Electrical Network-Based Time-Dependent Model of Electrical Breakdown in Water

A time-dependent, two-dimensional, percolative approach to model dielectric breakdown based on a network of parallel resistor–capacitor elements having random values, has been developed. The breakdown criteria rely on a threshold electric field and on energy dissipation exceeding the heat of vaporization. By carrying out this time-dependent analysis, the development and propagation of streamers and prebreakdown dynamical evolution have been obtained directly. These model simulations also provide the streamer shape, characteristics such as streamer velocity, the prebreakdown delay time, time-dependent current, and relationship between breakdown times, and applied electric fields for a given geometry. The results agree well with experimental data and reports in literature. The time to breakdown (tbr) for a 100 μm water gap has been shown to be strong function of the applied bias, with a 15–185 ns range. It is also shown that the current is fashioned not only by dynamic changes in local resistance, but that capacitive modifications arising from vaporization and streamer development also affect the transient behavior

Comparison of parameters in the formation of corrosive sulphide deposition on copper conductors

International audienceCopper is a catalyst that promotes the formation of corrosive sulphur but it is also corroded by the latter. Corrosive sulfur in oil has been identified as the cause of recent failures in power transformers and shunt reactors. The most common reason of such failures is arcing between adjacent disks or conductors of windings due to the formation of copper sulphide deposition on cellulosic insulating paper. Synergetic effects with temperature, time and oxygen are recognized to play a role in the formation of corrosive sulphur. Which of these factors has the most impact on copper sulphide deposition? To address this concern, a quantitative laboratory technique has been developed. It is shown that by using a series of laboratory experiments in accordance with ASTM D 1275 B, it is possible to investigate this problem and to map the influence of these parameters by manipulating some variables such as oxygen, temperature and time on the copper samples. The obtained results show that temperature is the most influential parameter in the formation of corrosive sulphur. The process is accelerated when both temperature and time act conjointly

Comparison of parameters in the formation of corrosive sulphide deposition on copper conductors

Copper is a catalyst that promotes the formation of corrosive sulphur but it is also corroded by the latter. Corrosive sulfur in oil has been identified as the cause of recent failures in power transformers and shunt reactors. The most common reason of such failures is arcing between adjacent disks or conductors of windings due to the formation of copper sulphide deposition on cellulosic insulating paper. Synergetic effects with temperature, time and oxygen are recognized to play a role in the formation of corrosive sulphur. Which of these factors has the most impact on copper sulphide deposition? To address this concern, a quantitative laboratory technique has been developed. It is shown that by using a series of laboratory experiments in accordance with ASTM D 1275 B, it is possible to investigate this problem and to map the influence of these parameters by manipulating some variables such as oxygen, temperature and time on the copper samples. The obtained results show that temperature is the most influential parameter in the formation of corrosive sulphur. The process is accelerated when both temperature and time act conjointly

Physiopathology of diarrhea in young calves: clinical signs and metabolic disturbances

The aims of the current study were to characterize the main clinical consequences of diarrhea and to identify metabolic disorders due to this neonatal disease in newborn calves (≤30 days of age). Forty seven calves of two selected dairy herds in the province of Constantine were involved in this study. Clinical examination and analysis of blood samples collected from untreated calves over 3 periods (birth to 7 days,8 to 15 days and over 15 days) were carried out from February to October 2013.Hematological (Hemoglobin (HGB) and Hematocrit (HCT)), biochemical (Sodium (Na+), Potassium (K+), Chloride (Cl-) and pH) and organic parameters (Total protein, Glucose, Urea and Creatinine) were analyzed at the onset of diarrhea, before any treatment in diarrheic calves and subsequently compared with the values obtained in clinically healthy calves and standards reported in the literature. Base excess (BE) and the strong ions difference (SID) were also calculated by the previous assays.Results of this study showed that respiratory rate was significantly higher in calves with diarrhea (P0.05) was observed in diarrheic calves. A significant increase in total protein, and an insignificant difference for the rest of the analyzed hematological and biochemical parameters in diarrheic calves were observed at the statistical level P0.05)

Surface modification of aluminum phosphate by sodium dodecylbenzenesulfonate (SDBS) A new nano-structured adsorbent for an improved removal of Ponceau S"

International audienceThe removal of increasing number of pollutants in water needs the search of new adsorbents, or the improvement of known adsorbents. In this paper, the adsorption capacity of aluminum phosphate AlPO4 was investigated after its chemical modification by adsorption of the surfactant sodium dodecylbenzenesulfonate (SDBS). The new adsorbent SDBS-modified AlPO4 was characterized by X-ray diffraction (XRD), Fourier Transform Infra-red (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and the Brunauer, Emmet and Teller (BET) method. SDBS-modified AlPO4 was applied to the removal of Ponceau S (PS) or Acid Red 112 which is suspected to be carcinogenic from aqueous solutions.The influential parameters like pH, PS concentration, contact time and temperature were studied. The results showed that the removal of PS was fast and that the equilibrium was reached in 30 min. The kinetics showed that adsorption followed a pseudo-second-order model and the adsorption at equilibrium was in agreement with the experimental values. The isothermal adsorption led to an adsorption capacity of 60.8 mg/g for SDBS-modified AlPO4. This result shows that the SDBS modification improves the adsorption efficiency of AlPO4. The adsorption models of Langmuir, Freundlich and Sips were applied. Sips model gave the best fitting. The temperature did not affect the adsorption. The regeneration of aluminum phosphate modified by SDBS was carried out by calcination leading to a material which was again modified by SDBS and then used as adsorbent of PS with an adsorption capacity of 28.13 mg/g. © 2020 Elsevier Ltd

A review on pre-breakdown phenomena in ester fluids. Prepared by the international study group of IEEE DEIS liquid dielectrics technical committee

In view of the contemporary scenario and importance of alternative liquid dielectrics, IEEE DEIS Technical Committee on Liquid Dielectrics laid emphasis on pre-breakdown phenomena of ester dielectric fluids. The present article reports the background knowledge on the breakdown theories and behavior of streamers in insulating oils. The major influencing properties of the streamers aroused in liquid insulating systems are discussed keeping in view of the ester based dielectric fluids. Importantly, modelling of streamers, testing approaches, and review of pre-breakdown phenomena in ester dielectric fluids has been presented

Propagation and structure of streamers in liquid dielectrics

International audienceOur purpose is to present a critical review of the current understanding of streamer propagation in dielectric liquids in order to help define the direction of future research. We show that the molecular structure has a significant effect on streamer propagation. The main parameter affecting propagation is the electronic affinity of the liquid molecule