Arc Formation Process Research Articles

Novel method for identifying the stages of discharge underwater based on impedance change characteristic

It is difficult to determine the discharge stages in a fixed time of repetitive discharge underwater due to the arc formation process being susceptible to external environmental influences. This paper proposes a novel underwater discharge stage identification method based on the Strong Tracking Filter (STF) and impedance change characteristics. The time-varying equivalent circuit model of the discharge underwater is established based on the plasma theory analysis of the impedance change characteristics and mechanism of the discharge process. The STF is used to reduce the randomness of the impedance of repeated discharges underwater, and then the universal identification resistance data is obtained. Based on the resistance variation characteristics of the discriminating resistance of the pre-breakdown, main, and oscillatory discharge stages, the threshold values for determining the discharge stage are obtained. These include the threshold values for the resistance variation rate (K) and the moment (t). Experimental and error analysis results demonstrate the efficacy of this innovative method in discharge stage determination, with a maximum mean square deviation of S cr less than 1.761.

Fluid modeling of CF3I/CO2 arc formation process

The environmentally friendly insulating gas CF3I is a promising replacement for SF6 due to its excellent insulation and arc extinguishing performance. In the arc chamber of high-voltage circuit breakers filled with CF3I/CO2, the near-electrode sheath dominates the current transfer process between contact and arc column during arc formation, which has a significant effect on the transition from glow to arc discharge. The 30%CF3I/70%CO2 was taken as the research object in this research, and a more perfect fluid model was established considering the influence of diffusion current. The arc formation process between the contacts at the preliminary stage of circuit breaker interruption was conducted. The results show that the arc formation process can be divided into three stages: glow discharge, abnormal glow discharge, and arc discharge. As the arc formation process proceeds, the thickness of the near-cathode sheath decreases gradually. When the arc reaches stability with the current density 8×106–1.6×107A·m−2, the thickness of the near-cathode sheath is 7 μm, the steep voltage fall near the cathode sheath is generated within 7 μm away from the cathode surface, and this voltage fall almost does not change with the current density. CF3I− is the dominant negative ion between the contacts, which indicates that CF3I has excellent electron adsorption performance and is beneficial to arc deionization. The computational results of this work were compared with the existing experimental ones, which shows that the model used in this work is accurate enough. Finally, suggestions for model optimization and future work are given.

Experimental Study on Thermal Characteristics of DC Arc Formation between Ice-Electrode Gap

The partial arc is a destructive discharge phenomenon for HVDC insulators under icing conditions, leading to flashover incidents. This study sets up a calibrated Schlieren system to examine the DC arc's thermal characteristics on an ice surface. The theoretical analysis shows that the plasma component changes significantly between 2000 K to 2882 K, which is the characteristic temperature of arc formation. Experimental results show that the temperature characteristics in the time domain depend on the discharge stages. A temperature jump appears at the spark discharge and then increases exponentially with the leakage current during the arc formation. However, the temperature in the corona and brush discharge is almost unchanged. Results also show that higher water conductivities increase the spark temperature and promote arc formation, but do not affect corona and brush discharge, which take place in the air gap. In the arc channel, the gas near the core comprises molecules, atoms, electrons, and ions, while the gas in other regions is mainly composed of neutral molecules. This study provides findings that might enhance our basic understanding of the ice surface's partial arc formation process.

Design constraints on new vacuum components of RFX-mod2 upgrade using electrical modeling of reversed field pinch plasma

The externally applied loop voltage, required to drive current carrying magnetic configurations, such as tokamaks or reversed field pinches (RFP), can induce currents between the plasma and the surrounding conducting components, such as limiters, divertor sections, stabilizing plates or enclosing stabilizing shells with insulated electrical gaps. An appropriate modeling of this problem can quantify these currents and give constraints for the design of new devices. In this paper a methodology based on lumped element circuit is used to evaluate this problem for the case of in vessel components of the RFX-mod2, which led to a redesign of the electrical connections of plasma facing components. In the new design some parts, having applied potential in the kV range, are still exposed to the weakly ionized scrape off plasma. The process of arc formation between them and their prevention had been experimentally investigated and possible arc suppression strategies identified.

초크코일을 이용한 SPD 조합회로의 잔류전압 저감기법

Gas Discharge Tubes (GDTs) are widely used as surge protectors for communication applications due to their small internal capacitance. In these days, however, they are mostly used in combined configurations, because the sparkover voltage required to initiate the discharge process in the GDTs and the time taken for arc formation process can be large enough to damage to sensitive circuits. For GDTs with a considerably high initial residual voltage, we should limit the peak voltage using a TVS or filter. We made a hybrid SPD circuits of common-mode type and differential-mode type with the filter using common-mode choke. Also, we applied lightning impulse voltage and ring wave voltage which frequency bandwidth are different each other and verified the characteristics of hybrid SPD circuits according to waveshapes. We describe how the applied SPDs operate in protection process steps with the actual data obtained from the residual voltage measurement at each step. The experiment results show that the surge voltage reduction with the choke coil is more effective in differential-mode circuit than in common-mode circuit.

MHD–PIC connection model in a magnetosphere–ionosphere coupling system

A new simulation model is developed, in which the interaction between the macroscopic and microscopic plasma processes is able to be taken into account self-consistently. Magnetohydrodynamic (MHD) simulation and particle-in-cell (PIC) simulation are directly connected and performed simultaneously. This MHD–PIC connection model is first applied to the study of the quiet auroral arc formation process. It is an example of our challenge to create the holistic simulation framework, that is, the heterogeneous schemes that can be unified by the state-of-the-art numerical technique. In this paper, we will explain the algorithm of our new model and show the results which have been calculated on the Earth Simulator.

Radar observations in the vicinity of pre-noon auroral arcs

Abstract. A combination of EISCAT incoherent scatter radar measurements, optical and magnetometer data is used to study the plasma in and around pre-noon structured precipitation and auroral arcs. Particular attention is paid to regions of comparatively low E-region density observed adjacent to arcs or structured precipitation in the EISCAT Svalbard radar field-aligned measurements. Comparison between luminosity and incoherent scatter electron density measurements shows that the low-density regions occur primarily due to the absence of diffuse precipitation rather than to a cavity formation process. Two cases of arcs and low density/luminosity regions are identified. The first is related to a strong Pc5 pulsation event, and the absence of diffuse precipitation is due to a large-scale modulation of the diffuse precipitation. In the second case the equatormost arc is on a shielding boundary and the low-density region coincides with a strong flow region just poleward of this arc. Regions of high electric field and low luminosity and conductance are observed prior to intensification of the structured precipitation in both cases. The ionospheric current is enhanced in the low conductance region, indicating that the strong electric fields do not result solely from ionospheric polarization electric fields, and thus are mainly driven by magnetospheric processes. The average energy of the precipitating electrons in the arcs and structured precipitation is, according to EISCAT measurements, 500eV and the energy spectra are similar for the pulsation and shielding cases. The average energy is thus significantly less than in the diffuse precipitation region which shows central CPS-like energy spectra. We suggest that the low ionospheric conductance of 0.7S in the low density regions is favorable for the arc formation process. This is in quantitative agreement with recent simulations of the ionospheric feedback instability. Keywords. Magnetospheric physics (Auroral phenomena; Magnetosphere-ionosphere interactions) – Ionosphere (Plasma convection)

Arc suppression in CO2 laser discharges

We have parameterized the times to arc formation in CO2 : N2 : He mixtures using a TEA configuration which produces homogeneous 10-liter laser discharges. The onset of arcing is suppressed by increasing the helium or decreasing the CO2 concentration. Arcs are also suppressed by adding a low-ionization-potential seedant such as tripropylamine. Direct variation of the uv spark intensity which establishes the initial preionization has minimal impact on the arc formation process.

Xenon flashlamp triggering for laser applications

Results of an investigation into the triggering of linear xenon flashlamps are presented, with particular reference to xenon flashlamps in laser applications. Measurements are described which give information on the arc formation process, trigger voltage thresholds, peak trigger currents, lamp energy output stability, and electromagnetic interference (EMI) for both series and parallel triggering. Particular attention is given to the performance obtained with both the correct and the incorrect polarities for the two types of triggering. The investigation makes extensive use of a high-speed streak camera and a wideband (100 MHz) continuous sweep spectrum analyzer, as well as more conventional instrumentation. It was found that: 1) the triggering process is extremely fast (≤50 ns) for both methods, but that parallel triggering produces trigger currents which are 100 times smaller than series; 2) the trigger current rather than the main energy, discharge current is the dominant EMI source; 3) the measured RF spectra show the corresponding EMI superiority of parallel over series; and 4) the two methods are equivalent in regard to the effect on lamp efficiency and stability.

Current distribution in the cylindrical source plane-electrode configuration

There are a number of instances in the operation of electric apparatus in which the physical situation may be approximated by a configuration in which a plane electrode conducts current which is received from or delivered to a cylindrical conducting path normal to its surface. Among these instances the most familiar examples are cases in which the conducting path is an ionized column resulting from sparkover (breakdown) of a solid, liquid, or gaseous dielectric between conductors, or the process of arc formation by the separation of initially juxtaposed conducting surfaces between which current is flowing. Typical situations correspond to circumstances accompanying insulation failures in apparatus, relay contact ���breaks,��� circuit-breaker operations, and to the sparkover phenomena utilized in electric spark machining.1���2 In each of these situations craters are formed on the electrode surface. Considerable attention3���5 has been given to the phenomena of crater formation for obvious reasons. Formation of the craters has been attributed to various causes1,5,6 and, indeed, the predominant cause may vary, depending on conditions of current formation, duration and magnitude, and on current-density distribution in the ionized column. In at least one range of physically realizable circumstances current density beneath the surface has been demonstrated3 to be significant in determining the depth of crater formed by a particular discharge. The relationship demonstrated was of a qualitative character only, however, owing to the lack of quantitative knowledge concerning both transient and steady-state subsurface current distribution. This paper describes the results of an analytical study of current distribution under appropriate conditions. In this study steady-state current distribution was determined from work by others on an analogous problem in hydrodynamics.7,8 Transient current distribution was determined by a solution which is described in some detail in the Appendix.

A Characteristic of the Copper Arc During the Formative Period

This paper gives the results of an investigation of the voltage characteristic of the copper arc in air during the process of arc formation. A pair of copper electrodes, initially in contact and carrying current, were separated and the voltage arising across the arc gap was studied. Cathode-ray oscillograms indicate that at the instant of contact separation there develops across the gap a voltage of about 12.2 volts. This voltage was attained in less than 10−5 seconds. This rapidly developed voltage was found to be independent of arc current for current values up to 100 amperes, which suggests that the rapidly developed initial voltage corresponds to the cathode fall of the arc.