Arc Root Movement Research Articles

Impact of contact rotation on the vacuum arc root movement

Impact of contact rotation on the vacuum arc root movement

Motion behavior of a high-current fault electric arc occurred in the dead zone of protection in a substation

Since the dead-zone fault in substations often has a relatively long removal time, it may damage the insulation of power equipment and even threaten the stability of the power system. In this paper, the movement of the dead-zone fault electric arc in a 220-kV substation is investigated. The arc chain model for the dead-zone fault electric arc is developed; the influences of electromagnetic force, thermal buoyancy, and the air resistance stressed on the electric arc are comprehensively considered. The electric arc velocity and displacement are computed. Then, the spreading characteristics of the dead-zone electric arc under various conditions are studied. The spreading trend of the dead-zone fault electric arc is summarized. Finally, measures to inhibit the spreading of the electric arc are suggested. The study indicates that the movement of the electric arc in the dead zone during the early stage is primarily influenced by the electromagnetic force resulting from the overpass and conductor, and the arc is concave and has an irregular trajectory. The inclination angle of the conductor significantly affects the direction of the electromagnetic force. If the conductor is laid horizontally, the electric arc is subjected to a smaller force. The electromagnetic force stressed on the electric arc is mainly attributed to the fault phase conductor and the electric arc body itself, whereas those from the other phase conductors are minor. The initial position of the arc root has a certain impact on the movement of the electric arc. The use of the insulating materials restricts the arc root movement.

Modeling and Performance Analysis of Municipal Solid Waste Treatment in Plasma Torch Reactor

Thermal plasma has emerged as a technology with tremendous promise for municipal wastes that should be disposed of sustainably. A numerical simulation of a symmetric turbulent plasma jet from a thermal air plasma torch was developed using COMSOL Multiphysics®5.4 engineering simulation software. The velocities, temperature, arc root motion, and joule heating of the plasma jet were examined under the impact of the gas mass flow rate and current. Moreover, the electrical power required for the municipal solid waste (MSW) processing was estimated. The enthalpy and the effectiveness of the plasma torch were analyzed and discussed. Subsequently an investigation was conducted into the gasification characteristics of MSW using air and steam gases. The torch’s power and efficiency could be enhanced with a higher mass flow rate and temperature. Three operating modes were identified from the current–arc flow combination. Among the plasma gas considered, the air gas plasma torch guarantees an acceptable thermal efficiency and a low anode erosion rate. Plasma gasification produces cleaner syngas with higher efficiency (84%) than the conventional process due to the elevated temperature used during the process that breaks down all the char, dioxins, and tars.

Research on dynamic characteristics of arc under electrode relative motion

The relative motion of the electrodes is a typical feature of sliding electrical contact systems. The system fault caused by the arc is the key problem that restricts the service life of the sliding electrical contact system. In this paper, an arcing experimental platform that can accurately control the relative speed and distance of electrodes is built, and the influence of different electrode speeds and electrode distances on arc motion characteristics is explored. It is found that there are three different modes of arc root motion: single arc root motion mode, single and double arc roots alternating motion mode, and multiple arc roots motion mode. The physical process and influence mechanism of different arc root motion modes are further studied, and the corresponding relationship between arc root motion modes and electrode speed is revealed. In addition, to further explore the distribution characteristics of arc temperature and its influencing factors, an arc magnetohydrodynamic model under the relative motion of electrodes is established, and the variation law of arc temperature under the effect of different electrode speeds and electrode distances is summarized. Finally, the influence mechanism of electrode speed and electrode distance on arc temperature, arc root distance, and arc root speed is clarified. The research results enrich the research system of arc dynamic characteristics in the field of sliding electrical contact, and provide theoretical support for restraining arc erosion and improving the service life of the sliding electrical contact system.

Dynamic physical characteristics of DC arc on arcing horn for HVDC grounding electrode line

The dynamic physical characteristics of a DC arc on an arcing horn for a high voltage direct current (HVDC) grounding electrode line are significantly different from those of the switching device arc, secondary arc, AC fault arc and pantograph-catenary arc. In this work, an experimental platform for the DC arc on the arcing horn was built, and mechanisms of the arc column short circuit and arc root movement were studied. This work further analyzes the characteristics and mechanisms of the arc motion when wind speed and direction, magnetic field and the expansion angle of the electrode are varied. Arc root movement is more likely to occur at the upper electrode. There is a competitive relationship between arc expansion and the transferring effect. The effect of wind on the arc column is greater than the effect on the arc root. The magnetic field has a significant driving effect on both the arc column and the arc root. The research results provide a comprehensive experimental basis for further probing the method of DC arc suppression, and the improvement of the arcing horn.

Exceeding 50% injected lightning energy not sourced: During the analysis of an OGW rupture accident caused by multiple lightning strikes

Overhead ground wire (OGW) is erected to protect transmission conductors from lightning strikes. However, OGW can be damaged or even ruptured due to lightning strikes, which threatens the stable operation of the power system. Thus, it is necessary to study the lightning-induced damage or rupture mechanism to provide a theoretical guidance for the structure optimization or selection criteria improvement for OGW. In this paper, an OGW rupture accident due to lightning arc root movement under multiple return strokes was analyzed. Firstly, based on the evidence at the accident scene and the damage characteristics of the sample, it was preliminarily inferred that multiple lightning strike points caused the rupture of OGW in the accident. An analytical model simulating the lightning arc root movement was established to prove the existence of lightning arc root movement phenomenon in the accident. In addition, the thermal ablation model of OGW was also established according to the existing numerical methods. The differences between OGW damage results of model and sample were compared. The results of this paper showed that the sliding movement and jumping movement of the lightning arc root caused the long axial ablation length and multiple lightning strike points of OGW in the accident, respectively. Existing numerical methods as well as the laboratory generated lightning strikes experiments did not accurately calculate the thermal ablation damage of OGW caused by the natural lightning strikes. For this accident sample, at least 66% injected lightning energy is not considered when simulating the physical process of the natural lightning striking OGW. Based on the research result, simulation test of lightning strike should be considered before OGW is put into operation. Moreover, for the existing simulation test method of lightning strike, the injected lightning energy should also be increased.

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.

Experimental study on the effect of argon shielding gas on the suppression of nitrogen arc anode ablation

The high heat flux density of the DC arc often leads to severe anode ablation, which is a key factor limiting the wider use of the DC plasma torches. In this study, a series of comparative experimental studies are conducted with the goal of suppressing nitrogen arc anode ablation by combining argon shielding flow and anode structure. It is found that for the planar electrode structure, the use of argon shielding gas can alleviate the ablation of the anode by nitrogen arc to some extent. If a boron nitride channel is installed on the anode surface to constrain the argon shielding flow, the electrode ablation can be significantly reduced. The experimental results show that there is no significant ablation on the anode surface after 1 h of operation of the nitrogen arc device with an arc current of 100 A. Further analysis reveals that, on the one hand, argon shielding gas can extend the range of motion of the nitrogen arc root along the anode surface and increase the speed of arc root motion, which has the effect of expanding the time-averaged arc anode attachment area. On the other hand, argon shielding gas can also increase the size of the nitrogen arc root and decrease the temperature of the arc root. The use of constraining channels can effectively control the range of motion of the arc root along the anode surface and strengthen the influence of argon shielding gas. The combination of these effects can substantially suppress the anode ablation of the DC arc device.

Simulation and Experimental Analysis of DC Arc Characteristics in Different Gas Conditions

The structures of high-voltage direct current (HVDC) relays are compact. In order to extinguish the arc, the external magnetic field is applied near the contact. HVDC relays with a large capacity are also filled with gas medium to enhance the ability of arc extinguishing. The research on the characteristics of the arc in different gases under different pressures is of great significance to improve the reliability and the lifetime of the HVDC relays. The characteristics of the arc in nitrogen, hydrogen, and nitrogen–hydrogen mixtures and that of the arc root motion in the magnetic field are simulated by means of magnetohydrodynamics (MHD). The arcing processes in N2 and air are tested by a high-speed camera, and the arc root coordinates are calculated by the image processing method, and the simulation models are verified. The result shows that under the same condition, the hydrogen arc voltage is the highest, and the moving speed of the arc root is the fastest, so that the arc extinguishing performance of the hydrogen is the best. Nitrogen–hydrogen mixture is also a superior arc extinguishing gas, and the higher the proportions of H2, the better the performance. With the increase of the pressure, arc voltage increases. Except H2, increasing the pressure of the gas is beneficial for arc motion.

A novel experimental method of investigating anode-arc-root behaviors in a DC non-transferred arc plasma torch

A novel experimental method of investigating anode arc root was presented, and a plasma torch with multiple anodes was designed. With this apparatus, the number of anode arc roots, their position, and movement with changes in plasma current and gas-flow rate were studied. Results showed that multiple anode arc roots can coexist and their number was more related to plasma current than gas-flow rate. The number of anode arc roots increased with increased plasma current. The anode arc root can move forward and backward in the arc plasma jet, and its position was related to current and gas-flow rate. The anode arc root moved forward with increased current, whereas the anode arc root moved forward first and backward with increased gas-flow rate. Based on the finding, a new non-transferred arc model was established. Finally, the anode arc root motion was classified as steady, slight vibration, alternating motion, jumping motion, and multiple arc root modes. These results can serve as a reference for revealing the mechanism of plasma discharge, optimization design of arc plasma jet, and high-quality plasma generation.

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

A low voltage circuit breaker (LVCB) is an important piece of protection equipment which will switch off the fault current in a power system. The moving contact of a low voltage circuit breaker with a higher rated current consists of two parallel contacts. Therefore, the convection effect on the air arc evolution process in a two parallel contact system is analyzed. A three-dimensional (3D) magneto–hydro–dynamic (MHD) model of arc simulation is built. In this model, the anode consists of two parallel contacts and a bonding conductor. A nonlinear voltage–current density characteristic is employed to represent the near-anode and near-cathode voltage. The current density, arc voltage and currents through every contact are obtained. The influence of convection and conduction on the arc evolution process are quantitatively calculated. The displacements of the arc roots are obtained and the asymmetry of the arc root motion is analyzed. The arc evolution process of a two parallel contact system is preliminarily revealed.

Stability and structures in atmospheric pressure DC non-transferred arc plasma jets of argon, nitrogen, and air

The stability of dc non-transferred arc plasma jets and their internal structures is investigated through fast photography, emission spectroscopy, and arc dynamics under different operating conditions. A novel method to explore structures inside extremely intense hot plasma jet is conceived and applied for the first time to investigate arc plasma jets. The study revealed distinct interesting structures and their evolution inside the plasma jet, apparently not reported earlier. The associated fundamental mechanisms are identified from direct experimental evidences. Respective steady state jet characteristics with and without air entrainment are obtained from computational fluid dynamic simulation. Arc root motion, air entrainment, and interaction between electromagnetic and fluid dynamic body forces are found to result in a variety of interesting dynamics and structures inside the plasma jet under different operating conditions. Observed behaviors are notably different in argon, nitrogen, and air plasma. While no unusual structures are found over a range of lower flow rates, interesting structures evolve at higher flow rates. Statistical behavior of these structures is found to have a significant dependence on the gas flow rate and torch power. Apart from air entrainment in the downstream, observed isolated temperature islands inside the jet in the upstream have potential to affect particle trajectory, physical processes, and process chemistry in a significant manner.

Experimental study on ignition characteristics of kerosene–air mixtures in V-shaped burner with DC plasma jet igniter

In this paper, we investigate the effects of DC plasma jet igniter on ignition characteristics of the kerosene–air mixtures in V-shaped burner. The primary principles of DC plasma igniter design have been put forward to prolong the igniter life and improve ignition performance. The main characteristic of plasma igniter is that the anode arc root is fixed at anode nozzle outside surface other than the anode inner surface in conventional design. The electric characteristics of the plasma jet igniter including voltage–current characteristics, the arc column propagation, emission spectrum and anode arc root movement in a quiescent environment are investigated with high speed CCD together with a recording of the voltage and current. The entire ignition process of the plasma jet igniter is recorded by high speed CCD and the ignition delay times of the kerosene–air mixtures defined by the interval between the onset of the plasma igniter and the establishment of a stable flame are measured with two photomultipliers with one of 10 mm band pass filter centered at 780 mm (the plasma igniter emission spectrum of OI) and the other of 10 mm band pass filter centered at 430 mm (direct flame emission of CH(A2Δ→X2Π)). Results show that the plasma igniter works in a restrike mode and the anode spot movement is irregular. The plasma igniter jet contains abundance active particles inferred from the emission spectrum. The ignition delay times increase at first and then decrease with the increase of excess air coefficient ranging from 0.91 to 6.38. The delay times increase quickly when the mixtures are extremely lean or rich.

A thermal model for accurate study of the effects of positive dc arc root temperature over an ice surface

After the formation of local violet arcs across air gaps on an ice-covered insulator, which is the first step of the flashover process, these arcs can extend along the ice surface and form a white arc under certain conditions. The white arc can propagate on the ice surface and reach a critical length of about two-thirds of the dry arc distance. This step, which includes the formation of a white arc and its propagation to a critical length, is the second step of the flashover process. It plays a crucial role because after this step the electric field between the column and root(s) of the arc and ground electrode (or HV electrode or both electrodes) is sufficient to result in a complete flashover at the third step. Besides the electrical breakdown process ahead of the arc column, increasing the thickness of the surface film, made of highly conductive water, on an ice surface may play a significant role in the movement of the arc root during the second step. Film thickness increase is mainly due to heating effect of the arc root temperature and joule heating of flowing leakage currents through the surface film. In this paper, the heating effect of the positive dc arc root temperature on the thickness of the surface film is accurately modeled and studied using COMSOL Multiphysics, a commercial software. Rotational temperature of an arc formed over an ice surface, which was measured in previous studies at CIGELE through optical emission spectroscopy, will be used as input parameter in the model. The simulation results show that the time taken for heat transfer to increase ice temperature from −12°C to its melting temperature is only a few seconds and can thus influence the arc root movement during the second step. The obtained results allow improvement over the previous hypothesis consisting of ignoring heat transfer effects of an arc during its propagation over the ice surface. These findings will be useful to improve prediction of critical flashover voltages of ice-covered insulators.

Effect of an external magnetic field on plasma torch discharge fluctuation

The effect of an external magnetic field on the anodic arc root movement inside a dc plasma torch has been investigated. In this letter, a virtual instrument technology was used to measure the arc voltage of the plasma torch at atmospheric pressure, and the rotating frequency of the anodic arc root was estimated by high-speed photography. The arc voltage fluctuation which represents the degree of the arc instability was reduced. And a new peak, whose frequency is consistent with the rotating frequency of the anodic arc root, was found in the Fast Fourier Transform spectra of the arc voltage signal. From the results, the helical instability generated directly by anodic arc rotation is put forward, and only the appropriate external magnetic field could inhibit and reduce the instability of the plasma torch and prolong the life of the anodic electrode. Furthermore, the measured voltage waveforms indicated that the arc root attachment mode would be controllable by an external magnetic field.

Three-Dimensional Unsteady MHD Modeling of a Low-Current High-Voltage Nontransferred DC Plasma Torch Operating With Air

We present, in this paper, the MHD modeling of a dc plasma torch operating with air under very peculiar high-voltage low-current conditions. The model developed is 3-D, is time dependent, and assumes local thermodynamic equilibrium (LTE). The study has been carried out considering an axial injection of air with flow rates varying in the range of 0.16-0.5 g/s and currents varying in the range of 300-600 mA. The numerical modeling has been developed using Code_Saturne, a computational fluid dynamics software developed by EDF R&D which is based on colocated finite volume. After a detailed description of the model, the results are presented, analyzed, and discussed. The influence of current and that of air flow rate over the arc characteristics are studied in terms of temperature, velocity, electrical potential, Joule heating, and arc root motion. Regarding numerical issues, the MHD modeling of low-current high-voltage arc discharge is particularly tricky since, below 1 A, the self-induced magnetic field becomes negligible and the convection effects induce a highly irregular and unstable motion of the arc column. However, despite these difficulties, the numerical model has been successfully implemented. Numerical results have shown good correlation and good trends with experimental ones despite a discrepancy which is probably due to the LTE assumption. The model gave fruitful and significant information on parameters that could hardly be obtained experimentally. This preliminary work is likely to open the way toward a better understanding of low-current arc discharges, which technologies are currently encountering an important development in many application fields.

Temperature of thermal plasma jets: A time resolved approach

Boltzmann Plot method is routinely used for temperature measurement of thermal plasma jets emanating from plasma torches. Here, it is implicitly assumed that the plasma jet is 'steady' in time. However, most of the experimenters do not take into account the variations due to ripple in the high current DC power supplies used to run plasma torches. If a 3-phase transductor type of power supply is used, then the ripple frequency is 150 Hz and if 3- phase SCR based power supply is used, then the ripple frequency is 300 Hz. The electrical power fed to plasma torch varies at ripple frequency. In time scale, it is about 3.3 to 6.7 ms for one cycle of ripple and it is much larger than the arc root movement times which are within 0.2 ms. Fast photography of plasma jets shows that the luminosity of plasma jet also varies exactly like the ripple in the power supply voltage and thus with the power. Intensity of line radiations varies nonlinearly with the instantaneous power fed to the torch and the simple time average of line intensities taken for calculation of temperature is not appropriate. In this paper, these variations and their effect on temperature determination are discussed and a method to get appropriate data is suggested. With a small adaptation discussed here, this method can be used to get temperature profile of plasma jet within a short time.

Fluctuation characteristics of arc voltage and jet flow in a non-transferred dc plasma generated at reduced pressure

A torch with a set of inter-electrode inserts between the cathode and the anode/nozzle with a wide nozzle exit was designed to generate plasma jets at chamber pressures of 500–10 000 Pa. The variation of the arc voltage was examined with the change in working parameters such as gas flow rate and chamber pressure. The fluctuation in the arc voltage was recorded with an oscilloscope, and the plasma jet fluctuation near the torch exit was observed with a high-speed video camera and detected with a double-electrostatic probe. Results show that the 300 Hz wave originated from the tri-phase rectified power supply was always detected under all generating conditions. Helmholtz oscillations over 3000 Hz was detected superposed on the 300 Hz wave at gas flow rates higher than 8.8 slm with a peak to valley amplitude lower than 5% of the average voltage value. No appreciable voltage fluctuation caused by the irregular arc root movement is detected, and mechanisms for the arc voltage and jet flow fluctuations are discussed.

Pantograph Arcing in Electrified Railways—Mechanism and Influence of Various Parameters—Part I: With DC Traction Power Supply

Pantograph arcing is a common phenomenon in electrified railway systems. This is also a source of broadband-conducted and radiated electromagnetic interference (EMI) for vehicle as well as traction power and signaling systems. In this paper and the companion paper, experimental analyses of pantograph arcing phenomena are presented for dc and ac feeding systems, respectively. Influences of different parameters on dc traction system, such as supply-voltage polarity, relative motion between pantograph and overhead contact wire, namely, forward motion along the track (longitudinal), and lateral sliding motion of the pantograph (zigzag) are presented here. From the voltage and current waveforms of the test runs, it is shown that pantograph arcing is a polarity-dependent phenomenon. For the positive-fed overhead traction system, where pantograph is cathode, the supply interruptions due to zigzag motion are comparatively less compared to negatively fed traction systems. As a result, the transients, due to pantograph arcing, are more frequent in negatively fed traction systems. It is found that the arc root movement along the electrode surfaces (pantograph-contact wire) is governed by the relative motion and polarity of the electrodes. The analyses presented in this paper also form a foundation to understand the pantograph arcing process and the corresponding influential parameters with the ac supply presented in the companion paper. The findings presented in this paper could be beneficial for coming up with appropriate mitigation techniques from the EMI due to pantograph arcing in dc-fed traction systems.

Prediction of the cathodic arc root behaviour in a hollow cathode thermal plasma torch

The upper part of a well type cathode (WTC) plasma torch is modelled for several conditions in an air medium in the presence of an electric arc. The plasma flow created by the electric arc is described and the results compared with the data from the literature. Special attention is paid to the description of arc root attachment and to its movement due to the balance of forces. A fine description of the magnetic field produced by the external solenoid is reported. The model is based on the @Fluent software implemented with specific developments to be adapted to the thermal plasma domain. The paper shows the necessity to provide an accurate description of the external magnetic field due to the strong influence of the radial magnetic field component. Overall, we propose an original approach for arc root movement description which contributes to the understanding of the flow behaviour in the WTC torch.