交流電圧印加条件の違いが真空中アルミナ絶縁筒内面の帯電分布に与える影響

In vacuum devices such as vacuum interrupters (VIs), surface flashover events are one of the obstacles for developing their higher performance. It is believed that such a surface flashover in vacuum has a close relationship with a charging phenomenon on the insulator surface. Therefore, it is important to grasp the charging characteristics on the inner surface of the VI. In this study, we have measured the charge distribution characteristics inside a cylindrical type insulator employed as a model insulator of VI after the AC voltage (50 Hz) application. This cylindrical insulator has shield rings to relax the electric field at triple junction at both ends of the insulator. We investigate the charging characteristics for samples having different gaps between the shield and insulator. As a result, in the case of first AC voltage application to each sample, the vacuum side of the cylindrical insulators were charged to a certain value. As repeating the AC voltage application several times, the amount of electric charge on the insulator surface was gradually reduced in each sample. However the reduction rate of the sample with the narrow clearance is larger than wide one. In addition, the sample with the wide clearance was charged on a larger surface area than that of the narrow clearance.

Effect of AC electric fields on the stabilization of premixed bunsen flames

A pulsed electroacoustic method (PEA) system with phase-resolving capability has been developed to measure space charge distribution at any phase angle of applied AC voltage in water-treed polyethylene. By comparing the observed charge distributions with theoretically predicted ones, it has been shown that the interfacial polarization due to the difference in conductivity between the treed and the untreed regions predominates the space charge behavior.

In this paper, the air purification effect of positively and negatively charged ions generated by discharge plasma at atmospheric pressure is reported. We have developed a novel ion generation device which consists of a cylindrical glass tube and attached inner and outer mesh electrodes. With the application of AC voltage between the electrodes, positively charged ions and negatively charged ions have been generated at atmospheric pressure. The ion densities of 3.0×104–7.0×104 counts/cm3 have been obtained with the AC voltage of 1.8–2.3 kV (effective value). We have examined the air purification properties of this device. By the operation of this device, the initial oxygen nitride (NO) density of 10 ppm in 1 m3 (in cigarette smoke) was decreased to 1 ppm after 30 min. The number of suspended germs in air has been significantly reduced by the use of this type of ion generation device.

Microphysiological systems (MPSs) have emerged as promising platforms for drug discovery and in vitro pharmacological testing. MPSs aid to reproduce physiologically relevant microenvironments, in which controlled perfusion can play important role. In this study, an on-chip AC electrothermal (ACET) pump was developed for pulsatile perfusion in microfluidic cell culture systems. The proposed pump generates fluid motion through the interaction between an applied electric field and temperature-dependent gradients in the electrical properties of the fluid. Pulsatile perfusion was produced by periodic application of an AC voltage to the electrode array, and the pulsation cycle could be controlled electrically. The maximum flow velocity increased with the applied AC voltage, demonstrating tunable flow generation by the ACET pump. To evaluate the applicability of the developed system to cell culture, human mesenchymal stem cells (hMSCs) were cultured under pulsatile perfusion conditions for five days. The results showed that osteogenic differentiation under pulsatile perfusion was higher than that under static culture conditions. These findings demonstrate the potential of the proposed on-chip ACET pump as a simple and effective platform for generating physiologically relevant pulsatile perfusion in microphysiological systems.

In the present work, an attempt has been made to obtain stable nanofluids by dispersing an appropriate amount of titania nanoparticles in transformer oil as base oil. The surfactant added in appropriate amount helps in achieving consistent dispersion of the nanoparticles in colloidal solution. A set of experiments were done for understanding the discharge trait because of particle movement in nanofluid and pure transformer oil. It is noted that the particle levitation voltage in nanofluids achieves an increment as compared to base transformer oil. It is realised that partial discharges are generated because of movement of particle in nanofluid which emits UHF signals with 0.9 GHz as major frequency content. The partial discharge trait in nanofluid is studied under AC, DC and composite voltages. The acquired UHF signals are fed to spectrum analyser to realise number of discharges that occurs on application of supply voltage. The number of discharges are noted to be lesser in nanofluids compared to transformer oil. For investigating the phase of supply where discharges are generated because of particle movement, Phase Resolved Partial Discharge (PRPD) studies were done for the motion of conducting particle in nanofluid on application of AC and composite voltages.

The authors investigated both the tree-initiation voltage and the length of the path generated in an LDPE (low-density polyethylene) specimen due to the electrical treeing under a needle-plane electrode system. They then measured both thermally stimulated current (TSC) and thermally stimulated surface potential (TSSP) generated in an LDPE specimen, which is biased by the application of either DC or AC voltage. The authors also investigated the mechanism of electrical breakdown initiated by the treeing by studying the relationship between the tree-initiation voltage determined by the experiment and the space charge field determined by the thermally stimulated electrical measurements. It was concluded that the distance between the centroid of the space charge formed in an LDPE film and the tip of the needle electrode was approximately the same as the length of the path generated by the electrical treeing. >

Superior performance of multilayered fluoropolymer films in low voltage electrowetting

We review a new experimental implementation of Kelvin probe force microscopy (KPFM) in which the dissipation signal of frequency modulation atomic force microscopy (FM-AFM) is used for dc bias voltage feedback (D-KPFM). The dissipation arises from an oscillating electrostatic force that is coherent with the tip oscillation, which is caused by applying the ac voltage between the tip and sample. The magnitude of the externally induced dissipation is found to be proportional to the effective dc bias voltage, which is the difference between the applied dc voltage and the contact potential difference. Two different implementations of D-KPFM are presented. In the first implementation, the frequency of the applied ac voltage, \(f_\mathrm {el}\), is chosen to be the same as the tip oscillation (\(f_\mathrm {el} = f_\mathrm {m}\): \(1\omega \)D-KPFM). In the second one, the ac voltage frequency, \(f_\mathrm {el}\), is chosen to be twice the tip oscillation frequency (\(f_\mathrm {el}= 2 f_\mathrm {m}\): \(2\omega \)D-KPFM). In \(1\omega \)D-KPFM, the dissipation is proportional to the electrostatic force, which enables the use of a small ac voltage amplitude even down to \({\approx }10\) mV. In \(2\omega \)D-KPFM, the dissipation is proportional to the electrostatic force gradient, which results in the same potential contrast as that obtained by FM-KPFM. D-KPFM features a simple implementation with no lock-in amplifier and faster scanning as it requires no low frequency modulation. The use of a small ac voltage amplitude in \(1\omega \)D-KPFM is of great importance in characterizing of technically relevant materials in which their electrical properties can be disturbed by the applied electric field. \(2\omega \)D-KPFM is useful when more accurate potential measurement is required. The operations in \(1\omega \) and \(2\omega \)D-KPFM can be switched easily to take advantage of both features at the same location on a sample.

We present a detailed study of the optoelectronic mixing effect in metal–semiconductor–metal detectors. Both analytical and numerical results are presented and the anisotropic effect is included in the calculations. Under transient bias voltage, the device shows two transient current responses: a fast one related to the displacement current and a slow one related to removal of carriers from the device. The mixing efficiency of the device increases with an increase in applied ac voltage and decreases with an increase in ac frequency. For anisotropic devices, rectification current exists. This rectification current varies not only with the ac voltage and optical power, but also with the ac frequency. This variation in current results in a self-clutter signal being observed in the experiments.

This study aims to establish an insulation diagnosis technique using partial discharge (PD) detection for cast resin transformers (CRTr). In the previous paper, the frequency components of PD current in a PD test of a CRTr by applying AC voltage between lumped high voltage and low voltage terminals were identified and analyzed in EMTP using an equivalent circuit model. On the other hand, another PD test is the test with an inductive voltage application in which an AC voltage is applied to the low voltage side of the transformer and then a high voltage is applied between the high voltage terminals in a transformer. This paper presents investigation on dominant frequency of PD current detected with high frequency current transformer (CT) in the inductive PD test of a 6.6 kV cast resin voltage transformer 6.6 kV CRTr-VT. An attempt is also made to identify PD signal source, the signal propagation path of the PD current, as well as the dominant frequency components.

Thermal power plant flue gas cleaning utilizing plasma chemical reactions promoted with partial discharges is studied. Characteristics of a partial discharge in a ferroelectric pellet layer have been studied using AC voltages with varying frequency or using square-wave voltages. The capacitance of the layer, C/sub t/, consists of the capacitance of the ferroelectric pellet, C/sub p/, and the capacitance of the air gap between each pellet, C/sub g/. Since C/sub g/ is much smaller than C/sub p/, the capacitance of the layer is determined mainly by C/sub p/. Therefore, packing of ferroelectric pellets with large dielectric constant values does not increase the value of C/sub t/ significantly, and excessive increase in the capacitive charging current can be avoided. With AC voltage application, the partial discharge takes place when the voltage crosses zero and ceases when the voltage reaches positive or negative peak value. When a square wave voltage is applied, a very large current can be obtained during the transient period of the voltage. >

The salt fog tests for silicone rubbers (SiR) were performed under DC or AC voltage application. During a test, intensive discharges occurred around an earth electrode when positive DC voltage was applied. In the case of negative DC voltage application, intensive discharges occurred around an electrode which the voltage was applied. In other words, the intensive discharge concentrated around a cathode electrode, which caused heavy erosion around the electrode. In contrast, for the case of AC voltage application, the intensive discharge and heavy erosion did not occur.

Polyvinylcarbazole (PVK) films have been prepared by solution method. Their absorption spectra, photoluminescence, and electroluminescence have been studied. Absorption in pure PVK is found to be high at lower wavelengths in UV region and decreases in visible range. In case of I2 doped PVK, absorption is observed in visible region also. The photoluminescence is obtained in pure PVK when exited by violet or blue light but in case of I2 doped PVK, similar excitation gives low intensity peaks in yellow–green region. The results indicate that I2 levels in PVK causes absorption in 400–600 nm wavelength range and makes the deexcitation of the molecules nonradiative. Light emission by application of ac voltage from mains up to 100 V has been studied. Nonlinear increase in emission intensity has been observed with increasing voltage. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 722–726, 2007

A rapid noncontact analysis method to identify liquid isomers using an insulating nanoparticle thin film is outlined in this study. Rapid electrical analysis of chemical liquids is a promising technique for on-site evaluation. A silica nanoparticle thin film is utilized as a sensing layer. Headspace vapor from the liquid is condensed in the nanoscale void between nanoparticles, and an ionic conduction through the condensed vapor occurs under the application of AC voltage. The transient response of the electrical impedance depends on the vapor pressure and conductivity of the liquid isomers. A chemical liquid of structural isomers was identified by monitoring the impedance during exposure to its headspace vapor. The response time of the film impedance was 10.6, 4.7, 7.5, and 2.4 s, in 1-butanol, 2-butanol, 2-methyl-1-propanol, and tert-butyl alcohol, respectively. The isomer recovery time after the exposure to ambient air was less than 2 s for all samples. It is feasible to identify polar chemical liquids rapidly by combining this sensing mechanism and machine learning models in the future.