Study on Long Front Time Wave Switching Impulse of Rod-Plane Air Gap

In long-distance transmission lines, the switching overvoltage waveform differs from that of ordinary lines. The wave front time is primarily distributed above 1000 & mu;s. And the switching overvoltage waveform has an important influence on the design of external insulation. This paper aims to deeply study the effect of various factors on the discharge of air gaps under the long front switching impulse voltage. This paper selects three kinds of rod-plane air gaps, and the switching impulse discharge experiments with different front lengths and absolute humidity under positive polarity are carried out. The effects of front time Tf, absolute humidity h, and gap distance d on the discharge characteristics of the air gap are analyzed. The results show that the U50% of an air gap is positively correlated with absolute humidity, front time, and gap distance. When considering the additional influence of humidity, the humidity additional influence factor c and the atmospheric parameter influence index n at different front times are almost unchanged. With the increase in gap distance, the influence of front time on U50% is more obvious. With the growth of the operating wave front time, the rising rate of U50% tends to slow down. The discharge time of the air gap under different conditions is mainly determined by the front time. The research results can provide a theoretical and experimental reference for the influence of front time Tf and atmospheric parameters on the discharge characteristics of air gaps under long front switching impulse.