80 research outputs found
Impulse-driven surface breakdown data : a Weibull statistical analysis
No full textSurface breakdown of oil-immersed solids chosen to insulate high-voltage, pulsed-power systems is a problem that can lead to catastrophic failure. Statistical analysis of the breakdown voltages, or times, associated with such liquid-solid interfaces can reveal useful information to aid system designers in the selection of solid materials. Described in this paper are the results of a Weibull statistical analysis, applied to both breakdown-voltage data and time-to-breakdown data generated in gaps consisting of five different solid polymers immersed in mineral oil. Values of the location parameter γ provide an estimate of the applied voltage below which breakdown will not occur, and under uniform-field conditions, γ varied from 192 kV (480 kV/cm) for polypropylene to zero for ultra-high molecular weight polyethylene. Longer times to breakdown were measured for UHMWPE when compared with the other materials. However, high values of the shape parameter β reported in the present paper suggest greater sensitivity to an increase in applied voltage – that is, the probability of breakdown increases more sharply with increasing applied voltage for UHMWPE compared to the other materials. Analysing peak-applied-voltage data, only PP consistently reflected a low value of β across the different sets of test conditions. In general, longer mean times to breakdown were found for solid materials of εr more closely matched to that of the surrounding mineral oi
Superposition of DC voltage and submicrosecond impulses for energization of electrostatic precipitators
No full textThis paper discusses the development of an impulsive microelectrostatic precipitation technology, which uses superposition of submicrosecond high-field pulses and dc electric field. Short impulses allow the application of higher voltages to the ionization electrodes of a precipitation system without the initiation of breakdown. These higher levels of electric field generate higher ionic concentrations, resulting in more efficient charging of the airborne particles, and can potentially improve precipitation efficiency. This work is focused on the analysis of the behavior of impulsive positive corona discharges in a coaxial reactor designed for precipitation studies. The efficiency of precipitation of coarse and fine particles has been investigated using different dc and impulse voltage levels in order to establish optimal energization modes
The triggered behavior of a controlled corona stabilised cascade switch
No full textCorona stabilised switches have been shown to have advantages in pulse power switching applications due to their high repetition rates and low jitter. Work performed in recent years by the High Voltage Technologies Group within the Department of Electronic and Electrical Engineering at the University of Strathclyde has shown that the operating voltage range of such switches can be extended by using a multi-gap cascade configuration. One particular multi-gap topology was shown to operate under pressure at 100 kV with a switching jitter of 2ns. It has since been shown that by modifying the topology of the corona sources on the electrodes, it is possible to control the grading of the voltage distribution across the gaps in the cascade. The voltages across each gap and the self-break behaviour of the cascade were found to be in close agreement with the values predicted from the corona emission characteristics for the tested electrode topologies. This paper reports on a further examination of the behaviour of the corona controlled switching topology, where triggered operation of the switch has been investigated for different voltage distributions across the cascade gaps
Bactericidal effect of corona discharges in atmospheric air
No full textThe present paper explores the possibilities of using impulsive and steady-state corona discharges for bio-decontamination operations. A high tension tubular corona electrode was stressed with positive or negative dc voltage with magnitude up to 26 kV, and a grounded mesh was used as an opposite electrode. Different operational regimes of this corona generator were investigated for the production of ozone in air flow and the inactivation of microorganisms. The test microorganisms used in this work were Escherichia coli and Staphylococcus aureus, populations of which were seeded onto agar plates. These bacterial plates were located behind the grounded mesh electrode to assess bactericidal efficacy. The results show that corona discharges have a strong bactericidal effect, for example positive flashing corona discharges were able to reduce populations of the test microorganism by 94% within a 30-60 sec time interval. Negative steady-state corona discharges also produce noticeable bactericidal effect, reducing population of E. coli and S. aureus by more than 97% within 120 sec energisation interval. The bactericidal efficiency of different corona discharge modes and its correlation with ozone levels produced by these discharges is discussed. The results obtained in this work will help in the design and development of compact plasma systems for environmental application
Masking of Lewis acidity trends in the solid-state structures of trichlorido- and tribromido(2,2′:6′,2′′-terpyridine-κ3N,N′,N′′)gallium(III)
No full textThe molecular structures of trichlorido(2,2':6',2 ''-terpyridine-kappa N-3,N',N '')gallium(III), [GaCl3(C15H11N3)], and tribromido(2,2': 6',2 ''-terpyridine-kappa N-3,N',N '')gallium(III), [GaBr3(C15H11N3)], are isostructural, with the Ga-III atom displaying an octahedral geometry. It is shown that the Ga-N distances in the two complexes are the same within experimental error, in contrast to expected bond lengthening in the bromide complex due to the lower Lewis acidity of GaBr3. Thus, masking of the Lewis acidity trends in the solid state is observed not only for complexes of group 13 metal halides with monodentate ligands but for complexes with the polydentate 2,2':6',2-'' terpyridine donor as well
Investigating ways to prevent electrical arc flash
No full textElectrical arc flash hazard mitigation techniques focus on the reduction of hazard levels in an electrical power system. Analysis of arc incident energies pre- and post-mitigation to reduce hazard levels shows that risk control measures can lead to significant reductions in potential harm and damage should an arc flash occur. However, mitigation methods alone do not necessarily prevent arc initiation. This paper reports an investigation into the initiation of electrical arcs within the context of a study into new approaches to reduce the hazard posed by arc flash. In addition to the local physical arrangement of the busbars, onset of the arc is influenced by specific weaknesses or defects of the insulation system. However, the influence of these local factors diminishes once the arc is formed. Thereafter, arc current and the power dissipated in the arc depend both on the ability of the surrounding network to sustain the electrical discharge and on transient interactions between the impedance of the feeder network and the impedance of the arc itself. To study arc initiation with the aim of identifying factors that could reduce the likelihood of arc onset, measurements of short-term arc characteristics under various initial conditions are presented. Measurements primarily concern the time-domain transient voltage and current waveforms in an experimental configuration designed to allow variation of parameters that may influence arc initiation. These waveforms are captured on a nanosecond timescale so that the temporal development of arc power and impedance can be analysed as a function of different initiation mechanisms. Results are analysed to show how the impedance of the electrical driving circuit and the quantity of electrical energy stored in the circuit physically close to the arc affect the arc evolution and the magnitude of the power dissipated
Field-time breakdown characteristics of air, N2, CO2, and SF6
No full textThe dielectric performance of gases in insulation systems used in high voltage power and pulsed power applications is a subject of intensive theoretical and experimental investigations. Transient breakdown processes in gases stressed with short, high-field impulses, have been studied for many decades. However, there are still significant gaps in the understanding of the main breakdown processes and mechanisms associated with fast transient breakdown processes in gases. This knowledge is important for the optimization of gaseous insulating systems and for the coordination of gaseous insulation in power and pulsed power apparatuses. This information is also required for the development of gas-filled components such as circuit breakers and plasma closing switches. This article is aimed at the analysis of the field-time breakdown characteristics of air, N2, CO2, and SF6, using kinetic and drift-diffusion approaches. The kinetic approach is based upon the avalanche-to-streamer transition criterion, while the fluid drift-diffusion model requires self-consistent numerical solution of the continuity equations for charged species, and the Poisson equation for the electric field. The time to breakdown as a function of the applied field was obtained for all investigated gases. The obtained analytical results agree well with the experimental data reported in the literature, which suggests that both approaches can be used for insulation coordination, and for the development of gas-insulated power and pulsed power systems and components
Author Correction: Chronicles of nature calendar, a long-term and large-scale multitaxon database on phenology (Scientific Data, (2020), 7, 1, (47), 10.1038/s41597-020-0376-z)
No full textOvaskainen, O., Meyke, E., Lo, C., Tikhonov, G., Delgado, M.M., Roslin, T., Gurarie, E., Abadonova, M., Abduraimov, O., Adrianova, O., Akimova, T., Akkiev, M., Ananin, A., Andreeva, E., Andriychuk, N., Antipin, M., Arzamascev, K., Babina, S., Babushkin, M., Bakin, O., Barabancova, A., Basilskaja, I., Belova, N., Belyaeva, N., Bespalova, T., Bisikalova, E., Bobretsov, A., Bobrov, V., Bobrovskyi, V., Bochkareva, E., Bogdanov, G., Bolshakov, V., Bondarchuk, S., Bukharova, E., Butunina, A., Buyvolov, Y., Buyvolova, A., Bykov, Y., Chakhireva, E., Chashchina, O., Cherenkova, N., Chistjakov, S., Chuhontseva, S., Davydov, E.A., Demchenko, V., Diadicheva, E., Dobrolyubov, A., Dostoyevskaya, L., Drovnina, S., Drozdova, Z., Dubanaev, A., Dubrovsky, Y., Elsukov, S., Epova, L., Ermakova, O.S., Ermakova, O., Esengeldenova, A., Evstigneev, O., Fedchenko, I., Fedotova, V., Filatova, T., Gashev, S., Gavrilov, A., Gaydysh, I., Golovcov, D., Goncharova, N., Gorbunova, E., Gordeeva, T., Grishchenko, V., Gromyko, L., Hohryakov, V., Hritankov, A., Ignatenko, E., Igosheva, S., Ivanova, U., Ivanova, N., Kalinkin, Y., Kaygorodova, E., Kazansky, F., Kiseleva, D., Knorre, A., Kolpashikov, L., Korobov, E., Korolyova, H., Korotkikh, N., Kosenkov, G., Kossenko, S., Kotlugalyamova, E., Kozlovsky, E., Kozsheechkin, V., Kozurak, A., Kozyr, I., Krasnopevtseva, A., Kruglikov, S., Kuberskaya, O., Kudryavtsev, A., Kulebyakina, E., Kulsha, Y., Kupriyanova, M., Kurbanbagamaev, M., Kutenkov, A., Kutenkova, N., Kuyantseva, N., Kuznetsov, A., Larin, E., Lebedev, P., Litvinov, K., Luzhkova, N., Mahmudov, A., Makovkina, L., Mamontov, V., Mayorova, S., Megalinskaja, I., Meydus, A., Minin, A., Mitrofanov, O., Motruk, M., Myslenkov, A., Nasonova, N., Nemtseva, N., Nesterova, I., Nezdoliy, T., Niroda, T., Novikova, T., Panicheva, D., Pavlov, A., Pavlova, K., Petrenko, P., Podolski, S., Polikarpova, N., Polyanskaya, T., Pospelov, I., Pospelova, E., Prokhorov, I., Prokosheva, I., Puchnina, L., Putrashyk, I., Raiskaya, J., Rozhkov, Y., Rozhkova, O., Rudenko, M., Rybnikova, I., Rykova, S., Sahnevich, M., Samoylov, A., Sanko, V., Sapelnikova, I., Sazonov, S., Selyunina, Z., Shalaeva, K., Shashkov, M., Shcherbakov, A., Shevchyk, V., Shubin, S., Shujskaja, E., Sibgatullin, R., Sikkila, N., Sitnikova, E., Sivkov, A., Skok, N., Skorokhodova, S., Smirnova, E., Sokolova, G., Sopin, V., Spasovski, Y., Stepanov, S., Stratiy, V.I., Strekalovskaya, V., Sukhov, A., Suleymanova, G., Sultangareeva, L., Teleganova, V., Teplov, V., Teplova, V., Tertitsa, T., Timoshkin, V., Tirski, D., Tolmachev, A., Tomilin, A., Tselishcheva, L., Turgunov, M., Tyukh, Y., Vladimir, V., Vargot, E., Vasin, A., Vasina, A., Vekliuk, A., Vetchinnikova, L., Vinogradov, V., Volodchenkov, N., Voloshina, I., Xoliqov, T., Yablonovska-Grishchenko, E., Yakovlev, V., Yakovleva, M., Yantser, O., Yarema, Y., Zahvatov, A., Zakharov, V., Zelenetskiy, N., Zheltukhin, A., Zubina, T., Kurhinen, J
Hydroxyl radical production in DC streamer discharge
No full textPlasma-induced advanced oxidation processes do not suffer from the drawbacks, such as carcinogenic by-products, associated with conventional water treatment, and enable the removal of micro-pollutants. The high oxidation strength of hydroxyl radicals enables degradation of resistant contaminants. Many reactions are known to occur at the plasma-water interface; however, the mechanisms of hydroxyl radical production are still not clear. To understand the physical and chemical processes occurring at the plasma-water interface, this research involved investigation of the hydroxyl radicals produced during d.c. streamer discharges. A needle-plate electrode configuration in atmospheric air was used, with the treated solution used as the ground electrode. To understand the effects of polarity and gas type on hydroxyl radical production, both positive- and negative-polarity energization in air, nitrogen and helium were investigated. Plasma filaments were developed from the needle electrode, which was in contact with the solution. Terephthalic acid (TA) was used as a scavenger of hydroxyl (OH) radicals, with OH density subsequently being quantified by fluorescence emission from 2-hydroxyterephthalic acid (HTA), which is formed through specific reaction between TA and OH. The power inputs in positive pulsed streamer discharges were 0.125 W, 0.18 W and 0.26 W in air, nitrogen and helium, respectively; the corresponding hydroxyl radical production efficiencies were 0.56 mmol/kWh, 1.1 mmol/kWh and 5.94 mmol/kWh, respectively. For negative pulsed streamer discharges in air, the power input was 0.063 W and the efficiency was 1 mmol/kWh. The hydroxyl radical production rates were 2.6× 10-7 Ms-1 in negative air discharges, and 2.7× 10-7 Ms-1, 1.8× 10-6 Ms-1, and 2.2× 10-6 Ms-1 in positive air, nitrogen and helium discharges, respectively
Free and wire-guided spark discharges in water : pre-breakdown energy losses and generated pressure impulses
No full textImpulsive underwater discharges have been investigated for many decades, yet the complex pre-breakdown processes that underpin their development are not fully understood. Higher pre-breakdown energy losses may lead to significant reduction in the magnitude and intensity of the pressure waves generated by expanding post-breakdown plasma channels. Thus, it is important to characterize these losses for different discharge types and to identify approaches to their reduction. The present paper analyses thermal pre-breakdown processes in the case of free path and wire-guided discharges in water: fast joule heating of a small volume of water at the high-voltage electrode and joule heating and the melting of the wire, respectively. The energy required for joule heating of the water and metallic wire have been obtained from thermal models, analysed and compared with the experimental pre-breakdown energy losses. Pressure impulses generated by free path and by wire-guided underwater discharges have also been investigated. It was shown that wire-guided discharges support the formation of longer plasma channels better than free path underwater discharges for the same energy available per discharge. This results in stronger pressure impulses developed by underwater wire-guided discharges. It has been shown that the pressure magnitude in the case of both discharge types is inversely proportional to the observation distance which is a characteristic of a spherical acoustic wave
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