. But if the effect of gas temperature was neglected, amount of ozone generation increases 10%.

View full abstract

With the goal of fabricating low-breakdown-voltage (varistor voltage) varistors, the effect of adding Ba to Bi-Co-Mn-added ZnO varistors on the ZnO grain size was investigated. In order to make the grain size of a ZnO uniform, calcined additives were mixed with ZnO powder to form the uniform liquid phase of Ba and Bi considering that grain growth of ZnO could be markedly promoted by adding both Ba and Bi. Furthermore, in order to make the grain size of a ZnO uniform without making small the grain size, small amount of Sb as an additive was added. ZnO grain size became large and both the nonlinearity index of voltage-current characteristics and varistor voltage increased with increasing calcination temperature of additives. However, the improvement of the tolerance characteristics to the electrical degradation was not found. Addition of small amount of Sb such as 0.01 mol% is effective in suppressing the deviation of the grain size of ZnO without making small the grain size and improved the tolerance characteristics to the electrical degradation, because the compound of Ba and Mn was not formed.

View full abstract

The effects of amount of Sb added to Bi-Mn-Co-Sb-Si-Cr-Ni-Zr-added ZnO varistors on the tolerance characteristics of electrical degradation were investigated. Furthermore, the effects of addition of both Zr and Y to Bi-Mn-Co-Sb-Si-Cr-Ni-added ZnO varistors (the same composition as one of commercial varistors) on the varistor voltage and leakage current were investigated. It was found that addition of Sb enhances the tolerance characteristics to the electrical degradation and the amount of Sb₂O₃ addition of approximately 1 mol% is the optimal. When the amount of added Sb increased, the amount of existence of a Zn_2.33Sb_0.67O₄-type spinel particle increased, because the amount of existence of Zr compound increased similarly. It was suggested that Zr compound was also related to the electrical degradation characteristic. Varistor voltage decreases a little when the amount of added Zr increases in simultaneous addition of Zr and Y. On the other hand, the value of nonlinear index α hardly changed. Without Zr, the increase in the leakage current accompanying the increase in the amount of added Y, which has been reported conventionally, was not found in this study. However, adding Zr of approximately 0.2 - 0.45 mol%, the leakage current increased by adding Y more than 1 mol% and adding Zr of approximately 0.6 mol%, it decreased.

View full abstract