Study on the Development of Residual Surface Insulation Strength Under Repetitive Nanosecond Pulses in Nitrogen

Repetitive high voltage nanosecond pulse generators have extensive applications in the material modification and environmental treatments. The structure of pulse generator is required to maintain its insulation strength under repetitive pulses (RP). Previous researches have shown that the flashover voltage of insulators under RP are extremely lower than those under single pulse (SP). Moreover, the surface flashover occurs after several pulses and the flashover voltage under RP nonlinearly depends on the repetitive rate. Traditionally, the performance of an insulator under RP is usually characterized by the total number of applied pulses $N\text{fl}$ and the withstanding time $T\text{fl}$ before flashover. However, $N\text{fl}$ and $T\text{fl}$ are parameters only reflecting the lifetime of an insulator under a specific working condition. The development of surface insulation strength in the withstanding stage and its influential factors are crucial for the determination of the insulation capability and comprehension of the mechanism of surface flashover under RP. In this paper, the concept of the residual surface insulation strength is proposed to reflect the development of surface insulation strength in the withstanding stage, defined as the instantaneous surface flashover voltage $U_{\text{res}}$ with RP continuously applied. $U_{\text{res}}$ and its influential factors are investigated including the repetitive frequency, applied voltage amplitude and surface distance.