Investigation of Surface Flashover Mechanisms in SF ₆ /N ₂ Mixtures Under Nanosecond Pulse

SF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub>/N<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixtures combine excellent insulating properties with favorable environmental characteristics and are widely used in high-voltage equipment. Under nanosecond pulse conditions, the probability of flashover occurring at the gas-solid interface significantly increases. However, current research lacks an understanding of the underlying mechanisms of the key influencing factors. In this study, a flashover discharge model under nanosecond pulses at the gas-solid interface was developed to investigate the mechanisms by which field-induced emission and electron detachment influence surface flashover. Additionally, the effects of pulse front rise rate and gas pressure on the discharge process were analyzed. After considering field-induced emission in the model, the electron density at the ground electrode significantly increases, leading to a bifurcation phenomenon at the jet head. Furthermore, when electron detachment is taken into account, the jet flow bifurcation disappears, and the flashover time is reduced by 27.42%. Increasing the pulse front rise rate from 3 kV/ns to 5 kV/ns results in a 6.7% reduction in flashover time and an intensification of the discharge severity. High gas pressure suppresses the discharge process, with flashover time increasing by 17.1% when gas pressure rises from 0.2 MPa to 0.5 MPa. Moreover, high gas pressure promotes the discharge to preferentially propagate along the gas-solid interface, further exacerbating the discharge severity.