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High Currents (high + current)

Distribution by Scientific Domains
Physics and Astronomy50%

Terms modified by High Currents

  • high current density
    		•
  • high current efficiency
    		•

    Selected Abstracts

    Application of High Current and Current Zero Simulations of High-Voltage Circuit Breakers

    CONTRIBUTIONS TO PLASMA PHYSICS, Issue 10 2006
    C. M. Franck
    Abstract This paper reports on the use of computational fluid dynamic (CFD) simulations to predict the interruption behaviour of high-voltage circuit breakers (HV-CB) using the self-blast principle. Two different levels of accuracy of the arc model are proven to be sufficiently accurate for simulating the high-current phase and the period around current zero (CZ). For the high-current phase, a simplified equivalent model of the arc is implemented to predict the pressure build-up, and even more important to accurately trace the hot gas from the arcing zone into the exhausts and the heating volume. A detailed analysis of the gas mixing in the heating volume for different arcing times and current amplitudes showed the optimum geometrical design of the heating volume. For the CZ phase, a more detailed arc model is needed including the effects of ohmic heating, radiative energy transfer, and turbulent cooling fully resolved in space and time. The validation with experiments was done and shows good agreement which justifies the use of the implemented model. With it, scaling laws varying only one parameter at a time (pressure and applied current slope) were derived and confirm previously found empirical laws. This is of particular interest, as it is very difficult to derive such scaling laws from experiments where the scatter is always very large and where it is impossible to vary only one parameter at a time. The influence of the most important geometrical parameters of the nozzle on the interruption performance is shown. In addition to previous experimental indications of this, the simulation reveals that turbulent cooling on the arc edge is the main reason for the difference in interruption performance. Moreover, the exact spatio-temporal build-up of arc resistance and with it the detailed understanding of the arc interruption process is possible and shown here for the first time. These simulations enable us to predict HV-CB performance and to minimise the number of development tests and are routinely used in new development projects. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Flow Velocity Effect on Leaf Litter Breakdown in Tufa Depositing System (Plitvice Lakes, Croatia)

    INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 4 2009
    Anita Belan
    Abstract Considerable amount of riparian leaf litter is annually supplied to the cascade Plitvice Lakes and trapped on tufa barriers where it decays together with aquatic macrophytes. These barriers are the sites of heavy calcite precipitation that can widely differ in terms of current velocity. We conducted a leafbag experiment at sites differing in flow velocity and tufa deposition rate. Decomposition of Petasites spp. and Fagus sylvatica was higher under high current (0.80 m/s) and high tufa deposition areas than in low current (< 0.20 m/s) and low tufa deposition areas (k = 0.085 vs. 0.021 for Petasites spp. and 0.009 vs. 0.002 for Fagus sylvatica). We concluded that although tufa deposition could interfere with decomposition by obstructing physical abrasion and also restricting microbial conditioning, thin calcite crusts developed on the surface of the leaves made them more fragile and thus accelerated their decomposition. High current velocity probably magnified this effect by supporting higher tufa deposition and coarser type of tufa fabrics. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    A mini linac based positron source

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009
    Patrice Pérez
    Abstract We have installed in Saclay a demonstration setup for an intense positron source in November 2008. It is based on a compact 6 MeV electron linac to produce positrons via pair production on a tungsten target. A relatively high current of 0.15 mA compensates the low energy, which is below the neutron activation threshold. The expected production rate is 4x1011 fast positrons per second. A set of coils is arranged to select the fast positrons from the diffracted electron beam in order to study the possibility to use a rare gas cryogenic moderator away from the main flux of particles. A first part of the commissioning of the linac has been performed. First attempts at measuring the fast positron flux are underway. This setup is part of a project to demonstrate the feasibility of an experiment to produce the H+ ion for a free fall measurement of neutral antihydrogen (H). Its small size and cost could be of interest for a university laboratory or industry for materials science applications. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    DC characteristics and high frequency response of GaN nanowire metal-oxide-semiconductor field-effect transistor

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    Jeng-Wei Yu
    Abstract We report selected site lateral growth of crystalline [110] GaN nanowire (NW) with high channel mobility of 1050 cm2/V-s on SiO2/p-Si. This scheme enables photolithographic fabrication of top-gated GaN NW-MOSFET of 60 nm dia. and 2 ,m gate length. Device parameters with gm of 25 ,S, saturation current of 90 ,A, and cut-off frequency fT at 14 GHz have been extracted. In an active load configuration of GaN NW-MOSFET inverter we reported voltage gain of 2 and a high current on/off ratio of 104. These observations suggest promising functional diversification of the GaN NW-MOSFET on the Si-based CMOS platform for the sub-50 nm technology nodes. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The Effect of the Anode Loading and Method of MEA Fabrication on DMFC Performance

    FUEL CELLS, Issue 3 2007
    T. V. Reshetenko
    Abstract The influence of the Pt-Ru anode loading and MEA preparation techniques on direct methanol fuel cell (DMFC) performance is studied. Two different anode catalyst layer preparation techniques are employed. One is the direct coating of anode catalyst ink on a membrane to form a catalyst coated membrane, CCManode, and the other is the coating of the ink on the diffusion layers, which generates a catalyst coated substrate, CCSanode. The power density of a combined CCManode/CCScathode MEA is higher than for a CCSanode/CCScathode MEA. The main difference in the performance is observed in the high current density region, where two-phase flow is present and mass transfer processes govern the performance. The CCManode and CCSanode have different macroscopic structures, while showing the same microscopic morphology. Based on their morphological differences, it is expected that the combination of the CCManode and carbon paper provides the more homogeneous removal of CO2 at high currents. The authors suggest that the application of the CCManode with an optimal anode loading improves anode mass transfer, reduces methanol crossover, and enhances the electrochemical reactions. [source]

    Relationship between Contact Voltage Drop and Frictional Coefficient under High-current Sliding Contact

    IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2010
    Takahiro Ueno Member
    Abstract Large DC motors are used in various industrial applications. These motors repeatedly generate arcs between the brush and commutator, because the load change is intense and the current value is also large. In particular, for the case in which the current is concentrated on a part of the brush, brush burnout may occur as a result of overcurrent. Therefore, excellent brushes to withstand arc generation and with good electrical properties are required. In the present paper, we discuss the relation between contact voltage drop and frictional wear for electrical sliding contacts when high currents flow to the brush. Specifically, we investigate the means by which to prevent brush burnout when high-current flows to the brush. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

    The iR drop , well-known but often underestimated in electrochemical polarization measurements and corrosion testing,

    MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2006
    W. Oelßner
    Abstract At first sight the problem of the iR drop and its compensation in electrochemical polarization measurements seems to have only minor significance, but it has actually troubled electrochemists and corrosion scientists for more than a hundred years. For reducing the iR drop in the electrochemical cell, its computation, experimental determination and numerical or automatic electronic compensation numerous scientific and experimental work has been carried out and appropriate suggestions were submitted. These efforts led to commercially available potentiostats with sophisticated facilities for automatic iR compensation. Nevertheless, to date these possibilities have been utilized with a certain hesitancy. Many users underestimate the iR drop, regarding it often merely as a marginal problem, which only has to be taken into account in experiments with very high currents or extremely low conductivity of the electrolyte. Furthermore, there are also doubts and prejudices regarding modern methods of iR compensation, resulting from previous unpleasant experiences or reports on failed experiments with inappropriate equipment or imperfect methods. Reduction or automatic compensation of the iR drop is necessary more frequently than generally assumed and also in most cases possible. On the other hand the application of the different methods is still not completely uncomplicated and requires special experimental experience and care. The aim of the present work is it therefore to give a comprehensive retrospective overview of the ohmic drop problem and the relevant activities to overcome it. [source]

    Thermal and nonthermal factors affecting the quantum efficiency of deep-ultraviolet light-emitting diodes

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2008
    H. Guo
    Abstract The optical characteristics of AlGaN-based multiple-quantum-well (MQW) light-emitting diodes (LEDs) with peak wavelengths ranging from 265,340 nm were characterized over a wide current range. It was found that thermal effects due to self-heating can be largely eliminated by pulsing the LEDs with a duty cycle below 0.2%. The current-induced energy shift up to 850 A/cm2 was negligible in the deep-UV LEDs, indicating the lack of localization effects. The quantum efficiency of the LEDs increased monotonically at low currents and attained a low saturated value at high currents. This is in contrast to the efficiency rolloff behavior of typical InGaN-based LEDs resulting from carrier delocalization at high injection levels. The efficiency saturation of the deep-UV LEDs suggests that defects play an important role in both carrier injection and recombination processes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]