Spark Conditioning Research Articles

Improvement of AC Conditioning Effect in Vacuum by High Frequency Voltage

To improve the dielectric strength in vacuum, spark conditioning through repetitive breakdowns by AC or impulse voltage is an effective method. AC conditioning at commercial power frequencies has been widely used due to its cost‐effectiveness, but the breakdown voltage after AC conditioning is generally lower compared to impulse conditioning. We have confirmed that multiple breakdowns occur successively in a half cycle of AC voltage application. It is considered that the multiple breakdowns are harmful for conditioning and triggered due to the previous breakdown in the same half cycle. In this paper, we discuss dielectric strength improvement by high frequency AC conditioning and how the multiple breakdowns are induced. We experimentally confirmed that the AC conditioning effect is improved by increasing the frequency of AC voltage for different applied AC conditioning voltages in a sphere‐plane electrode system. We focused on the breakdown position from the light emission images during AC conditioning to investigate whether the multiple breakdowns were induced or affected by the previous breakdown. We found that the multiple breakdowns occurred close to the previous breakdown position. The multiple breakdowns would be induced by the collision of metal particles due to the previous breakdown with the counter electrode. These breakdowns do not contribute to removing protrusion and would lead to damage to the electrode surface. The increasing frequency of AC conditioning would suppress the multiple breakdowns and improve the dielectric strength in vacuum. © 2024 The Author(s). IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Breakdown Charge Dependence of Counter Electrode Material Adhesion and Dielectric Strength After Spark Conditioning in Vacuum

Breakdown Charge Dependence of Counter Electrode Material Adhesion and Dielectric Strength After Spark Conditioning in Vacuum

Transient characteristics and sites of pre‐breakdown in spark conditioning for high‐voltage vacuum interrupter under power frequency voltage

AbstractThe objective of this paper is to determine the transient characteristics and sites of the pre‐breakdown (pre‐BD) in the spark conditioning under power frequency voltage (PFV) in vacuum. A multi‐angle optical path system was designed and made the determination of the pre‐BD sites in spark conditioning possible, through one camera at two viewing angles. The experimental results indicate that, in the spark conditioning under PFV, the pre‐BDs continuously occurred at a random moment. Within several half‐waves, the number of the pre‐BDs could reach dozens of times, which was the key for the treatment of the electrode surface in conditioning. Under the application of PFV, the single pre‐BD occurred at a random moment, in which it would last for several microseconds and the peak value of the current would reach several amperes. Moreover, the pre‐BD sites randomly distributed in the surface of the electrode and almost covered the whole surface of the electrode. The pre‐BDs took place independently in both time and space, in which there should be no effect between each other of two sequential pre‐BDs. To sum up, the transient characteristics and the sites of the pre‐BDs determined in this paper could reveal the physical mechanism of the pre‐BD on the treatment of electrode surface in the conditioning process, which is quite significant to improve the BD voltage of vacuum interrupter.

Influence of carbon nanotubes on the plasma electrolytic oxidation process of aluminum under “soft” sparking conditions

Plasma electrolytic oxidation of aluminum (PEO) was performed with dispersed multi-walled carbon nanotubes (MWCNTs) into the electrolyte. The effect of the carbon nanotubes concentration, as well as that of the electrical processing conditions, on the PEO process was investigated. From the point of view of the electrical response of the process, results show that the “soft” sparking regime appears earlier in presence of MWCNTs. The process time at which the transition to the “soft” regime occurs decreases linearly with the increase in the MWCNTs concentration. Over a concentration threshold, depending on the applied pulse bipolar current waveform, the PEO process is inhibited. The dispersion of MWCNTs in the electrolyte results in thicker but more porous alumina layers. More specifically, the proportion of the α-alumina phase relative to the γ-alumina phase decreases with the increase in the MWCNTs concentration. Results are explained by considering the increased coating growth kinetics and lower heat accumulation from MWCNTs addition. Finally, the present study gives new insights into the right management of the PEO process under “soft” sparking regime with dispersed carbon-based nanoparticles in the electrolyte.

Melting and Generation of Micro-Protrusions on Cathode Surface During Spark Conditioning Process in Vacuum

Spark conditioning is an effective method to increase the dielectric strength in vacuum by melting and removing micro-protrusions on the cathode surface. We aim to optimize the conditioning effect in vacuum for the application of vacuum circuit breakers (VCBs) to higher voltage levels. To obtain high breakdown (BD) voltage, the control of BD charge in the conditioning process is required. When a BD occurs, we have suggested that micro-protrusions can be generated on the cathode surface by particles from the anode. For the suitable control of BD charge, the meltability of generated micro-protrusions and their size are important. In this article, we focus on the generation of micro-protrusions on the cathode surface in conditioning process. First, we conduct spark conditioning by repetitive impulse voltages of rod–plane electrodes made of OFHC Cu in a vacuum chamber with different BD charges. Later, we observe the surface of rod cathode with a digital microscope in order to count the number of visible protrusions and measure their radii. By considering the meltability of micro-protrusions, we quantitatively reveal the existence of residual protrusions that cannot be completely melted by BD. Next, we estimate the maximum size of generated micro-protrusions by BD charge. In consideration of the collision of ions into the anode accelerated by the anode sheath voltage, we estimate the meltable amount of anode material by the BD charge. We confirm that the radii of experimentally measured protrusions are close to the estimated ones. Moreover, we consider the difference in dielectric strength due to the difference in the initial surface condition of the electrodes. We clarify that the dielectric strength is improved by applying acid wash and heat treatment to the electrodes before conditioning, which can be optimized by the BD charge and the initial surface condition of the electrode.

Analysis of electrical response, gas evolution and coating morphology during transition to soft sparking PEO of Al

The soft sparking regime of Plasma Electrolytic Oxidation (PEO) of valve metals attracts increasing attention as it enables a better process control with improved energy efficiency and coatings with enhanced performance to be obtained. Here, the discharges softening phenomenon was characterised by evaluation of changes in electrical signal, composition of gaseous products and morphology of the metal-oxide interface in PEO coatings on Al. The coatings were formed using two electrical regimes retarding or promoting soft sparking conditions. Harmonic analysis of PEO process has been performed using independent evaluation of the positive and negative half-waves of polarisation signal. The composition of gas evolved during the PEO process was evaluated by a quantitative gas analyser. Coatings were characterised by scanning and transmission electron microscopy with energy dispersive spectroscopy and small area electron diffraction. It was found that discharge softening is accompanied with a decrease in oxygen evolution rate, an increase in equivalent capacitance of anodic process as well as structural and compositional changes near the metal-oxide interface. The experimental findings provide further support to the explanation of discharge softening phenomenon by narrowing the active zone at the metal-oxide interface due to intercalation of hydrogen species into anodic alumina under cathodic polarisation. Such mechanistic understanding allows rational regime selection, in-situ process control and optimisation of the coating properties to be performed that paves the way to intellectual manufacturing approach based on careful process monitoring in operando.

An investigation into the effect of wire inclination in Wire-Electrical Discharge Turning process of NiTi-60 shape memory alloy

• A novel method of WEDT by inclining the wire electrode is introduced. • Inclining the wire leads to an improvement in both MRR and roughness values. • Formation of elongated craters and crater-channels are observed. • Arcing conditions produce shiny surfaces, and sparking conditions form dull surfaces. In this study, a novel method of Wire Electrical Discharge Turning (WEDT) by inclining the wire electrode is introduced. Response Surface Methodology (RSM) is employed to conduct the experiments by varying pulse-on-time, spindle rotational speed, and inclination angle at three levels, where Volumetric Material Removal Rate (VMRR) and the Average Surface Roughness (R a ) were considered as the response outcomes. It has been observed that the inclination of wire can improve the VMRR and R a . The surface microstructure has also been studied with the help of FESEM images, and accumulations of elongated craters leading to the formation of crater-channels are observed. The formation of these crater-channels is influenced by the inclination angle and the spindle rotational speed. The observed surface cracks in the generated surface are very less in number and in some localized positions only. The study also focuses on arc-spark characteristics of voltage waveforms taken during the experiments. It is observed that at arcing conditions, a shiny surface is produced, and on the other hand, sparking conditions produce a dull and burnt surface. Finally, a multi-stage WEDT strategy is proposed to produce a cylindrical surface with high VMRR and superior surface characteristics.

Incorporating Behavioral Trigger Messages Into a Mobile Health App for Chronic Disease Management: Randomized Clinical Feasibility Trial in Diabetes.

BackgroundAlthough there is a rise in the use of mobile health (mHealth) tools to support chronic disease management, evidence derived from theory-driven design is lacking.ObjectiveThe objective of this study was to determine the impact of an mHealth app that incorporated theory-driven trigger messages. These messages took different forms following the Fogg behavior model (FBM) and targeted self-efficacy, knowledge, and self-care. We assess the feasibility of our app in modifying these behaviors in a pilot study involving individuals with diabetes.MethodsThe pilot randomized unblinded study comprised two cohorts recruited as employees from within a health care system. In total, 20 patients with type 2 diabetes were recruited for the study and a within-subjects design was utilized. Each participant interacted with an app called capABILITY. capABILITY and its affiliated trigger (text) messages integrate components from social cognitive theory (SCT), FBM, and persuasive technology into the interactive health communications framework. In this within-subjects design, participants interacted with the capABILITY app and received (or did not receive) text messages in alternative blocks. The capABILITY app alone was the control condition along with trigger messages including spark and facilitator messages. A repeated-measures analysis of variance (ANOVA) was used to compare adherence with behavioral measures and engagement with the mobile app across conditions. A paired sample t test was utilized on each health outcome to determine changes related to capABILITY intervention, as well as participants’ classified usage of capABILITY.ResultsPre- and postintervention results indicated statistical significance on 3 of the 7 health survey measures (general diet: P=.03; exercise: P=.005; and blood glucose: P=.02). When only analyzing the high and midusers (n=14) of capABILITY, we found a statistically significant difference in both self-efficacy (P=.008) and exercise (P=.01). Although the ANOVA did not reveal any statistically significant differences across groups, there is a trend among spark conditions to respond more quickly (ie, shorter log-in lag) following the receipt of the message.ConclusionsOur theory-driven mHealth app appears to be a feasible means of improving self-efficacy and health-related behaviors. Although our sample size is too small to draw conclusions about the differential impact of specific forms of trigger messages, our findings suggest that spark triggers may have the ability to cue engagement in mobile tools. This was demonstrated with the increased use of capABILITY at the beginning and conclusion of the study depending on spark timing. Our results suggest that theory-driven personalization of mobile tools is a viable form of intervention.Trial RegistrationClinicalTrials.gov NCT04132089; http://clinicaltrials.gov/ct2/show/NCT004122089

On the Uniqueness and Stability of Dictionaries for Sparse Representation of Noisy Signals

Learning optimal dictionaries for sparse coding has exposed characteristic sparse features of many natural signals. However, universal guarantees of the stability of such features in the presence of noise are lacking. Here, we provide very general conditions guaranteeing when dictionaries yielding the sparsest encodings are unique and stable with respect to measurement or modeling error. We demonstrate that some or all original dictionary elements are recoverable from noisy data even if the dictionary fails to satisfy the spark condition, its size is overestimated, or only a polynomial number of distinct sparse supports appear in the data. Importantly, we derive these guarantees without requiring any constraints on the recovered dictionary beyond a natural upper bound on its size. Our results yield an effective procedure sufficient to affirm if a proposed solution to the dictionary learning problem is unique within bounds commensurate with the noise. We suggest applications to data analysis, engineering, and neuroscience and close with some remaining challenges left open by our work.

Initiation Process of Vacuum Breakdown Between Cu and CuCr Electrodes

During the breakdown process in a vacuum, plasma flares initiated on cathode and anode surfaces expand and collide. The plasma flare behavior is quite important for the optimization of the spark conditioning of vacuum interrupters. Here, copper–chromium alloys are widely used as an electrode material in the large-capacity vacuum circuit breakers. In this article, high-speed spectroscopy is conducted on the plasma flares generated between a CuCr (Cr-35wt%) anode and a Cu cathode in order to elucidate the plasma temperature, particle composition, and electron density. The experimental results show that the anode flare has 1024–1025m−3 electron, and its temperature is approximately 13 000 K. The composition ratio of vapor atoms consisting the anode flare is Cu:Cr = 6:4–7:3, which is almost the same with that of anode material composition.

Monte Carlo simulation of microparticle motion in vacuum gap

AbstractBreakdown voltages of vacuum gaps become lower when the gaps are contaminated by metallic and ceramic microparticles. In this paper, the motion of the microparticles in the gap is simulated using Monte Carlo method in order to evaluate the effect of parameters upon motion and the removal time of the microparticles. As the parameters, we focused on the material of the microparticle, the frequency, the peak value of the applied voltage, the gap length, and the diameter of the lower and upper electrodes. It turned out that the maximum time needed to remove all microparticles could be expressed as multiple regression function. It is suggested that the reliability of the microparticle removal can be increased by spark conditioning with opening/closing operation.

The role of cathodic current in plasma electrolytic oxidation of aluminium: current density ‘scanning waves’ on complex-shape substrates

This paper focuses on the factors that influence the surface distribution of the current density during plasma electrolytic oxidation of 2024 Al alloy under alternating polarisation. It was found that employing the combined current mode, including relatively long (100–2000 ms) pulse trains, improved coating uniformity even when the electrolyser provided a severe nonuniform primary electric field. An experimental investigation employing a sectioned sample showed that the nonuniform distribution of the primary electric field could be compensated by the changes in the coating properties induced by previous cathodic polarisation. Temporary changes in the secondary distribution of current density across the sample surface (attributed to the coating properties) caused dynamic redistribution of the anodic current density during the following AC pulse train, resulting in the so-called ‘scanning wave’ effect, i.e. migration of the maximum current density along the sample surface. Factorial experimental design, finite element modelling and analysis of the transient current–voltage curves were applied. A mechanistic explanation underlying the considered phenomenon has been suggested. In addition, the increase in plasma electrolytic oxidation efficiency under soft sparking conditions is considered as ‘electrocatalysis’ of anodic oxidation by previous cathodic treatment.

On uniqueness of sparse signal recovery

Abstract A basic issue of sparse signal recovery (SSR) is to explore the condition of the uniqueness with regard to the solution of the relevant optimization framework. However, the standard uniqueness conditions, such as spark condition, NSP (null space property), RIP (restricted isometry property) and mutual coherence condition, are with respect to any sparse signal with the same sparsity. Therefore, these four conditions require certain structural or metric properties of all possible sub-matrices from the measurement matrix corresponding to the possible support indices and are quite restrictive for a given sparse signal with its support indices fixed. This work mainly considers the uniqueness issue of SSR. With the extra information of the support indices, the requirements of the measurement matrix for guaranteeing the uniqueness are released. Theoretical analysis has been performed on the uniqueness for l0-norm and l1-norm frameworks, in which loosed conditions are further validated by constructed examples. These discoveries can explain the phenomena that the occasional success of SSR in numerical simulation occurs when the above four conditions cannot be satisfied. Besides, it is analyzed that the spark condition and NSP condition are the minimal requirements for the unique recovery of the standard l0-norm framework and the l1-norm framework respectively.

The Role of Cathodic Current in Plasma Electrolytic Oxidation of Aluminum: Phenomenological Concepts of the “Soft Sparking” Mode

A comprehensive analysis of experimental data relating to so-called "soft sparking" mode of plasma electrolytic oxidation (PEO) has been undertaken. The transition to the soft sparking mode is accompanied by a number of characteristic effects, such as a decrease in anodic voltage, acoustic and light emission, increase in hysteresis in transient current-voltage curves, improved uniformity of the discharge distribution on the surface, disappearance of atomic lines, and development of continuous radiation in the optical emission spectra. An explanation of the main features of PEO process operated under soft sparking conditions is proposed assuming the existence of a specific narrow region in the coating thickness, where the main anodic voltage drops. Because of high electric field in this "active zone", both anodic oxidation of the metal substrate and high-energy processes may take place. According to this assertion, the soft sparking mode of PEO is caused by cathodic polarization (a) eliminating the potential barrier at the oxide-electrolyte interface due to local acidification and (b) increasing electric field at the metal-oxide interface during subsequent anodic half-cycle due to narrowing of low-conductive part within the active zone. Based on this consideration, it is possible to account for the main characteristic phenomena accompanying the PEO process on aluminum under alternating polarization.

Optimum breakdown charge for maximum dielectric strength in spark conditioning in vacuum under a non-uniform electric field

Spark conditioning is an effective method of increasing the dielectric strength in vacuum. In this paper, we determined the breakdown (BD) charge dependence for spark conditioning in vacuum under various non-uniform electric fields and with different anode materials. We discuss the BD mechanism in terms of BD arising from anode heating or cathode heating. Experimental results revealed that for anode heating BD, the longer the gap distance, the larger the BD charge needed to obtain maximum dielectric strength. In contrast, for cathode heating BD, the BD charge for maximum dielectric strength was smaller than that for anode heating BD. From these results, we estimated the optimal BD charge to maximize the 50% BD electric field strength, i.e. the dielectric strength, for spark conditioning in vacuum.

Dependence of spark conditioning on breakdown charge and electrode material under a non-uniform electric field in vacuum

Spark conditioning is an effective method for improving dielectric strength in vacuum. In this paper, we discuss the dependence of spark conditioning on breakdown (BD) charge and electrode material in vacuum under various non-uniform electric field and circuit parameters. We applied a negative impulse voltage to a rod-plane electrode configuration with a cathode made of stainless steel (SS), Cu-Cr, or OFHC Cu (Cu), and an anode made of SS or Cu. We changed the gap distance, the tip radius of the rod electrode and the circuit parameters. As a result, the conditioning effect, i.e. improving BD electric field strength by the conditioning, depended on the BD charge (QBD) and reached its maximum value against QBD. The optimal QBD required to achieve the maximum conditioning effect decreased with the cathode melting point. Moreover, when BD caused by cathode heating (CH-BD) occurred readily, with the SS anode, the BD electric field strength at the cathode surface after conditioning depended on QBD, regardless of the gap distance and the tip radius. Thus, for CH-BD, we estimated the withstand voltage that could be achieved by spark conditioning from the electrode configuration and QBD. However, when BD caused by anode heating (AH-BD) occurred easily with the Cu anode, the optimal QBD was larger than that for CH-BD because the cathode temperature was lower for AH-BD than for CH-BD.

Surface characterisation and corrosion behaviour of niobium treated in a Ca- and P-containing solution under sparking conditions

The investigations of plasma electrolytic oxidation (PEO) process of Nb in a 1.5moldm−3 Ca(H2PO2)2 and 0.5moldm−3 Mg(CH3COO)2 solution at a constant anodic current density of 150mAcm−2 up to several limiting voltages (200, 300, 400 and 500V) were described. The resulting oxide layers were characterised in terms of their physicochemical properties and corrosion resistance (DC and AC techniques) in Ringer’s solution at 37.0±0.5°C. The growth of the oxide layers during the PEO treatment was monitored using a digital camera and the sparks formed on the surface of niobium were analysed. The effect of the anodisation voltage on the oxide layer thickness (from less than 1μm up to 150μm), incorporation of the electrolyte solution species (the relative content of Nb in the coatings dropped from 36.5 to 0.7 at%), adhesion strength (theLc2 increased from 6.31±0.38 to 14.10±0.47N) and corrosion resistance (the Rp changed from 10.4±2.7 to 60.9±13.7MΩ cm2) was described. Additionally, the phase and chemical compositions of the oxide layers were studied.

Analysis of conditioning and damaging process in vacuum based on breakdown probability distribution

For the enhancement of insulation strength in vacuum, spark conditioning is an important and effective method. In order to enhance the insulation performance of vacuum circuit breakers, we have to clarify the conditioning effect and improve a conditioning procedure. In this paper, we discuss the conditioning process of Cu and stainless steel rod electrodes based on breakdown (BD) probability distribution. We applied a negative impulse voltage to a rod-plane electrode configuration. We adopted two procedures for the voltage application, i.e. up-down and 3 times methods. For the Cu rod with the up-down method, BD voltage increased by the conditioning effect, however, the minimum BD voltage did not increase or even decreased due to the damaging effect by BD. A moderate conditioning procedure, e.g. 3 times method, could increase the minimum BD voltage as well as the stabilization of insulation strength. The Weibull analysis of the development of a BD probability distribution has enabled us to discriminate the conditioning and damaging effects. Based on these results, we can discuss a suitable conditioning procedure.

The nature of anodic gas at plasma electrolytic oxidation

The output of electro- and thermochemical reactions has been estimated quantitatively on the basis of analyses of the products obtained by plasma electrolytic oxidation (PEO) such as volume and composition of anodic gases evolved on aluminium, weight of oxide and metal passed in to solution. It was shown, that the main component of anodic gases is hydrogen (about 90 vol %). This testifies to preferential occurring of thermochemical processes such as vapor conversion of aluminium by water. Estimation of the hydrogen ‘energy yield’ has provided evidence of an excellent correlation between calculated and experimental results. The efficiency of thermal aluminium conversion in PEO processing under sparking conditions has been found to be approximately 50% and of water decomposition approximately 12%.

Effect of Spark Condition on Non-Linear Dynamic Characteristics of Natural Gas Engine

In the condition of equivalence ratio α=1 and different spark advance angle (SAA), non-linear dynamic characteristics of combustion process in spark ignition (SI) natural gas engine was studied. The results show that the attractors always have a non-periodic structure within a limited region .When SAA increases indicated mean effective pressure (IMEP) and the scale of attractors increase whereas the coefficients of cyclic variation and the correlation dimension of system decrease. It is observed that the correlation dimension of system is fractal and the largest Lyapunov exponent (LLE) of the system is always greater than zero. Therefore in condition of α = 1, combustion system is of obvious non-linear deterministic nature and the complexity of the system is reduced with the increase of SAA.