Direct Currents Research Articles

Intermetallic compounds formed in Sn droplet on Cu substrate under the impact of electric currents

The present paper investigates the influence of electric currents on the formation of Sn/Cu intermetallic compounds. Solidification experiments of Sn droplets on Cu substrate were performed under the impact of direct csurrents (DC) and pulsed electric currents (ECP), respectively. The results show that the precipitation of Cu6Sn5 from the Sn/Cu interfacial reaction is significantly enhanced by both DC and ECP. DC promotes the formation of Cu6Sn5 at the interface, whereas ECP triggers the detachment of Cu6Sn5 at the interface and favors the growth of freely floated Cu6Sn5 particles in the bulk Sn melt. Numerical simulations were conducted to calculate the distribution of electric current, induced magnetic field, Lorentz force and forced flow inside the Sn melt. The numerical results show that a strong downwards Lorentz force is generated adjacent electrode bottom owing to the interaction between electric current and induced magnetic field. As a result, a global forced flow is caused inside the Sn melt. It is possible that the forced flow induces the elements transport to promote the precipitation of intermetallic compounds. Moreover, a strong Lorentz force difference between Sn melt and Cu6Sn5 is generated under the application of ECP compared with that of DC, thereby increasing the potential to initiate the detachment of Cu6Sn5.

Corrosion behavior of 13Cr stainless steel under stress and crevice in high pressure CO2/O2 environment

In this work, through the self-developed setup for in situ electrochemical tests, the corrosion behavior of 13Cr stainless steel under the combined effect of stress and crevice in high pressure CO2/O2 environment was investigated. The results show that 13Cr stainless steel presents a self-passivation state. Under the action of stress, the anodic dissolution process of steel inside crevice is expedited. There is a galvanic effect between the stressed steel inside crevice and the unstressed steel outside crevice. The applied stress reduces the induction stage of crevice corrosion and induces a larger galvanic current, i.e., the applied stress promotes the development of crevice corrosion. Meanwhile, adding 0.1 MPa O2 is conducive to forming a more stable passive film but causes a greater galvanic effect.

Unified adaptive neuro-fuzzy inference system control for OFF board electric vehicle charger

This paper illustrates the control algorithm design for a two stage off board bidirectional smart electric vehicle (EV) charger architecture. The proposed EV charger is controlled to perform four quadrant operation (i.e. vehicle-to-grid (V2G) and grid-to-vehicle (G2V)) while compensating the load harmonics, simultaneously. Here, the 3-phase AC-DC converter and DC-DC converter are two main components, where the first one is controlled to regulate DC-link voltage as well as reactive power and current harmonics of nearby non-linear load while the second one regulates the exchange of active power. Generally, the AC-DC converter is controlled via two control loops, i.e. outer loop and inner loop. However, setting the gains of almost four proportional integral (PI) controllers and determining decoupling terms for inner control loops is very difficult, especially under the dynamic operating conditions. Therefore, an adaptive neuro-fuzzy inference system (ANFIS) has been designed to estimate the direct and quadrature axis reference currents directly while regulating two different quantities in single step only and hence, named as unified ANFIS controller. The proposed EV charger is simulated in MATLAB/Simulink and controller performance is validated with scaled down hardware model in real time.

Alternating (AC) Loop Current Attacks Against the KLJN Secure Key Exchange Scheme

Recently, several passive and active attack methods have been proposed against the Kirchhoff–Law–Johnson–Noise (KLJN) secure key exchange scheme by utilizing direct (DC) loop currents. The DC current attacks are relatively easy, but their practical importance is low. On the other hand, parasitic alternating (AC) currents are virtually omnipresent in wire-based systems. Such situations exist due to AC ground loops and electromagnetic interference (EMI). However, utilizing AC currents for attacks is a harder problem. Here, we introduce and demonstrate AC current attacks in various frequency ranges. The attacks exploit a parasitic/periodic AC voltage-source at either Alice’s or Bob’s end. In the low-frequency case, the procedure is the generalized form of the former DC ground-loop-based attack. In the high-frequency case, the power density spectrum of the wire voltage is utilized. The attack is demonstrated in both the low and the high-frequency situations. Defense protocols against the attack are also discussed.

Investigating crevice corrosion of copper and copper alloys using wire beam electrode

ABSTRACT A wire beam electrode (WBE) method for investigating the crevice corrosion has been demonstrated by mapping non-uniform corrosion processes occurring on copper and copper alloys including the pure copper UNS No. C11000 (Cu), brass UNS No. C28000 (Cu–Zn alloy) and tin bronze UNS No. C51900 (Cu–Sn alloy) in mass 0.6% NaCl solution with the crevice spacings of d=103 μm and 206 μm. It was found that the sequence of three copper alloys in susceptibility for the crevice corrosion was that Cu–Zn alloy > Cu–Sn alloy > pure Cu. The average galvanic current of the Cu–Sn alloy in the covered region was changed from cathode to anode when the crevice spacing was increased to 206 μm. To sum up, it is feasible to study the behaviours of crevice corrosion within the different crevice spacings with the WBE method.

Deformation steel rods periodic profile with operational damages

Introduction. In the transverse and longitudinal sections of the rods with a periodic profile, there are layers with different structural and phase states, physical and mechanical characteristics, stress state and resistance to external influences. The appearance of plastic deformations in the bases of the depressions and other defects of a periodic profile during stre­tching of the rods leads to a decrease in the resistance to corrosion damage due to the occurrence of galvanic pairs between inhomogeneous sections of the rod. This makes the computational and experimental studies of the deformed state of such rods under tension urgent.
 
 Materials and methods. The finite element modeling of the deformation process during the elastic-plastic work of steel was carried out using the ANSYS software complex and solid models of the rods under study. Experimental tests of the samples were carried out using an R-50 tensile testing machine with the recording of a load-elongation diagram in accordance with the requirements of GOST 1497. The process of deformation of the samples was displayed by photographic recording. After the destruction of the samples, the geometric dimensions (lengths, changes in cross-sections) were measured, the typical types of samples and their fragments, and fractures were photographed.
 
 Results. On experimental and finite-element models, it was found that during elastic-plastic deformation of steel rods in dangerous sections, a change in the angle of inclination of the banks of periodic protrusions (undercuts) affects the volume of plastically deformable material at the base of the undercuts. Such an analysis of the models in the limiting state has shown that the volume of the plastically deformed material is significantly reduced at the angles of the protrusions at their bases with the axis of the rod close to 900. The calculation established that the plastically deformed area at the base of sharp undercuts is more than a hundred times smaller than the corresponding volume at the base of the gently sloping undercuts. In samples with a group of protrusions, constraint of plastic deformations at the base occurs only for protrusions, the width of which is comparable to the diameter of the rod in weakened sections. The greatest development of equivalent plastic deformations is observed at the base between narrow projections. Damage to the outer layers of quasi-composite rods with a periodic profile causes significant changes in the stress-strain state of the rods under tension.
 
 Conclusions. The finite element modeling of the tensile work of steel rods with a periodic profile with a quasi-composite structure is a complex multifactorial problem. Plastic deformations develop in the depressions of the periodic profile. At the same time, undeformed areas remain in the metal of the protrusions. These zones have different potentials and between them the occurrence of internal galvanic currents is possible, leading to the acceleration of corrosion processes.

Ground Potential Rise in Wind Farms due to Direct Lightning

This paper investigates the ground potential rise (GPR) developed in wind farms subject to direct lightning currents representative of first and subsequent negative downward strokes and return strokes associated with upward negative flashes. The wind farm grounding system is studied considering different numbers of interconnected grounding systems and for distinct values of soil resistivity taking into account frequency-dependent soil parameters. A wideband multiport model of the wind farm grounding system is obtained and implemented in a time-domain electromagnetic transient tool to include the aerial elements in simulations, namely the wind turbine blades and tower. It is shown that interconnecting more wind turbine grounding systems in parallel leads to a significant reduction of the low-frequency grounding resistance, whereas the decrease of the impulse impedance is much lower, especially for low-resistivity soils and negative downward subsequent strokes or negative upward lightning return strokes. It is also shown that the presence of the aerial components significantly affects the GPR in the response to lightning currents representative of negative downward subsequent strokes and return strokes associated with negative upward flashes, which have higher frequency content compared to negative first return strokes. The presence of the aerial components increases the GPR peak.

Optimization of the morphology, structure and properties of high iron content Zn–Fe coatings by pulse electrodeposition

An additive-free gluconate based alkaline electrolyte was used to study the electrodeposition of Zn and Zn–Fe coatings. Cyclic voltammetry was performed to define the accurate deposition parameters and to identify the reactions taking place. Electrodeposition was performed using direct and pulse currents. Electrodeposits were characterized in terms of morphology, microstructure, mechanical and corrosion properties. Homogeneous Zn and Zn–Fe 7 wt% Fe were obtained, composed of hexagonal and blunted pyramidal grains respectively. Pulse current deposition was carried out to improve the morphology and to reduce the impact of hydrogen evolution reaction. Deposition parameters such as on-time/off-time/peak current density (ton/toff/jp) were investigated. The average current density jm seems to control the composition of Zn–Fe electrodeposits. High iron contents were obtained at low current densities and the iron content abruptly decreased when the current density increased for both direct and pulse currents electrodeposition. Incorporation of iron led to an increase of the micro-hardness of the coating. Scratch tests were performed in order to evaluate the damage of the coatings, and the coating adhesion could be assessed. Polarization curves in 3.5 wt% NaCl after 1 h of immersion at the open circuit potential did not show any change of corrosion potential between Zn and Zn–Fe 7 wt% Fe deposits. This potential was shifted to a more positive value for Zn–Fe 14 wt% Fe, which points out this coating as the best choice to reduce the galvanic corrosion between the steel substrate and the Zn–Fe deposit. These results were linked to the microstructure of the deposits and perhaps to the presence of Γ1-Fe5Zn21 phase for Zn–Fe 14 wt% Fe.

Changes in the interfacial charge-transfer resistance of Mg metal electrodes, measured by dynamic electrochemical impedance spectroscopy

The interfacial electrochemical characteristics of unpassivated Mg metal electrodes have been studied using Staircase Galvano Electrochemical Impedance Spectroscopy (SGEIS) in THF/C6H5MgCl/AlCl3 solutions over a wide range of applied dc currents. The results shed light on the mechanism of electrochemical deposition and dissolution of Mg. We found that at the stationary condition (at the OCV, when no current flows) there is a very high interfacial charge-transfer resistance of around 40,000 Ωcm2. The impedance decreases to several hundred Ωcm2 when dynamic, though steady, processes of Mg deposition or dissolution take place. The alternating process through which impedance spectroscopy is measured is superimposed on this system. We show that the high impedance measured at the OCV with a low direct current is due to interfacial adsorption phenomena. However, the adsorption phenomena affect the interfacial charge transfer in different ways depending on the direction of the reaction. During steady-state deposition, the adsorbed layer leads to a large distance for electron tunneling, which translates to a high charge-transfer impedance across the interface. Application of relatively large steady-state negative currents leads to changes in the composition of the adsorbed layer and a significant reduction in the charge-transfer resistance. During the opposite process, dissolution, the high interfacial impedance measured is probably predominantly due to migration of Mg ions away from the Mg metal surface, across the adsorbed layer, to the bulk solution. At relatively high direct currents (and overpotentials >100 mV) the interfacial resistivity obeys Butler–Volmer kinetics, which are not complicated by adsorption phenomena.

Skyrmion ratchet propagation: utilizing the skyrmion Hall effect in AC racetrack storage devices

Magnetic skyrmions are whirl-like nano-objects with topological protection. When driven by direct currents, skyrmions move but experience a transverse deflection. This so-called skyrmion Hall effect is often regarded a drawback for memory applications. Herein, we show that this unique effect can also be favorable for spintronic applications: We show that in a racetrack with a broken inversion symmetry, the skyrmion Hall effect allows to translate an alternating current into a directed motion along the track, like in a ratchet. We analyze several modes of the ratchet mechanism and show that it is unique for topological magnetic whirls. We elaborate on the fundamental differences compared to the motion of topologically trivial magnetic objects, as well as classical particles driven by periodic forces. Depending on the exact racetrack geometry, the ratchet mechanism can be soft or strict. In the latter case, the skyrmion propagates close to the efficiency maximum.

Galvanic corrosion study between low alloy steel A508 and 309/308 L stainless steel dissimilar metals: A case study of the effects of oxide film and exposure time

The effects of oxide film and exposure time on the galvanic corrosion between low alloy steel (LAS) A508 and 309/308L stainless steel (SS) dissimilar metals were studied by several electrochemical techniques and surface composition analytical tools. The zero resistance ammeter (ZRA) result shows that the trend of galvanic corrosion current between the coupled LAS A508 and 309/308L SS changes with respect to exposure time. Furthermore, from the ZRA measurement, the quantitative relationship between galvanic current and dissolution rate of the coupled LAS A508 anode metal was established by statistical approach. Electrochemical impedance spectroscopy (EIS) results and analyses demonstrated that the increasing galvanic corrosion rate observed between the coupled dissimilar metals as exposure time prolonged was suppressed by the oxide film effect. The suppression occurred as a result of the transformation of unstable oxides to stable oxide forms, and the oxide film thickening phenomenon experienced on the LAS A508 surface as exposure time prolonged. Generally, a synergy between both effects was observed in this study.

Multi-objective partition planning for multi-infeed HVDC system

The close proximity and the necessity of coordination between multiple high-voltage direct currents (HVDCs) raise the issue of grid partitioning in multi-infeed HVDC systems. A multi-objective partition strategy is proposed in this paper. Several types of relationships to be coordinated and complemented are analyzed and formulated using quantitative indices. According to the graph theory, the HVDC partition is transformed into a graph-cut problem and solved via the spectral clustering algorithm. Finally, the proposed method is validated for a practical multi-HVDC grid, confirming its feasibility and effectiveness.

Estimating the energy in current signals during electrical sounding: a novel approach

Despite the rapidity in the use of electrical sounding/expanding probe technique in the study of hydrology, mineralogy, contamination, and other geophysically based studies over decades, it appears that our ability to identify the relationships between the energy loaded in direct currents injected into the ground between two electrodes at low polarizing frequency is not yet realized and hence the drive for this research. This study is insightfully undertaken to address this problem by establishing the novel links associated with the existing geo-resistivity theories and the two complementary energies, the voltage-driven energy called charging energy and the charge-driven energy called the discharging energy. This was achieved by sorting the resistivity values realized from electrical sounding technique into regimes (trends of resistivities representing certain geologic layers) and plotting each regime in a location against the signal current low polarizing frequency measured from the relationship between power line frequency and the ratio of potential to current separations. The two energies, which are determinable from the slopes of regressed resistivity-period plots and the novel relations established in this work, depend on the dynamic parameters βv and βq, which are respectively called the voltage geometric index of energy and charge geometric index of energy. These indices connect earth resistivity to energy and frequency/relaxation period. Calculating the energy for each sounding at its polarizing frequency, the complementary charging and discharging energies were traced to be dependent on conductivity/resistivity of the geological sequence/regimes. The established equations, graphs, and contour maps give insightful and expanded information on the dependence of energy loaded on injected currents into the ground. The charging energy, which is enhanced in arenaceous layers, has low conductivity and is believed to have high permittivity and low energy loss factor, which is not determined in this work while discharging energy in argillites is high as conductivity and energy loss factor increase at decreasing permittivity. In all cases, the currents and its loaded energy are in comparatively minute magnitudes.

Head-Only Stunning of Turkeys Part 2: Subjective and Objective Assessment of the Application of AC and DC Waveforms.

Simple SummaryIn this study, we investigated various types of application of head-only electrical stunning to turkeys, in order to improve the effectiveness of the stunning process. We used recordings of physical responses and of electroencephalograms (EEGs) to assess effectivity of stunning and various waveforms: alternating current (AC) and pulsed direct currents (DC). Depending on the waveforms, voltages between 125 and 250 V produced an effective stun in turkeys in this study.Electrical stunning is likely to remain an important stunning method for turkeys at slaughter. The purpose of this study is to understand the application of various waveforms of alternating current (AC) and pulsed direct currents (DC), head-only, to turkeys and to improve the effectiveness of handheld stunning of turkeys. We evaluated the effectiveness of stunning by documenting physical responses and recording electroencephalograms (EEGs). For the assessment of physical responses, the stunning voltage was varied depending on the proportion of animals effectively stunned at a certain voltage level. If all turkeys in a group of 10 were stunned, the voltage was decreased, and the next group was stunned. This was repeated until not all turkeys showed signs of being effectively stunned. The experiment was then repeated at the voltage level just above the one that showed incomplete effective stunning. The effects of the stunning on the EEG recording was assessed in 16 turkeys to measure the occurrence of epileptiform EEGs, in 14 turkeys to assess epileptiform EEGs after neck-cut (bleeding), and in 14 turkeys to assess the effect of increased voltage and reduced frequency on epileptiform EEGs. Assessing EEGs in a laboratory setting contributes considerably to the understanding of electrical stunning procedures. Voltages between 125 and 250 V, depending on the waveform assessed, were effective in producing an effective stun in turkeys in this study.

Effects of Alternating Currents in the Hearth of Submerged Arc Furnaces

It is well known that alternating currents (AC) differ significantly from direct currents (DC) in large electrodes for Submerged Arc Furnaces (SAFs). The skin effect concentrates AC to the periphery of each electrode, while the proximity effect causes higher current concentration towards the leading electrode. In a presentation at INFACON XV it was further shown that there is also a significant proximity effect between electrode currents and induced currents in the furnace steel shell. Here, we will focus on differences and similarities between AC and DC below the electrodes. In many processes the current runs primarily vertically in a coke bed from each electrode to a metal bath, where it distributes to the other electrodes. In such coke beds we find no significant difference between AC and DC. In the highly conductive metal, there will be horizontal currents and a significant AC skin effect. Horizontal currents will also be present in the materials above the metal, depending on the electrical conductivity in this region. A simple model shows that there is a strong proximity effect between such adjacent currents, “pushing” the currents upwards within the slag/coke bed region. A simple estimate, based on furnace dimensions and assumed conductivities, will show whether this effect is significant, in which case DC computations are inadequate to estimate the current paths. The same proximity effect will significantly enhance induced currents in an electrically conductive lining. Finally, since the underlying Maxwell’s equations are linear, the fundamental current paths in 3-phase AC SAFs can be studied by computing two independent single-phase cases for a given geometry and distribution of electrical conductivities. Any other current distribution will be a linear combination of these two solutions.

Modification of Patients’ Sensitivity to Galvanic Current After the Administered Systemic Cryotherapy

Aim: The purpose of the study was to evaluate the sensitivity of patients to galvanic current after systemic cryotherapy. Material and Methods: Study group: 77 physiotherapists – hospital employees, aged 21-64 (AVG 29.4±9.5). The sensitivity was evaluated four times: before and immediately after the systemic cryotherapy procedure (1 session, 2 minutes, temperature -120°C), after exercising on a vertical cycle ergometer (20 minutes) and 4 hours after the procedure. The intensity of the galvanic current, which caused a slight tingling, was recorded. Two electrode placements were used: longitudinal on the upper limbs and transverse over the knee joints. Results: Statistical analysis revealed that the mean sensitivity to the galvanic current measured on both upper limbs or over the knee joints increases statistically significantly after systemic cryotherapy treatments. This effect persists even after 4 hours (Friedman’s ANOVA, p<0.001). Statistically significant increases in sensitivity to galvanic current were found compared to initial values for each pair of measurements, irrespective of electrode placement and test position (Wilcoxon test, p<0.01). The increase in sensitivity according to the measuring position concerned 68.8; 63.6; 72.7% of the participants on the left upper limb, on the right 61.0; 68.8; 74.0%, over the left knee joint 61.0; 68.8; 72.7% and over the right 58.4, 75.3 and 80.5% of the subjects in the study group. Conclusions: 1. After the administered systemic cryotherapy, sensitivity to galvanic current increases in most patients. 2. The increase in sensitivity to galvanic current depends on the time difference between treatments and is individually variable.

Electrical resistivity and setting characteristics of some biomaterials

Cement base materials are used under metallic restorations to minimize pain due to galvanic current. The setting time - current characteristics of dental cements show that, immediately after mixing of the powder-liquid, the resistivity of dental cements such as Zinc Polycarboxylate, Zinc Phosphate and Glass Ionomer is of the order of 103 Ω - m. The resistivity of these fully set cement is high and of the order of 107 Ω - m. Glass ionomer cement show prolonged conductivity suggesting that, clinically when used as bases under metallic fillings, they may not function adequately as insulators against the effects of galvanic currents on the pulp.

Improvement of modeling techniques of transients in transformers based on magnetoelectric equivalent schemes

Purpose. Use of an improved numerical method of calculating transient processes in electrical circuits for modeling electromagnetic processes in nonlinear magneto-electric circuits, and also development of a circuit model based on this method, which leads to the convenience of calculation. Methodology. Approximation of functions by Chebyshevs polynomials, numerical methods of differential equations integrating, matrix methods, spline interpolation, programming, theory of electric and magnetic circuits. Findings. On the base of the well-known method of transient process analysis in linear electric circuits, the method of numerical calculation of transient processes in nonlinear magneto-electric equivalent circuits of transformer has been developed. By the help of the proposed method it is possible to reduce processing time for modeling electromagnetic processes in transformers. The example of using the developed method is shown. The computer program for modeling of electromagnetic transient in a single-phase transformer based on the described method has been developed. This example shows reduction of processor time by more than four times compared to examples of calculations based on other known methods. Originality. The method in which the solution of state differential equations is presented in the form of decomposition into a series along orthogonal Chebyshevs polynomials is used in this work. The polynomial approximation applied in this work is not corresponding to the solution function itself, but its derivative, which significantly reduces the error of integration of differential equations. Differential equations of state are transformed into linear algebraic equations for special images of solution functions. A principle is developed of constructing magneto-electric substitution circuits in which images of solution functions appear. Images of true dynamic currents and magnetic fluxes in the proposed equivalent scheme are interpreted as direct currents and direct magnetic fluxes. The used method has shown advantages in accuracy and time of simulation of electromagnetic transient over other known methods based on application of magneto-electric substitution circuits. Practical value. The developed method opens up the possibility of using the apparatus of the theory of electric and magnetic circuits to work with images of currents and magnetic fluxes. Based on this, a universal software complex is being developed to calculate transients in transformers of various constructions.

Static characteristics of contactless converters of monitoring and control systems

The paper substantiates the need to use non-contact conversion and measurement of large direct currents using magnetic modulation contactless transducers of increased sensitivity for land reclamation, irrigation, industry, metallurgy and agriculture and water management in general, and the results of their design development are presented. It is shown that the developed converter, in contrast to the known ones, has increased accuracy and sensitivity, a technologically advanced design and low weight and dimensions with low material consumption and cost. Characteristics of information non-contact magnetic modulation converters statically are considered. It is shown that the value of the excitation value corresponds to a certain maximum value of the measured value. In this case, the maxima of the measured value, increasing in value with an increase in the excitation value, are shifted towards the increase in the measured value. The discrepancy between the experimentally and theoretically obtained static characteristics of the converter does not exceed 6 percent. The developed converter can be widely used in electrical systems in land reclamation and irrigation, in water supply, industry, railway transport, science, technology, and for checking electric meters at their installation site for contactless control of direct and alternating currents.

Folic acid conjugation of magnetite nanoparticles using pulsed electrohydraulic discharges

The sonochemical coprecipitation reaction with moderate ultrasound irradiation in a low vacuum environment was used to obtain aqueous colloidal suspensions of iron oxide nanoparticles (IONPs). The synthesized magnetite nanoparticles were conjugated directly by folic acid using electrohydraulic discharges as a processing technique before modification of the surface of the nanoparticles. Electrohydraulic discharges were applied in two operational modes with high and low power pulsed direct currents between the electrodes. The physical and chemical properties of the obtained samples were studied using X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). The investigation proved an inverse cubic spinel structure of magnetite with folic acid attachment to the magnetite surface (mean crystallite diameter in the samples, D, ranges 25?31 nm by XRD and SAXS). It was found that the processing with electrohydraulic discharges increased the colloidal stability of the folic acid-magnetite nanoparticle dispersions.