This research investigates the influence of cathode surface roughness on DC breakdown voltages and pre-discharge currents in pressurized synthetic air. A physics-based computational model is presented for predicting breakdown voltages in insulating gases under high-voltage stress. The model combines electron ionization and attachment processes along the discharge path to calculate the evolution of the primary electron avalanche. The model considers gas pressure, gap distance, electrode geometry and electric field distortions due to electron avalanches, and had been validated with a huge number of experimental breakdown measurement series with smooth electrode geometries in synthetic air. In the present work this model is extended to include the influence of electrode surface roughness on breakdown behavior. To accomplish this, cathodes with varying roughness levels were characterized using laser scanning microscopy and corresponding local field enhancements at the surfaces are calculated by numeric simulation. Those, locally non-uniform electric field distributions were used as input for the computational model to predict breakdown voltages. Finally, breakdown and pre-discharge measurements of sphere spark gaps with different electrode surfaces are presented and compared to the model predictions. Validations against these experiments at pressures up to 1.5 MPa show strong agreement between measured and calculated breakdown voltages. The results demonstrate that cathode surface features in the micrometer scale can significantly reduce the insulation strength of pressurized synthetic air and that the proposed model is able to predict this effect.
To investigate the influence of electrode surface roughness on gas discharge characteristics under micro-gap conditions, direct-current breakdown experiments were carried out in atmospheric air using a nano-positioning system. Breakdown tests were conducted for five metal electrodes over the electrode gap distances from 1 to 10 µm, and for one metal with different surface roughness levels over the electrode gap distances from 1 to 20 µm. Meanwhile, the electric field intensity distribution of aluminum electrodes (cathode) with different surface roughness values was simulated using Maxwell electromagnetic field simulation software. The experimental results show that, in the electrode gap distances from 1 to 5 µm, different metal electrodes exhibit different degrees of deviation from the Paschen curve, all of which are related to the work function. At the same electrode gap distance, the rougher the electrode surface, the larger the field enhancement factor β and the lower the breakdown voltage. Analysis indicates that surface protrusions cause local electric field intensification, allowing the field strength to reach the critical condition for field electron emission, thereby reducing the breakdown voltage. In the electrode gap distances from 10 to 20 µm, electrode surface roughness leads to a multiplication of the effective electron emission from the cathode surface, thus enhancing the surface electron emission process. Therefore, in the design of microelectronic devices, reducing electrode surface roughness and selecting metal electrode materials with higher work functions can effectively improve gas breakdown characteristics under small-gap conditions and optimize the insulation protection of microelectronic devices.
Xiao-Yang Li, Yan-Zhou Sun, Jiahao Zhi et al.· Journal of the Physical Soci...· 0 citations
Atmospheric pressure dielectric barrier discharge is generated to investigate the discharge parameters, transitioning from a filamentary to uniform appearing discharge. Uniform discharge is beneficial for modifying material surfaces owing to its intrinsic properties. For uniform discharge generation the wire-mesh electrodes of capacitive coupled reactor are linked to an alternating high voltage supply that can provide up to 42 kV at 50 Hz. The wire-mesh electrodes were shielded with glass dielectrics and Polyethylene Terephthalate sheets. Oxygen gas was supplied between the wire-mesh electrodes at a fixed flow rate of 70 ml/min controlled by a mass flow meter. The wire-mesh electrodes gap was set between 1 and 4 mm. After diagnosing the wire-mesh electrodes discharge, the results show a tendency towards uniform discharge at 27 kV under atmospheric pressure. The discharge Lissajous figure was obtained for various applied voltages to measure the fundamental parameters. The results indicate that increase in the applied voltage, enhances the capacitance of the dielectric and charge transfer process, while reducing the gap capacitance, cell capacitance and equivalent gap capacitance respectively.
Ali Akbar Khan, S. L. Yap, Wilayat Khan· Journal of Instrumentation· 0 citations
Possessing favorable environmental friendliness and excellent insulating properties, C4F7N has attracted extensive research attention and is considered a promising alternative to SF6. This paper constructs a two-dimensional plasma fluid model and employs finite element simulation to explore surface discharge triggered by free metallic particles in C4F7N/CO2 gas mixtures. The spatiotemporal evolution of electron density, ion density, electric field strength, electron energy, and breakdown voltage under different mixing ratios is analyzed. Simulation results reveal that elevating C4F7N content slows discharge propagation and extends breakdown duration. The duration from discharge inception to surface flashover under 5% C4F7N concentration is roughly half that under 10% concentration, and 18% C4F7N presents a prominent suppression effect on discharge development. Ion distribution analysis shows that CO2+ dominates the discharge at concentrations of 5% and 10%, and obvious charge accumulation occurs at metallic particle tips and ground electrodes. When the concentration rises to 18%, the proportion of CO2+ declines, while the fractions of C4F7N−increase. Charge accumulation only appears at particle tips, demonstrating that the discharge mechanism shifts from CO2 electron-impact ionization to the joint dominance of C4F7N adsorption and impact ionization. Through electrostatic-current field coupling, this work clarifies the microscopic mechanism of surface discharge varying with C4F7N concentration, offering theoretical references for insulation design and gas proportion optimization of electrical equipment.
This research investigated the effect of both the applied voltage and the anode area on the electrical and plasma properties of a DC glow discharge in low-pressure argon gas. The electrical properties included current-voltage (I-V) curves and Paschen's curves, while the plasma parameters included electron temperature and number density. The plasma was generated between two copper electrodes separated by a constant distance of (4 cm), using anodes of different diameters of (2, 4, 5, and 6 cm). The plasma was characterized by optical emission spectroscopy (OES), which was used to estimate the electron temperature (Te) and number density (ne). The experimental results showed that the discharge operates within an anomalous glow regime. Furthermore, decreasing the anode area led to a higher breakdown voltage required to initiate the discharge, while increasing the anode area resulted in higher spectral emission line intensity, electron temperature, and number density. When the anode diameter changed from (2-6) cm, the electron temperature ranged from (0.389-0.393) eV, while the electron density ranged from (3.26×10¹⁵ - 9.23×10¹⁵) cm⁻³. These results confirm the influential role of anode geometry in the distribution of the electric field and the processes of ionization and excitation, and thus in determining the electrical and plasma characteristics of the discharge.
Zahraa55 Noman, Abdulhussain A. Khadayeir· Al-Noor Journal of Engineeri...· 0 citations
Plasma-catalytic ammonia synthesis can operate without high temperatures and pressures, and its performance is closely tied to discharge modes. However, research on its microscopic discharge mechanisms remains limited. A 2D fluid model incorporating plasma-activated heterogeneous reactions was developed to investigate voltage polarity effects on discharge dynamics in an N2/H2 planar dielectric barrier discharge (DBD) reactor with catalyst-coated barriers. Under both polarities, discharge starts as a gas-phase streamer at the catalyst apex due to local field enhancement and then evolves into a surface ionization wave (SIW) with an order-of-magnitude higher electron density. Positive voltage restricts the SIW to the catalyst surface, whereas negative voltage induces SIWs on both the upper bare dielectric and the catalyst, driven by distinct charge accumulation patterns. During the short discharge pulse, the gas phase primarily functions as a radical generator, while surface reactions dominate NH3 synthesis. Because positive voltage effectively targets plasma energy to the catalyst surface, it yields a higher peak NH3 density near the catalyst (2.85 × 1019 m−3) compared to negative polarity (8.10 × 1018 m−3).
Surface charge accumulation on insulators is a critical concern for high-voltage direct current gas-insulated switchgear (HVDC GIS), as it distorts the electric field at the gas–solid interface and further initiates partial discharge or surface flashover. As an environmentally friendly alternative insulating medium, clean air has drawn extensive interest in engineering applications, yet the characteristics of gas-side dark current and its inherent contribution to surface charge accumulation remain unclear. In this work, dark current in clean air is investigated through combined experimental measurements and numerical simulations. A coaxial measurement system is used to examine the influences of electric field strength, gas pressure, electrode surface roughness and electrode material, whereby the dominant dark-current mechanisms under different operating conditions are identified. By correlating dark-current characteristics with surface charge observations on practical GIS insulators, an inherent correlation is established between dark-current mechanisms and two typical surface charge patterns: uniform background charge and localized charge speckles. The results show that, within the tested pressure ranges of 0.3–0.8 MPa for dark-current measurements and 0.2–0.6 MPa for surface-charge comparison, cosmic radiation-induced ionization dominates dark current generation at low electric fields (< ∼3 kV mm−1), whereas micro-discharges become predominant at higher electric fields (> ∼3 kV mm−1) under the present coaxial electrode configuration; field emission contributes only marginally within the investigated field range. Moreover, reducing electrode surface roughness or applying electrode surface coatings effectively suppresses dark current and mitigates charge speckles, providing a practical strategy for surface charge regulation. Among the compared insulating gases, clean air exhibits dark-current and surface-charge characteristics closest to those of SF6, indicating great application potential for HVDC GIS.
Boya Zhang, Hongyuan Ren, Jie Li et al.· Journal of Physics D: Applie...· 0 citations
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