Translated Abstract
Weather conditions such as sandstorm, rainfall and floating dust have been the main factors threatening the safety of outdoor insulation of electric power equipment. Rainfall in dusty weather is a common occurrence of extreme weather conditions, and seriously threats to the outdoor insulation safety of electrical equipment. Flashover and breakdown accidents caused by sandstorms and floating dust weather frequently occurred in the past years. Researchers have carried out investigations on the discharge characteristics of outdoor insulators in the sandstorms, rainfall, haze, however it is still necessary to investigate the discharge characteristics in floating dust with rainfall weather since the study is still undergoing and conclusions have not been fully agreed by the researchers.
In this paper, an artificial climate chamber is designed to simulate a stable dust condition and rainfall condition. It can be utilized to investigate the influence of floating dust, rainfall or rainfall under floating dust condition on breakdown voltage of the air gap. And then, the effect of floating dust with rainfall on breakdown voltage of air gap is investigated.
From the experiment, it is obvious that the minimum value may appear in the rod-rod electrode system with highly uniform electric field distribution. And the breakdown voltage of the air gap under floating dust decreased up to 10% . It may be higher than the value of clean air gap when the dust concentration is higher than 1000µg/m3. Meanwhile, the breakdown voltage decreases with the initial wind speed increasing. Rainfall intensity, rainwater conductivity and rainfall angle all have effects on breakdown voltage of rod-rod air gap. The breakdown voltage decreases with the increase of rainfall intensity and rainwater conductivity. However, it may increase when the rainfall angle increases. The ionic species contained in the rainwater have no effect on the breakdown voltage of the air gap. Rainfall will impact less on breakdown voltage when the gap distance becomes longer under the same condition. It is also found that the breakdown voltage of the air gap decreases more obviously when the floating dust concentration is higher and the rainfall intensity is stronger.
From the AC and lighting impulse experiment, it is clear that the dust particles are charged because of the friction and this will be more prone to field emission. As floating dust concentration increasing, mean free paths of electrons and photos decrease. And then, more free electrons and photons are absorbed by floating dust particles. Therefore, the minimum breakdown voltage may appear. Influence of breakdown voltage under rainfall is mainly caused by the characteristics of the water column. When the rainfall intensity is stronger, the water column becomes longer and the breakdown voltage becomes lower. Changing rainfall angle mainly affects the characteristics of raindrop on the top of the electrode. The surface electron work function of the floating dust particle is far lower than that of the raindrop. Therefore, more electrons will escape from the surface of the dust particles when the floating dust particles are absorbed by raindrops and the breakdown voltage may decrease.
In conclusion, the outdoor insulation of the electric power equipment is dramatically affected by the floating dust with rainfall. The results in this thesis can provide a theoretical guideline for outdoor insulation design of the electrical equipment.
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