Increase In Current Frequency Research Articles

Numerical Simulation of Electromagnetic Field in Slab Electroslag Remelting Process with Double Electrode Series

In this paper, a mathematical model of an electromagnetic field during an electroslag remelting process of industrial-scale slab was established using a Maxwell 3D module in Ansys Electromagnetics Suite. The distribution characteristics of the magnetic field intensity, current density and Joule heat density during the electroslag remelting process were analyzed in detail. On this basis, the influence of the current frequency on the electroslag remelting process of an industrial scale is studied, and the influence of process parameters such as the slag pool depth, electrode insertion depth and ingot height on the electromagnetic field is also considered. The results show that the Joule heat generated in the slag pool is much greater than that of the electrode and the ingot. The maximum Joule heat is located at the contact between the electrode corner and the slag pool, and the Joule heat near the middle of the two electrodes is greater than the rest. With the increase in the current frequency, the current density distribution in the slag cell is basically unchanged. The current density inside the two electrodes increases obviously with the current frequency. When the current frequency increases from 10 Hz to 50 Hz, the maximum current density at the inner surface of the electrode increases by 14.7%. The current distribution at the lower side of the electrode in the slag pool is relatively uniform, and the current density in this region decreases with the increase in the height of the slag pool and the increase in the depth of the electrode inserted into the slag pool.

Features of pulse-reverse modes for Ni–Fe nanogranular films electrodeposition: Correlation of structural parameters and MI effect

Through pulse-reverse electrodeposition with various reverse durations, the Ni–Fe films were synthesized. The film's structure was different. With an increase in the reverse duration, the average grain size and porosity increased to a certain point. As the reversal duration is increased, the porosity and average grain size decrease. Magnetic anisotropy was revealed through an analysis of magnetic characteristics. In particular, when the magnetic field was perpendicular to the samples, the remnant magnetization increased from 0.3 to 2.3 emu/g. The remnant magnetization varied from 77 to 91 emu/g with a parallel orientation. Research on the magnetoimpedance has revealed that at a frequency of 100 kHz, the magnetoimpedance coefficient is at a minimum due to resonance effects in both directions of the magnetic field. The magnetostatic model can be used to explain the mechanism of change in the magnetoimpedance in the low-frequency range. The magnetoimpedance occurs in the medium frequency range (from 10 kHz to 1 MHz) due to changes in the magnetic permeability caused by the impact of a magnetic field and an increase in current frequency, which modify the depth of the skin layer.With an increase in current frequency passing through the sample, the current density on the near-surface layer becomes non-uniform. This non-uniformity is significantly influenced by microstructure parameters such as porosity, average grain size, and the degree of texturization, all of which contribute to the conductor's impedance. It opens new direction for smart sensors development.

Numerical Study of Ti6Al4V Alloy Tube Heated by Super-Frequency Induction Heating.

Ti6Al4V alloys have a narrow processing window, which complicates temperature control, especially during large-scale production. Therefore, a numerical simulation and experimental study on the ultrasonic induction heating process of a Ti6Al4V titanium alloy tube were conducted to obtain stable heating. The electromagnetic and thermal fields in the process of ultrasonic frequency induction heating were calculated. The effects of the current frequency and current value on the thermal and current fields were numerically analyzed. The increase in current frequency enhances the skin and edge effects, but heat permeability was achieved in the super audio frequency range, and the temperature difference between the interior and exterior of the tube was less than 1%. An increase in the applied current value and current frequency caused an increase in the tube's temperature, but the influence of current was more prominent. Therefore, the influence of stepwise feeding, reciprocating motion, and stepwise feeding superimposed motion on the heating temperature field of the tube blank was evaluated. The coil reciprocating with the roll can maintain the temperature of the tube within the target temperature range during the deformation stage. The simulation results were validated experimentally, which demonstrated good agreement between the results. The numerical simulation method can be used to monitor the temperature distribution of Ti6Al4V alloy tubes during the super-frequency induction heating process. This is an economical and effective tool for predicting the induction heating process of Ti6Al4V alloy tubes. Moreover, online induction heating in the form of reciprocating motion is a feasible strategy for processing Ti6Al4V alloy tubes.

Method of Calculating Inductance Gradient for Complex Electromagnetic Rail Launcher

Electromagnetic rail launch technology has made impressive progress; however, the analytical method of calculating the inductance gradient for a complex electromagnetic launcher is still insufficient. By fully considering the characteristics of electromagnetics and current distribution in a device, this paper describes a model of the current skin effect by simplifying the line current distribution in the device. Based on Biot–Savart Law, an analytical method of calculating inductance gradient for an electromagnetic rail launcher with complex structure is proposed. This method has the advantages of fast calculation speed and accurate calculation results. Because of error analysis, the calculated value relatively corresponds to the simulation result of the eddy current field. To reflect the transient electromagnetic emission process, the effects of different configurations, current frequency, and armature position on the inductance gradient are further summarized. The results show that the error rate of this method in calculating the inductance gradient is about 4%, which meets the requirement for calculation accuracy. The inductance gradient of the enhanced four-rail electromagnetic launcher is about 2.22 times that of the nonenhanced one due to the equal conditions; the inductance gradient decreases with the increase in current frequency and decreases as the armature approaches the muzzle.

Drive Cycle Energy Efficiency of Fuel Cell/Supercapacitor Passive Hybrid Vehicle System

The electric vehicle with passive hybridization of fuel cells and supercapacitors leads to lower cost and compactness due to the absence of dc-dc converters. This article models such a vehicle and evaluates the energy efficiency of its powertrain system. The powertrain component losses, as functions of electric machine torque, speed and dc-link voltage, are modeled with a high level of detail, which are verified against available test data. Compared to a pure fuel cell system, the fuel cell efficiency is higher when supercapacitors are introduced under pulse current load, and it is higher at lower current amplitude. As the pulse current frequency increases, the fuel cell efficiency also increases due to higher proportional current from the high-efficiency supercapacitors. A multiplicity of drive cycles is selected, divided into a low, middle, and high-speed category to analyze the powertrain efficiency. The total powertrain energy efficiency varies between 53%-71% during propulsion for the studied drive cycles, whereas it is higher during braking ranging from 84% to 94%. The differences are closely related to the speed, acceleration, and dc-link voltage levels. The lower powertrain efficiency causes higher hydrogen consumption, leading to a reduced fuel cell efficiency at high speed, high acceleration, and low dc-link voltage.

Influences of Excitation Current Frequency and Amplitude on Corrosion Evaluation Based on Analytical Model for Surface Magnetic Field

The influences of excitation current on the evaluation of the corrosion with a cylindrical shape in a semi-infinite plate are presented in this paper. First, axi-symmetric model of the cylindrical coil above the corroded plate is established and an analytical solution to the surface magnetic field is derived by means of the truncated region eigenfunction expansion method (TREE). Then, the effect of the excitation current frequency and amplitude on the surface magnetic field is investigated and quantitatively evaluated. It is found that the radial magnetic induction intensity increases as the excitation current frequency increases, whereas the axial magnetic induction intensity decreases. The excitation current amplitude is proportional to the radial and axial magnetic induction intensities and does not affect the phase of magnetic induction intensity. As a result, the influence node for detecting the radius and the hollow depth for detecting the hidden depth are obviously dependent on the excitation current frequency in terms of the butterfly-shaped graph. The calculation results are in good agreement with the numerical simulation, showing that the developed model can be used to predict the optimal excitation current frequency. This work indicates that an appropriate excitation current frequency, such as f = 500 Hz, can improve the characteristic parameter resolution for detecting the corrosion radius. For the detection of hidden depth, the lower excitation current frequency, such as f = 100 Hz, can amplify the defect phenomenon and improve the detection accuracy. It is not only helpful to develop the analytical model for the surface magnetic field, but also to optimise the parameters of the test device.

Experiment research of post-arc current and cathode spots distribution in medium-high frequency vacuum arc

In this paper, the breaking process of the vacuum circuit breakers is briefly described, and the main factors that influence the post-arc process are analyzed. Based on the detachable vacuum interrupter, the experimental platform of AC breaking is built, and the experiments of the post-arc current measurement and cathode spot observation are completed. The voltage and current during the period of current zero are measured, and the images of cathode spots during the arcing process are obtained. The experimental results show that at the same frequency, the post-arc current Ipac and the post-arc charge Qpac increase with the increase in didtcz(didt at current zero). Under the same conditions of didtcz, Ipac and Qpac decrease with the increase in frequency, but both are unchanged with frequency when the frequency is high enough. With the increase in current frequency, the distribution diameter of cathode spots decreases under the condition of the same didtcz value. According to the characteristics of cathode spot distribution, the metal vapor density under different conditions is calculated. Comparing the calculation results of metal vapor with the experimental results of post-arc current, the concept of metal vapor ionization is put forward. An ionization process of metal vapor after the current zero crossing occurs. The ionization of metal vapor will cause an increase in the number of electrons after the current zero crossing, which affects Ipac, Qpac, and sheath growth.

The Simulation and Optimization of an Electromagnetic Field in a Vertical Continuous Casting Mold for a Large Bloom

The electromagnetic model of a large-bloom continuous casting was established to simulate the magnetic field. The model 3600 digital, high-precision, three-dimensional Gaussian meter was used to measure the internal magnetic field of mold electromagnetic stirring (M-EMS). The distribution of simulated magnetic field was basically consistent with that of the measured magnetic field; the accuracy of electromagnetic stirring model was verified. With the increase of current frequency, the electromagnetic force first increases and then decreases; when the current frequency is 9 Hz, the electromagnetic force reaches its maximum value. A bipolar electromagnetic stirring model is proposed; the influence of current intensity and distance were investigated. With the increase of current intensity of lower mold electromagnetic stirring (M-EMSB), the internal magnetic intensity of upper mold electromagnetic stirring (M-EMSA) gradually increases, and the middle region is gradually filled by magnetic field. With the increase of the distance, the range of the low-intensity magnetic field expands. When the current intensity of the M-EMSB is 320 A, and the distance is 400 mm, an 8 mT uniform magnetic field in the range of 1.2 m is formed. Compared with the traditional continuous casting electromagnetic agitator, the center equiaxial crystal of bipolar electromagnetic agitator increases from 30.3% to 49.5%.

Effect of pulse frequency on arc behavior and droplet transfer of 2198 Al–Li alloy by ultrahigh-frequency pulse AC CMT welding

In this study, 2198 Al–Li alloy, a low density and high-performance material for aerospace equipment, was welded using ultrahigh-frequency pulse alternating current cold metal transfer (UHF-ACCMT) welding technique. Influence of different ultrahigh-frequencies on arc behavior and droplet transfer were experimentally studied and theoretically analyzed. The results show that the UHF-ACCMT arc exhibited a good stability. During one cycle of arc burning, trends of arc length and diameter of UHF-ACCMT were similar to that of CMT arc. The average arc length of UHF-ACCMT decreased as the pulse current frequency increased from 20 to 60 kHz. An increase in the current frequency decreased the electrical conductivity, leading to a decrease in distance for sustaining arc from wire tip to base metal. The effect of average arc diameter with current frequency was inversely proportional to that of average arc length. Furthermore, the droplet diameter decreased whereas droplet length increased with an increase in the pulse current frequencies from 20 to 50 kHz. With regards to the pinch effect, an increase in the pulse current frequency enhanced the pinch force, which could be attributed to an increasing current density flowing through droplet per unit time. From 60 to 80 kHz, diameter of the arc and length of the droplet were maintained within an optimum range.

Relationship between porosity, pore parameters and properties of microarc oxidation film on AZ91D magnesium alloy

Microarc oxidation films on AZ91D magnesium alloy were prepared in sodium silicate-based electrolyte by a high-frequency bipolar pulsing mode. The effects of porosity and pore parameters on the properties of the films were studied. The results show that with the increased current frequency, the relative content of Mg element and the relative content of MgSiO3 phase in the films increase. The bonding strength of the films increases and the film microhardness decreases with the increased porosity respectively. Pore diameter could also affect the film properties to some degree. As the current frequency increases, the pore diameter and the film porosity decrease while the interpore distance and the pore circularity increase. The larger pore diameter and the higher porosity could promote the cracking behavior of the films while the larger interpore distance and the higher pore circularity could hinder the cracking behavior. Crack density is a better parameter than crack width when evaluating heat resistance. With decreased film porosity, the film impedance in 3.5% NaCl solution increases. The lower porosity and the better continuity of the films improve the anti-corrosion ability of the films.

Electric power frequency and nuclear safety - Subsynchronous resonance case study

Abstract The increase of the alternate current frequency results in increased rotational speed of the electrical motors and connected pumps. The consequence for the reactor coolant pumps is increased flow in primary coolant system. Increase of the current frequency can be initiated by the subsynchronous resonance phenomenon (SSR). This paper analyses the implications of the SSR and consequential increase of the frequency on the nuclear power plant safety. The Simulink MATLAB® model of the steam turbine and governor system and RELAP5 computer code of the pressurized water reactor are used in the analysis. The SSR results in fast increase of reactor coolant pumps speed and flow in the primary coolant system. The turbine trip value is reached in short time following SSR. The increase of flow of reactor coolant pumps results in increase of heat removal from reactor core. This results in positive reactivity insertion with reactor power increase of 0.5% before reactor trip is initiated by the turbine trip. The main parameters of the plant did not exceed the values of reactor trip set points. The pressure drop over reactor core is small discarding the possibility of core barrel lift.

Numerical simulation and experimental verification of electromagnetic field of continuous casting copper crucible

The electromagnetic field of continuous casting square copper crucible was simulated by numerical simulation using Ansoft Maxwell in order to clarify the influence of current frequency and intensity on the distribution of magnetic flux density in the crucible. The simulation results showed that as the current frequency increases or current intensity decreases, the distribution of the magnetic flux density in each vertical position of the crucible hardly changed, but the value of the magnetic flux density was gradually reduced, and the magnitude of the decrease was decremented from the maximum position of the magnetic flux density to the upper and lower ends. The maximum value of the magnetic flux density in different axial directions was proportional to the current intensity. In the radial direction, the magnetic flux density of the surface of the crucible was large, and gradually decreased toward the inner layer. The magnetic field at the slit was higher than the middle portion of the ridge due to the reinforcing effect at the slit. The small coil method was used to measure the actual electromagnetic field distribution in the crucible. It can be found that the magnetic flux density in the crucible decreased from the crucible wall to the crucible center, which is consistent with the results of the numerical simulation.

Numerical Simulation of Electromagnetic Field in Round Bloom Continuous Casting with Final Electromagnetic Stirring

A 3D mathematical model was developed to simulate the electromagnetic field in Φ600 mm round bloom continuous casting with final electromagnetic stirring (F-EMS), and the model was verified using measured data for the magnetic flux density in the stirrer centre. The distribution of electromagnetic force and the influence of current intensity and frequency were investigated. The results show that the Joule heat generated by F-EMS is very small and its influence on secondary cooling heat transfer in the stirring zone can be ignored. With an increase in current frequency, the electromagnetic force density at R/2 and R/3 of the Φ600 mm round bloom first increases and then decreases, reaching a maximum at 10 Hz.

Enhancement by citral of glutamatergic spontaneous excitatory transmission in adult rat substantia gelatinosa neurons.

Although citral, which is abundantly present in lemongrass, has various actions including antinociception, how citral affects synaptic transmission has not been examined as yet. Citral activates in heterologous cells transient receptor potential vanilloid-1, ankyrin-1, and melastatin-8 (TRPV1, TRPA1, and TRPM8, respectively) channels, the activation of which in the spinal lamina II [substantia gelatinosa (SG)] increases the spontaneous release of L-glutamate from nerve terminals. It remains to be examined what types of transient receptor potential channel in native neurons are activated by citral. With a focus on transient receptor potential activation, we examined the effect of citral on glutamatergic spontaneous excitatory transmission using the whole-cell patch-clamp technique to SG neurons in adult rat spinal cord slices. Bath-applied citral for 3 min increased the frequency of spontaneous excitatory postsynaptic current in a concentration-dependent manner (half-maximal effective concentration=0.58 mM), with a small increase in its amplitude. The spontaneous excitatory postsynaptic current frequency increase produced by citral was repeated at a time interval of 30 min, albeit this action recovered with a slow time course after washout. The presynaptic effect of citral was inhibited by TRPA1 antagonist HC-030031, but not by voltage-gated Na-channel blocker tetrodotoxin, TRPV1 antagonist capsazepine, and TRPM8 antagonist BCTC. It is concluded that citral increases spontaneous L-glutamate release in SG neurons by activating TRPA1 channels. Considering that the SG plays a pivotal role in modulating nociceptive transmission from the periphery, the citral activity could contribute toward at least a part of the modulation.

Electrical resistivity and strength properties of sodium hydroxide contaminated soil solidified with cement

Abstract Nine different contents of sodium hydroxide solutions, silt, and ordinary Portland cement were selected as basic materials to make the cemented soil blocks. The electrical resistivity under different current frequencies and unconfined compressive strengths were measured after curing for 3, 7, 14, 28, 60 and 90 days, respectively. The results show that the alternating current electrical resistivity decreases with the increase in current frequency for all content values. The higher the current frequency is, the smoother the electrical resistivity. The current frequency range of 5 × 104 to 106 Hz is recommended to reduce the error resulting from the slight variation of current frequencies. The strength and electrical resistivity increase logarithmically with the increase in curing time. With the increase in content, the strength first increases linearly and then decreases linearly. The strength reaches the peak value at the content of 7.5 g × kg−1. The electrical resistivity decreases exponentially. A useful prediction formula for the strength is proposed, which was established according to the linear relationship between the strength and the electrical resistivity. Based on the influencing degree of sodium hydroxide on the strength of cemented soil, an evaluation standard for the electrical resistivity of cement-solidified sodium hydroxide-contaminated soil is also proposed.

Study on finishing characteristics of magnetic abrasive finishing process using low-frequency alternating magnetic field

This paper describes a new ultra-precision magnetic abrasive finishing (MAF) process using alternating magnetic field. The process principle and the finishing characteristics are described. Specifically, the effects of finishing parameters such as cutting fluid, rotational speed of magnetic pole, and current frequency on change in material removal and surface finish are investigated respectively. Experimental results indicate that neat cutting oil is more suitable for this processing, which can obtain higher material removal and smoother finished surface compared with water-soluble cutting fluid and silicone fluid. The finishing force and material removal are gradually increasing with the increase of rotational speed of magnetic pole. It is confirmed that the angle variation of magnetic particles is decreasing with the increase of current frequency, and the few nanometer surface can be acquired in the condition of low frequency.

Carvacrol presynaptically enhances spontaneous excitatory transmission and produces outward current in adult rat spinal substantia gelatinosa neurons

Carvacrol, which is abundantly contained in oregano essential oils, has various pharmacological actions including antinociception. Although the oral administration of carvacrol results in antinociception, cellular mechanisms for this action have not been examined yet. We investigated the action of carvacrol on glutamatergic spontaneous excitatory transmission in substantia gelatinosa neurons which play a pivotal role in regulating nociceptive transmission from the periphery by using the patch-clamp technique in adult rat spinal cord slices. Carvacrol superfused for 2min produced either spontaneous excitatory postsynaptic current frequency increase or outward current at −70mV, or both of them in many of the neurons tested. The frequency increase and outward current had the EC50 values of 0.69mM and 0.55mM, respectively. The former action was inhibited by a selective TRPA1 antagonist HC-030031 but not a selective TRPV1 antagonist capsazepine, while the latter action was unaffected by their antagonists. The current–voltage relationship for the outward current indicated an involvement in the current of a change in the membrane permeability of K+ and its outward rectification. The outward current was inhibited in 10mM-K+ but not K+-channel blockers [tetraethylammonium and Ba2+]-containing and 11.0mM-Cl- Krebs solution. These results indicate that carvacrol increases the spontaneous release of l-glutamate from nerve terminals by activating TRPA1 but not TRPV1 channels and produces membrane hyperpolarization, which is possibly mediated by tetraethylammonium- and Ba2+-insensitive K+ channels, in substantia gelatinosa neurons. It is suggested that the hyperpolarizing effect of carvacrol could contribute to its antinociceptive action.

Flow field and its effect on microstructure in cold crucible directional solidification of Nb containing TiAl alloy

A 3D finite element model was established to investigate the flow field in TiAl melt under different process parameters that include the position of the solidification interface, the meniscus height, the heating power and the current frequency. A square cold crucible with an inner cross section of 36mm×36mm was employed to directionally solidify Ti–46Al–6Nb–B (at.%) ingots. The flow pattern in the melt is highly parameter-related. Generally, there are two flow swirls with opposite directions in the melt. The flow near the solidification interface can be minimized with an optimal meniscus height. The flow velocity is decreased with a decrease of heating power and an increase of current frequency. A weaker lateral flow near the solidification interface is beneficial for the continuous growth of columnar grains. The microsegregation of a directionally-solidified ingot can be reduced by controlling the flow in the melt, which is one of the advantages of cold crucible directional solidification.

Influence of field annealing on giant magneto-impedance effect of Co-based melt extraction amorphous wires

In order to investigate the influence of anneal treatment on the Co-based melt extraction wires, the soft magnetic properties and giant magnet-impedance （GMI） effect of the annealed Co75Fe40Si8B12Nb1 wire are investigated. Samples are prepared using melt extraction technology in vacuum and annealed at 450℃ without magnetic field or with miagntic field either longitudinal or transverse to the axis of wire of strength from 500 Oe to 4000 Oe，respectively. The magnetic softness and GMI response are measured using HP4192 Impedance Analyzer and Lakeshore7407 VSM. Test results show that the circular anisotropy and GMI response are reduced after longitudinal field anneal treatment. GMI profiles are single-peaked and the maximum impedance ratio ΔZ/Z is 131% and field sensitivity is 7%/Oe. The circular permeability and GMI response are improved after transverse field anneal treatments because of the increased circular anisotropy. At higher frequencies，the GMI profiles change from single-peaked to two-peaked after being annealed in strong transverse field. The circular permeability is increased and GMI effect gets stronger with the increase of current frequency and anneal field. The largest impedance ratio of 190% with a field sensitivity of 26%/Oe is obtained for the Co-based transverse field annealed wires at 10 MHz. The correlations between the circular permeability，the GMI effect and the current frequency are discussed in the light of a skin effect model.

Effect of exciting current of high frequency electromagnetic field on initial solidification of steel during electromagnetic continuous casting

A three-dimensional finite element model of the electromagnetic field and temperature field of electromagnetic continuous casting (EMCC) process was developed. The aim was to investigate the effects of induction heat of high frequency electromagnetic field on the early solidification process of molten steel in mould under various conditions of exciting current parameters. The results show that the induction heat has significant effects on the early solidification process, which appear as increasing the billet surface temperature, thinning the initial solidified shell and lowering the starting point of the initial solidification. The increases in exciting current frequency and density make the effects of induction heat on solidification process increase remarkably. Especially, with the exciting current frequency increase, the early solidification process and shell growth become non-uniform in billet circumferential direction. Furthermore, if the exciting current density exceeds a certain value, there occurs a high temperature region in the top of molten steel column, and then the initial solidification rate is greatly decreased. As a conclusion, the effects of induction heat on initial solidification process must be considered when the exciting current frequency and density are adjusted during the electromagnetic continuous casting process.