Current Injection Point Research Articles

Studying a spark discharge in the ground during reproduction of a negative lightning-current pulse using magnetic cumulation generators

Using an energy source based on a single BMΓ-160 generator, a current pulse with an amplitude of 50 kA and a rise time of 2 μs has been formed in a grounding rod electrode with a length of 1 m in the ground with a resistivity of 160 Ω m. The maximum length of spark channels on the ground surface from the point of current injection is 3–4 m. An energy source based on two BMΓ-160 generators connected in series allows an increase in the current pulse amplitude to 90 kA, the rise-time duration being the same, 2 μs. In this experiment, the maximum length of spark channels on the ground surface from the point of current injection exceeds 8 m.

Distribution of Currents in the Lightning Protective System of a Residential Building—Part I: Triggered-Lightning Experiments

We present the results of structural lightning protective system (LPS) tests conducted in 2004 and 2005 at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, FL. Lightning was triggered using the rocket-and- wire technique, and its current was directly injected into the LPS. The test configurations in 2004 and 2005 differed in the lightning current injection point, number of down conductors, grounding system at the test house, and the use of surge protective devices. The primary objective was to examine the division of the injected lightning current between the grounding system of the test house, and remote ground accessible via the neutral of the power-supply cable. In 2004, the mean value of the peak current entering the electrical circuit neutral in search of its way to remote ground was about 22% of the injected lightning current peak, while in 2005, it was about 59%. For comparison, more than 80% of the injected peak current was observed to enter the electrical circuit neutral in similar 1997 tests at the ICLRT in which a different test house with a different (poorer) grounding system was used (Rakov et al. 2002 [1]). An attempt to model the 2004 and 2005 experiments is presented in a companion paper.

Dynamics and dynamic modelling of H2S production in sewer systems

Accurate and reliable predictions of sulfide production in a sewer system greatly benefit formulation of appropriate strategies for optimal sewer management. Sewer systems, rising main systems in particular, are highly dynamic in terms of both flow and wastewater composition. In order to get an insight in sulfide production as a response to the dynamic changes in sewer conditions, several measurement campaigns were conducted in two rising mains in Gold Coast, Australia. The levels of various sulfur species and volatile fatty acids (VFAs) were monitored through hourly sampling for periods ranging from 8 to 29h. The results of these field studies showed large temporal as well as spatial variations in sulfide generation. A dynamic sewer model taking into account the hydraulics and the biochemical transformation processes was formulated and calibrated and validated using the data collected during the four measurement campaigns at the two sites. The model was demonstrated to reasonably well describe the temporal and spatial variations in sulfide, sulfate and VFA concentrations. Application of the model was illustrated with a case study aimed to optimize oxygen injection to one of the two mains studied, which is being used as a means to control sulfide production on this site. The model predicted that, moving the current oxygen injection point to a location close to the end of the sewer line could achieve the same degree of sulfide control with only 50% of the current oxygen use. This study highlighted that the location at which oxygen is injected plays a major role in sulfide control and a dynamic model could be used to make a proper choice of the location.

Direct Lightning Strikes to Test Power Distribution Lines—Part II: Measured and Modeled Current Division Among Multiple Arresters and Grounds

The division of return stroke current among the arresters and groundings of two unenergized test distribution lines, one horizontally configured and the other vertically configured, was studied at the International Center for Lightning Research and Testing in Florida. The division of return stroke currents for the vertically configured line was initially similar to the division on the horizontally configured line: at the time the return stroke current reached peak value (after one microsecond, or so) the two closest arresters/grounds on both lines passed about 90% of the total current. However, the time during which the return stroke current flowed primarily through the closest arresters to the neutral conductor was significantly shorter on the vertically configured line. On that line, the arrester current was about equally divided among all four arresters after several tens of microseconds. The arrester current division as a function of time measured on the vertical line was successfully modeled using the published VI-characteristic, while the division on the horizontal line after some tens of microseconds was only successfully modeled if the residual voltage of the two arresters closest to the current injection point was reduced by 20%. Based on the triggered lightning current division observed on our line, the minimum energy absorbed in each of the two arresters closest to the strike point during a typical natural first stroke is estimated to be 40 kJ.

Experimental and analytical studies on lightning surge characteristics of ground mesh

AbstractLightning surge characteristics of a ground mesh have an influence on electromagnetic transient behaviors in low‐voltage and control circuits. This paper describes experimental and analytical studies on lightning surge characteristics of a ground mesh. The experimental studies are carried out under various conditions. The experimental parameters considered in this measurement include earth resistances, current injection points, and injection current waveforms. These measured results are compared with calculated results based on the theoretical studies by Sunde. A comparison of the measured results with the calculated results shows good agreement. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 16– 23, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20559

Acceleration of a Suborbital Payload Using an Electromagnetic Railgun

Railguns are well-known for their capability to reach very high velocities (v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> > 2000 m/s) with overall efficiencies (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">kinetic</sub> /E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">electric</sub> ) over 30%. The high performance expected concerning velocity, efficiency, cost, and repetition rates makes this system attractive not only for military but also for space applications with the aim of accelerating lightweight payloads directly into the low earth orbit (500 km). This last application is very challenging, as far as the energy and power storage, the railgun length, and the rail materials are concerned, but seems promising. In a first step towards space launch, ISL and EADS have investigated, within the scope of two ESA financed studies, the possibility of using a railgun to replace a sounding rocket with the aim of accelerating a meteorological probe up to an apogee of 120 km. In this paper, a quantitative assessment of the concept of the railgun, coupled to the object to be accelerated, is proposed. The electric circuit necessary to drive the facility is given: electric energy sources, switches, pulse forming network as well as a first layout of the railgun itself (length, caliber, materials), and of its current injection points. A series of preliminary test shots of dummy projectiles with masses ranging from 1 to 4 kg using the existing PEGASUS railgun facility at ISL is reported. The projectiles were launched reliably and in a reproducible way with accelerations not exceeding 13000 g, except for one shot with the 2-kg projectile fired with an acceleration of 15700 g, thus, reproducing the suborbital launch conditions. A first estimation of how to delay the plasma occurrence of the sliding armatures used for the suborbital applications at low accelerations is also given in this paper

Analysis on the Transient Voltage Performance of a DC Superconducting Cable

Transient voltage distribution in a DC superconducting cable, comprising of four concentric metallic cylinders was analyzed. Of the four concentric cylinders, two carry the load current, and the other two comprise the cryogenic enclosure. Analysis was performed with transient current injected either to the innermost or the outermost cylinder. The outermost cylinder was either bare or insulated. The outer three cylinders were either solidly grounded or isolated from ground at the point of current injection. It was concluded that transient voltages will appear across the RETURN cryogen flow and also across the vacuum space in the cryogenic enclosure. As these two systems are designed for their thermal performance, they may suffer permanent damage caused by unwanted electrical transients

Experimental and Analytical Studies on Lightning Surge Characteristics of Ground Mesh

Lightning surge characteristics of a ground mesh have influence on electromagnetic transient behaviors in low voltage and control circuits. This paper describes experimental and analytical studies on lightning surge characteristics of a ground mesh. The experimental studies are carried out under various conditions. The experimental parameters considering in this measurement include earth resistances, current injection points and injection current waveforms. These measured results are compared with calculated results based on the theoretical studies by Sunde. A comparison of the measured results with the calculated results shows good agreement.

Theory of Four-Point Direct-Current Potential Drop Measurements on a Metal Plate

ABSTRACT Four-point direct-current potential drop techniques are well-suited for accurate, nondestructive measurement of material conductivity (or resistivity). From measurements of potential drop on a large metal plate, the electrical conductivity of the plate can be inferred if the thickness of the plate and the dimensions of the probe are known. In this work, an expression for the voltage measured by a four-point probe in contact with a large metal plate of arbitrary thickness is derived from an analytic series representation of the electric field in the plate. The position of the voltage pickup points is permitted to be offset with respect to the current injection points, allowing analysis of colinear, rectangular, and square-head probes. Analytical asymptotic expressions are derived in the limiting cases of plates that are thin or thick with respect to the dimensions of the probe. The range of plate thicknesses for which the asymptotic expressions are valid is determined as a function of relevant probe dimensions. The results of this study provide a useful guide in selecting the most appropriate arrangement of probe points for measurement of the electrical conductivity of large metal plates, depending on the level of accuracy required. Theory is compared with experimental data for measurements made with colinear probes on a variety of metal plates and very good agreement is obtained.

봉상 접지전극에시 전류유입위치에 따른 임펄스 접지임피던스의 특성

본 논문은 전류유입위치에 따른 봉상접지전극의 과도 및 실효임펄스임피던스의 특성에 관한 것으로 뇌격전류를 인가하여 실규모 접지봉에 대한 시간영역에서의 성능을 평가하였다. 임펄스전류가 가해진 봉상접지전극의 과도 접지임피던스는 접지저항보다 높게 나타났으며, 접지전극의 길이가 길어짐에 따라 접지저항과 실효임펄스접지임피던스는 감소되었다. 또한 실효임펄스접지임피던스는 짧은 시간범위에서는 급격하게 증가하였다. 접지저항의 저감은 접지시스템의 임펄스임피던스 특성의 개선에 결정적인 역할을 한다. 임펄스전류를 접지봉의 하단에 인가하였을 때 접지봉 전위의 파두부에 고주파의 진동 파형이 포함되고 실효임펄스임피던스는 다른 경우보다 높게 나타났다.

Laboratory simulation of direct lightning strokes to a modeled building: measurement of magnetic fields and induced voltages

In IEC 61312-2 equations for the assessment of the magnetic fields inside structures due to a direct lightning strike are given. These equations are based on computer simulations for shields consisting of a single-layer steel grid of a given mesh width. Real constructions, however, contain at least two layers of reinforcement steel grids. The objective of this study was to experimentally determine the additional shielding effectiveness of a second reinforcement layer compared to a single-layer grid. To this end, simulated structures were set up in the high current laboratory. The structures consisted of cubic cages of 2 m side length with one or with two reinforcement grids, respectively. The structures were exposed to direct lightning currents representing the variety of anticipated lightning current waveforms. The magnetic fields and their derivatives at several positions inside the structure as well as the voltage between “floor” and “roof” in the center were determined for different current injection points. From these data the improvement of the shielding caused by a second reinforcement layer is derived.

The effects of Dc bias current in large-scale SFQ circuits

The supply of bias current is one of the key problems to be overcome for fully operational large-scale SFQ circuits. Large currents cause various undesirable effects that degrade circuit operation. The magnetic field induced by a large DC bias current affects the operation of several SFQ cells, even with a microstrip-line structure applied for the bias lines. In this paper, experimental results using SQUIDs show that bias-line shielding is the most effective way to reduce the effect of the DC bias current. The operating margins of SFQ cells were also found to be sensitive to the current in the ground plane. The location of a ground bonding should be close to the point of current injection if we wish to avoid undesirable diffusion of current through the ground plane. We confirmed the effectiveness of bias-line shielding and of the location of ground bonding with a circuit composed of about 500 junctions.

Electrical properties of smooth muscle in the guinea-pig urinary bladder.

1. The effects of transmural nerve stimulation were examined on preparations of detrusor smooth muscle from guinea-pig urinary bladder using intracellular recording techniques. Most recordings were made from preparations in which spontaneous and evoked action potentials had been inhibited by nifedipine (10 microM), a dihydropyridine that blocks L-type Ca2+ channels. 2. Supramaximal stimuli evoked excitatory junction potentials (EJPs) which could be divided into three basic types. Type 1 EJPs had short latencies (< 30 ms) and fast rise times (< 60 ms). Type 2 EJPs consisted of two components: a small depolarization that was followed by a second depolarization with a faster rise time. In a third type of cell, at high strengths of stimulation, EJPs resembled type 1 EJPs but at lower strengths of stimulation were similar in time course to type 2 EJPs. 3. All EJPs were abolished by tetrodotoxin (1 microM) and reduced by omega-conotoxin (0.1 microM), but were unaffected by hexamethonium (0.1 mM), suggesting that they result from the release of transmitter from post-ganglionic nerve fibres. All responses persisted in the presence of atropine (1 microM) but were abolished following the desensitization of P2-purinoceptors with alpha, beta-methylene ATP (m-ATP; 10 microM). 4. Spontaneous excitatory junction potentials (SEJPs) were also recorded from most cells. SEJPs were similar in appearance to fast single-component EJPs; however, in general they had a briefer time course. SEJPs persisted in the presence of tetrodotoxin (1 microM). 5. The electrical properties of urinary bladder smooth muscle were also examined. Voltage changes induced by point current injection into cells had fast rates of rise and decay (time constant, 5-20 ms). The input resistance of cells ranged between 12 and 108 M omega. When recordings were taken from cells near the point of current injection, resultant electrotonic potentials could be detected in only a small proportions of cells. 6. The results are discussed in relation to the idea that transmural nerve stimulation in the guinea-pig urinary bladder causes the activation of at least two different membrane conductances. Cells appear to be electrically coupled with one another. However, it is likely that coupling exists within discrete bundles of the smooth muscle.

A 3-D SAR model for current source interstitial hyperthermia.

A three-dimensional (3-D) model is presented for the calculation of the specific absorption rate (SAR) in human tissue during current source interstitial hyperthermia. The model is capable of millimeter resolution and can cope with irregular implants in heterogeneous tissue. The SAR distribution is calculated from the electrical potential. The potential distribution is determined by the dielectric properties of the tissue and by the electrode configuration. The dielectric properties and the current injection of the electrodes are represented on a 3-D uniform grid. The calculated potential at an electrode current injection point is not the actual electrode potential at that point. To estimate this potential a grid independent representation of an electrode together with an analytical solution in the neighborhood of the electrode are used. The calculated potential on the electrode surface is used to estimate the electrode impedance. The tissue implementation is validated by comparing calculated distributions with analytical solutions. The electrode implementation is verified by comparing different discretizations of an electrode configuration and by comparing numerically calculated electrode impedances with analytically calculated impedances.

Three dimensional electromagnetic field due to electric discharge by an analytical approach

The analytical expression of the time behaviour of the current density due to an electric discharge on a three dimensional conducting slab has been obtained by means of an analytical method. The electric discharge is modeled by a current pulse injected in the slab. The current injection point can be arbitrarily positioned on the surface of the slab. The diffusion equation was solved in the s domain using the technique of the separation of variables. The time behaviour of the current density was determined applying the inverse Laplace transform to the solution. The analytical results were compared with results obtained with two numerical methods, the first based on an equivalent network formulation and the second based on a Finite Difference Time Domain method. The electromagnetic field in space has been simply determined from the knowledge of the current density distribution. >

Cable correction of membrane currents recorded from root hairs ofArabidopsis thalianaL.

Membrane currents were recorded under voltage clamp from root hairs of Arabidopsis thaliana L. using the two-electrode method. Concurrent measurements of membrane voltage distal to the point of current injection were also carried out to assess the extent of current dissipation along the root hair axis. Estimates of the characteristic cable length, λ, showed this parameter to be a function both of membrane voltage and of substrate concentration for transport. The mean value for λ at 0 mV was 103 ± 20 µm (n=17), but ranged by as much as 6-fold in any one cell for membrane voltages from −300 to +40 mV and was affected by 0.25 to 3-fold at any one voltage on raising [K+]0 from 0.1 to 10 mol m−3. Current dissipation along the length of the cells lead to serious distortions of the current-voltage [I–V) characteristic, including consistent underestimates of membrane current as well as a general linearization of the I–V curve and a masking of conductance changes in the presence of transported substrates. In some experiments, microelectrodes were also placed in neighbouring epidermal cells to record the extent of intercellular coupling. Even with current-passing microelectrodes placed at the base of root hairs, coupling was ≤5% (voltage deflection of the epidermal cell ≤5% that recorded at the site of current injection), indicating an appreciable resistance to current passage between cells. These results demonstrate the feasibility of using root hairs as a ‘single-cell model’ in electrophysiological analyses of transport across the higher-plant plasma membrane; they also confirmed the need to correct for the cable properties of these cells on a cell-by-cell basis.

The Electrical Properties of Plant Cell Membranes. IV. The Effects of the Nodal Conductance upon the Cable Properties and Measured Membrane Conductance of Charophytes

A theoretical treatment of the electrical 'cable' properties of cylindrical, radially symmetric, plant cells with two concentric membranes is presented, in which the effects of additional conductance elements located at the nodes (ends) of the cell are considered. It is shown that the measured 'membrane' conductance is effectively independent of the conductance between the vacuole and exterior at the nodes, providing the nodes are at least a cable-length distant from the point of current injection. However any 'leakage' between the cytoplasm and the cell exterior at the nodes (as might occur via unsealed plasmodesmata) can drastically affect measurements made with cytoplasmic electrodes remote from the point of current injection. It is shown that isolating the nodes of the cell with insulating external barriers of a suitable width can effectively remove any error due to the electrical properties of the nodes.

The Electrical Properties of Plant Cell Membranes. II.* Distortion of Non-linear Current-Voltage Characteristics induced by the Cable Properties of Chara

The electrical 'cable' properties of cylindrical, radially symmetric cells with non-linear membrane current-voltage (I-V) characteristics are considered. A numerical technique is described whereby, from a knowledge of the membrane I-V characteristics and the cellfelectrode geometry, it is possible to calculate the I-V characteristics that would be actually measured after distortion by the cable properties of the cell. Thus it is shown that the I-V characteristics of charophytes such as Chara and Nitella measured in some common experimental configurations can be significantly different from the actual I-V characteristics of the membrane. This distortion will always tend to linearize the measured I-V characteristics and consequently a major problem is that the magnitude of any such linearization cannot be simply estimated. In particular if the measured conductance increases with increasing magnitude of V, it is very difficult to determine the actual shape of the membrane I-V characteristics. However an iterative procedure is described which will permit derivation of the correct intrinsic membrane I-V characteristics from the distorted measured I-V characteristics, providing that V is measured at the point of current injection. This procedure is applied to some experimental I-V data of Chara to demonstrate the possible magnitude of the distortion arising from the cable properties.

Effect of a spatially inhomogeneous membrane upon the measured electrical properties ofChara

The electrical properties of radially symmetric, cylindrical cells are considered. It is shown that the presence of spatial inhomogeneities in the membrane conductance, that might occur as a consequence of pH banding inChara andNitella, can greatly influence the “cable” properties of the cell. Thus if current is injected into such a cell at only a single point, calculation of the area-specific conductance of the membrane at that point requires a knowledge of the spatial distribution of the transverse current flow through the membrane. If spatial inhomogeneities are present and are not explicitly allowed for, the estimated area-specific membrane conductance at the point of current injection can be drastically in error. Techniques are discussed whereby the actual area-specific conductance of the membrane in the acid and basic zones inChara can be experimentally determined.

Membrane conductance ofChara measured in the acid and basic zones

A sinusoidal AC current (usually at 1 Hz) was injected into either the acid or basic zone present in illuminated internodal cells ofChara. The “cable” properties of the cell were then studied by two techniques. The first involved measuring the dependence of the transverse AC membrane current (measured in the external medium) upon the distance away from the point of current injection. The second measured the AC membrane voltage at two different positions along the cell. It was found that AC current injected into an illuminated basic region left the cell close to the point of current injection, the effective cable lengthλ B being typically 3 to 5 mm. For AC current injected into an illuminated acid zone however, the cable lengthλ A was significantly longer (≈ 10 to 15 mm). From considerations of the properties of electrically inhomogeneous cables it was possible to estimate the individual area-specific conductances of the acid and basic zones. In strong illumination the conductance of the acid zones was typically 0.8 to 1.0 S/m2, whereas that of the basic zones was much higher (≈ 5 to 8 S/m2). Upon removal of illumination the conductance of each zone was found to slowly decrease, and after several hours the membrane conductance was relatively homogeneous over the cell surface. The large degree of longitudinal spatial inhomogeneity in the membrane conductance of illuminatedChara cells has important consequences for the interpretation of experimental results, and can produce large errors in the estimated membrane area-specific conductance if these inhomogeneities are not explicitly recognized and accounted for. An examination of the literature suggests that previous measurements utilizing point current injection might indeed have systematically underestimated the area-specific membrane conductance ofChara.