Current Rise Time Research Articles

Limits of lightning protection systems

Positive first strokes, less frequent but more powerful than negative return strokes, require a larger conductor. If the skin effect is accounted for, a near maximum value of the action integral of positive lightning can be estimated from the sizes of conductors specified by established building codes. The conductor size for watercraft could be increased: (1) to match that used for structures on land; (2) to avoid exceeding the maximum operating temperature of a dielectric hull; and (3) to limit magnetic stresses caused by 90° bends in conductor paths predicted by Ampere's law. Connecting a conductor at right angles to a ground plate may be problematic; a linear grounding electrode alternative is discussed. Destructive magnetic force can be caused by surface current on: a solid conductor; a hollow conducting mast; or a horizontal ground plate. Electric shielding, unless struck directly, might protect a dielectric hull, except from a subsequent stroke with a short current risetime. Thus, lightning protection systems do not always work, and lightning is best avoided.

Transient Response of the Top Structure of the Peissenberg Tower to Lightning

Subject matter of this paper is the analysis of the high-frequency oscillation of the lightning currents which have been measured at the top of the Peissenberg Tower, Germany. The oscillations appeared only during the initial period of fast-rising currents. In 2007, the tower top section was removed and replaced by a smaller construction. As a result, the frequency of the oscillation changed from formerly ∼12.5 to ∼6 MHz. The oscillations could be reproduced with simulations using the computer code CONCEPT II. It was found that the high-frequency current oscillation is caused by the transient response of the top structure of the Peissenberg Tower. The currents at lower sections of the tower as well as the nearby electric and magnetic field (∼190 m from the tower) contained less significant pulsation. As a major result, the presence of the tower increased the risetime of the fast-rising currents. Probably for this reason, the highest maximum current steepness ever recorded was limited to 155 kA/μs.

Nonlinear diffusion waves in high magnetic fields

The nonlinear diffusion of a magnetic field and the large-scale instabilities arising upon an electrical explosion of conductors in a superstrong (2-3 MG) magnetic field were investigated experimentally on the MIG high-current generator (up to 2.5 peak current, 100 ns current rise time). It was observed that in the nonlinear stage of the process, the wavelength of thermal instabilities (striations) increased with a rate of 1.5-3 km/s.

On the Analysis of Impulse Test Results on Grounding Systems

In this paper, an analysis of experimental results on the behavior under impulse currents of various grounding electrodes: rod and horizontal electrodes, a ground grid, and tower footings, is presented. The parameters used for analyzing transient performance are reviewed, and the differences are highlighted based on test data. The analysis is extended to the following: 1) to quantify the effect of impulse shape; 2) to quantify the effect of current magnitude; 3) to compare low-frequency and impulse performances; 4) to compare impulse and high-frequency performances; and 5) to examine the effects of the test setup on measured results, e.g., in the case of field tests, the effect of current return leads, and proximity and extent of return electrodes. A generalized impulse index is introduced to help elucidate the differences between different parameters used for the analysis of transient test results on ground electrodes. It is found that the analysis of test data based on different parameters may lead to different assessments of impulse performance. The results also show that the impulse parameters used for the analysis of test data can be influenced by several factors such as electrode length, impulse current rise time, and experimental setup. In addition, variable-frequency test results are analyzed by introducing a “harmonic coefficient” which quantifies the deviations of the harmonic impedance from the low-frequency resistance over different frequency ranges covering the entire lightning frequency spectrum. Significant variations of the harmonic coefficient with frequency were observed, highlighting the importance of taking the frequency dependence of soil properties when modeling the impulse and high-frequency behavior of grounding systems.

Experimental study of the nonlinear diffusion of a magnetic field and skin explosion of cylindrical conductors

The paper presents the results of an experimental study of the skin explosion of cylindrical conductors of diameter 1–3 mm (copper, aluminum, titanium, steel 3, and stainless steel) at a peak magnetic field of 200–600 T. The experiments were carried out on the MIG pulsed power generator at a current of up to 2.5 MA and a current rise time of 100 ns. The surface explosion of a conductor was identified by the appearance of a flash of extreme ultraviolet radiation. A minimum magnetic induction has been determined below which no plasma is generated at the conductor surface. For copper, aluminum, steel 3, titanium, and stainless steel, the minimum magnetic induction has been estimated to be (to within 10%) 375, 270, 280, 220, and 245 T, respectively.

Study of the strata formation during the explosion of foils in vacuum

The formation of the strata during fast explosion of metal foils at current densities of 0.1 GA/cm2 has been studied experimentally. To observe the strata, the soft x-ray radiation generated by an X-pinch was used. The study of the process of stratification during the foil explosion was carried out with a setup consisting of three generators. One of the generators (WEG-2), was operated to initiate the explosion of the foils, while the others (XPG radiographs) were used for diagnostics. The generator WEG-2 has the capacitance of 250 nF, the charge voltage of 20 kV, and the current rate of 16 A/ns. The radiographs XPG have the capacitance of 1 μF, the charge voltage of 43 kV, the current of 300 kA, and the current rise time of 180 ns. X-pinch produced by four Mo wires was a load for the radiographs. The delay between the operation of the WEG-2 and XPG generators was set using a DPG trigger pulse generator. We performed the experiments with the Al and Cu foils. The length of foil was 2 cm, the foil width was 1 mm, and the foil thickness was 6 μm. It has been revealed that strata were formed early in the explosion, i.e. at the stage when the metal melted. Analysis of the experimental results suggests that the most probable reason for the stratification is the thermal instability developing because of the increase in resistivity of the foil metal with temperature.

X-pinch soft x-ray source dynamics at a subnanosecond time resolution

The paper reports on an experimental study of the X-pinch soft x-ray source dynamics at a subnanosecond time resolution with the use of an x-ray imaging technique based on an AXIS-NX streak camera. The study was performed on a compact generator with a current amplitude of 300 kA to a short-circuit load and current rise time of 180 ns. It is shown that in the spectral range 1-1.55 keV, the X-pinch soft x-ray source in whole represents a set of sources which can be radially offset by ∼ 10 microns about the X-pinch axis. Each of the sources generates a pulse of duration 0.2-0.7 ns. The interval between the formation of the sources and hence between their radiation pulses is 0.5 ns and longer.

Shipborne LF-VLF oceanic lightning observations and modeling

Approximately 90% of natural lightning occurs over land, but recent observations, using Global Lightning Detection (GLD360) geolocation peak current estimates and satellite optical data, suggested that cloud-to-ground flashes are on average stronger over the ocean. We present initial statistics from a novel experiment using a Low Frequency (LF) magnetic field receiver system installed aboard the National Oceanic Atmospheric Agency (NOAA) Ronald W. Brown research vessel that allowed the detection of impulsive radio emissions from deep-oceanic discharges at short distances. Thousands of LF waveforms were recorded, facilitating the comparison of oceanic waveforms to their land counterparts. A computationally efficient electromagnetic radiation model that accounts for propagation over lossy and curved ground is constructed and compared with previously published models. We include the effects of Earth curvature on LF ground wave propagation and quantify the effects of channel-base current risetime, channel-base current falltime, and return stroke speed on the radiated LF waveforms observed at a given distance. We compare simulation results to data and conclude that previously reported larger GLD360 peak current estimates over the ocean are unlikely to fully result from differences in channel-base current risetime, falltime, or return stroke speed between ocean and land flashes.

Lightning current and luminosity at and above channel bottom for return strokes and M‐components

We measured current and luminosity at the channel bottom of 12 triggered lightning discharges including 44 return strokes, 23 M-components, and 1 initial continuous current pulse. Combined current and luminosity data for impulse currents span a 10–90% risetime range from 0.15 to 192 µs. Current risetime and luminosity risetime at the channel bottom are roughly linearly correlated (τr,I = 0.71τr,L1.08). We observed a time delay between current and the resultant luminosity at the channel bottom, both measured at 20% of peak amplitude, that is approximately linearly related to both the luminosity 10–90% risetime (Δt20,b = 0.24τr,L1.12) and the current 10–90% risetime (Δt20,b = 0.35τr,I1.03). At the channel bottom, the peak current is roughly proportional to the square root of the peak luminosity (IP = 21.89LP0.57) over the full range of current and luminosity risetimes. For two return strokes we provide measurements of stroke luminosity vs. time for 11 increasing heights to 115 m altitude. We assume that measurements above the channel bottom behave similarly to those at the bottom and find that (1) one return stroke current peak decayed at 115 m to about 47% of its peak value at channel bottom, while the luminosity peak at 115 m decayed to about 20%, and for the second stroke 38% and 12%, respectively; and (2) measured upward return stroke luminosity speeds of the two strokes of 1.10 × 108 and 9.7 × 107 ms−1 correspond to current speeds about 30% faster. These results represent the first determination of return stroke current speed and current peak value above ground derived from measured return stroke luminosity data.

Research of transportation efficiency of low-energy high- current electron beam in plasma channel in external magnetic field

Effective high current (5-20 kA) and low energy (tens of keV) electrons beam transportation is possible only with almost complete charging neutralization. It is also necessary to use quite high current neutralization for elimination beam self-pinching effect. The research is based on the self-consistent mathematical model that takes into account beam and plasma particles dynamic, current and charge neutralization of electron beam and examines the transportation of electron beam into a chamber with low-pressure plasma in magnetic field. A numerical study was conducted using particle in cell (PIC) method. The study was performed with various system parameters: rise time and magnitude of the beam current, gas pressure and plasma density and geometry of the system. Regularities of local virtual cathode field generated by the beam in the plasma channel, as well as ranges of parameters that let transportation beam with minimal losses, depending on the external magnetic field were determined through a series of numerical studies. In addition, the assessment of the impact of the plasma ion mobility during the transition period and during steady beam was performed.

High-current discharge initiation in a vacuum diode

The research results of forming a low-resistance high-current discharge in the vacuum gap by means of forced initiation of the cathode spot by auxiliary discharge are presented. The discharge with current of more than 30 kA at the current rise time of ∼100 ns is formed in a gap of 2.5 cm. In a next phase of the current interruption the energy of 180 J is dissipated in the diode gap.

Power Increase of the Electron Source Based on the Plasma-Filled Diode

The technique of a linear transformer driver (LTD) now allows building the generators of high-power nanosecond pulses with the current rise time of $\sim 100$ ns without intermediate power compression stages. This technique is being examined for use in high-current high-voltage electron sources based on plasma-filled diodes. The power of a plasma-filled diode is determined by the driving circuit parameters and the transition diode resistance. The problem of power rise can be solved by increasing the stored energy in the circuit inductance provided that the diode resistance rise rate is constant. In experiments on the LTD (53 nF, 480 kV), the possibility has been checked out for such increase in the stored energy. A current increase from 50 to 180 kA was obtained by increasing the current rise rate from 0.4 to 1.9 kA/ns. Stored energy has been increased, respectively, from 0.2 to 3.6 kJ. The time of energy transfer into the circuit inductance was about 120–140 ns. Maintaining the diode resistance rise rate at 0.5 $\Omega $ /ns has been shown. Diode power has been increased up to 170 GW. Further increase in power of the plasma-filled diode has been obtained using simulation circuit of the Megavolt (MV) range LTD. To simulate such a linear transformer, the driver circuit was made as Marx generator with coaxial water line (5.3 $\Omega $ , 56 ns, and 1.5 MV), providing a current input of 160 kA into the 550-nH inductance in 120 ns. Stored energy in the inductance was about 7 kJ. The following diode parameters were obtained: 150 kA, 1.9 MV, and 250 GW at a resistance rise rate more than 0.5 $\Omega $ /ns. The experiments prove that the resistance rise rate of the plasma-filled diode is constant on increasing the stored energy in the inductance up to 7 kJ. It allows scaling the power of an electron source based on the plasma-filled diode.

Characteristics of Resistance Triggering of a Pulsed Vacuum Arc Ion Source **Supported by the National Natural Science Foundation of China under Grant Nos 11105130 and 11475156.

Triggering scheme is a significant factor that may influence the process of vacuum arc initiation. In this work, the characteristics of resistance triggering of a pulsed vacuum arc ion source are investigated and compared with the independent pulse generator triggering. The results show that although the resistance triggering method is capable of triggering a vacuum arc ion source by properly choosing the resistance and electric parameters, it inevitably increases the rise time of the arc current. A high speed multiframe camera is used to reveal the transition process of arc initiation during one shot. From the images it is conjectured that the lower voltage between the cathode and the anode may be the reason that leads to the lower transition speed of discharge at the moment of arc initiation.

In fault ride through reactive current rise time requirements of various European grid codes—analysis based on a full‐converter wind turbine

AbstractThe European transmission system operators specify grid codes to ensure a safe and reliable operation of the electrical power system, even during grid faults. Wind power plants have to comply with such specific requirements prior to installation and operation. Some of the requirements, however, are open to interpretation, especially because of lack of specification, and therefore, they pose technical challenges to full‐converter wind turbines. In fact, different interpretations leave it open to debate on whether a requirement can be fulfilled or not. The rise time requirement across some European grid codes is discussed in this paper. First the uncertainties in some transmission system operators' definitions of rise time, step response time and settling time are presented, and then a comparative analysis is performed among calculation methods, such as instantaneous reactive current in alpha‐beta reference frame, direct and quadrature reference frame and root mean square of the positive sequence component. The comparison results of both ideal cases and randomly selected measurements from actual full‐converter wind turbine field tests show that the rise time of the reactive current is significantly affected by the calculation methods. This effect in some cases can make the difference between fulfilling the requirement or not. As a result of that, it is highlighted in this paper the need for a common understanding of the rise time requirements between industry and system operators, based on clear technical fundamentals. Copyright © 2015 John Wiley & Sons, Ltd.

FDTD simulation of LEMP propagation over lossy ground: Influence of distance, ground conductivity, and source parameters

AbstractWe have computed lightning electromagnetic pulses (LEMPs), including the azimuthal magnetic field Hφ, vertical electric field Ez, and horizontal (radial) electric field Eh that propagated over 5 to 200 km of flat lossy ground, using the finite difference time domain (FDTD) method in the 2‐D cylindrical coordinate system. This is the first systematic full‐wave study of LEMP propagation effects based on a realistic return‐stroke model and including the complete return‐stroke frequency range. Influences of the return‐stroke wavefront speed (ranging from c/2 to c, where c is the speed of light), current risetime (ranging from 0.5 to 5 µs), and ground conductivity (ranging from 0.1 mS/m to ∞) on Hφ, Ez, and Eh have been investigated. Also, the FDTD‐computed waveforms of Eh have been compared with the corresponding ones computed using the Cooray‐Rubinstein formula. Peaks of Hφ, Ez, and Eh are nearly proportional to the return‐stroke wavefront speed. The peak of Eh decreases with increasing current risetime, while those of Hφ and Ez are only slightly influenced by it. The peaks of Hφ and Ez are essentially independent of the ground conductivity at a distance of 5 km. Beyond this distance, they appreciably decrease relative to the perfectly conducting ground case, and the decrease is stronger for lower ground conductivity values. The peak of Eh increases with decreasing ground conductivity. The computed Eh/Ez is consistent with measurements of Thomson et al. (1988). The observed decrease of Ez peak and increase of Ez risetime due to propagation over 200 km of Florida soil are reasonably well reproduced by the FDTD simulation with ground conductivity of 1 mS/m.

Electric explosion of fine wires: Three groups of materials

Experimental data demonstrating differences in the structures of channels formed during nanosecond discharges through fine wires made of different materials are presented. In addition to the traditional two classes of metals and alloys (the copper and tungsten groups), a new class is proposed to which materials of the nickel type belong. Their properties combine the characteristic properties of the two traditional groups, due to which they occupy an intermediate position between the latter. This manifests itself in the unstable character of explosion, the type of which can change drastically when changing the ambient medium or other conditions. Most of the reported results were obtained at a small setup with maximum values of the current and voltage of 10 kA and 20 kV, respectively, the current rise time being about 300 ns. An attempt is made to construct a scenario of the development of a nanosecond explosion that would make it possible to qualitatively describe the formation of the discharge channel structure. The analysis is based on the recent experimental results indicating that the cores formed in the course of the discharge have a tubular structure.

Experimental and comparative study of gamma radiation effects on Si-IGBT and SiC-JFET

This paper deals with an experimental study and a comparative study of the effects of total ionising dose of 60Co gamma radiation on Si-IGBT and SiC-JFET. The response of the threshold voltage and the turn-on switching parameters are reported for both devices. Charge trapping in the gate oxide causes the decrease of the threshold voltage for Si-IGBT. The decrease of this parameter combined with the behaviour of Miller plateau during irradiation results in a decrease of the collector current rise-time, the collector-emitter voltage fall-time, and the turn-on switching energy and in an increase of the peak of the turn-on switching power and of the turn-on overshoot collector current. No changes in these parameters are observed for SiC-JFETs up to 2900Gy with a dose rate of 2.80Gy/h. This indicates that those SiC-JFETs have extremely high radiation resistance with respect to the TID effects compared to the Si-IGBTs.

Contribution of the Juxtatransmembrane Intracellular Regions to the Time Course and Permeation of ATP-gated P2X7 Receptor Ion Channels

P2X7 receptors are ATP-gated ion channels that contribute to inflammation and cell death. They have the novel property of showing marked facilitation to repeated applications of agonist, and the intrinsic channel pore dilates to allow the passage of fluorescent dyes. A 60-s application of ATP to hP2X7 receptors expressed in Xenopus oocytes gave rise to a current that had a biphasic time course with initial and secondary slowly developing components. A second application of ATP evoked a response with a more rapid time to peak. This facilitation was reversed to initial levels following a 10-min agonist-free interval. A chimeric approach showed that replacement of the pre-TM1 amino-terminal region with the corresponding P2X2 receptor section (P2X7-2Nβ) gave responses that quickly reached a steady state and did not show facilitation. Subsequent point mutations of variant residues identified Asn-16 and Ser-23 as important contributors to the time course/facilitation. The P2X7 receptor is unique in having an intracellular carboxyl-terminal cysteine-rich region (Ccys). Deletion of this region removed the secondary slowly developing current, and, when expressed in HEK293 cells, ethidium bromide uptake was only ∼5% that of WT levels, indicating reduced large pore formation. Dye uptake was also reduced for the P2X7-2Nβ chimera. Surprisingly, combination of the chimera and the Ccys deletion (P2X7-2NβdelCcys) restored the current rise time and ethidium uptake to WT levels. These findings suggest that there is a coevolved interaction between the juxtatransmembrane amino and carboxyl termini in the regulation of P2X7 receptor gating.

Effect of Ionic Conductivity on Response Speed of SrTiO3-Based All-Solid-State Electric-Double-Layer Transistor.

An all-solid-state electric-double-layer transistor (EDLT) with a Y-stabilized ZrO₂ (YSZ) proton conductor/SrTiO₃ (STO) single crystal has been fabricated to investigate ionic conductivity effect on the response speed, which should be a key parameter for development of next-generation EDLTs. The drain current exhibited a 4-order-of-magnitude increment by electrostatic carrier doping at the YSZ/STO interface due to ion migration, and the behavior strongly depended on the operation temperature. An Arrhenius-type plot of the ionic conductivity (σ(i)) in the YSZ and t(c)⁻¹, which is a current-rise time needed for charge accumulation at the YSZ/STO interface, shows a synchronized variation, indicating a proportional relationship between the two parameters. Analysis of the σ(i)-t(c) diagram shows that, in contrast to conventional EDLTs, the response speed should reach picosecond order at room temperature by using extreme miniaturization and superionic conductors. Furthermore, the diagram indicates that plenty of solid electrolytes, which have not been used due to the lack of criteria for evaluation, can be a candidate for all-solid-state EDLTs exceeding the carrier density of conventional EDLTs, even though the response speed becomes comparably lower than those of FETs.

Effect of the interface on UV–vis–IR photodetection performance of PbS/ZnO nanocomposite photocatalysts

Two PbS/ZnO nanocomposites with the same Pb/Zn molar ratio of 1:12 and different PbS/ZnO interface were prepared by depositing PbS nanocrystals on nano ZnO with the reaction between Pb(NO3)2 and Na2S through changing the sequence of adding Pb(NO3)2 and Na2S to the nano ZnO suspension: (A) first adding Pb(NO3)2 followed by adding Na2S (denoted PbS/ZnO-A); (B) first adding Na2S followed by adding Pb(NO3)2 (denoted PbS/ZnO-B). The PbS/ZnO nanocomposites are characterized by XRD, BET, Raman, TEM, XPS, and UV–vis–IR. The characterizations indicate that PbS/ZnO-A has an interface of PbS nanocrystal closely contacted to ZnO nanocrystal while PbS/ZnO-B has an interface of a disordered layer between PbS nanocrystal and ZnO nanocrystal. It is found for the first time that the PbS/ZnO interface plays an important role in their photodetection performance. PbS/ZnO-A exhibits much higher photoresponse current and lower rise and recovery time than both PbS/ZnO-B and a mixture of nano PbS and ZnO with the same Pb/Zn molar ratio as PbS/ZnO-A for visible and near-infrared photodetection. PL and the impedance measurement in dark and irradiation reveal that the superior photodetection performance of PbS/ZnO-A over PbS/ZnO-B is attributed to its lower e–h recombination and migration resistance under the irradiation of visible and infrared light due to its very good PbS/ZnO interface of PbS nanocrystals closely attached ZnO nanocrystals, through which photogenerated electrons inject efficiently from the conduction band of PbS to that of ZnO. In contrast, the defect sites in the disordered layer between PbS nanocrystal and ZnO nanocrystal for PbS/ZnO-B act as e–h recombination centers, significantly decreasing the e–h separation efficiency.