Study Of Switching Impulse Discharge Performance Of Rod-plane Air Gap Under Rain

In recent years, air pollution and rain conductance in some regions of our country are more and more serious. On the base of the operation of the ultra-high voltage transmission line, the discharge accidents of line-tower took place under rainstorm. But the effect of rain on the switching impulse discharge voltages was not considered in the insulation design. The study of switching impulse discharge performance of air gaps under rain was also very little in the world. The rod-plane air gap is the reference of discharge voltage design for air gaps. Therefore, there is an important engineering application value of the study of this paper.As the switching impulse voltage of negative polarity is still higher than that of positive polarity under rain, experimentation study was only taken for positive switching impulse discharge performance by the means of artificial rain. Positive switching impulse discharge model of 1m rod-plane air gap containing raindrops was established. The effects of raindrops on the discharge performance were analyzed so as to analyze the effect of rain. The man conclusions in the paper are as follows:The rain conductivity, the average rain intensity and the air temperature have influences on 50% breakdown voltage. The 50% breakdown voltage decreases with the increase of rain conductivity and average rain intensity, as well as air temperature. The influence of average rain intensity is most obvious, the influence of air temperature is the next, while the influence of rain conductivity is the least and can be ignored. The influence of rain on discharge voltage is associated with the gap distance. The influence decreases with the increase of the gap distance.According to the utmost test values, there is definite influence of rain on the positive switching impulse discharge voltage of 0.1~0.5m and 1m air gaps if air temperature and average rain intensity change heavily. On the contrary, the influence of rain can be ignored in the engineering. The influence of rain on the time to discharge time of the positive switching impulse of 0.1~0.5m and 1m air gaps is not obvious, and it can be ignored.The raindrop can't change the discharge order of the air gaps, that is to say that the discharge still begins with the rod and develops to the plane step by step. Before the vaporization of the raindrop, some charged particles will assemble on the surface of the raindrop. The raindrop is equipotential and the electric field on its surface is equal to zero, which changes the ambient electric field of the raindrop heavily and makes the ambient electric field swell at the same time. All of these are propitious to the development of discharge and the decrease of the discharge voltage. After the vaporization of the raindrop, there is no influence of the raindrop on the discharge. As the increase of rain intensity, the influence of rain on the charged particle density, potential and electric field increases. This is in favor of development of discharge and makes the discharge voltage decrease.Rain can increase the humidity and attachment coefficient. And this increases the discharge voltage. However, the raindrop as floating conductor can decrease the discharge voltage. So the both sides interact each other and make the influence of rain on the positive switching impulse discharge voltage not obvious.