Search Results (106)

Dissolved gas analysis (DGA) is an essential technique for the fault diagnosis and condition monitoring of oil-immersed power transformers. Among various characteristic gases, acetylene (C₂H₂) is a key indicator of high-energy discharge and arc faults. In this work, a high-sensitivity dissolved acetylene detection system is developed based on clamp-type quartz-enhanced photoacoustic spectroscopy (QEPAS). A specially designed clamp-type quartz tuning fork (Clamp-type QTF) is employed as the acoustic transducer to improve acoustic coupling efficiency and optical alignment tolerance. Compared with conventional standard quartz tuning forks, the clamp-type structure exhibits enlarged acoustic interaction volume, lower damping loss, and higher signal collection capability. A near-infrared distributed feedback (DFB) laser operating at 1531.6 nm is used as the excitation source. The dissolved gas is extracted from transformer oil using a headspace degassing module and introduced into the QEPAS cell for real-time measurement. Experimental results showed that the developed system achieves a 1σ-based SNR-estimated detection limit of 17 ppb at a 50 s integration time, derived from the continuous measurement of 0.75 ppm C₂H₂, with excellent linearity in the concentration range from 100 ppm to 500 ppm. The measured concentration of dissolved acetylene in transformer oil is in good agreement with gas chromatography (GC), validating the effectiveness and practical applicability of the proposed system. Full article

The pantograph–catenary system is a crucial component of rail transit vehicles, performing the vital function of electric energy transmission. During train operation, the current-carrying components continuously emit particulate matter into the surrounding environment due to friction, and these particulate emissions have a significant impact on human health. However, research on the correlation between the current-carrying friction of carbon contact strips and particulate matter emission characteristics is rarely reported. Based on a semi-enclosed pin-on-disc current-carrying friction and wear test rig, this paper investigates the effects of varying current intensity under different contact load conditions on the friction and wear performance of carbon/copper pairs, as well as the associated particulate matter emission behavior. It reveals the damage characteristics of carbon contact strips, the particulate matter emission characteristics, and the relationship between them under different service conditions. The results indicate that the wear mechanism and particulate matter emission behavior of carbon contact strips are jointly influenced by current magnitude and contact load. In the absence of current, increasing the load exacerbates the mechanical wear on the carbon friction pair surface, while elevating the emission concentration of particles of various sizes and stabilizing the particle size distribution. Under current-carrying conditions, a higher contact load effectively reduces the frequency of arc discharges between the friction pair. Meanwhile, the degree of arc erosion on the contact surface worsens with increasing current intensity. Arc discharges instantaneously lead to a sharp increase in particulate emissions, and the higher the discharge intensity or the greater the number of discharges, the higher the particulate concentration around the contact pair. Full article

Piezoelectric actuators enable ultra-fast switching due to their microsecond-scale response and high acceleration capability. This study experimentally investigates arc behavior in air, vacuum, and nitrogen using round and flat contacts driven by an amplified piezoelectric actuator. Unlike prior work focused mainly on actuation dynamics, this study provides a multi-medium comparison and investigates the coupled effects of drive operating time and contact geometry on arc characteristics. Arc tests were conducted using a capacitor discharge platform, with synchronized electrical measurements and high-speed imaging. In air (140 V, 350 A), arc voltage increased with rise time, reaching 800 V, 840 V, and 1080 V at 0.5 ms, 1 ms, and 2 ms, respectively, while shorter rise times reduced arc duration but promoted reignition. In vacuum (140–200 V), arc voltage stabilized at 80–90 V, with longer rise times extending arc duration; round contacts exhibited faster voltage rise and higher peaks. In nitrogen (140–200 V), higher voltages were obtained at shorter rise times, reaching 2680 V, 2600 V, and 2320 V at 0.5 ms, 1 ms, and 2 ms, respectively, with reduced arc duration. Across all media, round contacts consistently produced higher arc voltages than flat contacts. These results demonstrate that drive dynamics and contact geometry critically influence arc voltage and duration, providing practical guidelines for the design of high-speed piezoelectric-based switching devices. Full article

Low-voltage (LV) alternating current (AC) power distribution systems are widely used, where phase-to-neutral short-circuit faults are a major cause of electrically induced fires. Prior to a circuit breaker interruption, arc discharges may develop between conductors, leading to intense localized heating of the cable insulation and a potential ignition risk. In this study, a magnetohydrodynamic (MHD) model of 220 V AC short-circuit arcs is established to investigate the coupled electrical and thermal behavior of arc discharges and their induced heating effects on conductor insulation. The transient temperature distribution in the arc region and insulation layer is numerically analyzed under different tripping currents and tripping times, and insulation ignition risk is evaluated based on characteristic thermal thresholds. To validate the simulations, a controllable 220 V AC short-circuit experimental platform is developed using a motor-driven wire contact mechanism. Circuit breakers rated at 20 A, 32 A, and 63 A are tested, and short-circuit current and voltage waveforms are recorded. The results indicate that insulation ignition risk is jointly governed by short-circuit current magnitude and breaker tripping time. Delayed interruption significantly increases insulation temperature and ignition susceptibility, whereas rapid interruption effectively suppresses arc-induced heating. Full article

Vacuum degree inside vacuum interrupter (VI) deteriorates due to cracks from long-term operation of VI, gas emitted from internal arc heat, leakage through the joint, etc. Partial discharge occurs between the two contacts inside the VI or between the contact and floating shield, which leads to dielectric breakdown and electrical accidents of high voltage apparatus. In this paper, the study on the vacuum degree monitoring of distribution class vacuum interrupter according to non-contact method of coupling capacitor based on partial discharge was performed. In order to monitor the partial discharge between two contacts inside VI with high accuracy, a partial discharge sensing electrode (PDDE) was designed using the 3D finite element method (FEM). In addition, after calculating the internal capacitance according to the structure and size characteristics inside VI, the capacity of the coupling capacitor to detect the signal was calculated. The partial discharge characteristics according to the vacuum degree were analyzed by applying PDDE and a coupling capacitor. As results, it was found that the partial discharge characteristics inside VI differ depending on the voltage type. In addition, it was confirmed that even if VI has the same internal structure and size, the partial discharge characteristics appear differently. Based on the experimental results, we proposed maintenance criteria for VI for each voltage type. Full article

Currently, the lack of analysis and applicable circuit models for the evolution of cable joint faults is responsible for explosions or fire accidents in the distribution network system. In this paper, the modeling of high-resistance to low-resistance grounding faults for 10 kV cable joints is investigated. Firstly, the physical evolution from high-resistance to low-resistance grounding faults in 10 kV cable joints is analyzed. Secondly, the common discharge characteristics under different evolution stages are extracted by simulation experiments and fault-recording data. Thirdly, an interface breakdown circuit model and a radial breakdown circuit model are established to quantitatively describe the high-resistance to low-resistance grounding faults of cable joints. Fourthly, the corresponding arc resistance models are proposed, and the controlled parameter values of the models under different evolution stages are given. Finally, the fault identification control model is implemented for relay protection. This paper provides theoretical and modeling support for the fault identification of 10 kV cable joints, filling the knowledge gap of this critical fault type in relay protection. Full article

Tree contact discharge is a key contributing factor to wildfires caused by medium-voltage insulated conductors. Prolonged abrasion of the insulation layer by branches gradually creates weak points in the insulation. When subjected to lightning strikes, these areas are prone to forming lightning-induced pinholes, which can subsequently trigger partial discharge and even ignition. This study systematically investigates the discharge-induced ignition mechanism for 10 kV overhead insulated conductors in tree contact scenarios by establishing an experimental platform integrated with high-speed imaging, ultraviolet detection, and simulation methods. Three types of typical defects were set up in the experiments: complete insulation abrasion, lightning puncture holes accompanied by localized abrasion, and lightning puncture holes without abrasion. The development process and characteristics of different discharge forms were observed and analyzed. The results indicate that the tree contact discharge ignition mechanism can be categorized into two types: thermal accumulation and direct arcing. The former occurs when insulation abrasion or composite defects exist, where sustained partial discharge or a high-resistance current leads to gradual heat accumulation, resulting in an ignition delay lasting tens of seconds. The latter occurs when only small defects such as lightning puncture holes exist in the insulation layer. A concentrated arc forms due to gap breakdown under high voltage, leading to a millisecond-level ignition process. The study found that different discharge forms produce significantly distinct ablation and carbonization patterns on both the insulation layer and the branch surface, reflecting differences in energy transfer pathways. Simulation analysis further indicated that the thickness of the insulation layer affects the electric field distribution in the tree contact gap, with the initial discharge field strength decreasing as the thickness increases. This study provides experimental evidence and classification guidance for tree contact fault monitoring, insulation condition assessment, and wildfire prevention and control in medium-voltage distribution networks. Full article

Cu/Ni/Ag composite materials are widely used in the manufacturing of electrical connector contacts due to their excellent electrical conductivity and good wear resistance. During hot plugging and unplugging operations, electrical connectors inevitably generate arc discharge, leading to melting, splashing, and erosion of the contact material, which severely threaten system reliability and service life. To investigate the arc behavior of Cu/Ni/Ag composite electrical connectors during plugging and unplugging, this paper establishes a multiphysics coupling model incorporating electric field, fluid heat transfer, and laminar flow based on the COMSOL simulation software (version 6.2). The model employs a multiphysics coupling approach, incorporating electric field, fluid heat transfer, and laminar flow, to systematically simulate the formation and evolution mechanisms of the arc during plugging and unplugging. The study focuses on analyzing the effects of plugging and unplugging speed, operating voltage, and arc gap distance on the arc, exploring the temporal and spatial evolution characteristics and distribution patterns of arc temperature. The simulation results reveal that the arc temperature follows a radially decreasing gradient, with the core region exceeding 10,000 K. When the operating voltage increases to 1000 V, the arc peak temperature rises to 1.3 × 10⁴ K. As the arc gap distance increases, the arc coverage area expands, and the peak arc temperature increases by approximately 2% to 8%. As the plugging/unplugging speed is increased to 500 mm/s, the peak temperature of the arc increases from 1.19 × 10⁴ K to 1.3 × 10⁴ K. The distribution characteristics of the magnetic field are clearly correlated with the arc temperature field and the electric field intensity distribution and the current density also exhibits typical constriction characteristics. Prolonged arc duration is correlated with an upward trend in peak temperature. Further analysis indicates that the temperature distribution characteristics of the arc are constrained by the competition mechanism of energy deposition and diffusion, while the evolution characteristics of the arc are regulated by the coupling effect of electromagnetic field and mechanical work. The research results provide a theoretical basis and simulation methods for the design of arc-resistant structures in Cu/Ni/Ag composite electrical connectors. Full article

To systematically analyze the differences and underlying mechanisms of pantograph–catenary arc discharge characteristics under different operating conditions, this paper measures the complete transient waveforms of arc current, external electric field, and voltage between carriages under various operating conditions based on a unified experimental platform, using flexible current probes, electric field sensors, and active differential probes for synchronous acquisition. The research results reveal the quantitative correlation and physical mechanism between the mechanical parameters of the pantograph–catenary system and the electromagnetic transient responses under four typical conditions: fixed gap between the pantograph and catenary, pantograph raising, pantograph lowering, and pantograph–catenary separation vibration. These findings provide references for condition monitoring, fault warning, pantograph optimization design, and system-level electromagnetic compatibility evaluation of the pantograph–catenary system. Full article

With the rapid development of electrified railways in high-altitude regions, section insulators in catenary systems frequently experience gap breakdown and surface flashover under low atmospheric pressure conditions, posing serious threats to safe train operation. This paper investigates the discharge mechanisms of section insulators in high-altitude environments and conducts research on discharge characteristics under extremely non-uniform electric fields, along with structural optimization. First, the physical mechanisms of gap discharge and surface flashover in section insulators are analyzed. A three-dimensional electric field simulation model of the section insulator is established, and numerical analysis is performed to reveal the electric field distribution characteristics. The results indicate that the electric field is predominantly concentrated at the junction between metal electrodes and insulators, as well as at the tip of the arcing horn. The local maximum field strength reaches 3.84 × 10⁵ V/m, exceeding the corona inception field strength of air, which readily induces discharge. Subsequently, power frequency and lightning impulse discharge tests are conducted in both plain region and regions at an altitude of 4300 m. The results show that under high-altitude conditions, the power frequency breakdown voltage decreases by 28%, and the 50% lightning impulse breakdown voltage decreases by 42%. The discharge voltages under standard atmospheric conditions are obtained through correction. Finally, optimization schemes involving arcing horn structural modification and surface coating application are proposed. Adjusting the arcing horn angle to 55° and adding a grading ring structure with a radius of 70 mm reduces the local maximum field strength by 26%. After applying an RTV insulating coating, the field strength at the junction decreases by 35.9%, effectively enhancing the insulation performance of section insulators in high-altitude regions. Full article

The pantograph–catenary system is a critical component of the traction power supply network. Due to hard points on the overhead contact line and vibrations of the pantograph, pantograph–catenary separation may occur, leading to offline DC arc events. To investigate the characteristics of DC arcs generated during pantograph–catenary separation in metro systems, this study constructs a laboratory platform that simulates the offline process and analyzes the electrical characteristics, optical intensity, and arc-burn duration under different electrode separation conditions. First, a DC pantograph–catenary offline arc simulation platform is developed using a contact wire, a carbon-strip pantograph slider, and a linear motor, enabling slider movement in both horizontal and vertical directions. Second, offline discharge experiments are conducted to compare the discharge process and electrical arc characteristics with and without horizontal slider motion. Finally, arc luminosity and burn duration are measured under various electrode separation configurations, and the influence of voltage level, current level, and electrode material is examined. Experimental results reveal a significant polarity effect, where the arc burn duration is notably longer when the contact wire serves as the cathode than when the carbon slider serves as the cathode. At the instant of separation, the high electric field intensity within the micro-gap triggers pronounced “peak phenomena” in both arc resistance and power, accompanied by abrupt voltage surges and transient current dips. Furthermore, the introduction of horizontal motion modulates the arcing process, causing the stable arcing voltage to follow a distinctive trend of a slow increase followed by a gradual decrease, which differs from static separation characteristics. Finally, this study demonstrates that voltage levels exert a more dominant influence on arc luminosity and duration than current levels, while the maintenance voltage of the arc channel remains significantly lower than the air breakdown voltage. Full article

A plasma-assisted ammonia jet flame igniter was developed in this study to address the limitations of conventional spark ignition at high pressures. The effect of pressure on plasma discharge characteristics, optical emission spectra, and exhaust gas emission was systematically investigated, providing new insights into the mechanisms of plasma-assisted ammonia ignition under high-pressure conditions. The results indicate that increased chamber pressure elevates gas density, which in turn raises the voltage required to sustain an arc discharge at 0.4 MPa and markedly reduces the frequency of arc drift. Spectral analysis shows that higher pressure inhibits atomic oxygen lines (777.2 nm and 844.6 nm) while intensifying the molecular nitrogen bands between 350–450 nm. A corresponding decrease in electron excitation temperature is also observed. In terms of exhaust composition, hydrogen concentration demonstrates a bifurcated behavior, rising with pressure under fuel-rich conditions (the equivalence ratio φ > 1.2) and falling under fuel-lean conditions (φ ≤ 1). Conversely, NO concentration consistently decreases with increasing pressure across all test conditions. The ammonia concentration in the exhaust gas shows opposite pressure dependencies at different equivalence ratios. It increases with rising pressure for φ ≥ 1, while it decreases with increasing pressure for φ < 1. Full article

Micro-arc oxidation (MAO) coatings were produced on commercially pure titanium Grade 2 using a composite electrolyte containing sodium phosphate (Na₃PO₄) and sodium silicate (Na₂SiO₃), while varying the applied voltage. The surface morphology, phase composition, and structural features of the coatings were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The coatings exhibited a characteristic crater-like microporous surface morphology associated with the micro-arc discharge process. XRD analysis confirmed the formation of mixed TiO₂ phases in the anatase and rutile modifications, with higher voltages promoting the growth of the thermodynamically stable rutile phase. Corrosion and tribological properties were evaluated in a 3.5 wt.% NaCl solution using potentiodynamic polarization and a ball-on-disc test configuration, respectively. The results revealed a substantial improvement in both corrosion resistance and wear performance compared with bare titanium. The coating formed at 300 V demonstrated the highest wear resistance due to its denser microstructure, whereas the coating produced at 350 V exhibited the lowest friction coefficient and the greatest corrosion resistance, attributed to the increased rutile content. Overall, MAO coatings fabricated in the phosphate–silicate electrolyte effectively enhance the combined operational properties of titanium and can be recommended for applications requiring improved wear and corrosion resistance. Full article

Many studies have investigated tree-contact arcing ground faults. However, the effects of branch moisture content and wind speed are still not fully understood. Therefore, this paper addresses the wildfire risk caused by tree-contact arc grounding faults in distribution networks. A 10 kV distribution-line tree-contact arcing fault test platform is built. A two-dimensional multi-physics plasma model is also developed based on magnetohydrodynamics. Experiments and simulations are combined. The effects of wind speed, branch moisture content, and conductor type on arc evolution and fault characteristics are systematically studied. The results show that higher wind speed causes stronger arc-column deformation. The fault current contains more high-frequency components and sharp spikes. At 9 m/s and 16 m/s, the fault current shows strong disturbances and much lower stability. Higher moisture content increases the branch conductivity indirectly. It strengthens the carbonized conductive path and helps sustain stable arcing. For the high-moisture sample (64%), the current waveform is smooth, and its amplitude increases monotonically with fault development. For the low-moisture sample (30%), the current amplitude decreases, and spikes become more frequent. The arc tends to extinguish and reignite repeatedly, which indicates an unstable discharge process. The simulations further reveal the coupling between the arc-root temperature field and the airflow field under different wind speeds and conductivities. They also show clear differences in temperature evolution between bare conductors and insulated conductors. These findings provide experimental evidence and simulation support for identifying wildfires initiated by tree-contact arcing faults. Full article

To address the issues of narrow ignition limits and low combustion efficiency in ramjet combustors under low-temperature and low-pressure conditions, caused by low reactivity of liquid fuel and slow chemical reaction rates, a multi-channel gliding arc plasma excitation activation method for fuel–air mixtures is proposed. This method generates gaseous small molecules and highly active radicals. Focusing on the vaporizing flame holder of a subsonic ramjet combustor, this study investigates the fuel–air activation characteristics under different carrier gas flow rates, fuel flow rates, and numbers of discharge channels. The mechanism by which multi-channel gliding arc discharge plasma enhances fuel–air activation, ignition, and combustion performance is revealed. Full article