• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Convection effect on an arc plasma evolution process in a two parallel contact system

    2020-05-06 05:59:14JianningYIN尹健寧ShunguiLIU劉順貴FengTANG唐峰QishenLV呂啟深andXingwenLI李興文
    Plasma Science and Technology 2020年4期
    關(guān)鍵詞:興文

    Jianning YIN (尹健寧),Shungui LIU (劉順貴),Feng TANG (唐峰),Qishen LV (呂啟深) and Xingwen LI (李興文)

    1 State Key Laboratory of Electrical Insulation and Power Equipment,Xi’an Jiaotong University,Xi’an 710049,People’s Republic of China

    2 Shenzhen Power Supply Co.Ltd,Shenzhen 518020,People’s Republic of China

    Abstract

    Keywords: air arc,circuit breaker,MHD

    1.Introduction

    A low voltage circuit breaker(LVCB)is a crucial component for controlling and protecting a power distribution network,and its movable contact consists of two parallel contacts for products with a higher rated current [1].The arc will be ignited between movable contacts and a static contact when the fault current appears,and the arc evolution process will directly affect the breaking capacity of the LVCB.Therefore,the study of the arc evolution process of a two parallel contact structure is crucial.

    Many studies have been performed on air arc behaviors.For a magneto–hydro–dynamic (MHD) simulation of an air arc,the air plasma physical properties must be obtained first.Murphy et al[2,3]calculated the transport coefficients of air,nitrogen–air and oxygen–air plasma.They also calculated the air and different metal vapor mixture plasma properties.Ander et al [4,5] and Zhang et al [6] calculated the composition and thermodynamic properties of ablated vapors of Cu,PMMA,PA6-6,PETP,POM and PE.In addition,the modeling of the plasma–sheath boundary region and the influence of the surface structure on arc voltage were studied[7,8].A sheath with a voltage–current density characteristic was proposed to represent the near-anode and near-cathode voltage,and also,the formation process of a new arc root on a splitter plate is described by it [9].Based on the above parameters,the effects of several factors,such as different mixture plasma properties [10],the ferromagnetic material[11,12],the arc ignition position [13],the erosion of the splitter plate [14] and the moving contact motion [15–17] on the arc behavior,were studied by the MHD model.Also,the behavior of the arc root was studied in[18–20].However,the quasi-steady solution for a magnetic field was assumed in the calculation.Thus,the temporal variation of the magnetic field was neglected.The studies [21,22] calculated the eddy current in the splitter plate and electrodes.

    However,all of the above studies considered single contact models and few papers have been published studying the air arc evolution process in a parallel contacts model.

    In this paper,a 3D MHD simulation model of two parallel contacts is built to investigate the arc evolution process.To represent the voltage drop of the electrodes,a 0.1 mm sheath with a voltage–current density characteristic is applied.For the numerical method,in order to take the temporal variation of the magnetic field in the whole calculation domain into account,the ANSYS Emag solver is applied to calculate the time-varying electromagnetic field.The coupling between the flow field and electromagnetic field uses the coupling server MpCCI.Based on the above methods,the evolution process of the anode arc root is analyzed by the current density distribution.The convection and conduction flux densities of air plasma are calculated and their effects on arc motion are quantitatively analyzed.The shape of the arc column is analyzed.The asymmetry of the anode and cathode arc root is also studied.The arc motion process of the two parallel contact system is preliminarily revealed.The study in this paper is beneficial for understanding the arc evolution mechanism of a two parallel contact system,and provides theoretical support to optimize high performance low voltage circuit breakers.

    2.Numerical model and governing equations

    The arc evolution process is not only determined by the electromagnetic field,but also by the gas dynamic.The arc model presented here is based on the MHD approach,where the arc plasma is described as one fluid.The plasma characteristic justifies some assumptions for the simplification.

    2.1.Hypotheses

    (1) The conditions of the local thermodynamic equilibrium and the laminar flow are satisfied.

    (2) Evaporation from the electrodes and wall materials is not considered.The physical properties of air plasma are the functions of temperature and pressure [2].

    (3) No ferromagnetic materials in the domain are presented.

    2.2.Geometry model

    Figure 1(a) shows the simulation model for the fluid.This model is a simplification of the miniature circuit breaker,which includes the electrode domain and arc column region.The dimensions of the model are 8 mm × 8 mm × 30 mm in the x–y–z direction.The origin of the coordinate is on the left wall (z = 0).In order to solve the electro-magnetic field,a far-away domain is built in the model.The thickness of the electrodes is 1.5 mm,and 0.1 mm near electrode layers surround the electrodes.Figure 1(b) shows the anode geometry of two parallel contacts.The anode consists of two parallel contacts,and 12 solid contacts connect them.The dimensions of contact 1 (contact 2) are 3 mm × 1.5 mm × 23 mm,and the dimensions of the 12 solids are 8 mm × 1.5 mm × 2 mm.The dimensions of the cathode are 8 mm × 1.5 mm ×25 mm.The material of the electrodes is copper.The distance between the two electrodes is 5 mm.

    Figure 1.The geometry model.

    Table 1.Equations solved in the fluid model.

    2.3.Governing equations

    Basically,the plasma process is modeled in detail combining the finite-element and finite-volume methods based on an MHD approach [15].A thin layer of elements with a nonlinear voltage–current density characteristic is employed to represent the voltage drop of the electrodes [13].The MHD equations are a combination of Navier–Stokes flow equations extended to include arc specific source terms with additional Maxwell equations for the electromagnetic field [13].

    2.3.1.Fluid model.The Navier–Stokes flow equations are written in the form of the generalized conservation equation (1):

    where Φ is the variable solved,ρ is the mass density,t is the time,is the velocity vector,ΓΦis the diffusion coefficient andSΦis the source term.All the equations solved for the fluid model are summarized in table 1 [23,24].

    In table 1,

    whereσE2is the Joule heat,which represents the injected energy into the air plasma.The radiation is calculated by equation (6):

    whereεnis the net emission coefficient [25].

    In the above equations,vx,vy,vzare the velocities of the x,y,z direction,jx,jy,jzare the current densities of the x,y,z direction,Bx,By,Bzare the magnetic flux densities of the x,y,z direction,is the Lorentz force produced by the current loop,η is the viscosity,λ is the thermal conductivity,cpis the specific heat,qηis the viscous dissipation,p is pressure,and h is enthalpy.

    The Navier–Stokes flow equations are solved using the ANSYS Fluent solver [15].

    2.3.2.Electromagnetic model.The motion of an arc is not only affected by the gas dynamic,but also by the magnetic field (induced by the arc itself and the current loop of the anode–arc–cathode).Therefore,the Lorentz forceis added in the source item of the momentum balance equation as shown in equations (2)–(4).

    The magnetic vector potential method is adopted to solve the nonlinear transient electro-magnetic field.The equations are shown as follows [26]

    where μ0is the permeability of vacuum,and σ is the electrical conductivity.The electrical conductivity of plasma is the function of the plasma temperature and pressure,φ is the electrical potential,andis the magnetic vector potential.

    The electromagnetic equations (7) and (8) are solved using the ANSYS Emag solver.

    During the simulation,the data transfer between the two solvers is necessary due to the interaction between the gas flow field and the electro-magnetic field.This is done by using the MpCCI [15].The electrical conductivity σ is transferred from the ANSYS Fluent to the ANSYS Emag.The Lorentz force and Joule heat are transferred from the ANSYS Emag to ANSYS Fluent by user defined codes.

    The time-varying electromagnetic field induced by the current loop,including the electrodes and arc column,is calculated in this paper.Therefore,compared with most of the previous studies [5–13],the itemis included in equations (7) and (8).

    2.3.3.Near-electrode model.The near-electrode voltage is an important part of the arc voltage and must be considered in the calculation.The 0.1 mm layers with a nonlinear resistance surrounding the electrodes are applied and its effective electrical conductivity is calculated by equation (9) [27]:

    where J is the current density,Δyis the thickness of the near electrode layer,and Ulis the voltage drop in the near electrode layer.The value of the effective electrical conductivity is calculated by the voltage–current density characteristic [13].

    A higher voltage UIhas to be exceeded at a low current density to describe the formation process of the arc root.After the formation of the new arc root,the near-electrode voltage U0is a constant.In this paper,the higher voltage UIis set to 22.3 V,and the near-electrode voltage U0is set to 10.3 V [13].

    The near-electrode voltage (near-anode and near-cathode) is calculated by a nonlinear voltage–current density characteristic [13].The difference in voltage between the near-anode and near-cathode is not considered in this model.Therefore,the arc voltage may be reduced.In addition,if the difference in voltage between the near-anode and nearcathode is considered in the model,the temperature of the anode arc root will be higher.

    2.4.Boundary conditions

    (1) Velocity: for all walls,the velocity is set to no-slip conditions.

    (2) Temperature: for the side wall (including the front surface,back surface and left surface of the arc column region,as shown in figure 1(a)) and the electrode outside planes,the environment temperature of 300 K is applied to the thermal conditions.For the pressure outlet,as shown in figure 1(a),the temperature is set to 300 K[27].At the interface between the air plasma and electrode surfaces,the temperature is determined as [13]:

    (1) Pressure:for the pressure outlet,as shown in figure 1(a),the total pressure is set to 101325 Pa.

    (2) Electrical and magnetic field: the electrical and magnetic field is solved in ANSYS Emag.In order to ensure the current is freely distributed between the two contacts according to the position of the arc root,the arc current is applied on the surface ‘inlet’.The electrical potential is set to zero on the surface ‘outlet’,as shown in figure 1(a) [14].For the interface between the arc region and the electrode,the boundary condition of the electrical field is described by equation (11):

    For the side wall of the arc region and electrode outside planes,the boundary condition is described by equation(12):

    For the boundary of the magnetic field,the zero magnetic potential is set to a far-away domain boundary to calculate the magnetic field.At the interface between the arc region and electrode,equations (13) and (14) are used [26]:

    The calculating current is set tosin (ωt+π/12) A,whereω=2πf.The equations are solved with a time step of 2.5 μs,and the coupled solver of Fluent is used.To improve the initial convergence,the simulation begins with a steady state result.The position of the initial arc at z = 5 mm in this paper and this arc ignition point are determined by the distance between the arcing position and the outlet of the model according to the structure of the miniature circuit breaker.

    The difference between the model established in this paper and the previous model is mainly that this model considers the two parallel contacts and their interactions.Also,the eddy current in the whole domain (arc domain and electrodes) is considered.In addition,the convection flux is calculated and its effect on the arc plasma evolution process in a two parallel contact system is analyzed in this paper.

    Figure 2.Current density distribution sequences in the arc column domain.

    3.Numerical results and analysis

    Figure 3.Curves of current through two contacts and arc voltage.The whole process is divided into processes(1)–(6).S1–S4 represent stage (1)–stage (4).

    The arc evolution process in a two parallel contact system is simulated based on a 3D MHD approach.The current density distribution,temperature distribution and the arc voltage are obtained.The arc shape from the anode to the cathode is analyzed by the current density distribution.The displacements of the arc roots are obtained.The convection flux density and heat conduction flux density are calculated at various instants.The arc evolution process and the influence of convection on it in a two parallel contacts model are analyzed.

    3.1.Evolution process of an arc

    The current density distribution sequences in the arc column domain are shown in figure 2.The red lines represent the position of the two parallel contacts.The current flows from the anode to the cathode.

    The curves of the current through the two contacts and arc voltage are shown in figure 3.In figure 3,i is the arc current,i1and i2are the currents through arc branch 1 and arc branch 2,respectively,u is the arc voltage.The curves of the arc resistance (including total arc resistance,resistance of arc branch 1 and arc branch 2) are shown in figure 4.The resistance trend of the two arc branches is similar to the trend of the current flowing through the two arc branches.The arc motion process can be analyzed in the following stages according to the current curves,as shown in figure 3.

    3.1.1.The anode arc root only appears on contact 1(t=0–0.38 ms).The starting position of the arc is at z = 5 mm.After that,the arc column moves along the electrodes due to the gas flow force and Lorentz force,so the arc voltage increases,as shown in figure 3.Also,the arc column expands.The heated air flows from arc branch 1 to arc branch 2 due to the convection effect,which results in the air under contact 2 being heated; therefore,the electrical conductivity of the air plasma under contact 2 increases.At this stage,the arc root of the anode only appears on contact 1,as shown in figure 2(a),but the convective effect provides favorable conditions for the formation of a new arc root on contact 2.After t = 0.3 ms,the current through the arc branch 2 increases.

    Figure 4.Curves of arc resistance. Rarc is the total arc resistance, R1 and R2 represent the resistance of arc branch 1 and arc branch 2,respectively.

    3.1.2.A new arc root is formed on contact 2(t=0.38–0.495 ms).Stage 1 (t = 0.38–0.445 ms): the electrical conductivity of the air under contact 2 is constantly increased.At t = 0.38 ms,a new arc root is formed on contact 2,as shown in figure 2(b),and the arc voltage reaches its peak.

    After t = 0.38 ms,the arc column under the anode consists of two branches.The arc column under contact 1 is defined as arc branch 1 and the arc column under contact 2 is defined as arc branch 2 for the convenience of the following analysis.At t = 0.38 ms,the current density and arc column radius of arc branch 1 are larger than those of arc branch 2.The temperature gradient between the two arc branches is the largest.The air plasma of arc branch 2 is heated and the electrical conductivity is increased due to convection and conduction.Therefore,current i2increases.In contrast,current i1decreases.The resistance of the two arc branches is equal until t = 0.445 ms.

    Stage 2 (t = 0.445–0.495 ms): the current flowing through arc branch 2 continues to increase due to thermal inertia after t = 0.445 ms.The arc resistance of branch 2 is less than that of arc branch 1.Therefore,the current flowing through branch 2 will continue to increase due to the decrease of arc resistance R2.When t = 0.495 ms,the current flowing through arc branch 2 reaches its local peak.

    3.1.3.Current i1increases(t=0.495–0.655 ms).Stage 3(t = 0.495–0.565 ms): at t = 0.495 ms,as shown in figure 2(c),the current density and radius of arc branch 2 are larger than those of arc branch 1.After that,the electrical conductivity of arc branch 1 increases,which leads to an increase in the current through arc branch 1.The arc currents of the two branches are equal again at t = 0.565 ms.

    Figure 5.Schematic diagram of the dynamic u–i curves.

    Stage 4 (t = 0.565–0.655 ms): the current flowing through arc branch 1 continues to increase at this stage due to the decrease of arc resistance R1,which leads to an increase of the temperature gradient between the two arc branches.

    The arc evolution processes (4) and (6) are similar to process (2),and the evolution process (5) is similar to process (3).

    An alternative variation of R1and R2appears in the whole process.However,the total arc resistance always reduces in the arc evolution process according to figure 4;that is to say,the arc in a two parallel contact system always develops toward the direction in which the total arc resistance decreases.

    At process (2) and process (3) of the arc evolution process,the arc voltage decreases because the cross section of the arc column becomes larger.The arc voltage increases slightly from t = 0.655 ms to t = 0.8 ms,while it decreases again at t = 0.8 ms.After t = 1.0 ms,the arc voltage increases because of the elongation of the arc column.

    Figure 5 shows the dynamic voltage–current curves of the two arcs,where the curve of the black solid line represents the dynamic u–i1characteristic of arc branch 1 and the red dash line represents the u–i2characteristic of arc branch 2 [28].

    In order to analyze all possible intersections of the two curves,curves (1)–(3) show the possible situations of arc branch 1.The points a–f are possible points of intersection.

    Through the analysis of each intersection in figure 5,the two parallel arc branches hardly co-exist at points from‘a(chǎn)’–‘c’ (one of two arc branches will be extinguished).At points from‘d’–‘g’,the two parallel arc branches can co-exist.

    In summary,if conditions (1) du/di1> 0 and du/di2> 0 or (2) du/di1< 0 and du/di2< 0 are satisfied,that is to say,when the arc resistance characteristics of two arc branches are consistent,two parallel arc branches can coexist.

    It can be seen that the above-mentioned analysis based on the dynamic current–voltage curves could not explain the calculation results as shown in figure 3.It is predicted that the interaction between the two parallel arc branches should be considered from the view of a flow field.

    3.2.Calculation results of convection and conduction

    Figure 6.Temperatures on the cross section of y = 2.4 mm along the x-axis at four instants.

    In order to further analyze the arc evolution mechanism in a two parallel contact system,the temperatures at the cross section of the anode arc root(y = 2.4 mm)along the x-axis at four instants (figures 2(c)–(f)) are obtained and shown in figure 6.

    It can be noted that the position of arc root 1 and arc root 2 is at about x = 2.2 mm and x = 5.8 mm respectively.At t = 0.655 ms and t = 1.1 ms,the central temperature of arc root 1 is significantly higher than that of arc root 2,which leads to the direction of the temperature gradient along the positive direction of the x-axis.At t = 0.495 ms and t = 0.915 ms,the central temperature of arc root 2 is higher than that of arc root 1,which leads to the direction of the temperature gradient along the –x-axis direction.The convection and conduction are directly related to the temperature gradient.The convection and conduction will affect the movement of air plasma and the arc evolution process.

    In this paper,the convective flux density is defined as[29]:

    The conduction flux density is calculated by the following formula:

    The distribution of the x component of the conduction flux density on cross section y = 2.4 mm at four instants(figures 2(c)–(f)) is shown in figure 8.

    The arc motion process is mainly affected by convection and conduction.It can be seen that the convection flux density is much larger than the conduction flux density by comparing figures 7 and 8.That is to say,convection plays a dominant role in the arc evolution process.

    Figure 7.The x component of convective flux density on cross section y = 2.4 mm ((c) = 0.495 ms,(d) = 0.655 ms,(e) = 0.915 ms,(f) = 1.1 ms).

    Figure 8.The x component of conduction flux density on cross section y = 2.4 mm ((c) = 0.495 ms,(d) = 0.655 ms,(e) = 0.915 ms,(f) = 1.1 ms).

    In figure 8,the curves of (c)–(f) are evaluated for the cross section at z = 9 mm,z = 11.5 mm,z = 14.5 mm and z = 17 mm,respectively (the position of the black dash line in figure 9).Figure 8 shows that the conduction flux density is zero at x = 2.2 mm and x = 5.8 mm,respectively,and the heated air plasma diffuses to both sides of the arc root.The heated air plasma diffuses to the middle of the two arc roots due to conduction,therefore,the positions of the two anode arc roots are maintained in a fixed position.

    3.3.The convection effect on the arc evolution process

    The flow field distribution (on the cross section of the anode arc root)at the four instants is obtained and shown in figure 9.Based on this,the effect of convection and conduction on arc evolution behavior is analyzed.

    The boxes of the black dash line represent the positions of contact 1 and contact 2,as shown in figure 9(a).

    Figure 9.Velocity distribution at different instants.

    The vertical black dash line shows the position of the anode arc root with a larger current density.It is noted that the convective flux density in the position of the arc root equals zero at about at t = 0.495 ms,t = 0.655 ms and t = 1.1 ms,as shown in figure 7,because the velocity of the airflow is along the z-axis,while the x component of the velocity is very small,as shown in figures 9(a),(b),(d).At t = 0.915 ms,the convection flux density equals 2 × 108W m-2due to the large x component of velocity in the position of the arc root,as shown in figure 9(c).

    3.3.1.The evolution behavior at stage(2).The new arc root forms on contact 2 at t = 0.38 ms.The current density of arc root 1 is higher with the arc motion,resulting in the direction of convection being from arc branch 1 to branch 2.The electrical conductivity of arc branch 2 is increased and the arc resistance of arc branch 2 begins to decrease due to convection.Therefore,current i2increases.At point ‘a(chǎn)’,as shown in fgiure 4,i1= i2.The i2current continues to increase and i1decreases after point‘a(chǎn)’ due to the thermal inertia of the arc column.Until t = 0.495 ms (curve (c) as shown in fgiure 7),the convection fulx density is less than zero when z > 11.5 mm and the convection fulx density is greater than zero when z < 9 mm,which shows that the cool air behind the arc column folws to arc branch 2 and the heated air before the arc column flows to arc branch 1,as shown in fgiure 9(a).Therefore,the electrical conductivity of arc branch 1 is increased,so that current i1increases after t = 0.495 ms,as shown in figure 3.

    3.3.2.The evolution process at stage(3).From 0.495 ms to 0.565 ms,the arc resistance R1decreases and R2increases,as shown in fgiure 4,due to the effect of convection.Therefore,current i1increases and i2decreases.At t = 0.565 ms,current i1= i2at point ‘b’,as shown in fgiure 3.From 0.565 ms to 0.655 ms,the arc resistance R1continues to decrease due to thermal inertia,resulting in current i1continuing to increase and i2continuing to decrease.Therefore,the temperature gradient between the two arc roots increases with the increase of the difference value of current density between the two arc branches,which leads to an enhancement of the convection effect and its direction is from arc root 1 to arc root 2.At t = 0.655 ms,the difference value of the current density between the two arc branches is the highest.The heated air before the arc column folws towards branch 2,as shown in fgiure 9(b).The electrical conductivity of branch 2 increases due to convection(curve(d)as shown in fgiure 7).Therefore,current i2increases and i1decreases after t = 0.655 ms.This explains the current change process at stage (3) during the arc evolution process.

    The convection effects on the arc evolution process at stages (4) and (6) are similar to stage (2),and the convection effect on the arc evolution process at stage (5) is similar to stage (3).The arc evolution process is repetitive.

    As per the above mentioned analysis,the current densities of the two arc branches under the anode do not reach the steady state in the whole arc motion process because the arc motion process is a dynamic process.Therefore,the current change process of i1and i2is a dynamic equilibrium process.

    It can be seen that two arc roots appear in the anode with an increase in the current through the above analysis.The change in the current flowing through the two branches is mainly affected by the convection and arc resistance in the whole arc evolution process in the two parallel contact system according to the above analyses.However,the electrical conductivity of the arc branches will be changed due to convection.Therefore,the arc resistance of the two arc branches will be changed.In other words,the main physical mechanism of the arc evolution process is the influence of convection.

    Figure 10.The displacement of the anode and cathode arc roots.

    3.4.The shape of the arc column and displacements of arc roots

    3.4.1.Shape of arc column.It can be noted that the size of the two arc columns varies alternately from figure 2.The new arc root forms on contact 2 after 0.38 ms.The anode has two arc roots and the cathode has one after 0.38 ms.From the anode to the cathode,the two arc branches merge into one.Therefore,the shape of the arc column is ‘Y’ type.One reason is the electromagnetic attraction of the two arc branches.The other reason is the conduction effect as shown in figure 8,which leads to the heated air plasma diffusing to the middle of the two arc roots.These two reasons also explain the phenomena of the two anode arc roots maintained in a fixed position.

    3.4.2.The displacements of arc roots.The structure of the anode and cathode is different.The anode consists of two parallel contacts and the cathode consists of one contact.It will affect the displacements of the arc roots.The displacements of the arc roots will be analyzed in this section.The displacements of the anode and cathode arc roots are shown in figure 10.

    The arc is ignited at z = 5 mm.Before t = 0.38 ms,the velocity of arc root 1 is faster than the cathode arc root because of the higher current density.Therefore,the displacement of anode arc root 1 is larger.At 0.38 ms,anode arc root 2 forms at z = 7.5 mm and it is behind anode arc root 1 because of the tailing of the arc.The equivalent cross section of the anode arc root increases after the formation of anode arc root 2,so that the current density of the cathode arc root is larger.Therefore,there is a slower velocity of the anode arc root than the cathode arc root.Thus,the cathode arc root will catch up with the anode arc root and the displacements of the anode and cathode arc roots are equal until 0.62 ms.The current density of the anode arc root increases more than the cathode arc root with the increase of current after 0.62 ms.Therefore,the displacement of the anode arc root is greater than the cathode arc root at 1.1 ms again,as shown in figure 10.This phenomenon can also be seen in figure 2(f).

    4.Conclusions

    A 3D simulation model of a two parallel contact system has been built.The anode consists of two parallel contacts in the model.A 0.1 mm near-electrode layer with nonlinear resistance is applied to simulate the formation of the arc root.The convection flux density and conduction flux density are calculated.Based on this,the arc evolution behavior of a two parallel contact system is analyzed.It can be concluded that:

    (1) The arc root will extend from one contact to two contacts on parallel contacts with the arc motion.The size of two arc branches will change alternately during the arc motion process.

    (2) Two anode arc roots can co-exist during the arc evolution behavior.The arc column of the two parallel contact system always develops toward the direction in which the total arc resistance decreases.The arc current change process through each arc branch is a dynamic process,and they try to reach the steady point in the arc motion process.The arc evolution behavior is affected by convection.

    (3) The arc column is‘Y’type after the formation of a new arc root due to the attraction of two arc branches near the anode and heat conduction.The arc root motion is asymmetrical because of the structural asymmetry.

    In future work,more attention should be paid to the plasma–sheath boundary region modelling,and the influence of the electrode motion process and splitter plates.

    Acknowledgments

    This work is supported by the Natural Science Foundation of Shaanxi Province of China (No.2017ZDJC-16) and Shenzhen Power Supply Co.Ltd (No.SZKJXM20170480).

    猜你喜歡
    興文
    我校詹興文副校長(zhǎng)申報(bào)項(xiàng)目獲第三批海南省高校思想政治工作精品項(xiàng)目立項(xiàng)
    一個(gè)放羊娃成就的“書香之家”
    火紅的日子
    宜賓試驗(yàn)站打造蠶桑產(chǎn)業(yè)強(qiáng)鎮(zhèn)——興文周家鎮(zhèn)
    興文蠶桑產(chǎn)業(yè)創(chuàng)新驅(qū)動(dòng)發(fā)展的做法與成效
    這 里 是 北 京
    青年歌聲(2019年6期)2019-06-26 09:14:42
    大澤山:從賣葡萄到興文旅
    商周刊(2018年19期)2018-10-26 03:31:20
    興文塔的建筑特色與藝術(shù)價(jià)值
    興文農(nóng)商銀行中干競(jìng)聘
    四川興文世界地質(zhì)公園景觀特征與價(jià)值評(píng)價(jià)
    黄片大片在线免费观看| 欧美精品一区二区免费开放| 高清在线国产一区| 两性午夜刺激爽爽歪歪视频在线观看 | 久久精品人人爽人人爽视色| 人人妻人人澡人人看| 两个人看的免费小视频| 午夜两性在线视频| 国产伦理片在线播放av一区| 国产色视频综合| www.精华液| 色视频在线一区二区三区| 老司机福利观看| 天堂8中文在线网| 五月天丁香电影| 亚洲精品在线观看二区| 色94色欧美一区二区| 久久久久久久久久久久大奶| 亚洲综合色网址| 国产亚洲精品一区二区www | 黄色视频,在线免费观看| 制服诱惑二区| 啦啦啦在线免费观看视频4| 亚洲成人免费电影在线观看| 亚洲精品久久成人aⅴ小说| 男女之事视频高清在线观看| av片东京热男人的天堂| 99国产精品一区二区三区| 91成人精品电影| 90打野战视频偷拍视频| 18禁黄网站禁片午夜丰满| 国产成人av激情在线播放| 亚洲欧美激情在线| 1024香蕉在线观看| 后天国语完整版免费观看| 91大片在线观看| 欧美激情久久久久久爽电影 | 熟女少妇亚洲综合色aaa.| 欧美 亚洲 国产 日韩一| 十八禁高潮呻吟视频| 女人久久www免费人成看片| 国产欧美日韩一区二区精品| 啦啦啦中文免费视频观看日本| 精品国产超薄肉色丝袜足j| 美女午夜性视频免费| 一区福利在线观看| 动漫黄色视频在线观看| 国产在视频线精品| 在线亚洲精品国产二区图片欧美| 久热这里只有精品99| 亚洲熟女毛片儿| 男女高潮啪啪啪动态图| 中文字幕色久视频| 69av精品久久久久久 | 国产片内射在线| 男人操女人黄网站| 亚洲一码二码三码区别大吗| 精品一区二区三卡| 亚洲精品美女久久av网站| 一夜夜www| 久久久精品国产亚洲av高清涩受| 考比视频在线观看| 成年人午夜在线观看视频| 国产人伦9x9x在线观看| 老鸭窝网址在线观看| 岛国毛片在线播放| 在线观看一区二区三区激情| 日韩成人在线观看一区二区三区| 一级黄色大片毛片| 最新美女视频免费是黄的| 欧美成狂野欧美在线观看| 天堂动漫精品| 露出奶头的视频| 又大又爽又粗| 日韩中文字幕视频在线看片| 成人影院久久| 岛国在线观看网站| tube8黄色片| 91成年电影在线观看| 51午夜福利影视在线观看| 丝袜人妻中文字幕| 午夜老司机福利片| 亚洲综合色网址| 免费在线观看日本一区| 午夜福利影视在线免费观看| 动漫黄色视频在线观看| 搡老岳熟女国产| 十八禁网站免费在线| 精品免费久久久久久久清纯 | 免费女性裸体啪啪无遮挡网站| 中文字幕人妻熟女乱码| 国产男女内射视频| 超碰成人久久| 国产亚洲av高清不卡| 亚洲 国产 在线| 国产精品免费一区二区三区在线 | 精品少妇一区二区三区视频日本电影| 一级a爱视频在线免费观看| 午夜两性在线视频| 色在线成人网| 国产三级黄色录像| 亚洲性夜色夜夜综合| 在线观看免费午夜福利视频| www.熟女人妻精品国产| netflix在线观看网站| 丰满饥渴人妻一区二区三| 亚洲美女黄片视频| 老司机影院毛片| 美女主播在线视频| 色尼玛亚洲综合影院| 国产免费视频播放在线视频| 老司机深夜福利视频在线观看| 欧美亚洲日本最大视频资源| 亚洲第一青青草原| 欧美成狂野欧美在线观看| 亚洲欧美日韩高清在线视频 | 国产av又大| 怎么达到女性高潮| 国产成人欧美| 日韩三级视频一区二区三区| 波多野结衣一区麻豆| 日本av手机在线免费观看| 亚洲欧美精品综合一区二区三区| 他把我摸到了高潮在线观看 | 999久久久精品免费观看国产| 亚洲,欧美精品.| 久久性视频一级片| av网站在线播放免费| 午夜免费鲁丝| 不卡一级毛片| 日韩欧美三级三区| 亚洲一区二区三区欧美精品| 男女高潮啪啪啪动态图| 九色亚洲精品在线播放| 日韩 欧美 亚洲 中文字幕| 国产精品久久久人人做人人爽| 18禁国产床啪视频网站| 满18在线观看网站| tocl精华| 亚洲一卡2卡3卡4卡5卡精品中文| 日本wwww免费看| 亚洲成国产人片在线观看| 色尼玛亚洲综合影院| 99九九在线精品视频| 午夜两性在线视频| 国产成人系列免费观看| 啦啦啦 在线观看视频| 久久天躁狠狠躁夜夜2o2o| a级毛片在线看网站| 久9热在线精品视频| 色婷婷av一区二区三区视频| svipshipincom国产片| 国产精品亚洲一级av第二区| 久久久国产精品麻豆| 亚洲第一欧美日韩一区二区三区 | 天天添夜夜摸| 亚洲欧洲精品一区二区精品久久久| 精品一区二区三区视频在线观看免费 | 色播在线永久视频| 一进一出好大好爽视频| 久久这里只有精品19| 欧美人与性动交α欧美软件| 一本一本久久a久久精品综合妖精| 无人区码免费观看不卡 | a在线观看视频网站| 免费在线观看日本一区| 精品一品国产午夜福利视频| 亚洲国产av影院在线观看| 热99国产精品久久久久久7| 久久久欧美国产精品| 美女主播在线视频| 国产精品98久久久久久宅男小说| 视频区欧美日本亚洲| 成人三级做爰电影| 久久久久久免费高清国产稀缺| 精品久久久久久久毛片微露脸| 国产男女内射视频| 黑人巨大精品欧美一区二区蜜桃| 久久精品成人免费网站| 一本综合久久免费| 高清视频免费观看一区二区| 18禁裸乳无遮挡动漫免费视频| 一本综合久久免费| 99在线人妻在线中文字幕 | 99九九在线精品视频| 精品一品国产午夜福利视频| 老司机午夜十八禁免费视频| 亚洲三区欧美一区| 国产精品二区激情视频| 国产成人影院久久av| 精品熟女少妇八av免费久了| 日本一区二区免费在线视频| www.精华液| 夜夜骑夜夜射夜夜干| 亚洲精品国产区一区二| 日韩欧美一区视频在线观看| 午夜福利免费观看在线| 亚洲一卡2卡3卡4卡5卡精品中文| 久久国产精品人妻蜜桃| 老司机在亚洲福利影院| videos熟女内射| 啦啦啦 在线观看视频| 欧美精品一区二区免费开放| 国产高清videossex| 亚洲va日本ⅴa欧美va伊人久久| 极品少妇高潮喷水抽搐| 香蕉国产在线看| 午夜91福利影院| 在线永久观看黄色视频| 日韩大片免费观看网站| 久久久久久久国产电影| 一边摸一边抽搐一进一小说 | 国产在线一区二区三区精| 视频在线观看一区二区三区| 欧美 亚洲 国产 日韩一| 人妻一区二区av| 亚洲成a人片在线一区二区| 亚洲欧美激情在线| 一夜夜www| 亚洲欧美日韩高清在线视频 | 淫妇啪啪啪对白视频| 国产在线观看jvid| 国产欧美日韩综合在线一区二区| 日本黄色视频三级网站网址 | 欧美成人免费av一区二区三区 | 国产一区有黄有色的免费视频| 久久性视频一级片| 国产精品99久久99久久久不卡| 亚洲熟妇熟女久久| 久久久久精品国产欧美久久久| 男人舔女人的私密视频| 成年人黄色毛片网站| 热99国产精品久久久久久7| 捣出白浆h1v1| 丰满迷人的少妇在线观看| 国产精品麻豆人妻色哟哟久久| 大香蕉久久成人网| 国产精品国产高清国产av | 日本一区二区免费在线视频| 亚洲精品在线美女| 母亲3免费完整高清在线观看| 中文字幕高清在线视频| 亚洲精品美女久久久久99蜜臀| av网站在线播放免费| 大型黄色视频在线免费观看| 丰满人妻熟妇乱又伦精品不卡| 亚洲精品成人av观看孕妇| 日韩熟女老妇一区二区性免费视频| 一本—道久久a久久精品蜜桃钙片| 午夜91福利影院| 丰满饥渴人妻一区二区三| 水蜜桃什么品种好| 美女视频免费永久观看网站| www.自偷自拍.com| 亚洲精华国产精华精| 色综合婷婷激情| 国产不卡av网站在线观看| 久久这里只有精品19| 日本黄色视频三级网站网址 | 亚洲综合色网址| 成人国产一区最新在线观看| 如日韩欧美国产精品一区二区三区| 亚洲专区字幕在线| 久久精品人人爽人人爽视色| 国产精品电影一区二区三区 | a级毛片在线看网站| av电影中文网址| www.999成人在线观看| 午夜激情久久久久久久| 一个人免费看片子| 夜夜夜夜夜久久久久| 丝袜在线中文字幕| 亚洲一码二码三码区别大吗| 久久精品亚洲精品国产色婷小说| 天天添夜夜摸| 精品卡一卡二卡四卡免费| 欧美老熟妇乱子伦牲交| 亚洲成a人片在线一区二区| 飞空精品影院首页| 91国产中文字幕| 欧美日韩av久久| 国产一区二区三区在线臀色熟女 | 夫妻午夜视频| 久久狼人影院| 日韩中文字幕视频在线看片| 人人妻人人添人人爽欧美一区卜| 考比视频在线观看| 免费久久久久久久精品成人欧美视频| 欧美精品高潮呻吟av久久| 精品熟女少妇八av免费久了| 12—13女人毛片做爰片一| 亚洲国产欧美一区二区综合| 国产老妇伦熟女老妇高清| 大陆偷拍与自拍| 我的亚洲天堂| 人妻一区二区av| svipshipincom国产片| 新久久久久国产一级毛片| 欧美日韩一级在线毛片| 久久久久久久大尺度免费视频| 中国美女看黄片| 老司机深夜福利视频在线观看| 成人免费观看视频高清| 少妇猛男粗大的猛烈进出视频| 天堂动漫精品| 精品少妇久久久久久888优播| 蜜桃在线观看..| 一级片'在线观看视频| 丁香六月天网| 日本vs欧美在线观看视频| 久久久久久久国产电影| 日本一区二区免费在线视频| 男人舔女人的私密视频| 国产熟女午夜一区二区三区| 婷婷成人精品国产| 99riav亚洲国产免费| 久久精品亚洲熟妇少妇任你| 天堂中文最新版在线下载| 王馨瑶露胸无遮挡在线观看| 露出奶头的视频| 欧美精品av麻豆av| 黑人巨大精品欧美一区二区蜜桃| 日韩欧美免费精品| 少妇的丰满在线观看| 中文亚洲av片在线观看爽 | 麻豆成人av在线观看| 国产男靠女视频免费网站| 天堂动漫精品| 99riav亚洲国产免费| 大码成人一级视频| 午夜福利影视在线免费观看| av电影中文网址| 国产日韩欧美视频二区| 免费在线观看影片大全网站| 性高湖久久久久久久久免费观看| 桃红色精品国产亚洲av| 精品第一国产精品| 欧美黑人精品巨大| 成人三级做爰电影| 日韩 欧美 亚洲 中文字幕| 中文字幕色久视频| 国产精品麻豆人妻色哟哟久久| 热99re8久久精品国产| 精品国产亚洲在线| 后天国语完整版免费观看| 动漫黄色视频在线观看| 成人黄色视频免费在线看| 欧美成人午夜精品| a在线观看视频网站| 少妇 在线观看| cao死你这个sao货| 女性被躁到高潮视频| 成在线人永久免费视频| 午夜日韩欧美国产| 一个人免费在线观看的高清视频| 亚洲午夜理论影院| 国产精品av久久久久免费| 精品少妇内射三级| 丝袜美腿诱惑在线| 夜夜骑夜夜射夜夜干| 极品教师在线免费播放| 一本综合久久免费| 黄频高清免费视频| 岛国在线观看网站| 国产精品久久久久久人妻精品电影 | 国产免费av片在线观看野外av| 欧美成人免费av一区二区三区 | 国产野战对白在线观看| 亚洲一区二区三区欧美精品| 淫妇啪啪啪对白视频| 精品国产超薄肉色丝袜足j| 亚洲九九香蕉| 高清黄色对白视频在线免费看| 国产精品偷伦视频观看了| 一级片免费观看大全| 天天操日日干夜夜撸| 99riav亚洲国产免费| 午夜91福利影院| 两个人免费观看高清视频| 午夜成年电影在线免费观看| a级片在线免费高清观看视频| 久久久久精品国产欧美久久久| 国产精品国产av在线观看| √禁漫天堂资源中文www| h视频一区二区三区| svipshipincom国产片| 他把我摸到了高潮在线观看 | 国产亚洲欧美在线一区二区| 黑人操中国人逼视频| 国内毛片毛片毛片毛片毛片| 岛国在线观看网站| 这个男人来自地球电影免费观看| 黑人巨大精品欧美一区二区mp4| 99国产精品一区二区蜜桃av | 中文亚洲av片在线观看爽 | 成人18禁高潮啪啪吃奶动态图| 黄片小视频在线播放| 黄色丝袜av网址大全| a级片在线免费高清观看视频| 久久久久久久久免费视频了| 捣出白浆h1v1| 男男h啪啪无遮挡| 欧美黄色片欧美黄色片| 国产区一区二久久| 精品少妇一区二区三区视频日本电影| 亚洲男人天堂网一区| 精品久久蜜臀av无| 99九九在线精品视频| 99re在线观看精品视频| 亚洲欧美一区二区三区黑人| 日本撒尿小便嘘嘘汇集6| 老司机深夜福利视频在线观看| 亚洲伊人色综图| 成在线人永久免费视频| 菩萨蛮人人尽说江南好唐韦庄| 亚洲国产欧美在线一区| 12—13女人毛片做爰片一| 日韩人妻精品一区2区三区| 久久 成人 亚洲| 在线永久观看黄色视频| e午夜精品久久久久久久| 超碰97精品在线观看| av超薄肉色丝袜交足视频| 香蕉久久夜色| 欧美激情极品国产一区二区三区| 成人影院久久| 国产xxxxx性猛交| 日韩有码中文字幕| 精品国产亚洲在线| 亚洲国产欧美一区二区综合| av电影中文网址| 女人久久www免费人成看片| 91大片在线观看| 日韩欧美一区视频在线观看| 99久久精品国产亚洲精品| 国产精品麻豆人妻色哟哟久久| 国产精品久久电影中文字幕 | 成人亚洲精品一区在线观看| 色婷婷久久久亚洲欧美| 又大又爽又粗| 大型黄色视频在线免费观看| 精品久久蜜臀av无| 99国产精品一区二区三区| 交换朋友夫妻互换小说| 亚洲熟女毛片儿| av福利片在线| 国产一区有黄有色的免费视频| 欧美中文综合在线视频| 国产精品二区激情视频| 亚洲精品在线美女| 精品少妇黑人巨大在线播放| 日本av手机在线免费观看| 国产精品.久久久| 无限看片的www在线观看| 一级片免费观看大全| 另类精品久久| e午夜精品久久久久久久| 精品视频人人做人人爽| 50天的宝宝边吃奶边哭怎么回事| 老司机影院毛片| a级毛片黄视频| 超色免费av| 久久久久久人人人人人| 久久久久国产一级毛片高清牌| 另类亚洲欧美激情| 啦啦啦中文免费视频观看日本| 久久中文字幕人妻熟女| 亚洲欧美精品综合一区二区三区| 99香蕉大伊视频| 精品亚洲成a人片在线观看| 亚洲国产中文字幕在线视频| 日本黄色日本黄色录像| 丝袜美足系列| 一级片免费观看大全| 老汉色∧v一级毛片| 操美女的视频在线观看| 另类亚洲欧美激情| 男男h啪啪无遮挡| 亚洲一码二码三码区别大吗| 超碰97精品在线观看| 老司机午夜十八禁免费视频| 久久久精品免费免费高清| 免费在线观看日本一区| 18禁美女被吸乳视频| 在线观看66精品国产| av福利片在线| www.自偷自拍.com| 国产成人一区二区三区免费视频网站| 蜜桃国产av成人99| 一级片免费观看大全| 在线十欧美十亚洲十日本专区| 宅男免费午夜| 男女高潮啪啪啪动态图| 老熟女久久久| 1024视频免费在线观看| 黑人操中国人逼视频| 国产一区二区三区综合在线观看| 国产成人欧美在线观看 | 建设人人有责人人尽责人人享有的| 一夜夜www| 午夜福利视频精品| 久久久国产精品麻豆| 久久久久网色| 午夜精品久久久久久毛片777| 日韩成人在线观看一区二区三区| 久久热在线av| 免费观看人在逋| 亚洲中文字幕日韩| 最新在线观看一区二区三区| 亚洲第一青青草原| 日韩免费高清中文字幕av| 一级,二级,三级黄色视频| 天天躁夜夜躁狠狠躁躁| 国产亚洲午夜精品一区二区久久| 亚洲精品粉嫩美女一区| 老熟妇乱子伦视频在线观看| 亚洲天堂av无毛| 国产日韩欧美在线精品| 一级毛片女人18水好多| 最近最新中文字幕大全免费视频| 美女视频免费永久观看网站| 欧美成人免费av一区二区三区 | 肉色欧美久久久久久久蜜桃| 亚洲精品在线美女| 狂野欧美激情性xxxx| 深夜精品福利| 亚洲专区字幕在线| 欧美成狂野欧美在线观看| 天天躁狠狠躁夜夜躁狠狠躁| 国产日韩一区二区三区精品不卡| 香蕉丝袜av| 丰满饥渴人妻一区二区三| 久久久久久亚洲精品国产蜜桃av| 亚洲成人国产一区在线观看| 精品久久久精品久久久| 青草久久国产| 亚洲第一av免费看| 在线播放国产精品三级| 久久av网站| √禁漫天堂资源中文www| 国产日韩一区二区三区精品不卡| 热99久久久久精品小说推荐| 成人影院久久| 精品人妻熟女毛片av久久网站| 天堂8中文在线网| 岛国毛片在线播放| 成人永久免费在线观看视频 | 成人永久免费在线观看视频 | 午夜激情av网站| 久久亚洲真实| 国产亚洲av高清不卡| 成年人黄色毛片网站| 好男人电影高清在线观看| 18禁裸乳无遮挡动漫免费视频| 国产又爽黄色视频| 日韩大片免费观看网站| 精品国产一区二区三区四区第35| av一本久久久久| 宅男免费午夜| 黄色怎么调成土黄色| 亚洲视频免费观看视频| 亚洲精品国产色婷婷电影| kizo精华| 欧美成人免费av一区二区三区 | 国产福利在线免费观看视频| 不卡av一区二区三区| 黄色视频,在线免费观看| 我要看黄色一级片免费的| cao死你这个sao货| 亚洲三区欧美一区| 国产国语露脸激情在线看| 亚洲欧美色中文字幕在线| 正在播放国产对白刺激| 国产在线免费精品| av电影中文网址| 一级,二级,三级黄色视频| 亚洲国产欧美日韩在线播放| 国产成人av教育| 成人国产一区最新在线观看| 免费在线观看黄色视频的| 欧美 日韩 精品 国产| 午夜精品久久久久久毛片777| 每晚都被弄得嗷嗷叫到高潮| 免费人妻精品一区二区三区视频| 国产日韩欧美视频二区| 一区二区三区精品91| 热re99久久精品国产66热6| 久久午夜亚洲精品久久| 免费在线观看影片大全网站| 别揉我奶头~嗯~啊~动态视频| 日本五十路高清| 成人三级做爰电影| 1024香蕉在线观看| 窝窝影院91人妻| 黄频高清免费视频| 精品少妇一区二区三区视频日本电影| 成人黄色视频免费在线看| 国产在线一区二区三区精| 色综合欧美亚洲国产小说| 亚洲第一青青草原| 真人做人爱边吃奶动态| 视频区欧美日本亚洲| 国产老妇伦熟女老妇高清| 大香蕉久久成人网| 日韩欧美国产一区二区入口| 日韩中文字幕视频在线看片| kizo精华| 精品少妇内射三级| 久久久久久久精品吃奶| 精品少妇一区二区三区视频日本电影| 欧美日韩一级在线毛片| 亚洲国产毛片av蜜桃av| svipshipincom国产片| 日韩三级视频一区二区三区| 超碰成人久久|