Low-current Arc Research Articles

Hot-wire GTAW cladding: inconel 625 on 347 stainless steel

Gas tungsten arc (GTA) cladding has been widely applied in surface modification and repairing. In this study, low current gas tungsten arc welding (GTAW) cladding in the range of 60 to 100 A was performed with resistively heating hot-wire filler Inconel alloy (IN625) on the 347 stainless steel substrate. A 70 A or more primary current can be used to clad a continuous and uniform layer on the substrate by resistively heating the wire and varying the torch angle. Lower dilution and higher contact angle were observed for lower current clad. An analytical model has been used to understand the resistively heating hot-wire effect. The microstructure of the clad bead and the substrate was analyzed. A heat-affected zone (HAZ) cracking was observed in the higher range of primary current. An EDX analysis was performed to reveal iron (Fe) elemental dilution and elemental segregation.

Experimental Observations of Constricted and Diffuse Anode Attachment in a Magnetically Rotating Arc at Atmospheric Pressure

At atmospheric pressure, the anode attachment can appear in two different modes: constricted and diffuse. In this paper, a magnetically rotating arc plasma generator is built to investigate dynamics of anode attachment. A constricted and diffuse anode attachment, as well as the transformation between the two modes, are obtained. Results show the constricted anode attachment to be preferable for low arc currents and a low magnetic field, whereas the diffuse anode attachment is favored by the opposite conditions. With an increase in arc currents/magnetic field, the constricted anode attachment can transfer from a “restrike mode” with high voltage fluctuation to a “sliding mode” with low voltage fluctuation and then to a diffuse anode attachment with a long arc-shaped structure. An expanding arc column and high-temperature anode are suggested as essential conditions for the diffuse anode attachment because a thinner and hotter anode boundary layer may be promoted. In addition, the time-resolved transformation of different modes exhibits a strong mutual influence between the arc column and anode attachment, which indicates complex coupling mechanisms exist in the near-anode region.

Efficient methane-to-acetylene conversion using low-current arcs.

The proliferation of natural gas production had led to increased utilization of methane as a raw material for chemicals. The most significant bottleneck in this process is the high activation energy of methane. This paper reports the direct conversion of methane to acetylene in a novel rotating arc driven by AC electrical power. By feeding a sufficiently high concentration of CH4 (greater than 43%) diluted in H2 (the discharge gas) through the arc column, a low specific energy requirement (SER) of 10.2 kW h kg−1 C2H2 was achieved. The use of hydrogen as the discharge gas strongly suppressed soot formation during the methane conversion process under high methane concentration conditions, resulting in a carbon balance of greater than 95% and a C2H2 selectivity of greater than 90% while maintaining a methane conversion rate of greater than 70%, depending on the conditions. The novel rotating arc enabled the elongation of the arc column itself, which controlled heat loss and improved the energy use for reaction. The ability to control the arc length based on low-current type arc generation has additional benefits for reaction enhancement. These results demonstrate that arc control, optimization of the reaction conditions, and a full understanding of reaction pathway are viable means for the energy-efficient direct conversion of methane to acetylene.

Modeling the development of low current arcs and arc resistance simulation

Low current arcs in the range 0.5 ∼5 mA occur in power networks in situations such as on overhead line insulators and cable terminations. These arcs are important because of their potential contribution to surface ageing, asset failure and potential flashover. In this paper, the development of low current arcs is classified in three stages: a formative leakage current phase (∼μΑ), a stage where discharges occur but are unstable with each half power cycle ( 1 mA). Arc resistance is a key element in controlling arc behavior in each stage, and is modeled as the combination of a stable arc resistance, an oscillating resistance and a surface resistance. The resulting arc model has been developed in PSCAD/EMTDC, to simulate an arc/discharge in each development stage. Simulations compare well with experimental data. The simulation reveals that peak arc current plays a key role in the transition from an unstable to stable arc. Analysis shows a significant increase in discharge energy as a result of its stabilization. These models explain the conditions required for accelerated ageing of polymeric insulators and can be used to design and interpret testing regimes, and for polymeric insulator asset management.

An Experimental Investigation of Cathode Spot Motion in a Magnetically Rotating Arc Plasma Generator at Atmospheric Pressure

Cathode spots present complex forms in magnetically rotating arc plasma generators due to the coupling effect of the plasma flow and electromagnetic fields. In this paper, a magnetically rotating arc plasma generator is built to study cathode spot motion at atmospheric pressure. Cathode spot configuration is observed and discussed for different magnetic fields, arc currents, gas flow rates and cathode lengths. Results show that cathode spots with a slow rotation speed (less than 1 Hz) and different rotation directions occur on the cathode end. For a low magnetic field, low arc current, high gas flow, short cathode rod, the rotation direction of the cathode spot is consistent with the arc column rotation. With an increase in the magnetic field, increase in the arc current, decrease in gas flow, or increase in the cathode rod length, the rotation speed declines, and the cathode spot can move in a reversed direction (i.e., against the arc column rotation). The cathode spot area also appears to expand gradually when the spot motion shifts from the normal direction to the reversed direction, resulting in less cathode erosion at the reversed motion. Further analysis indicates that the cathode spot motion is similar to the retrograde movement that occurs in a vacuum arc with an external magnetic field. The rotation of cathode spot may thus be induced by the radial component of the magnetic field. The cathode spot area that affects the self-magnetic field in the cathode spot is potentially a direct determinant of spot motion.

The Development of Low-Current Surface Arcs Under Clean and Salt-Fog Conditions in Electricity Distribution Networks

Electricity distribution networks are built to deliver increasing amount of electricity from distributed energy resources (DERs) such as offshore and onshore wind and solar farms. Aging of network assets through low-current surface discharges is becoming a great concern for the security and reliability of the distributed energy supply. In particular coastal conditions can present a challenge for overhead line insulators through the environment of salt fog. Also, onshore areas may expose power lines to clean fog and agricultural or industrial pollution. In this paper, experimental studies are conducted to investigate electrical arc formation and growth on insulators, following the testing standards in accordance with IEC 61109. Dry-band arcs in both clean-fog and salt-fog environments are compared. It is identified that arcs are much faster to develop and have greater energy in salt-fog environments, due to the lower surface resistance and resulting higher leakage current. The time from a first arc to strike, to the situation where the arc is stable on the insulator surface is identified as a potentially critical parameter in controlling aging of an insulation surface. The time from initial appearance of an arc to full stability is eight times shorter in a salt fog of 16,000 $\mu \text{S}$ /cm compared to a clean fog of $600~\mu \text{S}$ /cm. This means the very existence of a stable low-current arc is much more likely in polluted conditions. Accumulated arc energy and heat dissipation have been calculated for both fog conditions. It is concluded that aging by low-current electrical arcs tends to be more severe in salt-fog environments, so that great care needs to be taken when designing overhead lines and insulators in such areas.

Suppression Mechanism of Low Current Auxiliary TIG Arc on High Speed TIG-MIG Hybrid Welding and Process Optimization

Suppression Mechanism of Low Current Auxiliary TIG Arc on High Speed TIG-MIG Hybrid Welding and Process Optimization

Ignitability of Diesel Fuel with an Inclusion of Ultrafine Carbon Particles

Nanosize carbon fuel additions were synthesized by the action of an electric discharge on a diesel fuel. Depending on the discharge regime, variously shaped carbon particles, including planar graphitized ones, were formed in the fuel. Ignitability of the produced samples was assessed by the method of initiation of a foamed fuel sample by a lowcurrent electric arc. The modified fuel showed the improvement of the ignition characteristics in the presence of a nanodispersed solid phase.

Size dependence of optical and magnetic properties of nickel oxide nanoparticles fabricated by electric arc discharge method

Abstract Nickel oxide nanoparticles with an average size of between 28 and 62 nm were fabricated by electric arc discharge method. The electric currents of 10, 100, 200, 300 and 400 A and oxygen pressures of 1, 2 and 3 atm. were tested. High yield production was observed for the samples prepared at low arc current. The samples were characterized using XRD and FESEM measurements. XRD results showed that the samples were pure and single phase of nickel oxide with cubic structure. The produced nanoparticles were cubic shaped and the average particle sizes increased by increasing the arc pressure, but decreased by increasing the arc current and their size distributions were uniform. The magnetic measurements confirmed a soft ferromagnetic behavior for the nickel oxide nanoparticles at low field region but the hysteresis loop tended to be antiferromagnetic like for the higher fields. By decreasing the particle size from 62 nm, the coercivity (H c ) increased but decreased when the particle size was less than about 57 nm. Such magnetic behavior which can be common for antiferromagnetic nanoparticles was interpreted based on a core-shell model.

Study of plasma-chemical NO-containing gas flow for treatment of wounds and inflammatory processes

This work is aimed at exhaustive and detailed study of chemical, physical and physico-chemical characteristics of NO-containing gas flow (NO-CGF) generated by a plasma-chemical generator of Plason device, which has been used in medical practice for more than 15 years for effectively healing wound and inflammatory conditions with exogenous nitric oxide (NO-therapy). Data was obtained on spatial structure of the gas flow, and values of its local parameters in axial and radial directions, such as nitric oxide content, velocity, temperature and mass flow density of nitric oxide, providing altogether the effectiveness of treatment by the exogenous NO-therapy method, were determined experimentally and by computations. It was demonstrated that plasma-chemical synthesis of NO from atmospheric air in a low direct current (DC) arc provides a high mass flow of nitric oxide at the level of 1.6-1.8mg/s, while in the area of impact of NO-CGF on the biological tissue, on its axis, NO content is 400-600ppm, flow velocity about 5m/s, nitric oxide mass flow density 0.25-0.40 mg/(s·cm2), temperature 40-60°C. Tendencies were determined for designing new devices for further experimental biological and medical research in the field of NO-therapy: lowering the temperature of NO-CGF to ambient temperature will enable variation, in experiments, of the affecting flow parameters in a wide range up to their maximum values: NO content up to 2000ppm, velocity up to 20m/s, nitric oxide mass flow density up to 2.5 mg/(s·cm2).

Experimental study and modeling of the deuterium releasing quantity in a pulsed vacuum arc discharge with a metal deuteride cathode

The pulsed vacuum arc discharge using a metal deuteride cathode is widely applied as a deuterium ion source, where the upper limit of the deuterium ion yield is largely determined by the deuterium releasing quantity (DRQ) from the cathode. This work aims to measure the DRQ at various discharge conditions, and meanwhile develop a simple thermoelectric model to evaluate the deuterium liberation from different sources, such as the crater vicinity during the arc power-on phase and the hot crater in the afterglow. The calculated DRQ are in accordance with the experimental results obtained by measuring the D2 pressure evolution in the early afterglow using a quadrupole mass spectrometer. Furthermore, the model reveals that at low arc current (<10 A), the DRQ orginates dominantly from the crater vicinity, leading to a low conversion efficiency of the released deuterium to ions and a high D:Ti elemental ratio in the released cathode vapor.

Investigation of low current gas tungsten arc welding using split anode calorimetry

Most previous split anode calorimetry research has applied high weld currents which exhibit pseudo Gaussian distributions of arc current and power density. In this paper we investigate low current arcs and show that both the current and power distributions have minima in the centre – varying significantly from the expected Gaussian profile. This was postulated due to the formation of the arc with the copper anode and the tungsten cathode. Furthermore, a number of parameters were varied including the step size between measurements, anode thickness and anode surface condition as well as cathode type and tip geometry. The step size between measurements significantly influenced the distribution profile and the anode thickness needed to be above 7 mm to obtain consistent results.

Interruption of Weakly Cooled Arcs in Air and Airplus

Switching of low current arcs in free burning or weakly cooled conditions is mainly determined by the thermal properties of the gas. Products with such switching conditions are widely found in secondary distribution medium voltage (MV) gas insulated switchgears (GIS). In this study, we compare the current interruption capability of synthetic air and AirPlusTM, i.e. a mixture of synthetic air with C5F10O fluoroketone (C5-FK). We focus on thermal interruption performance of the gases. AirPlus mixture corresponds to -25 °C condensation temperature of C5-FK. An arc is drawn between the contacts and cooled by blowing cold gas from a tank. Blowing pressure required for current interruption is compared. Within the measurement accuracy, the current interruption performance of both gases is similar. Chemical analysis of the AirPlus mixture after 69 shots was performed using Gas Chromatography Mass Spectroscopy (GCMS) and it shows very little decrease in the concentration of C5-FK.

Influence of low current auxiliary TIG arc on high speed TIG-MIG hybrid welding

Arc shape, droplet transfer, weld pool behavior and temperature fields were studied to investigate the influence of low current auxiliary TIG arc on weld formation and microstructure in TIG-MIG hybrid welding and compared with conventional MIG welding. Results indicated that the MIG arc is stabilized by a leading TIG arc while it is destabilized by a trailing TIG arc. Regardless of the TIG arc leading or trailing, it decentralized the MIG arc force and reduced the impingement of droplet. The backward fluid flow in the hybrid welding was decelerated relative to the conventional MIG welding. The slower backward fluid flow in hybrid welding impeded the accumulation of high temperature filler metal in the tail of weld pool and provided the molten metal more time to fill the weld toe which resulted in suppression of the undercut defect. The top surface temperature gradient at the middle and tail of the hybrid weld pool was lower than that in the MIG weld pool, albeit the welding heat input was increased. Microstructure analysis showed evidence of prominent dendrite formation at higher welding speeds with no obvious grain coarsening in the weld zone of TIG-MIG hybrid weld joint while its HAZ became narrower.

Arc tracks on nanostructured surfaces after microbreakdowns

Studying of initial steps of unipolar arc ignition process is important for reduction of probability of arcing between the plasma and the wall in thermonuclear devices. Tungsten nano-fuzz surface formed by helium plasma irradiation at high fluences and temperatures is a perfect material for arc ignition. Snowflake-like craters were detected on the fuzzy surfaces after short micro-breakdowns. Such sort of craters have not been observed before on any other metallic surfaces. These specific traces are formed due to unique properties of the fuzz structure. The nano-fuzz could be easily melted and vaporized by micro-breakdown current, due to its porosity and bad thermal conductivity, and formation of low conducting metallic vapour under the cathode spot causes discharge movement to the nearest place. Thus, even low current arc can easily move and leave traces, which could be easily observed by a secondary electron microscope.

Plasma torch for supersonic plasma spray at atmospheric pressure

This work presents a plasma torch able to operate at supersonic regime with axial injection of feedstock. In contrast to commonly used linear scheme, the principal axis of the plasma torch is perpendicular to feedstock injection direction, which is aligned with coming out plasma jet. The plasma torch has slightly ascending current voltage characteristics and fixed arc length. Electrical, thermal and kinetic characteristics outlined from comparison with conventional linear plasma spray torches are intermediate between APS, HVOF and VPS. The plasma torch developed in this work has an elevated arc voltage (370V) and low arc current (100A), which contribute to increase the electrode life and decrease the arc voltage relative fluctuation (10%). According to in-flight particle monitoring the CoNiCrAlY particles were sprayed at 500m/s and temperature of 2400°C, whereas the 7%YSZ at 491–683m/s and 2535–2636°C.

Some features of horizontally oriented low-current electric arc in air

The properties of an electric arc operating in open air at currents of lower than 1 A were studied experimentally. The rod cathode was oriented horizontally. Cylindrical rods and plane plates either installed strictly vertically in front of the cathode end or tilted at a certain angle served as the anode. It is shown that, with such an electrode configuration, it is possible to form a discharge channel much longer than the electrode gap length. Regimes of regular oscillations are revealed, and conditions for their appearance are established. The electric field strength in the arc column and the electron temperature near the anode are calculated.

Экспериментальное исследование низковольтной электрической дуги для целей релейной защиты

Experimental research of electric arc parameters are described in the article. Experiment of plasm specific electric conductivity determination at various temperatures is described in particular. Estimated function can be used in calculating of alternating low current arc volt-ampere characteristic. Developed methodology can be used in researching of high voltage electric arc, which accompanies most part of power grid faults. The research was performed for correction existing and detection new arc fault information sign for relay protection needs.

Low-current electric arc in the open air between the end of the cathode and long vertical anode

The electrical discharge was investigated experimentally in the open atmosphere at currents less than 1 A. The cylindrical rods and flat plates were used as anode. They were installed in front of the cathode rod vertically or obliquely. The modes in which the discharge makes regular self-oscillations were detected. Electric field intensity in the discharge column and the electron temperature were calculated.

Reactive Plasma-Sprayed Aluminum Nitride-Based Coating Thermal Conductivity

Recently, thick aluminum nitride/alumina (AlN/Al2O3) composite coatings were successfully fabricated through the reactive plasma spraying of fine Al2O3/AlN mixture in the N2/H2 atmospheric plasma. The coatings consist of AlN, Al5O6N, γ-Al2O3, and α-Al2O3 phases. This study will evaluate the thermal conductivity of these complicated plasma-sprayed coatings and optimize the controlling aspects. Furthermore, the influence of the process parameters on the coatings thermal conductivity will be investigated. The fabricated coatings showed very low thermal conductivity (2.43 W/m K) compared to the AlN sintered compacts. It is attributed to the phase composition of the fabricated coatings, oxide content, and porosity. The presence of Al2O3, Al5O6N and the high coating porosity decreased its thermal conductivity. The presence of oxygen in the AlN lattice creates Al vacancies which lead to phonon scattering and therefore suppressed the thermal conductivity. The formation of γ-Al2O3 phase in the coating leads to further decrease in its conductivity, due to its lower density compared to the α-phase. Moreover, the high porosity of the coating strongly suppressed the conductivity. This is due to the complicated microstructure of plasma spray coatings (splats, porosity, and interfaces, particularly in case of reactive spray process), which obviously lowered the conductivity. Furthermore, the measured coating density was lower than the AlN value and suppressed the coating conductivity. In addition, the spraying parameter showed a varied effect on the coating phase composition, porosity, density, and therefore on its conductivity. Although the N2 gas flow improved the nitride content, it suppressed the thermal conductivity gradually. It is attributed to the further increase in the porosity and further decrease in the density of the coatings with the N2 gas. Furthermore, increasing the arc did not show a significant change on the coating thermal conductivity. On the other hand, the influence of spray parameters was optimized by investigating the effect of simple heat treatment (at 1100 °C) as a function of the arc current and N2 gas flow. The heat treatment improved the coating thermal conductivity at the different spray parameters. Thus, after heat treatment, the coating porosity, γ-Al2O3, Al5O6N strongly decreased and therefore the conductivity improved. On the other hand, the N2 gas flow and/or arc current did not show any difference on the conductivity after heat treatment. Therefore, using higher N2 gas flow and higher arc current is economically useless. Finally, although the obtained conductivity of the coating was not so high (compared to the AlN value), the main factors that govern the conductivity of such complicated plasma-spraying composite coating was realized. Herein, in order to fabricate high thermal conductivity AlN plasma spray coating, adjusting the phase composition, oxide content, porosity, and microstructure (at low N2 gas flow rate and low arc current) through the post-heat treatment is the key factor.