Arc Behavior Research Articles

Transients Caused by Sequential Circuit Breaker Tripping Issued by Busbar Protection

A study of transients in a high voltage substation 400/110 kV is presented in the paper. An analysis was carried out after a fault on the 110 kV busbar, which caused severe damage in the substation. Investigation was focused on a time frame of several sequential circuit breaker trippings. A first step of the study was collection of data from the primary and secondary system in the substation and the control centre. After numerous analyses of data an attempt was made to construct a precision model, which could be used in the computation. Appropriate models were developed for circuit breakers, voltage (potential) and current metering transformers, power transformers, surge arresters, overhead lines and an equivalent grid. The components of the power system can be modelled for the very particular purpose, which means that a different frequency model should be used and each element in this analysis has a specific frequency response. An attempt was made at very detailed modelling of a power transformer, air blast and SF6 circuit breakers. Computed results of fault currents were compared with measurements captured by the disturbance recorders in the field, mainly in differential numerical relays. Different switching schemes and different tripping sequences of several 110 kV circuit breakers were analysed with a constructed model in the millisecond range. Models of circuit breaker with different types of media, air blast and SF6 gas were used in the cases investigated. Modelling of the circuit breakers’ electrical arc was an important item in all cases in order to take into account the interaction between electrical arc and circuit current during the process of current interruption. The Schwarz/Avdonin equation is applied to model the dynamic behaviour of an electric arc. The fault studied was accompanied by a large short circuit current. For this particular case two types of circuit breaker, air blast and SF 6 were modelled. An important conclusion from those analyses was that sequential tripping of several circuit breakers does not cause superposition of overvoltages, because interruption the current happens when it is passing through the zero. Even the record from the substation and the disturbances recorder proves that each particular circuit breaker was successfully opened. On that basis, focus was put only on the final opening of the breaker and its arc extinction. The conclusion can be drawn that such a substation fault should have no influence on excessive overvoltages that can threaten the insulation of components in the substation.

Failure Analysis of Power Relays With Multiple Breaks in the Electrical Endurance Experiments

Multiple breaks are favorable for arc extinguishment of relays switching heavy load. However, the existed asynchronous mechanical separation of contact pairs and associated unbalanced arcing behavior limit the electrical lifetime to some extent. In this article, the typical contact voltage and contact current waveforms of double breaks within power relays are presented. Based on the variations in bounce energy, contact resistance, and arc energy as a function of switching cycles, the effect of contact gap on the electrical lifetime of power relays is analyzed explicitly. Furthermore, the failure process of power relays with two bridges is characterized by the recorded breaking time difference of bridges. The observed significant asynchronous breaking phenomena in the end of electrical lifetime experiments attribute to the contact welding failure of power relays.

I-V characteristics and temperature response of unidirectional CFRP exposed to simulated lightning current in the fiber direction

This study examined the I-V characteristics and temperature response of unidirectional CFRP exposed to simulated lightning current by performing direct electrical conduction tests that could minimize the effects of thermal flux from the arc root, complex arc behavior, and shock wave. A numerical analysis was carried out to clarify the heating mechanisms. The results show that the electrical conductivity of unidirectional CFRP in the fiber direction under impulse current tests is almost identical to that measured in the steady-state and becomes constant during lightning current increasing. Cross-sectional observation of the specimen revealed that matrix cracks and delamination occurred in the temperature range where the CFRP thermal decomposition occurred. In addition, it was necessary to consider the formation energy of the pyrolysis gas to estimate the temperature response, which was estimated to be approximately 2.163 × 107 J/kg for the toughened epoxy CFRP.

Corrosion-fatigue crack growth behaviour of wire arc additively manufactured ER70S-6 steel parts in marine environments

A crucial part of the structural integrity assessment of marine structures is the analysis of the fatigue crack growth behaviour of the welded joints in seawater environments, where the cracks often initiate and propagate under corrosion-fatigue loading conditions. In recent years, technological developments have facilitated the fabrication of steel components and structures using additive manufacturing technologies. Among the existing technologies, the Wire Arc Additive Manufacturing (WAAM) technique has proven to offer great potentials for fabrication of large-scale structures. The present study investigates the corrosion-fatigue crack growth (CFCG) behaviour of the WAAM parts fabricated using ER70S-6 low carbon steel wire to assess the suitability of this technology for future marine structures. In this experimental study, the cracking behaviour and test duration in corrosion-fatigue tests were investigated and analysed in conjunction with the microstructural examination of the tested specimens. Moreover, the obtained results were compared with the recommended trends available in BS7910 standard for conventional welded joints and the data available in the literature on widely used offshore structural steel weldments. The CFCG results obtained from this study contribute to the overall knowledge and design requirements for the new optimised functionally graded structures made with WAAM technology for marine applications.

Investigations on Dry Sliding Wear Behavior of a Wire Arc Additively Manufactured Nickel-based Superalloy

ABSTRACT Wire Arc Additive Manufacturing (WAAM) is a low-cost method of fabricating large components from advanced materials such as nickel-based superalloys. Nickel-based superalloys have varied industrial applications and suit the WAAM method due to their excellent weldability when used in conjunction with metal inert gas welding equipment used in the current study. All WAAM specimens were subjected to a standard dry sliding wear test to examine wear behavior. During the wear study, load, sliding velocity, and sliding distance were all considered for both wrought and WAAM alloy. The lowest wear was observed at a lower load and higher sliding velocity, whereas the highest wear was observed at a higher load and lower sliding velocity. Wear mechanisms and wear debris corresponding to lowest and highest wear conditions were also being investigated. The transition from lowest to highest wear rate in both alloys was attributed to the transition from abrasive to adhesive and delamination wear mechanisms. Microstructure analysis revealed that the nickel-based WAAMed alloy had an equiaxed dendritic structure, whereas the nickel-based wrought alloy had a cellulose structure. Both specimens had a stable austenite structure in the Ni-Fe-Cr phase, as determined by X-ray diffraction analysis. The X-ray diffraction line profile analysis technique by the Williamson-Hall relationship revealed that WAAM alloys have higher micro-strain, higher dislocation density, and smaller crystallite size when compared to wrought alloys. The experimental results showed a 23% increase in hardness and a considerable improvement in wear resistance in the WAAMed alloy compared to the wrought alloy.

Hot corrosion and air oxidation behavior of pulsed current gas tungsten arc welded and CO2 laser beam welded SMO 254 at 800 °C

This research aims to investigate the hot corrosion behaviour of SMO 254 steel samples after PCGTA and CO2 laser beam welding, as well as air oxidation. A salt mixture simulated the waste incinerator environment involving 40 wt. % Na2SO4 + 40 wt. % K2SO4 + 10 wt. % NaCl + 10 wt. % KCl are employed. The hot corrosion tests were carried out for 103.33 h at 800 °C, with a thermogravimetric investigation availed to calculate the impact of corrosion. The weight gain rate for PCGTAW molten salt corroded specimens is greater (33.45 mg/cm2) than the weight gain rate for CO2 Laser molten salt corroded specimens, which is 67.55% higher. The weight of the hot corroded sample rises in the molten salt surroundings due to the creation of compounds including CrS, FeMo2S4, Na2S, Fe2O3, K2S3, Cl4CrNa2. CO2 LBW air oxidation has the lowest rate of corrosion due to the synthesis of beneficial oxides, such as NiCr2O4, NiO, and Cr2O3. Optical microscopy and SEM/EDS were employed on both surface and cross-sectional surfaces to get microstructure at the interface of the fusion region, parent metal, and fusion region using point mapping, line mapping, and X-ray mapping techniques. The corrosion products produced during corrosion were studied using XRD.

Investigation of the Corrosion Behavior of Wire Arc Additively Manufactured Alloy 825

Investigation of the Corrosion Behavior of Wire Arc Additively Manufactured Alloy 825

Narrow Groove Laser-Arc Hybrid Welding of Thick-Sectioned HSLA Steel Using Laser Beam Oscillation

In this study, a sine-oscillating laser was used to obtain narrow groove laser-arc hybrid welding (NGHW) of high-strength low-alloy (HSLA) steel. Then the effects of laser beam oscillation amplitude and space constraint on arc behavior, droplet transfer, weld geometry, and incomplete fusion of the weld beads were analyzed. Due to the minimum arc voltage principle and inherent arc self-regulation, when the laser did not oscillate, it was observed that the arc cathode spot was typically attached to one sidewall. As a result, the molten pool did not spread through the entire width of the gap , resulting in incomplete fusion. When the laser beam oscillated in a sinusoidal path, the energy density on both sides of the amplitude was higher than the centerline, and the aspect ratio of the weld decreased. The speed of the beam along the centerline was found to be much higher than the speed on both sides of the amplitude. The molten pool oscillated in the width direction under the action of the oscillating beam, forming a concave surface, which promoted melting of the sidewalls of the groove and suppressed incomplete fusion defects in the sidewalls. The technical feasibility of NGHW assisted by laser beam oscillation was verified using a 60-mm-thick weld, which was characterized by a smooth layer transition and the absence of visible defects.

The mechanisms of underwater wet flux-cored arc welding assisted by ultrasonic frequency pulse high-current

An ultrasonic frequency pulse high-current (UFPHC) was utilized to improve the stability of underwater wet flux-cored arc welding on Q235 steel. Based on the studies of the bubble evolution, arc behavior, droplet geometry, weld formation, and mechanical properties of the joint, the arc extinguishing phenomenon was suppressed effectively by the additional UFPHC, which decreased the amount of spatter on the workpiece and improved the appearance of the weld. The additional UFPHC reduced the average droplet radius by 40% and increased the average transition frequency by 99%, compared with the same value of additional welding current. The UFPHC enabled to decrease the hardness of the heat-affected zone by 15% due to the production of less martensite compared to results obtained by simply increasing the welding current. The vibration effect of the UFPHC in the welding pool was indirectly confirmed by the significantly decreased porosities in the final joint. The morphology of the impact fracture of different welding cases showed that the UFPHC was helpful to decrease the brittle fracture area in the weld joint and increase the value of the impact toughness for the weld joint.

Numerical Study on Multiple Arcs in a Pyro-Breaker Based on the Black-Box Arc Model

The arc behavior during commutation of a pyro-breaker is the main determinant of performance evaluation. The pyro-breaker discussed in this article is an explosive-driven, extremely fast and non-linear Direct Current circuit breaker. It has been developed for the Quench Protection System (QPS) of superconducting fusion facilities, such as the China Fusion Engineering Test Reactor (CFETR). The feasibility of the Schavemaker differential equation is verified in a simplified 40 kA commutation simulation. The Commutation Section of the pyro-breaker will form multiple gaps after the operation, which causes multiple arc ignitions during the explosion. The influence of the gap quantity on the commutation performance of the pyro-breaker has not previously been studied. A more accurate simulation, which takes the multiple-arc formation into consideration, is proposed and verified under the current of 60 kA. The simulation model, which takes the numerical analysis of the driving mechanism into consideration, will be the designing basis for the pyro-breaker in further development and implementation.

Corrosion-fatigue crack growth behaviour of wire arc additively manufactured ER100S-1 steel specimens

The wire arc additive manufacturing (WAAM) technology is a promising fabrication technique which has been proven to have many advantages for producing large structures; however, the fatigue and corrosion-fatigue performance of WAAM steel components for application in the marine environments is still unexplored. In this study, the WAAM technique was employed to fabricate four specimens made of ER100S-1 steel, which were then tested under cyclic loading conditions in seawater to assess the corrosion-fatigue crack growth (CFCG) behaviour and hence suitability of this fabrication technology for offshore renewable energy applications. The test duration, cracking mechanisms and CFCG rate were investigated for each specimen and the material’s behaviour was investigated by considering the microstructural examinations. Furthermore, the obtained results were compared with the BS7910 standard recommended trends and experimental data available in the literature for conventionally built weldments made of different grades of steel which are commonly used for offshore applications.

Effect of reverse-polarity hot wire on the tandem arc welding process

A novel three-dimensional two-step numerical model was developed and analyzed for a tandem process with a reverse-polarity hot wire. Magneto-hydrodynamic analysis was conducted and the free surface of the molten pool was tracked to investigate the arc and molten pool behaviors of the proposed process, respectively. The results indicated that a change in electromagnetic force by the hot wire reduced arc deflection, which increased the arc velocity in the co-axial direction of electrodes, thereby increasing the arc pressure and arc shear force acting on the molten pool. Consequently, the molten pool in the novel tandem process was wider and deeper than that in the conventional tandem process.

Enhanced optical and electrical properties of CeO2NPs/chitosan nanocomposites

Cerium oxide nanoparticles (CeO2NPs) of different ratios (x = 5, 10, 15, and 20 in wt%) are successfully incorporated into chitosan (CS) to synthesize CeO2NPs/CS nanocomposites by solution cast method. FTIR and XRD analysis confirmed the effective incorporation of CeO2NPs into chitosan nanocomposites. TGA and DTG showed that the thermal stability of the as-prepared nanocomposites is improved. The CeO2NPs/CS nanocomposites exhibited enhanced light absorption capacity in the UV-visible range as x increases, owing to the CeO2NPs’ large bandgap. The transmittance of UV decreased for x = 10 and 15 nanocomposites. Light scattering enhanced for x = 5 and 10 nanocomposites, increasing reflectance. Compared to CS (5.3 eV), the optical energy bandgap lowers to 4.94 eV and 5.1 eV, respectively. Impedance spectroscopy research validates the impedance spectroscopy parameters’ dependency on CeO2NPs concentrations. Because of the growth of multiple polarization types, generating interfaces of numerous defects, and space charge polarization, the dielectric constant increases with increasing x (up to x = 15). The dc conductivity (σ DC) and the frequency exponent (S) are estimated using the universal Josher’s power law and applied to the ac conductivity data (σ AC). Obviously, (S) decreases with increasing temperature, which refers to the electrical conductivity that follows the hopping mechanism. In addition, according to the CBH model, the Coulomb barrier of charge carriers (Um) is estimated, showing decreasing values as increasing x and recording the lowest value for x = 15 nanocomposites. Nyquist plots (Z″&Z′) indicate one semicircle arc behavior for all samples. As x rises, the radius of semicircular arcs reduces, suggesting that (σ DC) increases. The enhanced characteristics of CeO2NPs/CS nanocomposites make them suitable for future bio-applications.

Temperature-dependent oxidation behavior of arc evaporated Al–Ti–B–N coatings

Arc evaporated Al–Ti–B–N coatings were investigated concerning the oxidation behavior. The addition of B promotes the formation of an amorphous scale with mixed oxides of Al, Ti, and B, thus resulting in a higher oxidation rate than the Al–Ti–N coating at 800 °C. At higher temperatures (≥900 °C), B-containing coatings exhibit a better oxidation resistance. The oxidation at the interface between the oxide and nitride led to the continuous formation of the amorphous inner layer with excellent adhesion. Simultaneously, the crystalline outer oxide layer at elevated temperatures inhibited the inward diffusion of oxygen.

Effect of Arc Behaviour and Metal Transfer Process on Aluminium Welds during Ultrasonic Frequency Pulsed GMAW

In order to study the influence of a novel current waveform control method of ultrasonic-frequency pulse (UFP) on arc behaviour, metal transfer process and the welds formation, monitoring system and image processing algorithms were employed for extracting the welding characters. Mechanics, defect, microstructure and mechanical property analysis based on pulsed GMAW was carried out. The results showed that, compared with the conventional pulsed GMAW, the ultrasonic-frequency pulse not only increased axial arc plasma jet force, arc force and droplet falling acceleration, but also suppressed the welded porosity formation, decelerated the microstructure regional element segregations, refined the grain and increased the microhardness property of welded joint. The study helped to reveal the mechanism for improving welding quality of ultrasonic-frequency pulsed GMAW.

Study on arc behavior and droplet transfer in twin-electrode TIG-MIG indirect arc welding

Study on arc behavior and droplet transfer in twin-electrode TIG-MIG indirect arc welding

Corrosion Behavior of 7A52 Aluminum Alloy Plasma Arc Welding Joint in Simulated Marine Atmosphere Environment

Corrosion behavior of 7A52 aluminum alloy plasma arc welding (PAW) joint was investigated in simulation of marine atmosphere environment with salt water spray test. The surface morphologies were observed by scanning electron microscopy (SEM), and the effect of corrosion time on corrosion behavior was discussed. The depth of spot corrosion, the corrosion dynamic characteristics, and the distribution of element of 7A52 aluminum alloy welding joint were analyzed by 3D and XRD Microscope. Results show that pitting corrosion is main morphology in heat effect zone at initial stage, pitting corrosion appears in matrix and welding joint with time. The main component compounds existing in the film include Al and O. The depth of pitting corrosion in the heat effect region is the maximum (3.008μm). The law of power function is followed in both phases of the corrosion weight increasing curve, and the corrosion rate decreases with time.

Effect of Y additions on the oxidation behavior of vacuum arc melted refractory high-entropy alloy AlMo0.5NbTa0.5TiZr at elevated temperatures

The effects of yttrium (Y) addition on the oxidation resistance of AlMo0.5NbTa0.5TiZr refractory high entropy alloys (RHEAs) were investigated. The oxidation consists of the formation of passivating and complex oxide layer and the volatile oxidation of Mo, resulting in a power-law dependence of weight gain throughout the early stage of oxidation. Y addition induced the formation of continuous AlNbO4-based oxidation scales and reduced the volatile oxidation of Mo. The pegs-oxidized Y formed in the interfaces between oxide and substrate improved the adherence of the oxide scale. The high content of Y was disadvantageous to resisting oxidation at high temperature.

Numerical simulation of low-current vacuum arc jet considering anode evaporation in different axial magnetic fields

As the main source of the vacuum arc plasma, cathode spots (CSs) play an important role on the behaviors of the vacuum arc. Their characteristics are affected by many factors, especially by the magnetic field. In this paper, the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field (AMF) are studied. A multi-species magneto-hydro-dynamic (MHD) model is established to describe the vacuum arc. The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model. The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet. When the external AMF is high enough, a bright spot appears on the anode surface. This is because with a higher AMF, the contraction of the diffused arc becomes more obvious, leading to a higher energy flux to the anode and thus a higher anode temperature. Then more secondary plasma can be generated near the anode, and the brightness of the ‘anode spot’ increases. During this process, the arc appearance gradually changes from a cone to a dumbbell shape. In this condition, the arc is in the diffuse mode. The appearance of the plasma jet calculated in the model is consistent with the experimental results.

Numerical investigations on the electric arc behavior upon contact opening in a low-voltage switch under the effect of external magnetic field

This paper is devoted to investigate the effect of a strong external magnetic field on the electric arc created by contact opening in a low-voltage switch. The low-voltage switch is powered by a DC generator with an RL charge as in photovoltaic installations. During contact opening, the arc motion is dominated by Laplace and hydrodynamic forces. An external magnetic field is added to strengthen the magnetic forces and to accelerate the arc extinction. Significant differences depending on the external magnetic field intensity can be investigated. Numerical simulations, developed using COMSOL Multiphysics, are compared to experimental measurements performed on experimental device specially designed for tests to provide a better understanding of the physical phenomena involved.