Study On The Effect Of Space Charge On Discharge Path Of Rod-Plane Air Gap

Shielding failure is identified as the main cause of lightning outrages for both Ultra High Voltage (UHV) and Extra High Voltage (EHV) transmission lines. Even though line design meets the requirement of lightning protection, shielding failure could occur accidentally. In the researches of factors influencing striking points, it is found that space charge, whether generated from corona around protruded objects or formed due to the development of streamers or leaders, shows influence on striking points, which could be one of the reasons caused abnormal shielding failure.In order to study the effect of space charge on propagation path of air gap discharge, a test system has been set up with high speed video cameras working together to record the paths. On the one hand, under the condition of combining DC with impulse voltage, the effect of space charge under electrostatic field to the propagation path is studied Tests'results show that under negative composite voltage, space charge has relatively tiny effect on the development of propagation path while there's no obvious effect under positive composite voltage. On the other hand, the effect of space charge on propagation path is explored under pure positive lightning or switching impulse voltage. The statistical results show that the probability of visible discharge point further away from the tip of the rod in the condition of applying switching impulse voltage is larger than that under lightning impulse voltage. And it is noticed that the higher the peak value of positive impulse voltage goes, the larger the probability of the points locating further away from the tip becomes. The shape of the rod influences the generation of the space charge and the location of the discharge points. Changing the tip shape of the rod from sharp one to sphere one, it is obvious that discharge points tend to cluster on the face of the sphere. The experimental results show that the distribution of electric field in the vicinity of the tip is distorted greatly by space charge generated under switching impulse voltage, which leads to the visible discharge point further away from the tip. The effect of space charge is influenced by the different polarities, waveforms and peak values of the impulse voltage. In addition, shielding shell of electric field is also verified by simulation results.