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Characterization of a corona-stabilized switch in the single-shot regime, including triggering range, delay times, and jitter, is reported over the pressure range 0–3 bar gauge, as a continuation of work from similar characterization with this switch filled with SF6 with different gap spacings. When filled with mixtures of 1,3,3,3-tetrafluoropropene (HFO-1234ze) and N2, the breakdown voltage can be increased by up to ~306% and ~191% under negative and positive polarities, respectively, of that using 100% N2. These results were achieved with gas mixtures consisting of 80% N2 and 20% HFO-1234ze, by pressure. The maximum negative polarity triggering range was 13.6 kV, comparable to that achieved previously using SF6. The measured delay time and calculated jitter were generally found to increase with increasing pressure, and with increasing percentage (from 5% to 20%) of HFO-1234ze in the gas mixtures. von Laue statistical analysis of time-to-breakdown data showed that both the formative time and statistical time increased with increasing pressure, and with increasing percentage of HFO-1234ze in the gas mixtures. The formative time under negative polarity was significantly longer than that for positive polarity. The results indicate that HFO-1234ze may be considered as a suitable candidate to replace SF6 for switching applications, although there are some operational observations that require further investigation. [ABSTRACT FROM AUTHOR]

Surface discharges along oil-immersed solids used as insulators and supports in high-voltage pulsed-power equipment can lead to catastrophic system failures. To achieve reliable compact pulsed-power systems, it is important to quantify the electrical fields at which surface flashover, or other types of breakdown event, will occur for different dielectric materials. This paper reports the observed behavior of samples of polypropylene, low-density polyethylene, ultrahigh-molecular-weight polyethylene, Rexolite, and Torlon, which were subjected to impulse voltages of peak amplitude of 350 kV and a rise time of 1 \mu\s. The cylindrical samples were located between pairs of electrodes immersed in insulating oil. Breakdown events were studied under both nonuniform- and uniform-field conditions, with sample lengths being chosen so that the breakdown events occurred on the rising edge of the impulse. Ultrahigh-molecular-weight polyethylene showed the highest average breakdown field, which is 645 kV/cm, in uniform fields, and the corresponding breakdown field was reduced to \sim400 kV/cm in the nonuniform fields. Weibull plots of the various sets of results are presented, providing comparative data for system designers for the appropriate choice of dielectric materials to act as insulators for high-voltage pulsed-power machines. [ABSTRACT FROM PUBLISHER]

Comprehensive knowledge and understanding of the breakdown behavior of solid–gas interfaces are important for the development, optimization, and coordination of insulation in practical high-voltage (HV) gas-insulated systems (GISs) that are widely used in the power and pulsed power industries. However, despite significant research efforts focused on the characterization of the breakdown parameters and properties of complex gas-filled HV systems, the basic mechanisms that underpin the development of discharges in such solid–gas topologies are not fully understood. This lack of knowledge is particularly noticeable in the case of solid–gas interfaces stressed with HV impulses. This study is aimed at the experimental investigation of the breakdown behavior of solid–gas interfaces, formed between solid dielectrics and common gases: dry air, N2, and CO2 at atmospheric pressure. Four different solid-dielectric materials, PTFE, HDPE, Delrin, and Macor, with relative permittivities in the range from 2.1 to 6.3, were used in this work. The solid–gas interfaces formed by these dielectric materials and the surrounding gases were stressed with positive and negative HV impulses. The breakdown voltage and time to breakdown were obtained for all combinations of solid–gas interfaces using both positive and negative impulses, with a nominal rise time of $\sim 1.9~\mu \text{s}$. A digital camera operated in the open-shutter regime was used to obtain images of the breakdown spark channels that were classified according to their propagation paths. The results obtained in this study will help in further understanding of the breakdown behavior of solid–gas interfaces and can be used in the development and optimization of dielectric topologies for use in GISs. [ABSTRACT FROM AUTHOR]

This paper investigated hydroxyl radicals and hydrogen peroxide formation under a needle-plate electrode configuration using positive-polarity dc discharges generated in air, nitrogen, and helium. The discharge mode in air and nitrogen was found to change above ultrapure water; initially, a nanosecond pulse discharge was observed, transitioning to a diffuse discharge due to the increasing conductivity of the water. The discharge in helium was a nanosecond pulse discharge and the repetition rate increased with increasing water conductivity. It was found that hydroxyl radicals contribute to 7%, 78%, and 70% of hydrogen peroxide formation when using the ultrapure water in air, nitrogen, and helium, respectively. It is suggested that hydroxyl radicals are formed by water reactions with energetic positive ions and the neutral particles, such as N2+, He+, O, H, and HO2. Part of hydrogen peroxide is directly formed from atoms and radical reactions with water in nitrogen and helium, while oxygen reactions are heavily involved for hydrogen peroxide formation in air. A fluorophotometry method, using terephthalic acid, was used to directly quantify the formation of hydroxyl radicals and compared with the tert-butanol method. [ABSTRACT FROM AUTHOR]

One of the critical components of high energy density pulsed power systems used to generate short high-voltage and high-power impulses is gas-filled plasma closing switch (PCS). In recent years, significant research efforts have been aimed at finding environmentally friendly gases which can be used in the PCSs, and several gases including dry air, nitrogen, carbon dioxide, argon, and their mixtures have been considered as potentially suitable working fluids in such switches. However, the lack of knowledge of the breakdown characteristics of complex switching topologies filled with these gases limits their practical applications. Therefore, further investigation of the breakdown performance of PCSs is required, in order to establish their applicability for practical use in high-voltage pulsed power systems. This paper reports on the investigation of the breakdown characteristics of a triggered PCS topology with corona discharge electrodes. The self-breakdown voltage of the switch, variation in the self-breakdown voltage, time to breakdown, and jitter have been obtained for the switch filled with “zero grade” air, N2, CO2, and an Ar/O2 mixture up to a pressure of 10 bar (abs). It was shown that the switch can provide a stable breakdown performance with jitter as low as ~1 ns. [ABSTRACT FROM AUTHOR]

In this paper, the relationship between reduced electric field and ozone efficiency was determined between $\sim 120$ and 280 Td, with an optimized efficiency of $\sim 207$ g/kWh at $\sim 123$ Td. An equivalent circuit with stray capacitance was used to analyze the filament current in the barrier discharge. The statistical distribution of the filament currents was found to change with different conditions, observing decreased mean amplitude and a narrower distribution with increased pressure and barrier thickness. Under the same reduced electric field, higher ozone efficiency was achieved at a lower current and narrower distribution. [ABSTRACT FROM AUTHOR]

Chemical oxidation and the bactericidal capabilities of nonthermal plasma discharges can be used in different practical applications, such as biodecontamination, sterilisation of medical equipment, waste water treatment, syn-gas treatment, and others. In this paper, the oxidation and biodecontamination effects of impulsive plasma discharge, which propagate across a liquid sample/air interface (surface discharges), and through the bulk of a liquid sample (direct discharges), have been investigated. The oxidizing capability was analyzed by measuring the degree of decolorization of indigo carmine dye in water solutions. Gram-negative and gram-positive bacterias, E. coli and S. aureus, respectively, were used as model microorganisms in the investigation of the biocidal effects of plasma discharges. Surface and direct plasma discharges were generated by high-voltage impulses of both polarities, with the magnitudes of 20, 24, and 28 kV, and the chemical oxidation and biodecontamination capabilities of such discharges have been obtained and analyzed. It has been established that the defining factor in the chemical and biological effects of plasma discharges is the normalized delivered charge (dose). The results obtained in this paper show that surface discharges have greater biodecontamination capability as compared with direct transient plasma discharges. Also, it was shown that the decontamination rate of E. coli is more than double than that of S. aureus. [ABSTRACT FROM AUTHOR]

Pulsed electric fields (PEFs) can cause irreversible damage to bio-membranes and may result in inactivation of microorganisms. The aim of this paper is to investigate the PEF treatment of the yeast Saccharomyces cerevisiae, using a novel treatment cell with parallel-plane electrodes coated with a 2- \mu \textm thin TiO2 film. Two different PEF waveforms, square and exponential, with magnitudes of 67 and 80 kV/cm were used in this study. The efficacy of the PEF treatment was assessed by a comparison of the surviving treated and untreated yeast populations, and it was shown that a treatment cell with TiO2-coated electrodes can be successfully used for the PEF treatment of microorganisms: 3-log10 reduction in the yeast population was achieved with 100 impulses. The energy efficacy of the PEF process in the proposed treatment cell has been compared with the energy losses in the PEF treatment cell with uncoated, conductive electrodes. It is shown that the electrodes coated with TiO2 provide better performance compared with the traditional uncoated electrodes. [ABSTRACT FROM AUTHOR]

Air-borne micrometer and submicrometer particles produced by anthropogenic sources contaminate atmospheric air, especially in large cities where both population and industrial activities are higher leading to a reduced air quality. Recent research has pointed out particles less than 2.5 \mum in diameter (PM2.5) as a potential health hazard. To address this issue, stricter legislation has been put into force to reduce PM2.5 emissions. This paper is focused on the development of an impulsive microelectrostatic precipitation technology for charging and removal of fine air-borne particles in an economically feasible way. In this paper, a compact coaxial precipitator has been developed for possible indoor air cleaning applications. High-voltage impulses together with dc voltage have been used for energization of the reactor as it has been shown to enhance the precipitation efficiency. This precipitation system has been used for removal of fumes and fine air-borne particles from ambient air. In addition to the experimental part, analytical work has been conducted to optimize the electrostatic precipitation process and to reduce its power consumption. [ABSTRACT FROM PUBLISHER]