Interfacial Discharge Research Articles

Integrated modelling of vacuum flashover development: Above‐surface processes and breakdown threshold analyses

AbstractThe flashover in vacuum is a rapid interfacial discharge across the insulator surface when subjected to high applied voltage. Here a theoretical model covering above‐surface processes is introduced. The model calculates the flashover threshold in vacuum, with revised secondary electron emission avalanche theory and improved desorbed neutral transport model. The model serves as the first part of an integrated flashover model, aiming for consistent treatment of both above‐surface and subsurface processes during the entire flashover development. The flashover threshold is obtained by combining the desorbed neutral pressure at given applied voltage and the gas breakdown criterion dictated by the Paschen's law. An analytical formula for threshold estimation containing physical parameters, and a simplified formula consisting of empirical coefficients are introduced, catering for both conceptual understanding and practical application. The derived formulae are validated by experimental data for a variety of insulator materials. The theory generalisation for non‐uniform electric field distribution is further discussed.

Effect of Extremely Cold Weather and Shrinkage Stress on Interfacial Discharge Between Epoxy and Silicone Rubber in HV Cable Terminations

Gas insulated switchgear (GIS) cable terminations have higher failure rates at low temperatures. In this study, a 110-kV full-size GIS cable termination model is developed to investigate this failure mechanism. The coupling characteristics of the thermal and mechanical stress distributions in the termination are analyzed. A pressure-controlled interfacial discharge experimental setup is established, and the partial discharge characteristics and damage features of tracking are investigated for different interface pressures. At temperatures as low as -40 °C, pressure distortion is observed at the interface between the stress cone and epoxy bushing, such that the interface pressure can drop below 0.1 MPa. The tracking at low interface pressures has a higher growth rate and fewer and finer branches than at high interface pressures. The accumulated damage area tends to develop from the epoxy resin towards the silicone rubber. As the interfacial pressure drops, the characteristics of the partial discharge change from those for internal discharge type to those for coexistence between internal discharge and surface discharge. Finally, a scheme for tracking development and damage under different interface pressures is proposed to explain the failure process for cable termination in an extremely cold environment, which is highly consistent with the characteristics of actual failure.

Reproduction and Analysis of Decay-Like Aging Development Induced by Interfacial Discharge in Composite Insulators

In the last decade, the decay-like aging phenomena of fiber reinforced plastic (FRP) core rods in composite insulators appeared frequently, and have significantly affected the safety of power transmission lines. However, the mechanism of its occurrence and development is still unclear. In this work, a method based on rod-housing interfacial discharge is proposed to artificially reproduce the occurrence and development of decay-like aging in FRP core rods under laboratory conditions. The aging process is explored under a high-humidity environment, where high-acidity and high-temperature conditions are also provided by interfacial discharge. The micro- and macro-scopic structures, physicochemical properties and leakage currents of FRP samples are characterized during a 1000-hour aging process. The laboratory aged samples resemble the decay-like phenomena in on-site insulators, indicating the effectiveness of this method. Experimental results show that interfacial discharge can trigger the decomposition of epoxy resin in FRP core rods, leading to exposure of glass fibers. Electrical erosion slows down as aging time increases, and the erosion rate is positively related to the porosity of core rods. Further discussion indicates that erosion is impeded by glass fibers in the surface aging layer due to its high thermal and chemical stability, and a three-stage erosion process model is proposed. Finally, a semi-empirical model is proposed to describe this aging process, in which the influence of core rod porosity is taken into account. This work provides an effective laboratorial method to reproduce the decay-like aging of composite insulators, and reveals its erosion process and the underlying mechanism.

Synthesis and Surface Engineering of Carbon Quantum Dots by Electrical Discharges Generated Inside and in Contact with Liquid

In this paper electrical discharge plasma in liquid was used for synthesis of carbon NPs. In addition, targeted changes of the NPs surface properties could be selectively achieved via treatment of as-prepared NPs by a gas-liquid interfacial discharge produced in contact with the colloidal solution. For synthesis a high-voltage spark discharge was ignited in the solution between two graphite electrodes immersed in water. The discharge in contact with liquid was generated between a stainless-steel capillary electrode served as cathode and the surface of the liquid. The discharge was ignited by applying the high voltage of 3.6 kV using a dc power supply with argon flowing through the capillary tube. The discharge current was kept constant in the range of 1 - 5 mA [1, 2].The composition, morphology and optical properties of the synthesized and plasma treated NPs were studied by TEM, EDX, PL, FTIR, Raman and ultraviolet–visible spectroscopy The NPs obtained by the spark discharge in water looked like isolated spherical NPs with the average diameter about 3 nm as it followed from the TEM analysis. The HRTEM images of separate particles revealed that particles are crystalline and the measured interplanar distances were found to be 2.06 Å that correspond to the reflections between (111) planes in carbon having diamond-like structure. The SAED analysis further proved the formation of diamond-like structures with admixture of orthorhombic carbon phases, while the rings corresponding to graphitic structure were absent in the SAED patterns.For the further studies of the prepared C NPs Raman and XRD techniques were used. The Raman spectrum contained two distinct peaks: narrow G-band near 1578 cm-1 attributable to the ordered graphite and the broadened D-band at 1349 cm-1 which is associated with disodered carbon and the presence of a carbon sp3 defects in the prepared C-NPs. It should be noted that the D-band is rather broad thus covering the range 1310-1320 cm-1, typical to the diamond and orthorhombic carbon structures.Analogically, the results of the X-ray diffraction studies exhibited the broad peak in the region 20-40˚, so-called halo, indicated a presence of small particles with various carbon phases in the sample. Nevertheless, the diamond-like phases, observed in TEM measurements most probably are presented in the sample but only as very small particles that are produced through the condensation mechanism. It is known that NPs in electrical discharge are formed through two competing mechanisms namely via the condensation of the evaporated electrode material that are atoms, ions and small clusters with their subsequent growth into the NPs; and in result the destroying of the electrodes with the formation of the particles of much larger sizes. For the Raman studies, the colloid was deposited onto the substrate, and thus larger and better crystallized particles with graphite structure formed by the second route were dominant that can explain the contradiction of Raman and TEM results.To modify the properties of NPs, the colloidal solution of C NPs synthesized by spark discharge was treated by reactive non-equilibrium gas-liquid discharge plasma contacting with the solution. The results of these studies showed that different surface chemistry activated in different solutions could be due to different reactions induced by plasma electrons at the plasma–solution interface compared to plasma–water one. Changing the surface groups is believed to be effective in improvement of photoluminescence properties of the synthesized C-dots.Thus, the EDL technique has been demonstrated to be suitable for the preparation of carbon quantum dots with sizes 2-5 nm and narrow size distribution that are the part of the requirements for practical applications. In addition, a treatment of NPs by reactive non-equilibrium gas-liquid discharge plasma contacting with a colloidal solution can offer great opportunities for the NPs surface engineering and an improvement of the photoluminescent properties. Carbon NPs with size less than 10 nm – so called quantum dots due to their excellent biocompatibility, chemical inertness, and size-selective photoluminescence properties may find increasing applications in modern biotechnology as more suitable alternatives to the traditional semiconductor quantum dots.The work was supported by the National Academy of Sciences of Belarus under project Convergence 2.4.06.[1] A. Nevar, N. Tarasenka, M. Nedelko, N. Tarasenko Carbon Lett. – 2020 https://doi.org/10.1007/s42823-020-00147-9.[2] V.S. Burakov, V.V Kiris, M.I. Nedelko, N.N. Tarasenka, A.A. Nevar, N. V. Tarasenko, Eur. Phys. J. Appl. Phys., 79 10801 (2017)

Synthesis and Surface Engineering of Carbon Quantum Dots by Electrical Discharges Generated Inside and in Contact with Liquid

In this paper electrical discharge plasma in liquid was used for synthesis of carbon nanoparticles (NPs). In addition, targeted changes of the NPs surface properties were selectively achieved via treatment of as-prepared NPs by a gas-liquid interfacial discharge produced in contact with the colloidal solution. The results of the solution chemistry induced at the plasma-liquid interface for surface engineering of NPs are discussed.

Plasmas in and in contact with liquid for synthesis and surface engineering of carbon and silicon nanoparticles

Two types of plasma-liquid systems are discussed from the point of view of their capabilities for synthesis and surface engineering of nanomaterials. The high-voltage discharge between two electrodes submerged into liquid is used for the synthesis of carbon and silicon nanoparticles (NPs). The second system based on the gas–liquid interfacial discharge plasma generated between a capillary (hollow needle) with flowing argon and liquid surface is used for surface modification of as-prepared NPs directly in solution. The capabilities of the non-equilibrium gas–liquid discharge plasma for surface modification and improvement of photoluminescent properties of carbon and silicon NPs by their surface functionalization are discussed. The morphology and composition of the generated particles are examined in dependence both on plasma parameters and plasma induced processes in solution.

In vitro Demonstration of Cancer Inhibiting Properties from Stratified Self-Organized Plasma-Liquid Interface

Experiments on plasma-liquid interaction and formation of thinly stratified self-organized patterns at plasma-liquid interface have revealed a nontrivial cancer-inhibiting capability of liquid media treated at self-organized interfacial patterns. A pronounced cancer suppressing activity towards at least two cancer cells, breast cancer MDA-MB-231 and human glioblastoma U87 cancer lines, was demonstrated in vitro. After a short treatment at the thinly stratified self-organized plasma-liquid interface pattern, the cancer inhibiting media demonstrate pronounced suppressing and apoptotic activities towards tumor cells. Importantly, this would have been impossible without interfacial stratification of plasma jet to thin (of several µm) current filaments, which plays a pivotal role in building up the cancer inhibition properties. Furthermore, thinly stratified, self-organized interfacial discharge is capable to efficiently control the ROS and RNS concentrations in the cancer-inhibiting media. In particular, abnormal ROS/RNS ratios are not achievable in discharges since they do not form stratified thin-filament patterns. Our findings could be tremendously important for understanding the cancer proliferation problem and hence, the potential of this approach in tackling the challenges of high cancer-induced mortality should be explored.

Atmospheric pressure plasma in contact with liquid and its application for nanoparticles synthesis

The capabilities of atmospheric pressure gas-liquid interfacial discharge plasma for synthesis of metallic (Ag), oxide (ZnO) and composite (ZnO/Ag) nanoparticles are discussed. The gas-liquid boundary microplasma was generated between a capillary (hollow needle) with flowing argon and liquid surface in ambient air under the normal pressure. To optimize the synthesis process the main characteristics of the discharge plasma were studied using emission spectroscopy by varying the discharge current, gas flow rate and solution composition. The morphology and composition of the generated particles were found to be dependent on both plasma parameters and plasma induced processes in solution. The studies performed suggest that particle nucleation and growth can be attributed to the reduction reactions of the aqueous metal cations by electrons from the microplasma.

Degradation of Microcystin-LR by Gas-Liquid Interfacial Discharge Plasma

In this study, we report on the degradation of microcystin-LR (MC-LR) by gas-liquid interfacial discharge plasma. The influences of operation parameters such as average input voltage, electrode distance and gas flow rate are investigated. Experimental results indicate that the input voltage and gas flow rate have positive influences on MC-LR degradation, while the electrode distance has a negative one. After 6 min discharge with 25 kV average input voltage and 60 L/h air aeration, the degradation rate of MC-LR achieves 75.3%. H2O2 and O3 generated by discharge both in distilled water and MC-LR solution are measured. Moreover, an emission spectroscopy is used as an indicator of the processes that take place on the gas-liquid boundary and inside plasma. Varied types of radicals (O, ·OH, CO, O3, etc.) are proved to be present in the gas phase during gas-liquid interfacial discharge.

Electrochemistry of lithium–oxygen batteries using microelectrode voltammetry

The electrochemistry of non-aqueous lithium–oxygen (Li–O2) batteries on both reduction and oxidation was investigated using carbon black and single-walled nanotube (SWNT) microcavity electrodes. Two oxidative peaks were observed on oxidation (charge). The first peak at 3.0–3.7 V vs. Li/Li+ was limited in storable charge (∼8 × 103 C cm−3). The oxidation potential of this first peak was independent of Li2O2 thickness (as measured by total charge on reduction) and assigned to interfacial Li2O2, lying between the bulk of the Li2O2 and the carbon surface. A second peak between 4.0 and 4.6+ V showed significant discharge product thickness dependence on oxidation potential and was assigned to bulk Li2O2, away from the carbon surface. On reduction (discharge), deposition of the interfacial Li2O2 showed a significant overpotential indicated by the ratio of interfacial/bulk Li2O2 formed at varying reduction potentials. SWNT were shown to effectively decrease the Li–O2 average charge overpotential for a given charge by increasing the electrode surface area available for formation of interfacial discharge products.

(Invited) Controlled Functionalization of Carbon Nanotubes with Nanoparticles Using Gas-Liquid Interfacial Discharge Plasmas

A periodic structure of gold (Au) nanoparticles is formed by reducing an aqueous solution of gold chloride using novel plasma techniques, where the Au nanoparticles are synthesized on the carbon nanotubes (CNTs) working as a template or a spatio-periodically generated plasma is transcribed to the Au nanoparticle structure formed on the liquid surface under the strong magnetic field. In addition, it is found that a ring-shaped nanoparticle structure is formed corresponding to the shape of a ring electrode inserted into the plasma, where the nanoparticles are synthesized at the position without plasma irradiation due to the shielding by the ring electrode.

Creation of Nanoparticle–Nanotube Conjugates for Life-Science Application Using Gas–Liquid Interfacial Plasmas

Gold nanoparticles (AuNPs) conjugated with carbon nanotubes (CNTs) and/or biomolecules such as DNA are synthesized by a novel plasma technique combined with the introduction of ionic liquids or aqueous solutions for application to life sciences. We successfully generated the gas–liquid interfacial discharge plasma (GLIDP) using an ionic liquid, in which a large sheath electric field was formed on the ionic liquid and high-energy plasma ion irradiation to the ionic liquid was realized. Using this GLIDP, it is found that the high-energy ion irradiation to the ionic liquid is effective for the synthesis of AuNPs. Furthermore, controlled ion irradiation to the ionic liquid including functional groups can realize distance-controlled synthesis of AuNPs on CNTs by dissociation of the ionic liquid and the functionalization of CNTs by dissociated carboxyl and amino groups. On the other hand, DNA is used as the functional group that connects the AuNPs to the CNTs. Monodispersed and high-density AuNPs are synthesized on CNTs in the same way as the carboxyl and amino groups.

Synthesis of nano-bio conjugates for drug delivery systems using gas-liquid interfacial discharge plasmas

Size-controlled gold nanoparticles (AuNPs) covered with DNA are synthesized by using a pulsedriven gas-liquid interfacial discharge plasma (GLIDP) to reduce an aqueous solution of chloroauric acid trihydrate with DNA. The size and the assembly of the AuNPs are found to be easily controlled by changing the DNA concentration in the aqueous solution. The synthesized AuNP-DNA conjugates are forced to be encapsulated into double-walled carbon nanotubes (DWNTs) by superimposing a positive DC voltage on the pulse voltage. The AuNP-DNA-conjugate encapsulated DWNTs can be utilized in drug delivery systems when DNA is used as a drug molecule.

(Invited) Controlled Functionalization of Carbon Nanotubes with Nanoparticles Using Gas-Liquid Interfacial Discharge Plasmas

not Available.

Creation of Novel Nano-Bio Conjugates for Life Sciences Using Gas-Liquid Phases Plasmas

ABSTRACTThe gold nanoparticles (AuNPs) conjugated with carbon nanotubes (CNTs) and/or biomolecules such as DNA are synthesized using a novel plasma technique combined with introduction of ionic liquids or aqueous solution for application to life sciences.First, we successfully generate the gas-liquid interfacial discharge plasma (GLIDP) using an ionic liquid, in which the large sheath electric field is formed on the ionic liquid and the plasma ion irradiation to the ionic liquid with high energy is realized.Second, it is found that the high energy ion irradiation to the ionic liquid is effective for the synthesis of the AuNPs. Furthermore, the controlled ion irradiation to the ionic liquid including a carboxyl group can realize the density-controlled synthesis of the AuNPs on the CNTs by dissociation of the ionic liquid and the controlled functionalization of the CNTs by the dissociated carboxyl group.Third, the size- and morphology-controlled AuNPs covered with DNA are synthesized using the GLIDP with aqueous solution, where DNA prevents the AuNPs from further clustering, resulting in the small-sized AuNPs. The synthesized AuNPs conjugated with DNA can be encapsulated into the CNTs using the DC electric field. The CNTs work as vectors to deliver DNA into living cells because the CNTs have the unique ability to easily penetrate cell membranes with low cytotoxicity.

Rapid synthesis of water-soluble gold nanoparticles with control of size and assembly using gas–liquid interfacial discharge plasma

Water-soluble gold nanoparticles (AuNPs) are rapidly synthesized by a gas–liquid interfacial discharge plasma in association with DNA. The synthesis is free from the elaborate reaction requirements usually in conventional methods, e.g., the temperature control, continuous stirring, and ultraclean glassware for the reaction solution. Moreover, the size and morphology of AuNPs are simply tuned by varying the concentration and type of DNA which acts as a stabilizer through conjugating on AuNPs. The DNA conjugation prevents the AuNPs from a further coalescence, resulting in the formation of small-sized AuNPs. Furthermore, the assembly of the AuNPs is enhanced when DNA concentration is high.

Characterization of pulse-driven gas-liquid interfacial discharge plasmas and application to synthesis of gold nanoparticle-DNA encapsulated carbon nanotubes

Gas-liquid interfacial discharge plasmas are generated between ionic liquid and stainless steel electrodes, where a pulse power source is used to operate the discharges. The temporal evolution of the plasma is investigated as well as the spatial distribution of the plasma. The positive pulse discharge plasma can not be detected by a double Langmuir probe, which is attributed to the fast diffusion of the plasma toward the chamber wall due to its high positive potential. On the other hand, the negative pulse discharge plasma parameters can be measured and the density decreases with increasing the distance away from the ionic liquid electrode. The plasma is mostly an after-glow discharge plasma since the plasma density gradually decreases after the discharge in a long period. In addition, we synthesize gold nanoparticle-DNA encapsulated single-walled carbon nanotubes by superimposing a DC voltage to the pulse voltage.

Effects of interfacial pressure on tracking failure between XLPE and silicon rubber

XLPE power cables are increasingly used in power distribution system for their excellent mechanical and electrical performance. However, interface between XLPE and silicon rubber in cable joint remains one of the weakest part of the cable system, because aging and relaxation of silicon rubber may reduce the interfacial pressure and then cause interfacial discharge and tracking failure. Therefore, this paper investigates the effects of interfacial pressure on interface discharge and tracking failure at the interface. Test samples were made by pressing a piece of XLPE and silicon rubber together under different interfacial pressures. AC voltage was applied on a pair of needle-plate electrodes at the interface with the insulation distance of 10 mm. Both the initial discharge voltage and the time to tracking failure were recorded with variation of the interfacial pressure and the applied voltage. Meanwhile, the discharge light and the carbonized configuration were also captured by using a high-speed camera. In order to quantify the light and the carbonization, the methods of image processing and fractal dimension (FD) were employed to establish the relationship between the quantitative characteristics of tracking process and the interfacial pressures. The results show that both the initial discharge voltage and the time to tracking failure increase with the increase of interfacial pressure. With increasing the interfacial pressure, the FDs of discharge light and carbonization path show the decreasing tendency, which indicates that the higher interfacial pressure can effectively delay the interfacial discharges and the tracking failure.

Some Effects of Vapors on Electret Behavior

The effects of various vapors on the growth and decay of electret polarization have been studied. Particular emphasis was given to the effect of water vapor on polyvinyl acetate. The observed effects appear to arise from two causes: (1) a decrease in the relaxation time and an increase in the magnitude of the volume polarization following infusion of vapor into the dielectric; (2) an increase in the transfer of charge by means of interfacial discharge at the dielectric-electrode gap. The infusion of a polar vapor into a nonpolar solid dielectric gave anomalously large values of volume polarization. The dielectrics studied were polyvinyl acetate, polyethylene, two acrylic resins, and carnauba wax. The vapors used successfully were water and chlorobenzene; unsuccessful attempts were made to use benzene and isopropyl ether.