The Influence of Contact Space on Arc Commutation Process in Air Circuit Breaker

In this paper,a 3D magneto-hydrodynamic (MHD) arc simulation model is applied to analyze the arc motion during current interruption in a certain air circuit breaker (ACB).The distributions of pressure,temperature,gas flow and current density of the arc plasma in the arc region are calculated,and the factors influencing the commutation process are analyzed according to the calculated results.Based on the airflow in the arc chamber,the causes of arc commutation asynchrony and the back commutation are investigated.It indicates that a reasonable contact space design is crucial to a successful arc commutation process.To verify the simulation results,the influence of contact space on arc voltage and arc commutation is tested.This research can provide methods and references to the optimization of ACB design.     

Research on arc root stagnation when small current is interrupted in self-excited circuit breaker

The self-excited DC air circuit breaker (SE-DCCB) has been widely used in urban rail transit due to its excellent stability. It can realize forward and reverse interruption, but has difficulty interrupting small currents due to the phenomenon of arc root sticking at the entrance of the arc chamber in the splitting process, which is known as arc root stagnation. A coupling model of the self-excited magnetic field and magnetohydrodynamics is established for the SE-DCCB with the traditional structure. The magnetic field, temperature and airflow distribution in the arc chamber are investigated with an interrupting current of 150 A. The simulation results show that the direction and magnitude of the magnetic blowout force are the dominant factors in the arc root stagnation. The local high temperature of the arc chamber due to arc root stagnation increases the obstruction effect of the airflow vortex on the arc root movement, which significantly increases the arc duration time of small current interruption. Based on the research, the structure of the magnetic conductance plate of the actual product is improved, which can improve the direction and magnitude of the magnetic blowout force at the arc root so as to restrain the development of the airflow vortex effectively and solve the problem of arc root stagnation when the small current is interrupted. The simulation results show that the circuit breaker with improved structure has a better performance for a small current interruption range from 100 A to 350 A.     

Simulation and Experimental Analysis of Arc Motion Characteristics in Air Circuit Breaker

In this paper, to simulate the arc motion in an air circuit breaker (ACB), a three-dimensional magneto-hydrodynamic (MHD) model is developed, considering the influence of thermal radiation, the change of physical parameters of arc plasma and the nonlinear characteristic of ferromagnetic material. The distributions of pressure, temperature, gas flow and current density of arc plasma in the arc region are calculated. The simulation results show some phenomena which discourage arc interruption, such as back commutation and arc burning at the back of the splitter plate. To verify the simulation model, the arc motion is studied experimentally. The influences of the material and position of the innermost barrier plate are analyzed mainly. It proved that the model developed in this paper can efficiently simulate the arc motion. The results indicate that the insulation barrier plate close to the top of the splitter plate is conducive to the arc splitting, which leads to the signi?cant increase of the arc voltage, so it is better for arc interruption. The research can provide methods and references to the optimization of ACB design.     

Numerical simulation of the plasma acceleration process in a magnetically enhanced micro-cathode vacuum arc thruster

A particle-in-cell simulation is conducted to investigate the plasma acceleration process in a micro-cathode vacuum arc thruster. A coaxial electrode structure thruster with an applied magnetic field configuration is used to investigate the effects of the distribution of the magnetic field on the acceleration process and the mechanism of electrons and ions. The modeling results show that due to the small Larmor radius of electrons, they are magnetized and bound by the magnetic field lines to form a narrow electron channel. Heavy ions with a large Larmor radius take a long time to keep up with the electron movement. The presence of a magnetic field strengthens the charge separation phenomenon. The electric field caused by the charge separation is mainly responsible for the ion acceleration downstream of the computation. The impact of variations in the distribution of the magnetic field on the acceleration of the plasma is also investigated in this study, and it is found that the position of the magnetic coil relative to the thruster exit has an important impact on the acceleration of ions. In order to increase the axial velocity of heavy ions, the design should be considered to reduce the confinement of the magnetic field on the electrons in the downstream divergent part of the applied magnetic field.     

Simulation of Arc Rotation and Its Effects on Pressure of Expansion Volume in an Auto-Expansion SF6 Circuit Breaker

A 3D Magnetohydrodynamics (MHD) arc model in conjunction with an arc move¬ment model is applied to simulate the arc rotation as well as to solve its effect on the pressure in an auto-expansion circuit breaker. The rotation of the arc driven by an external electromagnetic force is simulated in the case with 200 kA of the short circuit current and 16 ms of arc duration. The arc rotating process and the speed of arc rotation have been obtained in the simulation. A comparison of the pressure in the expansion volume with and without an external magnetic field has been carried out based on the calculation results of two cases. The results of the simulation reveal that the arc rotation, which causes more energy exchange between the arc and its surrounding gas, can evidently bring about the pressurization in the expansion volume, which would contribute to more effective arc quenching at current zero and further reducing operation power.     

Coupling model of AC filter branch in SF6 circuit breaker during the break process

In this paper, a coupling model of the AC filter branch circuit with the arc plasma in the circuit breaker was built to investigate the arcing process considering the harmonic current. The comparisons among the current at power frequency (50 Hz), power frequency combining the 11th harmonic and power frequency combining the 24th harmonic show that the high-order harmonic current would lead to higher decreasing rate of current before current-zero period. In addition, the influence of arc on the amplitude of high-order harmonic current is not negligible. Thus, the coupling of arc with AC filter branch circuit is quite necessary in the numerical modeling of the circuit breaker in the AC filter branch at the high voltage direct current converter station.     

Study of double-chamber air arc plasma torch and the application in solid-waste disposal

Arc plasma can be applied in hazardous solid waste disposal for higher temperature than common heating methods, but some practical issues exist in practical engineering application. In this study, an air arc plasma torch with double chambers and magnetic controlling is designed to realize wide variable power and long electrode life. The detailed characteristics and laws of the air arc are studied. The condition parameters of arc current(I), air flow rate(G) and the structure parameters of inlet area ratios and electrode diameters influence both the arc voltage and arc root positions. The arc rotating driven by magnetic field effectively lengthens the electrode life. The gasification process and product of organic wastes by air plasma are influenced largely by the waste compositions and the air flow rate. A furnace structure with more even atmosphere and longer residence time should be considered for better gasification. Oxygen-deficient environment is important to suppress NOxformation during the application of air plasma. Inorganic solid wastes can be melt by the air plasma and cooled down to form compact vitreous structures in which heavy metals can be locked and the leaching rates significantly decrease down.     

Calculation of Nozzle Ablation During Arcing Period in an SF6 Auto-Expansion Circuit Breaker

The nozzle ablation process is described as two phases of heat and ablation in the interruption for an SF6 circuit breaker in this paper.Their mathematical models are established with the Fourier heat conduction differential equation respectively.The masses of nozzle ablation with different arc durations and arc currents are calculated through the model of the nozzle ablation combined with an MHD (magneto-hydrodynamic) arc model.The time of the temperature rise on the inner surface of the nozzle under a given energy flux and of reaching the pyrolysis temperature under different energy fluxes is respectively analyzed.The relations between the mass of nozzle ablation and breaking current and arc duration are obtained.The result shows that the absorbing energy process before the nozzle ablation can be neglected under the condition of the energy flux entering into nozzle q ＞ 109 W/m2.The ablation is the severest during the high-current phase and the ablation mass increases rapidly with the breaking current and with arc duration respectively.     

Effects of plasma radiation on the nonlinear evolution of neo-classical tearing modes in tokamak plasmas

The effects of plasma radiation on the nonlinear evolution of neo-classical tearing modes are investigated based on a set of reduced magnetohydrodynamic equations. It is found that the radiation can reduce the pressure near the rational surface. During the nonlinear evolution, the magnitude of perturbed bootstrap current is drastically enhanced in the presence of the radiation. Besides, the radiation can increase the growth rate of the magnetic islands by diminishing the pressure, such that the magnetic islands do not saturate compared with that without radiation. On the other hand, with the increase of the ratio of parallel to perpendicular transport coefficient ${chi }_{parallel }/{chi }_{perp },$ the reduction of pressure can further increase the growth rate of magnetic islands in the presence of plasma radiation. Finally, the mechanisms of the destabilizing effects driven by the radiation are discussed in detail as well.     

Simulation of Fault Arc Based on Different Radiation Models in a Closed Tank

This paper focuses on the simulation of a fault arc in a closed tank based on the magneto-hydrodynamic(MHD) method,in which a comparative study of three radiation models,including net emission coefficients(NEC),semi-empirical model based on NEC as well as the P1 model,is developed.The pressure rise calculated by the three radiation models are compared to the measured results.Particularly when the semi-empirical model is used,the effect of different boundary temperatures of the re-absorption layer in the semi-empirical model on pressure rise is concentrated on.The results show that the re-absorption effect in the low-temperature region affects radiation transfer of fault arcs evidently,and thus the internal pressure rise.Compared with the NEC model,P1 and the semi-empirical model with 0.7 α 0.83 are more suitable to calculate the pressure rise of the fault arc,where is an adjusted parameter involving the boundary temperature of the re-absorption region in the semi-empirical model.     

Measurement of electron density and electron temperature of a cascaded arc plasma using laser Thomson scattering compared to an optical emission spectroscopic approach

As advanced linear plasma sources, cascaded arc plasma devices have been used to generate steady plasma with high electron density, high particle flux and low electron temperature. To measure electron density and electron temperature of the plasma device accurately, a laser Thomson scattering(LTS) system, which is generally recognized as the most precise plasma diagnostic method, has been established in our lab in Dalian University of Technology. The electron density has been measured successfully in the region of 4.5?×?10(19)m~(-3) to7.1?×?10~(20)m~(-3) and electron temperature in the region of 0.18 eV to 0.58 eV. For comparison,an optical emission spectroscopy(OES) system was established as well. The results showed that the electron excitation temperature(configuration temperature) measured by OES is significantly higher than the electron temperature(kinetic electron temperature) measured by LTS by up to 40% in the given discharge conditions. The results indicate that the cascaded arc plasma is recombining plasma and it is not in local thermodynamic equilibrium(LTE). This leads to significant error using OES when characterizing the electron temperature in a non-LTE plasma.     

Pressure and Arc Voltage Measurement in a 252 kV SF6 Puffer Circuit Breaker

The pressure distribution in an arcing chamber is critically important for the SF6 puffer circuit breaker design.In this paper,the pressure variation of four locations in the nozzle was measured by piezoresistive and fiber optical pressure sensors at two current levels of 10 kA and 50 kA.An arc voltage measurement was also taken.The results demonstrate that using either type of sensor with a connecting tube is able to detect the fast pressure variation in circuit breakers,however the possible distortion and delay to the pressure transient caused by the tube need further study.     

Dynamic behavior of a rotating gliding arc plasma in nitrogen: effects of gas flow rate and operating current

The effects of feed gas flow rate and operating current on the electrical characteristics and dynamic behavior of a rotating gliding arc (RGA) plasma codriven by a magnetic field and tangential flow were investigated.The operating current has been shown to significantly affect the time-resolved voltage waveforms of the discharge,particularly at flow rate =21 min-1.When the current was lower than 140 mA,sinusoidal waveforms with regular variation periods of 13.5-17.0 ms can be observed (flow rate =21 min-1).The restrike mode characterized by serial sudden drops of voltage appeared under all studied conditions.Increasing the flow rate from 8 to 121 min-1 (at the same current) led to a shift of arc rotation mode which would then result in a significant drop of discharge voltage (around 120-200 V).For a given flow rate,the reduction of current resulted in a nearly linear increase of voltage.     

Effects of electron temperature on the ion extraction characteristics in a decaying plasma confined between two parallel plates

In this paper, a one-dimension particle-in-cell (PIC) code (EDIPIC) is employed to simulate the parallel-plate ion extraction process under an externally applied electrostatic field, focusing on the analysis of the influence of the initial electron temperature on the extracted ion fluxes to the metal plates during the ion extraction process. Compared with previously published results, the plasma oscillations on a timescale of the electron plasma period, and the excitation of the ion acoustic rarefaction waves resulting from the plasma oscillations originating from both the negative and positive electrodes, are studied for the first time. The modeling results show that both the negative and positive extractors can collect ions due to the plasma oscillations and the propagation of the ion acoustic rarefaction waves. With the increase of the initial electron temperature achieved by keeping other parameters unchanged, on the one hand, both the ion speed and flux to the negative and positive plates increase, which leads to a significant decrease of the ion extraction time, while on the other hand, the ion flux to the positive plate after the formation of a Child–Langmuir sheath is much more sensitive to an increase of the initial electron temperature than that to the negative plate. The PIC simulation results provide a deeper physical understanding of the influence of the initial electron temperature on the characteristics of the entire ion extraction process in a decaying plasma.     

The influence of weak transverse magnetic field on plasma dissipation process in the post-arc phase in a vacuum interrupter

Transverse magnetic field (TMF) contacts and applying external TMF are often adopted for reducing the ablation of the contact surface, but TMF will also affect the breaking performance of the vacuum interrupters. In this work, we investigated the influence of weak TMF on the expansion of the plasma in the post-arc phase with one-dimensional implicit particle-in-cell/Monte Carlo collision model, and we added an external circuit to the model to ensure the correctness of the calculation results. We simulated multiple magnetic field strengths (<30 mT), compared the plasma expansion process with the TMF strengths of 0 mT and 10 mT, and discussed the influence of metal vapor density on the insulation performance recovery of the vacuum interrupter. From the results, applying TMF with strength below 5 mT has little effect on the expansion of the plasma, and the TMF can increase the plasma density which improve the flow capacity of vacuum circuit breakers when the magnetic field above 10 mT, which is because the particles become more difficult to leave the discharge area under the force of the magnetic field. In general, we find that weak external TMF may adversely affect the breaking performance of the vacuum circuit breakers.     

Study of post-arc residual plasma dissipation process of vacuum circuit breakers based on a 2D particle-in-cell model

In order to get an insight into residual plasma radial motion during the post-arc stage, a two-dimensional (2D) cylindrical particle-in-cell (PIC) model is developed. Firstly, influences of a virtual boundary condition on the residual plasma motion are studied. For purpose of validating this 2D cylindrical particle-in-cell model, a comparison between one-dimensional particle-in-cell model is also presented in this paper. Then a study about the influences of the rising rate of transient recovery voltage on the residual plasma radial motion is presented on the basis of the 2D PIC model.     

The effect of positive/negative ion on the dust grain charging process in a Vasyliunas-Cairns (VC)-distributed dusty plasma system

Charging mechanism of dust particles has been considered as a growing research area in dusty plasma physics because of its exciting results. In this paper, we consider a low-temperature non- equilibrium multispecies plasma model, which consists of Vasyliunas–Cairns (VC) distributed electrons, negative/positive streaming ions, and negatively-charged dust grains to explain the charging mechanism of dust grains. The main theme of this work is to derive expressions of currents for negatively-charged dust grains (considering an equilibrium state position) in the plasma environment comprised of electrons and positive/negative streaming ions using the VC distribution function. Our proposed model shows that the dust grain surface potential is significantly affected by different plasma parameters such as the negative ion streaming velocity (S_n), positive ion streaming velocity (S_i), spectral indices of VC distribution, negative ion charging state (Z_n), positive ion charging state (Z_i), and negative ion number density (ρ).     

Experiment investigation on two-phase flow instability in a parallel twin-channel system

In this paper, the behavior of two-phase flow instability of a twin-channel system is studied experimentally. The two-phase flow instability between twin channels (FIBT) was observed in the experiments at three different system pressures, different inlet resistance coefficients and nonuniform heating condition. The instability boundaries of the twin-channel system are obtained in the phase plane of the subcooling and phase change number. The influences of inlet resistance, system pressure and nonuniform heating are obtained. In the end the numerical simulation results based on RELAP5/MOD3.4 code are also discussed.     

Influence of the axial magnetic field on sheath development after current zero in a vacuum circuit breaker

After current zero,which is the moment when the vacuum circuit breaker interrupts a vacuum arc,sheath development is the first process in the dielectric recovery process.An axial magnetic field (AMF) is widely used in the vacuum circuit breaker when the high-current vacuum arc is interrupted.Therefore,it is very important to study the influence of different AMF amplitudes on the sheath development.The objective of this paper is to study the influence of different AMF amplitudes on the sheath development from a micro perspective.Thus,the particle in cell-Monte Carlo collisions (PIC-MCC) method was adopted to develop the sheath development model.We compared the simulation results with the experimental results and then validated the simulation.We also obtained the speed of the sheath development and the energy density of the ions under different AMF amplitudes.The results showed that the larger the AMF amplitudes are,the faster the sheath develops and the lower the ion energy density is,meaning the breakdown is correspondingly more difficult.     

Gas pressure effect on plasma transport in a magnetic-filtered radio-frequency plasma source

Volume negative ion production relies on a magnetic filter(MF), where the plasma downstream of the MF is characterized by a strip-like pattern that consists of a bright and dense plasma region. In this work, we study, in a radio-frequency plasma source, the effects of operating pressure on this strip. This investigation, conducted using a Langmuir probe, shows that the plasma uniformity might be controlled through the gas pressure. Moreover, the operating pressure determines on which hemi-cylinder(side of magnetic field lines) the strip forms. This side inversion of the high-density plasma hemi-cylinder is due to an inversion of an ambipolar electric field that changes the E?×?B drift direction.