The Discharge Development and Arc Modes in Vacuum at A Long Gap Distance in Vacuum Interrupters

The influence of an arc current on the discharge development and the arc modes of a single coil type axial magnetic field （AMF） electrode were investigated by a high-speed charge couple device （CCD） video camera in a long gap distance of 40 mm. The distribution of the axial magnetic field of the single coil type AMF electrode was computed. By computational results, the single coil type AMF electrode could generate higher axial magnetic flux density than the slot type AMF electrode. It was found that the single coil type AMF electrode could perform better than the slot type AMF electrode with the same designing parameters. And the development of the arc modes experienced diffuse mode, constricted but unstable mode, and constricted and stable mode with the amplitude of the arc current increasing. The correlation between the vacuum arc and the noise components of arc voltage was investigated too. The interruption capability could be known in a practical commercial vacuum interrupter by the test results in a demountable vacuum interrupter （DVC） with a electrode diameter of 50 mm and a gap distance of 40 mm.The test results could provide reference to design the high voltage vacuum interrupter adopting the single coil type AMF electrode.     

Influence of Copper Vapor on Low-Voltage Circuit Breaker Arcs During Stationary and Moving States

The influence of copper vapor on the low-voltage circuit breaker arcs is studied. A three-dimensional （3-D） magnetohydrodynamics（MHD） model of arc motion under the effect of external magnetic field is built up. By adopting the commercial computational fluid dynamics （CFD） package FLUENT based on control-volume method, the above MHD model is solved. For the mediums of air-1% Cu and air-10% Cu, the distributions of stationary temperature, pressure, electrical potential and the arc motion processes are compared with those of a pure air arc. The copper vapor diffusion process in the arc chamber and the distribution of copper vapor mass concentration are also simulated. The results shows that the copper vapor has a cooling effect on the arc plasma and can decrease the stationary voltage as well. Moreover, the presence of copper vapor can decelerate the arc motion in the quenching chambers. The maximal copper vapor concentration locates behind the arc root because of the existence of a ＂double vortex＂ near the electrodes.     

Dual Torch Plasma Arc Furnace for Medical Waste Treatment

In this paper, characteristics of a treatment and operated at atmospheric pressure dual torch plasma arc used for hazardous waste are studied, and also compared with those of the multi-torch plasma arc and the single torch plasma arc. The dual torch plasma arc is generated between the cathode and anode with argon as the working gas. The temperature distributions of the plasma arc are measured using a spectroscope and line pair method with the assumption of local thermodynamic equilibrium （LTE） for the DC arc current I=100 A and argon flow rate Q = 15 slpm. The measurements show that the temperatures of the dual torch arc plasma in the regions near the cathode, the anode and the center point are 10,000 K, 11,000 K and 9,000 K, respectively. And the high temperature region of the multi torch plasma arc is of double or much wider size than that of a conventional dual torch plasma arc and single plasma torch. Based on the preceding studies, a dual torch plasma arc furnace is developed in this study. The measured gas temperature at the center region of the argon arc is about 11,000 K for the case of I=200 A and Q=30 slpm operated in atmosphere.     

Study and Measurement of Glidarc Driven by Magnetic Field

Non-thermal plasma at atmosphere was generated through glidarc discharge driven by magnetic field and observed by using a high speed charge coupled device （CCD） and photo multiplier tube （PMT）. The arc diameter projecting in the direction of arc motion （front-viewed diameter） and the diameter projecting in the perpendicular direction of arc motion （side-viewed diameter） were measured. The effect of both the arc current and the magnetic field was analysed. The front-viewed diameter was compared with the side-viewed one. Simultaneously the electricfield intensity was measured directly and analysed by considering the effect of the external magnetic field and arc current.     

Experimental Study of the Influence of Gassing Material on Blow Open Force and Arc Motion

The study of arc behavior is important to understand the dynamic phenomena concerning the interruption process in a variety of switching devices. This paper is devoted to investigate the influence of gassing material on blow open force and arc motion. To one double- breaker model, measuring the arc current, voltage and force acting on the moving conductor, the characteristics of the ratio of the emerging blow open force over arc power FB/（ui） could be obtained. With the help of a 2-D optical fiber measurement system, to one arc chamber model, arc motion behavior was measured, too. It is demonstrated that, with the action of gassing material, FB/（ui） will increase 2.5 times, and the arc will enter the splitter plates much easier.     

Temperature and Nitric Oxide Generation in a Pulsed Arc Discharge Plasma

Nitric oxide （NO） is increasingly being used in medical treatments of high blood pressure, acute respiratory distress syndrome and other illnesses related to the lungs. Currently a NO inhalation system consists of a gas cylinder of N2 mixed with a high concentration of NO. This arrangement is potentially risky due to the possibility of an accidental leak of NO from the cylinder. The presence of NO in the air leads to the formation of nitric dioxide （NO2）, which is toxic to the lungs. Therefore, an on-site generator of NO would be highly desirable for medical doctors to use with patients with lung disease.
To develop the NO inhalation system without a gas cylinder, which would include a high concentration of NO, NAMIHIRA et al have recently reported on the production of NO from room air using a pulsed arc discharge. In the present work, the temperature of the pulsed arc discharge plasma used to generate NO was measured to optimize the discharge condition. The results of the temperature measurements showed the temperature of the pulsed arc discharge plasma reached about 10,000 K immediately after discharge initiation and gradually decreased over tens of microseconds. In addition, it was found that NO was formed in a discharge plasma having temperatures higher than 9,000 K and a smaller input energy into the discharge plasma generates NO more efficiently than a larger one.     

Synthesis of Crystalline Carbon Nitride Thin Films by Pulsed Arc Discharge at Atmospheric Pressure

The preparation of crystalline C3N4 films was investigated using pulsed arc discharge from mixed methanol and ammonia water at atmospheric pressure. The X-ray diffraction （XRD） patterns of the films prepared at a substrate temperature of 450℃ suggested that the film was composed of α-C3N4 and fl-C3N4 crystallites. Raman spectra exhibited distinct peaks which are in good agreement with those predicted theoretically for C3N4 crystallites.     

Analysis of the Carbon Nano-Structures Formation in Liquid Arcing

Graphite electrodes were used for the direct current （DC） arc discharge in water. And high-resolution transmission electron microscopy （HRTEM） was used to investigate the products. Based on the experimental phenomena and nano-structure products, arc plasma characteristics in water were analyzed theoretically. Two growth regions and relevant growth modes were proposed to interpret the formation mechanisms of nano-structures by arc discharge in water. Furthermore, liquid nitrogen and cross magnetic field was applied to change the arcing state respectively, and new carbon nano-structures were obtained. Their formation mechanisms were also analyzed correspondingly.     

Study of Metal and Ceramic Thermionic Vacuum arc Discharges

The thermionic vacuum arc （TVA） is a new type of plasma source, which generates a pure metal and ceramic vapour plasma containing ions with a directed energy. TVA discharges can be ignited in high vacuum conditions between a heated cathode （electron gun） and an anode （tungsten crucible） containing the material. The accelerated electron beam, incident on the anode, heats the crucible, together with its contents, to a high temperature. After establishing a steadystate density of the evaporating anode material atoms, and when the voltage applied is high enough, a bright discharge is ignited between the electrodes. We generated silver and Al2O3 TVA discharges in order to compare the metal and ceramic TVA discharges. The electrical and optical characteristics of silver and Al2O3 TVA discharges were analysed. The TVA is also a new technique for the deposition of thin films. The film condenses on the sample from the plasma state of the vapour phase of the anode material, generated by a TVA. We deposited silver and Al2O3 thin films onto an aluminium substrate layer-by-layer using their TVA discharges, and produced micro and/or nano-layer Ag-Al2O3 composite samples. The composite samples using scanning electron microscopy was also analysed.     

Numerical Simulation of Low Current Vacuum Arc Supersonic Flow

Based on a two-dimensional axisymmetric magneto-hydrodynamic （MHD） model, low current vacuum arc （LCVA） characteristics are studied. The influence of cathode process under different axial magnetic fields and different anode radii on LCVA characteristics is also simulated. The results show that the influence of both cathode process and anode radii on LCVA is significant. The sign of anode sheath potentials can change from negative to positive with the decrease of anode radii. The simulation results are in part verified by experimental results. Especially, as the effect of ion kinetic energy is considered, ion temperature is improved significantly; which is in agreement with experimental results.     

Electrode Evaporation Effects on Air Arc Behavior

A numerical study of the effects of copper and silver vapours on the air arc behavior is performed. The commercial software FLUENT is adapted and modified to develop a twodimensional magneto-hydrodynamic （MHD） models of arc with the thermodynamic properties and transport coefficients, net emission coefficient for the radiation model of 99% ai-1% Cu, 99% air-1% Ag, and pure air, respectively. The simulation result demonstrates that vaporization of the electrode material may cool the arc center region and reduce the arc velocity. The effects of Ag vapour are stronger compared to those of Cu vapour.     

Transient Ablation Regime in Circuit Breakers

Nozzle wall ablation caused by high temperature electric arcs is studied in the context of high voltage SF6 circuit breakers. The simplified ablation model used in litterature has been updated to take into account the unsteady state of ablation. Ablation rate and velocity are now calculated by a kinetic model using two layers of transition, between the bulk plasma and the ablating wall. The first layer （Knudsen layer）, right by the wall, is a kinetic layer of a few mean-free path of thickness. The second layer is collision dominated and makes the transition between the kinetic layer and the plasma bulk. With this new coupled algorithm, it is now possible to calculate the temperature distribution inside the wall, as well as more accurate ablation rates.     

Analysis of Arc Characteristics and Flow Field in Arc Chamber of High-Voltage SF6 Auto-Expansion Circuit Breaker

A new magnetic hydro-dynamics model for nozzle arc emphasizing the interaction of arc with PTFE （polytetrafluorethylene） vapour is established based on the conservation equations. The interruption of auto-expansion circuit breaker is simulated numerically by finite element method and the influence of PTFE vapour on the arc is analysed with this model. The results reveal that the flow field inside the arc chamber is determined by the arc current, the arcing time, the nozzle arc and the clogging of its thermal boundary. The establishment of quenching pressure relies on both SF6 gas and PTFE vapour that absorbed arc energy in the nozzle. The PTFE vapour leads to an increase in the pressure of nozzle arc obviously, and a decrease in the temperature of arc. But it enhances the temperature of arc at zero current and slows down the decreasing rate of arc temperature as the current decreases.     

High Power Microwave Test System and Simulated Experiments for HT-7

In lower hybrid current drive （LHCD） experiments in HT-7, LH wave coupled to the plasma from 12 klystrons is launched by a phased multi-junction grill. High power microwave reflection or arc, which threatens the klystrons, the wave-guide ceramic windows and the vacuum of the tokamak, occur sometimes during the experiments. For the sake of safety, a high power microwave test system to perform simulations was developed. In the test experiments, the klystron and window can be well protected with an optimized microwave monitor and a PIN switch. The layout of the test system and the simulated experiments for HT-7 are described in this paper.     

Arc Behaviours in Vacuum Interrupters with Axial Magnetic Field Electrodes

To improve the limiting current interruption capability and minimizing vacuum interrupter with axial magnetic field （AMF） electrodes, it is significant to investigate the vacuum arc behaviours between the contacts. AMF distributions of the slot type electrodes were studied by both numerical analysis and experiments. Furthermore, the behaviours of vacuum arcs for different parameters of the slot type AMF electrodes were investigated by using high-speed CCD camera. The influences of gap distance, contact diameter and phase shift time between AMF and arc current on the vacuum arc were investigated. The results provide a reference for research and development of vacuum interrupters with slot type or other types of AMF electrode.     

Plasma-Neutral Gas Structure in a Magnesium Cathodic Arc Operating at Oxygen Gas with Experimental Comparison

The plasma-neutral gas structure generated in a magnesium cathodic arc operated with oxygen gas at a constant current of 50 A has been investigated by employing a simplified one-dimensional fluid model.The model includes elastic collisions and charge-exchange reactions between metallic particles and gas molecules,and also generation and recombination of gaseous ions by electron impact.The distribution profiles of density and velocity of species along the axial direction were obtained at diferent background gas pressures(in the range of 0.7~3.0 Pa)by this model.A comparison with the experiments was made.At lower gas pressures,the depositing particles were mainly the metallic ions with a larger kinetic energy.As the gas pressure increased,the magnesium atoms with smaller kinetic energy acted as the dominant depositing species.Determined by the minimization of the system’s total energy,MgO(100)or/and MgO(110)orientation appeared easily in the MgO films at lower gas pressures,and at higher gas pressures,the film preferred orientation was MgO(111).     

Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

In this study, the influence of the initial jet angles （IJAs） and ion number densities （INDs） at the cathode side on the low current vacuum arc （LCVA） characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.     

Study of Multi-Function Micro-Plasma Spraying Technology

A multi-functional micro-arc plasma spraying system was developed according to aerodynamics and plasma spray theory. The soft switch IGBT （Insulated Gate Bipolar Transistor） invert technique, micro-computer control technique, convergent-divergent nozzle structure and axial powder feeding techniques have been adopted in the design of the micro-arc plasma spraying system. It is not only characterized by a small volume, a light weight, highly accurate control, high deposition efficiency and high reliability, but also has multi-functions in plasma spraying, welding and quenching. The experimental results showed that the system can produce a supersonic flame at a low power, spray Al2O3 particles at an average speed up to 430 m/s, and make nanostructured AT13 coatings with an average bonding strength of 42.7 MPa. Compared to conventional 9M plasma spraying with a higher power, the coatings with almost the same properties as those by conventional plasma spray can be deposited by multi-functional micro-arc plasma spraying with a lower power plasma arc due to an improved power supply design, spray gun structure and powder feeding method. Moreover, this system is suitable for working with thin parts and undertaking on site repairs, and as a result, the application of plasma spraying will be greatly extended.     

Numerical simulation of constricted and diffusive arc–anode attachments in wall-stabilized transferred argon arcs

A numerical simulation is conducted to investigate arc–anode attachment behavior, especially the formation mechanism of the constricted arc attachment mode for the water-cooled anode of wall-stabilized transferred argon arcs. Argon molecular ions and the corresponding kinetic processes are included to the finite-rate chemistry model in order to capture the chemical nonequilibrium characteristics of the arc near the anode region. Modeling results show that constricted and diffusive arc–anode attachments can be self-consistently obtained at different arc currents while keeping other parameters unchanged. The dominant kinetic processes contributing to ionization and recombination in the arc center and fringes are presented. The results show that in arc fringes and the arc attachment region, molecular ion recombination plays an important role which leads to the rapid loss of electrons. The radial evolution of the production, loss and transport processes of electrons is further analyzed. It is found that for the constricted arc attachment mode, both the recombination and convection transport caused by the anode jet result in the loss of electrons at the arc fringes, which leads to the shrinkage of the arc column at the anode. The formation of the anode jet is due to the combined action of radial and axial Lorentz forces in the anode region.     

Motion and Splitting of Vacuum Arc Column in Transverse Magnetic Field Contacts at Intermediate—Frequency

Arc motion and splitting of vacuum arc at intermediate frequency（400-800 Hz） were investigated under transverse magnetic field（TMF）.The experiment was performed on cup-type TMF contacts with contact diameter of 40 mm and a contact gap of 4 mm in a single-frequency circuit.With high-speed photography we characterized the arc appearance at different arc currents from 3.3 kA-rms to 10 kA-rms at intermediate frequencies.As arc current increases from3.3 kA-rms to 10 kA-rms the arc appearance changes obviously.When current value is 3.3 kArms（current frequency 400-800 Hz）,there is almost no splitting arc;when the current exceeds5 kA-rms（current frequency 400-800 Hz）,the arc rotates at a speed above 20 m/s,accompanied by an observable splitting arc.The splitting arc could be observed at different frequencies and the arc-voltage had no noises when splitting occurred.The motion direction and the velocity of arc column were studied.Finally,the formation of a split arc was discussed.