Theoretical and numerical studies of breakdown phenomena triggered by microparticle in nitrogen gaps

This paper studies microparticle-triggered breakdown phenomena in mm-scale nitrogen gaps based on theoretical analysis and numerical simulation. Secondary electron and field emission contributions are both considered when predicting the microparticle-initiated breakdown voltage. In the present model, the ionization coefficient of the microscale discharge is modified to recognize the significant reduction in the number of collisions that occurs when a microparticle is present. The theoretical analysis indicates that small particles have little influence on the gas-gap breakdown voltage unless field-emission effects are dominant. However, when large microparticles (radius 50 μm) are present, a significant decrease (more than 20%) in the minimum breakdown voltage can be observed regardless of the particle position in the gas gap. Therefore, one should endeavor to exclude large microparticles from the discharge process. A fluid model is then used to simulate the microparticle-initiated breakdown process in a gas switch. The microparticle radius is 10 μm and the distance between the microparticle and cathode is 1 μm. It can be found that the electrode–particle microdischarge generates regions of high-density plasma that finally trigger main-gap breakdown when a voltage of 2.5 kV–3.5 kV is applied. The calculated results are consistent with our theoretical analysis. This paper provides a quantitative research method to evaluate the influence of microparticles on gas breakdown and contributes to improving gas-switch insulation performance.