Effects of Graphene Coatings on hindering Space Charge injection in Epoxy Resin

The reliability of epoxy resins (and dielectrics in general) employed for HVDC applications is significantly affected by space charge accumulation in the insulating material. Several methods have been tested to limit the injection and accumulation of space charge. In this work, planar specimens featuring graphene coatings were tested. Measurements of space charge accumulation, conductivity and permittivity at different temperatures (from 30°C to 60°C) and fields (from 30 kV/mm to 50 kV/mm) were carried out on epoxy specimens with and without coatings. Results show accumulation of space charge for low fields and temperatures in the reference specimens, while a reduction can be noticed with a layer of graphene coating. On the other hand, at higher fields or temperatures, the effect is reversed

Discovery of an unknown conduction mechanism in insulating polymers

Polymer dielectrics are widely used in electrical and electronic apparatus and devices because of their capability to insulate conductors, withstand high fields and suffer negligible conductive losses. Their near-to-zero conductivity has been explained in terms of long-accepted theories of electronic and ionic transport that lead to the accumulation of local net charge regions at high electric fields. Here the authors describe a previously unknown conduction mechanism consisting of small bipolar ultra-fast charge pulses crossing the polymer with the mobility, as large as, 4 to 5 orders of magnitude greater than that of the previously known. The authors show that this motion is a consequence of molecular relaxation processes triggered by the electric field locally enhanced by the pulses themselves. Pulse accumulation at the electrodes increases interface field and thus contributes substantially towards premature failure in insulating dielectrics in DC fields

Experimental Investigation of the Effect of Transient Overvoltages on XLPE-insulated HVDC Cables

HVDC cables are subject to several types of impulses superimposed on the rated DC voltage during their service lifetime. Temporary Overvoltages (TOVs) and Superimposed Switching impulses (SSIs) are considered some of the most challenging due to the relatively long impulse duration. This paper aims at investigating experimentally the effect of TOVs and SSIs on XLPE insulation for extruded HVDC cables. 0.15-mm-thick DC-XLPE specimens, aged by applying TOVs and SSIs, are characterized using dielectric analyzer and Fourier Transform InfraRed spectroscopy (FTIR) to detect the aging effects on the insulation. Results show an increase in the imaginary part of permittivity, ε", accompanied with the appearance of additional dipolar polarization losses peaks. The amplitude and frequency of the aforementioned peaks vary with the amplitude and the number of applied TOVs and SSIs. An increase in electrical conductivity is also noticed with aging. FTIR results show absorbance peaks in the aged specimens likely due to the intramolecular bonds rupture accompanied with the formation of aging products. In summary, SSIs and TOVs cause a noticeable reduction of insulating properties in XLPE specimens. The higher the peak of the transient, the greater the aging effect

Spatio-temporal distribution of the infestations of Coelaenomenodera lameensis Berti and Mariau (Coleoptera, Chrysomelidae) an oil palm tree (Elaeis guineensis Jacq.) pest in Toumanguié (Côte d’Ivoire)

Spatio-temporal distribution of Coelaenomenodera lameensis Berti and Mariau, 1999, pest of palm oil tree (Elaeis guineensis Jacquin, 1963) was carried out on 1226 ha of an industrial plantation at Toumanguié (south-east of Côte d’Ivoire). Temporal distribution of population established the existence, according to the years, of favorable periods of Coelaenomenodera lameensis infestations. Eight peaks of infestation were observed during 24 months. Infestation cycles proceeds each 90 days. Spatial distribution of the infestations revealed experimental plots having recorded between 0 and 8 months of infestation during the 2 years of investigation. This distribution proved to be independent of the age of the plots. Infestations were also independent of abiotic factors (rainfall, temperature and relative humidity). Larvae at stages 1, 2, 3 and 4 are mostly responsible of the damages observed in the fields.Key words: Coelaenomenodera lameensis; Elaeis guineensis; spatio-temporal distribution; Côte d’Ivoir

Simulation and modelling of transient electric fields in hvdc insulation systems based on polarization current measurements

Simulating and modelling electric field dynamics in the insulation of medium-and high-voltage DC electrical systems is needed to support insulation design optimization and to evaluate the impact of voltage transients on ageing mechanisms and insulation reliability. In order to perform accurate simulations, appropriate physical models must be adopted for the insulating material properties, particularly conductivity, which drives the electric field in a steady-state condition and contributes to determining the field behavior during voltage and load transients. In order to model insulation conductivity, polarization, and conduction, mechanisms must be inferred through charging and discharging current measurements, generally performed at different values of electric field and temperatures in flat specimens of the material under study. In general, both mechanisms are present, but one of them may be predominant with respect to the other depending on type of material. In this paper, we showed that models based on predominant polarization mechanisms were suitable to describe impregnated paper, but not polymers used for HV and MV DC insulation. In the latter case, indeed, trapping–detrapping and conduction phenomena were predominant compared to polarization, thus conductivity models had to be considered, in addition to or as a replacement of the polarization model, in order to carry out proper electric field simulations

Evaluation of the Baltimore Health Corps Pilot: An Economic and Public Health Response to the Coronavirus

The Bal­ti­more Health Corps was a city-run pilot launched in June 2020 and concluding in December, 2021. The pilot simul­ta­ne­ous­ly addressed two issues: the spread of COVID-19 and the result­ing employ­ment cri­sis faced by Bal­ti­more res­i­dents.The Bal­ti­more City Health Depart­ment and the Mayor's Office of Employ­ment Devel­op­ment led the Bal­ti­more Health Corps, draw­ing on their expe­ri­ences with equi­table recruit­ment and hir­ing prac­tices, work­force-sup­port­ing activ­i­ties and pub­lic health work­er train­ing. Togeth­er, they led a team of pub­lic and pri­vate part­ners that includ­ed the Bal­ti­more Civic Fund, Bal­ti­more Corps, Health­Care Access Mary­land (HCAM), Jhpiego and the Mayor's Office of Per­for­mance and Inno­va­tion.The ini­tia­tive tracked those who con­tract­ed the virus at the height of the pan­dem­ic and con­nect­ed COVID-19-pos­i­tive indi­vid­u­als with test­ing, resources and oth­er assis­tance. In doing so, the Bal­ti­more Health Corps also placed unem­ployed work­ers on a path to high-qual­i­ty, last­ing careers via tem­po­rary posi­tions as com­mu­ni­ty health work­ers with the Bal­ti­more City Health Depart­ment and Health­Care Access Mary­land (HCAM). The pro­gram hired from a pool of Bal­ti­more res­i­dents who reflect­ed the city's racial and eth­nic demo­graph­ics and were unem­ployed, under­em­ployed or fur­loughed because of the pandemic. By Sep­tem­ber 2021, 336 health work­ers had received train­ing and took on roles with­in either the Health Corps' con­tact trac­ing and out­reach pro­gram or the care coor­di­na­tion and access program.While these health work­er posi­tions were intend­ed to last just eight months, as the pan­dem­ic per­sist­ed, the jobs were extend­ed thanks to fund­ing from the Amer­i­can Res­cue Plan Act. As of May 2022, 126 Bal­ti­more Health Corps work­ers remain employed with either the health depart­ment or HCAM, while 119 for­mer staff mem­bers have since moved on to oth­er employ­ment opportunities.This is the Final Report to follow the Early Lessons Report for the Baltimore Health Corps Pilot Study. Readers are encouraged to review the Early Lessons Report for a detailed description of the formation of the Pilot Study, the role of each partner, as well as findings from the first year of the Pilot Study

Validation of an indirect nonthermal plasma sterilization process for disposable medical devices packed in blisters and cartons

Nowadays, the majority of the processes used to sterilize disposable medical devices have several drawbacks in terms of safety, energy consumption, and costs. In this work, a sterilization method based on an indirect nonthermal plasma treatment is presented. The main advantages of this method are low environmental impact, absence of harmful chemical compounds' storage, and backward compatibility relative to production, sterilization, and shipping chain. The sterilization of disposable devices, enclosed inside their protective packaging, is achieved by exploiting reactive species produced by a Dielectric Barrier Discharge plasma reactor. Various devices have been subjected to a 2-h treatment, achieving complete sterilization based on USP and EU-PHARMA protocols. Pretreatment of carton packaging has been necessary to guarantee a complete sterilization process

Characterisation of an atmospheric-pressure air DBD discharge

Combining the advantages of non-equilibrium plasmas with the ease of atmospheric-pressure operation, dielectric barrier discharges (DBD) are widely used in many fields and applications, including ozone production, sterilization, tumour treatments and surface modification

A reference protocol for comparing the biocidal properties of gas plasma generating devices

The growing interest in the use of non-thermal, atmospheric pressure gas plasmas for decontamination purposes has resulted in a multiplicity of plasma- generating devices. There is currently no uni versally approved method of comparing the biocidal performance of such devices and in the work described here spores of the Gram positive bacterium Bacillus subtilis (ATCC 6633) are proposed as a suitable reference biological agent. In order to achieve consistency in the form in which the biological agent in question is presented to the plasma, a polycarbonate membrane loaded with a monolayer of spores is proposed. The advantages of the proposed protocol are evaluated by comparing inactivation tests in which an alternative microorganism (methicillin resistant Staphylococcus aureus - MRSA) and the widely-used sample preparation technique of directly pipetting cell suspensions onto membranes are employed. In all cases, inactivation tests with either UV irradiation or plasma exposure were more reproducible when the proposed protocol was followed

Characterisation of an atmospheric-pressure dielectric barrier discharge in air and a protocol for comparing the biocidal properties of plasma devices [Abstract]

Characterisation of an atmospheric-pressure dielectric barrier discharge in air and a protocol for comparing the biocidal properties of plasma devices [Abstract