arXiv subjects

Haiyun Luo

Publications and source records attributed to Haiyun Luo.

4 recordsLinked to original sources

arXiv2025

Computational Model for Photoionization in Pure SF6 Streamer at 1-15 atm

Photoionization plays a crucial role in achieving accurate quantitative predictions in SF6 streamer simulations, but accurate models for SF6 photoionization remains limited, motivating this paper. First, we develop a computational model for SF6 photoionization and provide the detailed theoretical modeling process, as well as comparison between experiment and simulation. A concise summary of model parameters within the comprehensive pressure range of 1 - 15 atm is provided for direct reference. Then, we perform comparative studies against simplified approaches. The results demonstrate that the proposed model effectively captures the non-local effects of SF6 photoionization, enhancing both the spatial numerical convergence and the accuracy of the streamer structure. Finally, we perform comparative studies by artificially increasing the photoionization intensity through multiplying the photoionization source term Sph by a factor of 50 (50*Sph) relative to the baseline intensity. Regarding breakdown voltage prediction, 50*Sph leads to a significant underestimation of the breakdown voltage for positive streamers, introducing errors greater than 0.5 kV, while exerting a small impact on negative streamers. Regarding streamer propagation dynamics, the radius of the positive streamer head exhibits pronounced shrinking, and 50*Sph reduces this shrinking and significantly lowers the head field by more than 700 Td. In contrast, 50*Sph has little impact on the morphology of the negative streamers and slightly enhances the head field by less than 30 Td.

physics.plasm-ph↗

arXiv2025

SF6 streamer breakdown induced by floating linear metal particles: Following streamers and side streamers

The electrical breakdown of SF6 in the presence of floating metal particles is facilitated by two key factors: the role of floating metal particles and the nonlinear breakdown behavior of high-pressure SF6. However, the microscopic transient processes remain unclear, motivating this paper. Using 2D fluid models, we investigate SF6 streamer breakdown induced by a floating linear metal particle under negative applied voltage. First, We identify a characteristic double-end streamer inception in the combined gap. Then, we propose the following streamer (FS) mechanism to explain the metal particle's role. Two following streamers, FS1 and FS2, arise from the interaction between space charge and metal particle. FS1 facilitates breakdown via the negative space charge field generated by its head. FS2 facilitates breakdown by merging with FS1, accelerating its propagation and enhancing the electric field at the primary streamer head. Finally, we propose the side streamer (SS) mechanism to explain the nonlinear breakdown behavior of high-pressure SF6. The SS is identified as a new forward ionization wave that develops along the sides of the primary streamer, due to photoionization-driven negative ion accumulation. SS facilitates breakdown by merging with the primary streamer, increasing negative space charge and leading to three distinct propagation modes. Higher pressure increases the production rate of negative ions along the streamer sides, making SS more likely to form. Under overvoltage, the facilitating effect of SS diminishes as the background field (E/N)b strengthens, disappearing when (E/N)b exceeds 245 Td. This study provides new insights into the SF6 streamer breakdown mechanisms induced by floating metal particles and offers theoretical references for further investigation on the quantitative characterization.

physics.plasm-ph↗

arXiv2024

Spatial Fluctuation of the Electric Field within SF6 Streamer Channel in Highly Non-Uniform Fields: Phenomenon, Validation, and Mechanism

The electric field within the streamer channel is a critical parameter in the calculation model for the nonlinear breakdown voltage of SF6, motivating the research presented in this paper. By using a 2D fluid model, we investigate the microscopic characteristics of the SF6 streamer channel in highly non-uniform fields and uncover a previously unexplained coherent structure: the spatial fluctuation of the electric field (SFEF). We validate the physical validity of SFEF by modifying model parameters that could potentially introduce non-physical effects. Further comparative analysis reveals that SFEF is driven by an ion-conducting channel formed due to the strong electronegativity of SF6. This ion-conducting channel exhibits local characteristics, which fundamentally arise from the slow response of charged species to local charge relaxation. We identify that some charge separation originates from the accumulation of negative ions at the rear edge of the streamer head due to strong electric field shielding in this region. As the streamer propagates, charge separation is continuously generated and passively carried into the streamer channel, ultimately forming the SFEF. Finally, we confirm that SFEF does not occur in uniform fields, indicating that it is a phenomenon exclusive to highly non-uniform fields. These findings provide a deep insight into the electric field within the SF6 streamer channel and offer a potential avenue for further investigation into the mechanisms of SF6 nonlinear breakdown voltage.

physics.plasm-ph↗

arXiv2024

Microscopic characteristics of SF6 partial discharge induced by a floating linear metal particle

Direct current (DC) gas insulated transmission lines (GILs) have been widely used in power transmission, but might be threatened by partial discharge due to the presence of floating impurities (e.g., dust and metal particles) inside the sealed chamber. In this letter, by using a 2D fluid model we characterize the microscopic properties of the partial discharge induced by a floating linear metal particle in SF6 (both the discharge propagation and interaction between space charge and metal particle) under negative high voltage direct current (HVDC) conditions. Due to the strong electronegativity of SF6, the spatiotemporal distributions of the charged species (electrons, positive and negative ions), space charge, and reduced electric field are rather different from those in air. Notably, a negative ion region is observed around the top tip of the metal particle, and it plays an important role in the generation and propagation of primary and secondary streamers in SF6, which may lead to severe motion characteristics of the particle and aliasing of partial discharge signals. Additionally, we analyze the charging process and electric force reversal phenomenon, which may provide a more precise understanding of the underlying mechanisms of the firefly motion previously reported for DC GILs.

physics.plasm-ph↗