Temperature field at time of pulse current discharge in metal structure with elliptical embedding crack

Theoretical analysis is made on the temperature field at the time of pulse current discharge in a metal structure with an elliptical embedding crack. In finding the temperature field, analogy between the current flow through an elliptical embedding crack and the fluid flow through a barrier is made based on the similarity principle. Boundary conditions derived from this theory are introduced so that the distribution of current density and the temperature field expressions can be obtained. The study provides a theoretic basis to the applications of stopping spatial crack with electromagnetic heating.

Numerical simulation of a direct current glow discharge in atmospheric pressure helium

Characteristics of a direct current （DC） discharge in atmospheric pressure helium are numerically investigated based on a one-dimensional fluid model. The results indicate that the discharge does not reach its steady state till it takes a period of time. Moreover, the required time increases and the current density of the steady state decreases with increasing the gap width. Through analyzing the spatial distributions of the electron density, the ion density and the electric field at different discharge moments, it is found that the DC discharge starts with a Townsend regime, then transits to a glow regime. In addition, the discharge operates in a normal glow mode or an abnormal glow one under different parameters, such as the gap width, the ballast resistors, and the secondary electron emission coefficients, judged by its voltage-current characteristics.

Circle Points Discharge Tube Current Controller

Circle points discharge tube current controller is a new type device to limit the output of high voltage discharge current. Circle points uniform corona discharge to form air ionization current in the discharge tube. On the outside, even if the discharge electrode is spark discharging or the two discharge electrodes are short circuited, the air ionization current in the tube remains within a stable range, and there is no spark discharge. In this case, when the discharge current only increases slightly, the requirement to limited current is obtained. By installing the controller at a discharge pole with a small power but high voltage supply, we can realize the shift between the continuous spark line discharge and corona discharge. This provides a new simple device for spark discharge research and is a supplement to the Townsend discharge experiment.

Modeling Rogowski Coils for Monitoring Surge Arrester Discharge Currents

Rogowski coils(RCs)are widely used to measure power or high frequency currents based on their design.In this paper,two types of RCs that are circular(traditional)and cylindrical shapes wound using wire covered by varnish are constructed.This construction is carried out to be suitable for monitoring the discharge current of the surge arrester installed in the distribution system.Concerning high frequency RC modeling for both types considering transfer function is introduced.Self-integrating for both types is attained.Therefore,the experimental tests using function generator for both coils are carried out to identify the parameters of the transfer function representing the introduced model.The measured signals for current and induced voltages are denoised for the parameter identification process.The denoised process is achieved using the MATLAB code‘wdenoise’while the parameters are estimated using the system identification toolbox.Verification of the proposed model is achieved using experimental results for the two coils.The sensitivity of the two coils is investigated based on the induced output voltage.The application concerning the two coils for monitoring the discharge current of the surge arrester is done.The results confirm the accuracy of the introduced RC model,as well as the performance of the cylindrical shape,is better than the traditional one.The simulation is carried out using MATLAB and ATPDraw programs.

Comparison of the effect of different external electrodes on discharge plasma-assisted diffusion flame stabilization

To optimize the design of plasma injectors,the influence of different external electrodes on plasma-assisted flame stabilization was assessed by using a nonequilibrium plasma injector flame control setup.The electrical characteristics of the injector,flame structure parameters,flame intensity,discharge power,and cost-to-effectiveness ratio under different external electrodes(four mesh electrodes and one copper foil electrode)were analyzed using electrical and optical methods.The results show that reducing the mesh size of the external electrode leads to a decrease in breakdown voltage.Compared with a ceramic dielectric barrier-based injector,an injector with a quartz dielectric barrier produces a higher breakdown voltage under the same conditions.For the same actuation voltage,the discharge current increases as the mesh size of the external electrode decreases,and combustion is enhanced by the discharge plasma;therefore,it is better to adopt a smaller mesh hole size to realize good flame stabilization under a lower actuation voltage.However,under the studied working conditions,reducing the mesh hole size of the external electrode increases the cost-to-effectiveness ratio of plasma injector-based flame stabilization.Thus,considering the cost-to-effectiveness ratio and the weight of the injector,an external electrode with a larger mesh hole size should be chosen,which contradicts the above rule.

Electrical Characteristics of an Alternating Current Plasma Igniter in Airflow

The electrical characteristics of an alternating current （AC） plasma igniter were investigated for a working gas of air at atmospheric pressure. The discharge voltage and current were measured in air in both breakdown and stable combustion processes, respectively, and the current-zero phenomena, voltage-current （V-I） characteristics were studied for different working gas flow rates. The results indicated that the working gas between anode and cathode could be ionized to generate gas discharge when the voltage reached 8 kV, and the maximum current was 33.36 A. When the current came to zero, current-zero phenomena appeared with duration of 2 #s. At the current-zero moment, dynamic resistance between electrodes became extremely high, and the maximum value could reach 445 kf~, which was the main factor to restrain the current. With increasing working gas flow rates, the gradient of V-I characteristic curves was increased, as was the dynamic resistance. At a constant driven power, the discharge voltage increased.

Flow separation control over an airfoil using continuous alternating current plasma actuator

The flow separation control over an NACA 0015 airfoil using continuous alternating current(AC)dielectric barrier discharge(DBD)plasma actuator is investigated experimentally and numerically.This work is intended to report some observations made from our experiment,to which little attention is paid in the previous studies,but which is thought to be important to the understanding of control of complex flow separation with AC DBD.To this end,the response of separated flow to AC plasma actuation is visualized through the time-resolved particle image velocimetry(PIV)measurement,whereas numerical simulation is carried out to complement the experiment.The flow control process at chord-based Reynolds number(Re)of 3.31×105 is investigated.It is found that the response of external flow to plasma forcing is delayed for up to tens of milliseconds and the delay time increases with angle of attack increasing.Also observed is that at the intermediate angle of attack near stall,the forced flow features a well re-organized flow pattern.However,for airfoil at high post-stall angle of attack,the already well suppressed flow field can recover to the massively separated flow state and then reattach to airfoil surface with the flow pattern fluctuating between the two states in an irregular manner.This is contrary to one’s first thought that the forced flow at any angles of attack will become well organized and regular,and reflects the complexity of flow separation control.

CORRELATION INVESTIGATION BETWEEN CONTACT APPROACH SPEED OF HANDHELD METAL ROD AND DISCHARGE PARAMETERS FROM CHARGED HUMAN BODY

Characteristic measurement of contact discharge currents are made through a hand-held metal rod from charged human body. Correlation coefficients are obtained, through Statistic Package for Social Science (SPSS), for various charge voltages, which is based on the effect test of electrode contact approach speeds on discharge current parameters of current peaks, maximum rising slope and spark lengths. Discharge parameters at charge voltage 300V are independent on approach speed. For charge voltages equal to and higher than 500V, the contact approach speed has strong positive cor- relation with discharge parameters of the peak current and the maximum rising slope, whereas has strong negative correlation with the spark length.

Analysis of Effects of the Arc Voltage on Arc Discharges in a Cathode Ion Source of Neutral Beam Injector

A hot cathode bucket ion source is used for the EAST（experimental advanced superconducting tokamak）neutral beam injector.The thermal electrons emitted from the surface of the cathode are extracted and accelerated by the electric field formed by the arc voltage,which is applied between the arc chamber of the ion source and the cathode.This paper analyzes the effects of arc voltage on the arc discharge in a hot cathode high current ion source.

SIMULATION STUDY ON CAPACITOR DISCHARGE PERCUSION WELDING

Based on the network theory, the discharge circuit model of capacitor discharge percussion welding machine is established. The discharge current waveform is calculated by means of simulation method. A thorough inquiry into the factors affecting the discharge current waveform is made by using orthogonal design method. Results show that the calculation results of the calculation program proposed well coincide with the actual experiment data.

THERMAL STRESS FIELD WHEN CRACK ARREST IN AN AXIAL SYMMETRY METAL DIE USING ELECTROMAGNETIC HEATING

In order to solve the thermal stress field around crack tip in metal die when crack prevention using electromagnetic heating, a metal die with a half-embedded round crack was selected as the study object. The complex function method was used as a basis for the theoretical model of the space crack prevention in metal dies using electromagnetic heating. The crack arrest was accomplished by a pulse current discharge through the inner and outer. The theoretical analysis results show that the temperature around the crack tip rises instantly above the melting point of the metal. Small welded joints are formed at a small sphere near the crack tip inside the metal die by metal melting as a result of the heat concentration effect when the current pulse discharged. The thermal compressive stress field appears around the crack tip at the moment. The research results show that the crack prevention using electromagnetic heating can decrease the stress concentration and forms a compressive stress area around the crack tip, and also prevents the main crack from propagating further, and the goal of crack preventing can be reached.

硅橡胶环氧树脂复合材料电痕的实验研究(英文)

The use of polymer materials as electrical insulators on transmission and distribution lines has been increasing such as epoxy resin.Several advantages of using epoxy resin as an insulating material are its low density,better dielectric properties,and epoxy resin has higher volume resistivity than that of the glass and porcelain.However,epoxy resin has some disadvantages when it is used in tropical areas concerning with the humidity,high ultraviolet radiation, acid rain and effects of contaminants.Consequently,insulator surface will be easily damaged due to electrical tracking,which is indicated by the surface tracking.In this paper,the surface tracking on epoxy resin compound with silicon rubber has been investigated.The test was done based on the method of Inclined-Planed Tracking(IPT) IEC 587:1984 with NH_4C1 as contaminant.The test materials used were epoxy resins based on Diglycidyl Ether of Bisphenol A(DGEBA) and Methaphenylene Diamine(MPDA) compound with silicon rubber(SiR) with the dimensions of 50 mm×120 mm and the thickness of 6 mm.The flow rate of contaminant was 0.3 mL/min.The 3.5 kV AC high voltage 50 Hz was applied to the top electrodes.The experimental results show that the contact angle of hydrophobic was affected by compound of silicon rubber.The surface tracking,time to tracking and discharge current were affected by applied voltage,contamination and contact angle.By using micro-cameras,the surface damage was detected. The severest damaged sample surface on a sample had small contact angle.On the other hand,samples with the greatest contact angle needed longer time to have surface damage in the surface discharge.This shows that it is more difficult for large contact angle samples or more hydrophobic to have surface discharge.Epoxy resin compound with silicon rubber has contact angle of hydrophobic greater than epoxy resin without silicon rubber.

Evaluations of dielectric property and drug release profile of 5-FU patches based on plasma charged electrets

In the present study,the electret 5-fluorouracil patch was developed,the effective surface potential,piezoelectric coefficient d33,open-circuit thermally stimulated discharge（TSD） current spectra and shear adhesion of the patch were measured.The drug release profile of the patch was determined by using high performance liquid chromatography method.A stable potential difference which was positively dependent on the surface potential of the electret was generated on two sides of the patch.The measurements of d33 coefficient,TSD current spectra and adhesion performance showed that the electrostatic field of the electret could cause polarization and cohesive strength decreasing of the matrix molecules,change the distribution and interaction of the drug molecules in patch,therefore to increase the release of drug from the transdermal patch.

AC operation and runaway electron behaviour in HT-7 tokamak

Operation of HT-7 tokamak in a multicycle alternating square wave plasma current regime is reported. A set of AC operation experiments, including LHW heating to enhance plasma ionization during the current transition and current sustainment, is described. The behaviour of runaway electrons is analysed by four HXR detectors tangentially viewing the plasma in the equatorial plane, within energy ranges 0.3-1.2 MeV and 0.3-7 MeV, separately. High energy runaway electrons （~MeV） axe found to circulate predominantly in the opposite direction to the plasma current, while the number of low energy runaway electrons （~tens to hundreds of keV） circulating along the plasma current is comparable to that in the direction opposite to the plasma current. AC operation with lower hybrid current drive （LHCD） is observed to have an additional benefit of suppressing the runaway electrons if the drop of the loop voltage is large enough.

Growth of mirror-like ultra-nanocrystalline diamond(UNCD)films by a facile hybrid CVD approach

In this study, growth of mirror-like ultra-nanocrystalline diamond（UNCD） films by a facile hybrid CVD approach was presented. The nucleation and deposition of UNCD films were conducted in microwave plasma CVD（MPCVD） and direct current glow discharge CVD（DC GD CVD） on silicon substrates, respectively. A very high nucleation density（about 1×10^11 nuclei cm^-2） was obtained after plasma pretreatment. Furthermore, large area mirrorlike UNCD films of Φ 50 mm were synthesized by DC GD CVD. The thickness and grain size of the UNCD films are 24 μm and 7.1 nm, respectively. In addition, the deposition mechanism of the UNCD films was discussed.

Analysis of Fatigue and Microhardness in Metallic Powder Mixed EDM

The objective of this work research is to investigate the potential of using metallic powder mixed with electrical discharge machining (EDM) dielectric when machining hard electrically conductive materials. Nowadays, the development of industries requires hard materials for various applications. Machining the hard materials using the traditional processes lead to tool break and poor machined product. Even when the conventional EDM can machine hard material as long as it is electrically conductive materials, the machined parts still present drawbacks. Metallic powder mixed with EDM dielectric (PMEDM) was hypothesized to improve the machined part. The presence of metallic powder ensures uniform distribution of spark and the electrical density of the spark decreases which reduces craters, cracks and voids on machined surface. The transfer and deposit of alloying elements during powder mixed electrical discharge machining improve the machined surface properties particularly micro-hardness and fatigue. Discharge current (IP), gap voltage (GapV), ON-time (ON) and aluminum powder are selected as machined variable parameters and the output responses are fatigue performance, micro-hardness and surface topography. The workpiece material selected is molybdenum high speed steel. Micro-hardness was determined using micro-hardness tester device. The fatigue performance was determined using empirical equation. Analysis of material transfer was done using energy dispersive spectroscopy (EDS) attached to FESEM. EDS analysis involves the generation of an X-ray spectrum from the entire scan area of the SEM. The use of PMEDM improved the fatigue, the micro-harness and the machined surface morphology as the above-mentioned parameters increased.

Effect of actuating frequency on plasma assisted detonation initiation

Aiming at studying the influence of actuating frequency on plasma assisted detonation initiation by alternating current dielectric barrier discharge, a loosely coupled method is used to simulate the detonation initiation process of a hydrogenoxygen mixture in a detonation tube at different actuating frequencies. Both the discharge products and the detonation forming process which is assisted by the plasma are analyzed. It is found that the patterns of the temporal and spatial distributions of discharge products in one cycle are not changed by the actuating frequency. However, the concentration of every species decreases as the actuating frequency rises, and atom O is the most sensitive to this variation, which is related to the decrease of discharge power. With respect to the reaction flow of the detonation tube, the deflagration-todetonation transition（DDT） time and distance both increase as the actuating frequency rises, but the degree of effect on DDT development during flow field evolution is erratic. Generally, the actuating frequency affects none of the amplitude value of the pressure, temperature, species concentration of the flow field, and the combustion degree within the reaction zone.