Effect of Humidity on the Air-Dielectric Interface Breakdown under Nanosecond Pulse with Fluid Simulation

The influence of humidity on the air-dielectric interface discharge under nanosecond pulse is investigated with fluid simulation. The space distribution of electric field and particles are obtained. The simulation results show that the threshold of breakdown at air-dielectric interface increases with the growth of ratio of $\mathrm{H}_{2}\mathrm{O}$ in a certain range, which is in good agreements with experimental data. The theory analyses are done to study the evolution of discharge. Compared with $\mathrm{O}_{2}$, the attachment rate of $\mathrm{H}_{2}\mathrm{O}$ is larger, and the ionization rate of H2O is smaller. Therefore, the effective ionization rate decreases with the ratio of $\mathrm{H}_{2}\mathrm{O}$. Therefore, the surface flashover breakdown is more difficult to occur in humid air. These results can provide a deep understanding of the mechanism of air-dielectric interface breakdown.