In this paper, the dual-frequency atmospheric-pressure glow discharge is operated in helium with a small amount of oxygen. It is found that the plasma density increases, but the reactive atomic ...oxygen density decreases with high-frequency (HF) power. The plasma density also increases with low-frequency (LF) power, but it is weak as with HF power. However, the reactive atomic oxygen density increases with LF power. It shows that HF power is in favor of excited helium, but LF power is in favor of producing reactive O, N 2 , and OH. The discharge intensity decreases with oxygen gas admixture in working gas due to its electronegative nature. The generation rate of reactive oxygen atom has a trend of increasing first and then decreasing after 0.3% oxygen gas admixture.
Graphene supercapacitor, with its higher energy density and power density, is a promising solution for energy storage in many potential applications. The available energy from supercapacitors for ...stand-alone applications depends on their self-discharge. The effect of charge redistribution on the self-discharge and voltage recovery of graphene supercapacitors is investigated in this work. The self-discharge mechanism in graphene supercapacitors is found to be a combined effect of ohmic leakage and diffusion-controlled leakage due to charge redistribution. The charging process has a predominant effect on the self-discharge. With a higher initial voltage, the supercapacitors exhibit more self-discharge, but with longer charge holding time, the rate of self-discharge is low. The charge redistribution is attributed due to the difference in the accessibility of electrolyte ions to the electrode surface. A phenomenon of voltage recovery is observed in graphene supercapacitors even after complete discharge due to a charge redistribution mechanism. The voltage recovery increases with increasing charge/discharge current.
More and more transmission power cable circuits with lengths up to several tens of kilometers will be installed and put into operation. This contribution discusses basic aspects of selecting an ...on-site test voltage and the partial discharge measurement under on-site testing conditions of power cable lines with long length. On the one side, the generation of suitable test voltages for high capacitive loads, especially long cables, is evaluated and experiences of on-site measurements are described. On the other hand, the challenges for sensitive partial discharge measurement on long length power cables are discussed. Under this scope, partial discharge measurement by dual-sided measurement technique is described and examples are shown.
In this study, a direct-current multineedle-plate corona discharge with different parameters was used to treat Ammopiptanthus mongolicus (Maxim. ex Kom. Cheng f.) seeds and study the effect of corona ...discharge physicochemical etching on these seeds. Results showed that the surface of the seed coat of A. mongolicus had wind erosion after corona discharge treatment, a large number of small ravines were generated and the surface crack of the seed coat was serious. Analysis of Fourier transform infrared spectroscopy revealed that the hydrophilic functional groups increased and corona discharge changed the chemical structure of A. mongolicus seed coat. The apparent contact angle decreased significantly from 99.82° ± 4.86° to 60.11° ± 8.44°, suggesting that corona discharge could significantly improve the hydrophilicity of A. mongolicus seeds. All the corona discharge treatment groups had seed germination at 24 h, whilst the control group had zero germination. This finding suggested that corona discharge treatment could significantly affect the structure and properties of A. mongolicus seed coat, improve the seed hydrophilicity and water absorption rate and promote the germination and growth of A. mongolicus seeds. This study provided ideas and experimental data support for the analysis of the mechanism of corona discharge biotechnology and seed-surface modification.
We report a novel method to reduce layer number and structural defects of few-layer graphene (FLG) in He/H sub(2) arc discharge via rapid cooling treatment. By adjusting the parameters of He/H sub(2) ...mixtures appropriately, the effects of incremental cooling rates on the formation, morphology and structural defects of the raw soot have been investigated. According to observations of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM), such FLG affected by rapid cooling tends to be thinner than untreated counterpart. TEM and HRTEM observations show that such sample contains a large amount of FLG with a fraction of single-layer graphene (SLG). AFM results show the thickness of the thinnest flake in the soot equals 0.5 nm, indicating the presence of SLG. With the increasing of cooling rate, Raman-based estimations not only show the reduction of defect density by calculating the nanocrystallite size L sub(a), but confirm the thinning trend for layer number via Raman-assessed layer number. The possible reason for thinning effect is discussed on both aspects of crystal growth and fluid dynamics.
This article introduces a silicon carbide (SiC)-based high-voltage silicon-controlled rectifier (HV-SCR) for on-chip electrostatic discharge (ESD) protection. The SiC HV-SCR is formed by implanting a ...<inline-formula> <tex-math notation="LaTeX">\text{p}^{+} </tex-math></inline-formula> region into the n-well of SiC laterally diffused metal-oxide semiconductor (LDMOS) structures. Both LDMOS and HV-SCR structures were characterized using a transmission line pulse (TLP) system to investigate their ESD behaviors. The TLP measurement results show that the trigger voltage (<inline-formula> <tex-math notation="LaTeX">{V}_{\text {t1}} </tex-math></inline-formula>) of the SiC HV-SCR is <inline-formula> <tex-math notation="LaTeX">\sim 230 </tex-math></inline-formula> V and has minor dependence on the drift length. The <inline-formula> <tex-math notation="LaTeX">{V}_{\text {t1}} </tex-math></inline-formula> value of the SiC LDMOS decreases from 224 to 202 V when its drift length decreases from 6 to 4 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>. TLP measurements with 500-<inline-formula> <tex-math notation="LaTeX">\Omega </tex-math></inline-formula> impedance were conducted to obtain an accurate holding voltage (<inline-formula> <tex-math notation="LaTeX">{V}_{\text {h}} </tex-math></inline-formula>) and failure current (<inline-formula> <tex-math notation="LaTeX">{I}_{\text {t2}} </tex-math></inline-formula>) of HV-SCR and LDMOS. Relatively high <inline-formula> <tex-math notation="LaTeX">{I}_{\text {t2}} </tex-math></inline-formula> (i.e., 33 mA/<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>) of the HV-SCR structure was observed, which is much stronger than the LDMOS structure (i.e., 0.2 mA/<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>). The <inline-formula> <tex-math notation="LaTeX">{V}_{\text {t1}} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">{V}_{\text {h}} </tex-math></inline-formula> values of HV-SCR were also investigated with varying gate bias voltages. Moreover, technology computer-aided design (TCAD) simulations of the SiC HV-SCR and LDMOS were carried out to further understand their ESD behaviors.
Partial discharge (PD) is a common phenomenon in high voltage (HV) equipment, which will radiate light signals outward in the process of discharge, by detecting this optical signal, we can judge ...whether the HV equipment have PDs or not, the conventional detection methods under impulse voltage are very complex due to the interference of electromagnetic (EM) wave, but optical method does not have this problem. Fluorescent optical fiber is not affected by numerical aperture problem, so the sensitivity of fluorescent optical fiber sensor is much higher than that of traditional quartz optical fiber sensor. In this work, the fluorescent optical fiber sensor was manufactured and applied to the PD detection in gas insulated switch (GIS) and transformer, fluorescent optical fiber was used as a probe, which was connected with the transmission optical fiber by coupler, and the photomultiplier tube was used to convert the optical signal into electrical signal for displaying by oscilloscope. The discharge signal can be detected by the sensor when the impulse voltage was applied to the GIS and transformer, and it was less affected by the interference of EM wave signals. As the PD source at different positions in GIS, we found that the optical signal attenuates greatly when the optical was blocked by some internal structures, and the attenuation was increase with the increase of distance between PD source and the sensor. The optical signals of PDs can also be detected by the sensor in the transformer, but the attenuation of the optical signal in the transformer was greater than that in GIS, it was greatly affected by the blocking of windings. The two experiments were verified in the TracePro simulation software, and the average deviations between results of experiments and simulations were less than 10%.
It has recently been demonstrated that pulsed direct-current (dc) voltages show better performance in generating diffuse plasmas under various conditions. However, it still remains unclear whether ...the pulsewidth or the rising and falling times of the voltage pulse play the essential role in the improvement of the performance of the dielectric barrier discharges (DBDs). In this paper, we focus on the effect of pulsewidth. Pulsed dc voltages with pulsewidth varying from 0.2 mus to about 1 ms are used to drive the DBDs. High-speed photographs show that diffuse Ar plasmas can be generated by pulsed dc voltages with pulsewidths covering the entire investigated range. It is found that the pulsewidths of the applied voltages affect the discharge current durations significantly when the pulsewidth is shorter than 600 ns or the break between the two consecutive pulses is shorter than 600 ns.
Partial discharge (PD) has been identified as one of the root causes of stator insulation failure even for low voltage (LV) ac motors. For reliable operation of variable frequency drive motors, a ...standard acceptance test procedure (IEC STD 60034-18-41) to ensure PD-free operation of LV motors was developed. Although the test can verify whether PD exists in the stator for a surge with predetermined voltage level and risetime, the information on where PD activity is present in the stator insulation is not provided. In this article, a test method based on a new variable risetime surge generator is proposed for identifying the component of stator insulation where PD occurs in LV random wound stators. The proposed test allows the user to locate whether PD is in the turn, phase, or ground insulation. This information is critical for lowering the PD inception voltage for improving the motor reliability through insulation system design/manufacturing or motor/drive system reconfiguration. The test is implemented with a 4.5 kV variable risetime surge generator prototype, and seven LV ac motors are tested to show where PD is likely to occur in commercial LV motors.
We accurately established an air discharge simulation experiment system to obtain the variation of ozone concentration in air discharge process, which includes pin-to-plate discharge, air-gap ...discharge, creeping discharge as well as metal particle discharge model, consisting of voltage console, transformer, and discharge device, gas absorption cell, spectrometer, and computer. Through online monitoring, the ozone concentration in a relatively closed container to simulate internal partial discharges for an hour with the voltage increases from 3 to 0.2 kV increment, we obtained four basic models with discharge inception voltage grade of 4.0, 4.5, 4.7, and 4.1. Besides, we applied the method of Fourier transform-differential absorption spectroscopy to process and analyze the experimental data, and obtained the ozone concentration curve. The ozone concentration increases with the increasing voltage loading time, and it tends to be stable and reaches an equilibrium state under a certain voltage.
