Study On Rainfall's Influence On Positive Dc Discharge Of Rod-Plane Short Air Gap By Simulation & Experiments

With the development of electric power industry and the improvement of operating voltage level, the problem of the decrease in insulating strength of air gap due to the rainstorm is more and more serious. But up to now, there is no a comprehensive study result to report the positive DC discharge characteristic and mechanism of short air gap under rain at home and abroad. Therefore, this paper studied the discharge mechanism, characteristic and its influencing factors of short air gap under rain.Firstly, the analytic solutions of the potential and the field distribution in uniform field with rain drop were derived. And then a simulation model of rob-plate air gap under rain by the finite element software COMSOL 3.5 was established in this paper. The influence of rain drop size, rain drop shape, rain drop distribution, water film, water droplet and water stream etc. to the space electric field of the rob-plate air gap were analyzed by simulation. At last, in this paper, the influence of rainfall on positive DC discharge characteristics of rod-plane short air gap was systematically investigated under both experimental and natural conditions. By test study on the influence of rain intensity and water stream, the proposed models were proved to be right. Beyond this, we also had tests to find the influence of the rainwater conductivity and temperature on the discharge voltage.The simulation result shown that: rain droplets, especially the ones nearby the rod, could cause high field distortions, which may lead to ionization activity and reduce the discharge voltage; the larger the size of the rain droplet is, the more serious the field distortions around the rain droplet and rod terminal is; and the influence of the rain droplet distribution on the field distortions was significant; for the light rain, the increase in the number of rain droplets had little influence on the field of the rod-plane short air gap; but for the heavy rain, the increase in number of the larger rain droplets had a strong influence on the field of the rod-plane short air gap; water film and water droplet suspended at the rod terminal had little influence on the field of the rod-plane short air gap; for the water stream suspended at the rod terminal, on the one hand, it could cause serious field distortions, on the other hand, it could reduced the air gap. Due to the two aspects, the discharge voltage of rod-plane short air gap would seriously drop.The test study has shown that, the influence of rainfall on positive DC discharge characteristics of rod-plane short air gap was initially systematically investigated under both experimental and natural conditions. The result indicates that the positive DC discharge voltage of rod-plane short air gap after raining is a little higher than that in the dry condition; light rain had little influence on the positive DC discharge voltage of rod-plane short air gap; while the rain was getting heavier, it could obviously reduce the positive DC discharge voltage, and there was a significant negative correlation between discharge voltage and rain intensity. In addition, rainwater conductivity and temperature can influence the DC discharge characteristic of air gap.