Arc Voltage Measurements Research Articles

Experimental study of the effect of argon on the restrike characteristics of nitrogen arc

The arc restrike process is a typical mode of operation within a direct current arc plasma torch. By using a transfer arc device with a planar anode parallel to the gas flow direction, the effect of argon addition on the disappearance of downstream old arc roots, the overall arc downstream movement process and the generation of upstream new arc roots of the nitrogen arc restrike process is experimentally investigated. The experimental results show that for pure nitrogen arc, the restrike frequency is very high and the old arc root disappears very quickly. The addition of argon will significantly decrease the temperature of the arc root and prolong the coexistence time of the old and new arc roots. This phenomenon is caused by the rapid decay of charged particle density in the nitrogen arc, because the recombination process of charged particles in the nitrogen arc is faster than that in the argon arc. The breakdown field strength at the upstream location where the new arc root occurs is calculated by combining the measurements of arc voltage, arc grayscale image and temperature. The results show that as the percentage of argon increases, the boundary layer thickness becomes thinner and the critical electric field strength required for arc breakdown decreases, leading to the generation of new arc roots more likely to occur toward the upstream location. This study improves the understanding of the effect of argon on the nitrogen arc restrike process.

Arc voltage measurements for height control in pulsed arc additive manufacturing

Pulsed-gas tungsten arc additive manufacturing (P-GTA AM) is highly suitable for producing high-performance and large-size components. However, research work concerning monitoring and control to increase process automation and steadiness is extremely inadequate. Aiming at a stable deposition in P-GTA AM, an arc voltage (AV) measuring and feedback control strategy is proposed. The novelty is that noises in pulsed AV are removed via an empirical mode decomposition denoising method and the peak AV is determined as the optimal feedback signal to characterize height variations by conducting static and dynamic tests. A fuzzy logic PID controller is designed to control the peak AV by regulating the amount of filler wire. Thin walls are manufactured to check the controller’s robustness, and the application of the control system through feedback from AV measurements can excellently ensure stable deposition height in P-GTA AM with a maximum AV deviation of 0.4 V.

Online Assessment of Contact Erosion in High Voltage Gas Circuit Breakers Based on Different Physical Quantities

In this paper, an effort has been made to evaluate the online condition of arc contacts as a vital component of interruption chamber in high-voltage puffer-type SF6 circuit breakers. The relationship between eroded mass caused by short-circuit current interruption and different thermal stress indices, such as transferred electrical charge, current squared, and arc energy, is investigated by performing many experiments with different current amplitudes and arcing times. It is demonstrated that none of the known indices can solely determine mass erosion caused by the current interruption. Therefore, the equations including two of the defined parameters are proposed to evaluate mass erosion. The method using arc energy and transferred electrical charge owns the highest accuracy in evaluating mass loss. However, considering the complexity of arc voltage measurements, a second method using current and arcing time can be also utilized. In addition, the development of erosion during the lifetime of arc contacts is studied. It is shown that arc roots tend to form on new uneroded areas of the contacts during current interruption, resulting in different erosion rates between the first few and subsequent interruptions due to change of morphology of the contacts after the first few switching operations.

Online Condition Assessment of Interruption Chamber of Gas Circuit Breakers Using Arc Voltage Measurement

As a key element of a power system, a circuit breaker (CB) requires regular maintenance. Intelligent online condition assessment is increasingly becoming a requirement for key items of power plants, including CBs. The interruption chamber, as the most critical part of the CBs, plays an important role in the proper operation of CBs. Online assessment of this part is difficult from a technical perspective due to the high noise level and presence of a transient recovery voltage. This paper proposes a set up for the online measurement of the CB arc voltage during trip/close operations. In addition, a method has been proposed to evaluate the remaining useful lifetime of the interruption chamber based on the measured arc voltage and current. The setup and the proposed approach are verified experimentally.

Study of the arc interruption performance of SF6-CO2 mixtures as a substitute for SF6

CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> attracts a lot of attention of researchers as a possible substitute for SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> . The arc interruption capabilities of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> -CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixtures for different mixed ratios are investigated in this paper by carrying out tests with a 126 kV puffer gas circuit breaker prototype and calculations. Based on the measured arc voltage and current around current zero, the post-arc current characteristics and the thermal interruption properties are investigated for SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> -CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixtures under different rise rate of the recovery voltage RRRV and di/dt before current zero. It is found that the interruption performance of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> -CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> increases greatly with increasing SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> concentration, and the critical RRRV and di/dt before current zero of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> -CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixtures for SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> content of 0, 20 and 50% are about 39, 45 and 70% of that of SF6 respectively, at the short-circuit current of 10 kA. The pressure increment at current zero is found to have a great effect on the interruption of the short-circuit current. In addition, the pressure buildup in CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is much lower than that in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> for both no-load and loaded operations.

Optimization of magnetic arc oscillation system by using double magnetic pole to TIG narrow gap welding

A magnetic arc oscillation system for tungsten inert gas (TIG) narrow gap welding is developed to prevent insufficient sidewall fusion and improve efficiency and quality for thick component welding. The characteristic of the system is that a double magnetic pole is induced by exciting current flowing through the field coil to generate the magnetic field within the welding area. This optimization of double magnetic pole not only enhances magnetic flux density compared with conventional single magnetic pole but also provides reliable melting of the sidewall. In this article, a new experimental method for the determination of the resulting heat input into the workpiece is proposed. Measurements of arc voltage and welding current flowing through the sidewalls are used to validate the redistribution of the arc heat. Furthermore, the difference of linear heat input of the sidewalls caused by current division ratio difference and arc voltage difference was the main reason why the formation characteristics occurred.

Modeling of human welder behavior in gas tungsten arc welding of stainless steel tubes

While automated welding tends to be the mainstream in modern joining, manual welding still plays an irreplaceable role. Human welder’s experience and skills are critical for many applications where decisions need to be made based on interactions with the process. Understanding the mechanism of human welder intelligence may establish the foundation to develop new methods to better train welders and develop intelligent welding robots that combine intelligence with high physical strength and motion accuracy. As the first effort to study the welders’ behavior mechanism, this paper focuses on answering two fundamental questions: (1) What information that the welders acquire through their observation of the weld pool? 2) how human welders intelligently respond, i.e., adjust welding parameter(s), to the sensory information they obtain? In particular, the principle of welders’ behavior is analyzed from modeling’s point of view. To answer the first question, the weld pool surface is characterized to find the information which is able to indicate the weld quality/penetration. It is found that the length, width, and convexity of weld pool surface provide an optimal estimation of the weld penetration. They can be considered the characteristic parameters/information welders acquire. For the second question, the mechanism of a welder’s behavior/adjustment on welding current as a response to the characteristic parameters is mathematically formulated. The dynamic models of the welder’s behavior are obtained and analyzed. To demonstrate one of the applications of the obtained model, i.e., transferring the welder’s wisdom into automated welding, the dynamic model is implemented as a controller into the automated gas tungsten arc welding (GTAW). Experiments have been designed and conducted with different welding conditions (arc length, i.e., the length of arc by a conversion of the measured arc voltage and joint gap) and initial currents. It has been found that the model is capable of adjusting the current intelligently such that a consistent full penetration is achieved despite the variations in those conditions/parameters.

New Arc Control Design for Vacuum Interrupters

In this paper, we introduce a new design of an arc control exhibiting a behavior that is different from those observed with axial magnetic field (AMF) and Transverse/Radial Magnetic Field (TMF/RMF) arc controls. With this new arc control, the arc forming when the contacts are parted is a rotating diffuse columnar arc with a main arc column which can occupy up to half of the contact tip surface. We present the assessment of the arc behavior and its characteristics by means of high-speed video recordings of the arc, arc voltage measurements, and synthetic and direct testing, which show that the new arc control has the potential to offer better breaking performance than the existing AMF cup type arc control of the same size. In addition, because of the shape and behavior of the arc, the electric life of the new arc control is expected to be longer than the one of the TMF arc controls.

Vacuum arc deposition of Al2O3–ZrO2 coatings: arc behavior and coating characteristics

Al2O3–ZrO2 coatings were deposited using a vacuum arc deposition system equipped with two co-planar cathodes. The plasma was injected into a cylindrical magnetic duct through annular anode apertures toward a substrate or an electrostatic ion current probe positioned on the duct axis, in vacuum and in a low-pressure oxygen or argon + oxygen background. Ion current and arc voltage measurements and visual observation of the cathode spots were used to find stable arcing conditions, using a straight plasma duct configuration. The cathode spot operation and transport of the plasma beam in the duct were studied as a function of arc current (Iarc = 25–200 A) and oxygen or oxygen + argon pressures (P = 0.1–1.5 Pa). Coatings were fabricated by exposing Si or WC–Co substrates simultaneously to Al and Zr plasmas using a 1/8 torus filter configuration in O2 + Ar pressures. The coating composition, structure, microhardness, adhesion, and wear behavior were studied as functions of the deposition parameters. Favorable conditions for stable arcing were obtained with Iarc = 75 and 100 A for Al and Zr plasmas, respectively. The ion current decreased, and the arc voltage increased with the oxygen pressure. Behavior of the ion current and arc voltage suggested that cathode poisoning started at P = 0.5 Pa. Deposition rates were 0.3-0.6 μm/min, depending on the substrate position. All coatings were “Zr rich”, i.e., the Zr:Al ratio was in the range of 1.2–5.6 depending on the substrate position and deposition conditions. The coatings with higher ZrO2 concentration were harder and had better resistance to wear. The coating’s hardness reached a maximum of ~22–24 GPa at a deposition temperature of 500 °C or a negative bias voltage of 75–100 V.

Observations on Droplet and Arc Behaviour during Pulsed GMAW

The influence of the oscillation behaviour of the weld pool and the pendant droplet on the electric arc in pulsed GMA welding has been studied. High speed video images are related to measurements of the voltage. It is found that the weld pool is triggered into motion by the impact of the transferred liquid droplet. The increase of the current in the peak pulse period hardly affects the weld pool. The remaining liquid at the electrode tip may start to oscillate by the action of surface tension and gravity after the droplet is detached. It appears that the oscillation pendant droplet changes the structure of the arc. A conceptual model is derived to explain the observed behaviour: visual observations and voltage measurements. Two different regions can be distinguished in the arc, a bright region and a normal region. The bright arc region surrounds the droplet and shrinks and expands with the up and down movement of the droplet. The behaviour of the bright arc region can be correlated with the measured arc voltage. The shape of the droplet has a negligible effect on the measured voltage, it only initiates the changes occurring in the arc. The periodical release of additional metal vapour in the arc affects the arc voltage considerably. The results of the experimental work presented here cannot yet explain the mechanism behind the alteration of the arc structure and further research is required to elucidate these phenomena. The results presented in this paper focus on bead on plate-pulsed GMA welding in partial penetration conditions.

Comparison of Vacuum Arc Behaviors Between Axial-Magnetic-Field Contacts

We compared vacuum arc behaviors of three slot-type axial-magnetic-field (AMF) contacts at two fixed contact gaps using high-speed digital photography and arc-voltage measurements. Solid angle is subtended by anode at the center of cathode or the ratio of the anode diameter to the gap length (D/g). With coupled influence of the AMF, we observed that with the D/g ratio 48 mm/14 mm, the arc kept in low current modes until higher current compared with the D/g ratio 48 mm/8 mm case. With the D/g ratio 58 mm/14 mm, the arc-mode transitions with the increase of current were similar as the D/g ratio 58 mm/8 mm case. However, with the D/g ratio 66 mm/14 mm, the arc became high current modes at lower current compared with the D/g ratio 66 mm/8 mm case. Correspondingly, with the D/g ratio 48 mm/14 mm, arc voltages at current peaks were close to the D/g ratio 48 mm/8 mm case, whereas arc voltages at current peaks with the D/g ratio 58 mm/14 mm were close to that of the 58 mm/8 mm case. However, with a contact diameter of 66 mm, the arc voltages with the D/g ratio 66 mm/14 mm were higher than the 66 mm/8 mm case. The arcs with the D/g ratio 66 mm/8 mm were more diffuse than the 48 mm/8 mm case. Moreover, the arcs with the D/g ratio 66 mm/14 mm were also more diffuse than the 48 mm/14 mm case when the current peak was 17.8 kA and above. The relationship between interrupting capacity of vacuum interrupters with the slot-type AMF contacts could be expressed as I=ktimes(D/g)+b, where k and b are constants.

A Comparative Study of AC/DC Converters for High-Power DC Arc Furnace

Today, dc arc furnaces are supplied by thyristor rectifiers. Because of the phase control strategy on the rectifiers, the arc voltage swings induce large reactive power variations on the power network and a static VAr compensator (SVC) or a static synchronous compensator (STATCOM) is always added to avoid flicker effect. In this paper, the authors present a new control strategy which suppresses the flicker effect and increases the furnace productivity. To supply the dc arc furnace, the ac/dc converter is based on diode rectifiers and choppers with a constant power control strategy. Consequently, the ac/dc converter can operate without a STATCOM or an SVC. To evaluate the gain in flicker and furnace productivity, simulations are done with Matlab software. These simulations take into account arc voltage measurements on a 100-MW dc arc furnace and allow for comparison of the different solutions.

Calculation of the interruption Process of a self-blast circuit breaker

Because the physics occurring during an interruption process is not well known, it is not easy to analyze the characteristics of a self-blast circuit breaker neither theoretically nor experimentally. Fortunately, the available computational power and the numerical method improved recently made it possible to predict an interruption process as precisely and fast as possible. Therefore many researches using computational methods have been done for the interruption process of interrupters and applied to extend the information such as thermal and dielectric reignition. In this paper, we have simulated the interruption process of SF/sub 6/ self-blast circuit breakers with the arc plasma during the fault interruption of a 10-kA current. The computational fluid dynamics program used here is coupled with the electromagnetic field analysis, the radiation model, and the effects of turbulence. Through this work, we have obtained further information about the thermal performance as well as the behavior of the arc. The results have been compared with the measured arc voltage.

Numerical modeling of SF6 thermal plasma generated during the switching process

Computational fluid dynamics (CFD) has been extended to the fields of the electric and electronics as well as the mechanics because of increasing of computer power and developing of numerical schemes. The thermal plasma inevitably established by separating the contacts makes a complex interaction with surroundings, it is not easy to analyze the phenomena neither experimentally nor theoretically. Nowadays, the operating energy used to move the contacts is required as low as possible, because it is the key factor to compact the integral system and to increase the reliability. Therefore, it is indispensable to analyze the thermal plasma conditions of circuit breakers using CFD. The thermal plasma characteristics could be obtained with computing flow field and electromagnetic field simultaneously. In this paper, we have simulated the switching process of the thermal expansion SF6 gas circuit breaker (GCB) that is combination of two interruption techniques, the self-expansion by the arc itself and the arc rotation by coils. In order to calculate the governing equations describing the dominant physical processes accurately, the commercial CFD code, PHOENICS, which is customized to allow the inclusion of arc plasma modeling by Fortran subroutines externally has been used. Through this work, we have found that the energy produced by the arc causes the pressure-rise in the chamber during high current period. And as the current falls near current zero, furthermore, the gas flows back from this region over the arc and should extinguish the arc just after current zero. The results have been compared with various dimensions and verified with the measured arc voltage.

The dynamic voltage/current characteristics of vacuum arcs after breakdown at currents in the lower kHz‐range

AbstractA test set‐up is presented which is able to measure the arc voltage of vacuum interrupters after breakdown with currents in the lower kHz‐range. Arc voltage measurements from this set‐up are presented. The obtained dynamic voltage/current characteristics are discussed and compared to the known voltage current characteristic of a power frequency arc in vacuum. A simple vacuum arc model is presented describing the voltage current characteristic. The model is applied to assess the energy dissipation in the arc.

A new approach to arc resistance calculation

An important macroscopic arc parameter, describing its complex nature is arc resistance. As known, the fault arc resistance can be calculated by the Warrington formula. The authors investigated the results of Warrington's tests. Warrington derived a relation for the arc voltage by using the measured arc voltage gradient and arc current as input data. By analyzing these measurements and by taking into account the conditions under which they are obtained (inaccurate measurement devices), it is unquestionable that the results are highly empirical and not accurate and general enough. Laboratory testing, provided in the high power test laboratory FGH-Mannheim (Germany), in which long high current arcs are initiated, was the base for the research results presented. In this paper a new approach to arc resistance calculation is given. Two independent approaches delivered the same equation. Both approaches are based on a suitable and a simple arc model assuming the rectangular wave form of the arc voltage, which is in phase with the arc current wave form. The new formula for arc resistance is compared with the Warrington formula. The influences of arc elongation are also investigated.

Contact temperature and erosion in high-current diffuse vacuum arcs on axial magnetic field contacts

We have investigated the surface heating effects of drawn vacuum arcs for several industrial designs of axial magnetic field (AMF) contacts, using near infrared (IR) photography of the Cu-Cr arcing surfaces with an image-intensified charge-coupled device (CCD) camera and an IR pyrometer. This enables detailed contact temperature mapping immediately after a half-cycle of arc current. The very homogeneous temperature distribution observed at current zero stands in contrast to the visually nonhomogeneous high-current diffuse arc, which was studied in separately reported experiments using high-speed digital photography and arc voltage measurements. The peak temperature at current zero increased relatively linearly with the peak current I/sub P/, and reached well beyond the melting range. We combine the temperature maps with a heating model to determine the thermal sheath thickness after arcing and its dependence on I/sub P/. The results suggest that near the interruption limit of AMF contacts, the interaction of the stable high-current arc with the anode and cathode is dominated by processes induced by flowing liquid metal, which redistributes the heat input from the axially concentrated arc over most of the contact surface. Furthermore, the flow of liquid metal off the cathode and anode faces contributes to the overall contact erosion.

Visualization and characterization of high-current diffuse vacuum arcs on axial magnetic field contacts

We have investigated the behavior of drawn vacuum arcs for several designs of axial magnetic field (AMF) contacts using high-speed digital photography and arc voltage measurements, As the peak current was increased, a gradual transition occurred in the arc appearance from a multiple cathode-spot arc to the high-current diffuse mode, and then to a high-current diffuse columnar mode. Two relatively simple models based on the literature are used to explain the results. The first is an empirical criterion for using the arc voltage behavior to determine the maximum arc current for which an AMF geometry can produce a high-current diffuse mode from the initial bridge column arc. The second model predicts the highest arc current that can be forced into a fully diffuse mode for given values of the AMF and the contact arcing radius. The predictions of these models are compared to our experimental and analytical results.

Plasma Spraying Using Ar-He-H&lt;SUB&gt;2&lt;/SUB&gt; Gas Mixtures

In plasma spraying, the properties of the plasma-forming gas largely control the characteristics of the plasma jet and the momentum, heat, and mass transfers to the particles injected in the flow. The objective of this work was to investigate the effect of gas composition on the static and dynamic behaviors of the plasma jet. The latter behaviors were investigated from measurements of arc voltage and plasma jet velocity. Ternary gas mixtures of argon, helium, and hydrogen were used. The results were expressed as correlations between arc voltage and flow velocity, and the operating parameters of the gun for a specific nozzle diameter.

A method of making an equivalent circuit for breaking arc

AbstractThis paper considers breaking of the dc circuit by electrical contact and describes a method for measuring the voltage and current waveforms of the breaking arc and surge, as well as a method for deriving the arc equivalent circuit in the latter period of the breaking arc. The small inductance of the whole simulating circuit as well as the equivalent capacitance of the electrical contacts are determined so that the observed voltage waveform induced in the text circuit during the surge (i.e., the induced voltage waveform after chopping) and the voltage value in the resistor calculated in the simulating circuit agree.Next, the equivalent arc resistance, coherence, and the phase angle are calculated from the voltage and current waveforms of the breaking arc, which contain the high‐frequency components. Using the equivalent capacitance, equivalent arc resistance and phase angle, the arc equivalent circuit is estimated that can simulate the measured arc voltage and current waveforms. It is seen as a result that the arc equivalent circuit in the latter discharge period of the breaking arc can be represented as a series‐parallel circuit where resistor ra1 is connected to the parallel circuit (ra2/Ca) of resistor ra2 and the equivalent capacitance Ca. When, for example, the Ag electrical contact on a relay breaks the circuit of dc 36‐V and a noninductive resistor 3 ω, the arc equivalent circuit in the 105 ∼ 106 band in the latter period of the breaking arc is constructed by ra1 = 65 ω, ra2 = −68 ω, and Ca = 200 pF.