Current Impulse Research Articles

Clarifying the mechanisms of edge glow generation in CFRP laminates exposed to simulated lightning currents

This study examines edge glow mechanisms of CFRP laminates exposed to simulated lightning current by performing direct electrical conduction tests. An impulse electric current, in accordance with SAE ARP 5412B, was applied to the laminates. Numerical simulations based on finite element analysis (FEA) were performed to clarify the voltage and temperature distributions of the CFRP laminates. The analytical results were validated using the experimentally obtained I–V characteristics and temperature responses. Resultingly, edge glow was observed in quasi-isotropic but not in unidirectional and cross-ply laminates. The edge glow was suppressed more in silicone oil than in air. When the edge glow did not occur, the numerical simulation results, I–V characteristics, and temperature response, exhibited good agreement with the experimentally obtained results. Contrary to Joule heating, potential differences of several hundred volts between each layer, which cause dielectric breakdown in the testing atmosphere, are the criterion for edge glow formation.

Growth of Nb films on Cu for superconducting radio frequency cavities by direct current and high power impulse magnetron sputtering: A molecular dynamics and experimental study

The use of superconducting radio frequency (rf) cavities in particle accelerators necessitates that copper (Cu) surfaces are coated by thin niobium (Nb) films, predominantly synthesized by magnetron sputtering. A key feature of the rf cavities is that they exhibit a complex three-dimensional geometry, such that during Nb film growth vapor is not deposited on a flat substrate. The latter, combined with the line-of-sight nature of the deposition flux in conventional magnetron sputtering methods (including direct current magnetron sputtering; DCMS) yields films with porous columnar morphologies on surfaces of the cavities that do not face the magnetron source. High-power impulse magnetron sputtering (HiPIMS) is a variant of sputtering that generates highly-ionized fluxes. Using electrical fields, such fluxes can be deflected to trajectories that are closer to the substrate normal and, thereby, dense and uniform layers can be deposited on all surfaces of the rf cavities. In the present work, we use classical molecular dynamics simulations to model Nb film growth on Cu substrates at conditions consistent with those prevailing during DCMS and HiPIMS. Our computational results are in qualitative agreement with experimental data (also generated in the present study), with respect to film morphology. Based on this agreement and by studying the evolution of the simulated systems, we suggest that the morphology of HiPIMS-grown films (as compared to their DCMS counterparts) is the result of the combined effects of deflection of ionized sputtered particles to trajectories parallel to the substrate normal, bombardment-induced interruption of crystal growth, and ballistic atomic rearrangement along with dynamic thermal annealing caused by energetic film-forming species. Moreover, the predictions of our model with respect to dynamic processes at the film-substrate interface and their effect on local epitaxial growth are discussed.

The microstructure and mechanical properties of He charged Al films fabricated by HiPIMS/DCMS co-sputtering

Although magnetron sputtering is an effective method to prepare helium (He) charged films, due to the shadowing effect and low plasma density, the films prepared by this method are high porosity and residual stress. In order to solve this problem, the microstructure and properties of He charged aluminum (Al) thin films deposited by the direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HiPIMS)/DCMS co-sputtering were investigated carefully. The results show that, even with the same concentration of He content, He charged film deposited by HiPIMS/DCMS show relatively lower hardness than that of He charged films by DCMS, which the difference is about 0.75 GPa. This is mainly because increased gain size and decreased the number of dislocation loops, due to strong migration ability on the growth surface in HiPIMS/DCMS process. A denser, less columnar structure of He charged film was prepared by the HiPIMS/DCMS co-sputtering, which might help to promote the research on the properties of metal materials containing He bubbles.

Effect of Multiple Reclosing Time Intervals on Axial Vibration of Winding

When a transformer suffers a permanent fault, it will suffer a short-circuit impulse again after reclosing. If the previous vibration of the winding is not attenuated completely and the winding is subjected to a secondary impulse within a short time, the secondary vibration response will have a superposition. The aim of this study was to analyze the effect of the anti-short-circuit ability of operational transformers subjected to a secondary short-circuit current impulse. In this paper, a model is established for calculating axial vibration in transformer windings and effects on the vibration response of windings under different closing phase angles and short-circuit intervals are analyzed. The results show that the vibration acceleration of windings is a V-shaped variation at phase angles from 0° to 180°, reaching the maximum values at 0° and 180° and reaching the minimum value at 90°. When the transformer recloses on a permanent short circuit, due to the superposition effect, the vibration acceleration amplitude of the secondary impulse will be greater than that of the primary impulse, but as the reclosing interval increases, the superposition effect decreases continuously. When the interval is 600 ms, the superposition effect for the vibration acceleration of the secondary impulse attenuates to 83.3%. The superposition effect is not significant after 600 ms. The research provides a theoretical reference for transformer closing-control strategies.

One‐Step DcMS and HiPIMS Sputtered CIGS Films from a Quaternary Target

Using a quaternary compound target, Cu(In,Ga)Se2 films are prepared using one‐step, selenization‐free direct current magneton sputtering (DcMS) and high power impulse magnetron sputtering (HiPIMS) methods. This study investigates how the sputtering power affects the composition, microstructure, morphology, and electrical characteristics of the films. Film crystallinity is found to be affected by the sputtering power utilized. The films deposited at 0.25 kW are amorphous, whereas those formed at 0.5–1 kW display a chalcopyrite structure with a (112)–preferred orientation. With increased sputtering power, the films’ crystal quality improves, displaying a homogeneous and compact morphology free of peeling and cracking. Elemental measurement of the CIGS films reveals that, depending on the deposition method, the film composition deviates from that of the target. The electrical properties of the deposited films vary with increasing sputtering power.

Physiotherapy methods in medical rehabilitation of children with scoliosis

The article presents a review of the literature on the prevalence, relevance, and social significance of scoliosis in children. Much attention is given to the role and place of physiotherapy methods used in medical rehabilitation programs for children with scoliotic spinal deformity. Impulse currents occupy key positions among the numerous methods of physiotherapy for scoliosis (SMT, DDT, interference therapy, etc.) due to their specific effect on the neuromuscular apparatus in order to increase the tone of weakened muscles. The article presents the results of studies on the use of high-intensity impulse magnetic therapy, EHF therapy, vibrotherapy, biofeedback therapy (BFB), etc. in medical rehabilitation of scoliotic spinal deformity in children. In recent years, the role of balneotherapy and climatotherapy at the sanatorium-resort stage of the rehabilitation of such patients has increased. The methods of physiotherapy presented in the work are quite diverse, have different efficiency, and can be individually used in combination with physiotherapy exercises in numerous programs for medical rehabilitation of children with scoliosis.

Effect of peak current on the microstructure, mechanical properties and tribological behavior of MoxN coatings deposited by high power impulse magnetron sputtering

The MoxN coatings are deposited by direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HiPIMS). It is found that the MoxN coatings prepared by HiPIMS has a denser microstructure, higher hardness and wear resistance. Besides, the effect of peak current is investigated with respect to the microstructure, mechanical properties and tribological behavior of the coatings. As the peak current increases, the cross-sectional morphology of the coating transforms from featureless to columnar morphology, and the preferred orientation of the coating gradually transfers from (111) to (200). However, the hardness of the coating is not significantly influenced by the peak current. The MoxN coating with a peak current of 260 A owns a low friction coefficient of 0.28, which is better than that of the MoxN coating prepared by DCMS. The MoxN coating with a peak current of 300 A provides excellent wear resistance with the lowest wear rate of 5 × 10−8 mm3/(Nm).

Locally Reconfigurable Exchange Bias for Tunable Spintronics by Pulsed Current Injection

Unidirectional magnetic anisotropy induced by exchange bias (EB) between ferromagnetic and antiferromagnetic layers is of paramount importance in various spintronic devices. Traditional setting and optimization of EB involve cooling through the Néel temperature of the antiferromagnets under biasing field in vacuum furnace which takes hours of time and cannot realize localized control of EB. Herein, an alternative process to configure EB by injection of microsecond current impulse for locally heating of the heterostructure is reported. 180‐degree exchange bias switching has been realized in both anisotropic magnetoresistance and giant magnetoresistance units, resulting in tunable magnetic field sensing functionalities. This mechanism for pinpoint control of EB provides more freedom for the design and optimization of various sensing and logic spintronics.

Magnetic Properties of Lightning‐Induced Glass Produced From Five Mineral Phases

AbstractThe physical properties of minerals are modified by the high temperatures of volcanic lightning during explosive eruptions. Alteration involves rapid heating and volatilization, melting, and fusion of ash grains within the discharge channel, followed by rapid quenching into new glassy textures. High current impulse experiments reveal that lightning alters not only the morphology and mineralogy of volcanic ash but also its magnetic properties. We investigate lightning‐induced magnetic changes in five igneous minerals (<32 μm powders of albite, labradorite, augite, hornblende, and magnetite) by comparing hysteresis parameters before and after impulse experiments conducted at peak currents of 25 and 40 kA. Both the paramagnetic and ferrimagnetic behaviors of the samples were altered, which we interpret as a superposition of two processes. (a) Rapid melting allows iron contained within inclusions of Fe‐oxides and Fe‐bearing silicates to diffuse into the newly formed melt, thereby increasing the paramagnetism of the resulting glass. (b) Nucleation and growth of magnetite from the newly formed melt increases the ferrimagnetic behavior of the post‐experimental samples. Nominally non‐Fe‐bearing silicates like albite and labradorite have significantly increased paramagnetism and ferrimagnetism. Fe‐bearing silicates like augite and hornblende contain higher concentrations of ferrimagnetic inclusions, from which Fe diffuses into the newly formed melt, thereby increasing paramagnetism while decreasing ferrimagnetism. Experiments conducted on magnetite produced new magnetite crystals with dendritic habits. Although specific to volcanic ash, these results provide important insights into the magnetism of other materials affected by lightning on Earth, the Moon, and throughout the solar system.

Investigation of Impulse Aging of Energy-Absorption Elements for Hybrid DC Circuit Breakers

The state of the energy-absorption branch MOV in the hybrid DC circuit breaker (DCCB) has a very important impact on the short fault breaking operation of the circuit breaker. Therefore, it is necessary to evaluate the state of the MOV, which is also called the “sleep component”. Due to DCCB being placed indoors, the aging is mainly caused by short-circuit impulse current. Therefore, this paper mainly focuses on the study of the short-circuit impulse aging characteristics of the energy-absorption branch MOV. The dynamic simulation system of a hybrid DCCB was built to investigate the impulse of short-circuit current on the MOV of the energy-absorption branch during the circuit breaking process. Then, an accelerated impulse aging test platform was built and the accelerated impulse aging tests of the MOV were conducted. The aging characteristics of the MOV were analyzed in detail and detailed analysis was conducted of the macroscopic parameters and microstructure changes. The results indicate that the nonlinear coefficient α could be emphasized as a basis for judging the “sleeping” component states and aging degree of the hybrid DC circuit breaker, and can be expected to be applicable to MOV condition monitoring of BCCB in the future.

A novel flexible fault eliminator with active disturbance rejection and soft grid-connection in distribution networks

Among the possible fault types in the distribution networks, single-line-to-ground (SLG) fault has the highest probability. The SLG fault current and arc can easily cause personal injury and death. This study proposed a flexible fault eliminator (FFE) based on a cascaded H-bridge topology to limit the SLG fault current and extinguish fault arc in the medium voltage distribution networks. An active disturbance rejection controller for the FFE was designed to improve the current limiting performance of FFE in the presence of insulation parameter measurement errors and sampling errors from potential/current transformers. The controller with good robustness adapts to different ground fault resistances. In addition, a soft grid-connection control scheme based on bistable smooth switching was proposed to avoid the injected current impulse of FFE at the moment of grid connection. Simulation and experimental results showed that the fault current was limited to a small enough value and the fault arc was extinguished effectively. The output current and voltage of FFE at the time of grid connection were in a smooth transition, avoiding the impulse on the power grid system. The FFE can eliminate the SLG fault flexibly and stably.

Parallel Impulse Current Shunt Performance of Multiple MOVs for 500 kV Series Compensation

As an important component of the transmission line series compensation device, MOVs have the strong nonlinear characteristics to limit the overvoltage caused by line fault and protect the capacitor banks in 500kV lines. We studied the parallel impulse current shunt performance of multiple MOVs and the influence of the mixed-use of new MOVs with served MOVs for different numbers of MOVs on impulse shunt performance. We conducted 500 kV MOV parallel impulse shunt tests under three conditions of 9-served+2-new, 11-served and 9-served. We found that when MOVs with different V-I characteristics are connected in parallel, the impulse current action characteristics of a single MOV will not be affected. When the number of MOVs in parallel is changed from 11 to 9, the dispersion of impulse current does not change significantly. When two served MOVs are replaced with two new MOVs (with a 1% increase in DC U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2mA</sub> ), the average dispersion of impulse current increases by 2.81%, and the average maximum deviation increases by 5.93%. If the margin is sufficient when MOVs in the whole group are damaged, they can be replaced with matched new MOVs.

Power Efficiency Analysis based on Lightning Effect on Large-Scale Solar Photovoltaic System

Currently, a large-scale solar photovoltaic (LSSPV) has become one of the fastest developments of electrical generation power for Malaysian Renewable Energy. However, lightning strikes are common in Malaysia due to its geographical position and tropical climate, especially in the open space of large-scale site power plants. This paper discussed the scientific basis and key assumptions that should be included in the layout of a lightning protection scheme in a large-scale solar photovoltaic installation. The framework proposal aims to ensure compliance with standards and guidelines, mitigating the risk of significantly induced currents in the LSSPV power plant. A 2.5 MW solar PV farm system was modelled using MATLAB software for assessing a solar PV farm’s electrical performance under various lightning current waveforms and lightning magnitude currents. These lightning strikes will impact photovoltaic modules, thus deteriorating the system’s ratio generation. The effects of lightning current on LSSPV were accessed based on simulation work in MATLAB Simulink. The induced current protection scheme covered rating selection and collecting data on lightning that may hit the modules or arrays. This data was then analysed according to the standard guidelines to ascertain the most effective protection measures for the 50MW PV farm within the LSSPV system. Minimising the maintenance and replacement cost of equipment is possible. The performance of a 2.5MW solar PV power plant with a grid connection was evaluated. A maximum and minimum power output of 2.47MW and 522.50kW, respectively, were observed. However, when the lightning impulsive current is included through the system, the power output decrease to 407.33kW due to the high magnitude induced.

Short duration current impulse waveform effects on the degradation and energy absorption capability of zinc oxide varistors

Short duration current impulse waveform effects on the degradation and energy absorption capability of zinc oxide varistors

Electroplasticity Mechanisms in hcp Materials

Herein, the mechanisms of the electroplastic effect (EPE) in different hexagonal close‐packed (hcp) metals under varying loading conditions and current densities through the analysis of flow curves and microstructural changes are investigated. The investigations show a significant change in the forming behavior of the hcp materials as a result of superimposed electric current impulses. This behavior could be attributed to two effects. On the one hand, additional dislocation types are activated; on the other hand, new characteristic twin bands are formed. This is shown for all three hcp materials under investigation: Ti, Mg, and Zn. Furthermore, the hypothesis of the existence of a critical value of the current density at which a significant change in the plastic behavior occurs is verified by the experiments. The magnitude of this critical value for the analyzed hcp materials corresponds approximately to the theoretical values reported to be in the range of 1.6 to 2.0 kA mm−2. In addition to the current density, the duration of the pulses also has an influence on the EPE. Understanding the correlation between the individual activated deformation mechanisms during electric pulse treatment can be crucial for controlling the electroplastic forming processes in a systematic and targeted manner.

DEUTERIUM RETENTION IN N-SEEDED AND UNSEEDED TUNGSTEN LAYERS OBTAINED WITH DCMS AND M-HIPIMS TECHNIQUE

The retention of hydrogen isotopes in tungsten co-deposited layers is a subject severely understudied in the literature compared to hydrogen isotope implantation in bulk tungsten specimens. However, impurity seeding in future next-generation fusion devices can reduce the sputtering threshold of tungsten and potentially increase the contribution of the tungsten layers to the global tritium retention problem. This paper reports on the development of fusion-relevant tungsten-deuterium and nitrogen-seeded tungsten deuterium layers using direct current (DCMS) and multipulse high-power impulse magnetron sputtering techniques (HiPIMS). The four layers resulting from co-deposition in argon-deuterium and argon-deuterium-nitrogen atmosphere were investigated from the deuterium retention and release point of view. Supplementary the crystalline structure of all samples and particularly the composition of the nitrogen-seeded layers were also studied. The tungsten-deuterium layers produced using m-HiPIMS technology showed a higher crystalline coherence compared to layers deposited with DCMS in part owned to the enhanced ion bombardment of the forming layers during deposition. On the other hand, the nitrogen-seeded layers showed without exception the formation of the tungsten-nitride compound. Here on the contrary the crystalline coherence as revealed by X-ray diffraction measurements measurement showed that nitride formation is favored for DCMS compared with m-HiPIMS. The elemental areal densities of the layer constituents were analyzed using Rutherford Backscattering Spectrometry. In this case, only the two nitrogen-seeded layers were analyzed revealing that a higher nitrogen content by a factor of ~2 is retained in DCMS deposited layer compared to HiPIMS.The release of deuterium was higher in the case of m-HiPIMS layers and it was shown that despite the deposition method the release behavior occurs predominantly at temperatures above 800 K suggesting a high energy trapping of deuterium in tungsten layers. Nitrogen seeding influences both the retention mechanisms and increases the deuterium retention by two orders of magnitude in seeded layers compared to unseeded ones.

Effects of elevated temperature exposure on the residual stress state and microstructure of PVD Cr coatings on SiC investigated via in situ X-ray diffraction and transmission electron microscopy

Pure Cr coatings are being considered as corrosion-resistant layers for SiC-SiCf composite fuel cladding in light water reactors. The residual stress state and interdiffusion behavior of Cr coatings deposited on SiC substrates using bipolar high-power impulse magnetron sputtering (B-HiPIMS) and direct current impulse magnetron sputtering (DCMS) were studied using in situ X-ray diffraction experiments at 300 °C, 700 °C, and 1200 °C. After elevated temperature exposure, evolution of the coating microstructure and coating/substrate interdiffusion was characterized by transmission electron microscopy. The compressive residual stress of the dense B-HiPIMS coating at room temperature was gradually relieved at 300 °C, while the stress transitioned to a tensile state at 700 °C. Grain growth of the Cr coating and a Cr–SiC interdiffusion layer consisting of newly formed Cr–C and Cr–Si phases were observed in the B-HiPIMS coating after exposure at 700 °C. The phases in the interdiffusion layer were identified to be Cr7C3, Cr3Si, and Cr5Si3Cx experimentally and by thermodynamic predictions. For the DCMS coating, however, changes in residual stress and microstructure at the elevated temperatures were limited by the inherent porosity and inhomogeneous structure of the as-deposited coating. At 1200 °C, both coating types interacted rapidly with the underlying SiC substrate in the early stages of the experiment. The results from this study suggest that the characteristics of the Cr coatings do not significantly change at the reactor operating temperature of 300 °C, while changes in microstructure and stress state are expected in off-normal conditions of 700 °C and 1200 °C. The results from this study suggest the B-HiPIMS coating is best-suited as a protective coating for SiC fuel cladding.

Canonical Response Parameterization: Quantifying the structure of responses to single-pulse intracranial electrical brain stimulation.

Single-pulse electrical stimulation in the nervous system, often called cortico-cortical evoked potential (CCEP) measurement, is an important technique to understand how brain regions interact with one another. Voltages are measured from implanted electrodes in one brain area while stimulating another with brief current impulses separated by several seconds. Historically, researchers have tried to understand the significance of evoked voltage polyphasic deflections by visual inspection, but no general-purpose tool has emerged to understand their shapes or describe them mathematically. We describe and illustrate a new technique to parameterize brain stimulation data, where voltage response traces are projected into one another using a semi-normalized dot product. The length of timepoints from stimulation included in the dot product is varied to obtain a temporal profile of structural significance, and the peak of the profile uniquely identifies the duration of the response. Using linear kernel PCA, a canonical response shape is obtained over this duration, and then single-trial traces are parameterized as a projection of this canonical shape with a residual term. Such parameterization allows for dissimilar trace shapes from different brain areas to be directly compared by quantifying cross-projection magnitudes, response duration, canonical shape projection amplitudes, signal-to-noise ratios, explained variance, and statistical significance. Artifactual trials are automatically identified by outliers in sub-distributions of cross-projection magnitude, and rejected. This technique, which we call "Canonical Response Parameterization" (CRP) dramatically simplifies the study of CCEP shapes, and may also be applied in a wide range of other settings involving event-triggered data.

Review: Factors Affecting the Performance of Ground Electrodes under High Impulse Currents

Most studies have observed that the impedance values of ground electrodes under high impulse conditions (Zimp) are lower than the resistance values under steady-state conditions (RDC). It has been suggested that this is due to the ionisation process in soil, where streamers will propagate away from the electrodes, causing an increase in the ionisation zone, thus reducing the Zimp values. The percentage difference between Zimp and RDC is found to be dependent on several factors. This paper aims to review and present the findings of previously published work on the percentage difference between Zimp and RDC in relation to various factors.

Lightning Impulse Current Tests on some Electroconductive Fabrics

On the search of lightweight lightning protection materials that can be used as part of Lightning Protection Systems (LPS), we investigate some types of electroconductive fabrics by applying several high lightning impulse currents in laboratory. Samples of four commercially available electroconductive textiles were analyzed: two rip-stop, a plain-weave, a non-woven, and additionally a carbon-impregnated polymeric film. Under laboratory conditions, each sample was subject to several subsequent lightning-like currents, recording both voltage and current signals. Optical and scanning electron microscope observations were performed after tests, revealing some patterns or morphological changes on the fabric surface. Despite these changes, the investigated conductive textiles withstand the several lightning impulse currents applied. Results suggest that some conductive fabrics could be used in personal mobile shelters, to protect human beings against the earth potential rise caused by a close lightning discharge.