Pulsed discharge plasma and its application is one of the promising directions in civilian areas of pulsed power technology. In order to promote the research and development of the theory and ...application technology for pulsed discharge plasma, in this paper, recent progress on the mechanism of nanosecond-pulse gas discharge and the characteristics and applications of typical pulsed plasma at the Institute of Electrical Engineering, Chinese Academy of Sciences is reviewed. Firstly, progress on mechanism of nanosecond-pulse discharge based on runaway electrons and measurement technology of runaway electrons is introduced. Then, the characteristics of three typical discharges, including direct-driven pulsed discharge, pulsed dielectric barrier discharge and pulsed plasma jet, are reviewed. Furthermore, typical plasma applications of pulsed plasma on surface modification and methane conversion are presented.
Dielectric barrier discharge (DBD) excitation by unipolar high voltage pulses is a promising approach for producing non-thermal plasma at atmospheric pressure. In this study, a magnetic compression ...solid-state pulsed power generator was used to produce repetitive nanosecond pulses for the excitation. The DBD is created using two liquid electrodes. The electrical characteristics of the discharge voltage and current are illustrated under different experimental conditions. The nanosecond-pulse discharge current is of the order of tens of amperes. This differs from common DBD current excitated by high-voltage ac sources. Compared with the characteristics of two current pulses corresponding to two discharges for unipolar pulsed-excitation, the secondary discharge in this study is minor owing to the pulsed power and discharge configuration. Under the experimental conditions, the luminous emissions from the front and side views of the liquid electrodes show that no filament is observed and the discharge is homogeneous and diffuse in the whole discharge region. The effects of applied voltage amplitude, repetition rate, and air gap spacing on the discharge characteristic are investigated. The discharge mode does not change with the variation of the investigated parameters. A comparison of high voltage ac and nanosecond-pulse excitation is also presented. In addition, discussion of the experimental results is presented.
•Precise measurements of individual partial discharge pulses.•Comparison of AC and DC partial discharge pulses.•Classification of AC and DC partial discharges.•FFT of AC and DC partial discharge ...pulses.•Time characteristics of AC and DC partial discharges.
This study aims to classify and compare AC and DC partial discharge (PD) based on PD pulse waveform analysis. To achieve this goal, we designed a testbed that enables precise measurements of individual PD pulses. The testbed is used for collecting data from four different types of PDs including cavity, surface, corona, and floating potential discharges generated by individual PD source samples. All samples were examined under AC, positive DC, and negative DC electrical stresses, through which we captured thousands of PD pulses. We classify the waveforms of each PD type into representative groups associated to their discharge mechanisms. The statistical data of the measured pulses are utilized to identify the differences between AC and DC PDs while the clustered patterns of PD amplitude versus their temporal characteristics serve as a means to classify the types of PDs under AC and DC electrical stresses.
Residual charges produced in previous partial discharges (PDs) are considered as one aspect of memory effects that affect subsequent discharge behavior. In this paper, we review past studies about ...memory effects induced by residual charges during successive PDs. At first, surface charge dynamics for cavity and needle-to-dielectric discharges are presented. Subsequently, three methods used to unravel the memory effects are described, e.g. conditional distribution, pulse sequence analysis (PSA) and chopped PD (CPD). Then effects of residual charges on PD inception, discharge propagation and collective behavior are summarized. In addition, contributions of residual charges to the transitions between discharge modes and discharge patterns are presented. At last, some problems relevant to the memory effects are discussed, followed by suggestions for future work.
Surface flashover occurs at the external insulation of epoxy-based dry-type air-core reactors, which suffers from severe electric field distortion at the interface between the star-frame arm and ...epoxy/glass composites. A study on the triggering factors of ac and dc surface flashovers and their effects on the characteristics of ac/dc superimposed flashovers is urgently needed. In this study, the characteristics of surface flashover, partial discharge (PD), and surface charge were measured on the surface of epoxy composites using dc voltage, ac voltage, and ac/dc superposition with different voltage ratios. The PD intensity increases, the surface charge density decreases, and the flashover voltage lowers as the ac content of the ac/dc superimposed voltage increases. When the component of dc increases, the trends of flashover voltage, PD, and charge density are opposite to those for the ac component. According to the link between the three components, surface charge is the triggering issue of dc flashover, but PD rather than surface charge accumulation is the dominant factor of ac flashover. The main effect of surface charge accumulation is to distort the electric field at the high-voltage (HV) electrode's triple junctions (HTJs) and generate more initial electrons under dc voltage, while the main effect of PD in ac flashover is to directly intensify the gas discharge and generate more electrons. This study reveals the predominant triggering factors of ac and dc flashover and their impact mechanisms on ac/dc superimposed surface flashover, providing theoretical guidance for subsequent enhancement of ac/dc superimposed flashover characteristics of power equipment.
Magnetron sputtering deposition has become the most widely used technique for deposition of both metallic and compound thin films and is utilized in numerous industrial applications. There has been a ...continuous development of the magnetron sputtering technology to improve target utilization, increase ionization of the sputtered species, increase deposition rates, and to minimize electrical instabilities such as arcs, as well as to reduce operating cost. The development from the direct current (dc) diode sputter tool to the magnetron sputtering discharge is discussed as well as the various magnetron sputtering discharge configurations. The magnetron sputtering discharge is either operated as a dc or radio frequency discharge, or it is driven by some other periodic waveforms depending on the application. This includes reactive magnetron sputtering which exhibits hysteresis and is often operated with an asymmetric bipolar mid-frequency pulsed waveform. Due to target poisoning the reactive sputter process is inherently unstable and exhibits a strongly non-linear response to variations in operating parameters. Ionized physical vapor deposition was initially achieved by adding a secondary discharge between the cathode target and the substrate and later by applying high power pulses to the cathode target. An overview is given of the operating parameters, the discharge properties and the plasma parameters including particle densities, discharge current composition, electron and ion energy distributions, deposition rate, and ionized flux fraction. The discharge maintenance is discussed including the electron heating processes, the creation and role of secondary electrons and Ohmic heating, and the sputter processes. Furthermore, the role and appearance of instabilities in the discharge operation is discussed.
In this article, a 2-D fluid simulation model of a coaxial cylindrical DBD reactor filled with single solid spheres of two different materials is developed for plasma-assisted milling discharge ...studies. In this article, the evolution, quenching process, and comparison of the discharge characteristics, including its current, electron density distribution, and electric field distribution, of stainless steel and SiO<inline-formula> <tex-math notation="LaTeX">_{2}</tex-math> </inline-formula> spheres discharged at atmospheric pressure DBD were investigated separately, and the discharge images were captured by using an ICCD camera to further validate the results predicted by experimentally established models. The following conclusions were obtained from the study. First, in terms of current, the initial discharge moment of SiO<inline-formula> <tex-math notation="LaTeX">_{2}</tex-math> </inline-formula> spheres is slightly later than that of stainless steel-filled spheres. During the rising edge of pulse voltage, there was only one DBD current peak in stainless steel-filled spheres, while there were two current peaks in SiO<inline-formula> <tex-math notation="LaTeX">_{2}</tex-math> </inline-formula>-filled spheres, and the first current peak was smaller than the second, indicating that the second discharge was stronger than the first. Second, electron density distribution and ICCD images show that the discharge is mainly concentrated in the volume discharge at the top of the spheres when stainless steel-filled spheres are present. Comparatively, SiO<inline-formula> <tex-math notation="LaTeX">_{2}</tex-math> </inline-formula> spheres first experience a period of volume discharge, followed by a more diffuse discharge around the spheres, especially in the entire region between the top of the spheres and the dielectric layer. Overall, the SiO<inline-formula> <tex-math notation="LaTeX">_{2}</tex-math> </inline-formula> spheres show a more intense discharge compared to the stainless steel spheres.
Metal particles and dirty contaminants on the spacer surface are mainly considered to be the critical factor in sudden flashovers. Understanding the discharge characteristics as well as the ...detectability of metal particles in the gas-insulated switchgear (GIS) will be helpful in improving its safety and reliability. In this paper, a high-sensitivity measurement system based on cross-reference pulse current (PC) and ultra-high-frequency (UHF) methods was established. The PC and UHF signals generated by partial discharges (PDs) of metal particles of different lengths ( Φ = 0.5 mm, L = 2, 5, 8, and 10 mm) at different positions on a real spacer surface were studied. The PD characteristics and detectability of the metal particles on the spacer surface were obtained while the detection limitation was also discussed. It is found that under PD test condition, the apparent charge of the PDs is less than 1 pC for particles shorter than 5 mm, and the conventional PD detection method have limitations in detecting these short particles on the spacer surface. Under operation condition, only the apparent charge of particles longer than 8 mm can exceed 1 pC, which means it is difficult to detect the particles shorter than 8 mm in field. However, the result indicates that even the 5 mm long particle will be harmful to the GIS. Meanwhile, it is also been found that the detection sensitivity also has a great influence on the judgement of PD severity. This study is of great interest for understanding the PD characteristics, discharge levels, and detectability of short metal particles on spacer surface.
Since repetitive partial discharge (PD) leads to insulation breakdown, it is one of the most critical defects that affect operation life of electrical equipment. In this paper, four kinds of PD ...defects are identified with deep learning (DL) method according to the current waveforms. A modified IEC-60270 experiment platform with ultra-high frequency (UHF) and current probe is built to acquire PD current waveforms and their corresponding detecting pulse current and UHF pulse signal. Fourier transform, principle component analysis, and t-distributed stochastic neighbor embedding methods are applied to visualize the data set, which proves the feasibility of classifying the PD current waveform. Two basic parts of this DL framework are sparse autoencoder layer and softmax layer, the former extracting features of the input signal and the latter operating as the classifier. Hyper-parameters of the network such as sparsity, activation function, number of hidden nodes, and network depth were discussed. The final classifying accuracy of the proposed method is up to 99.7%, that is much better than the traditional identifying method. A comprehensive blind test is designed to prove the general validity and robustness of the proposed model.
Backward discharge, or reverse discharge, has been observed in experimental investigations under impulse discharge. We found the different residual charge accumulation characteristics under full and ...chopped lightning impulses in previous work, which is suspected to be caused by different surface backward discharge processes. However, the specific processes and mechanisms are not yet clear. In this study, the surface backward discharge patterns under full and chopped negative standard lightning impulses in C4F7N/CO2 mixtures are investigated. The residual charge distribution of the surface discharges under full and chopped impulses is studied, and their difference is discussed. The backward discharge under full impulse appears as streamer discharge with a lower intensity, and more charges are accumulated on insulator surface after discharge. The backward discharge under chopped impulse occurs through activating the discharge channels of forward discharge at the chopping moment. It exhibits a strong intensity and a longer discharge distance. Only a small amount of charge accumulates on insulator surface after backward channel activation discharge. The effect of chopping moment on backward discharge patterns is also studied. The formation conditions of the two types of backward discharges are determined, and the formation process of backward channel activation discharge is established. Due to the different patterns of surface backward discharge, surface charge accumulation is more prominent under full lightning impulse compared to chopped impulse. This will have an impact on the subsequent development of the surface discharge.
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