The triggered behavior of a controlled corona stabilised cascade switch

Corona 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

Superposition of DC voltage and submicrosecond impulses for energization of electrostatic precipitators

This 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

Zero-dimensional chemical kinetic simulation of ROS/RNSin pulsed pulsed-discharge exposed water

The concentration variations of reactive oxygen/nitrogen species in water, such as H2O2, NO2 −, and NO3 − generated by pulsed-discharge plasma exposure, are calculated using reaction rates of chemical reactions and acid-base equilibrium in water. The calculated concentrations and pH values are in good agreement with measured data within the range where the significant changes of the measured data are observed. The rate constant for ONOOH generation is estimated to be 7.8 × 103 M−2 s−1, and this value is in good agreement with previously reported values. The generation rates of H2O2, NO2 −, and NO3 − are estimated to be 7.70 × 10−7, 4.10 × 10−7, and 1.10 × 10−7 M s−1, respectively

Impulse-driven surface breakdown data : a Weibull statistical analysis

Surface 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

Comparison between RF and electrical signals from the partial discharge activity of twisted pair cables at reduced pressures

A pressure-controlled test facility has been set up that allows the PD behaviour of polymer insulated twisted pair samples exposed to 50 Hz AC voltages in the range of 0 to 10 kV to be characterised. Resulting PD activity is quantified using the methods defined in IEC standard 60270 and by using a simple monopole antenna to detect the RF signals excited inside the pressure vessel by the discharges. This paper gives the results of preliminary tests performed on samples of wire insulated with Ethylenetetraflourethylene, Silicon Rubber and Polyvinylchloride in the pressure range between 103 and 105 Pa in atmospheric air. The dependence of PD inception voltage on the environmental pressure is reported. Changes in the behaviour of the PD activity; the correlations between the RF and electrical measurements and the frequency components of the RF signals as the applied voltage and pressure are varied are characterised and discussed

Bactericidal effect of corona discharges in atmospheric air

The 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

The influence of magnetite nano particles on the behavior of insulating oils for pulse power applications

The effects of the addition of magnetite nanoparticles on the breakdown strength of three insulating liquids have been examined. The liquids considered are: a mineral transformer oil; a synthetic ester liquid, Midel 7131, and a specialist high permittivity liquid for pulse power applications THESO. The expected increases in breakdown strength were observed in the mineral oil and synthetic ester liquids. However in the case of the high permittivity liquid no significant changes in the breakdown strength were observed. Possible explanations for the differences in the observed behavior for the THESO insulating liquid are discussed

Polarity effects on breakdown of short gaps in a point-plane topology in air

Electrical breakdown in air in a point-plane topology involves complex processes that are still not fully understood. Unlike uniform-field topologies, the highly-divergent fields produced by point-plane topologies create pre-breakdown corona with volumetric space charge. It is known that space charges developed by corona discharge have significant impacts on the breakdown voltage in non-uniform electrode topologies. With large inter-electrode gaps (>cm) the breakdown voltage for a HV point cathode in air at atmospheric pressure is noticeably larger than a HV point anode. However, this paper shows that in shorter point-plane gaps in air (less than ~10 mm), in the air pressure range 0.1-0.35 MPa, an HV point anode has a similar breakdown voltage which eventually is surpassed by the HV point cathode as the inter-electrode gap is increased. The inter-electrode gap at which the HV cathode has a higher hold-off voltage is found to be dependent on the gas pressure and radius of the point electrode

Investigating the susceptibility of laboratory-generated bacterial aerosols to antimicrobial 405 nm light

Airborne transmission of infectious organisms is a major concern within the healthcare environment. A number of methods for 'whole room' decontamination, such as antimicrobial 405nm light, are being developed, and it is important that efficacy against airborne, as well as surface-deposited contamination is established. This study demonstrates evidence of the dose-response kinetics of airborne bacterial contamination when exposed to 405nm light. Aerosols of Staphylococcus epidermids, generated using a 6-Jet Collison nebuliser, were introduced into an aerosol chamber designed to maintain prolonged airborne suspension and circulation. Aerosolized bacteria were exposed to increasing doses of 405nm light, and air samples were extracted from the chamber using a BioSampler liquid impinger, with viability analysed using pour plate culture. Initial results have demonstrated successful aerosol inactivation, with a 98.4% reduction (1.8 log10 reduction) achieved with 1-hour exposure to low irradiance 405nm light (P=<0.001). Natural decay of the suspended aerosol was observed, however this was significantly less than achieved with light treatment (P=0.004). Inactivation using ultraviolet (UV) light was also investigated in order to quantify the comparative efficacy of these antimicrobial light regions.Overall, results have provided early evidence of the susceptibility of bacterial aerosols to antimicrobial 405 nm light. Although less germicidally efficient than UV-light, the benefits of 405 nm light in terms of increased safety for human exposure, provide advantages for a number of applications, including continuous 'whole room' environmental decontamination, where reducing levels of airborne bacteria should contribute to reducing infections arising from airborne contamination

Efficacy of antimicrobial 405 nm blue-light for inactivation of airborne bacteria

Airborne transmission of infectious organisms is a considerable concern within the healthcare environment. A number of novel methods for ‘whole room’ decontamination, including antimicrobial 405 nm blue light, are being developed. To date, research has focused on its effects against surface-deposited contamination; however, it is important to also establish its efficacy against airborne bacteria. This study demonstrates evidence of the dose-response kinetics of airborne bacterial contamination when exposed to 405 nm light and compares bacterial susceptibility when exposed in three different media: air, liquid and surfaces. Bacterial aerosols of Staphylococcus epidermidis, generated using a 6-Jet Collison nebulizer, were introduced into an aerosol suspension chamber. Aerosolized bacteria were exposed to increasing doses of 405 nm light, and air samples were extracted from the chamber using a BioSampler liquid impinger, with viability analysed using pour-plate culture. Results have demonstrated successful aerosol inactivation, with a 99.1% reduction achieved with a 30 minute exposure to high irradiance (22 mWcm-2) 405 nm light (P=0.001). Comparison to liquid and surface exposures proved bacteria to be 3-4 times more susceptible to 405 nm light inactivation when in aerosol form. Overall, results have provided fundamental evidence of the susceptibility of bacterial aerosols to antimicrobial 405 nm light treatment, which offers benefits in terms of increased safety for human exposure, and eradication of microbes regardless of antibiotic resistance. Such benefits provide advantages for a number of applications including ‘whole room’ environmental decontamination, in which reducing levels of airborne bacteria should reduce the number of infections arising from airborne contamination